Empty Wenckebach Pauses

Report:

Sinus rhythm

SVEB (second QRS, bottom strip)

Second degree AV block, Möbitz 1

Junctional beats, non-conducted

?Reentry beats of sinus origin

Atrial fusion beats, non-conducted

Comment:

In the upper strips, the Wenckebach sequences are terminated by retrograde P’ waves of opposite polarity to sinus P waves. They may well be reentry (echo) beats propitiated by the prolonging PR intervals. At any rate, their timing allows atrial fusion with sinus P waves - fusion so perfect in some of the cycles that the pause looks ‘empty45’ - totally bereft of any atrial activity! In fact the pause is crowded. A little wrinkle in the baseline can just be made out in the right place when looked for.

There is some sinus arrhythmia.

This patient’s 12-lead ECG, with a masquerading bundle branch block, is shown below. It is one of the causes of concordant precordial pattern.

Fig 64a. Someone put a hot plate on this ECG, probably during a night shift, adding to the masquerade. This type of masquerading BBB is called standard and precordial since both sets of leads – standard and left precordial – resemble LBBB. Lead V1 and marked LAD tell the true story: RBBB + marked LAHB.

Fig 65. 53 year old woman in the second hour of an acute inferior infarction.