A randomized prospective study of single coil versus dual coil defibrillation in patients with ventricular arrhythmias undergoing implantable cardioverter defibrillator therapy

ICD implantation is standard therapy for malignant ventricular arrhythmias. The advantage of dual and single coil defibrillator leads in the successful conversion of arrhythmias is unclear. This study compared the effectiveness of dual versus single coil defibrillation leads. The study was a prospective, multicenter, randomized study comparing a dual with a single coil defibrillation system as part of an ICD using an active pectoral electrode. Seventy-six patients (64 men, 12 women; age 61 +/- 11 years) were implanted with a dual (group 1, n = 38) or single coil lead system (group 2,n = 38). The patients represented a typical ICD cohort: 60% presented with ischemic cardiomyopathy as their primary cardiac disease, the mean left ventricular ejection fraction was 0.406 +/- 0.158. The primary tachyarrhythmia was monomorphic ventricular tachyarrhythmia in 52.6% patients and ventricular fibrillation in 38.4%. There was no significant difference in terms of P and R wave amplitudes, pacing thresholds, and lead impedance at implantation and follow-up in the two groups. There was similarly no difference in terms of defibrillation thresholds (DFT) at implantation. Patients in group 1 had an average DFT of 10.2 +/- 5.2 J compared to 10.3 +/- 4.1 J in Group 2, P = NS. This study demonstrates no significant advantage of a dual coil lead system over a single coil system in terms of lead values and defibrillation thresholds. This may have important bearing on the choice of lead systems when implanting ICDs.     

Examination of a middle cardiac vein defibrillation coil as stand-alone anode, auxiliary anode, and bystander electrode in a transvenous defibrillation circuit

In porcine studies anodes in the middle cardiac vein compare favorably with those in the RV. It has not been demonstrated whether the RV and middle cardiac vein or the middle cardiac vein alone anodes are superior when shocking to a conventional SVC and active housing cathode nor whether a bystander middle cardiac vein electrode exerts a passive electrode affect. Twelve pigs were anesthetized and had an active housing implanted in the left pectoral region and defibrillation coils placed at the RV apex and in the SVC. A custom-made defibrillation coil (Ela Medical) was advanced into the middle cardiac vein through a 9 Fr transvenous catheter. The DFT for three anodes (RV; RV and middle cardiac vein; middle cardiac vein) to the SVC and active housing was then assessed by a three reversal binary search, the order of testing was randomized. In seven animals DFT was assessed in the same way for the configuration of RV to SVC and active housing twice more, with and without a bystander middle cardiac vein coil electrode in place. The results were middle cardiac vein 7.5 +/- 1.7 J, RV and middle cardiac vein 7.3 +/- 1.7 J reduced DFT significantly compared to RV 13.8 +/- 4.2 J (both P < 0.000). There was no significant difference between the middle cardiac vein and the middle cardiac vein and RV (P = 0.67, 95% CI for difference -0.64-0.96). The DFT of RV to SVC and the active housing was the same with (13.2 +/- 4.0) and without (13.7 +/- 4.2) the middle cardiac vein bystander coil in place (P = 0.177, 95% CI for difference -0.33-1.33 J). Shocking to a SVC and active housing cathode, middle cardiac vein, and RV and middle cardiac vein anodes are equally effective in lowering DFT compared to the RV. The middle cardiac vein coil electrode does not exert a passive electrode affect on the RV to the SVC and active housing defibrillation.     

Adjustable atrial and ventricular temporary electrode for low-energy termination of tachyarrhythmias early after cardiac surgery

