Detection of a paced (VP) or sensed ventricular (VS) resets its clock an also initiates the ventricular refractory period (VRP) to prevent T-wave oversensing and initiates the post-ventricular atrial refractory period (PVARP) which helps prevent oversensing of retrograde P waves. VA interval (time from VP/VS to atrial firing) plus AVI (atrioventricular interval, roughly ~ PR interval) equals the LRI (VA + AVI = LRI).
Four rhythms are possible: 1. NSR 2. Atrial sensed, ventricle paced 3. Atrial paced, ventricle sensed 4. Atrial and ventricular pacing
Ensures that atrial events are followed by ventricular contraction, but inhibits itself if a native QRS is detected. Also ensures that an atrial contraction occurs, thus its advantage over VDD is that it guarantees atrial kick.
According to Kaplan (Box 25-4), the indications for pacemaker reprogramming are in anyone who is pacer-dependent, rate-responsiveness, certain clinical conditions (dilated cardiomyopathy, HOCM, pediatric patients), procedures in the chest/abdomen, and others (see Boxes 25-4 and 25-6)
Indications for Pacing (Adapted from Table 25-4 in Kaplan)
- Pacer dependence
- Rate responsiveness
- Dilated cardiomyopathy, HOCM, pediatric patients
- Procedures in the chest/abdomen
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