Out-of-hospital cardiac arrest. Use of electrophysiologic testing in the prediction of long-term outcome

Evidence rather than costs must guide use of the implantable cardioverter defibrillator

Randomized controlled trials have shown superior survival rates with implantable cardioverter defibrillators (ICDs) compared with antiarrhythmic drugs in survivors of cardiac arrest and life-threatening ventricular tachyarrhythmias, as well as in high-risk patients with ischemic heart disease and inducible ventricular tachycardia (VT). Current defibrillators are small and implanted with techniques similar to standard pacemakers. They provide high-energy shocks for ventricular fibrillation (VF) and rapid VT, antitachycardia pacing for monomorphic VT, and antibradycardia pacing. Limited evidence suggests that ICD therapy is cost-effective when compared with other widely accepted treatments. The use of ICDs is likely to continue to expand in the future. Ongoing clinical trials will define further prophylactic indications of the ICD and clarify its cost-effectiveness ratio in different clinical settings.

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.

Mode of onset of ventricular fibrillation in patients with Brugada syndrome detected by implantable cardioverter defibrillator therapy

OBJECTIVES

We sought to demonstrate the mode of spontaneous onset of ventricular fibrillation (VF) in patients with Brugada syndrome.

BACKGROUND

The electrophysiologic mechanisms of VF in Brugada syndrome have not been fully investigated.

METHODS

Nineteen patients (all male, mean age 47 +/- 12 years) with Brugada syndrome were treated with an implantable cardioverter defibrillator (ICD). The implanted devices were capable of storing electrograms during an arrhythmic event. We investigated the mode of spontaneous onset of VF according to the electrocardiographic features during the episode of VF, which were obtained from stored electrograms of ICDs and/or electrocardiographic (ECG) monitoring.

RESULTS

During a follow-up of 34.7 +/- 19.4 months (range 14 to 81 months), 46 episodes of spontaneous VF attacks were documented in 7/19 (37%) patients. The event-free period between ICD implantation and the first spontaneous occurrence of VF was 14.6 +/- 12.1 months (range 3.7 to 27.4 months). We investigated 33/46 episodes of VF, for which electrocardiographic features (10 to 20 s before and during VF) were obtained from ICDs and/or ECG monitoring in five patients. A total of 22/33 episodes of VF were preceded by premature ventricular contractions (PVCs), which were almost identical to the initiating PVCs of VF. Furthermore, in three patients who had multiple VF episodes, VF attacks were always initiated by the same respective PVC. The coupling interval of the initiating PVCs of VF was 388 +/- 28 ms.

CONCLUSIONS

Spontaneous episodes of VF in patients with Brugada syndrome were triggered by specific PVCs. These findings may provide important insights into the pathophysiological mechanisms causing VF in Brugada syndrome.

Management of malignant ventricular arrhythmias and cardiac arrest

Sudden cardiac death continues to be a major health problem in the United States, accounting for approximately 400,000 deaths per year. The last 10 yrs have seen major advances in the primary and secondary prevention of this problem. In patients who have survived an episode of cardiac arrest, the AVID study conclusively established the superiority of the implantable cardioverter defibrillator over empiric amiodarone. For patients with recurrent hemodynamically destabilizing ventricular tachycardia and ventricular fibrillation, intravenous amiodarone has emerged as a potent therapeutic agent, especially when other agents such as lidocaine and procainamide have not been effective. Finally, recent work has focused on the risk stratification of patients for sudden cardiac death. Both the MADIT and MUSTT studies suggest that patients with coronary artery disease, reduced ejection fraction, and nonsustained ventricular tachycardia who are inducible to a sustained ventricular arrhythmia at electrophysiology testing have improved survival with an implantable cardioverter defibrillator.

Implantable Cardioverter Defibrillator: Current Progress and Management

With greater technologic advances during the past decade, use of the implantable cardioverter defibrillator (ICD) has increased to more than 200,000 implants worldwide to date. Indications for ICD implant have expanded to include both patients who have survived sudden cardiac death (secondary prevention of cardiac arrest) and those who are at high risk for experiencing lethal arrhythmias (primary prevention of cardiac ar rest). Thus, it is likely that physicians will encounter defibrillators in their clinical practice and must be familiar with their indications for implant, basic opera tion, and long-term management of devices. Several prospective clinical trials have recently shown the long- term efficacy of ICD therapy at aborting sudden death in the high-risk patient population. Although still evolving, general guidelines and indications for ICD implant have been put forth and are discussed in this review. From the first defibrillation in humans during surgery in 1947 to the sophisticated dual-chamber pacing and memory functions of the modern device, ICD development has led to ever smaller devices with more complex technol ogy. The implant procedure of current ICDs parallels that used to place pacemakers. However, the anesthe sia team plays a vital role in initial ICD implantation by monitoring cardiopulmonary status during defibrilla tion threshold (DFT) testing. Additionally, long-term management of ICDs often requires repeat DFT testing with anesthesia involvement. Finally, possible electro magnetic (environmental) interactions with the ICD of which physicians should be aware are described in this article.

