The effect of propranolol and verapamil on external pacing threshold: a placebo-controlled study

External transthoracic pacing is frequently used in situations where cardiac medications are administered. In view of theoretical concerns of the effects of beta-blocking and calcium channel blocking agents on pacing threshold, these agents were studied in six normal subjects over a 90 minute period during external cardiac pacing. Subjects received 10 mg propranolol, verapamil or identical placebo intravenously on 3 separate days in a double-blinded trial with serial determination of pacing threshold. Neither placebo nor either active drug altered pacing threshold. It is concluded that propranolol and verapamil have no significant effect on the threshold required for external transthoracic pacing in normal subjects and concerns about a drug induced increase in threshold may be unfounded.