Journal of Cardiology 63 (2014) 313–319

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Journal of Cardiology
journal homepage: www.elsevier.com/locate/jjcc

Original article

A new concept of the contraction–extension property of the left
ventricular myocardium
Motonao Tanaka (MD, PhD, FJCC) a,∗ , Tsuguya Sakamoto (MD, PhD, FJCC) b ,Shigeo Sugawara (MD, PhD, FJCC) a , Yoshiaki Katahira (MD, PhD, FJCC) a ,Haruna Tabuchi (MD) a , Hiroyuki Nakajima (RMS) a , Takafumi Kurokawa (RMS) a ,Hiroshi Kanai (PhD) c , Hideyuki Hasegawa (PhD) c , Shigeo Ohtsuki (PhD) da

Cardiovascular Center, Tohoku Pharmaceutical University Hospital, Fukumuro 1-12-1, Miyagino-ku, Sendai 983-0005, Japan
Hanzomon Hospital, Kojimachi 1-14, Chiyoda-ku, Tokyo 102-0083, Japanc
Department of Electrical Engineering, Tohoku University, Aramaki-Aoba 6-6-05, Aoba-ku, Sendai 980-8579, Japand
Institute of Medical Ultrasound Technology, Yokohama 2-12-15, Sagamihara 229-1122, Japanba r t i c l e

i n f oArticle history:
Received 12 June 2013
Received in revised form 15 August 2013
Accepted 9 September 2013
Available online 27 November 2013
Keywords:
Myocardial contraction-Extension property
Strain rate distribution
Phase difference tracking method
Peristalsis and bellows action of theventricular wall
Non-uniformity of myocardial contractionand extensiona b s t r a c t
Objectives: Using newly developed ultrasonic technology, we attempted to disclose the characteristics ofthe left ventricular (LV) contraction–extension (C–E) property, which has an important relationship to
LV function.
Methods: Strain rate (SR) distribution within the posterior wall and interventricular septum was microscopically measured with a high accuracy of 821 ␮m in spatial resolution by using the phase difference
tracking method. The subjects were 10 healthy men (aged 30–50 years).
Results: The time course of the SR distribution disclosed the characteristic C–E property, i.e. the contraction
started from the apex and propagated toward the base on one hand, and from the epicardial side toward
the endocardial side on the other hand. Therefore, the contraction of one area and the extension ofanother area simultaneously appeared through nearly the whole cardiac cycle, with the contracting part
positively extending the latter part and vice versa. The time course of these propagations gave rise to theperistalsis and the bellows action of the LV wall, and both contributed to effective LV function.
The LV contraction started coinciding in time with the P wave of the electrocardiogram, and the cardiac
cycle was composed of 4 phases, including 2 types of transitional phase, as well as the ejection phase andslow ﬁlling phase. The sum of the measurement time duration of either the contraction or the extension
process occupied nearly equal duration in normal conditions.
Conclusion: The newly developed ultrasonic technology revealed that the SR distribution was important in evaluating the C–E property of the LV myocardium. The harmonious succession of the 4 cardiac
phases newly identiﬁed seemed to be helpful in understanding the mechanism to keep long-lasting pumpfunction of the LV.
© 2013 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.

Introduction
The mechanical properties of the myocardial ﬁber, the multiﬁber scale mechanical performance of the ventricular wall (LV),and their mutual correlations are fundamental determinants of LV
function.
Although experimental studies using isolated muscle ﬁber or
multi-cellular myocardial tissue or anesthetized animals havebeen published [1–8], it was difﬁcult to obtain exact in situ
information even from open-chest surgical operations. This is∗ Corresponding author. Tel.: +81 022 719 5161; fax: +81 022 719 5166.
E-mail addresses: m.tanaka@jata-miyagi.org, shin@jcc.gr.jp (M. Tanaka).

because the hemodynamics and the ﬂow structure will certainly
be changed under the atmospheric pressure [1–8]. To date, several
non-invasive trials using ultrasonic methods have been proposed[9–11], however, because of poor spatial resolution, an ideal
method for clinical application has not yet been described, particularly in respect to the differential properties of the various regionsof the ventricular wall.
Objective
Our aim was to obtain information regarding the contraction
extension (C–E) property of the regional myocardial tissue to investigate the mechanical performance of the LV wall. For this, wedeveloped a new method of measurement of the myocardial strain

0914-5087/$ – see front matter © 2013 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jjcc.2013.09.009

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M. Tanaka et al. / Journal of Cardiology 63 (2014) 313–319

rate (SR) with high resolution using a phase difference tracking
technique [12–16]. Then, we tried to verify the precise C–E property of the myocardial tissue on the microscopic and macroscopic
scales in situ, which had never been attempted before.

