Implantable defibrillation: eight years clinical experience

Effects of Rhythm and Rate-Controlling Drugs in Patients With Permanent His-Bundle Pacing

Introduction: Antiarrhythmic drug therapy can affect pacemaker parameters in both the atrial and ventricular myocardium. It is not known whether antiarrhythmic drugs impact His bundle pacing/sensing parameters and His to ventricle (H-V) intervals following permanent His bundle pacing (HBP). The aims of the study were to prospectively determine the influence of rhythm and rate-controlling drugs on pacing parameters and H-V conduction after His bundle lead implantation and to assess the impact of rhythm and rate-controlling drugs on the safety of HBP.

Materials and Methods: Patients (N = 140) with QRS duration < 120 ms who met permanent pacing indications were prospectively enrolled. Propafenone, lidocaine, and adenosine were injected intravenously after implantation of 3,830 lead during the procedure. Metoprolol succinate, amiodarone, and digoxin were taken orally for 1 month. Pacing parameters before and after drug intervention was measured, including His capture threshold, sensing and impedance, H-V interval, and conduction.

Results: There were no statistically significant differences in His bundle pacing thresholds, impedance, and sensing after drug intervention at implantation or during a 2-month follow-up (P > 0.05). The HV interval was not affected except in the large-dose propafenone group where HV interval prolonged (P = 0.001). All patients maintained 1:1 H-V conduction following drug administration.

Conclusion: There was no adverse impact on the HBP parameters or H-V conduction after the administration of commonly used dosage of rhythm and rate-controlling drugs. The drugs were safe in patients with permanent His bundle pacing.

Use of Antiarrhythmic Medications in Medicare Part D Patients With an Implantable Cardioverter-Defibrillator and Ventricular Tachycardia

Ventricular tachycardia (VT) is common in cardiomyopathy patients with an implantable cardioverter-defibrillator. This analysis evaluated antiarrhythmic medication use and change in use over time in patients with VT and structural heart disease. Query of Medicare claims identified patients with an implantable cardioverter-defibrillator and VT. Patients with atrial fibrillation or supraventricular tachycardia were excluded. Two cohorts were created of patients enrolled in Medicare Part D for the 12 months before 2007 and 2012. Patients were identified through a search for antiarrhythmic medication fills with a supply covering January 1 of the cohort year. Adjusted logistic regression modeling evaluated the association between patient characteristics and antiarrhythmic medication use. The 2007 (n = 2,334) and 2012 (n = 3,892) Medicare Part D cohorts had similar demographics: median age 76 years, 64%-67% male, and 87%-89% white. Of the 2007 cohort, 1,380 (59%) patients were on a beta blocker, and 484 (20.7%) were on an antiarrhythmic medication (70% amiodarone and 20% sotalol). Between 2007 and 2012, there was a statistically significant higher use of any antiarrhythmic medication (p = 0.014), beta blockers (p <0.0001), mexiletine (p = 0.005), and ranolazine (p <0.0001), while amiodarone use remained unchanged (p = 0.53). After multivariable adjustment, male gender and renal disease were associated with higher antiarrhythmic medication use. In conclusion, although antiarrhythmic medication and beta blocker use in patients with VT increased over time, <1 in 4 patients were on an antiarrhythmic medication and only 65% of the patients were on a beta blocker.

Management of pace-terminated ventricular arrhythmias

An implantable-cardioverter defibrillator (ICD) can terminate ventricular arrhythmias by delivering a shock or by antitachycardia pacing (ATP). The ATP works by capturing the excitable gap and disrupting re-entrant ventricular arrhythmias. Multiple studies have demonstrated that ATP is successful at terminating ventricular tachycardia (VT). Shocks from the ICD are associated with higher mortality. The data are conflicting about whether appropriate ATP is associated with higher mortality. In a patient with VT that is treated by ATP, the patient's guideline-based heart failure medications should be maximized. The use of VT ablation after appropriate and successful ATP requires additional studies.

The safety and efficacy of antithrombotic therapy in patients undergoing cardiac rhythm device implantation: a meta-analysis

AIMS

The meta-analysis was to assess the safety and efficacy of periprocedural antithrombotic therapy and to evaluate the risk factors potentially associated with bleeding among patients undergoing cardiac implantable electronic devices implantations.

METHODS AND RESULTS

A systematic literature search of PubMed, EMBASE, and Cochrane Controlled Trials Register was performed. Anticoagulation and antiplatelet therapies were assessed separately. Uninterrupted anticoagulation was associated with significant lower bleeding risk compared with heparin bridging strategy [odds ratio (OR) = 0.31, 95% confidence interval (CI) 0.18-0.53, and P < 0.0001], but there was no significant difference in thromboembolic risk between these two strategies (OR = 0.82, 95% CI 0.32-2.09, and P = 0.65). The haematoma rate was significantly increased in dual antiplatelet therapy group (OR = 6.84, 95% CI 4.16-11.25, and P < 0.00001), but not in single antiplatelet therapy (OR = 1.52, 95% CI 0.93-2.46, and P = 0.09). Clopidogrel increased the risk of haematoma vs. aspirin (OR = 2.91, 95% CI 1.27-6.69, and P = 0.01). Otherwise, a lower risk of haematoma was observed in pacemaker group vs. cardiac resynchronization therapy and/or implantable cardioverter defibrillator group (OR = 0.64, 95% CI 0.50-0.82, and P = 0.0004).

CONCLUSION

This meta-analysis suggested that uninterrupted oral anticoagulation seems to be the better strategy, associated with a lower risk of bleeding complications rather than heparin bridging, and dual antiplatelet therapy carried a significant risk of bleeding whereas single antiplatelet therapy was relatively safe among patients undergoing cardiac implantable electronic devices implantations. Meanwhile, cardiac resynchronization therapy and/or implantable cardioverter defibrillator implantations increase the bleeding.

Guidelines for the diagnosis, prevention and management of implantable cardiac electronic device infection. Report of a joint Working Party project on behalf of the British Society for Antimicrobial Chemotherapy (BSAC, host organization), British Heart Rhythm Society (BHRS), British Cardiovascular Society (BCS), British Heart Valve Society (BHVS) and British Society for Echocardiography (BSE)

Infections related to implantable cardiac electronic devices (ICEDs), including pacemakers, implantable cardiac defibrillators and cardiac resynchronization therapy devices, are increasing in incidence in the USA and are likely to increase in the UK, because more devices are being implanted. These devices have both intravascular and extravascular components and infection can involve the generator, device leads and native cardiac structures or various combinations. ICED infections can be life-threatening, particularly when associated with endocardial infection, and all-cause mortality of up to 35% has been reported. Like infective endocarditis, ICED infections can be difficult to diagnose and manage. This guideline aims to (i) improve the quality of care provided to patients with ICEDs, (ii) provide an educational resource for all relevant healthcare professionals, (iii) encourage a multidisciplinary approach to ICED infection management, (iv) promote a standardized approach to the diagnosis, management, surveillance and prevention of ICED infection through pragmatic evidence-rated recommendations, and (v) advise on future research projects/audit. The guideline is intended to assist in the clinical care of patients with suspected or confirmed ICED infection in the UK, to inform local infection prevention and treatment policies and guidelines and to be used in the development of educational and training material by the relevant professional societies. The questions covered by the guideline are presented at the beginning of each section.

