Left ventricular non-compaction is a rare congenital heart disease which develops as a consequence of absent or incomplete myocardial compaction during embryonic morphogenesis. Though two-dimensional echocardiography is the standard diagnostic tool for LVNC, cardiac MRI is useful to confirm or rule out LVNC when the apex is difficult to visualize. Normally, compaction progresses from epicardium to the endocardium and from the base towards the apex of the heart. LVNC is often accompanied by early development of systolic or diastolic dysfunction which may lead to heart failure and ventricular arrhythmias. Hypertrabecularization of the myocardium significantly increases the risk of systemic embolization as well [8].
Our present study showed decrease in global LV function as suggested by global strain and strain rate analysis among both LVNC and HCM subjects, being worst among non-compaction cases. However, diastolic function was reduced in both in comparison to controls with no significant intergroup difference. Regional deformation analysis showed presence of apico-basal gradient in longitudinal strain among LVNC, which was not evident among HCM subgroups. Various studies focusing on these populations have shown wide range of results [6, 9, 10]. In contrast to our findings, study by Haland et al. showed that LVNC exhibits homogenous reduction in longitudinal strain across basal and apical LV regions with no apico-basal gradient. This pattern of reduced apical function compared to basal segments in patients with non-compaction is possibly attributed to embryogenic theory which states that compaction of myocardium occurs from epicardium to endocardium and from base to the apex [1]. Though HCM manifests decreased global longitudinal strain, apico-basal LV segmental gradient was preserved in our study. This is in contrast to the study by Haland et al. which showed preserved apical and more reduced basal function in HCM.
In the normal heart, the LV base rotates clockwise while the apex rotates counter-clockwise during the systole, producing a “towel-wringing” motion of the heart. The net difference between LV base and the LV apex is called “net twist angle.” This twist is due to dynamic interaction of subepicardial and sub endocardial myocyte helices. Peak LV systolic twist is directed by sub-epicardial fibers due to their longer arm of movement whereas early LV systolic twist in opposite direction is directed by sub endocardial helix of myocardial fibers during isovolumic contraction. The LV twist represents a phenomenon that links systolic contraction with diastolic relaxation [11].
Speckle-tracking echocardiography can be used to accurately assess LV twist. Van Dalen et al. were the first using 2DSTE to demonstrate that the direction of LV basal rotation and that of LV apical rotation are the same, resulting in near absence of LV twist in patients with LVNC known as “LV solid/rigid body rotation” [12]. Varying degrees of maturation of two helices at the apical and basal region could be postulated for rigid body rotation.
To our knowledge, this is the only study conducted so far comparing left ventricular rotational mechanics in patients with left ventricular non-compaction, hypertrophic cardiomyopathy, and healthy subjects. A normal pattern of LV rotation was found in half of our patients whereas rigid body rotation was found in rest half of patients. F Peters et al. and Van Dalen et al. showed prevalence of rigid body rotation as 53.3 % and 83 %, respectively [12, 13]. The following reasons can be implicated in the lower prevalence of RBR in our study compared to Van Dalen et al. LVNC may be caused by different genetic profiles which may be affected by race and population studied and hence the manner of remodeling may be different. Selection bias may also have contributed to the differences involved. Van Dalen et al. included 17 patients with familial LVNC in their study of all whom showed RBR. However, in our study, patients were mostly non-familial LVNC (demonstrated by negative family history and absence of non-compaction on echocardiography in first degree relatives). Finally, referral bias would have contributed to the results. As most of the patients included in our study were symptomatic, our patients had a much lower ejection fraction compared to Van Dalen’s cohort. Uniform clockwise rotation of LV segments had assumed to be a hallmark feature of LVNC in most of the studies. In this study, unidirectional rotation in anticlockwise direction was found particularly among LVNC subjects, whereas two distinct direction of rotation at base and apex were noted among HCM and control groups. The exact mechanism of this counter-clockwise rotation of LV segments in our study is still unknown.
In this study, apical rotation and torsion was significantly reduced specifically among LVNC subjects in comparison to other two groups, whereas HCM showed increased torsion values in comparison to controls. F Peters et al. showed a significant lower apical and basal rotation in LVNC compared to controls. A decrement in both apical and basal rotation may be due to either a decrease in function of the subepicardial fibers or a combination of both helices having decreased function. Our study demonstrated that torsion in patients with HCM was higher compared to healthy subjects. Similar results were found in the study conducted by Young et al. and Saito et al. [14, 15]. Prinz et al. studies pediatric patients diagnosed with HCM and showed significant increase in torsion compared to healthy children [16]. In healthy heart, counter clockwise rotation of the subepicardial fibers dominates clockwise rotation of the sub endocardial fibers (due to larger radius). An increased torsion in patients with HCM is the result of increased lever arm (to subepicardial fibers) due to concentric hypertrophy.
Few limitations of this study warrants consideration. First, as it was a retrospective echocardiographic study, clinical variables like NYHA class, systolic and diastolic blood pressure, heart rate, and usage of cardiac drugs were not taken into account. Secondly, because of the retrospective nature of the study, the influence of various loading conditions like preload, afterload and contractility on LV twist was not documented. The presence and severity of LV dyssynchrony which can contribute to remodeling and ejection fraction was not taken into account. However, stable electrocardiographic recording showed that none of these patients had QRS duration more than 130 ms. We did not study the long-term follow-up of these patients which can provide information on the clinical consequences. Long-term follow-up is needed to know if patients with reduced torsion progress to RBR or if patients with RBR have unfavorable clinical consequences compared to patients with only reduced torsion.