Determinants of outcome in patients with sustained ventricular tachyarrhythmias: the antiarrhythmics versus implantable defibrillators (AVID) study registry

BACKGROUND

The prognosis of patients with sustained ventricular tachyarrhythmias varies according to clinical characteristics. We sought to identify predictors of survival in a large population of patients with documented sustained ventricular tachyarrhythmias not related to reversible or correctable causes included in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Registry.

METHODS AND RESULTS

We analyzed the impact of 36 demographic, clinical, and discharge treatment variables on the outcome for 3559 patients. Survival status was assessed with the use of the National Death Index. Multivariate analyses were performed with the use of the Cox proportional hazards model. After a mean follow-up of 17 +/- 12 months, 631 patients died. Actuarial survival was 0.86 (95% confidence interval [CI] 0.85 to 0.88), 0.79 (95% CI 0.78 to 0.81), and 0.72 (95% CI 0.70 to 0.74) at 1, 2, and 3 years. Multivariate predictors of worse survival included older age, severe left ventricular dysfunction, lower systolic blood pressure, history of congestive heart failure, diabetes, smoking or atrial fibrillation, and preexistent pacemaker. The hemodynamic impact of the qualifying arrhythmia was not a predictor of outcome. Defibrillator implantation and hospital discharge while the patient was taking a beta-blocker or an angiotensin-converting enzyme inhibitor were associated with better prognosis.

CONCLUSIONS

Despite therapeutic advances, the mortality rates of patients with sustained ventricular tachyarrhythmias remain high. Prognosis depends on the severity of underlying heart disease, as reflected by the extent of left ventricular dysfunction and the presence of heart failure. Well-tolerated ventricular tachycardia in patients with structural heart disease does not carry a significantly better prognosis than ventricular tachyarrhythmia with more severe hemodynamic consequences.

Large clinical trials in the management of ventricular arrhythmias. Applying group results to individual cases

Applying the results of clinical trials to everyday practice in an appropriate manner can be difficult. Earlier clinical trials focused on the secondary prevention of ventricular arrhythmias. Studying patients at high risk of recurrent ventricular arrhythmias is important, but the overall impact on arrhythmic death is low. Recent arrhythmia trials have studied specific patient populations for the primary prevention of ventricular arrhythmias. New trials will expand the investigation to other populations. This article summarizes the results of large clinical trials in the management of ventricular arrhythmias and attempts to provide guidelines for applying their results to everyday clinical practice.

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.

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.

[Prevention of sudden death in patients awaiting heart transplantation]

Sudden death, unexpectedly alters outcome in many patients awaiting heart transplantation. The prevention of sudden death in these patients has been the focus of intensive research to achieve a larger number of patients who finally receive transplants. Recent advances in the medical treatment of heart failure, have reduced mortality and in particular, that caused by sudden death. Nonetheless sudden death remains a frequent cause of mortality in patients awaiting cardiac transplantation. The recognition of patients at very high risk for sudden death is relatively easy, but most patients who suffer sudden death while awaiting cardiac transplantation, are not among those initially included in the overall high risk category. The betablockers, when patients are able to use them, can reduce sudden and total mortality. Class I antiarrhythmic drugs should not be used in patients with cardiac failure. Amiodarone does not increase mortality and may have a beneficial effect in some patients, but its efficacy is lower than that of the implantable defibrillator and its widespread use is not justified. The implantable defibrilator is the reference treatment to reduce sudden death in selected patients, awaiting transplantation.

