Total Pectoral Implantation: A New Technique for Implantation of Transvenous Defibrillator Lead Systems and Implantable Cardioverter Defibrillator

We describe a new approach to tolal pectoral implantation of cardioverter defibrillators with an endocardial defibrillation lead system. Endocardial lead configuration used was an FDA approved right atrial-superior vena cavo defibriliation spring electrode, right ventricular bipolar sensing electrode, and a pectoral patch. Endocardial leads were implanted via a cephalic or an axillary venesection. Pectoral patch was placed in a sabmuscular position. In case of failure to obtain satisfactory thresholds, a small intercostal thoracofomy was performed via fhe same skin incision and patch placed over the epicardium instead of submuscular position and used with Ihe right atrial spring electrode. The device was implanted in the pectoral region, submuscularly, over the patch. Sixteen consecutive patients underwent this approach. With a submascular patch, adequate defibrillation thresholds (< 15 joules [J]) were obtained in 14 (87.5%) patients. In the other two, defibrillation thresholds of ≤ 15) were obtained with a epicardial patch. Pectoral implantation of the device was feasible in all 16 patients and none needed repositioning. Average postimplant hospital stay was 5 days. During follow-up period (average 5 months), none of the patients reported any major local symptoms and no problems have been encountered in device interrogation. Thus, total pectoral implantation of the cardioverter defibrillator including the patch, leads, and the device is feasible. Furthermore, in case of foilure to obtain adequate defibrillotjon thresholds with submuscular patch, an epicardial patch can easily be implanted and allows 100% successful defibrillation at energy levels of ≤ 15 J with right atrial patch configuration.     

Right Side Implant of the Unipolar Single Lead Defihrillation System

The active can defibrillator has been designed for implantation in the left prepectoral region. Whether this system can be successfully implanted on the right side is unknown. We describe six cases in which placement of the unipolar single lead defibrillation system was successfully attempted in the right prepectoral region due to impediments on the left side. The mean age of the patients was 62 ± 12 years. Five patients had is–chemic heart disease and one idiopathic dilated cardiomyopathy. The endocardial defibrillation electrode was placed in the right ventricle through the right subclavian vein and positioned at the apex in two patients and in the septal position in four patients. Defibrillation threshold testing was performed using a step-up/step-down protocol beginning at 12 J with 3-J increments or decrements. Defibrillation threshold was defined as the lowest energy of the first shock able to terminate ventricular fibrillation. The generator models used were the Medtronic 7218C in 1 patient, the Medtronic 7219C in 3 patients, and the Ventritex Cadet 115 AC in 2 patients. The mean defibrillation threshold was 15 ± 3 J. The defibrillation thresholds were retested at 1,3, and 6 months, and showed no significant change in five patients but decreased from 15 J to 12 J in one patient. The presence of impediments on the left side should not preclude attempts to place the unipolar active can system in the right prepectoral region.     

The azygos defibrillator lead for elevated defibrillation thresholds: implant technique, lead stability, and patient series

Background: Conventional insertion of implantable cardioverter‐defibrillator (ICD) includes an evaluation of the defibrillation threshold (DFT). Implanting an ancillary defibrillation lead in the azygos vein has been introduced as a therapeutic option in patients with “high” DFT. This study reports the efficacy and stability of azygos defibrillation coils implanted for elevated DFTs. Methods: This is a retrospective review of seven consecutive patients with right and left pectoral, single‐ and dual‐chamber, and biventricular ICDs and elevated DFTs, in whom an azygos defibrillation coil was introduced. Results: Addition of an azygos defibrillator lead achieved a satisfactory safety margin during single energy defibrillation efficacy testing in four out of seven patients, with success at maximum device output in two patients. No satisfactory safety margin was achieved in the remaining patient, despite the further addition of a subcutaneous defibrillation coil. No change in lead position was observed over a mean radiographic follow‐up of 8 months. No complications were noted during a mean follow‐up of 14 months, including no deaths, and no ICD shocks. Conclusion: Implanting a defibrillation coil into the azygos vein is feasible and safe. In a majority of patients with failed defibrillation efficacy testing, adding an azygos coil achieves success on repeat testing. Therefore, this technique is one option for lowering the defibrillation threshold in patients who fail DFT testing of their ICD.     

