Nonthoracotomy Lead Research Articles

Implantable Intravascular Defibrillator: Evaluation of Defibrillation Waveforms with Inferior Vena Cava Electrode System

A percutaneously placed, totally intravascular defibrillator has been developed that shocks via a right ventricular (RV) single-coil and titanium electrodes in the superior vena cava (SVC) and the inferior vena cava (IVC). This study evaluated the defibrillation threshold (DFT) with this electrode configuration to determine the effect of different biphasic waveform tilts and second-phase durations as well as the contribution of the IVC electrode. Eight Bluetick hounds (wt = 30-40 kg) were anesthetized and the RV coil (first-phase anode) was placed in the RV apex. The intravascular defibrillator (PICD®, Model no. IIDM-G, InnerPulse Inc., Research Triangle Park, NC, USA) was positioned such that the titanium electrodes were in the SVC and IVC . Ventricular fibrillation was electrically induced and a Bayesian up-down technique was employed to determine DFT with two configurations: RV to SVC + IVC and RV to SVC. Three waveform tilts (65%, 50%, and 42%) and two second-phase durations (equal to the first phase [balanced] and truncated at 3 ms [unbalanced]) were randomly tested. The source capacitance of the defibrillator was 120 μF for all waveforms. DFT with the IVC electrode was significantly lower than without the IVC electrode for all waveforms tested (527 ± 9.3 V [standard error], 14.5 J vs 591 ± 7.4 V, 18.5 J, P < 0.001). Neither waveform tilt nor second-phase duration significantly changed the DFT. In canines, a totally intravascular implantable defibrillator with electrodes in the RV apex, SVC, and IVC had a DFT similar to that of standard nonthoracotomy lead systems. No significant effect was noted with changes in tilt or with balanced or unbalanced waveforms.

Coronary sinus lead extraction.

Complications are reported more frequently with the implantation of coronary sinus (CS) than other types of leads, and attempts to extract CS leads may also be associated with increased risks. The authors have performed nonthoracotomy lead extraction (LE) since 1981 and maintained a detailed database. By November 2001, 796 leads had been removed from 401 patients. We undertook review of our CS-LE experience to evaluate prevalence, safety, and efficacy. Of 14 patients referred for CS-LE, 7 were treated in the last year. In six the lead had been placed in the CS intentionally, and in eight inadvertently. One recent patient treated with biventricular pacing was septic and died before LE was undertaken. In nine men and four women (mean age 66 years) had one each CS lead and a total of 34 LEs (2.6/patient). Four CS leads had been in place for < 6 months (mean 1.5 month), whereas nine had been in place for between 6 months and 27 years. Several LE methods were used, from simple traction to the use of intraluminal locking stylets and powered sheaths. Complete removal of all leads was achieved in all patients. CS-LE required a mean of 13 minutes, including 1.8 minutes of fluoroscopy. There were no serious complications during the procedures, and the mean hospital stay was 4 days.

Temporal decline in defibrillation thresholds with an active pectoral lead system

OBJECTIVESThe objective of this study was to characterize temporal changes in defibrillation thresholds (DFTs) after implantation with an active pectoral, dual-coil transvenous lead system.BACKGROUNDVentricular DFTs rise over time when monophasic waveforms are used with non-thoracotomy lead systems. This effect is attenuated when biphasic waveforms are used with transvenous lead systems; however, significant increases in DFT still occur in a minority of patients. The long-term stability of DFTs with contemporary active pectoral lead systems is unknown.METHODSThis study was a prospective assessment of temporal changes in DFT using a uniform testing algorithm, shock polarity and dual-coil active pectoral lead system. Thresholds were measured at implantation, before discharge and at long-term follow-up (70 ± 40 weeks) in 50 patients.RESULTSThe DFTs were 9.2 ± 5.4 J at implantation, 8.3 ± 5.8 J before discharge and 6.9 ± 3.6 J at long-term follow-up (p < 0.01 by analysis of variance; p < 0.05 for long-term follow-up vs. at implantation or before discharge). The effect was most marked in a prespecified subgroup with high implant DFTs (≥15 J). No patient developed an inadequate safety margin (<9 J) during follow-up.CONCLUSIONSThe DFTs declined significantly after implantation with an active pectoral, dual-coil transvenous lead system, and no clinically significant increases in DFT were observed. Therefore, routine defibrillation testing may not be required during the first two years after implantation with this lead system, in the absence of a change in the cardiac substrate or treatment with antiarrhythmic drugs.