Increase in heart rate precedes episodes of ventricular tachycardia and ventricular fibrillation in patients with implantable cardioverter defibrillators: analysis of spontaneous ventricular tachycardia database

Patients with heart disease and decreased heart rate variability (HRV) have an increased risk of all-cause mortality as well as arrhythmic death. The question of acute changes in HRV immediately preceding arrhythmic events remains unanswered. We analyzed data from patients with implantable cardioverter defibrillators who had ventricular tachycardia (VT) or ventricular fibrillation (VF) detected by the device. The device stores 1,000 consecutive RR intervals preceding the arrhythmic event detection and before device interrogation. Compared to this control segment, the mean heart rate (HR) increased prior to the arrhythmic event for both VT (88.5 vs 72.7 beats/min, P < 0.0005) and VF (85.4 vs 73.3 beats/min, P < 0.05) patients. No difference in HRV (as analyzed by a time-domain, frequency-domain [fast Fourier transform], and a nonlinear technique) has been detected. We estimated the amount of ectopic beats from the number of RR intervals that differed from the preceding RR interval by > 10%. The frequency of such beats was significantly higher in the prearrhythmic data segments than in the control segments for VT (10.7 vs 6.6/50 beats, P < 0.05) although not for VF (9.8 vs 6.1/50 beats, NS). We conclude that the HR and frequency of ectopic beats are higher prior to onset of the arrhythmic events, although HRV does not change markedly. These results are consistent with sympathetic activation being the predominant autonomic change prior to VT/VF onset in this patient population.

Implantable defibrillators and antiarrhythmic drugs in patients at risk for lethal arrhythmias

The high mortality rate and frequency of ventricular arrhythmias in patients with congestive heart failure has prompted numerous clinical trials aimed at reducing mortality by addressing arrhythmic death. Recently completed trials have suggested that for patients who have survived cardiac arrest, the preferred treatment may be an implantable cardioverter defibrillator (ICD). From the standpoint of primary prevention, implantable defibrillators and amiodarone have received the most attention. It remains unclear, however, to which patients these studies apply, and if and how the results might be generalized. No available studies confirm an additional benefit of pharmacologic or device-based antiarrhythmic therapy beyond that offered by optimal treatment with beta blockers, angiotensin-converting enzyme inhibitors, and lipid-lowering drugs in the majority of patients with cardiomyopathy. Clinical trials are ongoing to address these issues.

Interaction of septadian and circadian rhythms in life-threatening ventricular arrhythmias in patients with implantable cardioverter-defibrillators

Previous studies have shown that life-threatening ventricular arrhythmias display both circadian and septadian (day of the week) periodicity. We hypothesized that assessing the relation between these circadian and septadian rhythms may provide important pathophysiologic information about the mechanism of sudden cardiac death. Using the database from a population of 683 consecutive patients with a third-generation implantable cardioverter-defibrillator (ICD), we examined the time pattern of ICD activations for rapid (prospectively defined as cycle length <280 ms) tachycardias for each day of the week. A total of 5,270 arrhythmic episodes were analyzed. Despite the fact that event distribution was significantly nonuniform (p <0.001) for both circadian and septadian analyses, the circadian pattern was strikingly similar for each day of the week with a relatively broad peak between 9 A.M. and 6 P.M. and a long nadir between 9 P.M. and 6 A.M. We conclude that the trigger factors responsible for the daily circadian distribution of life-threatening ventricular arrhythmias in a population with ICDs are similar throughout the week and may thus be unrelated to the standard work week. These data suggest that the physiologic modulators of circadian and septadian rhythms may be different.

Sudden cardiac death

SCD continues to be an important cause of death and morbidity. Despite expanding insight into the mechanisms causing SCD, the population at high risk is not being effectively identified. Although there is still much to do in the management phase of SCD (predicting the efficacy of various therapies), recent clinical trials have helped define the relative risks and benefits of therapies in preventing SCD. Trials are underway to determine whether treating other patient populations, including asymptomatic patients after MI, will improve survival rate. The approach to reducing mortality rate will always be multifaceted; primary prevention of coronary artery disease and prompt salvage of jeopardized myocardium are 2 important aspects of this approach. In addition to interventions for MI, such as myocardial revascularization when indicated, simple and easily administered therapies that are likely to remain the most effective prophylactic interventions are aspirin, ACE inhibitors, beta-blockers, and cholesterol-lowering agents. However, the MADIT and AVID data clearly demonstrate a role for ICD therapy in a subgroup of patients who have VT/VF and are at risk of cardiac arrest. Even though the absolute magnitude of benefit associated with ICDs is still to be determined, the AVID study and other recent reports provide convincing evidence that patients who have VT/VF fare better with ICDs than with antiarrhythmic drug therapy. For the high-risk population described in this article, in addition to aggressive anti-ischemic and heart failure therapy, ICDs are now a mainstay of life-saving treatment. Still to be surmounted is the challenge of identifying patients who have nonischemic substrates and of providing them with the appropriate therapy. Guided by genetic studies and new insight into the mechanisms of such problems as congenital long QT syndrome, life-saving and life-enhancing therapies may soon be available for the management of SCD.

