Differential antianginal responsiveness to acebutolol

Abstract

Six unselected males suffering from documented coronary insufficiency and grade II to III angina were submitted to graded multistage treadmill exercise test on 3 separate occasions, 3.5 hours after ingestion of either 0, 200 or 400 mg of acebutolol, a new cardioselective beta-blocker. Control measures included the random allocation to 6 balanced sequences of administration, the rigid standardisation of double-blind experimental conditions and measurements, and two types of variance analysis (latin-square and split-plot). Performance was evaluated by measuring time elapsed before occurrence of anginal pain and ECG changes, peak heart rate, peak double product (heart rate x systolic pressure), and peak oxygen consumption. The mean values for all 5 criteria showed improvement with the 200 mg dose of acebutolol, and even more so with 400 mg, but this overall effect resulted mainly from the excellent response of 3 of the patients. When patients were grouped into 2 categories of responders and non-responders, a significant Dose x Category interaction was found for all criteria. Furthermore, maximal response under acebutolol was negatively correlated with values under placebo (0 mg); this correlation reached significance for peak heart rate and peak double product. It is concluded that (a) in responders, the beneficial effect of acebutolol was significant on all 5 criteria (p less than 0.05), (b) patients definitely fell into 2 categories of responsiveness and (c) the sensitivity of responders was partly linked to their performance under placebo and partly to unidentified individual factors.