Abstract 2198: Left Ventricular Asynchrony Contributes to Symptoms in Patients with Hypertrophic Cardiomyopathy

Abstract

Objective: Hypertrophic cadiomyopathy (HCM) results in exertional symptoms due to limited cardiac output that improve after removal of the left ventricular outflow tract (LVOT) obstruction. We aimed to assess the effect of pharmacological stress on LV asynchrony in a group of patients with HCM limited by exertional breathlessness. Methods: We studied 17 normal controls (aged 58 ± 12 years) and 37 HCM patients (aged 54 ± 15 years, 13 female) with septal thickness >15 mm using Doppler echocardiography, at rest and at peak dobutamine stress. Stress end points were symptoms, >20 mmHg drop in systolic blood pressure, arrhythmia, or maximum dobutamine infusion of 40μcg/kg/min. Ventricular asynchrony was assessed by total isovolumic time and Tei index. Results: At rest: LVOT velocity was raised in HCM patients compared to normals (2.0 ± 0.9 v 1.0 ± 2.4, p<0.001, respectively). Total isovolumic time was not significantly different between HCM and normals (10.6 ± 4.4 v 12 ± 2 s/min, respectively), and Tei index was not significantly different between HCM and normals (0.6 ± 0.1 v 0.54 ± 0.2, p=NS, respectively). At peak stress: LVOT velocities increased in HCM compared to normals (4.3 ± 1.7 v 1.7 ± 1.0 m/s, p<0.005, respectively) due to systolic anterior movement of the mitral valve. Total IVT decreased in both HCM and normals (6.3 ± 5.2 v 5 ± 2 s/min,p<0.005, compared to resting values, respectively) as did Tei index (0.24 ± 0.04 v 0.23 ± 0.06, p<0.01, respectively). Total LV filling time decreased in HCM but increased in normals (HCM rest v stress: 29.6 ± 4.5 v 27.5 ± 4.5 s/min, p< 0.05; normals rest v stress 28 ± 4 v 33 ± 3 s/min, p<0.005). QRS duration increased with stress in HCM patients (rest v stress: 103 ± 28 v 110 ± 26 ms, p<0.01), but decreased in normals (rest v stress. 91 ± 9 v 87 ± 8 ms, p=NS). Conclusion: Stress results in LV outflow tract obstruction in HCM patients, resulting in known pathophysiological consequences– mitral regurgitation and raised left atrial pressure. In addition, increased ventricular asynchrony compromises filling time. The historical benefit from DDD pacing in this condition may be explained on the basis of LV resynchronisation rather than simply drop in outflow tract gradient.