Prevalence, correlates, and temporal trends in antiarrhythmic drug use at discharge after implantable cardioverter defibrillator placement (from the National Cardiovascular Data Registry [NCDR])

Patients with implantable cardioverter defibrillators (ICDs) can require antiarrhythmic drugs to manage arrhythmias and prevent device shocks. We sought to determine the prevalence, clinical correlates, and institutional variation in the use of antiarrhythmic drugs over time after ICD implantation. From the ICD Registry (2006 to 2011), we analyzed the trends in the use of antiarrhythmic agents prescribed at hospital discharge for patients undergoing first-time ICD placement. The patient, provider, and facility level variables associated with antiarrhythmic use were determined using multivariate logistic regression models. A median odds ratio was calculated to assess the hospital-level variation in the use of antiarrhythmic drugs. Of the cohort (n = 500,995), 15% had received an antiarrhythmic drug at discharge. The use of class III agents increased modestly (13.9% to 14.9%, p <0.01). Amiodarone was the most commonly prescribed drug (82%) followed by sotalol (10%). Among the subgroups, the greatest increase in prescribing was for patients who had received a secondary prevention ICD (26% in 2006% and 30% in 2011, p <0.01) or with a history of ventricular tachycardia (23% to 27%, p <0.01). The median odds ratio for antiarrhythmic prescription was 1.45, indicating that 2 randomly selected hospitals would have had a 45% difference in the odds of treating identical patients with an antiarrhythmic drug. In conclusion, antiarrhythmic drug use, particularly class III antiarrhythmic drugs, is common among ICD recipients at hospital discharge and varies by hospital, suggesting an influence from local treatment patterns. The observed hospital variation suggests a role for augmentation of clinical guidelines regarding the use of antiarrhythmic drugs for patients undergoing implantation of an ICD.

Fungal infection of implantable cardioverter-defibrillators: Case series of five patients managed over 22 years

BACKGROUND

With the increasing use of implantable cardioverter-defibrillators (ICDs), device complications are becoming more common. Fungal-related ICD infections have rarely been reported, and little is known about the presentation, prevalence, and treatment options for these morbid infections.

OBJECTIVES

The purpose of this study was to characterize the clinical features, treatment, and outcomes of patients with fungal ICD infections.

METHODS

We performed a retrospective review of ICD procedures performed at a single academic center and identified all ICD-related infections managed between 1983 and 2005.

RESULTS

Among a total of 3,648 ICD-related procedures performed between 1983 and 2005, we identified 47 (1.3%) cases of ICD infections, of which 5 (0.1%) were due to a fungal pathogen. Fungal infections were more likely to be associated with abdominal devices, to have a local rather than systemic infection, and to have a longer duration from the original implant to presentation. All patients were treated with ICD system explantation and antifungal therapy.

CONCLUSION

Fungal infection of ICDs is a rare but serious complication of device implantation that must be treated aggressively with complete hardware explantation and prolonged antifungal therapy. Because most infections are late complications and have indolent onsets, a high level of clinical suspicion is required for early diagnosis.

Indications for an implantable cardioverter defibrillator (ICD)

Since the first clinical use of implantable defibrillator in human, the technology and the function of implantable cardioverter-defibrillator (ICD) have been much improved and now, ICD can be implanted within the chest wall. ICD is the most reliable therapy to prevent sudden cardiac death (SCD) in patients with documented VT/VF and the efficacy is most clear in patients with depressed heart function. It is now extended as a tool of the primary prevention of SCD in high risk patients after myocardial infarction. However, such beneficial effect is not applicable to DCM though patients might have depressed heart function. ICD is not free from procedure- or device-related problems which need to be resolved. From unknown causes, VT/VF might recur in an incessant form and an emergency admission is needed. Therefore, even during ICD therapy, patients often require antiarrhythmic drugs or catheter ablation.

Implantable Cardioverter Defibrillator Events in Patients with Asymptomatic Nonsustained Ventricular Tachycardia:

Primary prevention trials have demonstrated that patients with coronary disease, reduced left ventricular function, and nonsustained ventricular tachycardia (NSVT) have improved survival with implantable cardioverter defibrillator (ICD) therapy, presumably secondary to effective termination of life-threatening arrhythmias. However, stored intracardiac electrograms were not always available and specific arrhythmias leading to ICD therapy were not always known. We examined the occurrence of ICD events in 51 consecutive patients who match the described patient profile to determine the frequency of appropriate and inappropriate ICD therapy. ICD detections were noted in 18 (35%) patients during a median follow-up period of 13.1 months. Appropriate therapy for sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) occurred in 11 (22%) patients, with appropriate shocks in 8 (16%) patients and appropriate antitachycardia pacing (ATP) in 4 (8%) patients. The time to first appropriate therapy occurred at a mean of 17 +/- 12 months (median 18 months, range 3-36 months). Inappropriate therapy occurred in 5 (10%) patients with inappropriate shocks in 4 patients and inappropriate ATP in 2 patients. Inappropriate therapy was delivered for supraventricular arrhythmias (SVAs) in 4 patients and for T wave oversensing in 1 patient. The reason for shock therapy was unknown in 1 patient (2%) due to ICD malfunction. The mean arrhythmia rate leading to appropriate therapy for VT/VF was 232 +/- 72 beats/min (range 181-400 beats/min), and the mean rate leading to inappropriate therapy for SVT was 168 +/- 10 beats/min (range 160-180 beats/min). Patients with coronary disease and asymptomatic NSVT commonly receive appropriate defibrillator therapy. These results support the need for ICD implantation for primary prevention, with attention to careful programming of the detection rate to prevent inappropriate therapy.

Sudden death in patients with implantable cardioverter defibrillators: the importance of post-shock electromechanical dissociation

OBJECTIVES

The purpose of this study was to determine the mechanisms of sudden death (SD) in patients with ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) treated with an implantable cardioverter defibrillator (ICD).

BACKGROUND

Despite ICD therapy, some patients with VT/VF still die suddenly. Optimal ICD use requires determination of the mechanisms of these residual SDs.

METHODS

We reviewed 320 patient deaths during trials of Medtronic transvenous ICD systems (Medtronic Inc., Minneapolis, Minnesota). Sudden deaths were further categorized according to mechanism. Post-shock electromechanical dissociation (EMD) describes a scenario where VT/VF was appropriately detected and treated by an ICD shock that restored a physiologic rhythm, but death still occurred immediately by EMD.