Subjects and methods
Subjects
Ten healthy male volunteers aged 30–50 (39.6 ± 10.4) years who
gave informed consent were investigated.

Methods
Acquisition of ventricular dynamics information
To obtain information on wall dynamics, a specially designed
ultrasonic machine (Aloka 6500 model, Hitachi Aloka Medical Ltd.,Tokyo, Japan) was used. In the supine or left lateral decubitus position, a transthoracic parasternal 90◦ sector scan was performed,
while selecting a scanning plane passing through 3 points (centers of both the aortic and mitral oriﬁces and the LV apex). Thisplane, including the center of the LV and left atrium (LA) and 2 ﬂow(inﬂow and outﬂow) axis lines, was named “longitudinal section
plane” as described in the previous paper [17]. The measurements
were done on this plane to minimize the acoustical measurement
error. Perpendicular to this plane is the short-axis plane.

Measurement of SR distribution of the myocardium
The 2D echocardiographic equipment had a pulsatile ultrasoundfrequency of 3.5 MHz, 4.5 kHz in repetition rate, 1.5 mm in beamwidth, and 0.5 ␮s in pulse width. The range of the limited angle of30◦ out of 90◦ was scanned at a high speed of 630–700 frame/s,
switching 5 beam directions evenly sectioned from the base to
the apex (1–5: sparse scan) (Fig. 1, top). The echo signals from theventricular wall for about 2–6 second received in every 1–5 beam
direction were recorded in the memory and processed off-line byusing our own developed software [12–15].
After determining the measuring range from the endocardium
to the epicardium (Fig. 1, bottom), the measuring width (821 ␮m)
was settled. Then, the velocity {(x1 ),(x2 )} of the tissue at the 2 terminal moving points (x1 and x2 ) of the measuring width (821 ␮m)
was successively calculated as follows.
The phase difference between 2 successive reﬂection pulses atthe x1 and x2 points was measured by the “quadrature demodulation”, and the velocities (v) at these 2 points were calculated, as
having a propagation velocity of 1600 m/s [18] in the myocardium.
SR was calculated using the bottom equation {Si (t)} [15].
The serial SR distribution in the wall was obtained by calculating
the SR, while shifting the measuring width (821 ␮m) every 200 ␮mthrough the endocardium and the epicardium (about 10 mm). The
accuracy of measurement was about 2 ␮m.
The time serial SR distribution was displayed on the M-mode
image by color-coded information (Fig. 2). The serial red lines of 1–5
indicate each beam direction from the base to the apex as shownin the top of Fig. 1.
The increment of the SR (contraction) was indicated by cold
color (dark to light blue tone) and the warm color indicated thedecrement of the SR (extension) (red to yellow tone). In between,
the black zero zone (B in Fig. 2) indicated the relaxation, where the
myocardium had near zero SR.
The C–E property in the LV myocardium was evaluated by thechanges in the time serial SR distribution as shown in Fig. 2.

Fig. 1. Principle of the measurement of high resolution strain rate in the
myocardium using the phase difference tracking method. Top: longitudinal 2D
echocardiogram to decide 5 beam directions (1 → 5; base → apex) separated by 7.5◦ .
These serial numbers correspond to the numbers shown in Fig. 2. Bottom: selectionof the measurement range (from epicardium = Epi to endocardium = End) and themeasuring width (821 ␮m). The velocity () in the myocardial tissue at 2 terminal
points (x1i , x2i ) are calculated, and then the strain rate is obtained by the bottom
equation (Si (t)). LV, left ventricular wall.

