Defibrillation Threshold Testing Research Articles

No benefit of a dual coil over a single coil ICD lead: Evidence from the Sudden Cardiac Death in Heart Failure Trial

Dual coil implantable cardioverter-defibrillator (ICD) leads with a superior vena cava (SVC) electrode have been considered standard of care despite sparse data suggesting improved ICD defibrillation efficacy. SVC coils increase lead complexity, cost, risk of lead failure, and lead removal. To compare all-cause mortality, sudden cardiac death, implant defibrillation threshold (DFT) test energies, appropriate shock rates, and first shock efficacy for ventricular tachyarrhythmias for dual coil vs single coil leads in the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT). In SCD-HeFT, 811 patients with heart failure received a single lead transvenous ICD (Medtronic model 7223) and underwent protocol-driven DFT testing. The selection of a dual vs single coil right ventricular (RV) lead was at the physician's discretion. DFT data were available in 717 patients. Dual coil leads were used in 563 and single coil in 246 patients. After 45.5-month follow-up, overall mortality was similar (19.4% for dual coil vs 21.5% for single coil; adjusted hazard ratio 0.95; 95% confidence interval 0.68-1.34; P = .78). Sudden cardiac death was also similar (3.6% for dual coil vs 3.7% for single coil; P = .96). First shock efficacy was 82.2% vs 91.9% (dual coil vs single coil; unadjusted odds ratio 0.41; 95% confidence interval 0.15-1.13; P = .085). Mean DFT was 12.1 ± 4.7 J vs 12.8 ± 4.8 J (dual coil vs single coil; P = .087). In the SCD-HeFT, the addition of an SVC coil for left-sided implants was not associated with improved outcome measures. We advocate returning to single coil RV ICD leads as the standard of care to decrease chronic lead complications.

Detection of myocardial injury due to defi brillation threshold checking after insertion of implantable cardioverter/defi brillators

Aims Possible myocardial damage caused by defi brillation threshold (DFT) control and its extent after insertion of implantable cardioverter/defi brillators (ICD) is still a matter for debate. This study aimed to identify the eff ect of DFT checking during ICD implantation, compared with permanent pacemaker (PPM) implantation, on the magnitude of myocardial damage as assessed by cardiac troponin-T (cTNT) and CK-MB.Methods and results A total of 133 candidates for ICD implantation were enrolled in the ICD group (mean age 60.66 ± 12.25 years; males 111 [83.5%]) as well as 130 candidates in the PPM group (mean age 69.56 ± 12.86 years; males 64 [49.2%]). DFT was controlled in all of the ICD patients. Serum levels of cTNT and CK-MB were measured at baseline plus 8 and 24 hours following the procedure. The results were adjusted for age, gender, and other confounding factors. The amount of cTNT rise after 8 and 24 hours in the ICD group was signifi cantly higher than in the PPM group (p < 0.001 for both). These diff erences remained signifi cant after adjustment for confounding factors. The level of CK-MB rise after 8 and 24 hours was also signifi cantly higher in the ICD group, although it lost its signifi cance after adjustment for age, gender and other confounding variables. There was no signifi cant relationship between the amount of energy delivered and enzyme elevation.Conclusion Elevation of cTNT and CK-MB after the ICD implantation was signifi cantly higher than that after the PPM implantation and may be attributed to the DFT testing shock and resulting myocardial injury.

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Defibrillation Success Is Not Associated With Near Field Electrogram Complexity or Shock Timing

BackgroundIt has been suggested that more-complex fibrillation requires higher energy shocks to terminate. Furthermore, animal studies have demonstrated that shock timing also plays a role. The objective of this study was to test these assertions in a clinical context. MethodsNear- and far-field electrograms were collected during defibrillation threshold testing. Fibrillation complexity was measured by quantifying the organization in the signals with wavelet-based methods, scaling exponent, and cross-correlation analysis. Receiver operator characteristic curves were used to determine predictive value. The effect of the phase at which defibrillation shocks were applied was also determined. ResultsNo measure was able to classify whether a particular shock would be successful. All performed very poorly. Shock timing played no role in defibrillation outcome. ConclusionsSignal organization of a local electrogram and phase of shock delivery do not relate to minimum defibrillation shock energy immediately after ventricular fibrillation onset.

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

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. 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). 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.

