Transthoracic echocardiographic evaluation of coronary flow reserve in patients with hypertrophic cardiomyopathy

Abstract

Recently, it has become possible to measure coronary flow reserve (CFR) non-invasively with transthoracic echocardiography (TTE). Twenty-one hypertrophic cardiomyopathy (HCMP) patients with asymmetric septal hypertrophy who had either not started medication or had stopped medication for at least 24 h were enrolled, along with 29 normal subjects. Mean diastolic coronary flow velocity (CFmv) and time velocity integral of diastolic coronary flow velocity (CFtvi) were measured at the distal left anterior descending artery with a 7 MHz transducer at the baseline and after dipyridamole infusion at a dose of 0.56 mg/kg. CFR was defined as the ratio of CFmv after dipyridamole over CFmv before dipyridamole. The baseline values for CFmv and CFtvi were significantly higher (0.40±0.09 vs. 0.31±0.06 m/s, p<0.001, 0.25±0.07 vs. 0.16±0.04 m, p<0.001, respectively), while that for CFR was significantly lower (2.01±0.42 vs. 3.06±0.39 m/s, p<0.001) in the HCMP patients, compared to the normal subjects. In the HCMP patients, CFR showed a moderate negative correlation with both baseline CFmv ( r=−0.522, p=0.015) and baseline CFtvi ( r=−0.495, p=0.034). Treadmill test was performed in 14 patients with Bruce protocol. CFR, baseline CFmv and baseline CFtvi did not correlate with maximal exercise time. In seven patients, the CFR measured after verapamil treatment was not significantly different from that measured before treatment. In conclusion, in patients with HCMP, CFR is probably reduced due to the recruitment of vasodilatory capacity at the resting state and this reduction is not directly related to reduced exercise capacity. Also, CFR is not affected by treatment with calcium antagonist.