Ethnic differences in response to beta-blockade: fact or artefact? A study with bisoprolol and propranolol

A randomized, double-blind, placebo-controlled study was performed in 8 white and 8 black volunteers matched for sex, age and mass. The effect of 3 intravenous doses of a new, cardioselective beta-adrenergic blocker, bisoprolol, on the heart rate increase after standardized exercise was compared to that of 3 doses of propranolol. As described previously for propranolol, black volunteers showed less response than whites to beta-blockade assessed in terms of the reduction in exercise-induced tachycardia. The effects of the two beta-blockers were similar and the apparent ethnic difference was seen with both drugs. It has previously been shown that black volunteers have a higher intrinsic heart rate (i.e. heart rate after parasympathetic and beta-adrenergic blockade of the heart) than whites, but their resting heart rates are similar because of greater parasympathetic tone in blacks. When exercise-load was calculated as increase in heart rate above that after atropinization, no ethnic differences were seen. It is suggested that in populations that are heterogenous in terms of the heart rate increase after atropine, work load should be standardized in terms of the increase in heart rate over the atropine heart rate rather than on absolute heart rate. The apparent ethnic difference represents a flaw in methodology as applied to a heterogenous volunteer population.