Atrioventricular blocks

Abstract

I wish to comment on the ECG of the month in the June 2010 issue of British Journal of Cardiac Nursing. The answer states that the ECG shows ‘Mobitz type II 2:1 AV block.’ Mobitz type II block refers to the presence of non-conducted sinus P waves without preceding lengthening of the PR interval, in contrast to Mobitz type I (Wenckebach) block, in which there is lengthening of the PR interval before a nonconducted P wave. Th e Mobitz classification cannot apply to 2:1 block because in this particular condition there are not two consecutive conducted P waves. In other words, no statement can be made as to whether or not the PR interval lengthens before the dropped beat. 2:1 block is a separate category of second degree block. However, in the section of ECG published there is quite clearly a sequence of beats towards the end of the strip which deviates from the 2:1 block pattern and shows an increasing PR interval before a dropped beat. Th is, therefore, is a typical example of a Mobitz type I (Wenckebach) sequence. A more accurate summary of the ECG, then, might be that it shows sinus rhythm with 2:1 and Mobitz I (Wenckebach) AV block.