Sudden Cardiac Death

Great strides have been made in the approach to the management of sudden cardiac death. Patients who have been successfully resuscitated from an episode of sudden cardiac death are at high risk of recurrence. Much larger groups of patients who have not had episodes of sudden cardiac death are also at substantial risk for this event, however. Because the survival rates associated with out-of-hospital cardiac arrest are dismal, these high-risk populations must be targeted for prophylaxis. Beta-blockers have been shown to be an effective pharmacologic therapy in patients who have had myocardial infarction and, most recently, in patients with congestive heart failure. When possible, these agents should be used in these populations. No class I or class III antiarrhythmic drugs, with the possible exception of amiodarone, have been shown to have efficacy as prophylactic agents for the reduction of mortality in these populations. In patients who have hemodynamically significant sustained ventricular tachyarrhythmias or an aborted episode of sudden cardiac death, the current therapy of choice is an implantable cardioverter-defibrillator (ICD). For prophylaxis of sudden cardiac death in patients who have not had a previous event, several approaches may be considered. Currently, the best therapeutic approach for prophylaxis of sudden cardiac death seems to be the ICD; however, use of this device can be justified only in patients at substantial risk of sudden cardiac death. Defining the high-risk populations that will benefit from ICDs is critical in managing the problem of sudden cardiac death.

Changes in health status and quality of life and the impact of uncertainty in patients who survive life-threatening arrhythmias

OBJECTIVE

The purpose of this study was to describe the changes in perception of health status and quality of life from before treatment to 6 months after and the impact of uncertainty on these variables in survivors of life-threatening arrhythmia.

DESIGN AND SETTING

A descriptive correlational design at a large urban teaching hospital.

MEASURES

We measured health status, quality of life, and uncertainty before treatment and 6 months after a life-threatening arrhythmia.

RESULTS

Survivors included 66 men and 15 women, 41 of whom received pharmacologic therapy and 36 of whom received an implantable cardioverter defibrillator (ICD), completed the Medical Outcomes Survey (SF-36), Ferrans and Powers Quality of Life Index (QLI), and the Mishel Uncertainty in Illness Scale (MUIS-C) before treatment and 6 months after. There were significant improvements in the mental and physical health composite summaries as measured by the SF36 (P <.01). Conversely, there were significant reductions in the overall score and specifically in socioeconomic and psychological/spiritual quality of life domains as measured by the QLI (P <.05). An increased perception of uncertainty was related to decreased perception of health status and quality of life at both measurement times, with higher correlations 6 months later.

CONCLUSIONS

Survivors demonstrated improvements in perceived health status, although this did not appear to translate into improvements in the subjective domains of quality of life. The overall quality of life and the domains of psychological/spiritual state and socioeconomic status were lower 6 months after a life-threatening arrhythmia. Uncertainty had a significant impact on these perceptions, identifying an area for nursing interventions.

The effect of procainamide on T wave alternans

INTRODUCTION

The measurement of microvolt level T wave alternans (TWA) is a technique for detecting arrhythmia vulnerability. Previous studies demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of antiarrhythmic drugs on TWA are unknown.

METHODS AND RESULTS

This was a prospective evaluation of intravenous procainamide on TWA in 24 subjects with inducible sustained ventricular tachycardia (VT). Measurements of TWA were performed at baseline in the drug-free state and after procainamide loading (1,204+/-278 mg). Recordings were made in normal sinus rhythm, and during atrial pacing at 100 beats/min and 120 beats/min. The magnitude of TWA in the vector magnitude lead was decreased by procainamide at all heart rates: 0.6+/-0.8 to 0.3+/-0.4 microV in sinus rhythm, 2.0+/-1.6 to 0.7+/-0.7 microV at 100 beats/min, and 3.0+/-2.0 to 1.7+/-1.8 microV at 120 beats/min (P<0.001 by analysis of variance). The sensitivity of TWA for the induction of VT at baseline was 5% in sinus, 60% at 100 beats/min, and 87% at 120 beats/min, while it decreased with procainamide to 5%, 19%, and 60%, respectively. Decreases in TWA in response to procainamide were independent of the antiarrhythmic effects on VT inducibility.

