Nonpharmacological therapy for malignant ventricular arrhythmias: implantable defibrillator trials

Cardiac amyloidosis treated with an implantable cardioverter defibrillator and subcutaneous array lead system: report of a case and literature review

BACKGROUND

Preventing ventricular arrhythmias in patients with cardiac amyloidosis is challenging since the amyloid protein deposition in the myocardium may interfere with the normal cardiac electric excitation. Most of these patients succumb to either progressive congestive heart failure, or sudden cardiac death (SCD). Implantable cardioverter defibrillator (ICD) offers a near sure means of preventing SCD.

HYPOTHESIS

Myocardial infiltration with amyloid results in elevated defibrillation threshold (DFT). Intra-operative strategies may fail to lower DFT during implantation.

METHODS

We present a case of a 64-year-old female who had cardiac amyloidosis, and was successfully treated with an ICD and a subcutaneous array lead system.

CONCLUSION

A subcutaneous array lead system is useful in reducing the DFT, and can terminate ventricular tachycardia or fibrillation by allowing more energy delivery and efficient defibrillation.

Implantable device therapy

Sudden cardiac death (SCD) accounts for two-thirds of fatal events related to heart disease. Coronary heart disease and non-ischemic cardiomyopathy are the most common causes of SCD. Data from major randomized trials have consistently shown that therapy with an implantable cardioverter defibrillator (ICD) results in a significant and meaningful effect on survival through a reduction in the risk of SCD in these population. These data have resulted in a marked increase in the application of implantable device therapy in the past 2 decades from secondary prevention with an implantable cardioverter/defibrillator (ICD) in survivors of a cardiac arrest to primary prevention of SCD in asymptomatic patients with ischemic and non-ischemic left ventricular dysfunction, and prevention of symptomatic heart failure progression and death with cardiac resynchronization therapy (CRT), and devices that combine CRT and ICD therapies (CRT-D). However, there are still areas of uncertainty regarding device therapy that include inconsistent benefit in risk-subgroups of patients with low ejection fraction; increased risk of heart failure after life-prolonging ICD therapy, and a considerable rate of device malfunction despite increasing sophistication. In the present review we focus on current data regarding the clinical indications as well as the safety and efficacy of implantable device therapy, including ICD, CRT, and CRT-D.

Comparison of the efficacy of a subcutaneous array electrode with a subcutaneous patch electrode, a prospective randomized study

The patch electrode and the array electrode are the two types of subcutaneous leads available as an adjunct to a transvenous lead system in patients with high defibrillation thresholds. A prospective randomized study was conducted in 30 consecutive patients comparing the efficacy and the long-term performance of a patch electrode with an array electrode. After determination of the defibrillation threshold for the transvenous lead alone, a subcutaneous patch or an array electrode was implanted in random order. Adding a patch electrode decreased the defibrillation threshold in seven out of 15 patients (47%) from 13.2+/-6.6 to 10.5+/-5.1 J (P<0.05). In 13 out of 15 patients (87%), the implantation of an array electrode caused a significant lowering of the defibrillation threshold from 15.4+/-6.6 to 8.2+/-5.0 J (P<0.0001). The array electrode was significantly more effective in lowering the defibrillation threshold than the patch electrode (P<0.01). Complications during follow-up associated with the subcutaneous patch electrode were observed in four patients whereas no complications were associated with the array electrode (P<0.01). The additional implantation of an array electrode is more effective and associated with fewer complications compared to a patch electrode.

Subpectoral cardioverter-defibrillator implantation using a lateral approach

INTRODUCTION

Third-generation cardioverter-defibrillators have revolutionized management of ventricular tachyarrhythmias. Implantation can be performed in the electro-physiology laboratory, with minimal morbidity. Generator size has shrunk to the point that subcutaneous implantation is feasible and safe, even under local anesthesia. The prepectoral technique, however, is associated with increased mechanical stress to the subcutaneous tissue and can predispose to device erosion or infection. These complications may be avoided by submuscular placement. Among subpectoral techniques, the lateral approach offers unrestricted ability to deploy patches or array electrodes, should the need arise, and may represent the optimal implant technique under some circumstances.

METHODS

We studied 29 male patients, aged 29-78 years, who presented with syncope or sustained ventricular tachycardia, and underwent subpectoral defibrillator implantation under general anesthesia or conscious sedation. All devices were third-generation active can systems with biphasic shock capability. Six dual-chamber defibrillators were used.

