Opposite effects of coronary artery disease and hypertrophic cardiomyopathy on left ventricular long axis function during dobutamine stress

Background The mechanism for reduced early diastolic long axis lengthening velocity in hypertrophic cardiomyopathy (HCM) is not known. Methods We measured simultaneous septal long axis amplitude and early lengthening velocity in 23 patients with HCM, 23 normal subjects and 22 patients with coronary artery disease (CAD) of left anterior descending artery. Results Resting amplitude and lengthening velocity were reduced in HCM 0.9±0.2 cm, 3.5±1.9 cm/s but equally in CAD 1.0±0.3 cm, 4.1±2.5 cm/s vs. 1.3±0.2 cm, 6.3±1.7 cm/s in normals, p<0.01 for both vs. normal. With dobutamine stress, lengthening velocity increased by 2.7±1.9 cm/s (p<0.001) in normals, by 2.8±2.5 cm/s (p<0.001) in HCM but not in patients with CAD 0.5±2.1, p=NS. Increment in total long axis amplitude was subnormal in CAD and HCM. However, increment in lengthening velocity was higher with stress for corresponding change in amplitude in HCM compared with CAD (χ2=16.5, p<0.001). An increase in early lengthening velocity by 2 cm/s was 77% sensitive and 70% specific in discriminating between HCM and CAD. Post-ejection shortening developed or worsened in all CAD patients indicating ischemia but not in any with HCM. Conclusions Reduced peak early lengthening velocity is not specific for HCM but also occurs in CAD. Unlike CAD, lengthening velocity increases in HCM with stress and there is no aggravation of post-ejection shortening, suggesting that the abnormal relaxation is not due to subendocardial ischemia in HCM. The greater recoil velocity per unit deformation in HCM compared with CAD, indicates elastic mechanism with increased passive muscle stiffness due to fibrosis or fibre disarray.