Sinus-Junctional Escape-Capture Bigeminy

Report:

Sinus rhythm 84/min

Borderline left atrial abnormality (LAA)

Second degree AV block, unspecified

Junctional escape beats

Escape-capture bigeminy

LVH with ST/T changes

Comment:

Only every third sinus P wave is conducted, with a PR interval just over 0.20”. This PR interval is not worth reporting here: there are far greater conduction problems than borderline first degree AV block.

Every third P wave is obviously blocked, standing lonely in the long cycles.

Every third P wave is also dissociated, half-buried in the junctional escape beat. It cannot properly be called blocked, since no opportunity for its conduction exists. It is usurped by the junctional escape beat. It leaves its mark in a different way, preventing the junctional beat from being conducted retrogradely. Thus sinus rhythm remains undisturbed in its control of the atria throughout the trace.

The nature of the AV block cannot be defined, since no two consecutive conducted P waves are present. However, with the narrow QRS and the even borderline first degree block, it is almost certainly nodal rather than ventricular and would be expected to show Wenckebach sequences at some stage.

The Q waves in the inferior leads may mean old inferior infarction, but this diagnosis remains uncertain in the absence of even a small Q in lead 2. The ST/T changes are best explained by LVH, whose sole diagnostic criteria in evidence are the borderline LAA and the more secure RV6 > RV5.

The tracing below (Fig 45a), in 1:1 conduction, was taken a day later. Although the AV block resolved spontaneously, the patent was paced (Fig 45b) in view of her otherwise unexplained symptoms.

Fig 45a. Sinus rhythm with borderline 1o AVB.

Fig 45b. Paced patient in DDD mode, sensing sinus P waves and pacing the right ventricle.

Fig 46. Cardiogenic shock in a 46 year old man with new LBBB.