Differences in the characteristics of induced and spontaneous episodes of ventricular fibrillation

Defibrillation effectiveness and safety of the shock waveform used in a contemporary wearable cardioverter defibrillator: Results from animal and human studies

INTRODUCTION

The wearable cardioverter defibrillator (WCD) is used to protect patients at risk for sudden cardiac arrest. We examined defibrillation efficacy and safety of a biphasic truncated exponential waveform designed for use in a contemporary WCD in three animal studies and a human study.

METHODS

Animal (swine) studies: #1: Efficacy comparison of a 170J BTE waveform (SHOCK A) to a 150J BTE waveform (SHOCK B) that approximates another commercially available waveform. Primary endpoint first shock success rate. #2: Efficacy comparison of the two waveforms at attenuated charge voltages in swine at three prespecified impedances. Primary endpoint first shock success rate. #3: Safety comparison of SHOCK A and SHOCK B in swine. Primary endpoint cardiac biomarker level changes baseline to 6 and 24 hours post-shock. Human Study: Efficacy comparison of SHOCK A to prespecified goal and safety evaluation. Primary endpoint cumulative first and second shock success rate. Safety endpoint adverse events.

RESULTS

Animal Studies #1: 120 VF episodes in six swine. First shock success rates for SHOCK A and SHOCK B were 100%; SHOCK A non-inferior to SHOCK B (entire 95% CI of rate difference above -10% margin, p < .001). #2: 2,160 VF episodes in thirty-six swine. Attenuated SHOCK A was non-inferior to attenuated SHOCK B at each impedance (entire 95% CI of rate difference above -10% margin, p < .001). #3: Ten swine, five shocked five times each with SHOCK A, five shocked five times each with SHOCK B. No significant difference in troponin I (p = 0.658) or creatine phosphokinase (p = 0.855) changes from baseline between SHOCK A and SHOCK B. Human Study: Thirteen patients, 100% VF conversion rate. Mild skin irritation from adhesive defibrillation pads in three patients.

CONCLUSIONS

The BTE waveform effectively and safely terminated induced VF in swine and a small sample in humans.

TRIAL REGISTRATION

Human study clinical trial registration: URL: https://clinicaltrials.gov; Unique identifier: NCT04132466.

Distinct spectral dynamics of implanted cardiac defibrillator signals in spontaneous termination of polymorphic ventricular tachycardia and fibrillation in patients with electrical and structural diseases

AIMS

To determine the spectral dynamics of early spontaneous polymorphic ventricular tachycardia and ventricular fibrillation (PVT/VF) in humans.

METHODS AND RESULTS

Fifty-eight self-terminated and 173 shock-terminated episodes of spontaneously initiated PVT/VF recorded by Medtronic implanted cardiac defibrillators (ICDs) in 87 patients with various cardiac pathologies were analyzed by short fast Fourier transform of shifting segments to determine the dynamics of dominant frequency (DF) and regularity index (RI). The progression in the intensity of DF and RI accumulations further quantified the time course of spectral characteristics of the episodes. Episodes of self-terminated PVT/VF lasted 8.6 s [95% confidence interval (CI): 8.1-9.1] and shock-terminated lasted 13.9 s (13.6-14.3) (P < 0.001). Recordings from patients with primarily electrical pathologies displayed higher DF and RI values than those from patients with primarily structural pathologies (P < 0.05) independently of ventricular function or antiarrhythmic drug therapy. Regardless of the underlying pathology, the average DF and RI intensities were lower in self-terminated than shock-terminated episodes [DF: 3.67 (4.04-4.58) vs. 4.32 (3.46-3.93) Hz, P < 0.001; RI: 0.53 (0.48-0.56) vs. 0.63 (0.60-0.65), P < 0.001]. In a multivariate analysis controlled by the type of pathology and clinical variables, regularity remained an independent predictor of self-termination [hazard ratio: 0.954 (0.928-0.980)]. Receiver operating characteristic (ROC) curve analysis of DF and RI intensities demonstrated increased predictability for self-termination in time with 95% CI above the 0.5 cut-off limit at about t = 8.6 s and t = 6.95 s, respectively.