RESULTS

Subpectoral implantation was successful in all cases, with an estimated blood loss of 28+/-17 mL and no immediate complications. Except for one patient who developed twiddler's syndrome and ultimately required revision to a subcutaneous pocket, the implant site was tolerated well, and no limitation in the range of motion of the upper limb was observed during 20 months of follow-up.

CONCLUSIONS

Subpectoral implantation using a lateral approach is technically straightforward and can be applied globally, with modest additional resource and equipment requirements. Familiarity with this approach can maximize the likelihood of successful defibrillator implantation in the electrophysiology laboratory.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

Effect of a single element subcutaneous array electrode added to a transvenous electrode configuration on the defibrillation field and the defibrillation threshold

Even with the use of biphasic shocks, up to 5% of patients need an additional subcutaneous lead to obtain a defibrillation safety margin of at least 10 J. The number of patients requiring additional subcutaneous leads may even increase, because recent generation devices have a < 34 J maximum output in order to decrease their size. In 20 consecutive patients, a single element subcutaneous array lead was implanted in addition to a transvenous lead system consisting of a right ventricular (RV) and a vena cava superior lead using a single infraclavicular incision. The RV lead acted as the cathode; the subcutaneous lead and the lead in the subclavian vein acted as the anode. The biphasic defibrillation threshold was determined using a binary search protocol. Patients were randomized as to whether to start them with the transvenous lead configuration or the combination of the transvenous lead and the subcutaneous lead. In addition, a simplified assessment of the defibrillation field was performed by determining the interelectrode area for the transvenous lead only and the transvenous lead in combination with the subcutaneous lead from a biplane chest X ray. The intraoperative defibrillation threshold was reconfirmed after 1 week, after 3 months, and after 12 months. The mean defibrillation threshold with the additional subcutaneous lead was significantly (P = 0.0001) lower (5.7 +/- 2.9 J) than for the transvenous lead system (9.5 +/- 4.6 J). With the subcutaneous lead, the impedance of the high voltage circuit decreased from 48.9 +/- 7.4 omega to 39.2 +/- 5.0 omega. In the frontal plane, the interelectrode area increased by 11.3% +/- 5.5% (P < 0.0001) and in the lateral plane by 29.5% +/- 12.4% (P < 0.0001). The defibrillation threshold did not increase during follow-up. Complications with the subcutaneous electrode were not observed during a follow-up of 15.8 +/- 2 months. The single finger array lead is useful in order to lower the defibrillation threshold and can be used in order to lower the defibrillation threshold.

Single-incision and single-element array electrode to lower the defibrillation threshold

Occasional patients have excessive defibrillation energy requirements despite appropriate transvenous defibrillation lead position and the use of biphasic shocks. A single-element subcutaneous array electrode was implanted in 2 patients with a high defibrillation threshold. The array electrode was implanted through the same infraclavicular incision that was used for implantation of the transvenous lead. The defibrillation threshold decreased from 30 J to 15 J and from 24 J to 9 J with the subcutaneous array electrode.

A summary and assessment of the findings and conclusions of the ESVEM trial

The Electrophysiologic Study Versus Electrocardiographic Monitoring (ESVEM) trial was completed in 1992 and the primary results were reported in 1993. Since then, considerable discussion about this trial has taken place and new trial results have been reported. Trial analysis has yielded seven principal findings to date concerning treatment of patients with ventricular tachyarrhythmias, ie: (1) similar accuracy of electrophysiologic study (EPS), Holter monitoring (HM), and EPS combined with HM for predicting antiarrhythmic drug efficacy; (2) greater efficiency and lower cost of HM; (3) improved survival associated with predicted drug efficacy; (4) predictors of response to EPS and HM; (5) greater efficacy and lower cost of therapy with sotalol compared with drugs with class-l effects; (6) lack of a relationship between presenting and recurring arrhythmia; and (7) preponderance of nonarrhythmic deaths in trial participants. A number of additional specific findings of the trial are reviewed in this symposium. Several criticisms of the trial's enrollment, methods, and efficacy criteria are reviewed and discussed. Some criticisms are valid. Many are related to misunderstandings of ESVEM trial methodology and to bias of the individual critics. Some are simply incorrect. The importance of the ESVEM trial in the present day may be limited by the growing use of implanted devices rather than drugs for treatment of ventricular tachyarrhythmias. If clinical trials ultimately prove devices to be no more effective than drugs, the findings of the ESVEM investigators will grow in importance.