A Prospective, Randomized Evaluation of a Nonthoracotomy Implantable Cardioverter Defibrillator Lead System

Nonthoracotomy lead systems for ICDs have been developed that obviate the need for a thoracotomy and reduce the morbidity and mortality associated with implantation. However, an adequate DFT cannot be achieved in some patients using transvenous electrodes alone. Thus, a new subcutaneous "array" electrode was designed and tested in a prospective, randomized trial that compared the DFT obtained using monophasic shock waveforms with a single transvenous lead alone that has two defibrillating electrodes, the transvenous lead linked to a subcutaneous/submuscular patch electrode, and the transvenous lead linked to the investigational array electrode. There were 267 patients randomized to one of the three nonthoracotomy ICD lead systems. All had DFTs that met the implantation criterion of ≤ 25 J. The resultant study population was 82% male and 18% female, mean age of 63 ± 11 years. The indication for ICD implantation was monomorphic VT in 70%, VF in 19%, monomorphic VT/VF in 6%, and polymorphic VT in 4% of the patients, respectively. The mean LVEF was 0.33 ± 0.13. The mean DFT obtained with the transvenous lead alone was 17.5 ± 4.9 J as compared to 16.9 ± 5.5 J with the lead linked to a patch electrode (P = NS), and 14.9 ± 5.6 with the lead linked to the array electrode (array versus lead alone, P = 0.0001; array versus lead/patch, P = 0.007). The results of this investigation suggest that the subcutaneous array may be superior to the standard patch as a subcutaneous electrode to lower the DFT and increase the margin of safety for successful nonthoracotomy defibrillation.     

Infections with Nonthoracotomy Implantable Cardioverter Defibrillators: Can These Be Prevented?

Nonthoracotomy ICDs are believed to be the best therapeutic modality for treatment of life-threatening ventricular arrhythmias. Little is known about the risk of infection with initial implantation of these devices. We studied the incidence, clinical characteristics, and risk factors associated with infections in 1,831 patients with nonthoracotomy ICD from the Endotak-C nonthoracotomy lead registry of Cardiac Pacemakers, Inc. A transvenous lead was implanted in 950 patients (51.9%) and a combination transvenous plus subcutaneous patch was used in 881 patients (48.1%). Nine preselected data variables were studied, and all investigators identified as having patients with infections were personally contacted. Infections occurred in 22 (1.2%) of 1,831 patients receiving this nonthoracotomy ICD system. The mean time to infection was 5.7 ± 6.5 months (range 1–25 months). Staphylococci were isolated in 58% of patients with reported infection. The presence of a subcutaneous defibrillator patch system was associated with the development of infection. Six of 950 patients (0.63%) with a totally transvenous lead system developed infection versus 16 of 838 (1.9%) patients with a transvenous lead plus subcutaneous patch system configuration (P = 0.015, Chi-square test), with an unadjusted estimated odds ratio of 3.06 (CI 1.19–7.86). The risk of infection encountered with the nonthoracotomy ICD is low, estimated from our data to be 1.2%. Placement of a subcutaneous defibrillator patch appears to be an independent risk factor for development of infection.     

Conversion Rates of Induced Versus Spontaneous Ventricular Tachycardia by a Third Generation Cardioverter Defibrillator

Seventy consecutive patients received the first VENTAK PRx pulse generators (Cardiac Pacemakers, Inc.) implanted in the United States. This multiprogrammable device has therapeutic options that include: (1) antitachycardia pacing; (2) low energy cardioversion; (3) defihrillation shocks; and (4) bradycardia pacing. There were 60 males and 10 females with a mean age of 65.3 ± 9.4 years. The anatomical diagnoses were coronary artery disease in 55 patients, cardiomyopathy in 7 patients, congenital heart disease in 2 patients, and miscellaneous disease in the remaining 6 patients. Thirty-six percent had a history of sudden cardiac death and 90% had documented monomorphic ventricular tachycardia. The mean ejection fraction was 32.7%± 12.2%. Thirty-three (49.3%) had an ejection fraction ≤ 30%. Electrophysiological testing was done preimplant, predischarge, and 1 to 2 months postimplant to define a specific electrical therapy and evaluate the efficacy of the device. Two hundred ninety-three of 367 (80%) episodes of induced ventricular tachycardia were successfully terminated by the VENTAK PRx programmed for antitachycardia pacing. There were 1,794 total therapy episodes for spontaneous ventricular tachycardia; 91% (1,641 episodes) were terminated by antitachycardia pacing and 153 episodes were converted by shocks during a minimal 6-month follow-up per patient. We conclude that documentation of a successful antitachycardia pacing modality in the electrophysiology laboratory predicts conversion of spontaneous episodes of ventricular tachycardia. Furthermore, antitachycardia pacing by the VENTAK PRx can terminate the majority of episodes of ventricular tachycardia.     