CONCLUSION

Consistent with the notion that fast organized sources maintain PVT/VF in humans, reduction of frequency and regularity correlates with early self-termination. Our findings might help generate ICD methods aiming to reduce inappropriate shock deliveries.

Computerized Analysis of the Ventricular Fibrillation Waveform Allows Identification of Myocardial Infarction: A Proof-of-Concept Study for Smart Defibrillator Applications in Cardiac Arrest

Background

In cardiac arrest, computerized analysis of the ventricular fibrillation (VF) waveform provides prognostic information, while its diagnostic potential is subject of study. Animal studies suggest that VF morphology is affected by prior myocardial infarction (MI), and even more by acute MI. This experimental in‐human study reports on the discriminative value of VF waveform analysis to identify a prior MI. Outcomes may provide support for in‐field studies on acute MI.

Methods and Results

We conducted a prospective registry of implantable cardioverter defibrillator recipients with defibrillation testing (2010–2014). From 12‐lead surface ECG VF recordings, we calculated 10 VF waveform characteristics. First, we studied detection of prior MI with lead II, using one key VF characteristic (amplitude spectrum area [AMSA]). Subsequently, we constructed diagnostic machine learning models: model A, lead II, all VF characteristics; model B, 12‐lead, AMSA only; and model C, 12‐lead, all VF characteristics. Prior MI was present in 58% (119/206) of patients. The approach using the AMSA of lead II demonstrated a C‐statistic of 0.61 (95% CI, 0.54–0.68). Model A performance was not significantly better: 0.66 (95% CI, 0.59–0.73), P=0.09 versus AMSA lead II. Model B yielded a higher C‐statistic: 0.75 (95% CI, 0.68–0.81), P<0.001 versus AMSA lead II. Model C did not improve this further: 0.74 (95% CI, 0.67–0.80), P=0.66 versus model B.

Conclusions

This proof‐of‐concept study provides the first in‐human evidence that MI detection seems feasible using VF waveform analysis. Information from multiple ECG leads rather than from multiple VF characteristics may improve diagnostic accuracy. These results require additional experimental studies and may serve as pilot data for in‐field smart defibrillator studies, to try and identify acute MI in the earliest stages of cardiac arrest.

Ventricular Fibrillation Waveform Analysis During Chest Compressions to Predict Survival From Cardiac Arrest

BACKGROUND

Quantitative measures of the ventricular fibrillation (VF) ECG waveform can assess myocardial physiology and predict cardiac arrest outcomes, making these measures a candidate to help guide resuscitation. Chest compressions are typically paused for waveform measure calculation because compressions cause ECG artifact. However, such pauses contradict resuscitation guideline recommendations to minimize cardiopulmonary resuscitation interruptions. We evaluated a comprehensive group of VF measures with and without ongoing compressions to determine their performance under both conditions for predicting functionally-intact survival, the study's primary outcome.

METHODS

Five-second VF ECG segments were collected with and without chest compressions before 2755 defibrillation shocks from 1151 out-of-hospital cardiac arrest patients. Twenty-four individual measures and 3 combination measures were implemented. Measures were optimized to predict functionally-intact survival (Cerebral Performance Category score ≤2) using 460 training cases, and their performance evaluated using 691 independent test cases.

RESULTS

Measures predicted functionally-intact survival on test data with an area under the receiver operating characteristic curve ranging from 0.56 to 0.75 (median, 0.73) without chest compressions and from 0.53 to 0.75 (median, 0.69) with compressions ( P<0.001 for difference). Of all measures evaluated, the support vector machine model ranked highest both without chest compressions (area under the receiver operating characteristic curve, 0.75; 95% CI, 0.73-0.78) and with compressions (area under the receiver operating characteristic curve, 0.75; 95% CI, 0.72-0.78; P=0.75 for difference).

CONCLUSIONS

VF waveform measures predict functionally-intact survival when calculated during chest compressions, but prognostic performance is generally reduced compared with compression-free analysis. However, support vector machine models exhibited similar performance with and without compressions while also achieving the highest area under the receiver operating characteristic curve. Such machine learning models may, therefore, offer means to guide resuscitation during uninterrupted cardiopulmonary resuscitation.

