Acute decrease in left ventricular diastolic chamber distensibility during simulated angina in isolated hearts.

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Abstract
It is not clear what factors contribute to the prompt and reversible decrease in left ventricular diastolic chamber distensibility during angina pectoris that is induced by an increase in myocardial energy demand due to exercise or pacing tachycardia. To simulate the demand ischemia that occurs clinically during pacing-induced angina, we used isolated, blood-perfused rabbit hearts with restricted coronary flow and increased myocardial energy demand. A constant left ventricular balloon volume model was used to measure left ventricular diastolic chamber distensibility during 6 minutes of low-flow global ischemia, induced by a reduction in coronary perfusion pressure from 100 to 20 mm Hg. To investigate the influence of different levels of myocardial energy demand, the effects of two different heart rates were studied during low-flow global ischemia; pacing tachycardia (6.4 +/- 0.2 Hz, n = 7) was compared with the rabbit's baseline heart rate of 4 Hz (n = 7). Low-flow ischemia caused a marked decrease in contractile function relative to the baseline preischemic state. In the pacing-tachycardia group, myocardial energy demand, as estimated by the rate X systolic pressure product, was significantly greater than in the constant heart-rate group. When tachycardia was imposed during low-flow global ischemia, there was a transient and reversible increase in isovolumic left ventricular end-diastolic pressure from 14 +/- 1 to 25 +/- 4 mm Hg (measured during long diastoles obtained with transient cessation of pacing) in the pacing-tachycardia group, but there was no increase in left ventricular end-diastolic pressure during low flow ischemia in the constant heart-rate group with lower energy demand (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)