Dizziness and two near-faints since this morning

2026-09-14

The case

78-year-old man. Dizziness and two near-faints since this morning

Lives alone and independent. Treated hypertension on amlodipine only — no beta blocker, no rate-limiting calcium blocker, no digoxin and no antiarrhythmic. No chest pain and no palpitations. Each episode came on standing at the sink: a few seconds of going grey and light-headed, no warning, no loss of consciousness and no injury.

On arrival

HR: 78
SpO₂ (%): 97
Respiratory rate: 16
Temperature (°C): 36.5
Systolic BP (mmHg): 138
Diastolic BP (mmHg): 76

Stage 1 of 2

He is comfortable and fully orientated, lying on the trolley. Heart sounds are normal, chest is clear, there is no murmur and no postural drop. This twelve-lead was recorded four minutes after he arrived, between episodes.

Tracing 1 of 2 for the quiz “Dizziness and two near-faints since this morning”. — Twelve-lead on arrival, 25 mm/s, 10 mm/mV. Open this tracing in the studio

What does this tracing show?

ARate-related aberrant conduction, of no immediate consequence Your answer
BRight bundle branch block, unchanged throughout the recording Your answer
CBundle branch block that alternates between right and left, with a run of complete AV block Correct answer Your answer
DAtrial fibrillation with a slow ventricular response Your answer

The QRS morphology alternates between a right bundle branch block pattern and a left bundle branch block pattern across the recording, and a run of P waves marching through without conducted QRS complexes shows complete atrioventricular block. Atrial fibrillation is excluded by regular, visible P waves throughout. Rate-related aberrancy would favour one bundle at a given rate and would not switch between both at this steady sinus rate.

Stage 2 of 2

He is put on the monitor. Twenty minutes later he says he feels grey again; the monitor records a 4.2-second pause before a slow escape returns. He does not lose consciousness. Bloods are back: potassium 4.2, magnesium 0.86, creatinine 94, troponin T 9 ng/L and TSH normal. He has taken nothing but amlodipine.

Tracing 2 of 2 for the quiz “Dizziness and two near-faints since this morning”. — Rhythm strip, 25 mm/s, 10 mm/mV. Open this tracing in the studio

Bloods

Troponin T (ng/L): 9
Magnesium (mmol/L): 0.86
Potassium (mmol/L): 4.2
Creatinine (umol/L): 94

Notes

Monitored pause 4.2 s, symptomatic. No AV-nodal blocking drug taken.

What does this commit you to?

AAtropine, and discharge if the dizziness settles Your answer
BDischarge with a 24-hour Holter and cardiology follow-up Your answer
COutpatient echocardiogram first, and decide about pacing on the result Your answer
DAdmit to a monitored bed and refer for permanent pacing Correct answer Your answer

Alternating bundle branch block demonstrates disease in both bundle branches, and the monitored symptomatic 4.2-second pause confirms intermittent complete atrioventricular block as the mechanism. With normal electrolytes and no atrioventricular nodal blocking drug, there is no reversible cause. Atropine acts on the atrioventricular node and will not reliably rescue infranodal block, and outpatient investigation defers a decision this tracing has already made.

Diagnosis

Alternating bundle branch block with intermittent complete AV block

This tracing captures the moment both bundle branches fail in the same recording. The initial complexes conduct with a right bundle branch block pattern, which gives way to a left bundle branch block pattern, with a run of complete atrioventricular block between them. Each near-faint was a pause like the monitored one.

Alternating bundle branch block with syncope is one of the clearest indications for permanent pacing. No drug trial, stress test or Holter will add to the decision this single twelve-lead has already made. The patient needs a monitored bed tonight and a pacemaker before discharge.

References

Brignole M, Moya A, de Lange FJ, et al. 2018 ESC Guidelines for the diagnosis and management of syncope. Eur Heart J. 2018;39(21):1883-1948.
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.

Embed

<script async src="https://www.squiggler.io/embed.js" data-case="dizziness-and-two-near-faints-since-this-morning"></script>

Or, where scripts are stripped:

<iframe src="https://www.squiggler.io/blog/dizziness-and-two-near-faints-since-this-morning/embed" title="Dizziness and two near-faints since this morning — ECG case from Squiggler" width="100%" height="900" style="border:0" loading="lazy"></iframe>

This tracing was generated, not recorded. It opens in the studio with every dial live.

Open the studio

Discussion

Comments are read before they appear. Disagreement about a reading is welcome — this is a teaching column and the arguments are the useful part. No account, no email.