AV Block: Nodal or Ventricular?

Report:

Sinus rhythm

Second degree AV block

Intermittent right bundle branch block & left posterior hemiblock

Prolonged QT interval

Comment:

The PR interval lengthens between the first and the second beat, but fails to grow observably longer between the second and the third beat. This may or may not be a Möbitz 1 (Wenckebach) block: Möbitz 2 is as likely.

The ventricular conduction defect is present in the two cycles before the blocked P wave. There is even money on the site of the second degree AV block being ventricular. The ventricular conduction may, on the other hand, reflect a rate-dependent RBBB + LPHB. It may be a phasic aberrancy, continued for two beats after a long-short sequence, or it may be a critical-rate dependent block.

This trace was presented at the Sydney ECG Club in 1975. There was talk of bundle branch Wenckebach by the senior Cardiologists, but no particular rationale was produced. Then as now, Humpty-Dumpty diagnoses34 abounded.

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