Does an SVC electrode further reduce DFT in a hot-can ICD system?

Systematic Review of Defibrillation Threshold Testing at De Novo Implantation

Background—

Recent results from the largest multicenter randomized trial (Shockless IMPLant Evaluation [SIMPLE]) on defibrillation threshold (DFT) testing suggest that while shock testing seems safe, it does not reduce the risk of failed shocks or prolong survival. A contemporary systematic review of DFT versus no-DFT testing at the time of implantable cardioverter–defibrillator implantation was performed to evaluate the current evidence and to assess the impact of the SIMPLE study.

Methods and Results—

Electronic searches were performed using 6 databases from their inception to March 2014. Relevant studies investigating implant DFT were identified. Data were extracted and analyzed according to predefined clinical end points. Predefined outcomes for interrogation were all-cause mortality, composite end point of implantable cardioverter–defibrillator efficacy (arrhythmic deaths and ineffective shocks), and composite safety end point (the sum of complications recorded at 30 days). Meta-analysis was performed including 13 studies and 9740 patients. No significant differences between DFT versus no-DFT cohorts were found in terms of all-cause mortality (risk ratio, 0.90; 95% confidence interval, 0.71–1.15; P =0.41), composite efficacy outcome (risk ratio, 1.24; 95% confidence interval, 0.65–3.37; P =0.51), and 30-day postimplant complications (risk ratio, 1.18; 95% confidence interval, 0.87–1.60; P =0.29). No significant difference was found in the trends observed when the results of the SIMPLE study were excluded or included.

Conclusions—

This systematic review of contemporary data suggests a modest average effect of DFT, if any, in terms of mortality, shock efficacy, or safety. Therefore, DFT testing should no longer be compulsory during de novo implantation. However, DFT testing may still be clinically relevant in specific patient populations.

ICD implantation without intraoperative testing does not increase the rate of system modifications and does not impair defibrillation efficacy tested in follow-up

AIM

The need for implantable cardioverter-defibrillator (ICD) defibrillation testing (DT) and subsequent intraoperative system modifications is discussed controversially. The study's goal was to prove that consequent abdication of intraoperative DT does not impair defibrillation efficacy and does not increase the rate of postoperative system revisions.

METHODS

In a prospective single-center observational study, 609 out of 648 consecutive patients underwent transvenous ICD implantation (left-sided, active can, dual coil lead, and biphasic shock waveform) waiving intraoperative DT. Defibrillation efficacy was validated prior to hospital discharge (PHD) by applying two 10 J safety margin (SM) shocks.

RESULTS

Following "schockless" implantation 580 out of 609 patients (95.2 %) met a 10 J SM with default programming. Shock path reversal provided 10 J SM in 13 out of 29 cases with initially failed DT. In four patients (0.7 %) maximum energy shocks were ineffective. There was no morbidity or mortality related to DT. The total rate of surgical ICD revisions was 1.8 %.

CONCLUSION

Routine ICD implantation without intraoperative DT does not lead to an increased rate of postoperative system modifications and does not decrease defibrillation efficacy as tested PHD.

Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study

The patch electrode and the array electrode are the two types of subcutaneous leads available as an adjunct to a transvenous lead system in patients with high defibrillation thresholds. A prospective randomized study was conducted in 30 consecutive patients comparing the efficacy and the long-term performance of a patch electrode with an array electrode. After determination of the defibrillation threshold for the transvenous lead alone, a subcutaneous patch or an array electrode was implanted in random order. Adding a patch electrode decreased the defibrillation threshold in seven out of 15 patients (47%) from 13.2+/-6.6 to 10.5+/-5.1 J (P<0.05). In 13 out of 15 patients (87%), the implantation of an array electrode caused a significant lowering of the defibrillation threshold from 15.4+/-6.6 to 8.2+/-5.0 J (P<0.0001). The array electrode was significantly more effective in lowering the defibrillation threshold than the patch electrode (P<0.01). Complications during follow-up associated with the subcutaneous patch electrode were observed in four patients whereas no complications were associated with the array electrode (P<0.01). The additional implantation of an array electrode is more effective and associated with fewer complications compared to a patch electrode.

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.

Energy steering of biphasic waveforms using a transvenous three electrode system

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV-->C) or a three (RV-->SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV-->C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV-->SVC + C). Configuration 3 (W3): The RV-->C was used for the first 25% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 4 (W4): The RV-->C was used for the first 50% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 5 (W5): The RV-->C was used for the first 75% of f+ and RV-->SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV-->C was used for f+ and RV-->SVC + C for f 2. As an increasing fraction of the waveform was discharged using the RV-->SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV-->SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV-->SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.

The middle cardiac vein--a novel pathway to reduce the defibrillation threshold

Defibrillation energy requirements of epicardial implantable cardioverter defibrillator systems are generally lower than endovascular systems currently used. The former has the disadvantage of requiring a thoracotomy and so has a greater morbidity and mortality than an endovascular procedure. The middle cardiac vein (MCV) is an epicardial structure that is accessible by a non-thoracotomy approach. This study investigated the merits of ventricular defibrillation from the middle cardiac vein. METHODS AND RESULTS. Defibrillation thresholds (DFT) were measured in 10 anesthetized pigs, weighing 34.5 +/- 44.1 kg (mean 39 kg). An Angeflex electrode (1.7 mm x 50 mm) was introduced via the left external jugular vein to the right ventricular apex. The MCV was identified with standard angiography techniques and a 4080 (Angeion Corp.) defibrillation electrode (1.6 mm x 65 mm) introduced into the vein. An active can was implanted in the left subpectoral region. The defibrillation thresholds (DFT) of the following defibrillation configurations were assessed using a modified four-reversal binary search: RV-->Can, RV + MCV-->Can and MCV-->Can. The DFT's for the three configurations were 15.5 +/- 2.8 J, 10.8 +/- 3.4 J and 13.7 +/- 2.4 J. Analysis of variance showed that the DFT with the RV + MCV combination was significantly less than the RV alone (p < 0.05)

CONCLUSIONS

Defibrillation is possible through the MCV and that incorporating an electrode in the MCV with RV-Can configuration can reduce the DFT by 30%.