RESULTS

A mode of death could be ascribed for 317 patients-90 (28%) were sudden, 156 (49%) were non-sudden cardiac, and 71 (22%) were noncardiac. A mechanism of SD was proposed for 68 patients-20 (29%) had post-shock EMD, 17 (25%) had VT/VF uncorrected by shocks, 11 (16%) had primary electromechanical dissociation, 9 (13%) had incessant VT/VF, 5 (7%) had VT/VF after their ICD was deactivated or removed, and 6 (9%) had single instances of various other terminal events. Only New York Heart Association functional class independently predicted SD by post-shock EMD.

CONCLUSIONS

The most common mechanism of SD in patients with an ICD is VT/VF treated with an appropriate shock followed by EMD. As this mechanism accounted for 29% of the SDs to which a cause could be ascribed, this mechanism of SD warrants further investigation.

Long-term infection rates associated with the pectoral versus abdominal approach to cardioverter- defibrillator implants

Infection is an uncommon (0% to 6.7%) but serious complication after implantable cardioverter-defibrillator (ICD) implantation. All ICD primary implants, replacements, or revisions performed at the Massachusetts General Hospital between April 1983 and May 1999 were reviewed. A total of 21 ICD-related infections (1.2%) were identified among 1,700 procedures affecting 1.8% of the 1,170 patients who underwent a primary implant, a generator change, or a revision of their systems. The mean follow-up time was 35 +/- 33 months. Of the 959 patients with long-term follow-up, 19 of the 584 patients (3.2%) with abdominal and 2 of the 375 patients (0.5%) with pectoral systems developed ICD-related infections (p = 0.03). There was no significant difference between the infection rate among the 959 primary ICD implants and the 447 replacements or system revisions. Only 5 of the patients (24%) had systemic signs of infection, including fever (T>100.5) and elevated white blood count >12,000. Cultures from the wound revealed staphylococcal species in 16 patients (76%). Nineteen patients were treated with removal of the entire ICD system in addition to intravenous antibiotics for 2 to 4 weeks. A decrease in the incidence of ICD-related infection has occurred since the advent of transvenous pectoral systems. The main organism responsible for ICD infection is Staphylococcus. The mainstay of ICD infection management consists of complete removal of the entire implanted system.

Matching cardiac rhythm management technology to patient needs: pacing/ablation/implantable cardioverter defibrillators

Data from 2 decades of clinical electrophysiologic studies have allowed great progress in the evaluation and treatment of patients with sustained ventricular arrhythmias and the appropriate identification of those patients at high risk for subsequent sudden death. The goals of treatment of the patient with ventricular arrhythmias are to suppress symptoms and prevent a fatal event. The steps in providing such therapy include (1) defining the cardiac anatomy; (2) assessing arrhythmia risk through noninvasive or invasive testing; and (3) prescribing treatment based on these results. Patients may be separated into high- and low-risk groups to help identify appropriate treatment. Although low-risk groups may benefit from reassurance or medications such as beta-blockers or verapamil, high-risk groups have been more difficult to treat. Recent randomized trials of implantable cardioverter defibrillators (ICDs) for ventricular arrhythmias suggest that they may provide better protection for high-risk patients than do antiarrhythmic medications.

The implantable cardioverter-defibrillator

Ventricular arrhythmias remain a major cause of cardiovascular mortality. Therapy for serious ventricular arrhythmias has evolved over the past decade, from treatment primarily with antiarrhythmic drugs to implanted devices. The implantable cardioverter-defibrillator (ICD) is the best therapy for patients who have experienced an episode of ventricular fibrillation not accompanied by an acute myocardial infarction or other transient or reversible cause. It is also superior therapy in patients with sustained ventricular tachycardia (VT) causing syncope or hemodynamic compromise. Controlled clinical trials have confirmed the utility of these devices. As primary prevention, the ICD is superior to conventional antiarrhythmic drug therapy in patients who have survived a myocardial infarction and who have spontaneous, nonsustained ventricular tachycardia, a low ejection fraction, inducible VT at electrophysiologic study, and whose VT is not suppressed by procainamide. The effect of the ICD on survival of other patient populations remains to be proven. The device is costly, but its price is generally accepted to be reasonable. The ICD has been a major advance in the treatment of ventricular arrhythmias.

Combining antiarrhythmic drugs and implantable devices therapy: benefits and outcome

At least 50% of patients who received an ICD have been treated with antiarrhythmic drugs (AAD). The potential indications for combining antiarrhythmic drugs and ICD are generally the following: reduction of the number of episodes of ventricular tachycardia or ventricular fibrillation and therefore of the number of shocks, improving patient's quality of life and extending the battery life of the ICD, prevention of supraventricular arrhythmias and/or control of their rate, lengthening of the tachycardia cycle length to allow ventricular tachycardia conversion by antitachycardia pacing and reduction of the number of episodes of syncope. Although previous papers reported conflicting results about pharmacologic therapy in reducing the frequency of iCD shocks, some recent randomized prospective studies showed the efficacy of pharmacologic therapy in reducing the frequency of ICD shocks. The use of antiarrhythmic drugs can have also adverse effect: an increase in the defibrillation threshold, an increase in the pacing threshold and an increase in the VT cycle length leading to detection failure. We have also to consider that some advantages derived from antiarrhythmic drugs can be reached by the new devices with atrial sensing and pacing and/or the possibility of atrial defibrillation or by using catheter ablation as adjunctive therapy to ICD. For these reasons, the concomitant use of antiarrhythmic drugs and ICD should be evaluated in each patient in relation to specific clinical and electrophysiologic features including: the frequency, the rate and the clinical presentation of the ventricular arrhythmia, the effect of the selected drug on the defibrillation threshold, the defibrillation threshold at the implant, the effect of the selected drug on the ventricular function and the likelihood of proarrhythmic events.

Concomitant device and drug therapy: current trends, potential benefits, and adverse interactions

Antiarrhythmic drug therapy in patients with implantable cardioverter defibrillators (ICDs) has decreased over the last 10 years. This trend, primarily seen with class I agents, has occurred mainly in patients with a cardiac arrest. However, despite this overall decrease, antiarrhythmic drug therapy remains an important adjuvant to ICD therapy. In addition to primary prevention of ventricular tachycardia and supraventricular tachycardia, antiarrhythmic drug therapy may potentiate tachycardia rate slowing and make ventricular tachycardia more tolerated hemodynamically and possibly more amendable to pacing therapy. Some of the class III antiarrhythmic drugs may actually lower defibrillation threshold. Unfortunately, these drugs may have adverse interactions with ICDs. An increase in defibrillation threshold or rate-dependent increase in pacing threshold may interfere with the effectiveness of device therapy. Proarrhythmic effects of antiarrhythmic drugs may enhance the frequency of device use. The bradycardic effects of antiarrhythmic drug therapy may similarly enhance the requirements for persistent bradycardia pacing and lead to early battery depletion and other adverse consequences. An awareness of potential benefits and adverse effects of antiarrhythmic drug therapy along with careful electrophysiologic assessment are necessary for optimum combination drug and device therapy.

