Trans venous-Subcutaneous Defibrillation Leads:

Effect of Transvenous Electrode Polarity on DFT. Introduction: The defibrillation threshold (DFT) of a transvenous-subcutaneous electrode configuration is sometimes unacceptably high. To obtain a DFT with a sufficient safety margin, the defibrillation field can be modified by repositioning the electrodes or more easily by a change of electrode polarity. In a prospective randomized cross-over study, the effect of transvenous electrode polarity on DFT was evaluated.
Methods and Results: In 21 patients receiving transvenous-subcutaneous defibrillation leads, the DFT was determined intraoperatively for two electrode configurations. Two monophasic defibrillation pulses were delivered in sequential mode between either the right ventricular (RV) electrode as common cathode and the superior vena cava (SVC) and subcutaneous electrodes as anodes (configuration I) or the SVC electrode as common cathode and the RV and subcutaneous electrodes as anodes (configuration II). In each patient, both electrode configurations were used alternately with declining energies (25, 15, 10, 5, 2 J) until failure of defibrillation occurred. The DFT did not differ between both configurations (18.3 ± 8.2 J vs 18.9 ± 8.9 J; P = 0.72). Eleven patients had the same DFT with both electrode configurations, 5 patients a lower DFT with the RV electrode as cathode, and 5 patients a lower DFT with the SVC as cathode. Four patients had a sufficiently low DFT (≤ 25 J) with only 1 of the 2 configurations.
Conclusion: A change of electrode polarity of transvenous-subcutaneous defibrillation electrodes may result in effective defibrillation if the first electrode polarity tested fails to defibrillate. In general, neither the RV electrode nor the SVC electrode is superior if used as a common cathode in combination with a subcutaneous anodal chest patch.     

Prospective Randomized Comparison of 65%/65% Versus 42%/42% Tilt Biphasic Waveform on Defibrillation Thresholds in Humans

Background: The waveform tilt of biphasic shocks yielding the lowest defibrillation threshold (DFT) is not well defined. Some evidence indicates that tilts less than 65% may improve DFTs. Methods: In 57 patients undergoing ICD implantation, DFTs were determined with truncated exponential biphasic waveform tilts at 65%/65% and at 42%/42%. An external defibrillator with custom software was used for testing. The effective capacitance of the defibrillator was 132-F for both waveforms. DFTs were determined using a binary search method starting with 12 Joules (J). Patients were randomly assigned to initial testing with either one of the two tilts. Thirty patients (Group 1) were tested with a two electrode (active can to RV coil, or SVC coil to RV coil) and 27 patients (Group 2) were tested with a three electrode system (subcutaneous patch or active can + SVC coil to RV coil). Results: Groups 1 and 2 did not differ in age, ejection fraction or antiarrhythmic medications. Group 1 delivered energy DFTs were 10.1 ± 5.5 J with the 65%/65% tilt and 10.1 ± 5.9 J for the 42%/42% tilt (p = 0.92). In group 2 the average DFT for the 65%/65% tilt was 8.4 ± 5.7 J and for the 42%/42% tilt was 8.1 ± 5.3 J (p = 0.70). There were no significant differences in DFTs for either group. The system impedance for Group 1 was 64 ± 12 ohms and for Group 2 was 39 ± 6 ohms (p < 0.0001). Conclusions: We found no differences in DFTs between 65%/65% tilt and 42%/42% tilt using either 2- or 3-electrode defibrillation systems. Further research is needed to optimize waveforms in order to minimize DFTs, which will result in smaller ICDs and/or greater safety margins for defibrillation.     

Comparison of Coronary Venous Defibrillation with Conventional Transvenous Internal Defibrillation in Man

Objective: Animal studies have shown that defibrillation in coronary veins is more effective than in the right ventricle. We aimed to assess the feasibility of placing defibrillation electrodes in the middle cardiac vein (MCV) in man and its impact on defibrillation requirements. Methods: A prospective randomised study conducted in a tertiary referral centre. 10 patients (9 male) undergoing ICD implantation (65 (12) yrs) for NASPE/BPEG indications were studied. Defibrillation thresholds (DFT) were measured, using a binary search and an external defibrillator after 10 seconds of ventricular fibrillation, for the following configurations in each patient (order of testing randomised): RV + MCV Can and RV SVC + Can. Interventions: A dual coil defibrillation electrode was placed transvenously in the right ventricle (RV) in the conventional manner. Using a guiding catheter a 3.2 Fr (67.5 mm length) electrode was placed transvenously in MCV. A test-can was placed subcutaneously in the left pectoral region. Results: Lead placement was possible in 8/10 pts. Time to perform a middle cardiac venogram and place the electrode was 21 (23) mins. No adverse events were observed. Defibrillation current was less (6.7 (2.7) A) with RV + MCV Can compared to the conventional RV SVC + Can configuration (8.9 (3.4) A, p = 0.03). There was no significant difference in defibrillation voltage or energy. However, shock impedance was higher in the former configuration (57 (10) v. 43 (6) , p = 0.001). Conclusions: In the majority of cases placement of a defibrillation lead in MCV is feasible. Defibrillation current requirements are 25% less when the shock is delivered using a MCV electrode.     

