A simplified, single-lead unipolar transvenous cardioversion-defibrillation system

[History of the implantable cardioverter-defibrillator in Germany]

The implantable cardioverter-defibrillator (ICD) was a breakthrough in the prevention of sudden cardiac death. After years of technical development in the USA, Michel Mirowski succeeded in proving reliable automatic defibrillation of ventricular tachyarrhythmias through initial human implantations in 1980, despite many obstacles. Nearly 4 years later, the first patients received ICDs at multiple centers in Germany. Subsequently, outside the USA, Germany became the country with highest implantation rates. The absolute number of implantations remained small as long as implantations required epicardial defibrillation electrodes and therefore thoracotomy by cardiac surgeons. Pacemaker-like implantation using a transvenous defibrillation electrode with a pectoral ICD became feasible in the early 1990s pushing implantation rates to the next level. Technical advancements were accompanied by clinical research in Germany, and often, the first-in-human studies were conducted in Germany. In 1991, the first guidelines for indications were established in the USA and Germany. Several randomized studies on indications were published between 1996 and 2009, mostly led by American teams with German participation, but also under German leadership (CASH, CAT, DINAMIT, IRIS). The DANISH study in 2016 questioned the results of these long-standing studies. Instead of providing ICDs to patients using a broad indication, future efforts aim to identify patients who, despite optimal medical therapy, cardiac resynchronization therapy (CRT), and/or catheter ablation, need protection against sudden cardiac death. Risk scores incorporating myocardial scars in magnetic resonance imaging (MRI) and genetic information are expected to contribute to more individualized and effective indications.

Development of the Implantable Cardioverter-Defibrillator: JACC Historical Breakthroughs in Perspective

Implantable cardioverter-defibrillators (ICDs) represent transformational technology, arguably the most significant advance in cardiovascular medicine in 50 years. The vision and determination of pioneers Mirowski and Mower was fundamental to this monumental achievement, working with limited resources and confronted by skepticism/criticism from medical establishment. The inventors were followed >35 years in which a multitude of innovative clinical scientists and engineers introduced technological advances leading to the sophisticated devices in practice today. A pivotal patient experiment with automated termination of ventricular fibrillation (1980) led to U.S. Food and Drug Administration approval. Transvenous lead systems converted ICDs from thoracotomy-based secondary prevention to primary prevention of sudden death devices in countless patients worldwide. ICD acceptance was solidified by prospective randomized controlled trials showing reduced mortality superior to antiarrhythmic drugs. ICDs eventually expanded from coronary disease to inherited arrhythmia conditions (eg, hypertrophic cardiomyopathy). The ICD breakthrough story demonstrates how significant progress is possible in medicine against all odds, given fearless imagination to pursue novel ideas that conflict with accepted wisdom.

Safety and feasibility of implanting a transvenous implantable cardioverter defibrillator (TV-ICD) in the left axilla

BACKGROUND

Transvenous implantable cardioverter defibrillator (TV-ICD) systems are commonly implanted in the left anterior chest because of an easier implantation and better defibrillation threshold. This study aimed to evaluate the safety and feasibility of left axillary implantations of TV-ICD systems.

METHODS

We performed left axillary TV-ICD implantations and compared that to the major complication rate and operation time of the conventional TV-ICD implantation site (left anterior chest). The electrical parameter trends were also assessed in the left axilla group.

RESULTS

Seventy-six consecutive patients were evaluated for the analysis. Thirty-one patients had their system implanted in the left axilla and the reasons for the implantations included 29 patients for cosmetic reasons and two for post-infection conditions. The operation time and major complication rate were similar between the two groups (left anterior chest vs. left axilla: 134±62.4 min vs. 114±33.5 min, p = .11, 1/45 patient, 2.2% [pocket hematoma] vs. 1/31 patient, 3.2% [lead dislodgement], p = .77). During the follow up period (4.9±2.3years), no lead interruptions were observed in either group. The electrical lead parameters at the time of the implantation and follow up were similar in the study group (R wave sensing 20.8±33.4 vs. 11.2±7.42 mv, p = .34; lead impedance 464±64.7 vs. 418±135ohm, p = .22; pacing threshold [at 0.4 ms] 1.0±0.76 vs. 1.21±0.93V, p = .49).

CONCLUSION

TV-ICD implantations in the left axilla were performed safely without increasing the operation time as compared to the conventional ICD implantation site. ICD implantations in the left axilla are an alternative in those not suitable for implanting TV-ICDs in the conventional implantation site.

Effectiveness of single- vs dual-coil implantable defibrillator leads: An observational analysis from the SIMPLE study

INTRODUCTION

Dual-coil leads (DC-leads) were the standard of choice since the first nonthoracotomy implantable cardioverter/defibrillator (ICD). We used contemporary data to determine if DC-leads offer any advantage over single-coil leads (SC-leads), in terms of defibrillation efficacy, safety, clinical outcome, and complication rates.