Supraventricular and ventricular tachycardias are common and serious postoperative complications early after cardiac surgery. We introduce a completely removable temporary adjustable defibrillation electrode (TADE) for low energy cardioversion/defibrillation of postoperative atrial and ventricular tachyarrhythmias. The electrode consists of three loops of steel wires connected to one steel wire, which are movable within an isolation sheet for adjusting the active surface to the individual size of the heart chambers. Evaluation of the electrode was performed in 10 open-chest beagles with a mean weight of 25.5 kg. The electrodes were first positioned on the left and right atrium. Atrial fibrillation (AF) was induced via a bipolar temporary heart wire. Atrial defibrillation thresholds (DFTs) were measured according to a step-down shock protocol (5-0.4 J). Thereafter, the electrodes were adjusted and positioned on the right and left ventricle. Ventricular fibrillation (VF) was induced and DFTs were recorded the same way. Aortic flow and pressure and left ventricular pressure were continuously monitored throughout the experiment. For termination of AF, mean DFTs were 0.4 +/- 0 J (lowest possible shock level) with a mean shock impedance of 70 +/- 7.6 ohms. VF was terminated with a mean DFT of 3 +/- 1.1 J with a mean impedance 56.1 +/- 7.9 ohms. Complete transcutaneous removal of the electrodes was possible in all animals without any complications. In conclusion, successful low energy termination of AF and VF is possible with the tested temporary adjustable electrode. A clinical study is planned for further evaluation.     

Electrical characteristics of a split cathodal pacing configuration

Several electrical configurations can be used for biventricular pacing to achieve cardiac resynchronization. Commercially approved biventricular pacing systems stimulate the RV with an endocardial lead and the LV with a unipolar lead positioned in the cardiac venous circulation using the tip electrodes of both leads linked as a common cathode. The distribution of current with this parallel circuit, split cathodal configuration is dependent on the separate impedances of the two leads. A total of 19 patients with left bundle branch block and congestive heart failure underwent implantation of a cardiac venous lead and standard bipolar right atrial and RV pacing leads. Stimulation thresholds and impedances were measured for the RV and LV in five electrical configurations: (1) unipolar LV from the cardiac venous lead; (2) bipolar LV using the tip electrode in the cardiac vein as the cathode and the ring electrode of the RV lead as the anode; (3) bipolar RV from the RV lead; (4) unipolar split cathodal stimulation of the cardiac venous and RV leads; and (5) bipolar split cathodal stimulation of the cardiac venous and RV leads. Repeat measurements of RV and LV thresholds were made from the pulse generator at 1-year follow-up. The LV stimulation threshold increased from 0.7 +/- 0.5 V in the unipolar configuration to 1.0 +/- 0.8 V in the unipolar split cathodal configuration (P = 0.01) and from 1.0 +/- 0.7 V in the bipolar configuration to 1.3 +/- 0.9 V in the bipolar split cathodal configuration (P < 0.001). The RV stimulation threshold increased from 0.3 +/- 0.2 V in the bipolar configuration to 0.5 +/- 0.2 V in the bipolar split cathodal configuration (P = 0.005). The bipolar impedance measured 874 +/- 299 Omega for the coronary venous lead, 705 +/- 152 for the RV lead, 442 +/- 87 in the split unipolar cathodal configuration, and 516 +/- 64 in the bipolar split cathodal configuration. At 1-year follow-up, the LV stimulation threshold was 1.8 +/- 1.6 in the unipolar split cathodal configuration and 2.4 +/- 1.6 in the bipolar split cathodal configuration (P = 0.003). The RV stimulation threshold at 1 year was 0.7 +/- 0.3 in the unipolar split cathodal configuration and 0.8 +/- 0.3 in the bipolar split cathodal configuration (P = 0.02). The split cathodal configuration significantly increases the apparent stimulation threshold for both the LV and the RV as compared with individual stimulation of either chamber alone. Programming to the bipolar split cathodal configuration further increases the apparent stimulation threshold. These observations support the development of pacing systems with separate LV and RV output circuits for resynchronization therapy.     

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.     

Present understanding of shock polarity for internal defibrillation: the obvious and non-obvious clinical implications

