Inadequate Defibrillation Safety Margin Research Articles

Defibrillation Safety Margin Testing in Patients With Congenital Heart Disease: ResultsFromthe NCDR.

This study analyzed the predictors of defibrillation safety margin (DSM) testing at the time of implantable cardioverter-defibrillator (ICD) insertion and factors associated with inadequate DSM in patients with congenital heart disease (CHD). There are few data about the prevalence and safety of DSM testing in those with CHD. A retrospective analysis was performed of all patients with atrial or ventricular septal defect, tetralogy of Fallot, transposition of the great vessels, Ebstein anomaly, or common ventricle undergoing a transvenous ICD procedure in the National Cardiovascular Data Registry (NCDR) ICD Registry from April 2010 to March 2016, and DSM testing was assessed. Inadequate DSM was defined as a lowest successful energy tested<10J than the maximum output of the ICD generator. Of all ICD recipients (N=7,024), DSM testing was performed in 52.0% (n=3,654). The mean lowest successful energy tested was 20.7 ± 7.3 J. Of those with DSM adequacy data available (n=3,623), an inadequate DSM occurred in 13.8% (n=501). After multivariable adjustment, DSM testing was not associated with in-hospital complications or death (odds ratio [OR]: 1.00; 95% confidence interval [CI]: 0.79 to 1.28) but was associated with lower odds of prolonged hospital stay (>3days) (OR: 0.71; 95%CI: 0.60 to 0.84; p<0.0001). An inadequate DSM was not associated with in-hospital death or complications (OR: 1.27; 95%CI: 0.79 to 2.04) or prolonged hospital stay (OR: 1.34; 95%CI: 0.995 to 1.81). DSM testing is being performed less frequently over time and seems safe in those with CHD. An inadequate DSM was not associated with worse in-hospital outcomes.

Prevalence, predictors and complications with defibrillation threshold testing in pediatric patients: Results from the NCDR

BackgroundThere are little data about the prevalence and safety of DFT testing in pediatric populations. We analyzed the predictors and outcomes of defibrillation threshold (DFT) testing at the time of implantable cardioverter-defibrillator (ICD) implant and factors associated with inadequate defibrillation safety margin (DSM) in pediatric patients. MethodsWe performed a retrospective analysis of initial transvenous ICD implantations in the National Cardiovascular Data Registry (NCDR) ICD Registry of patients ≤21 years. DSM was defined as the lowest successful energy tested <10 J than the maximum output of the ICD. Subjects were followed to hospital discharge. ResultsOf all ICD recipients (n = 3943), DFT testing was performed in 64.0% (n = 2522) though decreased over time. In those with DFT data available (n = 2500), an inadequate DSM occurred in 13.6% (n = 339). After multivariable adjustment, DFT testing was not associated with in-hospital complications or death (OR 0.789, 95% CI 0.579–1.076), but was associated with lower odds of prolonged hospital stay (>3 days) (OR 0.543, 95% CI 0.436–0.677). An inadequate DSM was associated with an increased risk of complications or death (OR 1.893, 95% CI 1.203–2.979) but not with a prolonged hospital stay (OR 1.307, 95% CI 0.878–1.947). ConclusionsIn the largest dataset of DFT testing in pediatric ICD recipients, we found that DFT testing use decreased over time and was not associated with an increase in in-hospital complications in pediatric patients. An inadequate DSM, however, was associated with a higher rate of in-hospital complications or death.

Abstract 17550: Predictors of High DFT in Single and Dual Coil Leads: Is There Still a Role for DFT Testing in Current Practice?

Background: Two recent changes in implantable cardioverter defibrillator (ICD) practice are the increased use of single coil leads and less frequent defibrillation threshold (DFT) testing at implantation. Single coil leads have higher mean DFTs which is of unclear clinical significance. Such leads were used in only a minority of subjects in SIMPLE, which showed no benefit of DFT testing. Hypothesis: Clinical characteristics can be used to predict patients at increased risk of an inadequate defibrillation safety margin with single coil leads. Methods: This analysis included 174 consecutive patients undergoing de novo left pectoral, single coil ICD implantation. A standardized modified step down testing algorithm at implantation was used to determine the delivered energy DFT. Logistic regression was used to assess predictors of DFT and of a high DFT (&gt; 25 J). Results: The patient population was 71.3 percent male and 35 percent African American (AA). The mean age was 60.8 ± 14.3 years and ejection fraction was 34.3 ± 15.6 percent. Of twelve clinical factors assessed, the univariate predictors of DFT were age (p &lt; 0.001), male sex (p &lt; 0.001) and AA race (p &lt; 0.001). After covariate adjustment, race, age and ejection fraction were found to be associated with a high DFT. The mean DFT (J) among AA was 16.1 ± 8.8 compared with 13.3 ± 6.5 for the rest of the cohort (p &lt; 0.05). Moreover, 13.1% of AAs had a high DFT compared with 1.7% for the rest of the cohort (p &lt; 0.005). Conclusions: Age, race and sex predict DFTs with single coil leads. AA are at increased risk for a high DFT and thus an inadequate defibrillation safety margin (&lt; 10 J) and should be considered for dual coil leads and/or defibrillation testing at implantation.