Causes of death in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial

OBJECTIVES

This study analyzed the causes of death in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial.

BACKGROUND

Both implantable cardioverter-defibrillators (ICDs) and antiarrhythmic drugs (AADs) are used as mainstays of treatment for life-threatening ventricular arrhythmias in patients who have survived either ventricular fibrillation or sustained ventricular tachycardia with hemodynamic compromise and serious symptoms. The AVID Trial compared the effectiveness of these two therapies. Survival was better with the ICD. Assessment of the cause of death should help to determine the mechanism of improvement in survival with the ICD.

METHODS

Of 1,016 patients enrolled in the AVID Trial, 202 patients died. The mode of death was determined by the unblinded Principal Investigator and independently by an Events Committee, which reviewed materials meticulously blinded with respect to treatment. Deaths were classified as cardiac or noncardiac. Cardiac deaths were further classified as arrhythmic or nonarrhythmic, and causes of noncardiac death were identified.

RESULTS

Deaths were more frequent in patients treated with an AAD (n = 122), compared with patients treated with the ICD (n = 80), unadjusted p < 0.001, p = 0.012 adjusted for sequential monitoring. In AVID, 157 deaths were cardiac, and 79 were arrhythmic. The major effect of the ICD was to prevent arrhythmic death (AAD = 55, ICD = 24, nominal unadjusted p < 0.001). Nonarrhythmic cardiac deaths were equal (AAD = 39, ICD = 39). Patients treated with an AAD had a slightly greater incidence of noncardiac deaths (28 vs. 17, p = 0.053), primarily due to pulmonary and renal causes.

CONCLUSIONS

The ICD is more effective than an AAD in reducing arrhythmic cardiac death, while nonarrhythmic cardiac death is unchanged. Of note, apparent arrhythmic death still seems to constitute 38% of all cardiac deaths despite treatment with an ICD. However, the ICD remains superior to an AAD in prolonging survival after life-threatening arrhythmias.

Sudden Electrical Death

Survivors of an episode of out-of-hospital ventricular fibrillation (not due to a reversible cause) or hemodynamically significant sustained ventricular tachycardia should in most cases receive an implantable cardioverter defibrillator (ICD) rather than antiarrhythmic drug therapy. A number of recently published clinical trials (summarized later) point to improved survival with ICD implantation. It is also important to identify the cause of the ventricular rhythm and to treat adequately the underlying cardiomyopathy with the appropriate angiotensin-converting enzyme (ACE) inhibitors, beta-blockers, and aspirin. The role of electrophysiologic study is a matter of debate, and it is used less commonly than it was a decade ago.

Azimilide decreases defibrillation voltage requirements and increases spatial organization during ventricular fibrillation

INTRODUCTION

Drugs with class III antiarrhythmic properties generally decrease defibrillation threshold (DFT). However, the concentration effect relation for this effect and drug effects on ventricular fibrillation (VF) itself are not well understood. The objectives of this study were to determine the effect of azimilide (NE-10064), a new class III agent, on DFT, and on spatial organization during VF.

METHODS

Defibrillation patch electrodes were sutured to the right and left ventricular epicardium in 12 open-chest anesthetized dogs. The delayed up-down algorithm was used to measure DFT and to estimate the shock strength (voltage) with a 50% probability of successful defibrillation (V50). The magnitude squared coherence (MSC), which measures the spatial relation in the frequency domain, was measured during VF between two unipolar epicardial electrodes 3 mm apart. The V50, MSC, electrophysiologic parameters, and plasma concentrations were determined before and after four cumulative i.v. doses of azimilide (2, 7, 17, and 30 mg/kg).

RESULTS

Azimilide elicited a dose dependent reduction of V50 and increase in MSC. Compared with baseline, azimilide lowered mean V50 by 2 +/- 9%, 10 +/- 18%, 11 +/- 14% and 19 +/- 5%, and increased MSC by 17 +/- 20%, 32 +/- 31%, 20 +/- 44% and 27 +/- 20% (p < 0.05 for dose effect) at 2, 7, 17 and 30 mg/kg, respectively. Mean increases in monophasic action potential duration at 90% repolarization (3-11%), ventricular effective refractory period (6-13%) at 400 msec paced cycle length, and VF cycle length (5-37%) (p < 0.01 for dose effect) were observed with the 4 increasing doses of azimilide, respectively.

CONCLUSION

Azimilide significantly decreases DFT and increases coherence in VF in a dose dependent manner.

Interactions between implantable cardioverter-defibrillators and class III agents

Although implantable cardioverter-defibrillators (ICDs) can successfully terminate ventricular arrhythmias, antiarrhythmic drugs are often required to prevent recurrent events. Class III antiarrhythmic agents have emerged as the safest, most effective, and widely used agents in the 40-70% of ICD patients who require concomitant antiarrhythmic medication. Antiarrhythmic agents can influence the effectiveness of ICDs to terminate arrhythmias through their effect on defibrillation threshold. All class III agents share the ability to prolong ventricular refractoriness and those with "pure" class III activity consistently decrease defibrillation threshold in the normal canine heart model. Sotalol, amiodarone, and bretylium all have other Vaughan Williams class actions that influence their respective effects on defibrillation threshold. Sotalol has been associated with a decrease in defibrillation threshold in both animal and in clinical studies, whereas amiodarone has been associated with variable effects in animal models and an increase in defibrillation threshold in clinical studies. Additionally, antiarrhythmic agents may prolong ventricular tachycardia (VT) cycle length, which may affect the ability to pace terminate or cardiovert VT. Amiodarone has a moderate slowing effect on the VT cycle length. Finally, class III drugs also have proarrhythmic potential that may affect the defibrillator's function. Sotalol can be associated with dose-related torsade de pointes, whereas amiodarone may slow the VT cycle length below the tachycardia detection rate cutoff. In conclusion, class III pharmacotherapy can be safely administered in conjunction with ICD therapy as long as the interaction between these therapeutic modalities is appreciated.

