Syncope — ECG cases

Stage 1 of 2

Her triage ECG is recorded.

The tracing for the quiz “Syncope”. — 12-lead ECG, 25 mm/s, 10 mm/mV Open this tracing in the studio

What is the rhythm?

AAtrial pacing with Mobitz type I AV block Correct answer Your answer
BDual-chamber pacing with ventricular capture failure Your answer
CSinus rhythm with blocked atrial ectopics Your answer
DAtrial pacing with intermittent oversensing Your answer

Pacing spikes are visible before every P wave but not before any QRS complex, confirming an atrial-only pacemaker. The PR interval lengthens progressively over successive beats until a paced P wave fails to conduct, followed by resumption with a shorter PR. This is the Wenckebach pattern. Dual-chamber pacing with loss of ventricular capture would produce a spike before each missing QRS, which is absent here.

What do the QRS morphology and axis indicate?

ARBBB and possible left posterior fascicular block Correct answer Your answer
BIsolated right bundle branch block Your answer
CLeft bundle branch block Your answer
DRight ventricular hypertrophy Your answer

Lead V1 shows an rSR' pattern and leads I and V6 show broad terminal S waves, confirming right bundle branch block with a QRS duration of 120 ms. The frontal axis is markedly rightward with a predominantly negative QRS in lead I. In the presence of RBBB, right axis deviation is consistent with left posterior fascicular block, though this diagnosis requires exclusion of right ventricular hypertrophy and other causes of rightward axis.

Stage 2 of 2

The pacemaker clinic confirms an AAI device implanted eight years ago for sinus node dysfunction, with normal atrial capture and sensing and adequate battery life. She takes bisoprolol 2.5 mg daily. Her clinic ECG eighteen months ago showed 1:1 conduction with a narrow QRS.

What is the most appropriate next step?

AUpgrade to a dual-chamber pacemaker Correct answer Your answer
BIncrease the atrial pacing rate Your answer
CStop bisoprolol and reassess in one week Your answer
DGive atropine and admit for monitoring Your answer

Progressive AV block with probable bifascicular disease beneath a functioning atrial pacemaker requires a ventricular lead. Increasing the atrial rate would present the AV node with faster impulses and worsen the block. Bisoprolol may contribute and should be reviewed, but RBBB with right axis deviation points to structural conduction disease that will not resolve by stopping a beta-blocker alone. She is haemodynamically stable, so atropine and temporary pacing are not indicated.

Diagnosis

Atrial pacing with Mobitz type I AV block, RBBB and right axis deviation

This tracing shows atrial pacing with Mobitz type I second-degree AV block. Pacing spikes precede every P wave, confirming normal atrial capture, but no ventricular spikes are present because this is a single-chamber atrial device. The PR lengthens progressively until a paced P fails to conduct, producing grouped beating at a ventricular rate of 53.

The QRS shows right bundle branch block with marked right axis deviation, consistent with left posterior fascicular block and so with probable bifascicular disease. Development of AV block is the recognised long-term limitation of single-chamber atrial pacing for sinus node dysfunction; in the DANPACE trial, atrial-only pacing carried twice the risk of pacemaker reoperation compared with dual-chamber pacing. The management is upgrade to a dual-chamber pacemaker. Rate-limiting drugs should be reviewed, but the structural conduction disease requires a ventricular lead.

References

Glikson M, Nielsen JC, Kronborg MB, et al. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. Eur Heart J. 2021;42(35):3427-3520.
Nielsen JC, Thomsen PE, Højberg S, et al. A comparison of single-lead atrial pacing with dual-chamber pacing in sick sinus syndrome. Eur Heart J. 2011;32(6):686-696.

Syncope

The case

On arrival

Diagnosis

References

Discussion