Case: Syncope during sexual activity – what is hidden in the ECG?

Sep 28
2 min read

A man in his 70s experienced a dramatic event during sexual activity alone. He lost consciousness and awoke shortly after, with associated urinary incontinence. The episode was unwitnessed, making the exact sequence of events uncertain.

He presented to the emergency clinic and was admitted to hospital.

Blood tests: NT-proBNP was normal, and troponin T was 40.
CT caput: Negative.
Telemetry: Later revealed high-grade AV block.

ECG findings

No obvious P-waves.
Right bundle branch block (QRS 135 ms).
Left axis deviation.

On closer inspection, P-waves were in fact present, but with such a long PQ interval (first-degree AV block) that they were hidden within the T-wave, giving the appearance of peaked T-waves. Overall, the findings were consistent with a trifascicular block.

What does this mean?

A trifascicular block indicates involvement of all three conduction pathways in the ventricular system:

Prolonged PQ interval → first-degree AV block.
Right bundle branch block (RBBB).
Left anterior fascicular block (LAFB).

This demonstrates a fragile conduction system, with high risk of progressing to complete AV block.

Why syncope during exertion?

At rest, the impaired conduction system can still manage slow sinus beats. During exertion or tachycardia, however, the conduction burden becomes too great, signals are blocked, and the result is asystole and syncope.

Learning points

Trifascicular block with syncope strongly suggests intermittent third-degree AV block and is a clear indication for pacemaker implantation.
In cardiogenic syncope, CT head is rarely useful, since the problem lies in the heart, not the brain.
Telemetry can be crucial to document arrhythmia in such cases.
Syncope can be accompanied by both seizures and urinary incontinence, potentially mimicking epilepsy.
Always look carefully for P-waves – they may be hidden within T-waves on the ECG.