ECG interpretation — atrial fibrillation and counselling
PLAB 2 & PRES 3 · cardiology / data interpretation · medium · 10 minutes
Candidate brief
You are an FY2 doctor in a GP surgery. Mr Alan Prescott, 71, has come for his annual hypertension review. The practice nurse felt an irregular pulse and performed a 12-lead ECG, which is in front of you (summary of the tracing below). His observations are normal apart from the pulse. ECG summary: Rate 108/min, irregularly irregular rhythm. No discernible P waves — the baseline is chaotic. QRS complexes are narrow. No ST-segment elevation or depression, no T-wave inversion. The nurse has written "irregular pulse" on the tracing. Observations: BP 138/84 mmHg, pulse 108 irregular, SpO2 98% on air, afebrile. He feels well. Please interpret the ECG, reach a diagnosis, and counsel the patient on what it means and what happens next.
What examiners look for
Read the ECG in a fixed order — rate, rhythm, P waves, PR, QRS, ST, T — and say it out loud. AF announces itself with two findings together: an irregularly irregular rhythm AND absent P waves. Either alone can mislead; together they are the diagnosis. AF's danger is the clot, not the quiver. A stable, asymptomatic man with a fast irregular pulse does not need blue lights — he needs a stroke-risk score and an honest conversation. Candidates who reach for drama miss the actual clinical work of this station. CHA2DS2-VASc is not trivia; it is the prescription. His score is 2 (age, hypertension) — anticoagulation is recommended, and the bleeding assessment (ORBIT in NICE NG196) exists to find modifiable risks like alcohol, not to find excuses to withhold a stroke-preventing drug from a man whose father died of one. Two drugs, two different jobs: the anticoagulant prevents clots and does nothing for symptoms; the rate controller calms the pulse and does nothing for stroke risk. Patients conflate them constantly — "I'm on the blood thinner, why do I still flutter?" — and the candidate who separates them on day one prevents a year of confused non-adherence. Aspirin is the classic wrong answer. It is not stroke prevention in AF, however familiar it feels. And a DOAC is not "set and forget": baseline bloods, renal function and weight before the first dose, adherence emphasis (short half-life, protection lapses), interaction and NSAID warnings, and an alert card. New AF is also a question: why now? Thyroid function, electrolytes, an echocardiogram for structural disease, alcohol, caffeine, sleep apnoea. Treating the tracing without asking the question is how the hyperthyroidism gets found by somebody else, later, worse.
Guideline references
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