Discussion
This present study investigated the hypothesis that cardiovascular
rehabilitation with a supervised exercise program would have a
positively impact on the LV contraction mechanics in a population after
an uncomplicated AMI. To date, to the best of our knowledge, there is no
other similar study that investigated this hypothesis in such a detailed
way, considering the large number of LV contraction parameters which
comprise ventricular systolic mechanics performed in our study.
Regarding the analysis of longitudinal, circumferential and radial
deformation, in a general analysis, the TRAINING group was not superior
to the CONTROL group up to 4 months post-AMI.
However, we identified a very interesting finding in relation to the LV
torsional mechanics. Compared to the CONTROL group, the TRAINING group
showed significantly lower values of rotation and rotational velocity
of the LV basal segments, as well as lower values of twist velocity,
torsion and torsional velocity after the 16-week training period.
Similar results were also observed by McGregor et al. in their elegant
exploratory study.31 These authors also described a
reduction in LV twist and twist velocity after 10-weeks of physical
training sessions, twice a week, in a similar population who suffered an
AMI and still maintained a preserved LV function (LVEF >
50%). Exploring their data, this final result on LV twist was linked to
a reduction in both basal and apical rotations. Finally, similar to our
study, they did not found a significant positive impact on LV strain
(longitudinal, circumferential or radial) determined by exercise.
Extrapolating to highly-trained athletes, despite some contrasts in the
findings, studies point to a common and final real impact of exercise on
LV torsional mechanics. Stöhr et al. described a reduction of apical
rotation and LV twist in individuals with high aerobic
fitness.32 The same was found by Nottin et
al.33 studying elite cyclist and Zócalo et
al.34 assessing professional soccer players. A
reduction of LV rates of basal and apical rotations, and torsional rate,
were described. Weiner et al. showed also interesting findings with
competitive rowing athletes. They described a so called “phasic
phenomenon” in a program of high level physical activity, comprised by
an acute phase of augmentation of LV twist, followed by a subsequent and
chronic reduction of this parameter.35 Driven by this
knowledge, it is valid to postulate that a possible greater enhancement
of LV twist as a result during exercise could represent a major
efficiency of systole in these individuals.36, 37
The design of the myocardial muscle architecture most accepted by the
scientific community was proposed by Dr. Francisco Torrent-Guasp who
described the heart as a muscle band “folded” in double helix, with
oblique endocardial fibers right-handed toward LV base and the apical
epicardial fibers, more robust, with an oblique and left-handed
helix.38, 39. Physiologically, as a result of this
myocardial tissue conformation, after a brief counterclockwise rotation
of the isovolumetric contraction phase, the base of LV contracts
predominantly in clockwise rotation, opposed to the counterclockwise
rotation apical, also after a slight initial clockwise rotation. This
resulting opposition of rotations is the wringing motion of LV (twist or
torsion). In terms of energy expenditure, this architecture would be a
more efficient form of contraction, as well as having a more homogeneous
distribution of cavity wall stress, with less myocardial oxygen
consumption, compared to a simple radial LV cavity
contraction.36
As in our study, McGregor et al. did not find a positive impact of
exercise on longitudinal strain. Despite the good accuracy and more
robust data in the literature on longitudinal strain, LV twist proved to
be a more sensitive parameter for evaluating LV global systolic gain in
response to physical exercise in this population.