What does strain and strain rate actually measure?
The relation between function imaging and physiology - contractility, load, work and phases of the heart cycle.
Faculty of Medicine,
NTNU Norwegian University of Science and Technology
|Any imaging modality, including strain and strain rate only shows muscle shortening, and thus only tells half the truth about cardiac contractility and work.||Function is contractile force,
and shortening is force versus load. Work is the
amount of shortening times load.
The spatial derivative of flow is
Pressure increase of 100 MMHg in 100 ml blood (LVEDV) = 13.3 J.
Ejection of 50 ml blood (at an EF of 50%) at a velocity of 1 m/s at
constant pressure, is about 0.025J. Thus, in terms of work, most of
it is generation of pressure, and thus isometric rather than
isotonic. The greatest great
part of the ventricular work - the isometric work, cannot be
described by deformation analysis (or any imaging modality) at all
as all functional analysis by cardiac imaging is about deformation. Load independent imaging
modalities doesn't exist. The full description of LV
work need to incorporate a measure of load,
either by invasive measures, or by externally measured pressure
(eventually pressure traces) in combination with mathematical
|Excitation-tension diagram. After Cordeiro (234). The Action potential triggers
the influx of calcium, which triggers further release of
Ca2+from sarcoplasmatic reticulum. Calcium
binds to troponin, and allows activated (by ATP) myosin
heads to bind to troponin sites on actin (cross bridge
forming) and release energy, causing the filaments to
slide along each other, as long as there is a high
calcium concentration in the cytoplasm. As the
cell membrane repolarised, this triggers the removal of
calcium from the cytoplasm, mainly by the SERCA pumping
it into the sarcoplasmatic reticulum again. Thus,
the forming of new cross bridges is inhibited, and
relaxation starts. The pumping of calcium is energy
dependent, and is the energy requiring part of the
relaxation cycle. In energy depletion (f.i. ischemia),
there will be less shortening in systole, but also
||Image of beating isolated
myocyte. The myocyte is treated with an agent that
fluoresces in the presence of free calcium in the
cytosol. We see that the cell lightens and shortens
simultaneously; stimulation causes an increase in free
calcium (released mainly from the sarcoplasmatic
reticulum), causing the cell to become lighter. The free
calcium is the trigger for the binding of ATP, and the
formation of activated ("cocked") cross bridges between
actin and myosin, and the subsequent release, which
leads to tthe buildup of tension in the cell. In the
unloaded isolated myocyte, (as in previous studies in
isolated papillary muscle), this will correspond almost
directly with the shortening, as virtually no energy is
used to overcome load. However, a small part of the
energy needs to be stored for diastolic lengthening,
even in isolated myocytes, as discussed in
the section on dioastolic function. Image courtesy
of Ph.D. Tomas
exercise research group (CERG), Dept. of
Circulation and Medical Imaging, Norwegian University of
Science and technology.
|Looking at various definitions, all taken
from medical dictionaries:
”a capacity for shortening in response to suitable stimulus.”
”capacity for becoming shorter in response to a suitable stimulus.”
- Total confusion of shortening and contraction
”the inotropic state of the myocardium”
- As inotropy is defined as change in contractility, this dfinition is absolutely circular: "contractility is contractility", which is correct, but useless
”the ability of muscle tissue to contract when its thick (myosin) and thin (actin) filaments slide past each other.”
”The ability or property of a substance, especially of muscle, of shortening, or developing increased tension.”
- The last two are better, but has no quantitative connotations, it is simply the ability to.... (ability is non qyantitative, capacity is quantitative) , and no consideration of load
"a measure of cardiac pump performance, the degree to which muscle fibers can shorten when activated by a stimulus independent of preload and afterload"
- Close, but no cigar, load independence, but still confusion of shortening and contraction
It could be argued that contractility don't need a definition, being hard to describe, but instantly recognizable when spotted, which is the elephant test: I can't define an elephant, but I know it when I see it, or the equivalent duck test: When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck (James Whitcomb Reilly). However, this is insufficient:
This is not a duck, it's a penguin!
|Isometric twitch i.e. contraction
without shortening, showing the tension. Peak tension,
rate of force development and time to peak tension are
all measures of contractile function.
||Isometric twitches, showing the
effect of inotropy (in this case noradrenaline), showing
an increase in both peak tension, RFD and a shortening
of time to peak tension.
|Stretching the muscle before
stimulation, increases tension. The increase in passive
tension will be present at rest, before twitch, and is
equal in baseline and inotropic state. During twitch,
there is an increase in total tension with increasing
pre twitch length. The increase in contractile tension
is then the diference between the passive and the total
curve. This effect is additional to the effect of
||Isometric twitces with increasing
pre-twitch length. In can be seen that as opposed to
inotropy, time to peak tension do not increase, even
though peak tension does, and, as a consequence of this
the rate of force development (as the rise to higher
peak during the same time gives higher rate).
|Hypothetical length tension
diagram, based on the sarcomere hypothesis, that by
increased fibre length initially will increase the
overlap between the myosin head regions and the troponin
regions on actin, optimising the number of cross bridges
that can be formed, and thus the peak tension
obtainable. In this model there is an optimal length,
then the available number of cross bridges, and thus the
peak tension decline again. This seems to be in
accordance with (208), as far as active tension is
||The Frank- Starlings law. Acute
increases in end diastolic filling, will increase the
stroke volume along the curve shown. This effect was
observed with both increased venous pressure, but also
with decreased stroke volume in previous beat, resulting
in an increased EDV. Within physiological limits there
is an increase, but with increasing dilatation, there
will be less response. However, at least in normal
hearts, there is little evidence for a descending limb
of the curves.
|Illustration of the preload. If a
weight is attatched to the unloaded muscle, this muscle
will be stretched, increasing the peak force the muscle
can develope. But the preload is also part of the force
the tension has to overcome in the contraction.
||In an intact ventricle, the preload
is also a function of size. In addition to the size
being a measure of the pre stretch of the muscle, the
intraventricular pressure acts on a larger surface, and
thus the force that has to be generated must be
proportional to the surface area. Assuming that the two
balloons have the same intracavitary pressure, the total
load on the wall (as illustrated by the larger number of
arrows in the larger balloon) is proportional with the
surface area, and thus a function of the radius
(F = P × A = P × 4 × × r2).
|Wall stress. A force acting on a segment is distributed across the cross section, thus a bigger cross section gives a smaller force per square unit as illustrated by the wider segment with smaller arrows on each half.|
|The difference between pre- and
afterload is illustrated here. After preload is added, a
support is placed, preventing further stretch of the
muscle when another weight is added. This second weight
is the afterload. When the muscle contracts, it has to
develop a tension that is equal to the total load,
before it can shorten. If the peak force is higher than
the total load, the muscle will then shorten without
generating more tension, in an isotonic
||Isotonic isometric twitches tension
diagrams above, length diagrams below, after (208).