Implantable cardioverter/defibrillator: long-term stability of the defibrillation threshold with a unipolar electrode configuration (active-can")

The majority of cardioverter/defibrillator (ICD) implantations are currently performed with a non-thoracotomy approach. From November 1993 to January 1995, 46 patients underwent implantation of a PCD 7219C with an "active-can" lead configuration at our institution. While the chronic stability of the defibrillation threshold (DFT) for an epicardial lead system is well established, the results are still inconsistent for non-thoracotomy lead systems. Accordingly, the aim of the present study was to compare the acute and chronic defibrillation thresholds of the ICDs implanted with an "active-can" lead system in order to assess the chronic stability of these systems. The defibrillation energy requirements were measured at implant, prior to hospital discharge, three, six and twelve months after implantation of the defibrillator. The patient group consisted of 8 females and 38 males with a mean age of 57.2 years. The mean left ventricular ejection fraction was 43.8%. The most frequent underlying heart disease was coronary artery disease in 31 of 46 patients. Eight patients had idiopathic dilated cardiomyopathy. In 39 of 46 patients, the defibrillation threshold could be successfully determined at all 4 time points after implantation. The mean defibrillation energy requirement at the time of implantation was 9.2 +/- 5.9 Joules (J). The subsequent mean energy requirements were 7.6 +/- 4.8 J at pre-hospital discharge, 8.6 +/- 5.7 J at the 3 month, 8.1 +/- 6.0 J at the 6 month and 8.6 +/- 5.8 J at the 12 month follow-up visits. The mean defibrillation threshold was lowest at the time of prehospital discharge, significantly lower than at the time of initial implantation (p = 0.021). However, at all later time points up to one year, there was no significant difference in the DFT as compared with the time of initial implantation. Comparing the DFT at the time of implantation and the DFT at all other time points, there were no significant differences (9.23 vs. 8.56 J, p = 0.291). Although there was an initial decrease in the DFT at seven to ten days, the long-term stability of the DFT up to one year remained stable in the devices with the "active-can" lead system.

Indicaciones actuales del desfibrilador automático implantable

Since the first implantation in man in 1980 implantable cardioverter defibrillator technology has greatly improved and the number of devices implanted has increased considerably in recent years. Non-thoracotomy lead systems and biphasic shocks are now the approach of choice, offering nearly a 100% success rate. This paper version reviews the current indications for the implantation of implantable cardioverter defibrillator and is an upgraded of an article previously published by the Arrhythmia's Section of the Spanish Society of Cardiology. Recommendations for qualification of centres implanting defibrillators and follow up are also addressed.

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.

Biphasic Waveforms Prevent the Chronic Rise of Defibrillation Thresholds With a Transvenous Lead System

