Tremor artefact or atrial fibrillation?
A 62-year-old man with Parkinson's disease is sent to the ECG room for a preoperative tracing. The room is air-conditioned at 18°C, and he has been waiting for 40 minutes. He is anxious and has a coarse resting tremor in both arms. The ECG shows narrow QRS complexes at a regular interval of about 680 ms. Between the QRS complexes there are irregular, rapid undulations in leads I, II, and aVL, and the automated interpretation prints 'atrial fibrillation, abnormal ECG.' The patient's radial pulse feels regular at 88/min. The technician notices the baseline undulations increase when the patient tenses his arms. There is no history of palpitations. The technician has only one machine and a queue of six patients. The referring ward clerk asks whether the report can be sent as it is because the patient is next for surgery.
1. What is the most likely explanation for the baseline undulations, and which features make atrial fibrillation unlikely?
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The undulations are most likely somatic tremor artefact, not atrial fibrillation. The key reasoning is that the QRS complexes occur at a regular interval of about 680 ms, giving a rate of about 88/min, and the radial pulse is also regular. Atrial fibrillation is characteristically irregularly irregular with varying R-R intervals. The baseline undulations increase when the patient tenses his arms, which supports muscle tremor rather than atrial electrical activity. The automated interpretation is a pattern-matching suggestion, not a diagnosis, and it can be fooled by a noisy baseline. The absence of palpitations and the regular ventricular rate further lower the probability of AF. The technician should not send the automated report as a confirmed diagnosis.
2. List the immediate practical steps you would take before sending the report.
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- Reassure the patient and explain that the tracing is noisy, not necessarily abnormal.
- Support both arms on a pillow and ask him to let the arms go limp; tremor often reduces when muscles are supported.
- Warm the room if possible, clean and dry the skin, and place limb electrodes on fleshy areas away from active muscle.
- Check that the electrodes are not over tendons or areas of coarse tremor and that lead placement is correct.
- Repeat the ECG at standard 25 mm/s and 10 mm/mV, observing the baseline while the patient is still.
- Annotate the original tracing as 'baseline artefact likely due to tremor' and keep it for comparison.
- Send the clean repeat tracing with a note that the automated AF label was artefact-related, and inform the referring clinician.
3. If the undulations persist on repeat, what should you do and what should you avoid?
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If the undulations persist but the QRS complexes and radial pulse remain regular, the most likely cause is still artefact. Try further measures such as repositioning the arms, using fresh electrodes, and recording a short rhythm strip while the patient is fully supported. Document the technical difficulty clearly. Avoid labelling the rhythm as atrial fibrillation or sending the automated report as definitive. Do not suggest starting or stopping any cardiac medicine. If there is genuine uncertainty, if the pulse becomes irregular, or if the patient develops symptoms, escalate to the clinician for review rather than filing the report silently.