Bidirectional Defibrillation Using Implantable Defibrillators: A Prospective Randomized Comparison Between Pectoral and Abdominal Active Generators

SANDSTEDT, B., et al. : Bidirectional Defibrillation Using Implantable Defibrillators: A Prospective Randomized Comparison Between Pectoral and Abdominal Active Generators. The objective of this study was to compare the effects of active abdominal and pectoral generator positions on DFTs in a bidirectional tripolar ICD system. Twenty-five consecutive patients had ICD systems implanted under general anesthesia. A transvenous single lead bipolar defibrillation system and an active 57-cc test emulator in the abdominal and pectoral positions were used in the same patient. A randomized, alternating stepdown protocol was used starting at 15 J with 3-J decrements until failure. The mean implantation time was  114 ± 23 minutes  , the mean arrhythmia duration was  14.5 ± 1.5 seconds  , and the mean recovery time was  5.4 ± 1.1 minutes  . The mean DFTs in the abdominal and pectoral positions were  10.9 ± 5.1  and  9.7 ± 5.2 J  , respectively (NS), the mean intraindividual DFT difference (abdominal minus pectoral) was  −0.89 ± 4.15 J  (  range −9.5 to + 5.8 J  ). The 95% confidence interval showed a  −2.60 to + 0.82 J  mean difference (NS). The DFT was < 15 J in 72% and 88% of the patients and the defibrillation impedance was  41 ± 3  and  44 ± 3 Ω  , abdominal versus pectoral positions. There was no difference in DFT between active abdominal and pectoral generator bidirectional tripolar defibrillation. The pectoral position may be considered the primary option, but in cases of high DFTs the abdominal site should be considered an alternative to adding a subcutaneous patch. In some patients, the anatomy may favor an abdominal position. Possible differences in the long-term functionality on the leads are not yet well known and need to be further evaluated.     

Bipolar Transvenous Defibrillation: Efficacy of Two Different Positions of the Anode

For most nonthoracotomy defibrillotion lead systems, the transvenous anode can be positioned independently of the right ventricular (RV) cathode. Usually a vertical position in the superior vena cava (SVC) is chosen. However, it is unknown if this position yields the optimal defibrillation threshold (DFT). There-fort, in 15 patients undergoing defibrillator implantation the SVC position was compared in a crossover study design with a horizontal position in the left brachiocephalic vein (BCV). Mean DFT was not different for SVC and BCV (19.2 ± 9.6) vs 18.5 ± 9.1 J) but DFT of individual patients differed by up to 12 joules. A positive correlation between impedance and DFT in the BCV position (r = 0.6; P ≤ 0.05) indicated that the improved geometry of the defibrillation field with the BCV position is opposed by a higher impedance found for this position (63 ± 15 Ω vs 52 ± 7 Ω). Thus, defibrillation is not improved in general although individual patients might benefit.     

Voltage dependence of ICD lead polarization and the effect of iridium oxide coating

Nonthoracotomy leads (NTLs) with an iridium oxide (IROX) coating exhibit lower defibrillation thresholds (DFTs) than uncoated NTLs. We tested whether adding an IROX coating to an active pectoral can would influence defibrillation efficacy. However, the primary purpose of this study was to examine the impedance changes that occur at different voltages for uncoated titanium NTLs and identical NTLs with an IROX coating. We studied anesthetized pigs with an NTL placed in the right ventricle and coupled this to an active pectoral can. Biphasic waveform DFTs were obtained for the four NTLs and can combinations: uncoated NTL and uncoated can, uncoated NTL and IROX can, IROX NTL and uncoated can, and IROX NTL and IROX can. The respective energy DFTs were: 23.6 +/- 6.9, 24.1 +/- 6.7, 21.3 +/- 6.0, and 21.4 +/- 7.0 J. The IROX NTL DFTs were significantly lower (P < 0.05) than the uncoated NTL DFTs (either can), confirming our previous study. We then used a low tilt monophasic waveform to assess impedance changes. The impedance rise for each NTL/can combination was measured at 50, 100, 300, and 700 V. Comparisons of impedance changes between voltage levels showed that the impedance rise was inversely related to voltage and was greatest with uncoated NTLs. The IROX coating of the NTL reduced the impedance rise at all shock voltages, but was particularly beneficial at the lower voltages. No advantage was seen when the pectoral can was coated with IROX regardless of which NTL was used. Our results suggest that low voltage applications, such as atrial defibrillation, would benefit most from the IROX-coated NTL, and further studies are warranted in this area.     