Effect of Electrode Polarity on Internal Defibrillation with Monophasic and Biphasic Waveforms Using an Endocardial Lead System

Defibrillation Electrode Polarity. introduction: To test the hypothesis that the effect of shock polarity on defibrillation depends on waveform duration, this study determined strength-duration defibrillation curves of monophasic and biphasic truncated exponential waveforms for both polarities. Methods and Results: Defibrillation thresholds (DFTs) were obtained in 32 pigs for catheter electrodes in the right ventricle (RV) and superior vena cava (SVC) using a modified Purdue technique. Both electrode polarities were tested in five different protocols. In part 1, DFTs were determined with 1- to 14-msec monophasic waveforms. In parts 2, 3, and 4, DFTs were determined with two different sizes of SVC electrodes for biphasic waveforms with a phase 1 of 4 or 6 msec and a phase 2 ranging from 1 to 10 msec. In part 5, DFTs were tested for monophasic waveforms ranging from 2 to 11 msec and for biphasic waveforms with a phase 1 duration corresponding to each monophasic waveform and a phase 2 held constant at 1 msec. Mean DFTs for monophasic waveforms were significantly lower when the RV electrode was an anode than when it was a cathode for waveform durations ≥ 3 msec. For biphasic waveforms in which phase 2 was ≤ phase 1 in duration, no significant difference in mean DFT was observed when polarity was reversed. Even a phase 2 as short as 1 msec could eliminate the DFT difference between polarities observed with monophasic shocks. When phase 2 was ≥ 2 msec longer than phase 1, polarity did affect the DFT of biphasic waveforms: it affected the DFT similarly to a monophasic waveform of the same polarity as phase 2. Phase 1 duration and electrode size also affected the difference in DFT produced by changing the electrode polarity. Conclusions: For phase durations most commonly used clinically because of their low DFTs. reversing polarity changed defibrillation efficacy for monophasic but not biphasic shocks. For inefficient biphasic waveforms with phase 2 ≥ 2 msec longer than phase 1, the DFT was lower when the RV electrode was an anode during phase 2, similar to the polarity difference for monopbasic waveforms, suggesting that a long second phase of biphasic waveforms defibrillates in a similar fashion to monophasic waveforms.     

Coronary sinus electrode does not reduce atrial defibrillation thresholds

BACKGROUND: Atrial defibrillation can be achieved with a conventional dual-coil, active pectoral implantable cardioverter-defibrillator (ICD) lead system. Shocking vectors that incorporate an additional electrode in the CS have been used, but it is unclear if they improve atrial DFTs. OBJECTIVE: The objective of this prospective, randomized study was to determine if a coronary sinus (CS) electrode reduces atrial defibrillation thresholds (DFTs). METHODS: This was a prospective study of 36 patients undergoing initial ICD implant for standard indications. A defibrillation lead with superior vena cava (SVC) and right ventricular (RV) shocking coils was implanted in the RV. An active can emulator (Can) was placed in a pre-pectoral pocket. A lead with a 4 cm long shocking coil was placed in the CS. Atrial DFTs were determined in the following 3 shocking configurations in each patient, with the order of testing randomized: RV --> SVC + Can (Ventricular Triad), distal CS --> SVC + Can (Distal Atrial Triad), and proximal CS --> SVC + Can (Proximal Atrial Triad). RESULTS: The Proximal and Distal Atrial Triad configurations were both associated with significant reductions in peak current (p < 0.01), but this effect was offset by significant increases in shock impedance (p < 0.01), resulting in no net change in the peak voltage or DFT energy in comparison to the Ventricular Triad configuration (Ventricular Triad: 4.9 +/- 6.6 J, Proximal Atrial Triad: 3.3 +/- 4.1J, Distal Atrial Triad: 4.4 +/- 6.7 J, p > 0.2). CONCLUSION: Shocking vectors that incorporate a CS coil do not significantly improve atrial defibrillation efficacy. Since the Ventricular Triad shocking pathway provides reliable atrial and ventricular defibrillation, this configuration should be preferred for combined atrial and ventricular ICDs.     