BACKGROUND: Uncertainty about the best electrode configuration has combined with the programming flexibility in modern implantable cardioverter-defibrillators (ICDs) to result in routine polarity reversal during an implant to deal with a high defibrillation threshold (DFT). We feel that this practice is not always supported by the clinical data and the present scientific understanding of defibrillation. METHOD: A meta-analysis of the clinical studies on ICD shock polarity was performed. Subgroup analyses were also performed to test the impact of high DFTs, various tilts, and the use of the hot can electrode. A review of the basic research surrounding the effects of polarity in defibrillation is also presented. RESULTS: A total of 224 patients were studied. The use of an anodal right ventricular (RV) coil lowers the mean DFT by 14.8% (P = 0.00001). It provides thresholds equal to or lower than cathodal defibrillation in 83% of patients. The fraction of patients with lower anodal DFTs was 94/224 versus 38/224 for cathodal polarity. This phenomenon may be explained by virtual electrode effects. In particular, anodal electrodes tend to produce collapsing wavefronts while cathodal electrodes tend to produce expanding proarrhythmic wavefronts. CONCLUSION: In an ICD implant, the RV coil should be the anode. Furthermore, DFT testing beginning with cathodal defibrillation is most likely unnecessary and needlessly extends the procedure's duration and increases the risks for the patient.     

Achieving low defibrillation thresholds at implant: pharmacological influences,RV coil polarity and position,SVC coil usage and positioning,pulse width settings,and the azygous vein

Approximately 30% of implantable cardioverter defibrillator (ICD) patients still die of sudden death. A major cause of these sudden deaths is the failure to defibrillate because of failure to achieve a low defibrillation threshold (DFT). Anti‐arrhythmic drugs can have a profound positive or negative effect on the DFT. Unfortunately, present clinical practice continues to feature many procedures and tactics that have minimal to negative DFT benefit. In addition, many demonstrated helpful tactics are not understood or followed. This review covers the optimal RV (right ventricular) coil position and polarity, superior vena cava (SVC) coil positioning and usage, pulse width settings, and azygous vein coil implants. Specifically, the RV coil should be set to an anodal polarity and never ‘reversed’. The optimal RV coil position appears to be along the mid‐septum. The SVC coil should be kept out of the right atrium and placed in the innominate vein junction. The SVC coil should be always on for high impedance patients. For low impedance patients, the SVC coil should be set on or off depending on which setting gives the lowest DFT. Pulse widths should be set to correspond to optimally charging and discharging a cardiac membrane time constant of between 3.5 and 4.5 ms. For the highest DFT patients, a separate coil should be placed in the azygous vein and connected to the ICD ‘SVC’ port. Anachronistic approaches such as the use of polarity reversal, apical RV coil tip forcing, and subcutaneous arrays are also discussed.     

Elevations in ventricular pacing threshold with the use of the Y adaptor: implications for biventricular pacing

Cardiac resynchronization therapy (CRT) is a new and promising therapeutic option for patients with severe heart failure and intraventricular conduction delay. Patients who are candidates for CRT and have a previously implanted device may utilize a "Y" IS 1 connector to accommodate the coronary sinus lead. This modification has the potential to alter biventricular pacing thresholds. During an 18 month period, successful biventricular pacemaker implantation was performed in 72 patients (age: 67 +/- 11 years, left ventricular ejection fraction: 20.5 +/- 5.6%). All of these patients had severe symptomatic congestive heart failure (NYHA Class III and IV). In 20 patients a special "Y" adaptor that bifurcates the ventricular IS 1 bipolar output to two bipolar outputs or one unipolar and one bipolar output was utilized. During initial implantation, LV thresholds obtained in a unipolar configuration prior to connecting to the "Y" adaptor were significantly lower than thresholds obtained after connecting to the "Y" adaptor (1.7 +/- 1.11 V at 0.5 ms pulse width versus 2.8 +/- 1.5 V at 0.5 ms pulse width [P = 0.01]). Two patients (10%) required left ventricular lead revisions due to unacceptably high left ventricular thresholds during device follow-up. The difference in measured left ventricular thresholds between the two configurations is best explained by a resistive element that is added to the circuit when performing threshold measurement of the LV lead through the "Y" adaptor (combined tip to RV ring configuration) versus measurement of the LV lead in a unipolar configuration. This resistive element represents multiple factors including anode surface area, resistive polarization at the tissue-electrode interface, and transmyocardial resistance. LV thresholds should be measured in an LV tip to RV ring configuration or ideally in a combined tip (LV and RV) to shared ring configuration in order to accurately assess LV thresholds. This observation has significant clinical implications as loss of capture may occur as a result of improper measurement of left ventricular thresholds at the time of implantation.     