From the diagrams, it is evident that shortening only
starts after tension have reached load, and then, the
tension is constant while the muscle shortens. Thus the
first part of an unloaded contraction is also
shortening, while the first part of a loaded contraction
is isometric, becoming isotonic after tension equals
load. Peak rate of force generation (RFD), occurs during
the isometric phase (except in the unloaded phase, where
there is no tension development). Peak rate on the other
hand occurs during the first part of the shortening,
after tension = load, and is thus later than peak RFD.
The figure also shows that shortening decreases as load
increases, as more of the total work is taken up in
tension development. This affects both peak maximal
shortening and peak rate of shortening.
|Shortening curves related to
afterload, modified from the figure above. The
shortening in percent, is equivalent to the longitudinal
strain of the muscle.
||Strain curves from a normal
subject. The strain curve is fairly similar to the
shortening curves to the left.
|Shortening velocity and total
shortening, Relation to preload and total load.
Both shortening and velocity can be seen to decrease
with increasing afterload (total load), but increase
||Shortening velocity and total shortening, Relation to total preload and inotropy. Both can be seen to increase with inotropy, but decrease with load.|
contraction, the muscle will increase tension, but
resulting in no shortening as long as the tension is
below the total load (isometric contraction). When
tension equals load, further contraction will result in
shortening at constant tension (isotonic contraction).
This is what we see in imaging.
an increasing load will both delay onset of
shortening, as the development of higher tension takes
longer time, but will also result in less shortening, as
well as a lower initial rate of shortening. The
effect of increased load in slowing relaxation (224)
is not shown in this simplified diagram. This would have
shown up in slowing the tension downslope, but the
lengthening would still be shortened by increased load.
will give a slower tension development and lower peak
tension. However, this has the same effect as increased
load on shortening, resulting in delay in onset of
shortening, lower rate of initial shortening and less
total shortening. The
relative incr4ase in load due to reduced contractility,
would still slow relaxation, (224),
but this is not shown here.
|Effect of load on work and power.
With increasing total load the muscle increases the work
and power, despite decreased shortening, but only up to
a peak. After that, increased load will decrease work
and power by decreasing shortening. Increased preload
increases shortening at all afterloads, and will
increase both work and power.
||Effect of inotropy on work and
power. Inotropy will increase work at any given total
load, by increasing shortening. It will also increase
power, by increasing velocity of shortening.
|Simplified pressure volume
diagram (Wigger's diagram) of a whole heart cycle. The
diagram shows the atrial, ventricular and aortic
pressure curves, the ventricular volume curve and the
ECG on a time axis. Mitral valve opening (MVO) and
closing (MVC) occurs about the crossover between
atrial and ventricular curves, aortic closure (AVC)
and opening (AVO) occurs near the ventricular and
aortic valve closure, while aortic valve closure
occurs at the aortic dicrotic notch pressure curves
having crossed much earlier during ejection.
Isovolumic contraction (IVC) is between MVC and AVO,
there being no volume change, this is a true isometric
contraction. Isovolumic relaxation is between
AVC and MVO, this is the isometric phase of
relaxation. The three peaks of the atrial pressure
curve, are a (atrial contraction), c (closure wave)
and v (ventricular contraction).
Below is shown the analogous isotonic - isometric twitches. As seen there is initial preload increase during atrial contraction, increasing passive tension as well as the subsequent tension and ate of force development. Then there is isometric contraction, during IVC. In the isolated muscle, there is isotonic contraction (shortening). In the working ventricle, there is less increase in tension (Systolic load can be considered more or less equal to central pressure during ejection for acute changes), but pressure continues to increase during first part of ejection due to aortic elastance, and then drop during last part of the ejection due to aortic run off. Thus, in the intact heart, the contraction is far from isotonic. The corresponding shortening curve as it would have been in an isolated muscle is shown in dark blue, pre stretch during atrial systole, peak shortening early in the isotonic contraction with lengthening still during isotonic contraction, returning to baseline length at the start of isometric relaxation. The true curve as it is in a working ventricle is, of course, parallel to the ventricular volume curve and shows continuous shortening during the whole ejection (isotonic analogy) and only partial return to baseline length even after completed relaxation.
The Wigger's diagram is fairly common in this form, but is incomplete, as rapid filling is shown as a passive event, and as valve openings and closures are shown at pressure crossover.
|Pressure volume diagram of a
heart where pressure is plotted against volume, a
pressure-Volume loop (PV-loop). The top version shows
the cardiac phases, with the same simplifications as
the Wigger's diagram to the left; rapid
filling is shown as a passive event, and as valve
openings and closures are shown at pressure
crossover. Time runs around the loop in a
counterclockwise direction. The width of the loop is
equal to the stroke volume. The top of the diagram
shows the pressure curve during ejection.
The red, dotted line touching the loop is the end systolic pressure - volume relation. The slope of the tangent is P / V, which is the common definition of elastance. In filling, the elastance is usually taken to mean how much (counter-) pressure a given volume generates, but end systolic LV elastance is a function of emptying. Thus this must be taken to mean how much volume reduction a given pressure has generated. The blue dotted line, the left ventricular end diastolic pressure relation, is the passive tension that the diastolic filling generates, i.e. at atrial filling.