Atrial defibrillation thresholds of electrode configurations available to an atrioventricular defibrillator

INTRODUCTION: Little investigation has been conducted to assess the atrial defibrillation thresholds of electrode configurations using electrodes designed for internal ventricular defibrillation (right ventricle [RV], superior vena cava [SVC], and pulse generator housing [Can]) combined with coronary sinus (CS) electrodes. We hypothesized that a CS-->SVC+Can electrode configuration would have a lower atrial defibrillation threshold than a standard configuration for defibrillation, RV-->SVC+Can. We also tested the atrial defibrillation thresholds of five other configurations. METHODS AND RESULTS: In 12 closed chest sheep, we situated a two-coil (RV, SVC) defibrillation catheter, a left-pectoral subcutaneous Can, and a CS lead. Atrial fibrillation was burst induced and maintained with continuous infusion of intrapericardial acetyl-beta-methylcholine chloride. Using fixed-tilt biphasic shocks, we determined the atrial defibrillation thresholds of seven test configurations in random order according to a multiple-reversal protocol. The peak voltage and delivered energy atrial defibrillation thresholds of CS-->SVC+Can (168+/-67 V, 2.68+/-2.40 J) were significantly lower than those of RV-->SVC+Can (215+/-88 V, 4.46+/-3.40 J). The atrial defibrillation thresholds of the other test configurations were RV+CS-->SVC+Can: 146+/-59 V, 1.92+/-1.45 J; RV-->CS+SVC+Can: 191+/-89 V, 3.53+/-3.19 J; CS-->SVC: 188+/-98 V, 3.77+/-4.14 J; SVC-->CS+ Can: 265+/-145 V, 7.37+/-9.12 J; and SVC-->Can: 516+/-209 V, 24.5+/-15.0 J. CONCLUSIONS: The atrial defibrillation threshold of CS-->SVC+Can is significantly lower than that of RV-->SVC+Can. In addition, the low atrial defibrillation threshold of RV+CS-->SVC+Can merits further investigation. Based on corroboration of low atrial defibrillation thresholds of CS-based configurations in humans, physicians might consider using CS leads with atrioventricular defibrillators.     

Biphasic Waveform Defibrillation Using a Three-Electrode Transvenous Lead System in Humans

Biphasic Transvenous Defibrillation. Introduction: Biphasic waveform defibrillation is not always more efficacious than monophasic waveform defibrillation.
Methods and Results: Waveform efficacy appears to vary with the lead system used. In this prospective, randomized study, defibrillation efficacy with biphasic and monophasic single capacitor 120μF, 65% tilt pulses was compared for a lead system consisting of right ventricular (RV), chest patch (CP), and superior vena cava (SVC) electrodes. Although this lead system is commonly used with monophasic pulses in transvenous defibrillators, few studies have examined the defibrillation efficacy of this lead system in man for biphasic waveform defibrillation. Fourteen cardiac arrest survivors undergoing defibrillator implantation were included in the study using pulses delivered from a cathodal RV electrode simultaneously to anodal SVC and CP electrodes. Biphasic and monophasic waveforms were recorded oscilloscopically to acquire defibrillation threshold (DFT) data on leading edge voltage requirements and for stored energy. The monophasic DFT voltage was 661 ± 177 V compared to the biphasic DFT voltage of 451± 185 V (P < 0.0001). The monophasic DFT stored energy was 28.0 ± 13.4 J compared to the biphasic DFT stored energy of 14.1 ± 12.4 J (P ± 0.0001). The stored energy DFT was < 15 J in only 2 of 14 patients (15%) with monophasic defibrillation but < 15 J in 10 of 14 (71%) patients with biphasic defibrillation.
Conclusion: These findings indicate that biphasic defibrillation with an RV, SVC, CP transvenous electrode system is substantially more efficient than monophasic defibrillation. allowing for higher numbers of patients to receive transvenous defibrillators with a relatively simple lead system at a satisfactory cutoff DFT safety margin of 15 J.     

