Supply-demand balance of subendocardial muscle: estimation from intramyocardial pressure

The ratio of the dihastolic pressure-time index (DPTI) to the systolic pressure-time index (SPTI) has been used as a predictor of subendocardial ischemia. The DPTI is thought to reflect the blood supply to the subendocardium, and the SPTI is thought to reflect the metabolic needs. In this study, the supply-demand balance of subendocardial muscle was evaluated directly from the pressure measured within the subendocardium. The blood supply to the subendocardial muscle, estimated from the area between the aortic pressure and the subendocardial pressure in diastole (3,370 mm Hg sec min-1) (mean +/- SEM) was lower than the DPTI (4,060 mm Hg sec min-1) (p less than 0.01). The metabolic demand of the subendocardial muscle, estimated from the area included in the subendocardial pressure (4,820 mm Hg sec min-1) was higher than the SPTI (2,480 mm Hg sec min-1) (p less than 0.01). The supply-demand balance, directly estimated from subendocardial pressure, 0.7, was markedly lower than the simultaneous DPTI/SPTI ratio, 1.6. In view of the prominent differences between the supply-demand balance estimated by these two indices, the DPTI/SPTI ratio as a predictor of subendocardial ischemia may require further evaluation.