Protective effect of beta-blockade on dipyridamole-induced myocardial ischaemia - Role of heart rate

This study was designed to investigate the effect of heart rate changes on dipyridamole echocardiographic tests in patients with coronary artery disease treated with propranolol. We prospectively studied 12 patients (8 men and 4 women; mean age 56.5 ± 8.7 years) selected by: (a) angiographic evidence of significant coronary artery disease; (b) adequate echocardiographic window; (c) positive dipyridamole echocardiography test results in baseline conditions (step I); (d) test reproducibility in the absence of treatment; (e) negative dipyridamole echocardiography test results after 7 days of treatment with propranolol (120 mg. day− θ1) in twice divided doses daily (step II). In all patients treated with propranolol, dipyridamole echocardiographic testing was repeated 24 h after the last negative test. In these patients, transoesophageal atrial pacing was performed at peak dipyridamole infusion to increase heart rate to values similar to those observed at baseline (step III). At baseline, heart rate and rate-pressure product were significantly lower in patients treated with propranolol (− θ20.3% and − θ22.5% in group II, P<0–001 vs step I; − θ24.3% and − θ26.4% in group III, P<0.05 vs step I), but the different treatments did not produce significant differences in systolic and diastolic blood pressure. At peak dipyridamole infusion, heart rate and rate-pressure product increased with either placebo or propranolol treatments with respect to baseline, while remaining significantly lower with propranolol as compared to placebo ( − θ29.6% and − θ29.5% in step II, P<0001). During treatment with propranolol plus transoesophageal pacing to maintain heart rate at values attained with placebo, the rate-pressure product did not change significantly with respect to placebo, nor did systolic blood pressure. Transoesophageal atrial pacing performed during propranolol treatment to restore heart rate to baseline values did not affect the dipyridamole echocardiographic test in eight patients (group I), and induced transient wall abnormalities in four patients (group II) (P= θns). Our data suggest that the anti-ischaemic effect of propranolol in man is not correlated only to reduction of heart rate.