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.