Antiarrhythmic drugs and devices for the management of ventricular tachyarrhythmia in ischemic heart disease

Ischemic heart disease is the most frequent cardiac abnormality in patients with sustained or nonsustained ventricular tachyarrhythmias. The goals of therapy in such patients are to decrease the severity and incidence of symptoms and prolong life. In this article, we review the current views on antiarrhythmic drug therapy and an implantable cardioverter-defibrillator (ICD) in patients with ischemic heart disease. The importance of beta blockade as part of the therapy is emphasized. In addition, the superiority of sotalol and amiodarone over class I drugs, the benefits of combined treatment with amiodarone and a beta blocker, and the impact and limitations of current trials comparing the effectiveness of drug therapy with that of an ICD are all considered. Also discussed is the combined use of an antiarrhythmic drug and an ICD. In this approach sotalol is generally the agent of choice, with amiodarone the second choice.

The psychosocial and physiological experiences of patients with an implantable cardioverter defibrillator

This article describes the relationships between anxiety, self-efficacy, as well as the psychosocial and physiological experiences of patients with an internal cardioverter defibrillator (ICD). Although survival rates with ICDs are impressive, patients experience psychological and physiological responses to their lifesaving devices. Thirty-nine patients completed questionnaires during outpatient clinic visits. Patients' anxiety levels were correlated with fears about ICD malfunction, fear of death, fear of being shocked, loss of control, trouble related to sleeping, inability to concentrate, overprotective family members, and depression. Patients with physical symptoms had higher anxiety levels than those without physical symptoms. There was not a significant relationship between anxiety and discomfort associated with discharge, the number of discharges, or ejection fractions. Low self-efficacy was significantly related to fears about ICD malfunction as well as patients' inability to work, engage in hobbies, and drive a car. Patients with low self-efficacy had more physical symptoms and lower ejection fractions. There were no significant relationships between self-efficacy and frequency of ICD discharge or patients' discomfort during ICD discharge.

Infections with nonthoracotomy implantable cardioverter defibrillators: can these be prevented? Endotak Lead Clinical Investigators

Nonthoracotomy ICDs are believed to be the best therapeutic modality for treatment of life-threatening ventricular arrhythmias. Little is known about the risk of infection with initial implantation of these devices. We studied the incidence, clinical characteristics, and risk factors associated with infections in 1,831 patients with nonthoracotomy ICD from the Endotak-C nonthoracotomy lead registry of Cardiac Pacemakers, Inc. A transvenous lead was implanted in 950 patients (51.9%) and a combination transvenous plus subcutaneous patch was used in 881 patients (48.1%). Nine preselected data variables were studied, and all investigators identified as having patients with infections were personally contacted. Infections occurred in 22 (1.2%) of 1,831 patients receiving this nonthoracotomy ICD system. The mean time to infection was 5.7 +/- 6.5 months (range 1-25 months). Staphylococci were isolated in 58% of patients with reported infection. The presence of a subcutaneous defibrillator patch system was associated with the development of infection. Six of 950 patients (0.63%) with a totally transvenous lead system developed infection versus 16 of 838 (1.9%) patients with a transvenous lead plus subcutaneous patch system configuration (P = 0.015, Chi-square test), with an unadjusted estimated odds ratio of 3.06 (CI 1.19-7.86). The risk of infection encountered with the nonthoracotomy ICD is low, estimated from our data to be 1.2%. Placement of a subcutaneous defibrillator patch appears to be an independent risk factor for development of infection.

A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias

BACKGROUND

Patients who survive life-threatening ventricular arrhythmias are at risk for recurrent arrhythmias. They can be treated with either an implantable cardioverter-defibrillator or antiarrhythmic drugs, but the relative efficacy of these two treatment strategies is unknown.

METHODS

To address this issue, we conducted a randomized comparison of these two treatment strategies in patients who had been resuscitated from near-fatal ventricular fibrillation or who had undergone cardioversion from sustained ventricular tachycardia. Patients with ventricular tachycardia also had either syncope or other serious cardiac symptoms, along with a left ventricular ejection fraction of 0.40 or less. One group of patients was treated with implantation of a cardioverter-defibrillator; the other received class III antiarrhythmic drugs, primarily amiodarone at empirically determined doses. Fifty-six clinical centers screened all patients who presented with ventricular tachycardia or ventricular fibrillation during a period of nearly four years. Of 1016 patients (45 percent of whom had ventricular fibrillation, and 55 percent ventricular tachycardia), 507 were randomly assigned to treatment with implantable cardioverter-defibrillators and 509 to antiarrhythmic-drug therapy. The primary end point was overall mortality.

RESULTS

Follow-up was complete for 1013 patients (99.7 percent). Overall survival was greater with the implantable defibrillator, with unadjusted estimates of 89.3 percent, as compared with 82.3 percent in the antiarrhythmic-drug group at one year, 81.6 percent versus 74.7 percent at two years, and 75.4 percent versus 64.1 percent at three years (P<0.02). The corresponding reductions in mortality (with 95 percent confidence limits) with the implantable defibrillator were 39+/-20 percent, 27+/-21 percent, and 31+/-21 percent

CONCLUSIONS

Among survivors of ventricular fibrillation or sustained ventricular tachycardia causing severe symptoms, the implantable cardioverter-defibrillator is superior to antiarrhythmic drugs for increasing overall survival.

Definition of predicted effective antiarrhythmic drug therapy for ventricular tachyarrhythmias by the electrophysiologic study approach: randomized comparison of patient response criteria

OBJECTIVES

We sought to compare efficacies of therapy for ventricular tachyarrhythmias selected by programmed stimulation using two different patient response efficacy criteria: <5 versus <16 repetitive ventricular responses.

BACKGROUND

Therapy selection for ventricular tachyarrhythmias by programmed stimulation requires definition of a patient response that predicts long-term efficacy. Such definitions have not been previously compared prospectively.

METHODS

Patients with sustained ventricular tachyarrhythmias were randomized to therapy selection using either the <5 or <16 repetitive response criterion of predicted effective therapy. The primary end point was sudden death or recurrence of ventricular tachyarrhythmia requiring intervention.

RESULTS

Predicted effective drug therapy was found for 23 (34%) of 68 patients randomized to the <5 criterion and 29 (36%) of 81 patients randomized to the <16 criterion (p = NS). Definition of therapy required 3.0 +/- 1.6 drug trials (mean +/- SD) in patients randomized to the <5 criterion and 2.9 +/- 1.8 trials in patients randomized to the <16 criterion (p = NS). Patients randomized to the <5 criterion had a lower 2-year probability of the primary end point (0.20 +/- 0.05) than did patients randomized to the <16 criterion (0.33 +/- 0.05, one-tailed p = 0.004). The advantage of the <5 criterion was also seen in subgroup analyses involving patients with and without an initial drug efficacy prediction.

CONCLUSIONS

The programmed stimulation approach to the selection of antiarrhythmic therapy for ventricular tachyarrhythmias using a patient response criterion of <5 repetitive ventricular responses results in a lower probability of recurrence of ventricular tachyarrhythmia than does use of a <16 repetitive response criterion.