1-year performance of a defibrillation lead with a small electrode surface for high impedance pacing: a randomized,controlled study

A small electrode surface reduces pacing current drain and can extend generator longevity. The study evaluated the performance of a tined, quadripolar defibrillation lead (model 6944) that has a small-surfaced, steroid-eluting electrode tip for high impedance pacing. In a prospective, controlled study, 34 patients with conventional ICD indications were randomized one to one to receive the high impedance model 6944 or a tined defibrillation lead with a conventional sized, steroid-eluting electrode tip model 6942. Lead performance was evaluated at implant, prior to hospital discharge, and 1, 3, 6, and 12 months thereafter. Baseline characteristics did not differ significantly between patients implanted with lead model 6942 (n = 16) or model 6944 (n = 17). One patient randomized to receive the model 6942 was excluded from the study and was implanted with an active-fixation lead after stable lead positioning was neither possible with the 6942 nor with the 6944 electrode. No other lead related adverse events were observed. At implant, there were no significant differences between pacing thresholds, sensing performance, defibrillation impedances, and defibrillation thresholds in both groups, but pacing impedance of the model 6944 (988.6 +/- 217.7 omega) was approximately twice as high as high as in the model 6942 (431.7 +/- 83.7 omega; P < 0.0001). This difference remained highly significant throughout the observation period of 12 months, while R wave amplitudes and pacing thresholds remained equal in both lead models. The use of a tined defibrillation lead with a small, steroid-eluting electrode tip appears safe and results in a high pacing impedance without compromising system performance.     

Internal Cardiac Defibrillation: Single and Sequential Pulses and a Variety of Lead Orientations

A sequential pulse system for internal cardiac defibrillation incorporating catheter and patch electrodes with two current pathways has been shown to reduce defibrillation threshold in comparison to the single pulse technique. The relative advantage of the sequential pulse over the single pulse technique with other lead systems is not known. We compared defibrillation thresholds using sequential and single pulses delivered to a variety of lead orientations with the same electrode surface areas, when possible. Defibrillation threshold totals determined in halothane-anesthetized open-chest pigs averaged: For the single pulse shock passed between (1) superior vena cava (SVC) and left ventricular apical patch (LVA), 27.2 +/- 9.1 joules (J) and (2) LV epicardial patch (LVE) to right ventricular epicardial (RVE) patch leads, 16.5 +/- 2.1 J; and for the sequential pulse shock with two pulses passed between: (1) the SVC to RV intracavitary apex (RVA) and a quadripolar catheter in the coronary sinus to the RVA, 11.6 +/- 1.0 J; (2) the SVC to LVA and the LVE to RVE, 9.6 +/- 1.3 J and (3) the SVC to RVA and the LVE to RVA, 8.9 +/- 0.4 J. Defibrillation thresholds for sequential pulse shocks were all significantly lower than either of the defibrillation thresholds for single pulse shocks (p less than 0.001). We conclude that the sequential pulse system provides a substantial reduction in defibrillation threshold over the single pulse regardless of the lead system when the surface area and pulse characteristics are controlled. Sequential pulse technique may be valuable in the design of an implantable automatic defibrillator.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potential benefit of transesophageal defibrillation: an experimental evaluation

INTRODUCTION: Because of the proximity of the esophagus to the heart, transesophageal defibrillation might increase defibrillation success. We assessed the defibrillation threshold (DFT) of transesophageal defibrillation compared with standard transthoracic defibrillation. METHODS: Defibrillation success and DFTs were determined in 22 female pigs with high (68+/-4 kg, n=12) or low body weight (39+/-1 kg, n=10). After induction of ventricular fibrillation, biphasic shocks were delivered between two cutaneous patch electrodes (sternal and apical position) or between an esophageal and two cutaneous patch electrodes in a sternal and apical position. The esophageal electrode was integrated into a latex sheath covering a standard transesophageal echocardiography probe. RESULTS: In 5 of 12 pigs with high body weight, external defibrillation failed despite 3 consecutive 200-J shocks, whereas subsequent transesophageal defibrillation was successful with the first shock. In the remaining 7 pigs, a more than 50% reduction in DFT was obtained with transesophageal defibrillation compared with standard biphasic external defibrillation (67+/-27 vs 164+/-23 J, P<.001). Pigs with lower body weight were successfully defibrillated by both transthoracic and transesophageal shocks. The DFT in pigs with low body weight was significantly lower using transesophageal defibrillation compared with transthoracic shocks (65+/-15 vs 99+/-38 J, P<.05). CONCLUSIONS: In this animal model, nonresponders to standard external defibrillation could successfully be defibrillated via an esophageal-cutaneous electrode configuration. Overall, an almost 50% DFT reduction was achieved by transesophageal defibrillation. Transesophageal defibrillation may provide an additional tool for terminating VF, which is refractory to external defibrillation, eg, in patients with very high body weight.     