Optimization of atrial defibrillation with a dual-coil, active pectoral lead system

INTRODUCTION: Atrial defibrillation can be achieved with standard implantable cardioverter defibrillator (ICD) leads, but the optimal shocking configuration is unknown. The objective of this prospective study was to compare atrial defibrillation thresholds (DFTs) with three shocking configurations that are available with standard ICD leads. METHODS AND RESULTS: This study was a prospective, randomized, paired comparison of shocking configurations on atrial DFTs in 58 patients. The lead system evaluated was a transvenous defibrillation lead with coils in the superior vena cava (SVC) and right ventricular apex (RV) and a left pectoral pulse generator emulator (Can). In the first 33 patients, atrial DFT was measured with the ventricular triad (RV --> SVC + Can) and unipolar (RV --> Can) shocking pathways. In the next 25 patients, atrial DFT was measured with the ventricular triad and the proximal triad (SVC --> RV + Can) configurations. Delivered energy at DFT was significantly lower with the ventricular triad compared to the unipolar configuration (4.7 +/- 3.7 J vs 10.1 +/- 9.5 J, P < 0.001). Peak voltage and shock impedance also were significantly reduced (P < 0.001). There was no significant difference in DFT energy when the ventricular triad and proximal triad shocking configurations were compared (3.6 +/- 3.0 J vs 3.4 +/- 2.9 J for ventricular and proximal triad, respectively, P = NS). Although shock impedance was reduced by 13% with the proximal triad (P < 0.001), this effect was offset by an increased current requirement (10%). CONCLUSION: The ventricular triad is equivalent or superior to other possible shocking pathways for atrial defibrillation afforded by a dual-coil, active pectoral lead system. Because the ventricular triad is also the most efficacious shocking pathway for ventricular defibrillation, this pathway should be preferred for combined atrial and ventricular defibrillators.     

Effect of an active abdominal pulse generator on defibrillation thresholds with a dual-coil, transvenous ICD lead system

INTRODUCTION: Many patients with implantable cardioverter defibrillators (ICDs) have older lead systems, which are usually not replaced at the time of pulse generator replacement unless a malfunction is noted. Therefore, optimization of defibrillation with these lead systems is clinically important. The objective of this prospective study was to determine if an active abdominal pulse generator (Can) affects chronic defibrillation thresholds (DFTs) with a dual-coil, transvenous ICD lead system. METHODS AND RESULTS: The study population consisted of 39 patients who presented for routine abdominal pulse generator replacement. Each patient underwent two assessments of DFT using a step-down protocol, with the order of testing randomized. The distal right ventricular (RV) coil was the anode for the first phase of the biphasic shocks. The proximal superior vena cava (SVC) coil was the cathode for the Lead Alone configuration (RV --> SVC). For the Active Can configuration, the SVC coil and Can were connected electrically as the cathode (RV --> SVC + Can). The Active Can configuration was associated with a significant decrease in shock impedance (39.5 +/- 5.8 Omega vs. 50.0 +/- 7.6 Omega, P < 0.01) and a significant increase in peak current (8.3 +/- 2.6 A vs. 7.2 +/- 2.4 A, P < 0.01). There was no significant difference in DFT energy (9.0 +/- 4.6 J vs. 9.8 +/- 5.2 J) or leading edge voltage (319 +/- 86 V vs. 315 +/- 83 V). An adequate safety margin for defibrillation (> or =10 J) was present in all patients with both shocking configurations. CONCLUSION: DFTs are similar with the Active Can and Lead Alone configurations when a dual-coil, transvenous lead is used with a left abdominal pulse generator. Since most commercially available ICDs are only available with an active can, our data support the use of an active can device with this lead system for patients who present for routine pulse generator replacement.     

Distal right ventricular coil position reduces defibrillation thresholds

Distal RV Coil Position Reduces DFTs. INTRODUCTION: Understanding the factors that affect defibrillation thresholds (DFTs) has important implications both for optimization of defibrillation efficacy and for the design of new transvenous leads. The aim of this prospective study was to test the hypothesis that defibrillation efficacy is improved with the right ventricular (RV) coil in a distal position compared with a more proximal RV coil position. METHODS AND RESULTS: A novel defibrillation lead with three adjacent RV defibrillation coils (distal 0.8 cm, middle 3.7 cm, proximal 0.8 cm) was used for this study to permit comparison of DFTs with the proximal and distal RV coil positions without lead repositioning. In the distal RV configuration, the distal and middle RV coils were connected electrically as the anode for defibrillation. In the proximal RV configuration, the middle and proximal coils were the anode. A superior vena cava (SVC) coil and active can were connected electrically as the cathode (reversed polarity, RV-->Can+SVC). In each patient, the DFT was measured twice using a binary search protocol with the distal RV and proximal RV configurations, with the order of testing randomized. The study cohort consisted of 31 subjects (mean age 65 +/- 12 years, mean left ventricular ejection fraction 30% +/- 16%, 81% male predominance). The mean delivered energy (8.2 +/- 5.3 J vs 11.2 +/- 6.1 J), leading-edge voltage (335 +/- 109 V vs 393 +/- 118 V), and peak current (11.6 +/- 5.2 A vs 14.9 +/- 7.3 A) at DFT all were significantly lower with the distal RV configuration compared to the proximal RV configuration (P < 0.01 for all comparisons). CONCLUSION: DFTs are significantly reduced with the distal RV configuration compared to the proximal RV configuration. Defibrillation leads should be designed with the shortest tip to coil distance that can be achieved without compromising ventricular fibrillation sensing.     

