alpha-Adrenergic receptors and coronary spasm: an elusive link.

Abstract

In 14 consecutive patients with variant angina we investigated the possible role of coronary alpha-adrenergic receptors in the genesis of coronary spasm. In eight patients, computerized, beat-by-beat analysis of the electrocardiogram recorded during continuous Holter monitoring failed to reveal any increase of heart rate and corrected QT interval (both indexes of cardiac sympathetic activation) in the period preceding the onset of ST segment changes in 197 episodes of ischemia caused by coronary spasm. In the same patients, analysis of the circadian distribution of ischemic episodes revealed a significantly higher incidence in the early morning hours, when sympathetic activity is at the lowest level. Twelve patients underwent serial provocative testing with cold pressor, phenylephrine, or norepinephrine infusion and administration of ergonovine maleate. Ergonovine consistently reproduced coronary spasm in all 12 patients, while results of cold pressor testing were positive in only one. Infusion of phenylephrine (eight patients) or norepinephrine after beta-blockade (four patients) failed to precipitate myocardial ischemia. In five patients infusion of phentolamine at the highest tolerated dose did not reduce significantly the number of ischemic attacks when compared with placebo. In contrast to results of previous reports, our data seem to rule out the hypothesis that an increase of sympathetic outflow to the heart plays an important role in the genesis of coronary spasm. We cannot, however, exclude the possibility of localized alpha-stimulation of epicardial arteries.