Escape-Capture Bigeminy

Report:

Sinus rhythm 92/min

Second degree AV block, probably 2:1[!xe "AV block:second degree:2-1" \b!]

Junctional escape beats[!xe "Junctional escape beats:second degree AV block" \b!]

Escape-capture bigeminy

Non-phasic aberration[!xe "Aberrant conduction:non-phasic" \b!]

Comment:

This rhythm was called pseudoreciprocal because of the P wave seen between the QRS complexes of each pair. Its position and polarity, however, distinguish this from a true reciprocal rhythm. Escape-capture bigeminy39 is both more accurate and more descriptive, although some semantic difficulties remain.40[!xe "Pseudoreciprocal rhythm" \t "See Escape-capture bigeminy" \b!]

The escape complexes are slightly different from the sinus ones. This form of aberrancy, termed non-phasic by Schamroth41, may be due to slightly different ventricular activation front from a junctional focus. Possibly, the escape beats appear smaller due to superimposition of negative sinus P waves, but the strip below excludes this mechanism.

The escape QRSs hide every third P wave.

Wenckebach sequences below start with impossibly short PR intervals. They are in fact initiated by junctional escape beats, smaller than the subsequent conducted sinus beats. Here their non-phasic aberrancy helps establish the diagnosis. Also, unlike the junctional escape beats in the original strips, they can be seen without any superimposed sinus P waves.