Submuscular Versus Subcutaneous Pectoral Implantation of Cardioverter-Defibrillators: Effect on High Voltage Pathway Impedance and Defibrillation Efficacy

Implantable cardioverter-defibrillator (ICD) pulse generators are now routinely positioned in a pectoral location, either submuscularly (under the pectoralis muscles) or subcutaneously (over the pectoralis muscles). Furthermore, in current ICDs, the generator shield usually participates in the defibrillation energy pathway (hot can). Consequently, the precise generator location could affect defibrillation system efficacy. To assess this issue, we compared high voltage pathway impedance and defibrillation threshold (DFT) in 20 patients undergoing submuscular and 46 patients undergoing subcutaneous pectoral implantation of an Angeion Sentinel>® ICD and an AngeFlex® dual-coil defibrillation lead. Measurements were performed at time of ICD implant, pre-hospital discharge, and 1, 3 and/or 6 months later. Following induction of ventricular fibrillation, 569 biphasic waveform shocks were delivered between the generator shield and either the distal defibrillation coil (RV/can configuration) or both proximal and distal coils (RV/SVC/can configuration). Impedance differences between submuscular and subcutaneous implants were approximately 3–4 Ohms (p value of 0.132 to <0.001 depending on time of follow-up and lead configuration). A significant increase in impedance over time was noted independent of implant location and lead configuration. The DFT at implant or pre-discharge was assessed in 27 individuals, and was 9.9±3.8 J in 8 patients in the submuscular group, and 7.4±3.3 J in 19 patients in the subcutaneous group (p = 0.057). In conclusion, anatomic location of a hot can ICD generator (submuscular versus subcutaneous) influences impedance to defibrillation current, but the impact is of small magnitude and does not appear to result in clinically important differences in DFT.     

Biventricular Shocking Leads Improve Defibrillation Efficacy

INTRODUCTION: A single lead active can configuration has been widely used in patients with life-threatening ventricular arrhythmias. Occasionally, however, such a defibrillation lead configuration may not achieve adequate defibrillation threshold (DFT). The purpose of this study was to determine whether addition of a left ventricular (LV) lead can improve defibrillation efficacy. METHODS AND RESULTS: Three transvenous defibrillation leads (8.3-French with a 5-cm long unipolar coil) were placed in the right ventricle (RV), LV, and superior vena cava (SVC), along with an active can (92 cm2) in the left subpectoral area. The DFT stored energy of seven combinations of these defibrillation leads were compared in a pig ventricular fibrillation model using a biphasic defibrillation waveform (125 microF, 6.5/3.5 msec). A biventricular leads active can configuration in which the RV and LV leads were of the same polarity reduced the DFT stored energy by approximately 35% when compared to a single RV lead active can configuration (9.6 +/- 3.0 J vs 15.0 +/- 7.2 J, respectively, P = 0.02). Moreover, adding a SVC lead further reduced the DFT energy (8.4 +/- 3.3 J). CONCLUSION: A biventricular leads active can configuration can significantly improve defibrillation efficacy as compared to a single lead active can configuration. In such a defibrillation lead configuration, the polarity of RV and LV leads should be the same.     

Effect of coronary sinus electrode on the optimal atrial defibrillation pathway for an atrioventricular defibrillator

INTRODUCTION: Previous studies have demonstrated significant failure in converting atrial fibrillation (AF) using a conventional ventricular pathway. The aim of this study was to assess the benefit of incorporating a coronary sinus (CS) lead into the atrial defibrillation pathway in atrial defibrillation threshold (ADFT) reduction in patients with persistent AF. METHODS AND RESULTS: This study was a prospective, randomized assessment of shock configuration on ADFT in 18 patients undergoing elective internal cardioversion for persistent AF (mean AF duration: 8 +/- 9 months). The lead system included a dual-coil defibrillation lead (Endotak DSP, Guidant) with a distal right ventricular (RV) electrode and a proximal superior vena cava (SVC) electrode, a CS lead (Perimeter, Guidant), and a left pectoral cutaneous electrode (Can). In each patient, dual step-up ADFTs were determined for each of three vectors: (1) RV --> SVC+Can; (2) CS --> SVC+Can; and (3) RV --> CS+SVC+Can (group 1, n = 8) or RV+CS --> SVC+Can (group 2, n = 10), using R wave-synchronized biphasic shocks. Successful defibrillation was achieved in all patients without any ventricular proarrhythmia. ADFT of CS --> SVC+Can (11.8 +/- 5.6 J) was significantly lower than ADFT of RV --> SVC+Can (16.5 +/- 7.8 J, P = 0.021). ADFT of CS --> SVC+Can was similar to RV --> CS+SVC+Can (group 1: 12.0 +/- 6.5 J vs 17.4 +/- 4.8 J, P = 0.16), but it was significantly higher than RV+CS --> SVC+Can (group 2: 9.0 +/- 3.9 J vs 11.6 +/- 5.0 J, P = 0.049). CONCLUSION: Patients with persistent AF of substantial duration can be reliably cardioverted using a conventional implantable cardioverter defibrillator (ICD) lead set; however, the incorporation of a CS lead to the conventional ICD lead configuration significantly lowered ADFT. The optimal shock vector that incorporates a CS lead for atrial defibrillation requires future studies.     