Implantable cardioverter defibrillator utilization among device recipients presenting exclusively with syncope or near-syncope

INTRODUCTION

Implantable cardioverter defibrillators (ICDs) are occasionally used in presumed high-risk patients with electrocardiographically undocumented syncope, although the incidence of ventricular tachyarrhythmias in this population is not well defined.

METHODS AND RESULTS

We studied 33 consecutive patients receiving an ICD (67% nonthoracotomy and 70% tiered therapy) after electrophysiologic testing for unmonitored "syncope" (n = 29) or "near-syncope" (n = 4). Atherosclerotic heart disease was present in 24 (73%); mean left ventricular ejection fraction (LVEF) was 0.39 +/- 0.15; and sustained monomorphic ventricular tachycardia (SMVT) was inducible in 18 (55%). Over a median follow-up of 17 months (range 4 to 61), 12 patients (36%) received > or = 1 appropriate ICD discharge triggered by SMVT (cycle length 230 to 375 msec) in 10 and ventricular flutter or fibrillation in 2--without concomitant antiarrhythmic medication in 8 of 12 cases. Inducible SMVT and LVEF < or = 0.35 were statistically significant, independent predictors of an appropriate ICD discharge (P < 0.02 and P < 0.03, respectively). Estimated 1-year cumulative survival free of appropriate discharge was 34% versus 87%, respectively, in patients with versus without inducible SMVT (P < 0.02), and 18% versus 56%, respectively, in patients with LVEF < or = 0.35 versus LVEF > 0.35 (P < 0.03).

CONCLUSION

In this highly select, multicenter population of ICD recipients with electrocardiographically undocumented syncope, a substantial incidence of appropriate device discharges was observed, particularly in patients with inducible SMVT and LVEF < or = 0.35. These findings support the notion that, in patients with LV dysfunction and inducible SMVT, ventricular tachyarrhythmias are likely to account for episodes of syncope or near-syncope.

Ventriculoatrial conduction capability and prevalence of 1:1 retrograde conduction during inducible sustained monomorphic ventricular tachycardia in 305 implantable cardioverter defibrillator recipients

Despite the advent of dual chamber ICDs, differentiation of VT (SMVT) with 1:1 VA conduction will remain a challenge. In this study, VA conduction capability and prevalence of inducible sustained monomorphic (SM) VT with 1:1 VA conduction was assessed in 305 ICD recipients. SMVT with a mean cycle length (CL) of 304 +/- 61 ms was induced in 161 (53%) patients. Twenty-six percent of the patients maintained 1:1 VA conduction to CL < or = 400 ms during incremental ventricular pacing, regardless of presenting tachyarrhythmia or presence of inducible SMVT. Among ten patients who had inducible SMVT with possible 1:1 VA conduction (based on SMVT CL comparable to the shortest CL associated with 1:1 retrograde conduction during ventricular pacing), all seven with available intracardiac tracings had documented 1:1 VA conduction during the induced SMVT--representing 4.4% of the patients with inducible SMVT (95% CI 1.2%-7.6%), and 2.3% of the entire ICD cohort (95% CI 0.6%-4.0%). We conclude that about one-fifth of ICD recipients possess 1:1 VA conduction to CL < or = 400 ms and that inducible SMVT with 1:1 VA conduction can be demonstrated in a small but nonnegligible proportion of ICD recipients. These data are relevant to the design of tachyarrhythmia-discrimination algorithms for dual chamber ICDs.

Current concepts in electrical defibrillation

The electrical defibrillator has been proven to be a life-saving device in the treatment of cardiac arrest due to ventricular tachycardia or ventricular fibrillation. An understanding of the physiology and technology behind this device is useful for providers of emergency care. In this article, we review the current concepts in electrical defibrillation and briefly discuss the developmental history. The physiology and the technical considerations will make up the bulk of the discussion. The latest developments in electrical defibrillation also will be reviewed.

The vanishing defibrillator syndrome: incidence, mechanism, and clinical relevance

Intraperitoneal migration of an abdominally implanted cardioverter defibrillator is a complication not yet fully described. In a consecutive series of 195 patients, migration occurred between 1 and 20 months in 5 (8%) of the 63 patients in whom a subrectus abdomini placement of the generator was chosen. It was unrelated to the patients' clinical characteristics or the defibrillator model. Dysuria and inability to interrogate the device were present in every subject, and the diagnosis was confirmed by the characteristic abdominal x-ray appearance and the findings at the time of surgery. Adhesions involving the omentum, and in one case, the small bowels, were present in three patients and seem to be related to the length of intraabdominal permanence of the generator. Because this complication may be due to specific anatomical characteristics of the aponeurosis of the abdominal muscles, it is likely that its incidence will be unchanged by the use of smaller devices. A close follow-up of the generators implanted deep to the rectus fascia is therefore advisable.

Does the initial presentation of patients with implantable defibrillator influence the outcome?

The influence of the clinical presentation on the long-term outcome in 213 consecutive patients with ICDs, ECG storage capability, and nonthoracotomy leads, was analyzed. Sixty-six patients presented with cardiac arrest (CA), 81 patients with hemodynamically stable VT, and 66 patients with syncope (SY). Patient characteristics were: mean age CA 62, VT 61, SY 61 years; mean ejection fraction CA 31%, VT 29%, SY 30%; coronary artery disease CA 71%, VT 71%, SY 64% (all P > 0.05 Fisher's exact test); female gender CA 40%, VT 14%, SY 19% (CA vs VT and SY, P < 0.005); inducibility by programmed stimulation CA 50%, VT 84%, SY 61% (VT vs CA and SY, P < 0.001, CA vs SY, P > 0.05). During a mean follow-up of 14.5 months, 29 patients died: CA 12%, VT 14%, SY 9% (P > 0.05). Comparing Kaplan-Meier curves, no difference in the time course of overall mortality was found (log-rank P > 0.05). In the CA, VT, and SY groups, 543, 1,630, and 189 ICD therapies (including antitachycardia pacing, low energy cardioversion, and defibrillation) were observed, respectively. Actuarial analysis showed a shorter interval between implantation and first ICD therapy for VT versus CA and SY (log-rank P < 0.005). Patients presenting with VT experienced earlier and more frequent ICD therapies than patients with CA or SY independent of age, ejection fraction, and heart disease. No difference in overall mortality and time course of fatal events was observed among the three groups.

