Efficacy of tuned waveforms based on different membrane time constants on defibrillation thresholds: primary results from the POWER trial.

BACKGROUND: The efficacy of tuned defibrillation waveforms versus the nominal fixed-tilt waveform has been previously studied. However, the optimal membrane time constant for tuning was not known. The POWER (Pulsewidth Optimized Waveform Evaluation tRial) trial was designed to determine the optimal membrane time constant for programming "tuned" biphasic waveforms. METHODS: This acute, multicenter study included 121 implantable cardioverter-defibrillator/cardiac resynchronization therapy defibrillator patients who were randomized at implant to any two of the three membrane time constant waveforms (2.5, 3.5, and 4.5 ms). Fixed pulse widths were programmed using the measured high voltage shock impedance. The defibrillation threshold (DFT) estimates were obtained using a hybrid protocol starting with an upper limit of vulnerability estimate followed by a step-up/step-down ventricular fibrillation induction process. RESULTS: DFT voltage was significantly lower using 3.5- and 4.5-ms waveforms as compared to the 2.5-ms waveform (P = 0.004 and 0.035, respectively). DFT voltage with both 3.5- and 4.5-ms waveforms was ≤ that obtained with the 2.5-ms waveform in 78.5% of the cases. The mean difference in DFT voltage using the 3.5-ms waveform and the 4.5-ms waveform was not significant (P = 0.4). However, the 3.5-ms waveform gave a lower DFT than the 4.5-ms waveform in 19 patients although the reverse was true in only nine (P = 0.02 not significant for multiple comparisons). CONCLUSIONS: The use of a 3.5- or 4.5-ms time constant-based waveforms had lower DFTs when compared to the 2.5-ms waveform. This study suggests that the first defibrillation attempt at implantation should be with 3.5- or 4.5-ms time constant-based waveforms. The 3.5-ms-based waveform trended toward the best choice.

Performance of dedicated versus integrated bipolar defibrillator leads with CRT-defibrillators: results from a Prospective Multicenter Study.

INTRODUCTION: Right ventricular (RV) anodal stimulation may occur in cardiac resynchronization therapy defibrillators (CRT-D) when left ventricular (LV) pacing is configured between the LV lead and an electrode on the RV defibrillator lead. RV defibrillator leads can have a dedicated proximal pacing ring electrode (dedicated bipolar) or utilize the distal shocking coil as the proximal pacing electrode (integrated bipolar). This study compares the performance of integrated versus dedicated leads with respect to anodal stimulation incidence, sensing, and inappropriate ventricular tachyarrhythmia detection in patients implanted with CRT-D. METHODS: Two hundred ninety-two patients were randomly assigned to receive dedicated or integrated bipolar RV leads at the time of CRT-D implantation. Patients were followed for 6 months. RESULTS: Patients with dedicated bipolar RV leads exhibited markedly higher rates of anodal stimulation than did patients with integrated leads. The incidence of anodal stimulation was 64% at implant for dedicated bipolar RV leads compared to 1% for integrated bipolar RV leads. The likelihood of anodal stimulation in patients with dedicated leads fell progressively during the 6-month follow-up (51.5%), but always exceeded the incidence of anodal stimulation in patients with integrated leads (5%). Clinically detectable undersensing and oversensing were very unusual and did not differ significantly between lead designs. There were no inappropriate ventricular tachyarrhythmia detections for either lead type. CONCLUSION: Integrated bipolar RV defibrillator leads had a significantly lower incidence of RV anodal stimulation when compared to dedicated bipolar RV defibrillation leads, with no clinically detectable oversensing or undersensing, and with no inappropriate ventricular tachyarrhythmia detections for either lead type.

A prospective randomized trial of defibrillation thresholds from the right ventricular outflow tract and the right ventricular apex.

