Basic Electrocardiography by Brent G. Petty

Author:Brent G. Petty
Language: eng
Format: epub, pdf
Publisher: Springer New York, New York, NY

Even though in classic cases of Mobitz I the consecutive R–R intervals decrease, it is clear that this is not always true (Fig. 4.4).

Fig. 4.4Mobitz I (Wenckebach). The PR interval gradually increases until a beat is dropped. The dropped beats actually fall in the middle of ventricular repolarization, and so they distort the normal configuration of the T waves (arrows). In this example, the R–R intervals do not shorten

Mobitz II is a higher degree of AV block than Mobitz I wherein a relatively constant fraction of P waves are conducted through the AV node to cause ventricular depolarization (Fig. 4.5). The PR intervals of the conducted beats are quite constant, rather than varying as in Mobitz I. The common ratios of conduction in Mobitz II are 3:1, 2:1, 4:1. While the ratio of P waves to QRS complexes is often constant, the ratio also may vary somewhat.

Fig. 4.5Mobitz II. In this example the block is 3:1, with three P waves present for each QRS complex. Note that the PR intervals of the conducted beats are constant at 0.18 s

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