Variability of the PR intervals in Wenckebach atrioventricular block.

The duration of the PR intervals in atypical Wenckebach atrioventricular block before and after a non-conducted P wave can exhibit a wide range of values and patterns. Understanding the different or at times puzzling manifestations of Wenckebach atrioventricular block in terms of its PR intervals can avoid diagnostic errors, especially the erroneous more serious diagnosis of Mobitz type II atrioventricular block.

Pseudo-2:1 bundle branch block. "Fusion causes confusion".

The fusion of narrow-QRS sinus-generated beats with end-diastolic ventricular extrasystoles occurring in bigeminy can produce an electrocardiographic pattern difficult to differentiate from parasystole. Such an ECG should not be interpreted as 2:1 RBBB because of the variability of the PR intervals.

Incomplete (partial) left anterior hemiblock.

This report describes two electrocardiograms (ECGs) showing unusual manifestations of left anterior hemiblock (LAH). One revealed different degrees of incomplete LAH and the other documented the occurrence of 2:1 LAH. Understanding different degrees of LAH helps to interpret the ECG with regard to intraventricular conduction disorders and other ECG abnormalities.