Coronary flow velocity reserve during exercise stress echocardiography in hypertrophic cardiomyopathy

Coronary flow velocity reserve (CFVR) can be assessed with transthoracic echocardiography (TTE) as the stress/rest ratio of coronary flow velocity (CFV). Reduced CFVR during vasodilator stress (adenosine or dipyridamole) is a powerful predictor of adverse outcomes in hypertrophic cardiomyopathy (HCM). However, the feasibility and correlates of CFVR during the more physiological - and recommended - exercise stress echocardiography (ESE) is unresolved.

To assess the feasibility and functional correlates of CFVR during exercise in HCM.

We studied 56 HCM patients (age=49±13 years, 33 [59%] males) and 44 age- and sex-matched healthy subjects with symptom-limited semi-supine ESE. ESE assessment included CFVR (stress/rest diastolic CFV) in the mid-distal left anterior descending coronary artery, systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate reserve (HRR, peak/rest heart rate).

CFVR was feasible in 46/56 HCM patients and in 41/44 controls (82% vs 93%, p=0.138). Median CFVR was significantly lower in patients with HCM compared to controls (1.72 [1.48; 2.10] vs 2.57 [2.25; 3.30], p<0.001), see Figure 1. In HCM patients, among resting parameters, CFVR was inversely correlated with left ventricular maximal septal thickness (r= -0.308, p=0.038), end-systolic diameter (r= -0.393, p=0.007), resting DBP (r= -0.398, p=0.006) and resting SBP (r= -0.321, p=0.030), while in controls CFVR correlated only with resting DBP (r= -0.322, p=0.040). During exercise, HCM patients with lower CFVR (<1.72, i.e. 1.72) showed lower peak CFV (78±20 vs 96±24 cm/s, p=0.003) and lower HRR (1.55±0.29 vs 1.76±0.25, p=0.020), see Figure 2. Exercise duration, peak stress workload or metabolic equivalents were not related to CFVR. In multivariable analysis, resting CFV (b=-0.034, 95% CI -0.037 and -0.030, p<0.001), resting DBP (b=-0.003, 95% CI -0.005 and -0.001, p=0.020), peak stress CFV (b=0.019, 95% CI 0.017 and 0.021, p<0.001) and HRR (b=0.126, 95% CI 0.005 and 0.247, p=0.041) were independently associated with CFVR.