METHODS AND RESULTS

In the Shockless IMPLant Evaluation study, 2500 patients received a first implanted ICD and were randomized to implantation with or without defibrillation testing. Two thousand and four hundred seventy-five patients received SC-coil or DC-coil leads (SC-leads in 1025/2475 patients; 41.4%). In patients who underwent defibrillation testing (n = 1204), patients with both lead types were equally likely to achieve an adequate defibrillation safety margin (88.8% vs 91.2%; P = 0.16). There was no overall effect of lead type on the primary study endpoint of "failed appropriate shock or arrhythmic death" (adjusted HR 1.18; 95% CI, 0.86-1.62; P = 0.300), and on all-cause mortality (SC-leads: 5.34%/year; DC-leads: 5.48%/year; adjusted HR 1.16; 95% CI, 0.94-1.43; P = 0.168). However, among patients without prior heart failure (HF), and SC-leads had a significantly higher risk of failed appropriate shock or arrhythmic death (adjusted HR 7.02; 95% CI, 2.41-20.5). There were no differences in complication rates.

CONCLUSION

In this nonrandomized evaluation, there was no overall difference in defibrillation efficacy, safety, outcome, and complication rates between SC-leads and DC-leads. However, DC-leads were associated with a reduction in the composite of failed appropriate shock or arrhythmic death in the subgroup of non-HF patients. Considering riskier future lead extraction with DC-leads, SC-leads appears to be preferable in the majority of patients.

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.

Blood pressure and heart rate immediately after termination of short-term ventricular fibrillation

BACKGROUND

Implantable cardioverter/defibrillators (ICDs) can detect ventricular fibrillation (VF) and terminate it. For determining the optimal defibrillation threshold, ventricular fibrillation is repetitively induced and terminated with DC shocks. Depending on the protocol, several fibrillation/defibrillation sequences are mandatory before the final implantation of an ICD. This procedure provides an elegant human model of circulatory arrest and resuscitation.

PATIENTS AND METHODS

In anesthetized 73 patients (15 females) of on the average 60+/-11 years, the end-expiratory pressure was set to zero. Left ventricular pressure (LVP) was monitored with a microtip-catheter, central venous pressure (CVP) through a cannula which was advanced into the superior V. cava. ECG was recorded. After testing, a monoexponential function was found to best fit the time courses of LVP, CVP and heart rate. Data are mean+/-S.D.

RESULTS

After termination of circulatory arrest, peak LVP increased with a time constant tau of 9.2+/-4.2 beats, CVP decreased with tau=2.8+/-1.5 beats, and RR-intervals decreased with tau=4.3+/-3.5 beats. Correlations between prefibrillatory values and steady-state values after termination of fibrillation were high: peak LVP: r=0.78; CVP: r=0.95; RRI: r=0.82.

SUMMARY

After DC termination of VF, the heart 'finds' relatively quickly a steady-state rhythm at the prefibrillatory level (22 beats), thereby normalizing CVP almost in parallel (14 beats). Peak LVP plateaus only after about 40 beats, although reasonable arterial pressures are reached within the first beats. Our data are limited to periods of ventricular fibrillation of no longer than 60s, which limits the generalisability to the setting of clinical cardiac arrest.

No benefit from defibrillation threshold testing in the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial)

OBJECTIVES

This study investigated whether defibrillation threshold (DFT) testing during implantable cardioverter-defibrillator (ICD) implantation predicts clinical outcomes.

BACKGROUND

Defibrillation testing is often performed during insertion of ICDs to confirm shock efficacy. There are no prospective data to suggest that this procedure improves outcomes when modern ICDs are implanted for primary prevention of sudden death.

METHODS

The analysis included the 811 patients who were randomized to the ICD arm of the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) and had the device implanted. The DFT testing protocol in SCD-HeFT was designed to limit shock testing in a primary prevention heart failure population.

RESULTS

Baseline DFT data were available for 717 patients (88.4%). All 717 patients had a DFT of < or =30 J, the maximum output of the device in this study. The DFT was < or =20 J in 97.8% of patients. There was no survival difference between patients with a lower DFT (< or =10 J, n = 547) and a higher DFT (>10 J, n = 170) (p = 0.41). First shock efficacy was 83.0% for the first clinical ventricular tachyarrhythmia event; there were no differences in shock efficacies when the cohort was subdivided by baseline DFT.

CONCLUSIONS

Low baseline DFTs were obtained in patients with stable, optimally treated heart failure during ICD implantation for primary prevention of sudden death. First shock efficacy for ventricular tachyarrhythmias was high regardless of baseline DFT testing results. Baseline DFT testing did not predict long-term mortality or shock efficacy in this study.

Comparison of defibrillation efficacy and survival associated with right versus left pectoral placement for implantable defibrillators

The preferred location for an implantable cardioverter-defibrillator (ICD) generator is the left pectoral region as a result of the shock vector formed by the active can and the lead system. However, a right pectoral site is necessary when left-sided implantation is contraindicated. The Low Energy Safety Study was a prospective, randomized trial conducted to assess chronic defibrillation efficacy in 627 patients, including 37 (5.9%) who received right pectoral implants and 590 (94.1%) who received left pectoral implants. Patients were followed for a mean of 24 +/- 13 months. There were no significant differences observed between patients who received left versus right pectoral implants in age, gender, indications, New York Heart Association classification, or ejection fraction. Patients who received a right pectoral implant had higher defibrillation thresholds at implantation (10.6 +/- 3.8 J) than those who received a left pectoral implant (8.9 +/- 4.2 J, p = 0.01) despite similar shock impedances. The conversion efficacy for spontaneous arrhythmia episodes among patients who received right and left pectoral implants were not significantly different (33 of 33 [100%] vs 255 of 263 [97%], respectively; p = 0.31). In addition, the conversion efficacy for induced ventricular fibrillation episodes were also similar (187 of 188 [99%] on the right vs 2429 of 2475 [98%] on the left, p = 0.18). However, the all-cause mortality rate was higher for patients who received right-sided implants (hazard ratio 1.93, p <0.004). In conclusion, defibrillation thresholds are higher with right pectoral implants compared with left-sided implants, but with a proper energy safety margin, there are no significant differences in spontaneous or induced shock conversion efficacy. However, the near doubling of the mortality rate among patients with right-sided implants needs to be considered when recommending such device therapy.

