Defibrillation efficacy comparing a subcutaneous array electrode versus an "active can" implantable cardioverter defibrillator and a subcutaneous array electrode in addition to an "active can" implantable cardioverter defibrillator: results from active can versus array trials I and II

Non-traditional implantable cardioverter-defibrillator configurations and insertion techniques: a review of contemporary options

Implantable cardioverter-defibrillators (ICDs) have revolutionized the treatment of acquired or inherited cardiac diseases associated with a high risk of sudden cardiac death due to ventricular tachyarrhythmias. Contemporary ICD devices offer reliable arrhythmia detection and discrimination algorithms and deliver highly efficient tachytherapies. Percutaneously inserted transvenous defibrillator coils with pectoral generator placement are the first-line approach in the majority of adults due to their extensively documented clinical benefit and efficiency with comparably low periprocedural implantation risks as well as the option of providing pain-free tachycardia treatment via anti-tachycardia pacing (ATP), concomitant bradycardiaprotection, and incorporation in a cardiac resynchronization therapy if indicated. Yet, expanding ICD indications particularly among younger and more complex patient groups as well as the increasingly evident long-term consequences and complications associated with intravascular lead placements promoted the development of alternative ICD configurations. Most established in daily clinical practice is the subcutaneous ICD but other innovative extravascular approaches like epicardial, pericardial, extra-pleural, and most recently substernal defibrillator coil placements have been introduced as well to overcome shortcomings associated with traditional devices and allow for individualized treatment strategies tailored to the patients characteristics and needs. The review aims to provide practical solutions for common complications encountered with transvenous ICD systems including restricted venous access, high defibrillation/fibrillation thresholds (DFTs), and recurrent device infections. We summarize the contemporary options for non-traditional extravascular ICD configurations outlining indications, advantages, and disadvantages.

Uso Racional dos Cabos-Eletrodos na Estimulação Cardíaca Artificial

Introdução: Os dispositivos cardíacos eletrônicos implantáveis (DCEIs) são terapia consagrada para o tratamento de bradiarritmias, prevenção de morte súbita ou insuficiência cardíaca. Desde o primeiro implante de marcapasso transvenoso há mais de 60 anos, ocorreram avanços tecnológicos dos dispositivos e melhorias nas técnicas cirúrgicas. No entanto esse tipo de terapia ainda está associado a complicações significativas, a maioria relacionada ao implante dos cabos-eletrodos transvenosos. Objetivo: apresentar uma reflexão sobre como praticar o uso racional do implante de cabos-eletrodos e propor estratégias e alternativas para postergá-lo ou evitá-lo, com base nos conhecimentos atuais nos diversos campos da estimulação cardíaca artificial. Métodos: Revisão da literatura que utilizou artigos de 1995 a 2019, de diversas plataformas e revistas. Conclusão:Há a expectativa de que nos próximos anos ocorram avanços tecnológicos e de conhecimento no campo da estimulação leadless, permitindo que esses dispositivos sejam incorporados na prática clínica de maneira rotineira. Atualmente, se o implante de eletrodos ventriculares nos casos de doença do nó sinusal com condução atrioventricular preservada for racionalizado, o implante de eletrodos atriais nos cardiodesfibriladores implantáveis (CDI) sem necessidade de estimulação antibradicardia ou dos eletrodos ventriculares nos casos sem a necessidade de estimulação antitaquicardia (ATP) considerando o implante de CDIs subcutâneos, este artigo terá cumprido o seu papel.

