Unreliability of conventional electrocardiographic monitoring for arrhythmia detection in coronary care units

To evaluate the reliability of conventional coronary care unit electrocardiographic monitoring, a study was made of 31 consecutive patients with uncomplicated verified acute myocardial infarction. All patients were monitored routinely with conventional equipment, and at the same time the electrocardiogram for each patient was recorded continuously on electromagnetic tape and stored for later analysis by an automated arrhythmia detection system. All patients studied were within 24 hours of the onset of chest pain and on entry into study all were free of shock, heart block, bundle branch block, severe heart failure or an existing arrhythmia. By conventional monitoring, premature ventricular contractions were recognized in 64.5 percent of patients compared with 100 percent using the automated detection system (P <0.01). The corresponding percentages for recognition of premature atrial contractions were 45.2 vs. 96.8 percent (P < 0.001); serious ventricular arrhythmias, 16.1 vs. 93.5 percent (P <0.001); multifocal premature ventricular contractions, 6.5 vs. 87.1 percent (P < 0.001); and consecutive premature ventricular contractions, 13.0 vs. 77.5 percent (P < 0.001), respectively. The delay from the time of first occurrence as detected by the automated system to recognition by the conventional monitoring system averaged 18 hours for premature ventricular contractions, 10 hours for serious ventricular arrhythmias and 23 hours for premature atrial contractions. The on-line use of an automated arrhythmia detection system in the coronary care unit is suggested if further improvement in the elimination of arrhythmias as a primary cause of death after myocardial infarction is to be achieved. The presence of serious ventricular arrhythmias in virtually all patients after myocardial infarction suggests that prophylactic antiarrhythmic agents be used in this setting; however, none of the presently available antiarrhythmic agents have been shown to reduce mortality when given prophylactically following myocardial infarction.