VVI Pacemaker Function
A VVI pacemaker paces the ventricle, senses the ventricle, and is inhibited by sensed ventricular activity—the correct answer is D.
Understanding the VVI Pacing Code
The three-letter pacemaker code describes the chamber paced, chamber sensed, and response to sensing:
- First V (Ventricle): The pacemaker delivers electrical impulses to the ventricle 1
- Second V (Ventricle): The device senses intrinsic ventricular electrical activity 1
- I (Inhibited): When the pacemaker detects spontaneous ventricular activity, it inhibits its pacing output and does not deliver an unnecessary impulse 1
Clinical Characteristics of VVI Pacing
VVI is described as "the classic prototypical pacing mode" where ventricular pacing is inhibited by sensed spontaneous ventricular activity 1. This means:
- The pacemaker continuously monitors for intrinsic ventricular depolarization 1
- If the patient's own ventricular rate exceeds the programmed lower rate limit, the pacemaker remains inhibited and does not pace 2
- If no ventricular activity is sensed within the programmed interval, the pacemaker delivers a ventricular pacing stimulus 1
Appropriate Clinical Indications
VVI pacing is particularly indicated for symptomatic bradyarrhythmias when 1:
- There is no significant atrial hemodynamic contribution (such as in persistent or paroxysmal atrial flutter/fibrillation) 1
- Pacing simplicity is a priority in cases of advanced age, terminal disease, or remote domicile from follow-up centers 1
- There is absent retrograde ventriculoatrial conduction 1
Important Clinical Caveat
VVI pacing is contraindicated when pacemaker syndrome is present or anticipated 1. Pacemaker syndrome includes light-headedness, syncope, or symptoms related to loss of AV synchrony, inadequate cardiac output from VA conduction, or patient awareness of beat-to-beat variations 1. In such cases, dual-chamber pacing modes that preserve AV synchrony should be considered instead 1.