Impact of the implantable defibrillator on mortality: the axiom of overall implantable cardioverter-defibrillator survival

As soon as it was established that the implantable cardioverter-defibrillator (ICD) effectively prevents sudden death, it became axiomatic that whether the ICD will prolong overall survival depends entirely on the population of patients to which it is applied. This axiom of overall ICD survival immediately reveals the only vital question that remains regarding usage of the ICD; namely, How does one select those patients in whom prevention of sudden death by the ICD will also prolong life? This axiom also reveals the essential futility of randomized trials now being conducted for the purpose of discerning the true efficacy of the ICD. Claims to the scientific high ground notwithstanding, if a study asks the wrong question from the beginning, then the design of that study (including whether the study is randomized or nonrandomized), is completely irrelevant. Ideally, funds now being spent on these randomized trials should be diverted to the design and initiation of more appropriate trials, trials that will teach us to select patients for the ICD more effectively. At the very least, however, we should recognize the problems inherent in the ongoing trials, so that when their results are finally published (and are loudly touted by whichever faction feels vindicated by them), we will not be carried away into inappropriate clinical behavior.

Securing life through technology acceptance: the first six months after transvenous internal cardioverter defibrillator implantation

PURPOSE

To understand the experience of living with a transvenous internal cardioverter defibrillator (ICD) during the first 6 months after implantation.

DESIGN

A grounded theory approach was used to gain an understanding of the antecedents, conditions, and consequences of the core process.

SETTING

Two midwestern community medical centers and patients' homes within a 250-mile radius from the medical centers.

SAMPLE

Ten women and 14 men between 22 and 78 years of age, who had undergone a new transvenous ICD implantation within the last week.

RESULTS

The core process that described the experience of living with a transvenous ICD during the first 6 months after implantation was the process of "securing life through technology acceptance." This core process was characterized by three major categories: choosing life with technology, integrating technology into life, and living life through technology.

IMPLICATIONS

Nursing interventions related to individualized assessment, education, and counseling are warranted to facilitate patient and family understanding and to plan for the cyclic process involved in integrating a transvenous ICD into their lives. Directions for further research are provided.

Interactions between pharmacologic and nonpharmacologic antiarrhythmic therapy

Whether patients with serious ventricular arrhythmias should be treated first with antiarrhythmic drugs or an implantable cardioverter-defibrillator (ICD) is not known. Many patients are ultimately treated with both an antiarrhythmic drug and on ICD. Early studies reported that 40-70% of patients who received an ICD were ultimately treated with an antiarrhythmic drug, although fewer patients are now being treated with both modalities. The beneficial interactions between antiarrhythmic drugs and an ICD are slowing of ventricular tachycardia, which yields improved hemodynamic tolerance; improved antitachycardia pacing and low energy cardioversion success; lowering of antiarrhythmic drug doses, which reduces the risk of side effects; limiting the number of arrhythmia episodes, which minimizes patients discomfort and prolongs ICD battery life; and preventing or slowing supraventricular tachyarrhythmias, which reduces the number of inappropriate shocks from the ICD. The disadvantages of combining pharmacologic therapy and the use of an ICD are the cost and side effects of both therapies. Adverse interactions between an ICD and antiarrhythmic drugs include slowed ventricular tachycardia, which may lead to failure to detect the arrhythmia; increased defibrillation and pacing thresholds; worsened hemodynamic tolerance of ventricular tachycardia; lengthened PR, QRS, or QT intervals causing multiple counting; and decreased size of the intracardiac electrogram, leading to failure to detect the ventricular tachycardia or fibrillation. Caution must be used when combining pharmacologic therapy with an ICD. Repeat electrophysiologic testing is frequently necessary after the initiation of antiarrhythmic drug therapy in a patient with an ICD to ensure successful therapy with the ICD.

Incidence of lead system malfunction detected during implantable defibrillator generator replacement

Implantable cardioverter-defibrillator (ICD) generator replacement due to a depleted battery is a frequently performed procedure. The frequency with which sensing and defibrillation system failures are identified during device replacement procedures has not been previously described. Therefore, the purpose of this study was to prospectively determine the frequency of lead system malfunction detected at the time of device replacement in 55 consecutive patients undergoing ICD generator replacement. The mean age of the patients was 63 +/- 10 years and 40 of them were men. Forty-nine patients had an epicardial lead system, and six patients had a nonthoracotomy lead system. Four [7%] of these 55 patients were noted to have previously undetected lead system failure, either sensing (n = 3) or defibrillation (n = 1), necessitating system revision. The lead systems that failed were 40 +/- 6 months old (33-49 months). In summary, during ICD generator replacement, previously undetected problems with sensing or defibrillation may be identified in approximately 10% of patients. Therefore, a comprehensive evaluation of the sensing and the defibrillation functions should be an essential component of the ICD generator replacement procedure.

Therapy of ventricular tachycardia in patients with nonischemic cardiomyopathies

In patients with IDCM and sustained VT, every effort should be made to exclude bundle branch reentrant tachycardia. We strongly believe that this mechanism of VT remains underdiagnosed despite electrophysiologic evaluation. In appropriate candidates with cardiomyopathies and "nonbundle branch reentrant VT," ICD implantation is frequently the treatment of choice, especially if the clinical presentation is that of hemodynamic collapse, or there is significant left ventricular systolic dysfunction. The role of amiodarone versus ICD, especially for patients with well-tolerated VT and milder forms of cardiomyopathies, is yet to be defined.

Implanted cardioverter-defibrillators are preferable to drugs as primary therapy in sustained ventricular tachyarrhythmias

The choice of initial therapy for patients with malignant ventricular tachyarrhythmias is examined based on clinical efficacy, patient safety, and cost. Antiarrhythmic drug therapy can be administered using a guided or empiric approach. Guided type-1 antiarrhythmic drug therapy has been associated with high arrhythmia recurrence rates (> 40% at 1 year) and moderate sudden death rates (10% at 1 year). Sotalol is associated with lower arrhythmia recurrence rates (20% at 1 year) that increase to 50% at 4 years. Beta-blocking agents have a limited role as stand-alone therapy in this condition. Empiric amiodarone therapy has sudden death-free survival rates of 82% at 2 years but has significantly poorer results in patients with ejection fractions < or = 40%. In contrast, implantable cardioverter-defibrillator (ICD) therapy has reported sudden death recurrence rates of 1% to 2% per year, with a cumulative index of 10% at 5 years. Total survival rate of ICD recipients ranges from 85% to 92% at 2 years. In patients with good left ventricular function, it approaches 90% at 5 years, whereas it is between 50% to 60% in patients with severe left ventricular dysfunction. Data from device memory indicate an absolute reduction in mortality rates with ICD intervention. Comparison of drug and device therapy has been performed in retrospective and prospective studies. Improved survival with device therapy is noted, particularly in patients with ejection fractions < or = 35% to 40% in retrospective studies. The results of two small prospective randomized trials also show significant survival advantage as compared with those for type-1C drugs and a mixed group of antiarrhythmic drugs. An initial strategy of ICD therapy was shown to be superior in the Netherlands Cooperative Study. The 30-day perioperative mortality rate of ICD therapy of 0.8% contrasts favorably with a 13% mortality rate in the ESVEM trial with antiarrhythmic drugs and a 3.5% mortality rate in the CASCADE study. Economic analyses show that drug therapy and device therapy are both within the range of other current cardiovascular therapies. An improving economic profile for device therapy has been observed with nonthoracotomy and pectoral implantation and direct use of ICD therapy because primary therapy shortens hospital stay and reduces costs. Based on available data, ICD therapy is preferable as initial therapy in patients with malignant ventricular tachyarrhythmias.

