Normal Right Ventricular Three‐Dimensional Architecture, as Assessed with Diffusion Tensor Magnetic Resonance Imaging, is Preserved During Experimentally Induced Right Ventricular Hypertrophy

Abstract

The three-dimensional architecture of the right ventricular myocardium is a major determinant of function, but as yet no investigator-independent methods have been used to characterize either the normal or hypertrophied state. We aimed to assess and compare, using diffusion tensor magnetic resonance imaging, the normal architecture with the arrangement induced by chronic hypertrophy. We randomized 20 female 5 kg piglets into pulmonary trunk banding (N ¼ 16) and sham operation (N ¼ 4). Right ventricular hypertrophy was assessed after 8 weeks. The excised and fixed hearts were subject to diffusion tensor imaging to determine myocyte helical angles, and the presence of any reproducible tracks formed by the aggregated myocytes. All banding animals developed significant right ventricular hypertrophy, albeit that no difference was observed in terms of helical angles or myocardial pathways between the banded animals and sham group animals. Helical angles varied from $70 degrees endocardially to À50 degrees epicardially. Very few tracks were circular, with helical angles approximating zero. Reproducible patterns of chains of aggregated myocytes were observed in all hearts, regardless of group. The architecture of the myocytes aggregated in the walls of the right ventricle is comparable to that found in the left ventricle in terms of endocardial and epicardial helical angles, however the right ventricle both in the normal and the hypertrophied state lacks the extensive zone of circular myocytes seen in the mid-portion of the left ventricular walls. Without such beneficial architectural remodelling, the porcine right ven-*Correspondence to:

Right Versus Left Ventricular Failure

“…60,94 As for the LV, the aggregated RV myocytes form helical angles and intrude in the oblique orientation from the epicardial to endocardial layers. 21,60 In response to afterload, the hypertrophied RV maintains this basic structure and does not form an extensive layer of circular myocytes, which may explain the previously discussed shift from a longitudinal to circumferential strain pattern. 21 Although shared myofibers likely play a role in mediating adverse ventricular-ventricular interactions, they may also constitute a target for therapeutic intervention.…”

“…21,60 In response to afterload, the hypertrophied RV maintains this basic structure and does not form an extensive layer of circular myocytes, which may explain the previously discussed shift from a longitudinal to circumferential strain pattern. 21 Although shared myofibers likely play a role in mediating adverse ventricular-ventricular interactions, they may also constitute a target for therapeutic intervention. We have developed a rabbit model of sustained increased RV afterload using adjustable pulmonary artery banding.…”

“…20 This observation is somewhat surprising in that diffusion tensor magnetic resonance imaging shows that fiber orientation in RV hypertrophy is not fundamentally different from normal. 21 Likewise, the functionally single systemic RV in hypoplastic left heart syndrome may adapt a more circumferential versus longitudinal contraction pattern after stage 1 of surgical palliation (a particularly vulnerable period for these patients). 22 Yet, the RV in hypoplastic left heart syndrome continuously faces systemic resistance from fetal through postnatal life, and it is difficult to attribute changes in RV contraction patterns to increased afterload alone.…”

Cardiac Magnetic Resonance in Adults with Congenital Heart Disease

“…25 The mechanisms for systemic RV dysfunction are incompletely understood but may include suboptimal myofiber arrangement, 26 myocardial ischemia from supplydemand mismatch, and a less robust conduction system. CMR can quantify the amount of systemic RV hypertrophy and the systemic ventricular size and function ( Figure 6).…”

Assessment of Ventricular Function in Normal and Failing Hearts Using 4D Flow CMR

“…The middle layer is the thickest. The myocardial fiber architecture in the RV is comparable to that in the LV except for the middle circumferential layer (12).…”