Effect of verapamil on absolute myocardial blood flow in hypertrophic cardiomyopathy

Angina, despite angiographically normal coronary arteries, is a common symptom in patients with hypertrophic cardiomyopathy (HC). Verapamil has been shown to ameliorate silent myocardial perfusion defects documented by thallium-201 in patients with HC. The aim of this study was to investigate the effects of verapamil on absolute regional myocardial blood flow and flow reserve, measured by positron emission tomography (PET) in patients with HC. Echocardiography, exercise stress testing, and measurements of myocardial blood flow at rest and after administration of intravenous dipyridamole (0.56 mg/kg) were undertaken in 20 patients with HC at baseline study and 8 ± 2 weeks after double-blind randomization to either slow-release verapamil 240 mg or placebo once daily. During treatment, resting myocardial blood flow in the interventricular septum was 0.81 ± 0.23 versus 0.96 ± 0.42 ml/min/g in the placebo and verapamil group, respectively (p = NS between groups and when compared with respective baseline study); resting myocardial blood flow in the left ventricular free wall was 0.67 ± 0.17 versus 0.74 ± 0.45 ml/min/g, respectively (p = NS). After dipyridamole infusion, myocardial blood flow in the interventricular septum was 1.42 ± 0.52 versus 1.92 ± 1.23 ml/min/g (p = NS between groups and when compared with respective baseline study); myocardial blood flow in the left ventricular free wall was 1.25 ± 0.41 versus 1.68 ± 1.37 ml/min/g, respectively (p = NS). Coronary flow reserve before and after treatment was 1.95 ± 0.82 versus 1.86 ± 0.73 (p = NS) in the interventricular septum and 2.15 ± 0.74 versus 1.98 ± 0.69 in the left ventricular free wall (p = NS) in the placebo and verapamil groups, respectively. Evidence of subendocardial underperfusion was found in 3 of 7 patients with interventricular septal thickness > 25 mm while not receiving treatment. Two of these 3 patients received verapamil, and in 1 normalization of transmural myocardial blood flow was observed. In conclusion, short-term treatment with 240 mg of slow-release verapamil once daily does not affect absolute myocardial blood flow and coronary flow reserve in patients with HC. Subendocardial underperfusion may occur in patients with this condition and verapamil may have a positive effect on transmural blood flow distribution.