The bottom diagram shows the LV work, which is the area within the PV-loop (cyan).
During isovolumic contraction pressure rises, with no change of volume. During ejection, volume is ejected, reducing ventricular volume from end diastolic volume to end systolic volume. During isovolumic relaxation, the relaxation reduces pressure from LVESP to LVDP, and during diastolic filling the volume increases from LVESP to LVEDP. The area within the loop is P × SV. The equivalent area with mean pressures is shown as the dotted rectangle, to give an intuitive visualisation of the P × V. The Ees is shown to increase with positive inotropy (red dotted line) and decrease with negative inotropy or failure (blue dotted line). The potential energy delivered to the remaining (end systolic) volume, which is not converted into ejection work, is the yellow shaded area.
As we have seen, work is load × shortening. Systolic load
is more or less equal to central pressure during ejection.
This is a simplified model, excluding the volume and wall
thickness part of the Laplace equation, but it is valid for
acute load changes, being proportional to pressure
changes. But the ejection phase occurs with a
non-constant pressure as seen above, so the contraction
during ejection is not isotonic.
LV end systolic elastance is defined as Ees = P / V, which is the slope of the line through the end systolic pressure-volume point in the PV loop as shown above. The relation of the PV loop to load and contractility, is illustrated below:
|Effect of preload. Increased
preload (increased LVEDV), will, through the
Frank-Starling balance increase stroke volume.
This increased stroke volume will be ejected at
the same pressure, thus returning to the same
point on the ESPVR line. Myocardial work, bing
BP×SV, will increase.
||Effect of afterload.
Increased afterload (increased SBP), will reduce
the stroke volume, This can be easily seen here,
as the end systolic point moves up the ESPVR line,
shortening the width of the loop, i.e reduced SV.
The effect on work is more uncertain, as SV
decreases while BP increases.
||Effect of inotropy. Inotropy
shifts the ESPVR line to the left, thus increasing
the force and thus LV emptying, increasing stroke
volume through reduced LVESV.
|In reality, an increased SV
will cause increase in SBP, causing an increased
afterload on the same beat, thus reducing
the effect on SV somewhat, through interaction
between pre- and afterload.
||In reality, an acute increase
in afterload, will reduce emptying (increased
LVEDV), so on the next beat, the preload
is increased, partly offsetting the effect of
afterload on SV.
||In reality, decreased LVESV,
without increased venous return, will in the
next beat result in reduced LVEDV, thus
offsetting the effect of inotropy somewhat by
Thus, as seen, above the ventricular elastance is a measure
of contractility, as it seems to be load independent (400),
and it has achieved a "gold standard" status for measurement
of contractility. In reality, this index is not easily
obtainable in the clinic, even in continuous invasive
monitoring, as volume measurements are not available in
routine monitoring. But in animal experiments, using
conductance catheters, where multiple pre- and afterload
manipulations can be done, and where the ESPVR can be
obtained by linear regression, it serves as a reference
method, to test other contractility indices.
However, the LV elastance may not be a perfect gold
- Firstly, using end ejection for end systole, means that measurements are done at a point in time where the myocardium is in relaxation (but not relaxed) phase.
- Secondly, as we see below, the true end systolic volume is not easily defined due to the protodiastolic volume decrease as discussed below.
Peak systolic pressure volume relation might be closer to
the real thing, but is not easily discernible.
Finally, however, of course these volume considerations are only related to acute changes. In inter individual differences in healthy individuals, as well as in LV dilation, the EDV is not a measure of preload, and the PV-loops can only be interpreted in relation to the individual. PCWP, on the other hand, is a measure of preload, that is relatively standardised and thus a more universal measure of preload when applied across individuals, although it does not take the Laplace effect into consideration.
As seen, a lot of phases can be seen in the motion and deformation curves. To understand their relation to the phases of the heart cycle, it is necessary to go into the heart cycle in a little more detail. Already Wiggers (402) was clear that the phase pattern was more complex than the original six phases depicted above.
The pre ejection period (PEP) is defined as the period from
the start of the first deflection of the QRS, to the start
of ejection, as defined by the aortic valve opening, or the
onset of flow in the LVOT (235).
Even this, is sub divided into periods.
To start with, there is electromechanical delay at the
cellular level, the action potential generating Calcium
influx, again generating release of more calcium form the
SR, resulting in onset of cell shortening as shown here.
This process takes about 30 - 40 ms (234),
and leads to onset of local shortening. Simultaneously,
there is propagation of the action potential over the whole
ventricle, this is the propagation that is seen as the QRS
potential, and the time it takes is the duretion of the QRS
(about 80 - 110 ms, although the last part may be activation
of the right ventricle).
Early experimental and invasive studies seemed to show that there is initial endocardial activation almost simultaneously in mid septum and mid lateral wall, after 10 - 15 ms after onset of ECG (350, 351), but this will be partly concomitant with EMD at the cellular level.
Active contraction with pressure rise in the ventricle, and
atrio-ventricular pressure crossover, has been seen to
occure before the closure of the mitral valve (236,
This is intuitive, the initial contraction being the force
for increased LV pressure that closes the mitral valve.
