Rebound myocardial ischaemia following abrupt interruption of intravenous nitroglycerin infusion in patients with unstable angina at rest.

Isolated observations prompted a prospective study of the possible occurrence of myocardial ischaemia following abrupt discontinuation of intravenous infusion of nitroglycerin in 46 consecutive patients with unstable angina. In 26 (55%, group 1), but not the remainder (45%, group 2), cessation of nitroglycerin produced in 10.3 +/- 5.8 (mean +/- SD) minutes ECG changes comparable with those of spontaneous angina without significant changes in heart rate and blood pressure. Reproducible results were observed in 18/20 patients in whom the test was repeated. In four patients with two positive tests, a third test failed to elicit ischaemia 15 min after sublingual administration of 5 mg isosorbide dinitrate. An ergonovine test performed in four other patients with a positive test produced similar ECG changes. Thus, acute interruption of intravenous nitroglycerin infusion in patients with unstable angina is often associated with acute myocardial ischaemia. The lack of preceding changes in heart rate and blood pressure and the similarities with the spontaneous episodes and with those produced by ergonovine, strongly suggest a rebound coronary vasoconstrictive phenomenon as the underlying mechanism.