Results
The results obtained in all 10 subjects were essentially uniform.
The minor difference was seen from beat to beat and among the
subjects, but the general tendency was unequivocal. The heart rate
gave the difference in the absolute value of the length of each phase,but there was little inﬂuence on the sequence of the SR distribution,
at least among the normal subjects.
Therefore, it seemed to be enough to describe the results of one
representative case in detail.
C–E property in the LV myocardium (Fig. 2, Table 1)
The contraction and extension and also relaxation did not occur
all at once, but occurred rather sporadically during one cardiac
cycle. Simultaneous or synchronous contraction or extension of
the whole wall muscles was never seen, and further, the C–E
property of the free wall (e.g. PW) was different from that of the
IVS.
Posterior wall
The contraction of the PW started from the apical epicardialside, coinciding in time with the P wave of electrocardiogram(ECG) (indicated by the thick black arrow at bottom), and propagated toward the endocardial side during ejection phase (Ej); also

M. Tanaka et al. / Journal of Cardiology 63 (2014) 313–319

315

Fig. 2. M-mode images of the strain rate (SR) distribution in the interventricular septum (IVS) and posterior wall (PW) during one cardiac cycle. Nos. 1–5 were obtainedwith the beam direction 1–5 in the upper graphic in Fig. 1. The cold color area shows an increment of the SR (contracting) and the warm color area decrement (extending).
The color bar demonstrates the grade of the SR. Large black arrow, beginning of the PW contraction; white narrow broken oblique lines, beginning of the PW extension;c, contracting muscle component; white narrow vertical lines, beginning and ending of the PW contraction; i, spotted distribution; ii, multi-layered distribution; iii, toned
distribution (apex (5): cold color, base (1): warm color); iv, stratiﬁed distribution; B, black area (relaxation); Alt 1, alternating appearance of the multi-layered distribution;
Alt 2, alternating appearance of the toned distribution; IC, isovolumetric contraction; Ej, ejection; IR, isovolumetric relaxation; ERF, early stage rapid ﬁlling; LRF, late stage
rapid ﬁlling; SF, slow ﬁlling; AC, atrial contraction; pre-ET, pre ejection transitional phase; post-ET, post ejection transitional phase.

contraction propagated toward the base until the anterior half ofthe early rapid ﬁlling phase (ERF).
During the contraction, 3 distribution patterns were demonstrated (Fig. 2, bottom), that is, the spotted distribution (i) at theapical part, the multi-layered distribution (ii) at the central andbasal parts, and the toned distribution (iii) at the basal part.
The extension began at the apical epicardial side, coinciding intime with the T wave of ECG (dashed white lines), and propagatedtoward the endocardial side, and ﬁnally reaching the ERF. Thereafter, the process continued to the phase of end of pre-ET trough thephase of slow ﬁlling (SF). Thus, the contraction was present even in
the timing of classic “diastole”.
During the extending period, 2 patterns were also observed fromthe apical part to the basal part, i.e., the toned distribution (iii) in
the phase of post-ET, and the stratiﬁed distribution (iv) in the phaseof SF.

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M. Tanaka et al. / Journal of Cardiology 63 (2014) 313–319

Table 1
Summary of the SR distribution patterns demonstrated in various cardiac phases (pre-ET, Ej, post-ET, SF) observed at the apical (Ap), central (Cent) and basal (Bas) parts of
the IVS and PW.
Pre-ET

Ej

Post-ETSF

IVS(1) Bas.
(3) Cent.
(5) Ap.

iii: Toned (Alt 2)iii: Toned (Alt 2)
ii: Multi-layered (Alt 1)iii: Toned
ii: Multi-layered
i: Spottediii: Tonediii: Toned
ii: Multi-layered (Alt 1)

iv: Stratiﬁed
iv: Stratiﬁed
ii: Multi-layered (Alt 1)

PW(1) Bas.

iii: Toned (Alt 2)

ii: Multi-layered

iv: Stratiﬁed(3) Cent.
(5) Ap.

iii: Toned (Alt 2)iii: Toned

ii: Multi-layerediii: Toned
ii: Multi-layered
i: Spotted

i: Spottediii: Toned

iv: Stratiﬁed
iv: Stratiﬁed

Alt 1: alternating appearance of the multi-layered distribution; Alt 2: alternating appearance of the toned distribution.