Objectives. The purpose of this study was to compare chronic changes in monophasic and biphasic defibrillation thresholds using a uniform transvenous lead system and testing protocol.Background. Defibrillation thresholds increase over time in patients with nonthoracotomy lead systems. This increase can result in an inadequate chronic defibrillation safety margin and could limit the safety of smaller pulse generators, which have a reduced maximal output. However, previous studies of the temporal changes of defibrillation thresholds evaluated complex lead systems or monophasic shock waveforms, neither of which are used with current technology.Methods. This study was a prospective, randomized assessment of the effects of shock waveforms on the changes of transvenous defibrillation thresholds over time. Paired monophasic and biphasic thresholds were measured both at implantation and at follow-up (250 ± 105 days) in 24 consecutive patients who were not receiving antiarrhythmic drugs. The lead system was a dual-coil Endotak C lead, and reverse polarity shocks (distal coil = anode) were delivered.Results. Monophasic defibrillation thresholds increased from (mean ± SD) 13.7 ± 6.0 J to 16.8 ± 6.7 J (p = 0.02), whereas biphasic thresholds were unchanged (10.4 ± 4.3 J to 10.2 ± 4.8 J, p = 0.86) in the same patients. Shock impedance chronically increased (47.0 Ω to 50.5 Ω, p = 0.02) and was unaffected by waveform.Conclusions. These results indicate that biphasic shocks prevent the chronic increase in defibrillation thresholds with a transvenous lead system.(J Am Coll Cardiol 1997;30:233-6)

Effect of a Passive Endocardial Electrode on Defibrillation Efficacy of a Nonthoracotomy Lead System

Objectives. We investigated the impact of an inactive endocardial lead on the 50% effective dose (ED50%) for successful ventricular defibrillation.Background. The presence of abandoned epicardial mesh patch electrodes detrimentally affects the defibrillation efficacy of an endocardial lead system. It is not known whether abandoned endocardial electrodes produce a similar effect.Methods. An endocardial lead system (ENDOTAK, model 0062, Cardiac Pacemakers, Inc.) was implanted in eight dogs (mean ±SD weight 23.7 ± 1.0 kg). The ED50% for each of seven lead configurations was determined by a three-reversal point protocol in a balanced-randomized order with and without a second electrically passive endocardial lead system in the right ventricle (power 0.97 to detect a 50-V difference). Biphasic shocks with 80% tilt were delivered 10 s after the induction of ventricular fibrillation. In one configuration the active electrode made contact with the passive electrode in the right ventricular (RV) apex. In another configuration the active electrode was placed in a more proximal position to avoid contact. Additionally, the ED50% was determined for the endocardial lead system with a passive pacing lead positioned in the RV apex.Results. ED50% values for peak voltage, peak current and delivered energy were not significantly different with or without a passive RV electrode, and this was true whether or not the active electrode touched the passive electrode. However, ED50% values were significantly higher when the active electrode was slightly proximal than when it was positioned at the apex.Conclusions. Physical contact between active and passive endocardial electrodes does not significantly alter defibrillation efficacy in this dog model. An increase in ED50% energy was caused by a slightly proximal position. Therefore, a good electrode position within the right ventricle is a more important determinant of defibrillation efficacy than is avoidance of the electrode touching a passive electrode.(J Am Coll Cardiol 1997;29:825–30)

Factors Associated With Elevated Impedance With a Nonthoracotomy Defibrillation Lead System

Peak current flow across the heart determines the success of defibrillation and is inversely dependent on impedance between defibrillation electrodes. Factors associated with elevated impedance in patients with implantable defibrillators using nonthoracotomy lead systems have not been well described. Clinical and echocardiographically derived variables were analyzed in 41 patients in whom implantation of a nonthoracotomy lead system was attempted. Lead impedance was measured at end-expiration with 5-J monophasic shocks. Successful defibrillation with or without addition of a subcutaneous patch with ≤20 J with a monophasic waveform was required for nonthoracotomy lead placement. Patients were divided into 2 groups based on impedance: low (≤47 ohms, n = 30) and high (>47 ohms, n = 11). Twenty-four patients had successful defibrillator implantation using a transvenous lead alone, 13 required placement of a subcutaneous patch, and 4 required epicardial patch placement. The mean left ventricular end-diastolic and end-systolic volumes were significantly smaller (p = 0.01 for both) in patients in the low- versus high-impedance groups and were significantly correlated with impedance (r = 0.44, p < 0.005 for both). Impedance was not significantly different between patients with successful defibrillation using a transvenous lead alone compared with those who required either subcutaneous or epicardial patches. Thus, impedance using a nonthoracotomy lead system with monophasic shocks is significantly correlated with both end-systolic and end-diastolic volumes, but elevated impedance does not predict increased defibrillation energy requirements.This study examined the influence of clinical, radiographic, and echocardiographic variables on impedance measured with 5-J monophasic shocks at end-expiration with a nonthoracotomy lead system in 41 patients. Significant correlations (r = 0.44, p < 0.005 for both) were found between impedance and both end-systolic and end-diastolic volumes, but elevated impedance did not predict increased defibrillation energy requirements with a nonthoracotomy lead or the need for either subcutaneous or epicardial patches.

