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.