Effect of cibenzoline on regional left ventricular function in hypertrophic obstructive cardiomyopathy

BACKGROUND: Cibenzoline, a class Ia antiarrhythmic drug, can be used to relieve left ventricular (LV) outflow obstruction in hypertrophic obstructive cardiomyopathy (HOCM). However, the mechanism of this agent in HOCM has been controversial. HYPOTHESIS: This study was designed to investigate the effect of cibenzoline on regional LV function and the acoustic properties in HOCM using ultrasonic integrated backscatter. METHODS: Ten patients with HOCM and 16 healthy volunteers were examined. In patients with HOCM, wall thickening (%WT) and the magnitude of cyclic variation of integrated backscatter (mag-CVIBS) in the interventricular septum (IVS) and LV posterior wall were measured before and after oral administration of cibenzoline. To assess asynchrony of contractile elements, the phase difference between CVIBS and %WT were measured from the LV posterior wall. Pressure gradients at the LV outflow tract were estimated using continuous-wave Doppler echocardiography. RESULTS: Although %WT decreased significantly in the LV posterior wall, %WT and mag-CVIBS remained unchanged in the IVS. The phase difference in the LV posterior wall was significantly greater in patients with HOCM than in healthy volunteers (HOCM:healthy volunteers, 1.57 +/- 0.23:1.00 +/- 0.03, p < 0.001) at baseline. After administration of cibenzoline, the phase difference shifted to normal value (from 1.57 +/- 0.23 to 1.28 +/- 0.27, p = 0.0382), and pressure gradients at the LV outflow tract decreased (from 109 +/- 55 to 58 +/- 48 mmHg, p = 0.0063). Changes in pressure gradients at the LV outflow tract and the phase difference were closely related. CONCLUSIONS: Regional function and the acoustic properties of myocardium in HOCM were altered by cibenzoline in the LV posterior wall but remained unchanged in the IVS. The normalization of the phase difference in the LV posterior wall was closely related to the decrease in pressure gradients at the LV outflow tract. These findings suggest that negative inotropic action and the improvement of asynchrony in the LV posterior wall rather than in the IVS may contribute to the reduction of pressure gradients at the LV outflow tract in HOCM.