Reduction in defibrillation threshold using an auxiliary shock delivered in the middle cardiac vein

Defibrillation in the middle cardiac vein (MCV) has been shown to reduce ventricular defibrillation thresholds (DFTs). Low amplitude auxiliary shock (AS) from an electrode sutured to the left ventricle at thoracotomy have also been shown to reduce DFT if delivered immediately prior to a biphasic shock (between the ventricular RV and superior vena caval (SVC) electrodes). This study investigates the impact on DFT of an AS shock from a transvenously placed MCV lead system. A standard defibrillation electrode was positioned in the RV in eight anesthetized pigs (35-43 kg). A 50 x 1.8-mm electrode was inserted in the MCV through an 8 Fr angioplasty guide catheter. A 150-V (leading edge) monophasic AS was delivered (95 microF capacitor) from the MCV-->Can with three different pulse widths (3, 5, 7 ms). A primary biphasic shock (PS) (95 microF capacitor, phase 1: 44% tilt, 1.6-ms extension and phase 2: 2.5-ms fixed duration) was delivered from the RV-->Can +/- AS. The four configurations were randomized and DFTs (PS + AS) assessed using a modified binary search. Ventricular fibrillation (VF) was induced with 60 Hz AC followed 10 seconds later by the test shock. The DFTs were compared using repeated measures analysis of variance (ANOVA). All configurations incorporating AS produced significant (P < 0.05) reduction in the DFT compared to no AS (13.8 +/- 7.4 J). There was no difference in the efficacy of differing pulse widths (P > 0.05); 3 ms (11.0 +/- 5.4 J), 5 ms (11.5 +/- 6.0), and 7 ms (10.6 +/- 5.3 J). In conclusion, delivering an AS from a transvenous lead system deployed in the MCV reduces the DFT by 23% compared to a conventional RV-->Can shock alone.     

Influence of Ventricular Fibrillation Duration on Defibrillation Energy in Dogs Using Bidirectional Pulse Discharges

The automatic implantable defibrillator device typically discharges 5-30 seconds after detection of ventricular fibrillation. To investigate the importance of the duration of ventricular fibrillation on defibrillation, the effects of ventricular fibrillation durations of 5, 15, and 30 seconds on the energy requirements for successful internal defibrillation were compared in 15 closed chest dogs with internal electrodes. The electrode configuration utilized a transvenous right heart catheter with two electrodes and a precordial subcutaneous patch electrode, with a single bidirectional pulse discharged between the distal catheter electrode and the proximal catheter and patch electrodes. Curves of energy vs. percentage of successful defibrillation were constructed and logistic regression was used to derive 90% and 50% successful energy doses (ED90 and ED50). The mean ventricular fibrillation activation interval just prior to defibrillation was determined from discrete RV endocardial electrograms. Four dogs died during testing, all because of inability to defibrillate after 30 s of ventricular fibrillation. In the remaining 11 dogs, the ED90 increased from (mean +/- SD) 27 +/- 13J at 5 s to 41 +/- 14J at 30 s (p less than .01). The mean ventricular fibrillation activation interval decreased from 107 +/- 21 ms at 5 s to 95 +/- 18 ms at 30 s (p less than .01). In conclusion, the energy required for internal defibrillation in dogs using this electrode configuration increases with longer durations of ventricular fibrillation, and is associated with more rapid ventricular fibrillation activation intervals.     

