901-104 Transmural Myocardial Blood Flow Distribution and Coronary Sinus pH During Stress in Hypertrophic Cardiomyopathy (HCM)

Clinical and pathological evidence suggest that myocardial ischemia is important in the pathophysiology of HCM. A reduction in coronary sinus pH, which reflects tissue acidosis, is an accepted metabolic marker of myocardial ischemia. The aim of this study was to investigate if the abnormalities of myocardial blood flow (MBF) demonstrable in patients with HCM and angiographically normal coronaries are associated with a drop in coronary sinus pH. In 5 patients with HCM (4 males, age 38±9 years), all with septal thickness of 20mm or more, we measured MBF in the septal subendocardial and subepicardial layers using H215O and positron emission tomography at baseline and following i.v. dipiridamole (Dip, 0.56mg/kg over 4min). In the same patients, at a separate study, a pH selective electrode was introduced into the coronary sinus via the subclavian vein and changes in pH were continuously monitored at baseline and during Dip (0.56mg/kg over 4min). At baseline, subendocardial blood flow was 1.10±0.34ml/min/g and did not increase significantly (1.39±0.19ml/min/g, p=NS) following Dip. Subepicardial blood flow increased significantly from 0.82±0.24ml/min/g at baseline to 1.5±0.21ml/min/g following Dip (p=0.04), resulting in a significant fall in the subendocardial/subepicardial flow ratio (an index of transmural MBF distribution) from 1.37±0.33 at baseline to 0.96±0.27 following Dip (p=0.04). All patients demonstrated a fall in coronary sinus pH during Dip stress, which averaged 0.07±0.05 (range 0.02–0.13), in association with typical anginal chest pain. Maximal pH change correlated inversely (R=0.9, P=0.03) with subepicardial flow reserve (i.e. Dip/baseline subepicardial MBF). In conclusion: Dip-induced chest pain in patients with HCM is associated with subendocardial hypoperfusion and metabolic evidence of myocardial ischemia despite angiographically normal coronary arteries