A Patch in the Pectoral Position Lowers Defibrillation Threshold

Implantable pacemaker cardioverter defibrillators are now available with biphasic waveforms, which have been shown to markedly improve defibrillation thresholds (DFTs). However, in a number of patients the DFT remains high. Also, DFT may increase after implantation, especially if antiarrhythmic drugs are added. We report on the use of a subcutaneous patch in the pectoral position in 15 patients receiving a transvenous defibrillator as a method of easily reducing the DFT. A 660-mm² patch electrode was placed beneath the generator in a pocket created on the pectoral fascia. The energy required for defibrillation was lowered by 56% on average, and the system impedance was lowered by a mean of 25%. This maneuver allowed all patients to undergo a successful implant with adequate safety margin.     

Impact of Transvenous Lead Position on Active-Can ICD Defibrillation: A Computer Simulation Study

Optimizing lead placement in transvenous defibrillation remains central to the clinical aspects of the defibrillation procedure. Studies involving superior vena cava (SVC) return electrodes have found that left ventricular (LV) leads or septal positioning of the right ventricular (RV) lead minimizes the voltage defibrillation threshold (VDFT) in endocardial lead→SVC defibrillation systems. However, similar studies have not been conducted for active-can configurations. The goal of this study was to determine the optimal lead position to minimize the VDFT for systems incorporating an active can. This study used a high resolution finite element model of a human torso that includes the fiber architecture of the ventricular myocardium to find the role of lead positioning in a transvenous LEAD→can defibrillation electrode system. It was found that, among single lead systems, posterior positioning of leads in the right ventricle lowers VDFTs appreciably. Furthermore, a septal location of leads resulted in lower VDFTs than free-wall positioning. Increasing the number of leads, and thus the effective lead surface area in the right ventricle also resulted in lower VDFTs. However, the lead configuration that resulted in the lowest VDFTs is a combination of a mid-cavity right ventricle lead and a mid-cavity left ventricle lead. The addition of a left ventricular lead resulted in a reduction in the size of the low gradient regions and a change of its location from the left ventricular free wall to the septal wall.     

Clinical Results with Electrophysiologist-Implanted Cardioverter-Defibrillators

With the advent of nonthoracotomy leads and smaller devices. implantation techniques for implantable cardioverters defibrillators (ICDs) have been simplified. We reviewed the outcome of pectoral ICD implantation by electrophysiologists in 51 consecutive patients, 47 males and 4 females, mean age 60 ± 12 years, presenting with aborted sudden cardiac death (14) and drug refractory hypotensive ventricular tachycardia (37). Patients were implanted with either the PCD Jewel^TM 7219D (37) or 72197C (14) Medtronic pectoral ICDs. The mean operative time was 98 ± 31 minutes. There was no operative mortality. Complications occurred in 2 (4%) patients: right ventricular lead dislodgement requiring lead repositioning occurred in 1 patient, and 1 patient treated with anticoagulants, who had received a subcutaneous patch lead, developed a hematoma not requiring surgical reintervention. The mean defibrillation threshold was 18.6 ± 5.5 J, but was significantly lower for the 7219C(14.1 ± 5.0 J) compared to the 7219D (20.6 ± 4.4J) device, P = 0.0001. A two-lead system consisting of a right ventricular electrode (RVA) and a superior vena caval lead (SVC) was utilized in 29, RVA/SVC-subcutaneous patch in 5 and active can in 17 patients, Patients were discharged after 4.3 ± 3 days. The procedure time was significantly shorter for the 7219C device (79.7 ± 18.9 vs 105.2 ± 32.8 minutes., P = 0.0035]. Over the fallow-up period of 8 ± 5 (range 1–20] months, 26% patients received appropriate therapy (95% antitachycardia pacing, 5% shock). Concomitant antiarrhythmic therapy was utilized in 41% of patients. Ninety-eight percent of patients are alive. One patient died of congestive heart failure. Clinical results with electrophysiologist-implanted pectoral ICDs demonstrate lou morbidity and no operative mortality in this clinical series and lower DFTs and shorter procedure times may be achieved with 7219C (active can) device.     

