Geometric Assessment of Asymmetric Septal Hypertrophic Cardiomyopathy by CMR

OBJECTIVES The aim of this study was to analyze the geometric pattern of hypertrophy (HT) in patients with asymmetrical septal hypertrophic cardiomyopathy (HCM) using cardiac magnetic resonance (CMR) and to test the hypothesis that at least in some patients, the HT follows a longitudinal spiral pattern. BACKGROUND The highly heterogeneous phenotypic expression of HCM is a well-known phenomenon. CMR has emerged as a robust 3-dimensional (3D) tomographic imaging technique that is increasingly used to explore phenotypic expression. METHODS Short-axis cine CMR was used to study the 3D extent of HT (i.e., radial, circumferential, and longitudinal extent, as well as the relation between circumferential and longitudinal extent). Inclusion criteria were septal wall thickness (WT) >= 15 mm and septal to free wall WT ratio >1.3. RESULTS CMR was performed in 132 patients. Maximal WT was 22 +/- 5 mm, with a circumferential extent of 131 +/- 51 degrees, and a longitudinal extent of 64 +/- 19%, resulting in a hypertrophied left ventricular (LV) surface of 26 +/- 15%. Linear regression analysis showed in 86% of patients a consistent course of HT along the longitudinal direction. The HT invariably started at the basal anteroseptum and rotated, except in 2 patients, in a counterclockwise direction (CC-spiral patients) with a mean global rotation of 116 +/- 68 degrees (range 5 degrees to 350 degrees). After the CC-spiral patients were divided according to magnitude of rotation quartiles (Q1: 5 degrees to 70 degrees, Q2: 75 degrees to 105 degrees, Q3: 110 degrees to 150 degrees, and Q4: 155 degrees to 350 degrees), Q4 patients were significantly older and had more LV outflow tract obstruction and hypertension than patients without the spiraling pattern. In 11 patients, continuation of HT into an apical form of HCM was found. CONCLUSIONS Using 3D analysis, we found that the majority of patients with asymmetrical septal HCM in fact showed a spiral pattern of HT following a counterclockwise (or "left-handed") spiral trajectory. The variation in magnitude of rotation among patients, however, was highly variable. Further research is warranted to better understand the significance of the current findings, in particular to relate them to the genetic and morphological substrate, hemodynamic consequences, and patient outcome. (J Am Coll Cardiol Img 2012;5:702-11) (C) 2012 by the American College of Cardiology Foundation