Multilevel atrioventricular block.

Arrhythmias displaying conduction disturbances consistent with block at more than one level within the atrioventricular conduction system were seen in 36 patients during a two year period in a community hospital. Two levels of block were postulated in each patient; one patient also demonstrated a third level of block. In 24 patients (Type A), there was an integral conduction ratio at the upper level of block. This pattern was most frequently seen in atrial flutter (mean atrial rate 284 +/- 35 beats/min) with 2:1 block at the upper level and Wenckebach at the lower level. Progression to 2:1 block at the lower level resulted in 4:1 block. Twelve patients (Type B) had a nonintegral conduction ratio of their block at the upper level with a mean atrial rate of 162 +/- 62 beats/min. Their conduction patterns consisted of Wenckebach block at the upper level with either integral (2:1) or nonintegral (Wenckebach) block at the lower level. The presence of multilevel block was not related to specific etiological diagnoses, medications, or electrolyte patterns. It is suggested that multilevel block is a common, frequently transient, conduction pattern seen in a variety of clinical conditions. It is readily recognized from a standard electrocardiogram and, of itself, has no short-term detrimental prognostic implications.