Tissue Doppler Imaging Consistently Detects Myocardial Contraction and Relaxation Abnormalities, Irrespective of Cardiac Hypertrophy, in a Transgenic Rabbit Model of Human Hypertrophic Cardiomyopathy

Abstract

Background —Hypertrophic cardiomyopathy (HCM) is diagnosed clinically by the presence of left ventricular hypertrophy (LVH). However, LVH is absent in a significant number of genotype-positive patients. Because myocyte dysfunction and disarray are the primary abnormalities in HCM, we reasoned that tissue Doppler imaging could identify contraction and relaxation abnormalities, irrespective of hypertrophy, in a transgenic rabbit model of human HCM. Methods and Results —M-mode, 2D, Doppler echocardiography and tissue Doppler imaging were performed in nontransgenic (n=24), wild-type β-myosin heavy chain-arginine 403 (n=14), and mutant β-myosin heavy chain-glutamic acid 403 (n=24) transgenic rabbits. Mean septal thicknesses were 2.0±0.3, 2.0±0.25, and 2.75±0.3 mm in the 3 groups, respectively ( P =0.001). LVH was absent in 9 of the 24 mutant rabbits. Left ventricular dimensions, systolic function, heart rate, mitral inflow velocities, and time intervals were similar in the groups. However, the difference between atrial reversal and transmitral A wave duration was increased in the mutant rabbits ( P <0.001). More importantly, systolic and early diastolic tissue Doppler velocities were significantly lower in all mutant rabbits (7.45±2.2 versus 10.8±2.3 cm/s in nontransgenic and 9.0±0.76 cm/s in wild-type; P <0.001), including the 9 without LVH. A systolic velocity <8.5 cm/s had an 86% sensitivity and 100% specificity in identifying the mutant transgenic rabbits. Conclusions —Myocardial contraction and relaxation were reduced in the mutant β-myosin heavy chain-glutamic acid 403 transgenic rabbit model of human HCM, irrespective of the presence or absence of LVH. In addition, tissue Doppler imaging is more sensitive than conventional echocardiography for HCM screening.