Provocation of coronary vasospastic angina using an isoproterenol head-up tilt test

The goals of this study were to determine the value of the isoproterenol (ISO) head-up tilt (HUT) test in detecting coronary vasospastic angina and to investigate the possible mechanism responsible for coronary artery spasm. The ISO + HUT test was performed in 16 patients with coronary artery spasm documented by the intracoronary ergonovine provocation test. Patients' blood pressure and heart rate were measured at baseline, during the ISO + HUT (phase I), and during HUT after discontinuation of ISO (phase II). Patients were categorized as test-positive if they developed angina with ST-segment elevation during testing. Eight patients (50%) were test-positive (5 in phase I and 3 in phase II). Between the test-positive and test-negative groups, no significant differences were noted in the changes in blood pressure throughout the test. However, there were significant differences in the changes in heart rate from supine to 2 minutes after HUT under ISO infusion (-17 +/-22 vs 11 +/-25 beats/minute; p=0.035). In those patients with a positive result in the phase I stage, the heart rate decreased initially after tilt-up, and then significantly increased later (from 85 +/-16 to 110 +/-27 beats/minute; p=0.043), when coronary vasospasm occurred. In those patients with a positive result in the phase II stage, coronary vasospasm occurred immediately after HUT, when there was an insignificant transient increase in heart rate from the supine to the HUT position (from 85 +/-12 to 92 +/-11 beats/minute; p=0.109). The ISO + HUT test can provoke coronary vasospasm with ST-segment elevation in 50% of the patients with coronary artery spasm, when combined with an extensional protocol of HUT after discontinuation of ISO. This study suggests that the induction of coronary artery spasm during HUT testing is associated with a rapid elevation of sympathetic activity during augmented parasympathetic activity.