Do we need defibrillation threshold testing?: A pilot study

Defibrillation threshold testing (DFT) is a standard procedure during implantable cardioverter defibrillator (ICD) implantation, however, it is not without risks. We compared the one-year follow-up period in ICD-implanted patients, with and without DFT performed during implantation, for preventive indication in regard to appropriate and inappropriate ICD detection and therapy. One group consisted of 20 patients without DFT; another was comprised of 20 patients where DFT had been performed. There was no difference in the development of ventricular tachyarrhythmias between the groups. Appropriate therapy of ICD was 100%. DFT is not a predictor for successful ICD detection and therapy of ventricular tachyarrhythmias.

Optimal Strength and Number of Shocks at Upper Limit of Vulnerability Testing Required to Predict High Defibrillation Threshold Without Inducing Ventricular Fibrillation

The upper limit of vulnerability (ULV) closely correlates with the defibrillation threshold (DFT). The aim of this study was to establish the optimal protocol for using the ULV test to predict high DFT (>20 J) without inducing ventricular fibrillation (VF). The 10-J and 15-J ULV test with 3 coupling intervals (-20, 0, and +20 ms to the peak of T-wave) and the DFT test were performed in 96 patients receiving implantable cardioverter defibrillator. ULV ≤ 10 J was confirmed in 47 (49%). ULV ≤ 15 J was confirmed in 70 (77%) of 91 patients (15-J ULV test could not be done in 5). The sensitivity and negative predictive value of both ULV >10 J and >15 J for predicting high DFT were 100%. The specificity and positive predictive value of ULV >15 J were higher than those for ULV >10 J (85% vs. 55%, 43% vs. 22%, respectively). The rate of VF inducibility for confirming ULV ≤ 15 J was lower than that for ULV ≤ 10 J (23% vs. 51%, P<0.0001). On analysis of single 15-J ULV test only at the peak of T-wave, VF was not induced in 79 of 91 patients, but 4 of these had high DFT. The 15-J ULV test with 3 coupling intervals could correctly identify high-DFT patients and reduce the necessity for VF induction at defibrillator implantation.

Role of Defibrillation Threshold Testing in the Contemporary Defibrillator Patient Population

Defibrillation threshold (DFT) testing has been performed to prove functionality of the implantable cardioverter defibrillator (ICD). Over the past years it has become increasingly controversial because of possible morbidity and mortality. The goal of this study was to determine unsuccessful shock testing and report strategies used to overcome these problems. A total of 314 patients with a de novo implantation of an ICD and 127 patients receiving a generator exchange were identified retrospectively. All patients underwent defibrillation threshold testing after induction of VF using a low-energy T-wave shock during the intervention, 2 shock tests after de novo implantations, 1 after generator change. A safety margin of 10 J or more was requested. Seven (2.3%) patients in the de novo group and 2 patients (1.4%) in the generator exchange group could not be defibrillated using the standard approach. All of those patients had either chronic amiodarone therapy, secondary prevention or a cardiac resynchronization therapy device (CRT). In univariate analysis, amiodarone therapy, dilated cardiomyopathy, and lower ejection fraction were predictors of failure. Our study's results as well as a review of the current literature favor shock testing, especially in patients with specific risk factors as mentioned above.

Predictors of High Defibrillation Threshold in the Modern Era

High defibrillation threshold (DFT) is a clinical problem in 1-8% of implantable cardioverter-defibrillator implants. Some clinicians and investigators question whether the benefits of routine DFT testing outweigh the risks. Identification of the predictors of elevated DFT may allow selective application of DFT testing. However, the clinical characteristics of patients with high DFT in the modern era have not been well-defined. All patients who underwent DFT testing in our institution during an 8-year period were reviewed for this retrospective study. High DFT was defined as less than a 10-J safety margin on initial testing. For each case, the two cases preceding and two cases following by the same implanter were selected as controls. Of the 2,138 patients who underwent DFT testing, 48 (2.2%) met criteria for high DFT. Compared to 192 control patients, patients with high DFT were more likely to be younger (P = 0.004), have nonischemic cardiomyopathy (P = 0.036), have a longer QRS interval (P = 0.026), and have a left ventricular ejection fraction (LVEF) ≤ 0.25 (P = 0.013). On multivariate analysis, only younger age (P = 0.016) and LVEF ≤ 0.25 (P = 0.010) remained statistically significant predictors of elevated DFT. High DFT was identified in 2.2% of ICD implants in our institution in recent years. Although younger age and depressed LVEF predicts this problem, elevated DFT occurred in patients of all ages and ejection fractions. Elimination of routine DFT testing appears to be premature given the prevalence and unpredictability of elevated DFT.