Effect of an active abdominal pulse generator on defibrillation thresholds with a dual-coil, transvenous ICD lead system

INTRODUCTION

Many patients with implantable cardioverter defibrillators (ICDs) have older lead systems, which are usually not replaced at the time of pulse generator replacement unless a malfunction is noted. Therefore, optimization of defibrillation with these lead systems is clinically important. The objective of this prospective study was to determine if an active abdominal pulse generator (Can) affects chronic defibrillation thresholds (DFTs) with a dual-coil, transvenous ICD lead system.

METHODS AND RESULTS

The study population consisted of 39 patients who presented for routine abdominal pulse generator replacement. Each patient underwent two assessments of DFT using a step-down protocol, with the order of testing randomized. The distal right ventricular (RV) coil was the anode for the first phase of the biphasic shocks. The proximal superior vena cava (SVC) coil was the cathode for the Lead Alone configuration (RV --> SVC). For the Active Can configuration, the SVC coil and Can were connected electrically as the cathode (RV --> SVC + Can). The Active Can configuration was associated with a significant decrease in shock impedance (39.5 +/- 5.8 Omega vs. 50.0 +/- 7.6 Omega, P < 0.01) and a significant increase in peak current (8.3 +/- 2.6 A vs. 7.2 +/- 2.4 A, P < 0.01). There was no significant difference in DFT energy (9.0 +/- 4.6 J vs. 9.8 +/- 5.2 J) or leading edge voltage (319 +/- 86 V vs. 315 +/- 83 V). An adequate safety margin for defibrillation (> or =10 J) was present in all patients with both shocking configurations.

CONCLUSION

DFTs are similar with the Active Can and Lead Alone configurations when a dual-coil, transvenous lead is used with a left abdominal pulse generator. Since most commercially available ICDs are only available with an active can, our data support the use of an active can device with this lead system for patients who present for routine pulse generator replacement.

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.

Intraoperative testing of the implantable cardioverter-defibrillator: how much is enough?

INTRODUCTION

Defibrillation testing of the implantable cardioverter-defibrillator (ICD) is considered a standard and required practice at the time of implantation. How much testing, if any in some cases, should be performed, however, remains unknown.

METHODS AND RESULTS

Included in this retrospective analysis were 835 patients (77% men; age 65 +/- 13 years) who received transvenous ICDs between January 1996 and December 2003. One hundred twenty-nine (15.5%) had intraoperative defibrillation threshold (DFT) testing, 503 (60.2%) had limited defibrillation safety margin testing, and 203 (24.3%) had no defibrillation testing. We compared the outcome (success of ICD therapies against spontaneous VT/VF events and survival) of the three groups of patients, who in some respects had important clinical differences. The success of the first delivered shocks against VT/VF was similar for DFT (91%), safety margin testing (91%), and no-testing (92%) groups; and the second shocks terminated the remaining episodes in all three groups. Sudden-death-free survival rates were similar in the three groups, however, the overall long-term survival rate was significantly lower in the no-testing group (58%) than in the DFT (74%) and safety margin testing (69%) groups (P < 0.0005). Multivariate analysis found no strong predictors of sudden death, but there were several independent predictors of overall mortality including lack of ICD testing (HR: 2.031, CI: 1.253-3.290, P = 0.004).

CONCLUSION

In this select patient cohort, success of ICD therapies and sudden-death-free survival were similar in patients who had DFT, safety margin testing, and no testing, but overall survival was significantly lower in the no-testing group. Thus in the absence of prospective mortality data, a minimum of safety margin ICD testing should remain standard practice.

Implantable Cardioverter Defibrillator Therapy

Sudden cardiac death (SCD) is a major healthcare problem worldwide. The majority of SCD events occur in patients with clinically recognized heart disease and most episodes result from ventricular tachyarrhythmias. Implantable cardioverter defibrillator (ICD) therapy prevents SCD in specific patient populations. Significant progress in the design and technology has been made since the Food and Drug Administration first approved the ICD in 1985. First-generation ICDs were large, were implanted in the abdomen, required a thoracotomy for placing epicardial defibrillation patches, and were nonprogrammable. Contemporary ICDs have been substantially downsized, are implanted via a transvenous approach, and are multiprogrammable. Device implantation has been simplified to be similar to that of a permanent pacemaker. In addition to treating life-threatening ventricular arrhythmias, ICDs now treat bradyarrhythmias, atrial arrhythmias, and congestive heart failure. The purpose of this article is to describe the evidence supporting the use of ICD therapy and to explain the current devices used in clinical practice.

Defibrillation threshold testing: is it really necessary at the time of implantable cardioverter-defibrillator insertion?

