VVIR

VVIR stands for ventricle paced, ventricle sensed, inhibited response, rate-modulated. It is a single-chamber pacemaker mode used to treat bradycardia with chronotropic incompetence. In VVIR, the device paces the right ventricle, senses ventricular activity, and inhibits pacing when intrinsic ventricular contractions are detected. The final “R” denotes rate modulation: a sensor adjusts the pacing rate in response to the patient’s activity or metabolic needs, allowing the ventricular rate to rise with exertion and fall at rest.

The ventricle is paced and sensed using a single lead in the right ventricle. Because sensing and pacing occur in one chamber and there is no atrial tracking, VVIR provides no atrioventricular synchrony and is not suitable for patients who require coordinated atrial and ventricular contractions.

Indications include symptomatic bradycardia due to sinus node dysfunction or AV block in patients who do not require atrial pacing or AV synchrony, and in individuals with chronic atrial fibrillation with a slow ventricular response. VVIR can be preferred when device simplicity, lead durability, and straightforward programming are advantageous.

Advantages of VVIR include a smaller, simpler system with reduced risk from an additional atrial lead and the ability to adapt pacing rate to activity. Limitations include loss of AV synchrony, potential for inappropriate rate response due to sensor misreads, and reduced hemodynamic benefit in patients who rely on atrial contraction for ventricular filling or who would benefit from AV synchrony.