Improving SVT discrimination in single-chamber ICDs: a new electrogram morphology-based algorithm.

INTRODUCTION: Wide-spread adoption of ICD therapy has focused efforts on improving the quality of life for patients by reducing "inappropriate" shock therapies. To this end, distinguishing supraventricular tachycardia from ventricular tachycardia remains a major challenge for ICDs. More sophisticated discrimination algorithms based on ventricular electrogram morphology have been made practicable by the increased computational ability of modern ICDs. METHODS AND RESULTS: We report results from a large prospective study (1,122 pts) of a new ventricular electrogram morphology tachycardia discrimination algorithm (Wavelet Dynamic Discrimination, Medtronic, Minneapolis, MN, USA) operating at minimal algorithm setting (RV coil-can electrogram, match threshold of 70%). This is a nonrandomized cohort study of ICD patients using the morphology discrimination of the Wavelet algorithm to distinguish SVT and VT/VF. The Wavelet criterion was required ON in all patients and all other supraventricular tachycardia discriminators were required to be OFF. Spontaneous episodes (N = 2,235) eligible for ICD therapy were adjudicated for detection algorithm performance. The generalized estimating equations method was used to remove bias introduced when an individual patient contributes multiple episodes. Inappropriate therapies for supraventricular tachycardia were reduced by 78% (90% CI: 72.8-82.9%) for episodes within the range of rates where Wavelet was programmed to discriminate. Sensitivity for sustained ventricular tachycardia was 98.6% (90% CI: 97-99.3%) without the use of high-rate time out. CONCLUSIONS: Results from this prospective study of the Wavelet electrogram morphology discrimination algorithm operating as the sole discriminator in the ON mode demonstrate that inappropriate therapy for supraventricular tachycardia in a single-chamber ICD can be dramatically reduced compared to rate detection alone.

Multi-center clinical experience with a lumenless, catheter-delivered, bipolar, permanent pacemaker lead: implant safety and electrical performance.

PURPOSE: Reduced lead diameter and reliability can be designed into transvenous permanent pacing leads through use of redundant insulation and removal of the stylet lumen. The model 3830 lead (Medtronic Inc., Minneapolis, MN, USA) is a bipolar, fixed-screw, steroid-eluting, lumenless, 4.1-Fr pacing lead. Implantation can be performed in a variety of right heart sites using a deflectable catheter (Model 10600, Medtronic). Lead performance and safety were studied. METHODS: Two prospective trials of 338 implanted subjects from 56 global sites were conducted. Electrical and safety data were obtained at implant, pre-discharge, and up to 18 months post-implant. Leads were implanted at traditional and alternate right heart sites. RESULTS: The study enrolled 338 subjects (204 males, 70.6 +/- 11.6 years) followed-up for a mean of 10.2 months (range, 0-21.6). Mean P-wave amplitudes ranged from 3.2 mV at 3 months to 2.9 mV at 18 months, while mean atrial pulse width thresholds at 2.5 V ranged from 0.07 ms at 3 months to 0.09 ms at 18 months. Mean R-wave amplitudes ranged from 11.3 mV to 11.1 mV and mean ventricular pulse width thresholds at 2.5 V ranged from 0.10 ms to 0.14 ms. There were 22 ventricular and 12 atrial lead complications within 3 months post-implant. Survival from lead-related complications improved to a clinically acceptable rate in the cohort of patients when revised implant techniques were employed. CONCLUSIONS: With the use of recommended implant techniques, the study results support the electrical efficacy and safety of a catheter-delivered, lumenless lead in traditional or alternate right atrium or right ventricle sites through 18 months post-implant.

The circadian variation of atrial defibrillation thresholds.

BACKGROUND: A circadian variation exists for ventricular defibrillation thresholds (DFTs) with a morning peak and a corresponding decrease in therapy success rates from implantable cardioverter defibrillators. Such a variation in atrial DFTs may have implications for the timing of internal cardioversion of atrial arrhythmias. The aim of this study was therefore to determine the circadian variation of atrial DFTs in patents with recurrent atrial fibrillation (AF). METHODS AND RESULTS: Data were collected as part of the worldwide Jewel AF-only study. Patients had recurrent persistent AF and no history of ventricular arrhythmias. The atrial DFT was assessed at device implantation using a step-up protocol and was recorded for 100 patients (age 63.0 +/- 11.7, 74% male, ejection fraction 49.6 +/- 17.8%, left atrial diameter 46 +/- 9 mm). The mean atrial DFT was 6.3 +/- 4.3 J. For the most commonly tested lead configuration (right atrium to coronary sinus in 56 patients), the atrial DFT for patients implanted in the morning (3.3 +/- 1.5 J) was significantly lower than for both the DFT measured in the afternoon (5.8 +/- 3.4 J, p < 0.01) and the DFT measured in the evening (7.4 +/- 5.9 J, p < 0.01). CONCLUSION: There may be a significant variation in measured atrial DFT for the right atrium to coronary sinus configuration, with a nadir in the morning. This is the converse to measurements of ventricular DFTs suggesting different regulatory electrophysiological mechanisms. Further investigation of this possible variation is warranted.

Effect of an implantable cardioverter defibrillator with atrial detection and shock therapies on patient-perceived, health-related quality of life.

BACKGROUND: This study used a device (DDD implantable cardioverter defibrillator [ICD]) capable of delivering pacing and shock therapies to restore normal sinus rhythm in patients with atrial tachycardias or atrial fibrillation (AF). The purpose of this study was to assess the effect of the device on patient-perceived, health-related quality of life (QOL). METHODS: The DDD ICD was implanted in 267 patients with drug refractory, symptomatic AF from 45 centers across Europe, the United States, and Canada. Patients completed self-reported, validated QOL assessments at baseline and at 3- and 6-month follow-up visits (The Medical Outcomes Short Form 36 [SF-36] and the Symptom Checklist [SCL]). RESULTS: The mean age of the study group was 62 +/- 12 years, and 73% of the patients were male. A total of 150 patients completed SF-36 assessments, and 138 patients completed SCL assessments at all 3 times. Baseline scores were more impaired (P <.05) on most SF-36 scales compared with norms for a general population, but were similar to a comparison group of patients with AF who were referred to tertiary care centers. The role-physical, physical functioning, vitality, mental health, and social functioning scales all improved significantly with time (all P <.04). Similarly, symptom frequency and severity (SCL) also improved significantly from baseline to 6 months (both P <.01). Shock therapy was delivered in 86 of the 150 patients (57%) with complete SF-36 evaluations. There was no evidence that receiving shocks decreased the relative improvement in QOL associated with implantation of the device. CONCLUSIONS: In a 6-month period, QOL improves after implantation of a DDD ICD with atrial shock and pacing therapies. These improvements were not attenuated by receipt of shocks.