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.

Contemporary rates and outcomes of single- vs. dual-coil implantable cardioverter defibrillator lead implantation: data from the Israeli ICD Registry

Aims

Dual-coil leads were traditionally considered standard of care due to lower defibrillation thresholds (DFT). Higher complication rates during extraction with parallel progression in implantable cardioverter defibrillator (ICD) technology raised questions on dual coil necessity. Prior substudies found no significant outcome difference between dual and single coils, although using higher rates of DFT testing then currently practiced. We evaluated the temporal trends in implantation rates of single- vs. dual-coil leads and determined the associated adverse clinical outcomes, using a contemporary nation-wide ICD registry.

Methods and results

Between July 2010 and March 2015, 6343 consecutive ICD (n = 3998) or CRT-D (n = 2345) implantation patients were prospectively enrolled in the Israeli ICD Registry. A follow-up of at least 1 year of 2285 patients was available for outcome analysis. The primary endpoint was all-cause mortality. Single-coil leads were implanted in 32% of our cohort, 36% among ICD recipients, and 26% among CRT-D recipients. Secondary prevention indication was associated with an increased rate of dual-coil implantation. A significant decline in dual-coil leads with reciprocal incline of single coils was observed, despite low rates of DFT testing (11.6%) during implantation, which also declined from 31 to 2%. In the multivariate Cox model analysis, dual- vs. single-coil lead implantation was not associated with an increased risk of mortality [hazard ratio (HR) = 1.23; P= 0.33], heart failure hospitalization (HR = 1.34; P=0.13), appropriate (HR = 1.25; P= 0.33), or inappropriate ICD therapy (HR = 2.07; P= 0.12).

Conclusion

Real-life rates of single-coil lead implantation are rising while adding no additional risk. These results of single-coil safety are reassuring and obtained, despite low and contemporary rates of DFT testing.

Ablation as targeted perturbation to rewire communication network of persistent atrial fibrillation

Persistent atrial fibrillation (AF) can be viewed as disintegrated patterns of information transmission by action potential across the communication network consisting of nodes linked by functional connectivity. To test the hypothesis that ablation of persistent AF is associated with improvement in both local and global connectivity within the communication networks, we analyzed multi-electrode basket catheter electrograms of 22 consecutive patients (63.5 ± 9.7 years, 78% male) during persistent AF before and after the focal impulse and rotor modulation-guided ablation. Eight patients (36%) developed recurrence within 6 months after ablation. We defined communication networks of AF by nodes (cardiac tissue adjacent to each electrode) and edges (mutual information between pairs of nodes). To evaluate patient-specific parameters of communication, thresholds of mutual information were applied to preserve 10% to 30% of the strongest edges. There was no significant difference in network parameters between both atria at baseline. Ablation effectively rewired the communication network of persistent AF to improve the overall connectivity. In addition, successful ablation improved local connectivity by increasing the average clustering coefficient, and also improved global connectivity by decreasing the characteristic path length. As a result, successful ablation improved the efficiency and robustness of the communication network by increasing the small-world index. These changes were not observed in patients with AF recurrence. Furthermore, a significant increase in the small-world index after ablation was associated with synchronization of the rhythm by acute AF termination. In conclusion, successful ablation rewires communication networks during persistent AF, making it more robust, efficient, and easier to synchronize. Quantitative analysis of communication networks provides not only a mechanistic insight that AF may be sustained by spatially localized sources and global connectivity, but also patient-specific metrics that could serve as a valid endpoint for therapeutic interventions.

Safety threshold of R-wave amplitudes in patients with implantable cardioverter defibrillator

OBJECTIVE

A safety threshold for baseline rhythm R-wave amplitudes during follow-up of implantable cardioverter defibrillators (ICD) has not been established. We aimed to analyse the amplitude distribution and undersensing rate during spontaneous episodes of ventricular fibrillation (VF), and define a safety amplitude threshold for baseline R-waves.

