Electrocardiographic features at onset of ventricular fibrillation in acute myocardial infarction. Relation to intraventricular conduction defects, configuration of initiating QRS complex, preceding heart rate and initiating coupling interval.

In prospectively collected consecutive patient data from two coronary care units (CCU), 32 patients with acute myocardial infarction (AMI) developed primary or complicating ventricular fibrillation (VF). A 12-lead ECG on the day of admission was available in 30 patients, and was compared to similar ECGs from a control group of 90 consecutive AMI patients without VF. Left anterior hemiblock (LAH) occurred in 33% of the VF patients and in 11% of the controls; the difference is statistically significant. In 20 of the 32 patients the VF occurred during continuous ECG registration. The QRS complex initiating the VF was as frequently of left as it was of right bundle branch block configuration. When compared with a second control group of 77 consecutive AMI patients under continuous ECG recording who did not develop VF, the heart rate in the VF patients was significantly higher just prior to the development of this arrhythmia. The VF initiating coupling interval was shorter than the upper normal limit of the QT interval in 40% of the VFs. In primary VF and in patients not treated with antiarrhythmic drugs the coupling intervals were close to the upper normal limit of the QT interval. In complicating VF and particularly when antiarrhythmic therapy was used the coupling intervals showed a wider variation.