Rational Use of Leads in Artificial Cardiac Pacing

Introduction: Cardiovascular implantable electronic device (CIEDs) are a proven therapy for the treatment of bradyarrhythmias, prevention of sudden death or heart failure. Since the first transvenous pacemaker implantation more than 60 years ago, technological advances in devices and improvements in surgical techniques have occurred. However, this type of therapy is still associated with significant complications, most of them related to the implantation of transvenous leads. Objective: To present a reflection on how to practice the rational use of lead implantation and propose strategies and alternatives to delay or avoid it, based on the current knowledge in the various fields of artificial cardiac stimulation. Methods: Review of literature that used articles from 1995 to 2019, from several platforms and periodicals. Conclusion: There is an expectation that in the coming years there will be technological and knowledge advances in the field of leadless stimulation, allowing these devices to be incorporated into clinical practice in a routine manner. Currently, if the implantation of ventricular electrodes in cases of sinus node disease with preserved atrioventricular conduction is rationalized, the implantation of atrial electrodes in implantable cardioverter-defibrillators (ICD) without the necessity of antibradicardia stimulation or ventricular electrodes in cases without the necessity of antitachycardia stimulation (ATP) considering the subcutaneous ICD implantation, this article will have fulfilled its role.

Higher defibrillation threshold in methamphetamine cardiomyopathy patients with implantable cardioverter-defibrillator

INTRODUCTION

Identification of patients with an increased risk of high defibrillation thresholds (DFTs) is important in planning implantable cardioverter-defibrillator (ICD) procedures. Clinical observations have suggested that patients with methamphetamine cardiomyopathy (MACMP) have significantly elevated defibrillation thresholds. We hypothesized that MACMP patients would have higher DFT thresholds than controls and would require procedural changes during ICD implantation to accommodate higher thresholds.

METHODS

We identified consecutive patients with MACMP undergoing ICD implantation at the academic center from 2003 to 2007. We then compared DFTs against age-and sex-matched controls.

RESULTS

The MACMP (n = 10) group showed significantly increased DFT thresholds (23.7 ± 6.7 J) compared with age and sex-matched controls (14.5 ± 4.6 J, p < 0.005). Additionally, patients with MACMP had evidence of more severe congestive heart failure, with increased B-type natrieutic protein (BNP) levels (1173 ± 784 vs 260 ± 349, p = 0.02) and decreased left ventricular ejection fraction (LVEF) (17.8 ± 9.4 vs 35.9 ± 15.2, p = 0.02). MACMP patients required high output devices than controls (50% versus 0%, p = 0.03). Differences between groups remained significant despite adjusting for LVEF.

CONCLUSIONS

Planning for ICD implantation should take into consideration a history of methamphetamine abuse, mandating DFT testing and empiric consideration of high output devices for such patients.

Thoracoscopic Implantation of An Array Electrode in the Pericardium Transverse Sinus to Reduce Defibrillation Threshold

Among the implantable cardioverter defibrillator recipients, there is still a subgroup of patients in whom the defibrillation threshold is too high and the maximal shock output of the implantable cardioverter defibrillator can fail to terminate a ventricular arrhythmia. We report a new thoracoscopic minimally invasive approach to place a standard array electrode in the transverse pericardial sinus of a patient implanted with a cardiac resynchronization and defibrillation therapy device with persistent high defibrillation threshold. This approach was developed to achieve very low shock impedance with a consequent increase in the current flow and reduction of defibrillation threshold.

Risk Factors for Inadequate Defibrillation Safety Margins Vary With the Underlying Cardiac Disease: Implications for Selective Testing Strategies

INTRODUCTION

In view of the shift from routine toward no or selective defibrillation testing, optimization of the current risk stratification for inadequate defibrillation safety margins (DSMs) could improve individualized testing decisions. Given the pathophysiological differences in myocardial substrate between ischemic and nonischemic heart disease (IHD/non-IHD) and the accompanying differences in clinical characteristics, we studied inadequate DSMs and their predictors in relation to the underlying etiology.

METHODS AND RESULTS

Cohort of routine defibrillation tests (n = 785) after first implantable cardioverter defibrillator (ICD)-implantations at the Radboud UMC (2005-2014). A defibrillation threshold >25 J was regarded as an inadequate DSM. In total, 4.3% of patients had an inadequate DSM; in IHD 2.5% versus 7.3% in non-IHD (P = 0.002). We identified a group of non-IHD patients at high risk (13-42% inadequate DSM); the remainder of the cohort (>70%) had a risk of only 2% (C-statistic entire cohort 0.74; C-statistic non-IHD 0.82). This was based upon two identified interaction terms: (1) non-IHD and age (aOR 0.94 [95% CI 0.91-0.97]); (2) non-IHD and the indexed left ventricular (LV) internal diastolic diameter (aOR 3.50 [95% CI 2.10-5.82]).

