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Patient
67-year-old man with a history of atrial fibrillation referred to the department due to discovery of irregular bradycardia suggesting the need for implanting a pacemaker;
Trace
Sinus activity (positive in leads I, II, V5, V6 and negative in aVR) with significant RR interval variability; in the initial portion of the T wave, there is an ectopic atrial activity corresponding to a blocked atrial extrasystole (not followed by a QRS) with a post-extrasystolic sinus pause explaining the pseudo sinus bradycardia;
Exergue
An atrial premature complex 1) can be difficult to identify on the electrocardiogram because it may be "concealed" within the T wave and non-conducted, 2) evokes the differential diagnosis of sinus pause, 3) may originate from a focus located at the ostium of one of the pulmonary veins and represent the trigger for the induction of atrial arrhythmia episodes.
This patient was referred due to irregular heart rate and "sinus pauses". A careful inspection of the tracing allows the highlighting of a notch in the T wave preceding the pause corresponding to a blocked atrial extrasystole explaining the ensuing post-extrasystolic pause.