CONCLUSIONS

These results indicate that the magnitude of TWA decreases with acute procainamide loading and this effect decreases the sensitivity of TWA for the induction of sustained VT.

Secondary prevention of sudden death: the Dutch Study, the Antiarrhythmics Versus Implantable Defibrillator Trial, the Cardiac Arrest Study Hamburg, and the Canadian Implantable Defibrillator Study

Although indisputably effective in the prevention of sudden death, use of implantable cardioverter defibrillator (ICD) therapy may not necessarily affect all-cause mortality, as most patients at risk also present with severely depressed left ventricular dysfunction. Correction of the sudden death risk in these patients creates a new clinical condition in need of a careful assessment. Should all-cause mortality be affected by the expected reduction in sudden death rate associated with ICD therapy, issues of critical importance, such as the time extent of life prolongation and the associated quality of life, still remain to established. To investigate the potential benefit of ICD therapy compared with antiarrhythmic drug treatment, 4 prospective studies--the Dutch trial, the Antiarrhythmics Versus Implantable Defibrillators (AVID) study, the Cardiac Arrest Study Hamburg (CASH), and the Canadian Implantable Defibrillator Study (CIDS)--have been conducted in which patients with documented sustained ventricular arrhythmia were randomized to 1 of these 2 treatment strategies. The enrollment criteria differed in these 4 studies: (1) in the Dutch trial, they included cardiac arrest secondary to a ventricular arrhythmia, old (> 4 weeks) myocardial infarction, and inducible ventricular arrhythmia; (2) in AVID and CIDS, ventricular fibrillation or poorly tolerated ventricular tachycardia; and (3) in CASH, cardiac arrest secondary to a ventricular arrhythmia regardless of the underlying disease. With regard to the antiarrhythmic drugs, the Dutch trial tested class I and III agents, whereas AVID and CIDS compared ICD therapy with class III agents (mostly amiodarone). In CASH, 3 drug subgroups were investigated: propafenone, amiodarone, and metoprolol. All trials used all-cause mortality as the primary endpoint. Data from these trials provide support for ICD as a therapy superior to antiarrhythmic drugs in prolonging survival in patients meeting the entry criteria. This review briefly summarizes the methods, results, limitations, and clinical implications of these 4 studies.

New-onset sustained ventricular tachycardia after cardiac surgery

BACKGROUND

The de novo occurrence of sustained ventricular tachycardia (VT) after CABG has been described, but the incidence, mortality rate, long-term follow-up, and mechanism are not well defined.

METHODS AND RESULTS

This prospective study enrolled consecutive patients undergoing CABG at a single institution. Patients were followed up for the development of sustained VT, and a detailed analysis of clinical, angiographic, and surgical variables associated with the occurrence of VT was performed. A total of 382 patients participated, and 12 patients (3.1%) experienced >/=1 episode of sustained VT 4.1+/-4.8 days after CABG. In 11 of 12 patients, no postoperative complication explained the VT; 1 patient had a perioperative myocardial infarction. The in-hospital mortality rate was 25%. Patients with VT were more likely to have prior myocardial infarction (92% versus 50%, P<0.01), severe congestive heart failure (56% versus 21%, P<0.01), and ejection fraction <0.40 (70% versus 29%, P<0.01). When all 3 factors were present, the risk of VT was 30%, a 14-fold increase. Patients with VT had more noncollateralized totally occluded vessels on angiogram (1.4+/-0.97 versus 0.54+/-0.7, P<0.01), a bypass graft across a noncollateralized occluded vessel (1.50+/-1.0 versus 0.42+/-0.62, P<0.01), and a bypass graft across a noncollateralized occluded vessel to an infarct zone (1.50+/-1.0 versus 0.17+/-0.38, P<0.01). By multivariate analysis, the number of bypass grafts across a noncollateralized occluded vessel to an infarct zone was the only independent factor predicting VT.

CONCLUSIONS

The first presentation of sustained monomorphic VT in the recovery period after CABG is uncommon, but the incidence is high in specific clinical subsets. Placement of a bypass graft across a noncollateralized total occlusion in a vessel supplying an infarct zone was strongly and independently associated with the development of VT.