CONCLUSION

The present study on risk stratification for an inadequate DSM not only confirms the importance of making a distinction between IHD and non-IHD, but also shows that risk factors in an entire cohort (LV dilatation, age) may only apply to a subgroup (non-IHD). Appreciation of this concept could favorably affect current risk stratification. If confirmed, our approach may be used to optimize individualized testing decisions in an upcoming era of non-routine testing.

Incidence of ineffective safety margin testing (<10 J) and efficacy of routine subcutaneous array insertion during implantable cardioverter defibrillator implantation

The purpose of this study was to assess (1) the incidence of safety margin testing <10 J (SMT) and (2) the efficacy/safety of routinely adding a subcutaneous array (SQA) (Medtronic 6996SQ) for these patients.

Patients with SMT smaller than a 10-J safety margin from maximum output were considered to have very high readings and underwent SQA insertion. These patients were compared with the rest of the patients who had acceptable SMT (≥10 J).

A total of 616 patients underwent ICD implantation during the analysis period. Of those, 16 (2.6%) had SMT <10 J. By univariate analysis, younger age, and non-ischemic cardiomyopathy, were all significant predictors of SMT <10 J (p < 0.05). In all 16 cases, other methods to improve SMT prior to array insertion were attempted but failed for all patients: reversing shock polarity (n = 15), removing the superior vena cava coil (n = 14), reprogramming shock waveform (n = 9), and repositioning right ventricular lead (n = 9). Addition of the SQA successfully increased SMT to within safety margin for all patients (32 ± 2 versus 21 ± 3 J; p < 0.001). Follow-up (mean 48.1 ± 21 months) was available for all patients with SQA, only 2 cases with inappropriate shocks due to atrial fibrillation had to be noted. None of the patients experienced complications due to SQA implantation.

SMT <10 J occur in about 2.6% of patients undergoing ICD implantation. SQA insertion corrects this problem without procedural/mid-term complications.

Implantation of additional subcutaneous array electrode reduces defibrillation threshold in ICD patients - preliminary results

INTRODUCTION

Among the recipients of implantable cardioverter-defibrillators (ICDs), there is a group of patients in whom the defibrillation threshold (DFT) is too high to enable a sufficient safety margin between the DFT and the maximal available output of the device. The aim of the study was to investigate the ability of an additionally implanted single-coil subcutaneous array electrode to reduce the DFT in such patients.

MATERIAL AND METHODS

Medtronic 6996SQ electrode was implanted in 15 patients selected from our follow-up group of 741 ICD patients: 10 of them had insufficient post-implant DFT safety margin, and 5 had ineffective first maximal energy shock as recorded by the device. In 6 cases the patients had CRT-D devices, in 5 cases - dual-chamber ICDs, and in 4 cases - single-chamber ICDs. In all patients but one the defibrillating electrode was single-coil. In one patient it was dual-coil. The underlying disease was coronary artery disease in 10 patients, dilated cardiomyopathy in 4 patients and hypertrophic cardiomyopathy in 1 patient.

RESULTS

The subcutaneous electrode was successfully implanted in all the patients qualified for the procedure. No technical issues or perioperative complications were observed. Mean DFT was reduced from 33.3 ±4.1 J before the procedure to 25.3 ±4.4 J after the implantation procedure (p < 0.01).

CONCLUSIONS

Our results show that the use of a single-coil subcutaneous electrode to reduce the DFT is a safe and effective procedure. Further studies are necessary to confirm these results.

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.