A Prospective Randomized Cross-Over Comparison of Mono- and Biphasic Defibrillation Using Nonthoracotomy Lead Configurations in Humans

Biphasic Defibrillation with Nonthoracotomy Leads. Introduction: For current implantable defibrillators, the nonthoracotomy approach to implantation fails in a substantial number of patients. In a prospective randomized cross-over study the defibrillation efficacy of a standard monophasic and a new biphasic waveform was compared for different lead configurations.
Methods and Results: Intraoperatively, in 79 patients receiving nonthoracotomy defibrillation leads, the defibrillation threshold was determined in the initial lead configuration for the mono-and biphasic waveform. In each patient, both waveforms were used alternately with declining energies (20, 15,10, 5 J) until failure of defibrillation occurred. Three different initial lead configurations were tested in different, consecutive, nonrandomized patients using a bipolar endocardial defibrillation lead alone (A; n = 36) or in combination with a subcutaneous defibrillation patch (B; n = 24) or array (C; n = 19) lead. The lowest successful defibrillation energy with the biphasic waveform was less than, equal to, or higher than with the monophasic waveform in 64%, 28%, and 8% of patients, respectively, and on average significantly lower with the biphasic waveform for all three lead configurations (A: 11.3 ± 4.4 J vs 14.5 ± 4.5.); B: 9.7 ± 4.7 J vs 15.1 ± 4.5 J; C: 7.9 ± 4.5 J vs 12.4 ± 4.9 J). Defibrillation efficacy at 20 J was significantly improved by the biphasic waveform (91% vs 76%).
Conclusion: In combination with nonthoracotomy defibrillation leads, the biphasic waveform of a new implantable cardioverter defibrillator showed superior defibrillation efficacy in comparison to the standard monophasic waveform. Defibrillation thresholds were improved for lead systems with and without a subcutaneous patch or array lead.     

Effect of Electrode Configuration and Capacitor Size on Internal Atrial Defibrillation Threshold Using Leads Currently Used for Ventricular Defibrillation.

Background: Previous studies have shown that endocardial atrial defibrillation, using lead configurations specifically designed for ventricular defibrillation, is feasible but the substantial patient discomfort might prevent the widespread use of the technique unless significant improvements in shock tolerability are achieved. It has been suggested that the peak voltage or the peak current but not the total energy delivered determines the patient pain perception and therefore, lower defibrillating voltage and current achieved with modifications in lead and waveforms may increase shock tolerability. This study was undertaken to evaluate the effect, on the atrial defibrillation threshold (ADFT), of the addition of a patch electrode (mimicking the can electrode) to the right ventricle (RV)-superior vena cava (SVC) lead configuration. The influence of capacitor size on ADFT using the RV-SVC+skin patch configuration was also assessed.Methods: In 10 patients (pts) (Group 1) cardioversion thresholds were evaluated using biphasic shocks in two different configurations: 1) right ventricle (RV) to superior vena cava (SVC); 2) RV to SVC+skin patch. In a second group of twelve patients (Group 2) atrial defibrillation thresholds of biphasic waveforms that differed with the total capacitance (90 or 170 µF) were assessed using the RV to SVC+skin patch configuration.Results: In Group 1 AF was terminated in 10/10 pts (100 %) with both configurations. There was no significant difference in delivered energy at the defibrillation threshold between the two configurations (7.1 ± 5.1 J vs 7.1 ± 2.6 J; p < 0.05). In group 2 AF was terminated in 12/12 pts (100%) with both waveforms. The 170 µF waveform provided a significantly lower defibrillating voltage (323.7 ± 74.6 V vs 380 ± 70.2 V; p < 0.03) and current (8.1 ± 2.7 A vs 10.0 ± 2.3 A; p < 0.04) than the 90 µF waveform. All pts, in both groups, perceived the shock of the lowest energy tested (180 V) as painful or uncomfortable.Conclusions: The addition of a patch electrode to the RV-SVC lead configuration does not reduce the ADFT. Shocks from larger capacitors defibrillate with lower voltage and current but pts still perceive low energy subthreshold shocks as painful or uncomfortable.     