OBJECTIVES

The purpose of this study was to (1) determine how often implantable cardioverter-defibrillator (ICD) system modifications were needed to obtain an adequate safety margin for defibrillation, (2) identify how often and for what indications defibrillation threshold (DFT) testing was not performed, and (3) identify factors predicting the need for modification.

BACKGROUND

Ventricular fibrillation (VF) typically is induced at the time of ICD insertion. Although DFT testing often is minimized, a safety margin of 10 J has been utilized as a standard of care. However, current devices offer technology such as biphasic waveforms and high outputs, and the need for testing has been questioned.

METHODS

We reviewed the records of the last 1,139 patients undergoing initial ICD placement, generator replacement, or revision.

RESULTS

Seventy-one patients (6.2%) were identified as having an unacceptably high DFT (<10 J safety margin) requiring intervention, and some required >1 modification. Use of a high-output device alone was not enough to obtain an adequate DFT in 48% (34/71) of patients who required modifications (3% of the total population). No arrhythmia inductions were performed in 54 patients (4.7%) because of well-defined clinical conditions. Patients who required system modification had a lower ejection fraction, were younger, were less likely to have coronary artery disease, were more likely to be undergoing upgrade/generator replacement, and were more likely to be taking amiodarone. Long-term mortality was not different between the group of patients who required modification compared with those who did not (17% vs 20%, P = NS).

CONCLUSIONS

Routine VF induction and documentation of effective defibrillation still remains a reasonable part of ICD placement because an inadequate safety margin may occur in >6% of patients. The incidence of patients who were inappropriate for testing based on well-defined clinical conditions is small (<5%) in this unselected large series. Although some clinical features may predict the need for system modification, additional studies are needed to better define "acceptable efficacy" of ICDs in preventing sudden death prior to altering these standards in selected patients.

Optimization of Atrial Defibrillation with a Dual-Coil, Active Pectoral Lead System

INTRODUCTION

Atrial defibrillation can be achieved with standard implantable cardioverter defibrillator (ICD) leads, but the optimal shocking configuration is unknown. The objective of this prospective study was to compare atrial defibrillation thresholds (DFTs) with three shocking configurations that are available with standard ICD leads.

METHODS AND RESULTS

This study was a prospective, randomized, paired comparison of shocking configurations on atrial DFTs in 58 patients. The lead system evaluated was a transvenous defibrillation lead with coils in the superior vena cava (SVC) and right ventricular apex (RV) and a left pectoral pulse generator emulator (Can). In the first 33 patients, atrial DFT was measured with the ventricular triad (RV --> SVC + Can) and unipolar (RV --> Can) shocking pathways. In the next 25 patients, atrial DFT was measured with the ventricular triad and the proximal triad (SVC --> RV + Can) configurations. Delivered energy at DFT was significantly lower with the ventricular triad compared to the unipolar configuration (4.7 +/- 3.7 J vs 10.1 +/- 9.5 J, P < 0.001). Peak voltage and shock impedance also were significantly reduced (P < 0.001). There was no significant difference in DFT energy when the ventricular triad and proximal triad shocking configurations were compared (3.6 +/- 3.0 J vs 3.4 +/- 2.9 J for ventricular and proximal triad, respectively, P = NS). Although shock impedance was reduced by 13% with the proximal triad (P < 0.001), this effect was offset by an increased current requirement (10%).

CONCLUSION

The ventricular triad is equivalent or superior to other possible shocking pathways for atrial defibrillation afforded by a dual-coil, active pectoral lead system. Because the ventricular triad is also the most efficacious shocking pathway for ventricular defibrillation, this pathway should be preferred for combined atrial and ventricular defibrillators.

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.

A randomized prospective study of single coil versus dual coil defibrillation in patients with ventricular arrhythmias undergoing implantable cardioverter defibrillator therapy

ICD implantation is standard therapy for malignant ventricular arrhythmias. The advantage of dual and single coil defibrillator leads in the successful conversion of arrhythmias is unclear. This study compared the effectiveness of dual versus single coil defibrillation leads. The study was a prospective, multicenter, randomized study comparing a dual with a single coil defibrillation system as part of an ICD using an active pectoral electrode. Seventy-six patients (64 men, 12 women; age 61 +/- 11 years) were implanted with a dual (group 1, n = 38) or single coil lead system (group 2,n = 38). The patients represented a typical ICD cohort: 60% presented with ischemic cardiomyopathy as their primary cardiac disease, the mean left ventricular ejection fraction was 0.406 +/- 0.158. The primary tachyarrhythmia was monomorphic ventricular tachyarrhythmia in 52.6% patients and ventricular fibrillation in 38.4%. There was no significant difference in terms of P and R wave amplitudes, pacing thresholds, and lead impedance at implantation and follow-up in the two groups. There was similarly no difference in terms of defibrillation thresholds (DFT) at implantation. Patients in group 1 had an average DFT of 10.2 +/- 5.2 J compared to 10.3 +/- 4.1 J in Group 2, P = NS. This study demonstrates no significant advantage of a dual coil lead system over a single coil system in terms of lead values and defibrillation thresholds. This may have important bearing on the choice of lead systems when implanting ICDs.