Ventricular arrhythmias, electrophysiologic studies, and devices

Because of the high incidence of heart disease in the elderly, ventricular tachyarrhythmias are not infrequent. Determining the nature and extent of the underlying heart disease and identifying precipitating causes is required prior to instituting long-term therapy. Recent studies suggest that for hemodynamically unstable ventricular tachyarrhythmias, mortality is lower with the implantable cardioverter-defibrillator compared with pharmacologic therapy. This benefit is likely to be more modest in the elderly because of competing cardiac and noncardiac causes of death. For similar reasons, the favorable results reported with the prophylactic use of the implantable cardioverter-defibrillator are likely to be attenuated in the elderly.

Suppression of sustained ventricular tachyarrhythmias: a comparison of d,l-sotalol with no antiarrhythmic drug treatment

OBJECTIVES

This study evaluates the clinical efficacy of d,l-sotalol in patients with sustained ventricular tachyarrhythmias.

BACKGROUND

D,l-sotalol is an important antiarrhythmic agent to prevent recurrences of sustained ventricular tachyarrhythmias (VT/VF). However, evidence is lacking that an antiarrhythmic agent like d,l-sotalol can reduce the incidence of sustained ventricular tachyarrhythmias in comparison to no antiarrhythmic drug treatment.

METHODS

A prospective study was performed in 146 consecutive patients with inducible sustained ventricular tachycardia or ventricular fibrillation. In 53 patients, oral d,l-sotalol prevented induction of VT/VF during electrophysiological testing and patients were discharged on oral d,l-sotalol (sotalol group). In 93 patients, VT/VF remained inducible and a defibrillator (ICD) was implanted. After implantation of the device patients were randomly assigned to oral treatment with d,l-sotalol (ICD/sotalol group, n=46) or no antiarrhythmic medication (n=47, ICD-only group).

RESULTS

During follow-up, 25 patients (53.2%) in the ICD-only group had a VT/VF recurrence in comparison to 15 patients (28.3%) in the sotalol group and 15 patients (32.6%) in the ICD/sotalol group (p=0.0013). Therapy with d,l-sotalol, amiodarone or metoprolol was instituted in 12 patients (25.5%) of the ICD-only group due to frequent VT/VF recurrences or symptomatic supraventricular tachyarrhythmias. In nine patients, 17% of the sotalol group, an ICD was implanted after VT/VF recurrence, three patients (5.7%) received amiodarone. Total mortality was not different between the three groups.

CONCLUSIONS

D,l-sotalol significantly reduces the incidence of recurrences of sustained ventricular tachyarrhythmias in comparison to no antiarrhythmic drug treatment.

Ventricular tachycardia during follow-up in patients resuscitated from ventricular fibrillation: experience from stored electrograms of implantable cardioverter-defibrillators

OBJECTIVE

The purpose of this study was to use the electrogram storage capabilities of the implantable cardioverter-defibrillator (ICD) to categorize any arrhythmic event during follow-up in a group of patients who had survived an episode of ventricular fibrillation (VF) and to possibly identify clinical predictors of future arrhythmic events.

BACKGROUND

Little is known about the electrophysiologic characteristics of ventricular arrhythmias recurring during follow-up in survivors of VF as the sole documented arrhythmia at the time of resuscitation.

METHODS

Forty patients (58+/-10 years; 73% men; left ventricular ejection fraction 42+/-18%; 70% with coronary artery disease) who had survived an episode of VF and subsequently received an ICD capable of intracardiac electrogram recording and storage were followed for 23+/-11 months. In all patients, the arrhythmogenic substrate was investigated by means of programmed electrical stimulation (PES).

RESULTS

Among the 40 patients, 41 episodes of ventricular arrhythmias were documented in 13 patients (33%): 36 episodes of ventricular tachycardias (VT) were recorded in 11 patients (28%) and 5 episodes of VF were recorded in the remaining 2 patients (5%). Age, gender, cardiac disease and left ventricular ejection fraction failed to distinguish between patients with clinical recurrences and patients without. The sensitivity, specificity and positive accuracy of PES were 29%, 63% and 46%, respectively, for prediction of ventricular arrhythmia recurrence; 45%, 70% and 36%, respectively, for prediction of VT; and 50%, 98% and 50%, respectively, for prediction of VF during follow-up.

CONCLUSIONS

In survivors of VF receiving ICD therapy, VT is the most common ventricular arrhythmia recorded on device-incorporated electrograms during follow-up. This finding, associated with the relatively well-preserved ventricular function, may account for the ability of these patients to survive at time of the index arrhythmia; the use of antitachycardia pacing as a modality to treat arrhythmia recurrences may contribute to reduce the incidence of shock during follow-up in these patients.