Defibrillation efficacy of a subcutaneous array lead: A case report

We report a case of Brugada syndrome with a high defibrillation threshold (DFT) in whom a subcutaneous array lead was used to lower the DFT in combination with a transvenous right ventricular defibrillation lead. The patient had previously received pacemaker implantation due to sick sinus syndrome. An implantable cardioverter defibrillator (ICD) with a transvenous right ventricular defibrillation lead alone required a high DFT. A subcutaneous array lead improved defibrillation efficacy in combination with a right ventricular lead. These data suggest that a subcutaneous array lead facilitates implantation of an effective ICD lead system in patients requiring a high DFT.

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.

A comparison of the output characteristics of several implantable cardioverter-defibrillators

BACKGROUND

Implantable cardioverter-defibrillators (ICDs) are effective for primary and secondary prevention of sudden cardiac death due to ventricular arrhythmias. However, despite wide clinical use, there are no generally accepted standardized protocols to characterize and report the output capabilities of ICDs.

OBJECTIVE

The objective of this study was to measure and compare the output characteristics of standard-output and high-output ICDs from several manufacturers under a common set of conditions.

METHODS

The output characteristics of ICDs randomly selected from hospital stock were measured. The energy delivered for each shock to a range of fixed loads (25-75 Omega) was computed from the voltage waveform and the corresponding load.

RESULTS

Delivered energy varied by approximately 4 J over the range of loads tested and varied between devices (high-output 33.8-35 J; standard-output 26.7-28.6 J, at 50 Omega). Leading-edge voltage varied by approximately 6% over the range of loads tested and varied between devices (high-output 738-792 V; standard-output 593-797 V, at 50 Omega). Pulse width varied by a factor of approximately 3 over the range of loads tested and varied between devices (high-output 10-14.5 ms; standard-output 9-12.2 ms, at 50 Omega). Observed variations between devices and with load were significant (P <.001).

CONCLUSIONS

Potentially important differences in output characteristics of different ICD systems exist and merit further clinical investigation. The reporting of ICD output characteristics should be standardized. Additionally, it is recommended that manufacturers report output characteristics as a function of load over the typical range of patient loads clinically encountered.

Benefit of millisecond waveform durations for patients with high defibrillation thresholds

BACKGROUND

Patients with a high defibrillation threshold (DFT) present an atypical but vexing problem with regard to implantable cardioverter-defibrillator (ICD) therapy. Their implant procedures are lengthy and involve more risk of complications. These patients often sustain a reduced safety margin that may compromise their survival.

OBJECTIVES

The purpose of this study was to evaluate the use of fixed millisecond duration model-optimized biphasic waveforms compared with conventional tilt-based waveforms in patients having a high DFT.

METHODS

We compared a 65%/65% tilt biphasic waveform to a millisecond duration biphasic waveform based on the biphasic burping theory using a 90-microF shock capacitor.

RESULTS

Fifty-four patients were evaluated. Mean DFT with tilt was reduced from 11.0 +/- 5.5 J to 8.8 +/- 4.1 J, for a mean reduction of 20% (P < .0001). For the 13 patients with tilt-based DFTs > or = 15 J, DFT was reduced from 18.7 +/- 4.1 J to 13.4 +/- 3.5 J, for a mean DFT reduction of 28% (P = .009). The population peak DFT was reduced from 29.0 J to 17.5 J, for a 41% reduction (P = .03).

CONCLUSION

Use of simple millisecond biphasic waveforms instead of conventional tilt-based waveforms can lead to substantial reductions in DFT, especially in patients with high DFT.

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.

Long-term experience with subcutaneous ICD leads: a comparison among three different types of subcutaneous leads