METHODS

Data were obtained from an observational multicentre registry conducted at 48 centres in Spain. Baseline R-wave amplitudes and VF events were prospectively registered by remote monitoring. Signal processing algorithms were used to compare amplitudes of baseline R-waves with VF R-waves. All undersensed R-waves after the blanking period (120 ms) were manually marked.

RESULTS

We studied 2507 patients from August 2011 to September 2014, which yielded 229 VF episodes (cycle length 189.6±29.1 ms) from 83 patients that were suitable for R-wave comparisons (follow-up 2.7±2.6 years). The majority (77.6%) of VF R-waves (n=13953) showed lower amplitudes than the reference baseline R-wave. The decrease in VF amplitude was progressively attenuated among subgroups of baseline R-wave amplitude (≥17; ≥12 to <17; ≥7 to <12; ≥2.2 to <7 mV) from the highest to the lowest: median deviations -51.2% to +22.4%, respectively (p=0.027). There were no significant differences in undersensing rates of VF R-waves among subgroups. Both the normalised histogram distribution and the undersensing risk function obtained from the ≥2.2 to <7 mV subgroup enabled the prediction that baseline R-wave amplitudes ≤2.5 mV (interquartile range: 2.3-2.8 mV) may lead to ≥25% of undersensed VF R-waves.

CONCLUSIONS

Baseline R-wave amplitudes ≤2.5 mV during follow-up of patients with ICDs may lead to high risk of delayed detection of VF.

TRIAL REGISTRATION NUMBER

NCT01561144; results.

Tachyarrhythmia Cycle Length in Appropriate versus Inappropriate Defibrillator Shocks in Brugada Syndrome, Early Repolarization Syndrome, or Idiopathic Ventricular Fibrillation

Background and Objectives

Implantable cardioverter–defibrillators (ICDs) are indicated in patients with Brugada syndrome (BS), early repolarization syndrome (ERS), or idiopathic ventricular fibrillation (IVF) who are at high risk for sudden cardiac death. The optimal ICD programming for reducing inappropriate shocks in these patients remains to be determined. We investigated the difference in the mean cycle length of tachyarrhythmias that activated either appropriate or inappropriate ICD shocks in these three patient groups to determine the optimal ventricular fibrillation (VF) zone for minimizing inappropriate ICD shocks.

Subjects and Methods

We selected 41 patients (35 men) (mean age±standard deviation=42.6±13.0 year) who received ICD shocks between April 1996 and April 2014 to treat BS (n=24), ERS (n=9), or IVF (n=8). Clinical and ICD interrogation data were retrospectively collected and analyzed for all events with ICD shocks.

Results

Of the 244 episodes, 180 (73.8%) shocks were appropriate and 64 (26.2%) were inappropriate. The mean cycle lengths of the tachyarrhythmias that activated appropriate and inappropriate shocks were 178.9±28.7 ms and 284.8±24.4 ms, respectively (p<0.001). The cutoff value with the highest sensitivity and specificity for discriminating between appropriate and inappropriate shocks was 235 ms (sensitivity, 98.4%; specificity, 95.6%). When we programmed a single VF zone of ≤270 ms, inappropriate ICD shocks were reduced by 70.5% and appropriate shocks were missed in 1.7% of these patients.

Conclusion

Programming of a single VF zone of ≤270 ms in patients with BS, ERS, or IVF could reduce inappropriate ICD shocks, with a low risk of missing appropriate shocks.

Defibrillation Threshold Testing: Who Doesn't Get It?

Defibrillation testing has been routinely performed as part of the implantable cardioverter-defibrillator (ICD) implantation procedure, and is currently supported by practice guidelines; however, more recently, this practice has been called into question. Such testing is safe, and serious complications are rare. With modern ICD systems, physicians will rarely encounter a patient in whom defibrillation will fail. This article reviews the literature regarding the utility, necessity, complications, and cost of routine operative and follow-up defibrillation testing, and, it is hoped, clarifies the issue of "Who doesn't get it?"