Effects of Respiration Phase on Ventricular Defibrillation Threshold in a Hot Can Electrode System

The impedance of defibrillation pathways is an important determinant of ventricular defibrillation efficacy. The hypothesis in this study was that the respiration phase (end-inspiration versus end-expiration) mayalter impedance and/or defibrillation efficacy in a "hot can" electrode system. Defibrillation threshold (DFT) parameters were evaluated at end-expiration and at end-inspiration phases in random order by a biphasic waveform in ten anesthetized pigs (body weight: 19.1 ±2.4 kg; heart weight: 97 ± 10g). Pigs were intubated with a cuffed endotracheal tube and ventilated through a Drager SAVrespirator with tidal volume of 400–500 mL. A transvenous defibrillation lead (6 cm long, 6.5 Fr) was inserted into the right ventricular apex. A titanium can electrode (92-cm² surface area) was placed in the left pectoral area. The right ventricular lead was the anode for the first phase and the cathode for the second phase. The DFT was determined by a "down-up down-up" protocol. Statistical analysis was performed with a Wilcoxon matched pair test. The median impedance at DFT for expiration and inspiration phases were 37.8 ±3.1 Ω and 39.3 ± 3.6 Ω, respectively (P = 0.02). The stored energy at DFT for expiration and inspiration phases were 5.7 ± 1.9 J and 6.0 ± 1.0 J, respectively (P = 0.594). Shocks delivered at end-inspiration exhibited a statistically significant increase in electrode impedance in a "hot can" electrode system. The finding that DFT energy was not significantly different at both respiration phases indicates that respiration phase does not significantly affect defibrillation energy requirements.     

Implantation of a Subcutaneous Lead Array in Combination with a Transvenous Defibrillation Electrode via a Single Infraclavicular Incision

Occasional patients have excessive defibrillation energy requirements despite appropriate transvenous defibrillation lead position and modification of defibrillation waveform and configuration. Preliminary data suggest that use of subcutaneous defibrillation electrode arrays with nonthoracotomy systems is associated with a substantial reduction in defibrillation threshold. The current operative approach to subcutaneous lead array implantation involves the use of a separate left chest incision. We present two cases in which implantation of a subcutaneous lead array in combination with a transvenous defibrillation electrode was performed via a single infraclavicular incision and associated with a reduction in defibrillation threshold. Such an approach simplifies implantation and avoids the potential morbidity of the additional incision required of a left lateral chest approach.     

Comparison of Right– and Left–Sided Pectoral Implantation Parameters with the Jewel Active Can Cardiodefibrillator

A total of 1,207 patients received a Medtronic jewel active, can ICD (models 721BC, 7219C), with a Transvene had in 97 centers in Europe and North America. Nineteen implants were from the right pectoral region. Patients with right–sided ICDs did not differ in terms of mean age. % male, left ventricular ejection fraction, New York Heart Association Functional Class, antiar–rhythmic drug therapy, indication for the implantable cardioverter defihrillator, and R wave values at implantation, but tended to have slightly higher pacing thresholds (1.2 ± 0.5 V vs 1.0 ± 0.6 V, P = 0.012) and higher defibrillation thresholds (14.7 ± 6.4 J vs 11.5 ± 6 J, P = 0.11) compared with patients with left sided implants. Patients with right–sided implants had a longer implantation time compared with patients with left–sided implants (118 ± 70 minutes vs 91 ± 46 minutes, P = 0.074). In follow–up, 5 patients with right–sided implantation received successful therapy for either ventricular fibrillation, (8 episodes) or ventricular tachycardia (5 episodes). No ineffective therapy from the device was delivered in any patients with right–sided implantation. Right–sided pectoral implants are feasible with the Medtronic Jewel active can ICD.     