Beat-to-beat repolarization lability identifies patients at risk for sudden cardiac death

INTRODUCTION

Recent studies have implicated repolarization lability in the genesis of malignant ventricular arrhythmias. However, few data exist on assessment of temporal QT interval variability and its relation to arrhythmogenesis. We tested the ability of the QT variability index (QTVI), a measure of beat-to-beat QT interval fluctuations measured on a single ECG lead, to identify patients presenting with malignant ventricular arrhythmias and predict their subsequent occurrences.

METHODS AND RESULTS

We measured the QTVI in 95 patients presenting for electrophysiologic study (EPS). The ability of the QTVI to identify patients with sudden cardiac death (SCD) or sustained monomorphic ventricular tachycardia (MVT) on presentation and during follow-up of 23.7+/-14.3 months was compared with spatial QT dispersion, T wave alternans ratio during atrial pacing, MVT inducibility at EPS, signal-averaged ECG, heart rate variability, and ejection fraction. The QTVI was higher in patients with heart disease than in controls (-0.7+/-0.7 vs -1.1+/-0.5, P < 0.05), and higher in patients presenting with SCD than in other patients with heart disease (0.0+/-0.6 vs -0.8+/-0.5, P < 0.05). The QTVI was the only clinical variable that identified patients who presented with SCD (P = 0.004, odds ratio = 12.5) on stepwise, logistic multiple regression. Fourteen patients had arrhythmic events during follow-up. In a Kaplan-Meier analysis of arrhythmic events, QTVI> or =0.1 was a discriminator for higher risk of arrhythmic events (P < 0.05).

CONCLUSIONS

(1) This noninvasive measure of temporal repolarization lability identified patients with SCD and predicted arrhythmia-free survival. (2) Further studies are needed to determine the mechanisms that mediate beat-to-beat QT interval variability.

Evolution and revolution in drug labeling: regulation of antiarrhythmic drugs by the Food and Drug Administration 1962-1996

Between 1962, when the Kefauver-Harris Drug Amendments were passed, and 1996, 20 pharmaceutical compounds were approved and labeled by the FDA as effective antiarrhythmic drugs for some specified cardiac arrhythmia. Drug research and development in the 1970s and 1980s were focused on treatment of premature ventricular beats as a marker for sudden cardiac death and ventricular tachycardia. The Cardiac Arrhythmia Suppression Trial in 1989 irrevocably altered this approach. Recent drug development programs have targeted atrial fibrillation (AF) as epidemiologic data have predicted an increase in the incidence of AF as the United States population ages, and as treating premature ventricular beats has fallen from favor. The FDA, the scientific community, and the pharmaceutical industry have all participated in and been affected by this evolution in drug development.

Routine Coronary Arteriography Following Thrombolytic Therapy for Acute Myocardial Infarction: An Unsettled Controversy

Although coronary artery disease remains the leading cause of death in industrialized countries, the management of patients recovering from acute myocardial infarction varies significantly. The issue of routine arteriography and revascularization following thrombolytic therapy remains controversial despite substantial evidence associating infarct-related artery patency with improved cardiac function and survival. Randomized trials of routine intervention after myocardial infarction have generally failed to demonstrate advantages of this invasive approach but methodological problems limit their application to current practice. High-risk patients should be referred for arteriography. While awaiting definitive trials addressing the influence of routine arteriography on patient survival and its cost effectiveness, the management of other patient groups must be individualized.

Lack of benefit of very short basic drive train cycle length or repetition of extrastimulus coupling intervals for induction of ventricular tachycardia

INTRODUCTION

There are considerable variations of uncertain importance in basic drive train cycle lengths and degree of repetition of extrastimuli used in programmed ventricular stimulation protocols in different laboratories. We compare prospectively three different stimulation protocols to examine the influence of a short basic drive train cycle length and repetition of extrastimuli on induction of ventricular tachycardia.

METHODS AND RESULTS

Thirty consecutive patients who had documented ventricular tachycardia or fibrillation based on underlying coronary artery disease underwent programmed ventricular stimulation with each of the three study protocols. Protocol A used a basic drive train cycle length of 400 msec with each extrastimulus coupling interval delivered only once. Protocol B used the same basic drive train cycle length, but with each extrastimulus coupling interval repeated three times before decrementing. Protocol C used 300 msec as the cycle length of basic drive trains without repetition of extrastimuli. Sixty-three percent, 67%, and 63% of the study patients had ventricular tachycardia inducible with protocols A, B, and C, respectively (P = NS). Ventricular fibrillation was induced in 23% of the 30 patients in all three protocols. There were no significant differences in the mean cycle lengths of induced ventricular tachycardia, the number of extrastimuli used, and the coupling interval of the last extrastimulus inducing ventricular tachycardia among the three protocols.