The Effect of Direct Current Stimulation versus T-Wave Shock on Defibrillation Threshold Testing

INTRODUCTION

There are several methods to induce ventricular fibrillation (VF) during defibrillation threshold (DFT) testing. Delivering a shock at a critical time during the T wave (T-shock) is the conventional approach, while delivering a constant direct current voltage (DC stim) from the implantable cardioverter defibrillator is an alternative method. Only a few reports compare VF induction methods. The purpose of this study was to evaluate the effects and safety of DC stim versus T-shock.

METHODS

We retrospectively investigated 414 consecutive patients undergoing DFT testing. We compared the two groups (DC stim and T-shock) with respect to clinical characteristics, electrocardiogram (ECG) changes, and complications.

RESULTS

Ventricular arrhythmia, including ventricular tachycardia (VT) and VF, was induced by DC stim in 93 patients or T-shock in 321 patients. No more than three attempts were performed during one procedure. There was no significant difference in the baseline ECG, induced tachycardia cycle length (TCL), or complications between the two groups. However, the induced TCL was significantly shorter than the clinical TCL regardless of induction method (P = 0.001). Five patients suffered major complications (i.e., electromechanical dissociation or incessant VT). A history of atrial fibrillation was significantly greater in patients with major complications than the others (80% vs 24%, P = 0.004), and was an independent predictor on multivariate analysis.

CONCLUSIONS

There is no significant difference in induced TCL or complications between the DC stim and T-shock. The induced TCL is significantly shorter than clinical TCL regardless of induction method.

Underdetection of ventricular fibrillation despite ICD testing and high sinus R wave

Apart from monitoring shock efficacy, proof of flawless detection of induced ventricular fibrillation (VF) is a decisive argument in favor of implantable cardioverter defibrillator (ICD) testing. On the other hand, it has been observed that undersensing of VF is extremely rare with good sensing of the intrinsic R wave of  ≥ 5-7 mV. The case presented here shows limitations in both argumentations: Neither optimal R wave sensing during sinus rhythm nor repeated ICD testing could rule out or predict multiple erroneous detections of clinical VF episodes. This must be taken into consideration in the current discussion on the necessity of defibrillation testing. Further optimization of sensing technology should be a focus in the development of modern ICD systems so as to improve the safety and efficacy of ICD therapy.

Cycle length characteristics differentiating non-sustained from self-terminating ventricular fibrillation in Brugada syndrome

AIMS

Limited information is available on self-terminating (ST) ventricular fibrillation (VF). Understanding spontaneous fluctuations in VF cycle length (CL) is required to identify arrhythmia that will stop before shock. Using Brugada syndrome (BS) as a model, the purpose of the study was to compare ST-VF and VF terminated by electrical shock and to look for spontaneous fluctuations in ventricular CL.

METHODS AND RESULTS

Occurrence of ST-VF and VF was studied in 53 patients with 46 VF episodes: (i) spontaneously, (ii) during defibrillation threshold testing, (iii) during programmed ventricular stimulation (PVS). Fifteen presented ST-VF (average duration 25 s): 11 during PVS, 1 during defibrillation threshold testing, and 3 spontaneously (at device interrogation). Self-terminating ventricular fibrillation was compared with 31 VFs terminated by electrical shock. Mean ventricular CL was longer (192.5 ± 22 vs. 149 ± 19 ms) (P < 0.0001) and CL became longer or did not change in ST-VF (187 ± 28 vs. 200 ± 25 ms) (first vs. last CL)(NS) in contrast with progressively shorter CL in electrical shock-terminated VF (177 ± 14.5 vs. 139 ± 12 ms) (first vs. last CL before electrical shock) (P < 0.0001). Ventricular fibrillation had more CL variability (average 16.4 ± 6.5 ms) for the first 50 beats than ST-VF (average 4.08 ± 2) (P < 0.0001). Cycle length range for the first 50 beats was 9.6 ± 1 ms for ST-VF and 44 ± 15 for VF (P < 0.002).

CONCLUSION

Self-terminating ventricular fibrillation in BS was not rare (28%). Ventricular CL was longer and progressively increased or did not change in ST-VF compared with electrical shock-terminating VF. Cycle length variability and CL range could differentiate VF and ST-VF within the first 50 beats. These parameters should be considered in the algorithms for VF detection and termination.