Transvenous Atrial Cardioversion Threshold in Patients with Implantable Cardioverter Defibrillator: Influence of Active Pectoral Can

Recent studies have shown that transvenous atrial cardioversion is feasible with lead configurations primarily designed for implantable cardioverter defibrillators (ICD). The purpose of this study was to examine the influence of an active pectoral ICD can on the atrial cardioversion threshold (ADFT). Forty consecutive patients received a transvenous single lead system (Endotak DSP 0125, CPI, St. Paul, MN, USA) in combination with a left subpectoral ICD (Ventak Mini, CPI) for treatment of malignant ventricular tachyarrhythmias. Patients were randomized into two groups: 21 received a Hot Can 1743 and 19 patients a Cold Can 1741. Step-down testing of the ventricular defibrillation threshold (VDFT) was performed intraoperatively and evaluation of the ADFT for induced atrial fibrillation (AF) at predischarge. After testing, each patient received a 2-J shock and was asked to quantify discomfort on a numerical scale ranging from 0 to 10. Both groups were comparable with regard to all clinical parameters studied. The mean VDFT in patients with a Hot Can device was significantly lower than in patients with a Cold Can (7.5 ± 2.3 J vs 9.8 ± 3.8 J; P < 0.03). The mean ADFT in the Hot Can group tended to be lower than in the group with Cold Cans (3.4 ± 1.4 J vs 4.5 ± 2.4 J; P = 0.07), and the proportion of patients in whom atrial cardioversion was accomplished at low energies (≤ 3 J) was higher in patients with active compared with patients with inactive pulse generators (57% vs 26%; P < 0.04). The mean discomfort reported after delivery of a 2-J shock was comparable in both groups (Hot Can 5.2 ± 1.9; Cold Can: 5.3 ± 2.1; P = NS). We conclude that the inclusion of an active left subpectoral can in the defibrillation vector of a ventricular ICD seems to reduce the energy requirements for atrial cardioversion without increasing the discomfort caused by low energy shocks.     

A Prospective, Randomized, Comparison in Patients Between a Pectoral Unipolar Defibrillation System and That Using an Additional Inferior Vena Cava Electrode

The decrease of defibrillation energy requirement would render the currently available transvenous defibrillator more effective and favor the device miniaturization process and the increase of longevity. The unipolar defibrillation systems using a single RV electrode and the pectoral pulse generator titanium shell (CAN) proved to be very efficient. The addition of a third defibrillating electrode in the coronary sinus did not prove to offer advantages and in the superior vena cava showed only a slight reduction of the defibrillation threshold (DFT). The purpose of this study was to determine whether the defibrillation efficacy of the single lead unipolar transvenous system could be improved by adding an electrode in the inferior vena cava (IVC). In 17 patients, we prospectively and randomly compared the DFT obtained with a single lead unipolar system with the DFT obtained using an additional of an IVC lead. The RV electrode, Medtronic 6936, was used as anode (first phase of biphasic) in both configurations. A 108 cm2 surface CAN, Medtronic 7219/7220 C, was inserted in a left submuscular infraclavicular pocket and used as cathode, alone or in combination with IVC, Medtronic 6933. The superior edge of the IVC coil was positioned 2-3 cm below the right atrium-IVC junction. Thus, using biphasic 65% tilt pulses generated by a 120 microF external defibrillator, Medtronic D.I.S.D. 5358 CL, the RV-CAN DFT was compared with that obtained with the RV-CAN plus IVC configuration. Mean energy DFTs were 7.8 +/- 3.6 and 4.8 +/- 1.7 J (P < 0.0001) and mean impedance 65.8 +/- 13 O and 43.1 +/- 5.5 O (P < 0.0001) with the RV-CAN and the IVC configuration, respectively. The addition of IVC significantly reduces the DFT of a single lead active CAN pectoral pulse generator. The clinical use of this biphasic and dual pathway configuration may be considered in patients not meeting implant criteria with the single lead or the dual lead RV-superior vena cava systems. This configuration may also prove helpful in the use of very small, low output ICDs, where the clinical impact of ICD generator size, longevity, and related cost may offset the problems of dual lead systems.     