Effect of defibrillation threshold testing on heart failure hospitalization or death in the Multicenter Automatic Defibrillator Implantation Trial–Cardiac Resynchronization Therapy (MADIT-CRT)

Defibrillation threshold (DFT) testing is commonly practiced at the time of implantable cardioverter-defibrillator (ICD) implant. The clinical consequence of ICD shocks delivered during DFT testing is unknown. The purpose of this study was to determine the impact of ICD shocks and ICD shock energy level delivered during DFT testing in patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy (MADIT-CRT) on clinical outcomes. Patients who underwent DFT testing within 1 month of device implant were categorized by the number of ICD shocks delivered during DFT testing (0, 1, 2, ≥3 shocks) and according to high vs low (>20 J vs ≤20 J) energy ICD shocks. Clinical outcomes consisting of heart failure (HF) or death, death alone, HF alone, and ventricular tachycardia or ventricular fibrillation were analyzed in each group. DFT testing was performed in 1,659 patients within 1 month of device implant (1 shock in 365 patients, 2 shocks in 896 patients, 3+ shocks in 398 patients). High-energy ICD shocks were delivered in 609 patients. Increasing number of ICD shocks during DFT testing was not associated with an increase risk for the primary end-point of HF or death or for any of the secondary end-points of HF alone, VT/VF alone, or death. Delivery of high vs low-energy ICD shocks was not associated with adverse clinical outcomes. In patients with mild symptoms of HF, increasing number of ICD shocks and delivery of high energy ICD shocks during DFT testing was not associated with increased risk for HF or death or future VT/VF episodes.

Current is better than energy as predictor of success for biphasic defibrillatory shocks in a porcine model of ventricular fibrillation

ObjectiveThe evidence that monophasic defibrillation success is mainly determined by current is secure. However, modern defibrillators use biphasic waveforms. The aim of this study was to compare energy, peak voltage and peak current in predicting biphasic shock success in a porcine model of ventricular fibrillation (VF) where the impedance varies within a wide of ranges. MethodsIn 14 domestic male pigs weighing between 27 and 38kg, VF was electrically induced and untreated for 15s. Animals were randomized to receive defibrillation attempts from one of two defibrillators with different impedance compensation methods. A grouped up-and-down defibrillation threshold testing protocol was used to maintain the average success rate in the neighborhood of 50%. After a recovery interval of 5min, the testing sequence was repeated for a total of 60 test shocks for each animal. ResultsA high defibrillation success was observed when high peak current was delivered. The area under ROC curve for predicting shock success was 0.681 for peak current, 0.585 for peak voltage and 0.562 for energy. The odds ratio revealed that peak current was a better predictor (OR=1.321, p<0.001) for defibrillation outcome compared with energy (OR=0.979, p<0.001) and peak voltage (OR=1.000, p=0.69) when multivariable logistic regression was conducted. ConclusionIn this porcine model of VF within a wide range of transthoracic impedance, peak current was a better indicator for shock success than the currently used energy for biphasic defibrillatory shocks. This finding may encourage design of new current-based biphasic defibrillators.

Feasibility of Defibrillation and Automatic Arrhythmia Detection Using an Exclusively Subcutaneous Defibrillator System in Canines

This study reports the experimental process leading to development of an automatic totally subcutaneous implantable cardioverter defibrillator (SICD) system engineered for human use. Two studies were conducted to test defibrillation and detection feasibility of an SICD system located in the left chest. In the first study, 2 pockets were created in 15 canines for placement of an anterior electrode adjacent to the left edge of the sternum and a lateral electrode at the site along the axillary line between the 4th and 6th intercostal space. Stainless steel flat electrodes with active surface areas of 5, 10, 20, and 25 cm(2) or rod electrodes were subsequently positioned and the defibrillation threshold (DFT) was measured for multiple combinations. In the second study, the ability to induce, detect, and provide shock delivery in response to ventricular fibrillation (VF) using an SICD system engineered for clinical use was tested in 5 canines. One hundred and three DFT tests with 11 different dual electrode combinations were performed. All combinations terminated VF with a DFT of 35 ± 16 J (range: 9-79 J). Nineteen VF episodes were induced and recognized by the chronic SICD, leading to automatic capacitor charge and shock delivery in all cases. Subcutaneous defibrillation using different electrode combinations with shock energies less than 80 J terminated all induced VFs. An automatic SICD proved effective in detecting and activating shock delivery in all cases.

