Is this Complete Heart Block?

Is this complete heart block?

Image 1 - ECG case

Image 2 - Ladder diagram

First and foremost, we can right away rule-out complete heart block if the RR interval is irregular. If it is irregular then some of the sinus beats were conducted.

In this case, the rhythm is sinus (upright P waves in II, III and aVF) but most likely it is sinus arrhythmia because of the irregularity at a rate of about 100 bpm. There is ventriculophasic sinus arrhythmia. This means that the PP interval enclosing a QRS complex is shorter compared to the PP interval not enclosing a QRS complex.

RR intervals of the following are the same (~880 ms) which favors that they are from the same focus (junction - accelerated junctional rate ~70):

R1R2 R2R3 R3R4 R4R5 R10R11 and R11R12

There is lengthening of the RR interval R5R6. There is shortening of the RR interval between R6R7 and R7R8 which is due to the lengthening of the PR interval. This is indicative of Wenckebach. The P wave after QRS# 9 is not conducted.

Sinus beats were not conducted because the AV junction is refractory from a prior junctional beat.

Thus, this is ventriculophasic sinus arrhythmia with AV dissociation (accelerated junctional rhythm), period of capture with Wenckebach and resumption of AV dissociation after the Wenckebach cycle due to acceleration of a junctional pacemaker.


...Or a unifying explanation is second degree advanced heart block due to a Type I (Wenckebach) mechanism.

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