Predictors of an Inadequate Defibrillation Safety Margin at ICD Implantation: Insights From the National Cardiovascular Data Registry

BackgroundDefibrillation testing is often performed to establish effective arrhythmia termination, but predictors and consequences of an inadequate defibrillation safety margin (DSM) remain largely unknown. ObjectivesThe aims of this study were to develop a simple risk score predictive of an inadequate DSM at implantable cardioverter-defibrillator (ICD) implantation and to examine the association of an inadequate DSM with adverse events. MethodsA total of 132,477 ICD Registry implantations between 2010 and 2012 were analyzed. Using logistic regression models, factors most predictive of an inadequate DSM (defined as the lowest successful energy tested <10 J from maximal device output) were identified, and the association of an inadequate DSM with adverse events was evaluated. ResultsInadequate DSMs occurred in 12,397 patients (9.4%). A simple risk score composed of 8 easily identifiable variables characterized patients at high and low risk for an inadequate DSM, including (with assigned points) age <70 years (1 point); male sex (1 point); race: black (4 points), Hispanic (2 points), or other (1 point); New York Heart Association functional class III (1 point) or IV (3 points); no ischemic heart disease (2 points); renal dialysis (3 points); secondary prevention indication (1 point); and ICD type: single-chamber (2 points) or biventricular (1 point) device. An inadequate DSM was associated with greater odds of complications (odds ratio: 1.22; 95% confidence interval: 1.09 to 1.37; p = 0.0006), hospital stay >3 days (odds ratio: 1.24; 95% confidence interval: 1.19 to 1.30; p < 0.0001), and in-hospital mortality (odds ratio: 1.96; 95% confidence interval: 1.63 to 2.36; p < 0.0001). ConclusionsA simple risk score identified ICD recipients at risk for an inadequate DSM. An inadequate DSM was associated with an increased risk for in-hospital adverse events.

Echocardiographic parameters to predict inadequate defibrillation safety margin in patients receiving implantable cardioverter defibrillators for primary prevention

Implantable cardioverter defibrillators (ICDs) have become an important part of the management of patients with congestive heart failure. At the time of ICD implantation, ventricular fibrillation (VF) is induced to assess adequate energy required for defibrillation. There are multiple parameters which influence the defibrillation safety margin (DSM); however, these factors are not well-established when ICDs are implanted for the primary prevention of sudden cardiac death (SCD) in patients with severe systolic dysfunction. We evaluated multiple clinical and echocardiographic parameters as predictors of adequate DSM in patients referred for ICD implantation for the primary prevention of SCD. We prospectively enrolled 41 patients for ICD implantation with clinical indications for the primary prevention of SCD. Two blinded independent readers evaluated the prespecified echocardiographic parameters. These included left ventricular (LV) mass, indices of right ventricular and LV systolic and diastolic functions, and LV geometric dimensions. Basic clinical demographics, including age, gender, comorbidities, and etiology of cardiomyopathy, were also evaluated. DSM was established using our standard protocol for defibrillation testing which includes VF with successful first shock terminating VF at a value at least 10J below the maximum output of the implanted device. High defibrillation thresholds (DFT) were defined as >21J. The mean age is 61.8 ± 14.7years, with men comprising the majority of the patients (73%). The only clinical variables which predicted the high DFT were age (in years) (54.5 ± 17.5 vs. 65.7 ± 11.3, p = 0.044), QRS duration (in milliseconds) (116.0 ± 29.5 vs. 110.5 ± 21.8, p = 0.03), LV mass (in grams) (241.0 ± 77.9 vs. 181.9 ± 52.3, p = 0.006), and LV mass index (in grams per square meter) (111.1 ± 38.2 vs. 86.4 ± 21.1, p = 0.02). On multivariate logistic regression analysis, LV mass was the only independent predictor of low DFT (≤22J) in patients with ICD implanted for the primary prevention of SCD. LV mass may help predict an adequate DSM in patients who are referred for ICD implantation for the primary prevention of SCD. These results may help distinguish the patients who may require high-energy devices prior to the implantation procedure. These results may help distinguish patients requiring high-energy devices, coils, or advanced programming prior to implantation and appropriate referral to electrophysiologists.