Mortality, morbidity, and complications in 3344 patients with implantable cardioverter defibrillators: results fron the German ICD Registry EURID

ICDs are the therapy of choice in patients with life-threatening ventricular arrhythmias. Mortality, morbidity, and complication rates including appropriate and inappropriate therapies are unknown when ICDs are used in routine medical care and not in well-defined patients included in multicenter trials. Therefore, the data of 3,344 patients (61.1 +/- 12.1 years; 80.2% men; CAD 64.6%, dilated cardiomyopathy 18.9%; NYHA Class I-III: 19.1%, 54.3%, 20.1%, respectively; LVEF > 0.50: 0.234, LVEF 0.30-0.50: 0.472, LVEF < 0.30: 0.293, respectively) implanted in 62 German hospitals between January 1998 and October 2000 were prospectively collected and analyzed as a part of the European Registry of Implantable Defibrillators (EURID Germany). The 1-year survival rate was 93.5%. Patients in NYHA Class III and aLVEF < 0.30 had a lower survival rate than patients in NYHA Class I and a preserved LVEF (0.852 vs 0.975,P = 0.0001). Including the 1-year follow-up, 49.5% of patients had an intervention by the ICD, 39.8% had appropriate ICD therapies, 16.2% had inappropriate therapies. Overall, 1,691 hospital readmissions were recorded. The main causes for hospital readmissions were ventricular arrhythmias (61.3%) and congestive heart failure symptoms (12.9%). Thus, demographic data and mortality of patients treated with an ICD in conditions of standard medical care seems to be comparable and based on, or congruent with, the large secondary preventions trials. When ICDs are used in standard medical care, the 1-year survival rate is high, especially in patients with NYHA Class I and preserved LVEF. However, nearly half of all patients suffer from ICD intervention.

Automatic implantable cardioverter-defibrillators

Ventricular fibrillation, a loss of synchronous electrical activity in the heart which leads to hemodynamic collapse, is a leading cause of death. Because of the devastating personal and societal effects of this phenomenon, the automatic cardioverter-defibrillator has been developed for automatic detection and termination of the arrhythmia and is in widespread clinical use. Advances in circuits, leads, waveforms, and signal processing along with increased knowledge of the mechanisms of fibrillation have led to continuing improvements in this device, extending its use to many patients. A device has also been developed for the automatic or semiautomatic treatment of atrial fibrillation, an arrhythmia less life-threatening than ventricular fibrillation, but still a serious health problem. Continued improvement of these devices and the development of qualitatively new approaches hold great promise for exciting therapeutic advances in this area.

Successful implantation of a cardioverter defibrillator in an infant

We report the successful implantation of a cardioverter defibrillator (ICD) in a 12-month-old infant. A single-lead ICD using an epicardial patch and a cathodal pulse-generator titanium shell electrode was very useful for implantation in this infant.

Temporal decline in defibrillation thresholds with an active pectoral lead system

OBJECTIVES

The objective of this study was to characterize temporal changes in defibrillation thresholds (DFTs) after implantation with an active pectoral, dual-coil transvenous lead system.

BACKGROUND

Ventricular DFTs rise over time when monophasic waveforms are used with non-thoracotomy lead systems. This effect is attenuated when biphasic waveforms are used with transvenous lead systems; however, significant increases in DFT still occur in a minority of patients. The long-term stability of DFTs with contemporary active pectoral lead systems is unknown.

METHODS

This study was a prospective assessment of temporal changes in DFT using a uniform testing algorithm, shock polarity and dual-coil active pectoral lead system. Thresholds were measured at implantation, before discharge and at long-term follow-up (70 +/- 40 weeks) in 50 patients.

RESULTS

The DFTs were 9.2 +/- 5.4 J at implantation, 8.3 +/- 5.8 J before discharge and 6.9 +/- 3.6 J at long-term follow-up (p < 0.01 by analysis of variance; p < 0.05 for long-term follow-up vs. at implantation or before discharge). The effect was most marked in a prespecified subgroup with high implant DFTs (> or =15 J). No patient developed an inadequate safety margin (< 9 J) during follow-up.

CONCLUSIONS

The DFTs declined significantly after implantation with an active pectoral, dual-coil transvenous lead system, and no clinically significant increases in DFT were observed. Therefore, routine defibrillation testing may not be required during the first two years after implantation with this lead system, in the absence of a change in the cardiac substrate or treatment with antiarrhythmic drugs.

