Retrograde Wenckebach at the Atrioventricular Junction

Retrograde Wenckebach at the atrioventricular junction

Sometimes the impulses from the AV  junction in a case of junctional rhythm gets conducted retrogradely into the atria in a Wenckebach fashion across the atrioventricular junction. This results in a narrow QRS rhythm with retrograde P waves and a progressive prolongation of RP intervals. The cycle may terminate in an echo beat when the RP interval is long enough for the anterograde conduction to recover from the previous activation. Alternatively the cycle may terminate in a loss of atrial capture. Then the cycle restarts again. In a typical retrograde Wenckebach, the retrograde PP intervals will progressively shorten as atrium is the distal chamber for the conduction and the increments of prolongation of RP interval are decremental.

Differential diagnosis of progressive shortening of PP interval is a Wenckebach periodicity at the sinoatrial junction. But in that case the P waves will be from the sinus node and conducted downwards in the atria resulting in positive P waves in leads II, III and aVF. The retrograde P waves are usually inverted in leads II, III and aVF and upright in lead V1. Retrograde AV Wenckebach is type 1 second degree VA block. Retrograde Wenckebach conduction has also been described in atrioventricular nodal tachycardia, ventricular tachycardia, atrioventricular bypass tracts and ventricular paced rhythm.