Signal-averaged electrocardiographic detection of terminal QRS deflection suggesting late potentials

A terminal QRS deflection on a 12-lead electrocardiogram (previously described as peri-infarction block) most likely represents slowed conduction in a large area of myocardium near the infarct zone. We have described a patient with peri-infarction block, abnormal findings on signal-averaged electrocardiogram, and reentrant ventricular tachyarrhythmias. Our observation underscores the need to recognize the importance of terminal QRS deflections in the appropriate clinical situation.