BACKGROUND: Right ventricular outflow tract (RVOT) pacing has been suggested to improve hemodynamics and to help prevent pacing-induced cardiomyopathy. Pacing from the RVOT is feasible and equivalent in terms of sensing and stimulation threshold. However, physicians have been reluctant to use RVOT pacing because of concerns that defibrillation efficacy might be adversely affected. To date, there have been no randomized-controlled trials published comparing the defibrillation threshold in leads implanted in the RVOT and the right ventricular apex (RVA). OBJECTIVE: The purpose of this study was to compare defibrillation thresholds (DFT) in the RVOT and RVA. Ventricular sensing and stimulation thresholds were also compared. METHODS: This prospective, randomized, multicenter study included 87 patients (70 males, age 69 +/- 11 years). At implantation, the patient's ventricular implantable cardioverter-defibrillator (ICD) lead position was randomized to either the RVOT or RVA. A four-shock Bayesian up-down method was used to determine the DFT. Patients were followed for 3 months postimplant. RESULTS: DFTs were not significantly different in leads implanted in the RVOT (median 8.8 J [6.28, 12.9] vs. 7.9 J [6.20, 12.6], P = 0.65). Threshold and impedance measurements were stable in both RVOT and RVA groups from implant to follow-up. All ICD leads remained stable chronically at the 3-month follow-up. CONCLUSION: DFTs in leads placed in the RVOT and RVA are comparable. RVOT ICD lead placement is safe and exhibits similar lead stability, threshold, and impedance measurements as the traditional RVA location.

Hybrid epicardial-endocardial ablation using a pericardioscopic technique for the treatment of atrial fibrillation.

BACKGROUND: Catheter ablation is an effective treatment for medically refractory, disabling atrial fibrillation (AF). Ablation success may be limited in patients with persistent or long-standing persistent AF. A pericardioscopic, hybrid epicardial-endocardial technique for AF ablation may be a preferred approach for such patients. Limited data are available using such an approach. OBJECTIVE: To evaluate 1-year outcomes of a hybrid technique for AF ablation. METHODS: A cohort of 101 patients underwent AF ablation using a transdiaphragmatic pericardioscopic, hybrid epicardial-endocardial technique. Patients were followed with 24-hour Holter monitors at 3-, 6-, and 12-month intervals. Symptom severity was assessed at baseline and follow-up by using the Canadian Cardiovascular Society Severity of Atrial Fibrillation scale. RESULTS: Mean AF duration was 5.9 years; 47% were persistent and 37% were long-standing persistent. Mean left atrial size was 5.1 cm (range 3.3-7 cm). Overall, 12-month arrhythmia-free survival was 66.3% after a single ablation procedure and 70.5% including repeat ablation. Repeat ablation was required in 6% of the patients and antiarrhythmic drug therapy in 37% of the patients. Quality of life improved significantly and was durable over 12-month follow-up. There were 2 deaths, which occurred in the early postoperative period: one due to atrioesophageal fistula and the second due to sudden cardiac death without apparent cause by autopsy. CONCLUSIONS: We report the largest series to date of a hybrid epicardial-endocardial, stand-alone ablation procedure using a pericardioscopic technique for the treatment of AF. While respecting the identified complications, our results demonstrate a high potential for successful treatment in a challenging patient population with AF.

Simultaneous catheter and epicardial ablations enable a comprehensive atrial fibrillation procedure.

OBJECTIVE: Transmural and contiguous ablations and a comprehensive lesion pattern are difficult to create from the surface of a beating heart but are critical to the successful treatment of persistent, isolated atrial fibrillation. A codisciplinary simultaneous epicardial (surgical) and endocardial (catheter) procedure (Convergent procedure) addresses these issues. METHODS: Patients with symptomatic atrial fibrillation who failed medical treatment were evaluated. Using only pericardioscopy, the surgeon performed near-complete epicardial isolation of the pulmonary veins and a "box" lesion on the posterior left atrium using unipolar radiofrequency ablation. Simultaneous endocardial catheter radiofrequency ablation completed pulmonary vein isolation, performed a mitral annular and cavotricuspid isthmus line of block, and debulked the coronary sinus. Twelve-month results for the Convergent procedure were compared with 12-month results for concomitant and pericardioscopic (stand-alone transdiaphragmatic/thoracoscopic) atrial fibrillation procedures using unipolar radiofrequency ablation. RESULTS: Sixty-five patients underwent the Convergent procedure (mean age, 62 y; mean body surface area, 2.17 m²; mean atrial fibrillation duration, 4.8 y; mean left atrial size, 5.2 cm). Ninety-two percent were in persistent or long-standing persistent atrial fibrillation. At 12 months, evaluation with 24-hour Holter monitors found 82% of patients in sinus rhythm, while only 47% of pericardioscopic and 77% of concomitant patients treated with unipolar radiofrequency ablation were in sinus rhythm. CONCLUSIONS: Simultaneous epicardial and endocardial ablation improves outcomes for patients with persistent or longstanding persistent atrial fibrillation. This successful collaboration between cardiac surgeon and electrophysiologist is an important treatment option for patients with large left atriums and chronic atrial fibrillation.