Coronary microvascular dysfunction in patients with symptomatic hypertrophic cardiomyopathy

Abstract

Background: Patients with hypertrophic cardiomyopathy (HCM) have been shown to have reduced myocardial perfusion in the presence of normal epicardial arteries. The mechanism of abnormal microvascular function is not well understood. Hypothesis: A possible mechanism for the reduction in CFR may be that the microcirculation is already near maximal dilation in the basal state and is therefore limited in the ability to further dilate and compensate for the increase in myocardial demand. Methods: Eight patients with symptomatic HCM and eight age- and sex-matched controls were studied. All patients underwent coronary angiography and coronary hemodynamic assessment with an intracoronary Doppler wire to determine total coronary blood flow, coronary resistance, and coronary flow reserve (CFR). Phasic blood flow parameters were also obtained. Results: Compared with controls (n = 8), patients with HCM (n = 8) had higher coronary blood flow (52±19 versus 33±11 mL/min, P = 0.03), lower coronary resistance (2.12±0.91 versus 3.13±0.93 mm Hg/mL/min, P = 0.05), and lower CFR (2.1±0.7 versus 3.4±1.0 mm, P = 0.02). There was a direct correlation between CFR and coronary resistance (r = .5, P = .05). HCM patients also had abnormal phasic coronary flow characteristics with lower systolic velocities or reversal of flow during systole, and a more rapid deceleration of diastolic blood flow (40.7±13.2 versus 27.5±8.5 cm/sec2, P=.03). Conclusion: The reduction of CFR in HCM patients may be secondary to near maximal vasodilatation of the microcirculation in the basal state rather than narrowing of intramyocardial small arteries. Symptomatic HCM patients also have abnormal phasic coronary blood flow with a greater dependence on diastolic flow and a more rapid deceleration of diastolic blood flow.