Automated Vulnerability Testing Identifies Patients With Inadequate Defibrillation Safety Margin

Implantable cardioverter-defibrillator system efficacy is tested at implant by induction of ventricular fibrillation (VF). Defibrillation safety margin can be assessed without VF induction using upper limit of vulnerability methods, but these methods have required manual determination of T-wave timing. To test the feasibility of an inductionless system of implant testing, a multicenter prospective study of an automated vulnerability safety margin system was conducted, which measured T-wave timing using an intracardiac electrogram during a ventricular pacing train. The system delivered up to 4 T-wave shocks of 18 J. Lack of VF induction by all 4 shocks was considered evidence of defibrillation adequacy. Patients subsequently underwent conventional defibrillation testing to meet a standard implant criterion. The 95% lower CI for defibrillation success at 25 J for noninduced patients was found using Bayesian statistics. Sixty patients were enrolled at 6 centers. Vulnerability testing and defibrillation success results were obtained from 54 patients. Vulnerability testing induced VF in 10 (19%) patients, of whom 2 required system revision. All patients not induced by vulnerability testing were successfully defibrillated twice at ≤25 J. The Bayesian credible interval was 97% to 100% for the population success rate of defibrillation at 25 J for automated vulnerability safety margin noninduced patients. An automated system identified all patients who failed conventional safety margin testing, while inducing only 19% of patients. Although limited by sample size, this study suggests the feasibility of automated implant testing that substantially reduces the need for VF induction in patients receiving implantable cardioverter-defibrillators.

Pre-discharge defibrillation testing: clinically important or obsolete?

This editorial refers to ‘Pre-hospital discharge testing after implantable cardioverter defibrillator implantation: A measure of safety or out of date? A retrospective analysis of 975 patients’ by M. Guenther et al. , on page 217 One of the most controversial and hotly debated topics in implantable cardioverter-defibrillator (ICD) management is the role of defibrillation testing. As with most areas of clinical controversy, the lack of controlled studies to guide the decision process is largely responsible for the ongoing differences in opinion. In the early period of ICD use, defibrillation testing was mandatory given the frequency of shocks, high defibrillation thresholds (DFTs) with monophasic waveforms and the relatively unsophisticated sensing algorithms for the detection of ventricular fibrillation (VF). An inadequate defibrillation safety margin was associated with worse outcomes.1 In the primary prevention era this mandate is less clear. Most patients will not have an appropriate discharge over the first 3–5 years of follow-up2 and defibrillation systems have improved significantly so that failed shocks are now infrequent events. The use of …

Induction by direct current pulse versus 50-Hz pacing on ventricular fibrillation and defibrillation

Ventricular fibrillation (VF) induced by different modes of induction may have different characteristics and defibrillation thresholds. This study compares the cycle lengths and defibrillation of VF induced by direct current (DC) pulses vs 50Hz. We compared induction by DC pulses and 50-Hz pacing in this single-centre observational study of 259 consecutive patients with implantable cardioverter defibrillators in 2007-2008. Patients with inadequate defibrillation safety margin (DSM), defined as unsuccessful defibrillation at 25J, were identified. Of the 259 patients, 132 underwent induction with DC pulses and 127 with 50-Hz pacing. DC pulses induced VF of shorter cycle lengths (207 ± 16 vs 231 ± 24ms, p < 0.001) compared to 50-Hz pacing. There were 17 patients (6.6%) with inadequate DSM-13/132 (9.8%) with DC pulse vs 4/127 (3.1%) with 50-Hz pacing (p < 0.001). The induced VF cycle lengths were shorter in patients with inadequate DSM (186 ± 25 vs 221 ± 21ms, p < 0.001). On multivariate analysis, only the induced VF cycle length (p = 0.002) was independently associated with inadequate DSM. VF of shorter cycle lengths is independently associated with inadequate DSM. DC pulses are associated with greater proportion of patients with inadequate DSM as it induces VF of shorter cycle lengths compared to 50-Hz pacing.

The Effect of Dofetilide on Ventricular Defibrillation Thresholds

High defibrillation threshold (DFT) with an inadequate defibrillation safety margin remains an infrequent but troubling problem associated with defibrillator implantation. Dofetilide is a selective class III antiarrhythmic drug that reduces DFTs in a canine model. We hypothesized that dofetilide would reduce DFTs in humans, obviating the need for complex lead systems. Sixteen consecutive patients with DFTs > or =20 J delivered energy at implant-received dofetilide therapy and underwent follow-up DFT testing acutely following drug loading and/or chronically (128 +/- 94 days). Amiodarone was discontinued in four patients at implantation. With dofetilide, DFTs decreased from 28 +/- 4 J to 19 +/- 7 J (P < 0.0001), resulting in a safety margin of 15 +/- 8 J for the implanted devices. Five patients subsequently had spontaneous arrhythmias terminated successfully with shocks. Dofetilide reduces DFTs sufficiently to prevent the need for more complex lead systems. This strategy should be considered when an inadequate defibrillation safety margin is present.