In the pre-ET, the toned distribution was alternatively observed
during either contraction or extension (Alt 2).
Furthermore, the string-shaped contracting pattern (C of 3 and
4 in Fig. 2) was observed near the epicardium in the mid-PW during
the phase of RF through SF, indicating that a superﬁcial contracting muscle group exists at the area near the epicardium from thecentral to the basal parts, assisting the active dilatation of the LV.
All the while, gentle extension (stratiﬁed distribution) of thewall was observed in the phase of SF. At the epicardial side of theapical part, there was relaxation during SF [black area (B): nearlyzero SR].
Interventricular septum
As shown in Fig. 2, IVS 4 and 5, the apical contraction began at
the LV side coincided in time with the end of the P wave of ECG.
Following the temporal extension, the contraction propagatedtoward the right ventricular (RV) side until the ERF. The apicalextension coincided with the T wave of ECG and propagated fromthe LV side to RV side until ERF. Thereafter, the extension continued
until the next P wave of ECG and showed the Alt 1 SR distribution at
the apical part, and the stratiﬁed distribution (iv) at the central part.
During the contracting period, the spotted distribution (i) at theapical part, the multi-layered distribution (ii) at the central part,and the toned distribution (iii) at the basal part were observed.
At the basal part, the contraction began at the P wave of ECG,
but in the pre-ET, Alt 2 pattern of the SR distribution was seen.
Thereafter, the contraction progressed from the RV side to the LVside during Ej.
The extension began coincidentally with the end of T wave of
ECG (Fig. 2, IVS,1) and ca. 35–37 ms prior to the IIa sound.
The extension occurring during the post-ET phase was causedby the expansion of the LV outﬂow tract in this period, then further progressed with the stratiﬁed distribution with B until the AC
through SF.
The process of the C–E property within the IVS was not always
similar to that of the PW. Especially, the alternating pattern of the(+) and (−) SR (Alt 2) was demonstrated at the central and basal
parts as the toned distribution (iii) in the pre-ET phase. At the apicalpart in IVS, multi-layered distribution (Alt 1) was alternatively seen
until the pre-ET phase through the SF.
During the SF, the stratiﬁed distribution was observed in thearea near the LV side at the basal part. Thus, the characteristics of
the C–E property of the IVS were considerably different comparedwith that in the PW.
The myocardial C–E property estimated by the time serial SR
distribution
The myocardial C–E property analyzed by the time serial SR
distribution showed the following features.

a) Both contraction (C) and extension (E) of the wall spread fromthe epicardial side toward the endocardial side.
b) Both C and E began from the apex and spread toward the base.
c) The LV contraction began coinciding with the P wave of ECG andcontinued up to the RF phase in the PW. The extension began at
the T wave of ECG and continued to the IC.
d) The length of the contracting process and that of the extending
process had nearly equal duration.
e) In every 5 parts of the IVS, the beginnings of the (+)SR or (−)SR
were nearly the same during one cardiac cycle. On the contrary,
the beginning and ending of the (+)SR or (−)SR of the PW werequite different through 5 parts as shown by the narrow whitevertical lines in Fig. 2. The time delay of the apical part became
bigger toward the base.
f) During one cardiac cycle, cardiac phases composed of theisolated contraction, isolated extension, and another 2 transitional phases were observed. During the transitional phases,
both the contracting state and extending state were observed
simultaneously in the different parts of the ventricular wall
(Figs. 2 and 4).
g) One cardiac cycle was then logically divided into 4 phases:
pre-ejection transitional phase (pre-ET), ejection phase (Ej),post-ejection transitional phase (post-ET), and slow-ﬁllingphase including the atrial contraction (SF).
Discussion
First of all, it should be kept in mind that the usual physiologic terms are not valid in the present article. The former
cardiac physiology deﬁned the contraction as mainly the systolic
event and the relaxation as solely the diastolic event except atrial
systole.
In our study, the term of “contraction” means the positive
strain rate of muscle ﬁber, irrespective of the timing throughout
the cardiac cycle, and does not necessarily mean the previously
deﬁned systole. This contraction does exist during conventional
diastole. The counterpart is “extension” which has a negative SR, in which the muscle ﬁber is not in the static state,but in active extension. Conventionally, the extension may becalled diastole, but the extension does occur even during classic
systole.
In between, there is the time when the muscle ﬁber is in neither
contraction nor extension, i.e. the SR is near zero, and the hue in
Fig. 2 is black. This is deﬁned as “relaxation” in this paper, and isseen during diastole, but may be observed in several timings during
the cardiac cycle.
As far as we are aware, there are no published articles similar
to the present study that deal with the microscopic observationof the physiological aspects of cardiac muscle ﬁber. This is due tothe lack of adequate in situ methodology to monitor cardiac muscle

