Intraoperative defibrillation threshold testing during implantable cardioverter-defibrillator insertion: do we really need it?

Routine DFT testing in patients undergoing ICD implantation does not improve mortality: A systematic review and meta-analysis

Defibrillation threshold (DFT) testing has been an integral part of implantable cardioverter-defibrillator (ICD) implantation to confirm appropriate sensing of ventricular fibrillation and to establish an adequate safety margin for defibrillation. However, there is a lack of evidence regarding benefits of routine DFT testing. Therefore, we performed a meta-analysis to assess its mortality benefit. We searched MEDLINE for studies comparing mortality outcomes in ICD recipients who underwent DFT testing to those who did not. For the second analysis, studies comparing outcomes in patients with high- vs low-energy DFT were included. Odds ratio and standard errors were calculated, and inverse variance method in a random-effect model was used to combine effect sizes. Fifteen studies with 10,975 subjects comparing outcomes in patients who underwent routine DFT testing during ICD implantation and those who did not were included. There was no difference in the group that did not undergo DFT testing with regards to all-cause mortality (OR 0.935; CI 0.725-1.207; P = 0.606), cardiac mortality (OR 0.709; CI 0.385-1.307; P = 0.271), noncardiac mortality (OR 0.921; CI 0.701-1.210; P = 0.554), and arrhythmic mortality (OR 1.152; CI 0.831-1.596; P = 0.396). Percentage of successful appropriate first shocks among the two groups showed no difference. Five studies with 2278 subjects were included in the second analysis comparing patients with low DFT vs high DFT. Patients with high DFT had no significant increase in all-cause mortality compared to patients with low DFT (OR 0.527; CI 0.034-8.107; P = 0.646). Patients requiring higher DFT had no increased all-cause mortality compared to patients with lower DFT. Routine DFT testing during ICD implantation does not confer any significant benefit.

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 Shock, Not Ventricular Fibrillation, Causes Elevation of High Sensitive Troponin T after Defibrillation Threshold Testing--The Prospective, Randomized, Multicentre TropShock-Trial

BACKGROUND

The placement of an implantable cardioverter defibrillator (ICD) has become routine practice to protect high risk patients from sudden cardiac death. However, implantation-related myocardial micro-damage and its relation to different implantation strategies are poorly characterized.

METHODS

A total of 194 ICD recipients (64±12 years, 83% male, 95% primary prevention of sudden cardiac death, 35% cardiac resynchronization therapy) were randomly assigned to one of three implantation strategies: (1) ICD implantation without any defibrillation threshold (DFT) testing, (2) estimation of the DFT without arrhythmia induction (modified "upper limit of vulnerability (ULV) testing") or (3) traditional safety margin testing including ventricular arrhythmia induction. High-sensitive Troponin T (hsTnT) levels were determined prior to the implantation and 6 hours after.

RESULTS

All three groups showed a postoperative increase of hsTnT. The mean delta was 0.031±0.032 ng/ml for patients without DFT testing, 0.080±0.067 ng/ml for the modified ULV-testing and 0.064±0.056 ng/ml for patients with traditional safety margin testing. Delta hsTnT was significantly larger in both of the groups with intraoperative ICD testing compared to the non-testing strategy (p≤0.001 each). There was no statistical difference in delta hsTnT between the two groups with intraoperative ICD testing (p = 0.179).

CONCLUSION

High-sensitive Troponin T release during ICD implantation is significantly higher in patients with intraoperative ICD testing using shock applications compared to those without testing. Shock applications, with or without arrhythmia induction, did not result in a significantly different delta hsTnT. Hence, the ICD shock itself and not ventricular fibrillation seems to cause myocardial micro-damage.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01230086.

Effect of defibrillation threshold testing-induced ventricular fibrillation on renal function

INTRODUCTION

The effect of defibrillation threshold (DFT) testing with induction of ventricular fibrillation (VF) on renal function is currently unknown. This study examined the acute effect of DFT testing on renal function in patients undergoing implantable cardioverter defibrillator (ICD) implantation.

