Diastolic coronary vascular reserve: A new index to detect changes in the coronary microcirculation in hypertrophic cardiomyopathy

OBJECTIVES: The present study introduces a modification of the diastolic coronary conductance concept that maintains its sensitive properties to detect changes in the coronary microcirculation in human hypertrophy. BACKGROUND: Decrements of coronary flow in hypertrophy have been explained by changes in the coronary microcirculation. No measure is available to detect these changes. METHODS: Doppler velocity catheters were introduced into the left anterior descending artery (LAD) and left circumflex coronary artery (LCx) of patients with obstructive hypertrophic cardiomyopathy (HCM) (n = 11) and into the LAD of cardiac transplant recipients (n = 9). The diastolic coronary conductance was measured at rest and after maximal hyperemia induced by a bolus injection of adenosine. Diastolic coronary vasodilator reserve (DCVR) was calculated as the hyperemic diastolic coronary conductance, divided by the coronary conductance during resting conditions. RESULTS: Left ventricular outflow tract gradient in the HCM group (83 ± 31 mm Hg) was significantly higher (p < 0.05). Septal wall thickness was significantly increased (p < 0.05), while wall thickness was unchanged in the posterior wall of the HCM group. The coronary flow reserve was significantly decreased in the HCM-LCx region (to 64 ± 7% of control) and in the HCM-LAD regions (to 57 ± 7% of control). The DCVR was only decreased in the HCM-LAD (to 46 ± 3% of control) and not in the HCM-LCx group (86 ± 6%, p > 0.05). Esmolol did affect the pressure gradient and systolic shortening, but did not affect the maximal diastolic conductance. CONCLUSIONS: The DCVR, in contrast with the coronary flow reserve, is decreased in those regions that display a disturbance in the microcirculation and may, therefore, offer a new way to study coronary adaptations in patients with hypertrophy.