M. Tanaka et al. / Journal of Cardiology 63 (2014) 313–319

Fig. 3. Schematic representation of the propagation of C–E in the left ventricular (LV)wall. Top: in the contracting process, the “h” (wall thickness) gradually increases,
then the front of contraction progress from 1 to 3, and the R (radius) will decrease
from 1 to 3. Accordingly, the power produced is easily centralized to the central
area of the LV and the positive pressure increases (left ﬁgure: contraction). In theextending process, both the “h” and the “R” are reversed and negative pressure
increases (right ﬁgure: relaxation, expansion). Bottom: schematic representationof the distribution of contraction and extension in the myocardium at the pre-ETand post-ET phases of the LV wall. Yellow area is in the extending state and brownarea in the contracting state. Blue arrow (P), pressure; black arrow (F), expectedblood ﬂow direction; pre-ET, pre-ejection transitional phase; post-ET, post-ejection
transitional phase; MO, mitral oriﬁce; AO, aortic oriﬁce; T, tension appeared in theendocardial area in the posterior wall.

contraction and extension. In this regard, the methodology in thepresent study, i.e. the phase difference tracking method for measuring the high resolution SR appears to be extremely valuable. It isbecause the accurate measurement of SR distribution is considered
to reﬂect the performance at the sarcomere level and to indicate
the contractility or extensibility in the muscle ﬁber level.
The microscopic study disclosed that the myocardial contraction
or extension does occur asynchronously, leading to the uniformity
in all muscle ﬁbers of the wall. Their timing and also magnitude
were different in the parts of the ventricular wall. For example, during the apical contraction, the base was in the state of extension,and the events in the epicardial side differed from that of the endocardial side. Therefore, generally speaking, the contracting process
and the extension process coexist independently during the same
cardiac phase. Despite this complexity, the SR distribution showedsome regularities in the onset and magnitude of the SR at the basal
parts of the PW and the IVS during Ej.
The beneﬁcial effects on the cardiac muscle function evidenced
by the C–E property studied by the SR distribution were as follows:
1) Propagation and integration of the C–E from the epicardial side
to the endocardial sideThis propagation behavior [16] is important in that the force
of contraction becomes stronger as the propagation progresses

