Electrocardiographic monitoring of patients receiving phase I cancer chemotherapy.

Previous reports have characterized the various non-drug-induced cardiac disorders in cancer patients as well as the cardiotoxicity of commonly used anticancer agents. This study was conducted to determine the non-drug-related incidence of arrhythmias in patients receiving phase I antineoplastics. Twenty-four-hour Holter monitors were placed on 36 consecutive patients about to receive phase I agents. A 1-4-hour baseline was obtained before treatment was begun. Sixty-four percent of the patients observed had a wide variety of ventricular and supraventricular dysrhythmias which did not increase during or after chemotherapy. Eighty-four percent of these arrhythmias were not detected during routine monitoring consisting of baseline 12-lead ECGs and 1-minute rhythm strips prior to, during, and after treatment, but were detected with the Holter monitor. Thirty-six percent of the dysrhythmias detected by the Holter monitor were considered potentially treatable arrhythmias requiring further evaluation and possible therapeutic intervention. During the early development of phase I agents, careful evaluation should be exercised so as not to confuse pre-existing, undiagnosed arrhythmias with drug-induced changes. To more accurately determine the true arrhythmogenic potential of phase I agents, Holter monitoring should be considered as a standard part of patient assessment prior to entry of a patient in phase I trials.