Electrode system influence on biphasic waveform defibrillation efficacy in humans.

BACKGROUND. Several clinical studies have demonstrated a general superiority of biphasic waveform defibrillation compared with monophasic waveform defibrillation using epicardial lead systems. To test the breadth of utility of biphasic waveforms in humans, a prospective, randomized evaluation of defibrillation efficacy of monophasic and single capacitor biphasic waveform pulses was performed for two distinct nonthoracotomy lead systems as well as for an epicardial electrode system in 51 cardiac arrest survivors undergoing automatic defibrillator implantation. METHODS AND RESULTS. The configurations tested consisted of a right ventricular-left ventricular (RV-LV) epicardial patch-patch system, an RV catheter-chest patch (CP) nonthoracotomy system, and a coronary sinus (CS) catheter-RV catheter nonthoracotomy system. For each configuration, the defibrillation current and voltage waveforms were recorded via a digital oscilloscope to measure defibrillation threshold voltage, current, resistance, and stored energy. Biphasic waveform defibrillation proved more efficient than monophasic waveform defibrillation for the epicardial RV-LV system (4.8 +/- 4.1 versus 6.7 +/- 4.9 J, p = 0.047) and the nonthoracotomy RV-CP system (23.4 +/- 11.1 versus 34.3 +/- 10.4 J, p = 0.0042). Biphasic waveform defibrillation thresholds were not significantly lower than monophasic waveform defibrillation thresholds for the CS-RV nonthoracotomy system (15.6 +/- 7.2 versus 20.0 +/- 11.5 J, p = 0.11). Biphasic waveform defibrillation proved more efficacious than monophasic waveform defibrillation in 13 of 20 patients (65%) with RV-LV epicardial patches, 10 of 15 patients (67%) with an RV-CP nonthoracotomy system, and nine of 16 patients (56%) with an RV-CS nonthoracotomy system. CONCLUSIONS. Biphasic pulsing was useful with nonthoracotomy lead systems as well as with epicardial lead systems. However, the degree of biphasic waveform defibrillation superiority appeared to be electrode system dependent. Furthermore, for a few individuals, biphasic waveform defibrillation proved less efficient than monophasic waveform defibrillation, regardless of the lead system used.     

Optimization of transvenous coil position for active can defibrillation thresholds

INTRODUCTION: Lead systems that include an active pectoral pulse generator are now standard for initial defibrillator implantations. However, the optimal transvenous lead system and coil location for such active can configurations are unknown. The purpose of this study was to evaluate the benefit and optimal position of a superior vena cava (SVC) coil on defibrillation thresholds with an active left pectoral pulse generator and right ventricular coil. METHODS AND RESULTS: This prospective, randomized study was performed on 27 patients. Each subject was evaluated with three lead configurations, with the order of testing randomized. Biphasic shocks were delivered between the right ventricular coil and an active can alone (unipolar), or an active can in common with the proximal coil positioned either at the right atrial/SVC junction (low SVC) or in the left subclavian vein (high SVC). Stored energies at defibrillation threshold were higher for the single-coil, unipolar configuration (11.2 +/- 6.6 J) than for the high (8.9 +/- 4.2 J) or low (8.5 +/- 4.2 J) SVC configurations (P < 0.01). Moreover, 96% of subjects had low (< or = 15 J) thresholds with the SVC coil in either position compared with 81% for the single-coil configuration. Shock impedance (P < 0.001) was increased with the unipolar configuration, whereas peak current was reduced (P < 0.001). CONCLUSION: The addition of a proximal transvenous coil to an active can unipolar lead configuration reduces defibrillation energy requirements. The position of this coil has no significant effect on defibrillation thresholds.     