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.

Spectral methods to distinguish ventricular fibrillation from artefact in implantable cardioverter-defibrillators

BACKGROUND

Despite the proven benefit of implantable cardioverter-defibrillators (ICDs), inappropriate shocks remain a significant problem. Recent trends have shown an increased incidence of lead failure and an increased exposure of devices to extreme electromagnetic interference environments.

AIMS

The goal of the current study is to evaluate the spectral characteristics of ventricular fibrillation (VF) detected in an ICD at time of defibrillation threshold testing and use of the findings to predict event types from a population of clinical VF and artefact events.

METHODS AND RESULTS

A modelling group was created from induced VF and artefact events at time of ICD implantation and DFT testing. Power spectral density evaluation was performed on each event and used to calculate an energy ratio (ER; the ratio of energy under the first three harmonics to the entire spectrum). The model was then applied to a database of clinical VF and artefact events to determine its sensitivity and specificity. The far-field ER of the modelling group was significantly larger for VF (0.888 ± 0.110) than artefact (0.265 ± 0.156, P < 0.0001). In the test group, the far-field ER of VF (0.882 ± 0.088) was also significantly larger than artefact (0.344 ± 0.128, P < 0.0001). At a cut-off of >0.526, the far-field ER had a sensitivity of 100% [confidence interval (CI) 100-100%] and a specificity of 92.4% (CI 84.9-98.5%) to distinguish clinical VF from clinical artefact.

CONCLUSION

Far-field signal during VF detected by an ICD has a distinct spectral pattern that can distinguish VF from artefact.

[Is intraoperative ICD-testing still necessary?]

Intraoperative ICD-testing is traditionally performed in many hospitals in order to ensure reliable sensing, detection, and defibrillation of induced ventricular fibrillation. The technical progress of defibrillators allows rapid detection and delivery of high energy shocks which defibrillates effectively in the vast majority all patients at implant. This review describes arguments pro and contra of systematic testing of the defibrillation threshold in all patients. Many reasons argue against testing in all patients: experimental considerations, patients' specific and nonspecific factors, e.g., underlying severity of cardiac disease, ischemia, and medication, as well as factors specific to the ICD system, e.g., implanted type and location of electrodes and active cans. Finally, the testing method is very important, since it bears the risk of false negative test results because the a priori probability of a positive test result is >95%. Therefore, data from prospective randomized studies are necessary in order to abandon the tradition of ICD-testing on an evidence-based background.

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

BACKGROUND

The assessment of defibrillation efficacy using a safety margin of 10 J has long been the standard of care for insertion of implantable cardioverter-defibrillator (ICD), but physicians are concerned about complications related to induction test. Therefore, the need for testing has been recently questioned. The aim of our study was to assess the impact of defibrillation threshold (DFT) testing of ICD on the efficacy of ICD therapy.

METHODS

We analyzed data obtained from follow-up visits of 122 consecutive patients who underwent ICD implantation at our institute from April 1996 to June 2008, with (n = 42) or without (n = 80) DFT testing. Patients in the DFT group were less likely to be men (83.3% vs 96.3%, P < .031) than those in the non-DFT group. Conversely, the 2 groups were similar in age, left ventricular ejection fraction at baseline, functional class, and underlying cardiovascular disease. Results during a 12-month follow-up, 13 (31.0%) and 30 (37.5%) ventricular tachyarrhythmic episodes were recorded in the DFT and non-DFT groups, respectively (P = .472). Antitachycardia pacing (ATP) terminated most of episodes, reducing the need of defibrillation at 7.7% in the DFT group and 3.3% in the non-DFT group (P = .533). Similar percentages of inappropriate ATP interventions (7.1% vs 3.8%, P = .413) and shock deliveries (2.4% vs 5.0%, P = .659) were recorded between DFT and non-DFT groups.

CONCLUSIONS

At 1-year follow-up, the performance of DFT testing does not seem to add any significant efficacy advantage in patients undergoing ICD implantation. Prospective randomized trials and long-term follow-up are warranted to clarify whether routine DFT testing may be safely abandoned leading to a revision of current guidelines.