Alternative Locations for Internal Defibrillator Electrodes

Successful defibrillation is described in two patients in whom the defibrillating electrode was positioned in the coronary sinus and right ventricular outflow tract as alternative sites. Internal cardiac defibrillation has been successful with single or multiple endocardial electrodes, epicardial patch electrodes, and subcutaneous surface electrodes (patch, array) in varying combinations and recently with an active can electrode. While the traditional location of the endocardial electrode has been the right ventricular apex, we describe two patients in whom defibrillation was successful in alternate locations, the coronary sinus and the right ventricular outflow tract.     

Measurement of body surface energy leakage of defibrillation shock by an implantable cardioverter defibrillator

Leakage of electrical current from the body surface during a defibrillation shock delivery by an ICD device was evaluated in 27 patients with life-threatening ventricular tachyarrhythmias. All patients underwent the implantation of the Medtronic Jewel Plus ICD system, and the defibrillation shocks were delivered between the active can implanted in the left subclavicular region and the endocardial lead placed in the right ventricle. At the time of measurement of the effect of electrical energy delivery for defibrillation, the shocks were delivered in a biphasic form at the energy level of 20 or 30 J. During each delivery of the defibrillation shock, the electrical current to the body surface was measured through large skin electrodes (6.2 cm2) that were pasted at the following positions: (1) parallel position: the electrodes were placed at the left shoulder and the right low-chest, and the direction of the electrode vector was parallel to the direction of the defibrillation energy flow, and (2) cross position: the electrodes were placed at the right shoulder and the left low-chest, and the vector of the electrodes was roughly perpendicular to the direction of the energy flow. The energy leakages were measured in 80 defibrillation shocks. The peak leakage current during the shock delivery at energy of 30 J was 48 +/- 26 mA at the parallel position and 19 +/- 15 mA at the cross position (P = 0.0002). The energy leakage at a 30-J shock was 7.4 +/- 7.2 mJ at the parallel position and 1.4 +/- 2.3 mJ at the cross position (P = 0.0002). The actual maximum energy leakage was 105 mA, 29 mJ, and 106 V that appeared at the parallel position. The body surface leakage of the defibrillation energy of the ICD device was evaluated. The power of the energy leakage strongly depended on the angle between the alignment of the recording electrodes and the direction of the energy flow. The highest current leakage to the body surface reached a considerable level, but the energy leakage was small because of the short duration of the defibrillation shock.     

Implantation of Submammary Implantable Cardioverter Defibrillators

Implantable cardioverter defibrillators (ICDs) are routinely placed in the left pectoral area using a transvenous approach. This approach may result in poor cosmetic outcome and cause psychological problems, especially in younger patients. To avoid this, several alternative implantation techniques have been developed. For cosmetic reasons, we used a submammary technique to implant ICDs into three young women. Apart from defibrillation threshold testing, the procedures were performed under local anesthesia. Threshold testing was done under general anesthesia. Appropriate defibrillation thresholds were obtained in all three cases, and all the patients tolerated the procedure well. There were no complications in a mean of 22 months of follow-up, and the cosmetic results were very good.(PACE 2004; 27[Pt. I]:779–782)     

European clinical experience with a dual chamber single pass sensing and pacing defibrillation lead

Dual chamber ICDs are increasingly implanted nowadays, mainly to improve discrimination between supraventricular and ventricular arrhythmias but also to maintain AV synchrony in patients with bradycardia. The aim of this study was to investigate a new single pass right ventricular defibrillation lead capable of true bipolar sensing and pacing in the right atrium and integrated bipolar sensing and pacing in the right ventricle. The performance of the lead was evaluated in 57 patients (age 61 +/- 12 years; New York Heart Association 1.9 +/- 0.6, left ventricular ejection fraction 0.38 +/- 0.15) at implant, at prehospital discharge, and during a 1-year follow-up. Sensing and pacing behavior of the lead was evaluated in six different body positions. In four patients, no stable position of the atrial electrode could intraoperatively be found. The intraoperative atrial sensing was 2.3 +/- 1.6 mV and the atrial pacing threshold 0.8 +/- 0.5 V at 0.5 ms. At follow-up, the atrial sensing ranged from 1.5 mV to 2.2 mV and the atrial pacing threshold product from 0.8 to 1.7 V/ms. In 11 patients, an intermittent atrial sensing problem and in 24 patients an atrial pacing dysfunction were observed in at least one body position. In 565 episodes, a sensitivity of 100% and a specificity of 96.5% were found for ventricular arrhythmias. In conclusion, this single pass defibrillation lead performed well as a VDD lead and for dual chamber arrhythmia discrimination. However, loss of atrial capture in 45% of patients preclude its use in patients depending on atrial pacing.     