Pacing threshold increase in nonthoracotomy implantable defibrillator leads: implications for battery longevity and margin of safety.

Just as a stable defibrillation threshold is required for implantable defibrillators to maintain efficacy and a margin of safety for the conversion of life-threatening ventricular arrhythmias, a stable pacing threshold is also required to provide bradycardia support and pacing to terminate ventricular tachycardias. This article reports the temporal course of pacing thresholds in patients treated with a tripolar, tined endocardial defibrillator lead capable of bipolar sensing and pacing, and defibrillation. Seventeen patients who underwent implantation of an implantable defibrillator system using an integrated bipolar pacing/sensing system were prospectively studied over 18 months. There were 16 males and one female, with a mean age of 69 +/- 5 years (range 61-75 years). At implantation, predischarge, and every 2 months thereafter, the pacing pulse-width threshold was tested at both 2.5 and 5.0 V stimulus amplitudes. After a mean follow-up of 363 +/- 173 days (range 34-597 days), the pacing threshold increased from 0.08 +/- 0.08 ms to 0.5 +/- 0.3 ms at the 2.5 V amplitude (p < or = 0.01, CI-0.57 to -0.27) and from 0.04 +/- 0.02 ms to 0.25 +/- 0.14 ms at the 5.0 V amplitude (p < or = 0.01, CI -0.28 to -0.14). Eight of the 17 patients (47%) received spontaneous implantable defibrillator shocks for clinically detected arrhythmias, and the total number of joules delivered via the leads did not correlate with the pacing threshold changes. We conclude that the pacing threshold for the nonthoracotomy implantable defibrillator lead system studied is not stable and increases with time. This finding has implications for defibrillator battery life in patients who use implantable defibrillators for bradycardia pacing.

Evaluation of a programming algorithm for the third tachycardia zone in a fourth-generation implantable cardioverter-defibrillator.

The clinical efficacy of electrical algorithms for termination of slow ventricular tachycardia (VT) and ventricular fibrillation (VF) in implantable cardioverter-defibrillators (ICDs) is well established. Such algorithms have not been equally well defined for fast VT reversion. We report the testing of a prospectively designed algorithm for ICDs to treat fast VT that is inherently less responsive to antitachycardia pacing than slow VT. Fourth-generation ICD devices were programmed to three prospectively defined tachycardia detection zones as follows: cycle lengths < or = 260 ms for VF, 270-330 ms for fast VT, and > 330 ms for slow VT. The initial selected therapy for the VF zone was a high-energy biphasic shock (> 15 J), while a 3- or 5-J biphasic shock was usually administered for fast VT, and antitachycardia pacing was initially attempted for slow VT. Initial therapy was followed by backup therapy with high-energy shocks. Twenty-eight patients, 24 of whom were males, all with organic heart disease, with a mean age of 65 +/- 9 years, received either a Medtronic 7219D (23 patients), 7219C (2 patients), 7218SP1 (2 patients), or 7218C (1 patient) ICD with a nonthoracotomy lead system. The defibrillation threshold was 10 +/- 5 J. At predischarge electrophysiologic testing, a single 3- or 5-J shock terminated all episodes of fast VT tested. During a follow-up of 18 +/- 9 months, there were four nonarrhythmic deaths. Fourteen patients (50%) had a total of 21 VF, 44 fast VT, and 202 slow VT episodes. Twenty-three of 24 (96%) VF, 33 of 39 (84%) fast VT, and 193 of 202 (95.5%) slow VT episodes were terminated with the first delivered therapy in each therapy algorithm (p = NS). The overall efficacy of the entire electrical therapy algorithm was 100% for VF, 100% for fast VT, and 98% for slow VT episodes (p = NS). No patient experienced syncope or presyncope during fast VT or VF in this study. We conclude that a third detection and therapy zone can be successfully programmed in ICDs to define a range of fast VT episodes that can be effectively terminated with lower energy cardioversion shocks with comparable success and freedom from arrhythmic symptoms to electrical therapies used for slow VT and VF.