Cardiac Dysfunction and Prolonged Hemodynamic Deterioration After Implantable Cardioverter-Defibrillator Shock in Patients With Systolic Heart Failure

We investigated the acute effects of implantable cardioverter-defibrillator shock on myocardium, cardiac function, and hemodynamics in relation to left ventricular systolic function. We studied 50 patients who underwent implantable cardioverter-defibrillator implantation and defibrillation threshold (DFT) testing: 25 patients with left ventricular ejection fraction (LVEF) ≥ 45% and 25 patients with LVEF <45%. We measured cardiac biomarkers (creatine kinase, creatine kinase-MB, myoglobin, cardiac troponin T and I, and N-terminal probrain natriuretic peptide). Left ventricular relaxation was assessed by global longitudinal strain rate during the isovolumetric relaxation period using speckle-tracking echocardiography. Blood sampling and echocardiography were performed before, immediately after, and 5 minutes and 4 hours after DFT testing. Mean arterial pressure was measured directly during DFT testing. Cardiac biomarkers showed no significant changes in either group. LVEF was decreased until 5 minutes after DFT testing and had recovered to the baseline at 4 hours in the group with reduced LVEF (P<0.001), whereas LVEF reduction was not observed in the group with preserved LVEF (P=0.637). Global isovolumetric relaxation period was decreased until 5 minutes after DFT testing and had recovered to the baseline at 4 hours in both groups (preserved LVEF: 0.39 ± 0.14 versus 0.23 ± 0.13* versus 0.23 ± 0.13* versus 0.40 ± 0.13 s(-1), *P<0.001 versus baseline; reduced LVEF: 0.15 ± 0.05 versus 0.08 ± 0.04† versus 0.09 ± 0.04† versus 0.15 ± 0.05 s(-1), †P<0.001 versus baseline, repeated-measures ANOVA). Time to recovery of mean arterial pressure to the baseline was prolonged in the group with reduced LVEF (P<0.001). Implantable cardioverter-defibrillator shock transiently impairs cardiac function and hemodynamics especially in patients with systolic dysfunction, although significant tissue injury is not observed.

The Implantable Cardioverter-Defibrillator Minimalist

The implantable cardioverter-defibrillator (ICD) was devised to satisfy the unmet need for an effective, instantaneous therapy to prevent sudden cardiac death (SCD) due to ventricular fibrillation (VF) in at-risk, ambulatory patients. That therapy was a high-voltage electric shock delivered directly into the heart muscle. More than 3 decades later, shocks are still the defining operating characteristic of ICDs, and no other instantaneously effective therapy for VF exists. This elite status was clinched by large randomized clinical trials1,2 which demonstrated that ICDs improved mortality in patients with reduced left ventricular ejection fraction, regardless of pathogenesis or accompanying symptoms of heart failure (HF), by primary prevention of SCD due to ventricular tachyarrhythmia (VTA). Like bradycardia pacemakers for asystole, the ICD resides as a therapy genre of one, with no peer, and no competitor on the horizon. These sibling therapies for lethal heart rhythm disturbances will stand prominently among the greatest medical achievements of the 20th century. The ICD is a mature technology, and neither the technique nor the tools have changed much for several decades. Despite a certain evolutionary elegance of the operating system, the ICD is still a blunt instrument. Although it is true that some innovation has occurred, it is still a matter of a shock delivered by insulated metal conductors residing somewhere in direct proximity to the heart. No innovation beyond the fundamental of a timed shock for VF has proven to enhance mortality benefit. The basic design persists simply because no one can think of a suitable alternative and the self-satisfying aphorism that “shocks save lives.” Yet there is a growing intellectual dissatisfaction with the unintended consequences of this powerful, irreplaceable therapy. The stimulus for this self-inspection is an awareness of the very high morbidity risk overhead borne by the primary prevention patient, in particular, …

Vertebral artery dissection secondary to defibrillation threshold testing

We report a case of vertebral artery dissection presenting 2 days after ICD implantation with defibrillation threshold testing in a 57-year-old man with ischemic cardiomyopathy. The association between vertebral artery dissection and neck trauma and the role of DFT testing in ICD implantation are discussed.