The Dilemma of ICD Implant Testing

Ventricular fibrillation (VF) has been induced at implantable cardioverter defibrillator (ICD) implant to ensure reliable sensing, detection, and defibrillation. Despite its risks, the value was self-evident for early ICDs: failure of defibrillation was common, recipients had a high risk of ventricular tachycardia (VT) or VF, and the only therapy for rapid VT or VF was a shock. Today, failure of defibrillation is rare, the risk of VT/VF is lower in some recipients, antitachycardia pacing is applied for fast VT, and vulnerability testing permits assessment of defibrillation efficacy without inducing VF in most patients. This review reappraises ICD implant testing. At implant, defibrillation success is influenced by both predictable and unpredictable factors, including those related to the patient, ICD system, drugs, and complications. For left pectoral implants of high-output ICDs, the probability of passing a 10 J safety margin is approximately 95%, the probability that a maximum output shock will defibrillate is approximately 99%, and the incidence of system revision based on testing is < or = 5%. Bayes' Theorem predicts that implant testing identifies < or = 50% of patients at high risk for unsuccessful defibrillation. Most patients who fail implant criteria have false negative tests and may undergo unnecessary revision of their ICD systems. The first-shock success rate for spontaneous VT/VF ranges from 83% to 93%, lower than that for induced VF. Thus, shocks for spontaneous VT/VF fail for reasons that are not evaluated at implant. Whether system revision based on implant testing improves this success rate is unknown. The risks of implant testing include those related to VF and those related to shocks alone. The former may be due to circulatory arrest alone or the combination of circulatory arrest and shocks. Vulnerability testing reduces risks related to VF, but not those related to shocks. Mortality from implant testing probably is 0.1-0.2%. Overall, VF should be induced to assess sensing in approximately 5% of ICD recipients. Defibrillation or vulnerability testing is indicated in 20-40% of recipients who can be identified as having a higher-than-usual probability of an inadequate defibrillation safety margin based on patient-specific factors. However, implant testing is too risky in approximately 5% of recipients and may not be worth the risks in 10-30%. In 25-50% of ICD recipients, testing cannot be identified as either critical or contraindicated.

Defibrillator Implantation Without Induction of Ventricular Fibrillation

An increasing number of cardiac electrophysiologists are fortunate not to have endured the challenges of implanting monophasic waveform cardioverter-defibrillators (ICDs). With early technology, ICDs were routinely tested during the implantation procedure and then again before discharge, with a not-infrequent need for system revisions. With transvenous, high-output devices and biphasic shocks, the number of patients who have an inadequate defibrillation safety margin (DSM) has become so small that questions have been raised about the need for testing at all. However, given the fact that ICDs are designed to be potentially lifesaving, it is incumbent on physicians to obtain a high level of assurance that the device will work as designed if needed. It also should be noted that all clinical trials of ICD therapy for the prevention of sudden cardiac death incorporated testing for the adequacy of the DSM. Article p 2382 Despite the fact that we usually call the sequence of induction of ventricular fibrillation (VF) and defibrillation at different energies in the electrophysiology laboratory “defibrillation threshold testing,” it is, in fact, usually a DSM that is determined.1 Particularly with the typical protocol of 2 defibrillations at a minimum of 10 J below the maximum output of the device, a true probability curve for defibrillation success cannot be constructed. Regardless, this protocol is well accepted in practice. An alternative approach is upper limit of vulnerability testing, which closely correlates with the defibrillation threshold.2 This method requires only 1 initiation of VF, but strictly performed, multiple shocks may need to be delivered before VF is induced and the energy corresponding to the upper limit of vulnerability is determined. In the present issue of Circulation , Day et al3 present the results of the Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation (ASSURE) …

A Biventricular ICD System with Biventricular Defibrillation

We describe the case of a 59-year-old gentleman with severe dilated cardiomyopathy requiring implantation of a dual-chamber biventricular implantable cardioverter-defibrillator (ICD). High defibrillation thresholds (DFT) were encountered at implant with an inadequate defibrillation safety margin. Testing of all possible shock vectors/polarities with and without the SVC coil and optimization of the distal RV coil position all proved inadequate. A satisfactory defibrillation safety margin was achieved following placement of a second lead in the coronary sinus to enable biventricular defibrillation. This case highlights an additional strategy for combating high DFTs and is an option even in dual-chamber biventricular ICD systems.