Elevated Defibrillation Threshold When Right-Sided Venous Access is Used for Nonthoracotomy Implantable Defibrillator Lead Implantation

Right/Left-Sided ICD Implantation. Introduction: Although myriad factors influence the defibrillation threshold, the relation between the site of transvenous lead entry into the vascular system and the defibrillation threshold has not been reported. This study examines the influence that venous entry site has on defibrillation success for a transvenous implantable cardioverter defibrillator lead with two defibrillating coils. Methods and Results: The study population comprised 345 patients. Their mean age was 61 ± 13 years and, left ventricular ejection fraction was 0.33 ± 0.13. A left-sided approach was used in 324 (93.9%) of the patients, and a right-sided approach was used in the remaining 21 (6.1%) patients. There was no difference in the gender, age, left ventricular ejection fraction, or underlying cardiac disease in the two groups. For all patients, with a transvenous lead used either alone or with a submuscular or subcutaneous patch, the biphasic defibrillation threshold was 9.9 ± 4.8 J when a left-sided approach was used, and 14.0 ± 7.3 J when a right-sided approach was used (P = 0.02). When a transvenous lead was used with a submuscular or subcutaneous patch (115 patients), the biphasic defibrillation threshold was 9.5 ± 4.3 J when a left-sided approach was used, and 12.0 ± 10.0 J when a right-sided approach was used (P = 0.98). When a transvenous lead was used without a submuscular or subcutaneous patch (230 patients), the biphasic defibrillation threshold was 10.1 ± 5.0 J when a left-sided approach was used, and 14.6 ± 6.6 J when a right-sided approach was used (P < 0.01). For the entire group of patients and for each specific lead arrangement, there was no significant difference in the defibrillating lead system impedance when right-sided versus left-sided approaches were compared. Conclusion: Left-sided approaches to implant transvenous leads with two coils for defibrillation result in lower biphasic defibrillation thresholds than when right-sided approaches are used.     

Clinical Efficacy of Low Energy Cardioversion in Automatic Implantable Cardioverter Defibrillator Patients

The inclusion of low energy Cardioversion capability into modern implantable antiarrhythmic devices, although an appeahing idea, is nevertheless unproven with regard to its potential benefits. Moreover, since occasional reports have surfaced suggesting that ineffective application of low energy shocks may prejudice subsequent arrhythmia reversion, we examined the effectiveness and risks of this feature in a large series of patients performed as part of a US Food and Drug Administration clinical trial performed under an invesfigational device exemption. A total of 813 induced monomorphic ventricular tachycardias were studied in 244 patients. We found that many of the arrhythmias could be reverted to sinus rhythm with small amounts of energy. Cardioversion energy was ≤6 joules (J) for 84 (53.2%) and ≤14 joules in 105 (66.4%) of the 158 patients tested at implant and subsequently remained unchanged through ≥ 4 months follow up. The incidence of noncardioversion, acceleration or holh occurred in 12.7%, 5.7%, and 13.1%, respectively on a per patient basis. On a per episode basis, noncon-version occurred in 51 (6.3%) and acceleration in 61 (7.5%) of the 813 inductions. There was no correlation between the occurrence of nonconversions and accelerations. The devices were allowed to recycle in the event the arrhythmia was not reverted. The subsequent shock was almost always effective, and in any event, no patient failed to be reverted by the second 30-J rescue shock. Over the entire follow-up period as long as 17 months, there were 17 deaths. Neither the incidence nor the mode of death was correlated with nonconversion or acceleration. We conclude that low energy Cardioversion is effective in treating monomorphic ventricular tachycardia and if unsuccessful, does not prejudice the success of subsequent higher energy therapy.