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Two episodes of sudden loss of consciousness

The case

76-year-old man. Two episodes of sudden loss of consciousness

Retired carpenter. Hypertension treated with amlodipine. No previous cardiac history. His wife witnessed two brief episodes of syncope today, each lasting about ten seconds, with no warning and no post-ictal confusion. He has fully recovered between episodes.

On arrival

HR
62
Spo2Percent
97
Respiratory rate
16
Temperature (°C)
36.6
Systolic BP (mmHg)
138
Diastolic BP (mmHg)
76

Stage 1 of 1

A 76-year-old man presents to the emergency department after two witnessed syncopal episodes today, each lasting about ten seconds with immediate recovery. His wife describes no seizure activity. He is haemodynamically stable between episodes. A twelve-lead ECG is recorded.

The tracing for the quiz “Two episodes of sudden loss of consciousness”.
Twelve-lead ECG recorded in the emergency department Open this tracing in the studio
The QRS complexes are broad. What is the conduction abnormality responsible for the QRS morphology in V1?

V1 shows a broad QRS with an rsR' pattern, which is the characteristic morphology of right bundle branch block. The QRS duration is about 127 ms, confirming a complete rather than incomplete block. Left bundle branch block would produce a broad monophasic or notched R wave in V1 without the secondary R', and there is no slurred upstroke or short PR to suggest ventricular pre-excitation.

The frontal QRS axis is markedly negative. Which additional conduction structure is blocked?

The frontal axis is about minus 55 degrees, representing marked left axis deviation. In the presence of right bundle branch block, this pattern points to an additional block in the left anterior fascicle, producing bifascicular block. Left posterior fascicular block would cause right axis deviation, not left. The sinoatrial node and accessory pathways are not conduction structures whose block produces left axis deviation.

The PR interval is prolonged at 270 ms. Considering the full conduction picture, what does this pattern most likely explain in a patient presenting with syncope?

Right bundle branch block with left anterior fascicular block means two of the three fascicles are permanently blocked. The prolonged PR at 270 ms suggests slow conduction through the remaining left posterior fascicle. In a patient presenting with syncope, intermittent failure of that last pathway causing transient complete heart block is the most likely explanation. Sinoatrial disease would not produce this combination of findings.

Diagnosis

Trifascicular block with syncope from intermittent complete heart block

This tracing demonstrates trifascicular conduction disease: right bundle branch block visible in V1, left anterior fascicular block producing the marked left axis deviation, and first-degree atrioventricular block with a PR of 270 ms suggesting impaired conduction through the remaining left posterior fascicle. Each syncopal episode was almost certainly a brief period of complete heart block.

The practical lesson is to read the three findings together. Any one alone might be an incidental finding in an elderly man. Together, in a patient presenting with syncope, they identify extensive infranodal disease that will need permanent pacing.

References

  1. Dhingra RC, Palileo E, Strasberg B, et al. Significance of the HV interval in 517 patients with chronic bifascicular block. Circulation. 1981;64(6):1265-1271.
  2. 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.
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This tracing was generated, not recorded. It opens in the studio with every dial live.

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Discussion

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