Avoidance of defibrillation threshold testing at the time of internal defibrillator insertion: is it safe?

This article consists of a subject review supported by a short-term pilot study which was conducted prospectively to shed light into the controversial question regarding the necessity of having the defibrillation threshold measured at the time of the implantable cardioverter defibrillator implantation. Answering this question will have an important impact on reducing the well-documented morbidity and mortality, making the operation simpler and cost-effective.

Arrhythmia discrimination using hemoglobin spectroscopy in humans

Inappropriate therapies are frequently delivered by implantable cardioverter-defibrillators (ICDs). We have investigated muscle perfusion as a means of augmenting arrhythmia discrimination by using implanted near-infrared spectroscopy. To evaluate hemodynamic stability by monitoring muscle perfusion from within the ICD pocket, in fresh tissue and inside the scar capsule on preexisting ICD generators, during induced cardiac arrhythmias, in humans. The sensor was implanted on or under the pectoral muscle, during ICD defibrillation threshold testing. A microvascular oxygenation trend indicator (O2 Index) was computed during 74 induced ventricular fibrillation and 34 normal sinus rhythm episodes in 34 patients and also during 28 atrial and 90 ventricular overdrive pacing episodes as simulations of supraventricular and ventricular tachycardias, respectively. On average, the change in oxygenation, based on the O2 Index, was statistically significant (P <.003) from baseline within 3 seconds following cardiac arrest. An optimized O2 Index, used for detecting the hemodynamic trend, exhibited a decreasing trend during ventricular fibrillation (P <.0001) and was different from that during normal sinus rhythm (P <.0001). The sensitivity for the detection of ventricular fibrillation was 100%, and the specificity for the rejection of normal sinus rhythm was 82% in the presence of scar tissue on the optical sensor. For a 35-mm Hg drop in the mean arterial pressure as the threshold for hemodynamic instability, the specificity for the rejection of hemodynamically stable atrial and ventricular pacing episodes was 93% and 71%, respectively. An implantable near-infrared spectroscopic sensor may be useful for hemodynamic monitoring during cardiac arrhythmias to prevent inappropriate therapy.

A Plea for Delivery of High-Voltage Shocks During Implantable Cardioverter-Defibrillator Replacement or System Upgrade

We report the case of a faulty lead that led to failure to defibrillate during defibrillation threshold testing at the time of elective generator replacement. Standard lead measurements failed to detect the malfunction. Many centres perform neither defibrillation threshold testing nor commanded high-energy shock delivery. Even changes in the position of the lead in relation to the generator may cause problems that will go undetected without high-voltage shock delivery. We therefore caution against the wholesale abandonment of high-voltage shock testing in patients with pre-existing implanted leads.

Risk of defibrillation threshold testing in severe heart failure patient: A case of cardiac resynchronization therapy (CRT-D) with acute myocardial infarction

Defibrillation threshold (DFT) testing is usually recommended after device implantation to confirm appropriate implantable cardioverter defibrillator (ICD)/cardiac resynchronization therapy defibrillator (CRT-D) function [1,2]. However, induction of ventricular fibrillation may result in hemodynamic compromise, and cardioversion itself may cause myocardial injury [3,4]. We report on a CRT-D patient with acute myocardial infarction who died due to multiple organ failure 1 day after DFT testing. Our case emphasizes the importance of deciding whether DFT testing should be performed for patients with very severe heart failure in the acute stage of myocardial infarction.

Successful Reduction of a High Defibrillation Threshold by a Combined Implantation of a Subcutaneous Array and Azygos Vein Lead

A 72-year-old man with nonischemic cardiomyopathy was referred because his implantable cardioverter defibrillator had failed to terminate spontaneous ventricular fibrillation (VF). Defibrillation threshold (DFT) testing confirmed that 830-V shocks failed to defibrillate VF despite optimization of the biphasic waveform and reversal of shock polarity. The placement of a new right ventricular lead and the addition of a subcutaneous array failed to defibrillate VF at 830 V. The combination of a subcutaneous array and azygos vein coil successfully defibrillated VF. The mechanism for successful DFT reduction was likely greater current supplied to the posterior basal left ventricle by the azygos vein lead.