It was suggested that this was because of the inertia of the inflowing blood, flowing against a small pressure gradient, keeping the valves open for a short while (403). But this would mean a continuing inflow as well as volume increase during proto systole. Newer experiments with high fidelity conductance catheters (173), as well as the evidence from tissue Doppler, clearly shows the opposite, a volume reduction in this phase. In the initial situation, with open mitral valve, the left ventricle is close to unloaded, and active contraction should lead to shortening rather than pressure increase. This would mean that the PEP motion would give a very small volume decrease, before the mitral valve closes, but without any regurgitation, as the valve moves within the stationary blood volume. But is still means active ventricular contraction, and, at the stop of the blood, this will mean closure of the mitral valve as the cusps stay in the stationary blood stream. This, again would give a small volume reduction in the pressure - volume loop, by exclusion of part of the blood volume, even without regurgitation. This has been shown experimentally (173), and is illustrated below. This also means that the isovolumic contraction phase, defined as the period from MVC to aortic opening, starts later and is shorter than PEP (235), and also than the duration from onset of contraction to start ejection
|At the end of late filling (atrial systole), there is again equal pressures in atrium and ventricle, and no flow. The start of contraction will then lead to closure of the mitral valve, as they move in a stationary blood column, they will be pushed toward the base and toward the middle. The motion of the leaflets is mainly lateral, i.e. towards the middle, and thus may be greater than the longitudinal displacement of the annulus.This motion of the nitral ring would tend to displace the mitral eaflets towars the middle, and thus be a part of the closing mechanism. The mitral leaflets move towards the middle, and thus the displacement of the ring towards the apex is far less than the motion of the leaflets towards the base.||Volume reduction due to pre ejection shortening. This volume reduction is also evident from displacement and strain traces.This volume reduction is not due to flow, but the fact that the mitral annulus excludes part of the blood volume by , sliding along a stationar column of blood that then is "atrialised", illustrated by the light red cyllinder in the image above.|
This means that there is a small volume decrease at end
diastole, calculated to about 4.7% of the largest end
diastolic volume (173).
|Pre ejection spikes evident
bt tissue Doppler, both septally and laterally.
||By colour tissue Doppler they
can be seen to be simultaneous
||And they correspond to a very
small pre ejection displacement of the annulus,
which stops abruptly, presumably at MVC.
Schematic representation of the findings in (173), showing that as onset of contraction results in shortening, this is interrupted by MVC (onset of IVC), when mitral valve is stented (red curve), this results in a smooth non-interrupted transition to ejection velocities.
|In this recording, the pre
ejection spike (middle vertical marker line) is seen to
start after the onset of ECG (left vertical line), but
before the onset of the first heart sound (right line).
In the Doppler recording, the ECG can be seen to precede
the first heart sound, which precedes the start of
|Ultra high frame rate tissue Doppler from the base of the septum a subject with atrial fibrillation. Even with no atrial activity, there is the same pattern of double velocity spikes, showing them to be ventricular in origin. Image modified from (268).||Ultra high frame rate tissue Doppler from the base of the septum a subject with 2nd degree AV block, as seen by the second P-wave following the first heartbeat, with no QRS nor ejection velocities. The atrial recoil can be seen as three velocity spikes (arrows), indicating that the mitral ring bounces. However, this is in a situation without LV myocardial tension. At start of the first heart cycle, there may be some fusion between atrial recoil and vetricular contraction as seen by the timing. this may be due to longer PQ time. Image modified from (268).||Ultra high frame rate tissue Doppler from the base of the septum a subject with 1st degree AV block. (This is a highly trained, healthy subject, the AV block is physiological)Three spikes are seen before ejection (arrows). Here, the initial spike must be atrial recoil, coming before start of the the QRS, it cannot be ventricular i origin. Even the second spike may be atrial, or a fusion of an atrial bounce and ventricular contractioncontraction. Both middle and left images shows that there is atrial activity i the pre ejection phase, but that the visibility of this may be dependent on the PQ interval. in shorter PQ interval, the presence of ventricular tension may modify or abolish the atrial component. Image modified from (268).|
|Pre ejection spike
can be seen to be lower than peak ejection
|-by spectral tissue
||by colour tissue
||and by speckle
|By tissue Doppler,
although this might seem closer to the reality of bing
higher (absolute) than peak systolic SRI,
||THis is also the
method giving the highest variability due to noise.
||Also in speckle
tracking pre ejection peak is less than peak systolic
SR, although in ST, there is substantial under sampling
|The geyser Strokkur at Haukadalir, Iceland at pre eruption (pre ejection). In a geyser, the water is heated deep below the surface, at high pressures. Thus the water becomes superheated before it boils, building up heat in a delayed boiling, when it boils, the pressure builds up and the column of steam will rise through the water, causing the water above to bulge (no isovolumic, then). To the left, the steam can be seen within that bulge, steam just breaking through the surface at one point. To the left, the steam breaks through, and the water is driven out both by the steam and the pressure below, resulting in the start of an eruption (ejection).|
The true isovolumic contraction
time (IVC) is defined from MVC to the start of
ejection. In this phase, there is no volume change, and, hence, no
deformation. Thus, in this phase there is no volume change, and,
hence, should be no deformation. This phase it on the other hand,
the period of most rapid pressure rise, peak dP/dt, which occurs
during IVC (241).
represents the most rapid rate of force development (RFD), as there
is no volume change, and may also be one correlate of contractility.
As it occurs before AVO, it is not afterload dependent, and is a
useful invasive index of contractility. However, as seen fom the
length force relation above,
this maximal force measure is not preload independent(395,
|Peak systolic annular velocity (S'), which is early systolic, compared to peak annular displacement (MAPSE), which is end systolic. S' is actually the peak rate of annular displacement, and is thus closer to contractility, while MAPSE is end systolic and thus closer to ejection fraction.||Peak strain rate, being early systolic, compared to peak strain, which is mainly end systolic, and closer even, to ejection fraction.|
The total of the arterial effect can be described by the arterial
elastance: Ea = P / V and ventriculo arterial coupling (405):
The exact time of aortic valve closure, is not evident from imaging alone, except high frame rate imaging of the aortic valve itself, or by imaging the valve click in Doppler recordings. But it is not entirely evident from all images.
