R-on-T Pacing

Report:

Sinus rhythm 82/min 1

Ventricular pacemaker rhythm 58/min 1

Intermittent failure to sense 3

R-on-T pacing 3

Acute or recent inferior infarction 2

Comment:

The first paced beat is paced just after the apex (or nadir, depending on the lead) of the preceding T wave. Its coupling interval is very short – 0.30 sec. The third paced beat is similarly early. Both block the subsequent sinus beat and allow an additional paced beat to occur.

The last pacemaker spike is just before the apex of the T wave – the ventricle is refractory, rather than vulnerable, at this time. As in many similar traces, the need for pacing is no longer apparent and the unit should be switched off.

Below (Fig 78a) is the patient’s admission ECG, with “natural” R-on-T phenomenon from the bigeminal VEBs. Oddly enough, nothing ever happened.

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