Novel electrode design for potentially painless internal defibrillation also allows for successful external defibrillation

Background: Implantable cardioverter defibrillators (ICDs) save lives, but the defibrillation shocks delivered by these devices produce substantial pain, presumably due to skeletal muscle activation. In this study, we tested an electrode system composed of epicardial panels designed to shield skeletal muscles from internal defibrillation, but allow penetration of an external electric field to enable external defibrillation when required.
Methods and Results: Eleven adult mongrel dogs were studied under general anesthesia. Internal defibrillation threshold (DFT) and shock-induced skeletal muscle force at various biphasic shock strengths were compared between two electrode configurations: (1) a transvenous coil placed in the right ventricle (RV) as cathode and a dummy can placed subcutaneously in the left infraclavicular fossa as anode (control configuration) and (2) RV coil as cathode and the multielectrode epicardial sock with the panels connected together as anode (sock-connected). External DFT was also tested with these electrode configurations, as well as with the epicardial sock present, but with panels disconnected from each other (sock-disconnected). Internal DFT was higher with sock-connected than control (24 ± 7 J vs. 16 ± 6 J, P < 0.02), but muscle contraction force at DFT was greatly reduced (1.3 ± 1.3 kg vs. 10.6 ± 2.2 kg, P < 0.0001). External defibrillation was never successful, even at 360 J, with sock-connected, while always possible with sock-disconnected.
Conclusion: Internal defibrillation with greatly reduced skeletal muscle stimulation can be achieved using a novel electrode system that also preserves the ability to externally defibrillate when required. This system may provide a means for painless ICD therapy.     

Importance of Electrode Conductive Surface Area and Edge Effects on Ventricular Defibrillation Efficacy

Surface Area, Edge Effects, and Ventricular Defibrillation. Introduction: The role of edge effects and electrode surface area of the right ventricular (RV) trausveuous lead (TVL) on defibrillation efficacy is unknown.
Methods and Results: Defibrillation threshold (DFT) testing was conducted randomly in 12 dogs using ring electrode leads in an RV/SVC (superior vena cava) or RV/SVC/patch system. The leads (RV-4, RV-8t, RV-8, RV-15) had electrode surface areas of 20%, 20%, 40%, and 70%, respectively. A computer model predicted the magnitude of electrode surface current (RV-8t > RV-4 > RV-8 > RV-15) and the potential distribution (PD) at four sites: electrode surface (site a ) and at 2 mm ( b ), 4 mm ( c ), and 8 mm ( d ) away from the surface. Despite different near-field PDs (sites a, b, c ), PDs were nearly identical at site d. Resistance decreased as the surface area increased. DFT energy for the RV-15 lead was lower than the RV-4 and RV-8t. There was no difference between energy requirements for the RV-15 and RV-8 leads. No difference was found in DFT current for each lead. Comparison of the RV-8t and RV-4 leads showed no difference in DFT energy despite a lower resistance and a greater number of edges.
Conclusions: Increasing the RV TVL surface area lowered the resistance. However, surface area coverages ≥ 40% did not lower DFT energy. No significant change in DFT current occurred despite different predicted near-Held current densities. PDs were nearly identical 8 mm from the electrode surface. Thus, the far-field current density appears to play a more important role in determining defibrillation success.     

A Systematic Evaluation of Conventional and Novel Transvenous Pathways for Defibrillation

Introduction: Conventional implantable cardioverter defibrillators employ endocardial (shock) electrodes with a lead located in the right ventricular apex (RV) and a hot-can electrode located subcutaneously in the left pectoral region. In the event of a high defibrillation threshold (DFT) a third electrode is frequently employed in the superior vena cava (SVC). We report the comparison of conventional and novel locations of additional electrodes with the RV/Can configuration, in a porcine model.Method: In 12 anesthetized pigs (30–45 kg), endocardial defibrillation electrodes were randomized to the following locations: RV/Can, RV/Can + SVC, RV/Can + main pulmonary artery (MPA) and RV/Can + left pulmonary artery wedge position (PAW), RV/Can + high inferior vena cava (HIVC), RV/Can + Low inferior vena cava (LIVC). Ventricular fibrillation (VF) was induced using 60 Hz alternating current. After 10 seconds VF a rectangular biphasic shock was delivered by the ARD9000 (Angeion Corp). The DFT was determined for each configuration using a modified four-reversal binary search. All configurations were compared using a repeated measures analysis of variance (ANOVA) statistical test and the five 3-electrode configurations were compared to the RV/Can position using a Dunnett test.Results: Mean DFTs: RV = 21.5 ± 4.8 J, SVC = 16.8 ± 4.7 J (p < 0.05 vs. RV), HIVC = 21.1 ± 4.7 J (p <. 0.05), LIVC = 19.1 ± 5.7 J (p <. 0.05 vs. RV), MPA = 16.0 ± 5.8 J (p < 0.01), PAW = 17.5 ± 4.6 J (p < 0.05 vs. RV).Conclusions: Relative to the RV/can configuration the addition of a third electrode in the PA, PAW or SVC significantly reduces the DFT in the pig. The addition of an electrode to the IVC did not significantly reduce the DFT in our model.