Cost savings with nonthoracotomy implantable cardioverter-defibrillators

We analyzed hospital and physician charges for 99 consecutive patients who underwent implantable cardioverter-defibrillator (ICD) implantation at our institution. Eighteen patients received an epicardial lead system and 81 were scheduled to receive a nonthoracotomy lead system, the generator being implanted either abdominally (n = 62) or pectorally (n = 19). The epicardial group had a significantly longer convalescent stay (11.6 ± 2.5 days; mean ± SEM) than the abdominal nonthoracotomy group, analyzed by intention to treat (4.6 ± 0.5 days) or by treatment received (3.8 ± 0.2 days; p < 0.0001). Postoperative stay for the pectoral group was shorter still (2.9 ± 0.4 days; p < 0.033). Total charges for the epicardial group were $99,081 ± $25,094, significantly higher than those for any of the nonthoracotomy groups (p < 0.017). Total charges for the pectoral group were $44,128 ± $2,465, significantly less than those for the abdominal nonthoracotomy group, analyzed by intention to treat ($59,961 ± $1,369; p < 0.05) or by treatment received ($56,679 ± $635; p < 0.05). Cost reductions in the nonthoracotomy groups were primarily due to decreased in-hospital convalescence period, lower surgeon and anesthesiologist fees, and lower procedure-day hospital charges in the pectoral group. The use of ICDs with nonthoracotomy leads can result in significantly shorter in-hospital convalescence and a reduction in total implant-related charges of 40% to 55%. The use of pectorally implanted ICDs results in further reduction in hospital stay and further cost reduction of 22% to 26%. The trend toward shorter convalescent stay without postimplant testing is likely to reduce further the overall costs of ICD implantation.

Chronic Rise in Defibrillation Threshold With a Hybrid Lead System

Nonthoracotomy leads have become standard for implantable cardioverter-defibrillators (ICD) because of low perioperative morbidity, mortality, and expense. Reported increases in defibrillation thresholds (DFTs) with these lead systems, however, have raised the possibility of an eventual loss of defibrillation efficacy. The mechanism of this increase is unknown. In contrast, defibrillation efficacy of traditional epicardial lead systems has been demonstrated to remain relatively stable. In the present study, we examined the implantation and chronic DFTs in 45 patients with a hybrid system (a high right atrial coil and an extrapericardial patch) that combines elements from both the thoracotomy and nonthoracotomy approach. The mean threshold increased from 11.7 ± 3.0 to 15.8 ± 10.0 J (p <0.001) and mean impedance increased from 37.0 ± 7.7 to 48.8 ± 9.0 ohms (p <0.0001). There was a marked (≥ 10 J) increase in DFT in 11 patients (24%) including 4 who required reoperation to obtain an adequate safety margin. The increase in DFT was unrelated to any of the analyzed variables. We conclude that the presence of an extrapericardial patch does not prevent the increase in DFT reported with nonthoracotomy lead systems. This increase is unpredictable and occurs in almost 25% of patients.