it can also be easily demonstrated by the method of transferring
the opening and closing events from Doppler recordings to the
worksheet of analysis software, to be used in other quantitative
|Apical recording of Doppler flow of the LVOT. At end ejection, the valve click can easily be seen as the short spike. This is coincident with the start of the phonocardiographic first heart sound as seen by the phonocardiogram. However, in the last heart cycle, there can be seen a small oscillation earlier in the others, a small noise spike (red arrow). Thus the Doppler is the gold standard, and the phono has to be calibrated.||Aortic valve closure seen by tissue Doppler in long axis view. The AVC is identified by the start of rapid positive velocities (toward the probe/apex) in the sample volume in teh LVOT. (Blood velocites are filtered out by the low amplitude as explained here. (The rapd upstroke is not an aliasing of the high downward velocities seen imidiately before, this can be seen as the shift from negative to positive occurs at lower velocities than the peak negative velocity in the a' wave, which doesn't aliase)|
|Propagation of mechanical wave along septum, as visualised by ultra high frame rate TDI. The wave is identified by the peak positive acceleration in each point, showing this to be earliest in the base, lowest near the apex. The orange frame shows the velocity curves, the blue frame the acceleration curves. Image courtesy of Svein Arne Aase, modified from (172).||Point of peak acelleration can also be shown by this method to be later in the lateral wall than in the septum. Image courtesy of Svein Arne Aase, modified from (172).|
|Colour strain rate M-mode from the septum of a normal subject. It is evident that there is an elongation in mid septum, resulting in initial negative velocities in mid and basal septum before closure of the aortic valve. Notice also how the initial elongation of the mid septum occurs before the closure of the aortic valve, i.e. the initial negative velocities in the basal and mid septum are protodiastolic.||Thus, AVC comes after the foirst
positive strain rate spike following the ejection phase.
|Proposed mechanism for the aortic closure. During ejection the ventricle can be seen to shorten, and there is ejection (arrow), keeping the cusps open. Ejection is decreasing towards the end of the ejection period, as shown by the decreasing length of the arrow. At end ejection, there is no flow, and the relaxation that started during ejection as a reduction in tension, leads to a slight elongation (blue arrows). The aortic cusps then are closed due to the valve motion in the now stationary blood column, similar to what happens if a scoop is put into the water (opening forward) from a boat that is moving forward. In this case, the motion of the cusps are mainly lateral, i.e. towards the middle, and thus may be greater than the longitudinal displacement of the annulus|| Volume increase due to proto diastolic lengthening. This volume increase is also
evident from displacement and strain traces. This
volume increase is not due to flow, but the fact that
the aortic annulus includes part of the blood volume by
, sliding along a
stationary column of blood that then is
"ventricularised", illustrated by the light
red cylinder in the image above.
|Motion of the mitral ring,
mitral leaflet and mitral tip. Bottom; zoomed to
the time period of interest. The septal mitral ring
(yellow curve) can be seen to "bounce" after AVC,
meaning that it has apical motion during IVR. This
motion is of course imparted also to the mitral leaflet,
and means that the start of apical motion do not mark
||Velocity traces of the same points as seen to the
left. The start of apical motion of the mitral ring
(yellow curve) corresponds to a shft from negative to
positive velocities after the protodiastolic negative
velocity spike (i.e. the crossing of the zero line.
|A sample volume at the middle of the mitral leaflet
(green curve), will have the same motion as the ring,
although with some delay. However, we see that apical
motion starts around the middle of IVR, before MVO.
||This corresponds to positive
velocities in the last half of IVR (green curve).
|The sample volume at the
mitral tip (red curve) shows no apical motion during
IVR, rater motion in the opposite direction, but an
abrupt start of apical motion at the end of AVR, at the
same time as the mitral ring shifts to motion toward the
base. Thus, this is an independent leafet motion, and
marks the MVO, and it can be seen that during IVR, there
is ballooning away from the apex of the mitral leaflets.
Both mitral valve traces can be seen to deflect sharply downwards at a later time point (white markers) , this is due to aliasing of the tissue velocity when the velocities reaches the Nykvist limit.
|The mitral tip (red curve) can be seen to have
negative velocities (moving away from the apex) during
IVR, and to cross from negative to positive velocities at
the same time as the mitral ring crosses from positive to
The points of aliasing can be seen at the abrupt downward stroke in the traces from the mitral leaflets (White markers), which is earlier at the tip than in the middle of the leaflet. Only in the mitral ring can AVC be seen with certainty.
|Looking at the mitral ring, which would reflect the overall volume changes, there is concomitant negative velocities (basal motion during the protodiastolic event in both parts of the mitral ring. But after AVC, we se negative velocities continuing in the lateral part, while there is a positive motion (bounce) in the septal part. This is consistent with no volume change, but a tilting of the left ventricle during the IVR. Mitral opening thus possibly corresponding to the start of basal motion as seen by the septal curve. Only after MVO do the septal part start basal motion concomitant with the lateral part. And only then will there be overall elongation (volume increase). This do correspond to s shioft in the septal velocity curve from posisitve to negative. It is the second zero crossing after the protodiastolic dip.|
|Colour M-mode in normal
subject. The mitral valve is included, and to the left
the colur is removed from the same two cycles in the
same recording, to locate the point of mitral valve
||IVRT: Zooming in on the
images, at end ejection can se the valve click as a
vertical bar (Just as in pulsed Doppler recordings as
thus, the IVR is very easily defined, and apically
directed flow (red) above the mitral valve, i.e.
intraventricular can be seen during the IVR.
|Strain rate tracings in this subject show positive strain rate (lengthening) during IVR in the septal apical and lateral apical and midwall segments, concomitant with negative strain rate (shortening) in the basal segments.||Peak negative strain occurs later in base and midwall. AVC can be seen best by strain curves in the midwall segment. No definite deflection can be seen to correspond to the event assumed to be MVO transferred from the Velocity/displacement traces.|
|Diastolic filling. There are
three distinct phases. Early filling (E - wave),
where there is inflow from the atrium to the left
ventricle (red curve and arrows), the ventricle
increases the volume, evident by the velocities of the
annulus away from the apex (dark blue arrows. Diastasis,
with little or no movement. There may or may not be some
passive flow into the left ventricle in this
phase. Atrial systole (A - wave), where there is
atrial contraction, pushing blood into the
ventricle again (light red) and a new motion of the
mitral ring away from the apex (light blue), due to
pressure increase, or direct pull from atrial
contraction, or both. The resulting flow and
tissue velocity curves are illustrated below.