Transvenous biventricular defibrillation

The recent success of biventricular pacing with transvenously implantable left ventricular leads suggests that left ventricular leads may be useful for other modes of therapy. Animal studies showed small leads inserted into a left ventricular vein dramatically reduced defibrillation strength requirements. This article describes a human investigation of the feasibility of biventricular defibrillation. Fifty-one patients undergoing implantable cardioverter defibrillator (ICD) implantation were enrolled. After insertion of a standard ICD lead, a prototype over-the-wire left ventricular defibrillation lead was inserted through the coronary sinus and into a vein on the left ventricle. Lead insertion was guided by retrograde venography. The left ventricular lead's location was randomized to the anterior or posterior vein. Randomized, paired defibrillation threshold (DFT) testing was performed to compare a standard ICD shock configuration (Control: right ventricle- --> superior vena cava+ + CAN+) to 1 of 3 biventricular shock configurations. In the anterior vein, the left ventricular lead was tested with either a single biphasic shock from right ventricle + left ventricle- --> superior vena cava+ + CAN+ or a dual biphasic shock. In the posterior vein, the left ventricular lead was tested with a dual biphasic shock. Dual shocks consisted of a 40% tilt biphasic shock from right ventricle- --> superior vena cava+ + CAN+ followed by another 40% tilt biphasic shock from left ventricle- --> superior vena cava+ + CAN+, delivered from a single 225 microF capacitance. Left ventricular lead positioning was successful in 41 of 46 patients (89%). Mean left ventricular lead insertion time was 17 +/- 17 minutes and 13 +/- 15 minutes for anterior and posterior locations, respectively. Mean DFTs were not statistically lower for the left ventricular shock configurations, but retrospective analysis showed a well-defined region of the posterolateral left ventricle where consistent DFT reduction was achieved with dual shocks (14.0 +/- 2.7 J vs 7.8 +/- 0.9 J; n = 5; p = 0.04). There were no adverse events requiring intervention due to the use of the left ventricular lead. Biventricular defibrillation is feasible and safe under the conditions used in this study. Additional studies are needed to verify whether dual shocks with posterolateral left ventricular lead positions consistently reduce DFTs.

Two-coil versus single-coil transvenous cardioverter defibrillator systems: comparative data

Two types of new-generation transvenous implantable cardioverter defibrillator (ICD) systems, incorporating a two-coil (62 patients, group 1) versus single-coil (32 patients, group 2) lead system were compared among 94 consecutive patients. The two groups were comparable in age (58 +/- 13 vs 59 +/- 14 years), presenting arrhythmia (ventricular tachycardia versus ventricular fibrillation 77%/21% vs 84%/13%), cycle length of induced VT (294 +/- 4 vs 289 +/- 44 ms), number of unsuccessful antiarrhythmic drugs (1.7 +/- 0.8 vs 1.7 +/- 0.7), and left ventricular ejection fraction (35 +/- 12% vs 34 +/- 9%). Both systems were successfully implanted strictly transvenously in all patients. Biphasic shocks were used in all patients. Active shell devices were used in 79% and 84% patients of groups I and II, respectively (P = NS). Intraoperative testing revealed comparable defibrillation threshold (DFT) values (10.2 +/- 3.7 J in group 1 versus 9.3 +/- 3.6 J in group 2 system), and pacing threshold (0.7 +/- 0.3 vs 0.7 +/- 0.3 V), but R wave amplitude and lead impedance were lower in group 1 (13 +/- 5 vs 16 +/- 5 mV, P = 0.003; and 579 +/- 115 vs 657 +/- 111 ohms, P = 0.002, respectively). Lead insulation break requiring reoperation occurred in one patient with an Endotak lead, and two patients with Transvene leads had initially high DFT with a single one-lead/active can system, which was converted to a two- or three-endocardial-lead/inactive can configuration. We conclude that both single-coil and two-coil transvenous ICD systems were associated with high rates of successful strictly transvenous ICD implantation and a low incidence of lead-related complications. Significant differences were noted in the sensed R wave and lead impedance, probably reflecting the active fixation characteristics of the Transvene lead. However, in order to obviate the sporadic need for implantation of additional endocardial leads, as was the case in two patients in this series, a double-coil lead may be preferable.

Use of a single coil transvenous electrode with an abdominally placed implantable cardioverter defibrillator in children

While transvenous defibrillator electrode placement avoiding a thoracotomy is preferable, electrode size, a large intercoil spacing, and the need for subclavicular device placement preclude this approach in most children. We investigated a single RV coil to an abdominally placed active can ICD device. Five children ages 8-16 years (weight 21-50 kg, mean 35 kg) underwent ICD placement. Placement of a single coil Medtronic model 6932 or 6943 electrode was performed via the left subclavian vein approach and the electrode positioned in the RV apex with the coil lying along the RV diaphragmatic surface. The ICD (Medtronic Micro Jewel II model 7223 Cx) was implanted in a left abdominal pocket with the lead tunneled from the infraclavicular region to the pocket. Implant DFTs were < or = 15 J using a biphasic waveform. DFTs rechecked within 3-month postimplant were unchanged. Lead impedance at implant ranged from 38 to 56 omega, mean 51 omega. Follow-up was 3-21 months (total 82 months) with no electrode dislodgment, lead fractures, or inappropriate discharges. Two of the five patients have had successful appropriate ICD discharges. Transvenous ICD electrode placement can be performed in children as small as 20 kg with the device implanted in a cosmetically acceptable abdominal pocket that is well tolerated. Excellent DFTs can be achieved. This approach avoids a thoracotomy in all but the smallest child, does not require subclavicular placement of the device, and avoids use of a second intravascular coil.

Hybrid therapy for ventricular arrhythmia management

Optimum arrhythmia management has evolved to couple ICD therapy with catheter ablative and drug therapy to attempt to eliminate or reduce arrhythmia risk. No longer should the clinician approach such therapy as a choice among single alternative strategies only. Optimum patient management includes not only recognition of the indications and benefits of such hybrid therapy but also a complete understanding of potential pitfalls of such therapy.