Serial defibrillation lead impedance in patients with epicardial and nonthoracotomy lead systems.

The stability of implantable cardiac defibrillation lead impedance subsequent to implantation has not been reported and may have important clinical implications. The objective was to characterize the incidence and degree of impedance changes occurring after implantation of defibrillation lead systems. The study cohort consisted of patients who received epicardial or nonthoracotomy lead systems. Defibrillation impedance was recorded at implantation, prior to hospital discharge (predischarge), and during follow-up. For each individual the magnitude of the impedance change relative to implantation was characterized. Among patients with an epicardial system, a significant decrease in impedance was observed at predischarge (mean 9.3 omega). The magnitude of the decrease was large in 39% and moderate in 31% of individuals. Subsequently, a gradual rise in mean impedance was apparent. At 18-21 months postimplantation, impedance was significantly increased relative to implantation (mean 6.8 omega). At this time, the magnitude of the increase was large in 46% and moderate in 23% of patients. Among patients with a nonthoracotomy lead system including a subcutaneous patch, a significant decrease in mean impedance was observed at predischarge (mean 3.5 omega). The magnitude of the decrease was large in 8% and moderate in 50% of individuals. Subsequently, a gradual rise in impedance was apparent. At 5-6 months, it was significantly increased relative to implantation (mean 2.3 omega). The magnitude of the increase was large in 10% and moderate in 33% of patients. Among the group of patients whose nonthoracotomy lead system did not include a subcutaneous patch, there was no significant change in mean impedance at predischarge relative to implantation. In subsequent intervals, a gradual rise was apparent. At 5-6 months, impedance was significantly increased relative to implantation (mean 4.3 omega). The magnitude of the increase was large in 16% and moderate in 47% of individuals. Significant changes in defibrillation lead impedance occur after implantation of epicardial and nonthoracotomy defibrillation lead systems. These data may serve as a standard for identifying the anticipated maximum change in lead impedance and thus may be useful as a tool for recognizing problems with defibrillation lead integrity.

Incidence of lead system malfunction detected during implantable defibrillator generator replacement.

Implantable cardioverter-defibrillator (ICD) generator replacement due to a depleted battery is a frequently performed procedure. The frequency with which sensing and defibrillation system failures are identified during device replacement procedures has not been previously described. Therefore, the purpose of this study was to prospectively determine the frequency of lead system malfunction detected at the time of device replacement in 55 consecutive patients undergoing ICD generator replacement. The mean age of the patients was 63 +/- 10 years and 40 of them were men. Forty-nine patients had an epicardial lead system, and six patients had a nonthoracotomy lead system. Four [7%] of these 55 patients were noted to have previously undetected lead system failure, either sensing (n = 3) or defibrillation (n = 1), necessitating system revision. The lead systems that failed were 40 +/- 6 months old (33-49 months). In summary, during ICD generator replacement, previously undetected problems with sensing or defibrillation may be identified in approximately 10% of patients. Therefore, a comprehensive evaluation of the sensing and the defibrillation functions should be an essential component of the ICD generator replacement procedure.

Nonpharmacological therapy for malignant ventricular arrhythmias: Implantable defibrillator trials

Implantable cardioverter-defibrillators (ICDs) are an important nonpharmacological option in the treatment of malignant ventricular arrhythmias. Technological advances in current devices permit nonthoracotomy implantation with transvenous lead systems using biphasic shocks. Decreasing device size has resulted in pectoral implantation. Battery longevity is still short in comparison with that of pacemakers. Lead failure rates as well as pacing thresholds are significantly higher than those for cardiac pacing lead systems. Other complications of ICD systems include infection, perforation, and thrombosis. The long-term performance of nonthoracotomy lead systems for ICD devices has now been extensively studied. Sudden death recurrence rates for these systems are less than 2% in 3 years and less than 5% at 5 years. Clinical trials with both monophasic and biphasic systems show a high degree of prevention of sudden death. Comparison of ICD outcome with that of drug therapy in three large retrospective studies and two small prospective randomized trials favors improved survival and sudden death prevention with device therapy. However, these studies need corroboration from large prospective trials. Two large prospective trials, CIDS and the AVID study, are now in progress to address this issue.