Electrode Polarity Is an Important Determinant of Defibrillation Efficacy Using a Nonthoracotomy System

Experimental and clinical data using epicardial patch electrodes and monophasic waveform suggest that electrode polarity may be an important determinant of defibrillation efficacy. Our objective was to examine the effect of electrode polarity in an animal model using a nonthoracotomy system and monophasic and biphasic waveforms for defibrillation. We examined the effect of lead polarity in 14 pentobarbital anesthetized dogs (21.1 ± 2.4 kg) using monophasic and biphasic shocks and a nonthoracotomy system. Monophasic and single capacitor biphasic shocks of 10-msec total duration were used. The lead system consisted of a right ventricular catheter electrode with 4-cm² surface area and a left chest wall subcutaneous patch electrode with 13.9-cm² surface area. Electrode polarities RV(?)-Patch(+) and RV(+)Patch(?) were tested using both monophasic and biphasic waveforms. Alternating current was used to induce ventricular fibrillation and test shocks were delivered after 10 seconds of ventricular fibrillation. Each polarity configuration for monophasic and biphasic waveforms was tested four times at five different capacitor voltage levels (200–600 V, in 100-V increments). Defibrillation efficacy curves were constructed using logistic regression analysis for each animal and energies associated with 80% probability of successful defibrillation (E80) were determined. The mean E80 ± SD values were as follows. Monophasic waveform: RV(?)Patch(+) 23.4 ± 7.5 J; RV(+)Patch(?) 20.9 ± 7.9 J(P <0.03). Biphasic waveform: RV(?)Patch(+) 15.8 ± 6.8 J; RV(+)Patch(?) 12.5 ± 6.0 J (P < 0.03). The mean impedance values for both waveforms using either polarity ranged from 65.4 to 67 ohms and were not significantly different. Biphasic waveforms were superior to monophasic (P < 0.01), regardless of lead polarity. For either waveform, reversal of lead polarity in some animals resulted in improved defibrillation efficacy and worsening in others, butasagroup, the RV(+)Patch(?) electrode configuration was superior. Conclusions: These observations suggest that electrode polarity is an important determinant of defibrillation efficacy for nonthoracotomy defibrillation. The optimal electrode configuration cannot be determined a priori, suggesting that alternate polarity configurations should be tested to maximize the defibrillation safety margin.     

Prospective randomized comparison of 50%/50% versus 65%/65% tilt biphasic waveform on defibrillation in humans

It is unknown if there is a single optimal biphasic waveform for defibrillation. Biphasic waveform tilt may be an important determinant of defibrillation efficacy. The purpose of this study was to compare acute defibrillation success with a three-electrode configuration in humans using 50%/50% versus 65%/65% tilt truncated exponential, biphasic waveforms delivered through a 110-microF capacitor. Acute DFTs for biphasic waveforms with 50%/50% versus 65%/65% tilt were measured in random order in 60 patients using a binary search method. The electrode configuration consisted of a RV coil as the cathode, and a SVC coil plus a pectoral active can emulator (CAN) as the anode. The waveforms were derived from an external voltage source with 110-microF capacitance, and the leading edge voltage of phase 2 was equal to the trailing edge voltage of phase 1. Stored energy DFT (9.2 +/- 5.7 [50%/50%] vs 10.8 +/- 6.4 [65%/65%] J, P = 0.007), current DFT (10.9 +/- 4.0 [50%/50%] vs 12.0 +/- 4.4 [65%/65%] A, P = 0.002) and voltage DFT (391 +/- 118 [50%/50%] vs 424 +/- 128 [65%/65%] V, P = 0.004) were significantly lower for the 50%/50% tilt waveform versus the 65%/65% tilt waveform using this three-electrode configuration and a 110-microF capacitor. For an RV(-)/SVC plus CAN(+) electrode configuration and a 110-microF capacitor, a 50%/50% tilt biphasic waveform results in a 15% reduction in energy DFT, 9% reduction in current DFT, and 8% reduction in voltage DFT versus a 65%/65% tilt biphasic waveform.     