317

toward the endocardium by the integration of the contraction.
In addition, the concave shape of the LV internal surface acts asa centralizer of the power produced by the contraction or theextension (Fig. 3, top). When the radius (R) changes from 1 to
3, the thickness (h) will increase proportionally, giving greater
power of contraction.
Assuming that the contractility or extensibility per unit volume of the muscle tissue is constant, the simple Laplace
equation (P = ·h/R, where P is intraventricular pressure,  isstress of the wall, h is wall thickness, and R is internal radius)[1,19] indicates the pressure (P) either rapidly increases in
the contracting process or rapidly decreases in the expanding
process.
2) Propagation of the C–E from the apex to the baseDuring isovolumetric contraction (IC) and isovolumetricrelaxation (IR), it has been supposed that the ventricular muscles
are in the static state. However, there was deﬁnite contraction
or extension as evidenced by the SR distribution, i.e. blood ﬂow
develops even during these phases.
As demonstrated in the bottom diagram of Fig. 3, during
pre-ET, the SR distribution clariﬁed that the contraction at theapical part accompanied with the simultaneous basal extension.
This indicates that the pressure change (P) primarily occurs at
the apex, and immediately transmits toward the outﬂow orinﬂow tract, and thus the basal blood ﬂow is obliged to change.
The basal part expanded and the rotating ﬂow is produced
during IC [17]. While in post-ET, the apical part relaxed while
the basal part contracted, giving downward ﬂow in the ventricle
during IR [20].
3) Energy consumption of the ventricular muscle
Although the contracting part (e.g. apex) and the extending
part (e.g. base) are observed simultaneously, the time delay ofboth parts is clear in the PW, but not so in the IVS. This implies
that the contracting energy positively extends the relaxing partto save energy consumption due to the muscle contraction.
4) Peristalsis and bellows action of the LV
The propagation sequence of contraction or extension fromthe apical to basal part inevitably produces the peristalsis of
the PW, whereas the difference of the C–E between PW and IVS
produces the bellows action of the LV.
The peristalsis and the bellows action of the PW seem tocause the squeezing effect [17] to the intraventricular blood
during Ej (aortic ejection [21]) and the suction effect [20] to
the inﬂow blood during RF (mitral inﬂow). In this sequence,
the importance is that the PW and the IVS have different but
interacting contributions to the LV pump function.
5) A new division of the cardiac phase
The overwhelming importance of the present study is the
conﬁrmation of 4 newly identiﬁed cardiac phases, which havenever been proposed by any previous cardiac physiologists[1–3,8]. The contraction and the extension of the LV wall are
not independent events, but interact dependently upon eachother. This conclusion is based on the deﬁnite observation of
the SR distribution during the transitional phases, in which bothcontraction and extension are observed at the same time. In thisrespect, we ﬁnally categorized the 4 cardiac phases including
the pre-ET and post-ET transitional phases as shown in Fig. 4.
Surprisingly enough, the sum of the duration of total contraction and that of total extension are nearly equal at least
in normal subjects. This may indicate that the LV is able tohave smooth movement like a rotary pump without giving a
speciﬁc load in any areas of the LV muscle. This assumption isparticularly important to conditions such as the crisis of thesudden change in the pressure, volume, or an accelerated heart
rate by keeping smooth muscular action and thus adequate
pump function continuously.

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M. Tanaka et al. / Journal of Cardiology 63 (2014) 313–319

Fig. 4. Schematic representation of the contraction–extension (C–E) property of the left ventricular wall (upper graph), and schematic display of the correlation among C–E
property, electrocardiogram (ECG), Phonocardiogram (PCG), Doppler ﬂow velocity curve (DFVC, blue colored curve) and the timing of the contraction and extension (lower
graph). Upper graph: red thick arrows, extending process; blue thick arrows, contracting process; Ba, basal part; Ce, central part; Ap, apical part; EndC, endocardial part;
EpiC, epicardial part; AC, atrial contraction; IC, isovolumetric contraction; IR, isovolumetric relaxation; RF, rapid ﬁlling; SF, slow ﬁlling. Lower graph: pre-ET, pre-ejection
transitional phase; Ej, ejection; post-ET, post-ejection transitional phase; I, 1st heart sound; II, 2nd heart sound.

Limitations
Although the results were similar in all cases, the sampling
was small, so that further accumulation of normal as well as
pathological data may be needed to reach the ﬁnal conclusions. At
present, the examination was off-line which required a long time
for the analysis. In future, this should be replaced by on-line toalleviate the time loss of examination.
The technology of “phase difference tracking method in ultrasonics” is not widely recognized because it was developed in
our laboratory; therefore, the understanding of our results might
be difﬁcult. We welcome candid criticism and will accept anyquestions.
Conclusions
The new method for measuring the SR distribution in the
LV myocardium was introduced to analyze the C–E property of the cardiac muscle noninvasively with high spatial
resolution.
There was no synchronous contraction or extension of the LV
muscles, and the time serial SR distribution during cardiac cycle
disclosed the C–E property of the myocardium in situ, where independent contraction or extension was evident through the cardiac
cycle. The PW and the IVS had a different C–E property and gave
the peristalsis and bellows action.
The harmonious succession of the 4 newly identiﬁed cardiac
phases seemed to be of help to understand the mechanism of keeping long-lasting pump function of the LV.
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