||Mitral flow curve. The conventional measures of diastolic function are shown: E: Peak flow velocity of early filling phase; a measure of rate of relaxation during this phase. Dec-t: Deceleration time of early flow; measured from peak E along the slope of velocity decline to the baseline. IVRT: Isovolumic relaxation time; the time between end ejection and start of mitral flow. It's conventionally measured from the valve click at AVC to the start of mitral flow. A: peak flow velocity of atrial systole. The E/A ratio shows the relative contributions of the two phases to filling, and is a more sensitive index of reduced early filling.|
The main point is that when there is pressure drop (negative P) concomitant with volume expansion
(positive V), this means that there is negative compliance C = V / P, which means suction, as argued already by Katz (407)
|Suction driven filling (vis a fronte; a force acting from the front), versus pressure driven (vis a tergo; a force acting from behind) filling of a chamber (B). In this simplified model, the level of fluid (and, hence, pressure) in chamber A is assumed to be constant during filling. In both cases the flow is driven by the pressure gradient between A and B (i.e. there is a potential energy in A versus B that drives the flow, shown by the blue arrows), but in vis a fronte, energy is applied to creating a pressure drop in chamber B, in vis a tergo, the force application (energy) is applied to the fluid in chamber A.|
|In suction driven filling, there is a force, F, applied to the piston, expanding chamber B. This creates a pressure drop in the chamber, and a pressure gradient between A and B. Thus, the energy is applied to the creation of a pressure drop in chamber B. Flow (Q) is gain driven by the pressure gradient between A and B.||Looking at LV diastolic function, seeing that flow velocity is the rate of volume change, and thus volume increase, it seems that early filling is vis a fronte (red); showing volume increase of the LV (chamber B) with simultaneous pressure drop (negative dP/dV), the driving force being left ventricular recoil, while late filling is vis a tergo (blue) showing volume increase with pressure increase (positive dP/dV), the driving force being atrial contraction.||In pressure driven filling, the force driving the piston is the pressure in chamber A (actually the pressure difference between chamber A and B. The force, F (black arrow), is the pressure * area, and the pressure is a function of the height of the level of A over B, and the density of the fluid. Thus, the energy for the movement of the force is potential energy of the pressure difference. Flow (Q) is driven by the pressure gradient between A and B. In this case the pressure increases in chamber B up to the level of A. This transmits the force to the piston expanding the chamber B by the pressure.|
|Revised Wigger's cycle showing the
valve closures as phono traces, with pressure crossover
and a small volume expansion before MVC, dividing the
pre ejection interval into three; EMD, proto diastole
and IVC, also the small volume reduction in proto
diastole before AVC, and also the pressure drop during
early (rapid) filling concomitant with rapid volume
||Revised PV-loop, based on the full
cycle as it is. The small volume reduction in proto
systole and the small volume increase in proto diastole
before valve closures is shown as the red shaded areas.
The two notches before valve closures is in accordance
with experimental findings (173).
In addition, the diastolic part of the PV-loop is shown
with the first part having pressure drop and concomitant
volume increase, in accordance with the established
physiology of early filling.
Velocity and displacement in the base of the septum, showing systolic motion toward the apex, protodiastolic motion away, and the the two basis diastolic phases, early (e') and late (a') motion way from the apex, separated by diastasis.
|In strain and strain
rate, the pattern can be seen to be much more complex in
these tracings from the base alone. There are at least
four positive spikes (elongation) during diastole, this is
reflected by much more "steps" towards zero in the strain
curves. As strain rate is fairly
susceptible to noise, this might have been interpreted as
noise (as is the small negative spikes between) , but
integrating to strain eliminates the random noise, and
shows what is real.
|Diastolic strain rate. The strain
rate M-mode reveals that some of the diastolic phases has
the characteristics of elongation waves between base and
apex. The differences between base, midwall and apex
can be seen clearly in the traces diagram to the left,
showing that not only are there more elongation phases,
but they don't even coincide in the different levels of
|Tissue M-mode from the septum, showing the dip of the AVC event, and the time delay from base to apex of the initiation of downward motioning the filling phase.||Diastolic
strain rate. Diastolic events seen by strain rate. Both
the curved M-mode and the traces shows the separation
1: Midwall protodiastolic lengthening
2: Apical isovolumic lengthening
3: Early filling propagating from base to apex and back
4: Late filling propagating from base to apex and back.
|Tilting the M-modes 90°, the motion is downwards and the elongation wave propagates upwards, as in a conventional M-mode of a myocardial wall that is shown to the left. The relaxation rate can be seen by the slope of the red line. The forward (downward motion of the first car is shown by the black line, being equivalent to the motion of the mitral ring,.|
|Diastolic strain rate propagation. M-mode from a myocardial wall, velocities at the top, and strain rate at the bottom. During the two diastolic phases, there is blue colour showing downward motion, which can be seen by the tissue lines as well. The elongation can be seen to propagate from the base to the apex over time.||Diastolic strain rate propagation velocity is the slope of the elongation wave.|
|Relation between diastolic strain rate propagation of the E-wave and the peak early diastolic velocity of the annulus. If the wave propagates slower, the resulting velocity wave of the annulus will be broader and lower, even with regional strain rate may be the same, but the strain rate propagation is dependent on both local diastolic strain and the properties of the wall. .||In reduced diastolic function as shown here to the
right, there is a lower peak diastolic annular velocity as
well as a reduced early magnitude of motion of the mitral
|Elongation and simultaneous
thinning of the wall can be seen to propagate from the
base to the apex simultaneously with the motion of the
mitral ring. The local early diastolic strain
rate is shown as the arrows indicating wall thinning
(but thinning and elongation has to be simultaneous as
and shows how local early diastolic strain is delayed
in the apex compared to the base. This is illustrated
|The AV plane. It consists of a fibrous plane connecting the rings of the pulmonary artery (PA), the aorta (Ao), the Mitral (MV) and the tricuspid (TV) valves, and surrounded by the muscular base of the heart. The sections of the mitral ring cannot be seen as indepndently moving structures. Thus, segments will interact within this framework.||And both ventricles move the
AV plane. (It might seem to be slightly flexible, as the
motion of the tricuspid corner (tapse) is higher than
the mitral motion, but still the palne will move as a
whole, even if there is some deformation. The velocities
of the lateral left wall are higher than the septum, but
is due to the longer wall. The overall systolic strain rate
is not so different.
