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The automatic gain feature of defibrillators can mask ventricular standstill—a crucial message for all practitioners who use rhythm display fibrillators for heart monitoring. This wake up call comes from a case report of a 5 year old girl presenting to an accident and emergency department after three days of abdominal pain and copious vomiting and one brief seizure, lasting seconds. Initial bradycardia remained after oxygen and intravenous saline treatment. Only after two brief bouts of loss of consciousness and seizures— and recording a second rhythm strip on the heart monitor—was it realised that the change in heart rhythm was due to rapid atrial activity (150/min), amplified by the automatic gain feature to look like small QRS complexes, and not a tachycardia as assumed from the first recording. The seizures were Stokes-Adams attacks due to ventricular standstill. A 12 lead electrocardiogram confirmed complete heart block. In fact the girl had myocarditis of the ventricular septum and with appropriate treatment recovered without mishap.

Circumstances conspired to confuse and to delay the correct diagnosis. But they could have been avoided by awareness of the effects of an automatic gain feature on the recording—a salutary lesson for all clinicians who use cardiac monitoring devices. After all, as the authors point out, fast atrial activity is less likely in adults but to be expected in a young child.