Transthoracic DC Shock May Represent a Serious Hazard in Pacemaker Dependent Patients

External defibrillation is widely used for the termination of various atrial and ventricular tachyarrhythmias, including pacemaker patients. Our study was intended to evaluate the effects of DC shocks in 36 patients with unipolar pacemakers implanted in the right pectoral region (25 DDD, 10 VVI, 3 AAI). The shocks were delivered with paddles on the anterior surface of the thorax, as far as possible away from the pacemaker. The pacing output was programmed at 0.5 msec and 5 V (25 patients), 4 V (1 patient), and 2.5 V (10 patients). Transient loss of capture occurred in 18 patients (50%). These patients, compared with those without capture failure, received higher peak and cumulative shock energies, respectively, 216 ± 99 versus 123 ± 50 joules (P < 0.002) and 352 ± 62 versus 147 ± 98 joules (P < 0.004) and had a lower pacemaker pulse amplitude (4.0 ± 1.2 vs 4.6 ± 1.0 V, P = 0.11). Failure to capture lasted from 5 seconds to 30 minutes (mean 157 sec). In 15 patients the ventricular stimulation threshold was measured before and serially after cardioversion. A six-fold threshold increase was observed 3 minutes after the shock (P < 0.004) with gradual recovery to nearly baseline values at 24 hours. Transient sensing failure occurred in 7 of the 17 patients in whom it could be evaluated (41%). Furthermore, three cases of shock induced pacemaker malfunctions were observed requiring replacement of the stimulator in two patients. In conclusion, the incidence of loss of capture in pacemaker patients subjected to electrical cardioversion/defibrillation is high. The phenomenon is due to an abrupt rise in stimulation threshold, caused by the electrical shock, and may represent a serious hazard in pacemaker dependent patients. The risk of pacing failure could be reduced by utilizing low shock energies when possible, and by programming the pacemaker at its maximal output before cardioversion.     

A Comparison of Transvenous Atrial Defibrillation of Acute and Chronic Atrial Fibrillation and the Effect of Intravenous Sotalol on Human Atrial Defibrillation Threshold

The comparative efficacy and safety of transvenous defibrillation for acute and chronic AF and the effect of antiarrhythmic agents on this therapy have not been evaluated. Transvenous atrial defibrillation was performed in 25 patients with chronic AF and 13 patients with acute AF by delivering R wave synchronized, biphasic shocks between the right atrium and coronary sinus. The lowest energy and voltage resulting in successful defibrillation were considered to be atrial defibrillation threshold (ADFT). Intravenous sotalol (1.5 mg/kg) was thengiven over 15 minutes and ADFT was determined again. The mean ADFT was 1.5 /and 3.6 J for acute and chronic AF, respectively, and the threshold was highly reproducible. Sotaloi reduced ADFT in patients with acute AF while the reduction in chronic AF group was not significant. There was no significant increase in creatinine kinase nor reduction in blood pressure, but prolonged pause after successful defibrillation required ventricular supporting pacing. We conclude that transvenous atrial defibrillation is a safe and effective means for defibrillating both acute and chronic AF. ADFT was lower in acute AF than in chronic AF. ADFT was highly reproducible during repeated defibrillation. Sotalol reduced ADFT in acute AF and to a lesser extent in chronic AF, and increased the defibrillation success rate. Ventricular pacing will often be required because of prolonged pause after successful defibrillation.