METHODS AND RESULTS

We performed a prospective cohort study of 148 consecutive patients who underwent ICD implantation from January 1, 2007 to May 30, 2008. Patients were assigned to one of two cohorts: a DFT group who underwent DFT testing at device implantation and a no-DFT group that was not tested. Baseline and 24-h postprocedure renal function were assessed with measurements of serum creatinine and estimated glomerular filtration rate (GFR) by the Modified Diet in Renal Disease equation. Changes in serum creatinine and estimated GFR were compared between cohorts. Ninety-eight patients (66%) underwent DFT testing (average VF induction count, 1.5 ± 0.9; mean VF duration, 10 ± 4 s). Fifty patients (34%) were not tested. Patients in the no-DFT group had lower mean left ventricular ejection fraction, higher New York Heart Association class, higher atrial fibrillation incidence, and greater intravenous contrast utilization at device implant. Baseline and postprocedure serum creatinine values were similar between groups (baseline, 1.25 ± 0.45 mg/dL; post-ICD, 1.26 ± 0.5 mg/dL). Baseline GFR was lower in the DFT cohort (55.2 ± 18.8 mL/min/BSA vs 63.7 ± 22.7 mL/min/BSA, p = 0.023). No significant differences between groups were observed in the mean change in serum creatinine or estimated GFR.

CONCLUSIONS

DFT testing at the time of ICD implantation is not associated with acute adverse effects on renal function.

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.

Shock or no shock - a question of philosophy or should intraoperative implantable cardioverter defibrillator testing be recommended?

OBJECTIVES

Implantation of implantable cardioverter defibrillators (ICDs) in patients with a high risk for life-threatening ventricular arrhythmias is a standard therapy. The development of new ICD leads, shock algorithms, high-energy defibrillators and rapid energy supply has improved the devices. Nevertheless, the discussion regarding 'shock or no shock' to test the system intraoperatively has not silenced yet.

METHODS

In this study, all 718 patients (60.0 ± 14.2 years old, 570 male) who were treated with a first ICD at our institution since 2005 were analysed. The indication for implantation was primarily prophylactic in 511 patients (71.3%). Underlying diseases included ischaemic cardiomyopathy (358 patients, 50%), dilated cardiomyopathy (270 patients, 37.7%) and others (12.3%). Mean ejection fraction was 27.4 ± 11.8%. Intraoperative ventricular fibrillation was induced with a T-wave shock or burst stimulation. The primary end-point was failing the initial intraoperative testing.

RESULTS

During the initial testing, 28 patients (3.9%) had a defibrillation threshold (DFT) >21 J. The mean age of these patients was 51 ± 14 years, ranging from 22 to 71 years, 20 were male, and the ejection fraction was 23.8 ± 11.8%. The indication for ICD implantation was prophylactic in 13 patients. Twenty-one of the 28 patients suffered from dilated cardiomyopathy, whereas seven patients had ischaemic cardiomyopathy. Twenty-four ICDs were implanted on the left side and four on the right side. None of the patients had been treated with amiodarone at the time of implantation. All patients achieved a sufficient DFT ≤ 21 J by changing the ICD leads, device repositioning and/or optimizing the shock configuration.

CONCLUSIONS

The standard of care intraoperative ICD testing remains necessary.

More safety with more energy: survival of electrical storm with 40-J shocks

We report the first clinical case of ineffective high-voltage therapy with 36 J and subsequent effective therapy with 40 J in a patient with electrical storm who had previously received a high-energy implantable cardioverter defibrillator (ICD, Fortify VR, 1233-40Q St. Jude Medical, Sylmar, CA, USA). Using a combination of high energy and optimized fixed millisecond duration biphasic waveform shock, successful defibrillation could be achieved at 8 J below the programmed maximum energy level.

Defibrillation thresholds in hypertrophic cardiomyopathy

BACKGROUND

Defibrillation threshold (DFT) testing is performed in part to ensure an adequate safety margin for the termination of spontaneous ventricular arrhythmias. Left ventricular mass is a predictor of high DFTs, so patients with hypertrophic cardiomyopathy (HCM) are often considered to be at risk for increased defibrillation energy requirements. However, there are little prospective data addressing this issue.

OBJECTIVE

To assess DFTs in patients with HCM and evaluate the clinical predictors of elevated DFTs.

METHODS

Eighty-nine consecutive patients with HCM and 600 control patients with ischemic or nonischemic cardiomyopathy underwent a uniform modified step-down DFT testing protocol. DFT was compared between the control and HCM populations. Predictors of elevated DFT were evaluated in the HCM group.

RESULTS

There was no difference in DFT between HCM and control groups (10.4 ± 5.8 J vs 11.2 ± 5.6 J, respectively). Among patients with HCM, clinical parameters such as left ventricular ejection fraction, interventricular septal thickness, left ventricular mass, and QRS duration were not predictive of an elevated DFT. Only 3 patients (3.4%) with HCM had a DFT >20 J.

CONCLUSION

Patients with HCM do not have elevated DFTs as compared to more typical populations undergoing implantable cardioverter-defibrillator implant; high-energy devices or complex lead systems are not needed routinely in this population.