Pacemaker/ICD Puzzle

Clinical History: • 62-year-old male • CAD • Ischemic Cardiomyopathy • EF 20% • Sustained Monomorphic Ventricular Tachycardia • S/P ICD implantation ICD: - MDT: Gem® 7227 - V Lead: MDT: 6945 Sprint • Routine scheduled remote evaluation: 4/28/08 Medications: • Toprol XL 50 mg daily • Lisinopril 10 mg daily • ASA 81 mg daily • Lipitor 40 mg daily

Pacemaker/ICD Puzzle Question: Which of the following is demonstrated in the recording shown in Figure 1? (A) Phantom Reprogramming (B) Hysteresis (C) Class I Pacemaker Dependency (D) Ventricular Rate Stabilization (E) Back-up Mode Pacing

Answer: (D) Ventricular Rate Stabilization (VRS) • VRS is a preventive pacing algorithm designed to eliminate the long pause that follows a premature ventricular depolarization. • VRS is designed to prevent the “short-long-short” sequences of ventricular cycle lengths that have been clinically observed to precede the onset of some spontaneous ventricular tachyarrhythmias. • VRS acts as a constant rate-smoothing algorithm. VRS: • Each ventricular event begins a VRS escape interval equal to the sum of the previous ventricular interval and the VRS interval increment value (or the minimum VRS interval, if it is larger than the sum). • Programming options include: - VRS on or off - Minimum interval (ms) is the shortest allowable VRS interval - Interval increment (ms) is the value added to the previous V-V interval to determine the current VRS interval

More Information about VRS: • If the escape interval expires before a ventricular sensed or paced event occurs, the ICD delivers a pacing pulse. • The ICD then recalculates the VRS escape interval for the next pacing pulse using the last ventricular interval. • The VRS escape interval lengthens, from beat to beat, by a value equal to the programmable VRS interval increment. • When the rate generated by VRS operation slows to the intrinsic or programmed rate, the ICD returns to normal operation.

Episodes Counters: • % pacing reports the percentage of ventricular pacing during the reporting period. • V. Rate Stabilization Paces reports VRS paces (i.e., VRS escape interval timeouts). • VRS paces are not included in the % pacing counters.

Interpretation: • T wave oversensing invoked the VRS algorithm and resulted in inappropriate periods of ventricular pacing. • Episode counters revealed delivery of 75,514 VRS runs encompassing a total of 217,058 beats. • VVI pacing above the intrinsic rate disclosed T wave oversensing. • Oversensing of the paced T wave could be resolved with increasing the pace blanking period to 340 ms or decreasing the sensitivity to 0.45 mV. • A longer pace blanking period may interfere with the use of VRS due to encroachment of the tachycardia sensing window. • The sensitivity was reprogrammed to 0.45 mV, with no further episodes of inappropriate pacing. • Repeat DFTs were not necessary since testing at implant was done at the minimum programmable sensitivity. • The pulse generator eventually reached ERI and was replaced in June 2008.

Management Options for Inappropriate Ventricular Pacing Due to Autoperpetuation of VRS Algorithm: • Program VRS off • Reprogram ventricular paced blanking period • Reprogram ventricular sensitivity