ICD therapy in the new millennium

Remarkable progress has been made in the 15 years since ICD therapy was approved for human use. The early "shock boxes" had almost no diagnostic capabilities and required thoracotomy for epicardial patch implantation with typical duration of hospitalization of about a week. Pulse-generator longevity was less than 2 years. Modern devices provide detailed information about the morphology and rate of electrocardiographic signals before, during, and after arrhythmia therapy. The down-sizing of pulse generators and improvements in lead design and shock waveforms allow the simplicity of defibrillator implantation to approach that of pacemakers, with defibrillation thresholds comparable with those initially observed with epicardial patches. Despite the marked reduction in size and increase in diagnostic capabilities, device longevity is now longer than 6 years. Routine outpatient ICD implantation is presently feasible and will increase in frequency if ongoing primary prevention trials prove beneficial. Further advances in lead technology and arrhythmia discrimination should increase the efficacy and reliability of therapy. Finally, devices have the capabilities to treat multiple problems in addition to life-threatening ventricular arrhythmias including atrial arrhythmias and congestive heart failure.

Optimization of transvenous coil position for active can defibrillation thresholds

INTRODUCTION

Lead systems that include an active pectoral pulse generator are now standard for initial defibrillator implantations. However, the optimal transvenous lead system and coil location for such active can configurations are unknown. The purpose of this study was to evaluate the benefit and optimal position of a superior vena cava (SVC) coil on defibrillation thresholds with an active left pectoral pulse generator and right ventricular coil.

METHODS AND RESULTS

This prospective, randomized study was performed on 27 patients. Each subject was evaluated with three lead configurations, with the order of testing randomized. Biphasic shocks were delivered between the right ventricular coil and an active can alone (unipolar), or an active can in common with the proximal coil positioned either at the right atrial/SVC junction (low SVC) or in the left subclavian vein (high SVC). Stored energies at defibrillation threshold were higher for the single-coil, unipolar configuration (11.2 +/- 6.6 J) than for the high (8.9 +/- 4.2 J) or low (8.5 +/- 4.2 J) SVC configurations (P < 0.01). Moreover, 96% of subjects had low (< or = 15 J) thresholds with the SVC coil in either position compared with 81% for the single-coil configuration. Shock impedance (P < 0.001) was increased with the unipolar configuration, whereas peak current was reduced (P < 0.001).

CONCLUSION

The addition of a proximal transvenous coil to an active can unipolar lead configuration reduces defibrillation energy requirements. The position of this coil has no significant effect on defibrillation thresholds.

A prospective, randomized, comparison in patients between a pectoral unipolar defibrillation system and that using an additional inferior vena cava electrode

The decrease of defibrillation energy requirement would render the currently available transvenous defibrillator more effective and favor the device miniaturization process and the increase of longevity. The unipolar defibrillation systems using a single RV electrode and the pectoral pulse generator titanium shell (CAN) proved to be very efficient. The addition of a third defibrillating electrode in the coronary sinus did not prove to offer advantages and in the superior vena cava showed only a slight reduction of the defibrillation threshold (DFT). The purpose of this study was to determine whether the defibrillation efficacy of the single lead unipolar transvenous system could be improved by adding an electrode in the inferior vena cava (IVC). In 17 patients, we prospectively and randomly compared the DFT obtained with a single lead unipolar system with the DFT obtained using an additional of an IVC lead. The RV electrode, Medtronic 6936, was used as anode (first phase of biphasic) in both configurations. A 108 cm2 surface CAN, Medtronic 7219/7220 C, was inserted in a left submuscular infraclavicular pocket and used as cathode, alone or in combination with IVC, Medtronic 6933. The superior edge of the IVC coil was positioned 2-3 cm below the right atrium-IVC junction. Thus, using biphasic 65% tilt pulses generated by a 120 microF external defibrillator, Medtronic D.I.S.D. 5358 CL, the RV-CAN DFT was compared with that obtained with the RV-CAN plus IVC configuration. Mean energy DFTs were 7.8 +/- 3.6 and 4.8 +/- 1.7 J (P < 0.0001) and mean impedance 65.8 +/- 13 O and 43.1 +/- 5.5 O (P < 0.0001) with the RV-CAN and the IVC configuration, respectively. The addition of IVC significantly reduces the DFT of a single lead active CAN pectoral pulse generator. The clinical use of this biphasic and dual pathway configuration may be considered in patients not meeting implant criteria with the single lead or the dual lead RV-superior vena cava systems. This configuration may also prove helpful in the use of very small, low output ICDs, where the clinical impact of ICD generator size, longevity, and related cost may offset the problems of dual lead systems.

Biventricular shocking leads improve defibrillation efficacy

INTRODUCTION

A single lead active can configuration has been widely used in patients with life-threatening ventricular arrhythmias. Occasionally, however, such a defibrillation lead configuration may not achieve adequate defibrillation threshold (DFT). The purpose of this study was to determine whether addition of a left ventricular (LV) lead can improve defibrillation efficacy.

METHODS AND RESULTS

Three transvenous defibrillation leads (8.3-French with a 5-cm long unipolar coil) were placed in the right ventricle (RV), LV, and superior vena cava (SVC), along with an active can (92 cm2) in the left subpectoral area. The DFT stored energy of seven combinations of these defibrillation leads were compared in a pig ventricular fibrillation model using a biphasic defibrillation waveform (125 microF, 6.5/3.5 msec). A biventricular leads active can configuration in which the RV and LV leads were of the same polarity reduced the DFT stored energy by approximately 35% when compared to a single RV lead active can configuration (9.6 +/- 3.0 J vs 15.0 +/- 7.2 J, respectively, P = 0.02). Moreover, adding a SVC lead further reduced the DFT energy (8.4 +/- 3.3 J).

