VVIR & DDDR: Mode Switch

Atrial Undersensing

Report:

Sinus tachycardia 100/min 1

Atrial-sensing ventricular pacemaker rhythm 100/min (first two cycles) 2

Ventricular pacemaker rhythm, VVIR mode, 98-84/min 5

VEB 1

LAA 1

Comment:

The pacemaker picked up and dropped sinus rate repeatedly, implying intermittent loss of atrial sensing. This was a DDDR unit, switching its mode to VVIR. Mode switch is a programmable parameter designed to protect the heart from rapid atrial rhythms, especially AF; it is different from upper rate limit, which retains the original DDD configuration (and wastes the battery by needless atrial spikes, also producing palpitations from irregular ventricular response).

In this case, the switch was unintended; it was caused by atrial undersensing.

Below (Fig 58a) is another episode, showing recognition of sinus tachycardia by the pacemaker.

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