Sick Sinus Syndrome: Repetitive Atrial Tachycardia

Report:

Repetitive atrial tachycardia 180-230/min 5

Atrial and pacemaker escape beats 3

DDD pacemaker pacing at 66/min 2

Comment:

This is an atrial tachycardia, with P waves not unlike sinus P waves in the frontal leads; the term SVT, while technically correct, would be unduly general in this case.

The tachycardia becomes irregular before its termination at the beginning of the tracing and its last beat encounters a relative AV block, resulting in a paced QRS complex. The latter is only 0.12” broad, suggesting a “tad of fusion” – but in fact there isn’t any – fully paced complexes below, during AF, have the same contour and duration (Fig 103a).

The native escape beat (just after the middle of the recording) is not sinus – it is a monophasic upright wave in V1 and resembles those of the tachycardia. Its escape cycle is short, corresponding to a rate of 130/min. Its PR interval is also short – about 0.12” – and it triggers a native QRS. It only called escape because it is late with respect to the rest of the tachycardia. The next two escape cycles are paced by the atrial electrode. Atrial pacing is then suppressed by the resumed tachycardia, as it is below, during AF. Not so the ventricular pacing, “fooled” by the AF into rates over 100/min.