Effects of verapamil on regional myocardial diastolic function in pacing-induced ischemia in dogs.

The upward shift in the left ventricular diastolic pressure-volume relationship during pacing-induced angina may be related to increased cytosolic calcium availability with persistent contractile element interaction in diastole. To assess the influence of calcium channel blockade on these changes in diastolic function, we studied the effects of verapamil in dogs with 90% stenoses of the left anterior descending and circumflex coronary arteries. Ultrasonic crystals were implanted in the myocardium to monitor anterior wall and lateral wall segment length. Left ventricular pressure was measured with a micromanometer catheter. The left atrium was paced at a rate 1.5 times that of the resting heart rate for 3 min. An upward shift of the left ventricular diastolic pressure-segment length relationship developed after pacing tachycardia, with a rise in the left ventricular end-diastolic pressure (LVEDP) from 4.7 +/- 1.2 to 14.3 +/- 2.2 mmHg (P less than 0.01, n = 13), and pressure was higher at any segment length throughout diastole. Increases in end-diastolic segment length were small (12.3 +/- 1.9 to 12.7 +/- 2.0 mm for the anterior wall, P less than 0.05; 15.1 +/- 1.4 to 16.4 +/- 1.5 mm for the lateral wall, P less than 0.01). Pretreatment with verapamil (0.08 mg/kg iv) did not reduce this upward shift: LVEDP rose from 6 +/- 1 to 16 +/- 1 mmHg (P less than 0.01, n = 7) and there were similar small increases in end-diastolic segment length.(ABSTRACT TRUNCATED AT 250 WORDS)