Human experience with transvenous biventricular defibrillation using an electrode in a left ventricular vein

This study investigated the safety and feasibility of transvenous biventricular defibrillation in ICD patients. Some patients may have high DFTs due to weak shock field intensity on the LV. Animal studies showed a LV shocking electrode dramatically lowered DFTs. This approach might benefit heart failure patients already receiving a LV lead or conventional ICD patients with high DFTs. A modified guidewire was used as a temporary left venous access defibrillation electrode (LVA lead). In 24 patients receiving an ICD, the LVA lead was advanced through a guide catheter in the coronary sinus (CS) and into a randomized LV vein (anterior or posterior) using a venogram for guidance. Paired DFT testing compared a standard right ventricular defibrillation system to a biventricular defibrillation system. There were no complications or adverse events. As randomized, LVA lead insertion success was 87% and 71% for anterior and posterior veins, respectively, and 100% after crossover. Total insertion process time included venogram time (32.5 +/- 26.9 minutes, range 5-115, mode 15 minutes) and LVA lead insertion time (15 +/- 14 minutes, range 1-51, mode 7 minutes). An apical LVA lead position was achieved in 11 (45%) of 24 patients and 7 (64 %) of these 11 displayed a DFT reduction; however, mean DFTs were not statistically different. Transvenous biventricular defibrillation is feasible and was safe under the conditions tested. Additional clinical studies are justified to determine if optimized LV lead designs, lead placement, and shock configurations can yield the same large DFT reductions as observed in animals.     

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.     

Effects of Polarity for Monophasic and Biphasic Shocks on Defibrillation Efficacy with an Endocardial System

Electrode polarity has been reported to be one of the factors that affect defibrillation efficacy. We studied the influence of polarity on defibrillation efficacy when monophasic and biphosic waveforms were used with an endocardial lead system. In six anesthetized pigs, defibrillation catheters were placed in the right ventricular (RV) apex and at the junction of the superior vena cava (SVC) and right atrium. Monophasic shocks were 6 ms in duration, while for biphasic shocks the first phase was 6 ms and the second was 4 ms in duration. Four electrode configurations were tested: R:S, M (the RV electrode, cathode; the SVC electrode, anode, with a monophasic shock); S:R. M; R:S, B (the RV electrode, first phase cathode; the SVC electrode, first phase anode, with a biphasic shock); S:R, B. Defibrillation probability of success curves were determined using an up/down protocol requiring 15 shocks for each configuration. For monophasic shocks, total delivered energy at the 50% probability of success point was significantly lower when the RV electrode was an anode than when it was a cathode (R:S, M: 24.4 ± 7.4 J [mean ± SD] vs S:R, M: 16.4 ± 5.5 J; P < 0.05). For biphasic shocks, total energy was not affected by polarity reversal of the electrodes (R:S, B: 8.7 ± 1.4 J vs S:R, B: 8.4 ± 2.5 J; P = NS). The endocardial electrode configuration with the RV electrode as an anode requires less energy for defibrillation with a monophasic but not a biphasic waveform.     

Placement considerations for measuring thermodilution right ventricular ejection fractions

BACKGROUND AND METHODS: Clinical examination of right ventricular (RV) performance has been hampered by the inability to measure easily RV volumes and ejection fraction. This study was performed to examine the effects of catheter position on thermodilution RVEF measurements. Six pigs (80 to 100 kg) were instrumented with an RV thermodilution catheter in the pulmonary artery, an injectate catheter in the right atrium, an atrial pacing electrode, and a systemic arterial catheter. RVEF measurements were determined using thermodilution in two ways: a) with incremental increases in pulmonary valve to thermistor distance; and b) with incremental increases in injectate port to tricuspid valve distance. These measurements were obtained at a paced rate of 102 +/- 2 beats/min and then repeated with pacing-induced tachycardia (140 beats/min). RESULTS: There was no significant difference in thermodilution RVEF measurements with the thermistor positioned 0 to 10 cm from the pulmonary valve at either heart rate. A significant reduction in RVEF occurred with the injection port located 5 to 7 cm proximal to the tricuspid valve, with this decrease becoming more pronounced during tachycardia. CONCLUSIONS: These results demonstrate that RVEF measurements can be reliably obtained using thermodilution. In these large hearts, thermodilution RVEF measurements appear to be independent of thermistor position within the pulmonary artery. However, large distances from injectate port to tricuspid valve reduced RVEF measurements.