Clinical predictors of defibrillation energy requirements in patients treated with a nonthoracotomy defibrillator system

Many factors can influence defibrillation energy requirements (DER) in patients with a nonthoracotomy defibrillator. No large studies, however, have correlated clinical characteristics with the DER. In this study, 124 patients underwent the same DER protocol with the identical biphasic waveform, nonthoracotomy lead system, and lead configuration. These patients were 63 ± 12 years old (mean ± SD); 99 were men; the ejection fraction was 0.32 ± 0.13 and 36 were taking an antiarrhythmic medication. New York Heart Association congestive heart failure class I was present in 28, class II in 70, and class III in 26 patients. Male sex (454 ± 94 V vs 406 ± 91 V for female sex) was associated with a significantly higher DER ( p = 0.02) and an increased risk of a DER >550 V ( p = 0.047). No other clinical variable was associated with the DER or a DEr >550 V. In conclusion, women tend to have lower DERs than men.

Clinical efficacy and safety of atrial defibrillation using biphasic shocks and current nonthoracotomy endocardial lead configurations

We undertook a prospective randomized clinical trial evaluating efficacy and safety of internal atrial defibrillation in patients with drug-refractory atrial fibrillation (AF). Consecutive patients with paroxysmal or chronic AF were randomly tested with 3 internal atrial defibrillation lead configurations and biphasic shocks. Patients with implanted cardiac pacemakers were tested with the right atrium (RA) and left pulmonary artery or coronary sinus (CS) configuration. Shocks were initially delivered without anesthesia to assess parient tolerance. The need for backup ventricular defibrillation and pacing support was evaluated. Eighteen patients with (n = 15) or without (n = 3) structural heart disease, mean left ventricular ejection fraction 36 ± 14%, and mean left atrial diameter 4.5 ± 0.6 cm were studied. The mean defibrillation threshold in the best randomized lead configuration was 9.9 ± 7.7 J. Mean defibrillation threshold for the right ventricle (RV) and superior vena cava configuration was 13.3 ± 5 J, which was significantly lower than the RA and axilla configuration (20.1 ± 7.4 J, p < 0.04) but not the RV to RA configuration (16.5 ± 11 J, p > 0.2). The mean defibrillation threshold using the RA-left pulmonary artery/ CS configuration was 8.9 ± 9 J (p > 0.2 vs RV-superior vena cava). There was a bimoaal distribution of defibrillation thresholds. Low atrial defibrillation thresholds correlated with absence of heart disease, higher ejection fraction, and smaller left ventricular end-diastolic diameter. Shocks were hemodynamically well tolerated, but 18 patients (11%) had nonsustained ventricular tachycardia after shock delivery. Eighteen patients (33%) had postshock brad/arrhythmias. Fourteen of 16 patients perceived shocks ≥3 J as intolerable. We conclude that internal atrial defibrillation is clinically effective at energies ≤20 J using existing nonthoracotomy lead systems. Specific lead configurations may achieve lower defibrillation thresholds. Shocks are hemodynamically well tolerated but can induce bradyarrhythmias ana ventricular arrhythmias. Backup ventricular pacing and defibrillation are desirable. Patient tolerance for shocks >2 J is limited. Thus, this technique is applicable for infrequent application. Adjunctive therapy will be needed in patients with frequent or drugrefractory AF.