ICDs provide protection against sudden cardiac death in patients with life-threatening arrhythmias. Nevertheless, efficacy of defibrillation remains an important issue to guarantee the future safety of patients who receive an ICD. There is a significant number of patients who need an additional subcutaneous lead to obtain a defibrillation safety margin of at least 10 J between the maximum output of the ICD and the energy needed for ventricular defibrillation. However, few data exists about the long-term performance of different types of subcutaneous leads. Therefore, the aim of this study was to analyze the long-term experience with three different types of subcutaneous leads. The study included 132 patients (109 men, 23 women; mean age 59.8 years [SD +/- 10.7 years]). All of them received a subcutaneous lead in addition to a single chamber or dual chamber ICD between October 1990 and April 2002. Two patients received a second subcutaneous lead after the first lead had been removed so that a total of 134 subcutaneous leads were evaluated. Inclusion criteria for the implantation of an additional subcutaneous lead were (1) unsuccessful ventricular defibrillation at implant without a subcutaneous lead, (2) insufficient safety margin (< 10 J) between the maximum output of the ICD and the energy needed for ventricular defibrillation, or (3) clinical evaluation of a new subcutaneous lead (Medtronic 13014). There were no significant differences between the three study groups with regard to age, sex, underlying cardiac disease, left ventricular ejection fraction, NYHA class assessment and clinical arrhythmia. The results of the DFT testing during follow-up (prehospital discharge test and 1 and 3 years) were compared to the baseline value obtained during the implantation procedure. All lead related complications were analyzed. Eighty-two single element subcutaneous array electrodes (SQ-A1), 31 subcutaneous three-finger electrodes (SQ-A3), and 21 subcutaneous patch electrodes (SQ-P) were implanted during the study period. The median follow-up was 1,499 days (25th percentile: 798 days, 75th percentile: 1,976 days) in the SQ-A1 group, 2,209 days (25th percentile: 1,242 days, 75th percentile: 2,710 days) in the SQ-A3 group, and 1,419 days (25th percentile: 787 days, 75th percentile: 2,838 days) in the SQ-P group. None of the three groups had a significant change of the DFT during follow-up compared to baseline. Major complications occurred in six (7.3%) patients in group SQ-A1 and in two (9.5%) patients in group SQ-P. There were no major complications in group SQ-A3. Kaplan-Meier curves analyzing freedom from subcutaneous lead related complications did not show a significant difference between the three study groups (P = 0.16). SQ-A1, SQ-A3, and SQ-P leads provide stable DFTs during long-term follow-up. Major complications are rare. However, a careful follow-up including chest radiographs at regular intervals is needed to detect potentially fatal complications like lead fractures.

Distal Right Ventricular Coil Position Reduces Defibrillation Thresholds

Distal RV Coil Position Reduces DFTs.

INTRODUCTION

Understanding the factors that affect defibrillation thresholds (DFTs) has important implications both for optimization of defibrillation efficacy and for the design of new transvenous leads. The aim of this prospective study was to test the hypothesis that defibrillation efficacy is improved with the right ventricular (RV) coil in a distal position compared with a more proximal RV coil position.

METHODS AND RESULTS

A novel defibrillation lead with three adjacent RV defibrillation coils (distal 0.8 cm, middle 3.7 cm, proximal 0.8 cm) was used for this study to permit comparison of DFTs with the proximal and distal RV coil positions without lead repositioning. In the distal RV configuration, the distal and middle RV coils were connected electrically as the anode for defibrillation. In the proximal RV configuration, the middle and proximal coils were the anode. A superior vena cava (SVC) coil and active can were connected electrically as the cathode (reversed polarity, RV-->Can+SVC). In each patient, the DFT was measured twice using a binary search protocol with the distal RV and proximal RV configurations, with the order of testing randomized. The study cohort consisted of 31 subjects (mean age 65 +/- 12 years, mean left ventricular ejection fraction 30% +/- 16%, 81% male predominance). The mean delivered energy (8.2 +/- 5.3 J vs 11.2 +/- 6.1 J), leading-edge voltage (335 +/- 109 V vs 393 +/- 118 V), and peak current (11.6 +/- 5.2 A vs 14.9 +/- 7.3 A) at DFT all were significantly lower with the distal RV configuration compared to the proximal RV configuration (P < 0.01 for all comparisons).

CONCLUSION

DFTs are significantly reduced with the distal RV configuration compared to the proximal RV configuration. Defibrillation leads should be designed with the shortest tip to coil distance that can be achieved without compromising ventricular fibrillation sensing.