CONCLUSION

A biventricular leads active can configuration can significantly improve defibrillation efficacy as compared to a single lead active can configuration. In such a defibrillation lead configuration, the polarity of RV and LV leads should be the same.

Pectoral cardioverter defibrillators: comparison of prepectoral and submuscular implantation techniques

The purpose of this study was to compare the two techniques of pectoral ICD implantation, prepectoral and submuscular, performed by an electrophysiologist in the catheterization laboratory with use of general or local anesthesia in 45 consecutive patients. Over a period of 30 months, we implanted pectoral transvenous ICDs in 43 men and 2 women, aged 59 +/- 12 years, with use of general (n = 20) or local (n = 25) anesthesia in the catheterization laboratory. Patients had coronary (n = 30) or valvular (n = 4) disease, cardiomyopathy (n = 10) or no organic disease (n = 1), a mean left ventricular ejection fraction of 31%, and presented with ventricular tachycardia (n = 40) or fibrillation (n = 5). One-lead ICD systems (18 Endotak, 10 Transvene/8 Sprint, 2 EnGuard) were used in 38 patients, 2-lead (5 Transvene, 1 EnGuard) systems in 6 patients, and 1 atrioventricular lead ICD system in 1 patient. The prepectoral technique was employed in 29 patients with adequate subcutaneous tissue, while the submuscular technique was used in 16 patients who had a thin layer of subcutaneous tissue. The defibrillation threshold averaged 9-10 J in both groups and there were no differences in pace/sense thresholds. All implants were entirely transvenous with no subcutaneous patch. Biphasic ICD devices were employed in all patients. Active or hot can devices were used in 39 patients. There were no complications, operative deaths, or infections. Patients were discharged at a mean of 3 days. All devices functioned well at predis-charge testing. Over 14 +/- 8 months, 20 patients received appropriate device therapy (antitachycardia pacing or shocks). No late complications occurred. One patient died at 3 months of pump failure; there were no sudden deaths. In conclusion, for exclusive pectoral implantation of transvenous ICDs, electrophysiologists should master both prepectoral and submuscular techniques. One can thus avoid potential skin erosion or need for abdominal implantation in patients with a thin layer of subcutaneous tissue. Finally, there are no differences in pacing or defibrillation thresholds between the two techniques.

A comparison of pectoral and abdominal transvenous defibrillator implantation: analysis of costs and outcomes

Traditionally cardioverter-defibrillator implantation was performed by surgeons under general anesthesia. However, with advances in lead and pulse generator technology, the surgical implantation technique has been simplified and routine pectoral pulse generator placement without general anesthesia is now possible. To assess the economic benefit of pectoral implantation, we analyzed 43 consecutive initial transvenous defibrillator implantations. The patients were grouped according to whether the implant was abdominal by a surgeon in the operating room (n = 23) or pectoral by an electrophysiologist in a laboratory (n = 20). The duration of hospitalization was significantly longer in the operating room than in the laboratory group (8.1 +/- 3.4 vs 5.8 +/- 2.4 days, p = 0.01), which was due primarily to the postoperative stay which averaged 1.9 days longer. Total costs were $40,274 +/- 6,861 for the operating room cohort and $32,546 +/- 3,634 for the lab group (p < 0.001). This reduction was due to a 32% lowering of professional costs and an 18% lowering of facility costs. We conclude that pectoral defibrillator implantation is cost effective and results in significant reductions of hospital stay.

Clinical experience with downsized lower energy output implantable cardioverter defibrillators. Ventak Mini II Clinical Investigators

BACKGROUND AND STUDY OBJECTIVE

Technical improvements in cardioverter defibrillators technology has resulted in decrease in can size coupled with improved electrodes technology. A decrease in maximum energy output allows further decrease in device size. The aim of this study was to evaluate the feasibility of a single lead transvenous implant employing a downsized cardioverter-defibrillator (volume 59 cm3), with a related decrease in maximum energy output (29-31 joules as stored energy and 25-27 joules as delivered energy).

METHODS AND RESULTS

Fifty-five patients with ventricular tachyarrhythmias were enrolled in 17 European institutions for implantation. At implantation step-down defibrillation threshold (DFT) was determined and the device was implanted only if a safety margin > or =10 joules was maintained between DFT and maximum programmable output. Implantation was performed in 54 of the 55 referred patients (98%) in a single electrode-device configuration. Step-down DFT testing was performed in 44 patients (43 finally implanted) and DFT was 7.77+/-4.41 joules (range 3-20). In 20 of the tested patients (45%) DFT was < or =5 joules, in 26 patients (59%) was < or =8 joules and in 34 patients (77%) it was < or =10 joules. No differences were found in DFT comparing patients with left ventricular ejection fraction < or = or >40% or patients treated or not with antiarrhythmic drugs or beta-blockers. Mean implant duration was 85+/-34 min.

CONCLUSIONS

Employing a downsized cardioverter defibrillator, successful transvenous implantation can be achieved in 98% of the patients, with maintenance of adequate defibrillation safety margins despite a reduction in stored energy to 29 joules.