Comparison of early and late complications in patients undergoing coronary artery bypass graft surgery with and without concomitant placement of an implantable cardioverter defibrillator

Previous studies have reported a significant morbidity and mortality associated with coronary artery bypass graft (CABG) surgery in conjunction with the placement of an implantable cardioverter defibrillator (ICD) with an epicardial lead system. In the absence of a control group, how significantly the component of concomitant placement of the ICD system contributes to these untoward outcomes remains unknown. The purpose of this study was to assess the short- and long-term complications in patients undergoing CABG surgery in conjunction with the placement of an ICD with epicardial leads and to compare these complications with those of patients who had only CABG surgery (control group). The study group (group A) consisted of 56 patients who underwent CABG surgery and placement of an ICD pulse generator with epicardial leads. A control group (group B) consisted of 56 patients who underwent CABG surgery only during the same time period. The two groups were matched for age, sex distribution, left ventricular function, surgical approach, number of bypass grafts per patient, bypass pump time, and length of follow-up period. The early mortality for group A was 7.1% versus 1.8% for group B ( p > 0.05). The incidence of early morbidity (congestive heart failure, infection, supraventricular and ventricular arrhythmias) for groups A and B was similar (26.8% vs 25.0%, p > 0.05). The incidence of late mortality and morbidity (progression of congestive heart failure, recurrence of coronary events, chronic atrial fibrillation) for groups A and group B were 7.7% versus 5.5% ( p > 0.05) and 23.1% versus 21.8% ( p > 0.05), respectively. However, death caused by cardiopulmonary difficulties was more frequent in group A than group B (12.5% vs 1.8%, p < 0.05). With the availability of the nonthoracotomy lead system and the pulse generator capable of delivering biphasic shock waveform, to place such an ICD system at a later time after the CABG surgery appears to be the preferred approach to treat patients who need both surgical coronary revascularization and ICD.

Effect of Rapid Pacing and T-Wave Scanning on the Relation Between the Defibrillation and Upper-Limit-of-Vulnerability Dose-Response Curves

The critical-point and upper-limit-of-vulnerability (ULV) hypotheses predict that the ULV dose-response curve should be steeper and to the right of the defibrillation (DF) curve. Yet, some recent experimental data contradict this prediction. Two studies are presented that test two explanations for the contradiction: (1) Testing at a single point in the T wave underestimates the ULV dose-response curve and (2) ULV testing at normal heart rates does not mimic the mechanical or electrical state of the heart in ventricular fibrillation (VF). A nonthoracotomy lead system with a biphasic waveform was used throughout. In eight dogs, the dose-response curve widths (a measure of steepness) were compared between DF data and ULV data gathered at the peak (ULVPK), middownslope (ULVDWN), midupslope (ULVUP), and all times (scanning or ULVSCN) in the T wave. In another eight dogs, ULV data (ULVRAP) were gathered by scanning the T wave after 15 rapidly paced beats (166- to 198-ms pacing interval). The rapid pacing interval was chosen to more closely mimic the hemodynamics and activation rate of early VF. ULV data (ULVSTD) at normal heart rates were gathered for all animals. In the first study, scanning significantly reduced the ULV curve width (ULVSCN, 63.5 +/- 29.7 V; ULVPK, 81.9 +/- 45.2 V; ULVDWN, 116 +/- 36.5 V; DF, 105 +/- 22.0 V; P < .03) and significantly shifted the ULV curve to the right (ULV80 SCN, 410 +/- 62.6 V; ULV80 PK, 266 +/- 35.3 V; ULV80 DWN, 355 +/- 80.4 V; DF80, 427 +/- 60.9 V; P < .001). The subscript 80 signifies that the subject was left in normal sinus rhythm 80% of the time after that stimulus strength was delivered. In the second study, the ULVRAP curve was shifted dramatically to the right, the average ULV50 RAP being greater than the average DF90. Furthermore, 92% of the ULVRAP VF inductions occurred between 10 ms before and 50 ms after the peak of the T wave, suggesting that scanning of the entire T wave may not be necessary. With a single rapidly paced ULV sequence with limited T-wave scanning, it may be possible to estimate highly effective defibrillation doses with few VF episodes and high-voltage stimuli.