|Diagram of longitudinal segment interaction. the longitudinal shortening of one segment results in shortening of the segment itself (orange arrows), but also in motion (red arrows) of the segments basally to it. (In this illustration, the red arrows show the motion of the middle of the segment, meaning that it also included the effect of the shortening of the apical half of the segment itself.)and the motion of each segment is equal to the summation of the shortening of the segments apically. However, the primary effect is force generation. And this means that contraction in one segment results in a force applied to the neighboring segments. This force has different effects, as the apex is considered anchored (by the recoil force from ejected blood), while the midwall segment has force applied from both sides, and the basal segment is freely movable. The main point is that the force from neighboring segments may be considered part of the load of each segment, and that motion is secondary to deformation, but deformation is secondary to force and load.|
contraction, the muscle will increase tension, but
resulting in no shortening as long as the tension is
below the total load (isometric contraction). When
tension equals load, further contraction will result in
shortening at constant tension (isotonic contraction).
This is what we see in imaging.
an increasing load will both delay onset of
shortening, as the development of higher tension takes
longer time, but will also result in less shortening, as
well as a lower initial rate of shortening. In
these diagrams, the effect of load in slowing
is not shown. This effect would show up in prolanged
duration of the downslope in the tension diagram.
However, the lengthening phase would still be shortened
by the load.
||Reduced contracility will give a slower tension development and lower peak tension. However, this has the same effect as increased load on shortening, resulting in delay in onset of shortening, lower rate of initial shortening and less total shortening. Thus, reduced contractility would also have effect on relaxation (224), seen in the tensin curves, but this is not shown here.|
|Symmetrical forces in all segments,
will result in symmetrical shortening. Thus, all
segments shorten equally (orange colour), which means
that the base moves most (the sum of shortening of all
segments), as the apex is stationary.
||Loss of contractility in a basal
segment (smaller black arrows in the left basal
segment), results in less shortening in the affected
segment. However, this means that the load on
the more apical segment is reduced, and thus, this
segment will shorten more Red colur9 , not due to
hypercontractility, but to less load. Also, the
total force acting on the base is reduced, resulting in
reduced total shortening (smaller red arrows in the
||Even more reduced tension in a
basal segment will result in the segment actually
stretching, while the apical segment shortens even more
in response to the basal segment stretches. This will
not result in reduced motion of the regional
mitral ring point, mainly a shift in the distribution of
shorteningbetween segments, and a reduced global
||Reduced tension and stretch of an
apical segment may result in increased shortening of the
opposing wall, as well as the basal segment, but
this may result in a rocking of the apex toward the
||Symmetrical weakening of the apical
segments, may result in increased shortening of the
basal segments, but as the apex stretches, the motion of
the AV-plane is more reduced.
||S' (cm/s pwTDI)||S' (cm/s cTDI)||Segmental SRs (s-1)
intra subject variation (max - min)
|MAE(mm)||S' (cm/s pwTDI)||S' (cm/s cTDI)||Segmental SRs (s-1)||Mean SRs (s-1) per
is no regional reduction of mitral motion in
||Only global reduction of mitral motion, and segmental hypokiesia with resiprocal hyperkinesia.|
The full deformation pattern in acute ischemia was shown early in
the experimental work of Tennant and Wiggers (46):
|Figure modified from (46), the time course of segmental myocardial deformation after acute LAD occlusion. The deformation (myogram) curves have been inverted to orient them as customary for strain curves today. Thus, the sequence starts at the bottom with A, and progression of ischemia is upwards, following the letters to the left. The numbers to the right, denotes the number of heartbeats after occlusion. As we see, in A there is a normal strain curve, the first change is an abbreviation (B) of the duration, and then delayed onset and reduction of the magnitude systolic strain (D), followed by initial systolic stretch and an increasing post systolic shortening peak (E-G). At the end, the systolic stretch lasts through systole - i.e. holosystolic stretch, but with post systolic shortening that exceeds the amount of systolic stretch )H-J), and finally there is virtually only passive stretch and recoil (K).||Myocardial ischemia in the LAD area
during dobutamine stress echo shown by the strain
curves. The different colours
of the curves correspond to differently placed ROIs in
the lateral apex (cyan), septal apex (yellow) and
basal septum (red). To correspond to the image to
the left, the time course of ischemia is from bottom to
top, so the four panels are baseline (bottom, then 10ug
dobutamine/kg/min, then twenty, and finally 30 at the
top. The different regions have different
degree of ischemia during the stress. At
baseline there is slight post systolic shortening in the
apical lateral part, increasing ischemia at 10 ug where
there is initial akinesia (even a little stretch),
reduced systolic shortening and finally post systolic
shortening. This is similar to stage F at the left. At
20 ug there is initial stretch, systolic akinesia and
post systolic shortening in the apicolateral segment,
increasing to holosystolic stretch and post systolic
shortening at peak, corresponding to stage G-H to the
left. The two other segments showing less ischemia,
although the septal apex shows hypokinesia and post
systolic shortening at 20 ug awhich is increasing at
peak, while the basal septum shows slight ischemia at
It is evident that in a segment being stretched in systole, if
there is any elasticity at all, the segment will recoil in
diastole, i.e. as a function of the elastic force stored in the
segment. (also, if the segment had not returned to the original
shape, the whole heart would have been turned inside out in the
time of a few minutes. Thus, stretch / recoil is a mechanism
for post systolic shortening. In ischemia, post systolic
shortening develops before there is systolic stretching (46,
), i.e. while there still is systolic shortening as shown in the
stress example. This this can be explained by the timing of the
tension interaction between segments.
|1: Two segments with equal tension
(red and blue) will shorten equally and symmetrically.
