Pacemaker/ICD Puzzle

Clinical History I • 59-year-old male • Chronic ETOH Abuse • Dilated Cardiomyopathy • EF 20% • Complete Heart Block • S/P Dual Chamber Pacemaker • Chronic RV Pacing w/ NYHA Class III Symptoms • Optimal Medical Therapy

Clinical History II • Upgraded to CRT-D - Cognis® HE, Model N119 (Boston Scientific, Natick, MA) - RA Lead: CapSureFix® Novus, Model 4086 (Medtronic, Minneapolis, MN) - RV Lead: ENDOTAK RELIANCE® G, Model 0185 (Boston Scientific) - LV Lead: EASYTRAK®, Model 4553 (Boston Scientific) • Presents for routine device evaluation

Medications • Coreg 12.5 mg twice a day • Lisinopril 10 mg daily • ASA 325 mg daily • Lasix 40 mg daily • Lanoxin 0.25 mg daily

Question 1#: Which of the following is demonstrated in the recordings shown in Figures 1A and 1B? (A) Ventricular Fibrillation (B) Ventricular Oversensing (C) Concealed Conduction (D) Ventricular Rate Stabilization (E) Back-up Mode Pacing

Answers to the puzzle can be found below:

Question 1#: Answer Revealed

The answer is (B) Ventricular Oversensing. A basic requirement of implantable cardioverter-defibrillators (ICDs) is reliable sensing of low-amplitude ventricular depolarization signals during ventricular fibrillation (VF), while simultaneously avoiding sensing of T waves and extracardiac signals. This technically challenging process is accomplished by an automatic adjustment of either gain or sensing threshold. These auto-adjusting algorithms usually function adequately and VF is correctly detected, while spurious device activations due to oversensing are infrequent.1 Inappropriate high voltage therapy (HVT), most commonly associated with supraventricular tachycardia, can also be triggered by oversensing of cardiac signals (i.e., T waves, P waves) or by sensing of nonphysiologic signals (i.e., lead fracture, device malfunction, electromagnetic interference, far-field R wave sensing and myopotential oversensing).2-3 Myopotential signals can occur during deep inspiration, forced exhalation, coughing and during the Valsalva maneuver. Diaphragmatic myopotentials are low-amplitude signals and have been primarily observed in patients with an integrated bipolar defibrillation lead;3-4 they are more common if the ventricular lead is implanted at the right ventricular (RV) apex and if bradycardia pacing is present, as ICD sensitivity is higher after a paced event.5 In the absence of sensed complexes, the ICD must ensure VF detection. Pacing onset triggers a rapid increase in ventricular channel sensitivity that can lead to oversensing of intracardiac or extracardiac signals, resulting in spurious ICD discharges and catastrophic inhibition of pacing in a pacemaker-dependent patient.1 This problem can usually be solved by reprogramming the sensitivity to a less sensitive setting or by extending the tachycardia detection time to avoid inappropriate HVT.

Intermittent Ventricular Oversensing Even though nonphysiologic signals are present on the stored EGM in Figures 1A and 1B, only intermittent oversensing is noted, due to three new features of this device: - A new bandpass filter that has a narrower frequency range (20-85 Hz), designed to minimize noise such as myopotential oversensing (Figure 1B). - Dynamic Noise Algorithm (DNA) uses the characteristics of a noise signal (frequency and energy) to identify a signal as noise. It will maintain the sensitivity floor above the amplitude of the noise. - Less sensitive nominal setting.

Clinical History (continued) Provocative maneuvers were unable to reproduce these nonphysiologic signals. Since DFTs were done at 1.5 mV with a five-second delay, the ventricular sensitivity was reprogrammed from AGC 0.5 mV to AGC 1.5 mV. Figure 2 was obtained during the one-week post reprogramming evaluation.

Question #2: What is the most appropriate next step? (A) Implant a Separate RV Rate-Sensing Lead (B) Reprogram the Ventricular Sensitivity to a Less Sensitive Parameter (C) Program on Biventricular Trigger Pacing During Sinus Rhythm (D) Program on Rate Smoothing

Question #2: Answer Revealed The answer is (C) Program on Biventricular Trigger Pacing During Sinus Rhythm. The biventricular trigger is designed to promote synchronized RV and left ventricular contraction in the presence of RV-sensed events. It does this by pacing the left and right ventricles immediately after any sensed RV event, including PVCs and nonphysiologic signals up to the maximum tracking rate (MTR). Biventricular trigger operates between the lower rate limit and the maximum pacing rate (MPR). During VDD(R), or DDD(R) modes, MTR limits the biventricular trigger MPR.6 Since oversensing in this patient was intermittent, this feature was selected since the patient was pacemaker dependent.