Current approaches in patients with ventricular tachyarrhythmias

The article has summarized the studies and ongoing trials looking at the significance and treatment of ventricular tachyarrhythmias. In most instances, the presence of these arrhythmias is associated with an increased risk of future arrhythmic events. Electrophysiologic studies are helpful in risk stratification in patients with coronary artery disease but can be misleading in the setting of dilated cardiomyopathy and often produce nonspecific results in patients with HCM. The need for an invasive electrophysiologic study is crucial in the diagnosis of certain ventricular arrhythmias that are amenable to cure with radiofrequency catheter ablation, such as idiopathic ventricular tachycardia and BBR-VT. The correct approach for patients with SVT not amenable to catheter ablation remains to be determined. In deciding whether to use a device or drug therapy, however, one should take into consideration the degree of left ventricular dysfunction and the overall health status of the patient. For example, device implantation clearly reduces sudden death in patients with severe left ventricular dysfunction but may not change total mortality because these same patients may die of congestive heart failure. Device therapy might be more cost-effective for patients with less severe depression of left ventricular function.

Postoperative lead-related complications in patients with nonthoracotomy defibrillation lead systems

OBJECTIVES

This study sought to document postoperative complications attributable to nonthoracotomy defibrillation lead systems in a large cohort.

BACKGROUND

The incidence of postoperative complications specifically associated with nonthoracotomy defibrillation lead systems is unknown.

METHODS

Postoperative lead-related complications were evaluated in 170 patients with a nonthoracotomy defibrillation lead system who were followed up for a mean (+/- SD) of 17 +/- 12 months. Each system incorporated one or more intravascular leads. In 117 patients (69%), the system incorporated a subcutaneous defibrillation patch. All implantations were performed in an operating room by cardiothoracic surgeons. Defibrillation thresholds were measured at implantation, before hospital discharge (mean 3 +/- 2 days) and at 4 to 18 weeks after implantation. Patients were evaluated every 2 to 3 months after implantation or as indicated by clinical exigency.

RESULTS

Twenty-seven patients (15.9%) were diagnosed with a lead-related complication that either extended the initial hospital period or led to a second hospital admission. Complications included endocardial lead or subcutaneous defibrillation patch dislodgment in eight patients (4.7%), which was diagnosed between 2 and 345 days after implantation; endocardial or subcutaneous patch lead fracture in six (3.5%), which was diagnosed between 53 and 600 days after implantation; subcutaneous patch mesh fracture in one, which was diagnosed at 150 days after implantation; subclavian vein thrombosis in three (1.8%), which was diagnosed at 2 to 50 days after implantation; and unacceptably elevated defibrillation threshold (within 5 J of maximal device output) in nine (5.3%), which was documented at one of the two postimplantation evaluations in eight patients or at the time of failure to terminate a spontaneous ventricular tachycardia in one. Seventeen of the 27 patients required reoperation for correction of their complication. In addition, system infection requiring complete explantation occurred in seven other patients (4.1%) at an interval from implantation ranging from 14 to 120 days.

CONCLUSIONS

Postoperative complications related to a nonthoracotomy defibrillation lead system were common and frequently required reoperation for correction. The rate of system explantation due to infection was also significant. Postoperative defibrillation testing and vigilant outpatient follow-up evaluation are necessary to ensure normal lead function.

Description and evaluation of the Res-Q Arrhythmia Control Device

The Res-Q Arrhythmia Control Device (Intermedics Inc.) is one of the latest entries into the growing implantable cardioverter defibrillator (ICD) market. Dysrhythmias are classified according to their zone of detection, with a bradycardia zone, up to 3 tachycardia zones, and a fibrillation zone. Detection criterion, therapies, and redetection criterion within each zone are independently programmable, tailoring the setup to each individual's needs. In a hierarchical manner, this allows efficacy, urgency, and patient comfort to be appropriately balanced. Tachycardia therapy options include antitachycardia pacing (ATP), low-energy cardioversion, and high-energy shock, while VVI pacing provides bradycardia therapy. ATP programming is extremely flexible. Biphasic waveform and a maximum output of 700 V have yielded a high rate of successful implantation. Unique features include the multiprogrammable sensing autogain, which tracks evoked T waves during pacing, as well as the use of the pulse generator to perform implant testing. Major strengths include programming flexibility and individualized therapy for multiple dysrhythmias. The major shortcoming relates to a lack of stored electrograms. Although long-term follow-up is not yet available, the Res-Q appears to be a capable challenger to a peer group of advanced generation ICDs.

The usefulness of a stretch-polyester pouch to encase implanted pacemakers and defibrillators

This study was undertaken to assess the effects of enclosing permanent pacemaker and ICD pulse generators in a stretch-polyester pouch prior to implantation. Follow-up of 223 patients with oversized pacemakers and with ICDs and 344 with standard-sized pacemaker pulse generators showed that the pouch was effective in decreasing the frequency of pulse generator migration and extrusion.

Survival and incidence of appropriate shocks in implantable cardioverter defibrillator recipients who have no detectable structural heart disease. CEDARS Investigators

Prognosis of patients with episodes of hypotensive ventricular tachycardia (VT) or ventricular fibrillation (VF) in the absence of structural heart disease is poorly defined. To solve this problem, this study analyzed a subgroup of 25 such patients chosen from 468 consecutive patients who had an initial implantable cardioverter defibrillator (ICD) inserted between May 1984 and May 1990 in 9 medical centers and were followed up for at least 1 year. The patient group consisted of 17 men and 8 women, aged 8 to 75 years. Cardiac arrest occurred in 20 patients, 3 patients had recurrent VT, and 2 patients had both. Left ventricular ejection fraction ranged from 50% to 70%. During electrophysiologic study, a specific response was seen in 13 patients, defined as monomorphic VT (5 patients), or VF in those who had a history of VF (8 patients). In 8 patients, only a nonspecific response was seen. No arrhythmia could be induced in 4 patients. Of the 13 patients with a specific response, antiarrhythmic drug was tested in 9; in 3 of them the arrhythmia was suppressed. Within the first year, 6 of the 25 patients (24%) received appropriate shock. In the remaining 436 patients who had organic heart disease, 155 (36%) received appropriate ICD shock (p = NS). Therefore, ICD implantation appears to be warranted in patients with a history of life-threatening arrhythmias, not only in the presence but also in the absence of demonstrable structural heart disease.