||2: If one segment becomes ischemic,
this will lead to:
1: slower tension buildup, leading to initial stretch,
2: lower total shortening, and concomitant increased shortening of the healthy segment as the load on this is reduced
3: prolonged tension in the ischemic segment, leading to increased shortening as the two tension curves cross, the ischemic segment shortens as the healthy relaxes. This is post systolic shortening.
|3: As ischemia progresses and
tension becomes lower, the initial stretch increases,
and shortening becomes less and later, while post
systolic shortening remains.
||4: At one point, there will be only
stretch during systole. However, the remaining post
systolic shortening after normal contraction, is a
sign that there is still active tension
||5: Finally, with total loss of
tension, there is only stretch. The post systolic
shortening is still present, but only as a recoil
phenomenon, with no sign of active tension.
from a real stress echo, as described in full below. The
cyan curve is apicolateral segment, which is maximally
ischemic, and shows conformance to the model above. The
red curve is basal septal, which conforms bst to the
non/ischemic segment, while the yellow curve is
apicoseptal, and ischemic, although to a lesser degree.
The white vertical line shows the AVC.
Severe ischemia in all walls in a patient with severe three vessel disease (among other things stenosis left main, occluded LAD filled from RDP, even with occluded RCA filled from collaterals) . Visually, the most striking finding is fall in EF with increasing stress.
rate colour M-mode. No significant PSS can be
seen (Except possibly apicolaterally). Thus at first
glance, the M-mode looks normal, at least concerning
||Strain rate curves (top) and strain (botom) of the ventricle at peak stress. Again, no significant PSS can be seen (Except possibly apicolaterally), demonstrating clearly that there are little PSS when there are no segments with normal contraction-relaxation cycles. The AVC is evident from the phono traces. The strain curves show delayed and prolonged shortening, but more or less in all segments. This is equivalent to the balanced ischemia of scintigraphy.|
|Circumferential strain in a symmetrical ventricle model. For simplicity, the wall is divided into two layers. As the wall thickens, there is thickening and inward shift of the midwall line of both layers, but the innermost layer is in addition shifted inwards, cusing both a greater wall thickening (due to lack of room), and a greater midwall circumferential strain, both due to this, and due to the inward displacement of the innermost layer due to thickening of the outer layer.||Akinesia of the inner (sub endocardial) layer. In this case there will be normal wall thickening and cicumferential shortening of the outer layer, and almost no thickening of the inner layer. Still, there will be inward shift of the inner layer due to thickening of the outer, this will reduce the space and may cause some thickening even without function. Mainly due to inward shift, there will still be midwall circumferential shortening of the inner layer.||Reduced
circumferential strength in a segment, will result in
the normal segments contracing more (due to reduced
regional circumferential load, and the affected
segment may stretch. In that case this will also
result in thinning, as the segmental volume stretches.
Changes in timing of different segments may occur without
concurrent reduction in contractility. In especially left bundle
branch block, there is different inset of contraction in different
segments or walls, leading to some segments (or walls) contracting
while others are passive, both at the start and end of the
contraction-relaxation cycle, and where both intraventricular
pressure and elasticity contributes to specific patterns of
shortening that are quite different from the normal patterns. In
this case, it is differences in timing, that leads to
different segments or walls having different tension.
left bundle branch block may have very different mechanical
effects. This is due to the very large variability in how much,
and which parts of the left bundle that are affected, and to what
Basically, left bundle branch block means a reduced conduction velocity in the left bundle, below that of the right bundle, causing the septum activation direction to shift from left-right to right-left, but also meaning that parts of the left ventricle are activated later than the right, and later than normal, causing a widening of the QRS. The mechanical effects of the LBBB may be quite various, however:
|The "septal beaking" in M-mode , a short inward motion starting at the peak of QRS, and peaking at the same time as the onset of inward motion of the inferolateral wall. The contraction of the lateral wall is the force terminating the septal flash, so the time from onset of septal flash to onset of inferolateral wall thickening is the true mechanical delay between the walls.||The same phenomenon is seen in B-mode of the same patient as "septal flash", which consists of a short inward and then outward motion of the septum, the outward motion start about simultaneously with inward motion of the lateral wall. The "septal flash" is evident in both parasternal long axis and short axis. Images from patient with normal systolic function.|
After mechanical activation, there is an intial shortening seen in the velocity traces as a positive spike of short duration - the pre ejection spike. This initial contraction gives a small pressure rise which closes the mitral valve (236) about 30 ms after initial contraction (268).Delayed intraventricular conduction, on the other hand, will lead to delayed activation of the lateral wall.
As the walls contract in parallel, they will give rise to isovolumic contraction where there is pressure increase without deformation, and then ejection when ventricular pressure exceeds aortic, the ejection phase is characterised by longitudinal shortening and wall thickening.
However, active contraction is in terms of force, and cannot be seen by deformation, as the continuing ejection will result in continuing shortening despite tension decrease. The development of active contraction do not continue during the whole of the ejection, tension decrease starts around mid ejection, probably at the time of peak pressure / peak strain rate, after this there is tension release. Thus, the tension buildup is an event of much shorter duration than ejection. After this there is still tension, although decreasing, during the last part of ejection the ejection is partly driven by inertia.
|Septal activation alone. leading to
septal shortening and thickening, with concomitant
lateral stretch - the septal flash. No pressure
||Lateral wall activation, ending the
septal flash which peaks) with remaining septal tension
(or else there would be only rocking, no pumping). In
this case there is pressure buildup, MVC,
IVC and probably start ejection.
||During most of the ejection there
will be shortening, but part of this may be partly
passive due to volume decrease, especially in the
||In the last end of the ejection
there will be little or no remaining tension in the
septum, which then will stretch, due to the remaining
tension in the lateral wall (which have been activated
later). Thus, there will be stretch of the septum and
shortening of the lateral wall.
||Finally, there is no tension in the
lateral wall, which relaxes. In this phase there will be
elastic tension in the septum due to the previous
stretch, which will shorten in
post systolic shortening, while the lateral wall
stretches (due to both septal
shortening, and also in the course of normal early