CONCLUSION

This study showed no clinical benefit for repetition of extrastimuli that have failed to induce a ventricular tachyarrhythmia during programmed ventricular stimulation. A short basic cycle length of 300 msec was not superior to 400 msec for induction of ventricular tachyarrhythmias. We recommend the use of basic cycle length 400 msec with delivery of each extrastimulus interval only once as the initial protocol for programmed ventricular stimulation.

Ventricular arrhythmia following successful myocardial revascularization: incidence, predictors and prevention

OBJECTIVES

We estimated the risk of sudden cardiac death (SCD), from a spontaneous episode of ventricular arrhythmia (VT/VF), after a successful surgical myocardial revascularization (coronary artery bypass grafting; CABG) procedure. Predictors of these events were identified, and long term benefits of the prophylactic regimes, that were used to control these events, were evaluated.

METHODS

We selected 8642 consecutive patients, who had undergone an isolated and first time CABG procedure, between 1/3/1980 and 1/3/1995. A standard hazard function model (1) was used for statistical analysis. Efficacy of the prophylactic regimes, was examined in a group of 350 high risk patients, with a preoperative left ventricular ejection fraction 30% or less, who were recently operated since 1/1/1988. Electrophysiologic (EP) guided prophylaxis was used in 92 (26%) patients, who had survived a documented episode of SCD, and remaining 258 patients were maintained on antiarrhythmic medication on an empirical basis. A sequential EP evaluation was performed, when indicated.

RESULTS

During an early phase of hazard, which mainly lasted for up to 3 months after CABG, incremental risk factors were preoperative LVEF 30% or less (P = 0.0007) and preoperative episodes of VT/VF (P = 0.04). This phase was followed by a constant phase with a low risk of the events, which merged into a slowly rising late phase after 6 years. EP guided prophylaxis, reduced the risk of SCD in high risk patients (P = 0.03). A sequential EP evaluation, helped to detect the problems of drug resistance and a cross over from non-sustained to sustained runs of VT/VF.

CONCLUSIONS

Despite a successful CABG surgery, risk of VT/VF persists. A routine EP evaluation before and after a CABG procedure is recommended in all patients with a poor left ventricular function.

[Current indications for implantable automatic defibrillators]

Since the first implantation in man in 1980 implantable cardioverter defibrillator technology has greatly improved and the number of devices implanted has increased considerably in recent years. Non-thoracotomy lead systems and biphasic shocks are now the approach of choice, offering nearly a 100% success rate. This paper version reviews the current indications for the implantation of implantable cardioverter defibrillator and is an upgraded of an article previously published by the Arrhythmia's Section of the Spanish Society of Cardiology. Recommendations for qualification of centres implanting defibrillators and follow up are also addressed.

Mechanisms for spontaneous termination of monomorphic, sustained ventricular tachycardia: results of activation mapping of reentrant circuits in the epicardial border zone of subacute canine infarcts

OBJECTIVES

The objective of this study was to determine why sustained ventricular tachycardias (VT) sometimes stop without outside intervention.

BACKGROUND

Sustained, monomorphic VT in patients with ischemic heart disease is often caused by reentrant excitation. These tachycardias can degenerate into rapid polymorphic rhythms or occasionally terminate spontaneously.

METHODS

Sustained VT was induced by programmed stimulation in dog hearts 4 to 5 days after ligation of the left anterior descending coronary artery. Activation in reentrant circuits in the epicardial border zone of the infarct was mapped using 192 to 312 bipolar electrodes.

RESULTS

Spontaneous termination of sustained VT always occurred when the reentrant wave front blocked in the central common pathway in reentrant circuits with a figure-of-eight configuration. Two major patterns of termination were identified from activation maps of the circuits that were not distinguishable from each other on the surface electrocardiogram: 1) Abrupt termination was not preceded by any change in the pattern of activation or cycle length. It could occur at different locations within the central common pathway, was not related to the directions of the muscle fiber orientation and was not caused by a short excitable gap. 2) Termination caused by premature activation (after a short cycle) either resulted from shortening of the functional lines of block around which the reentrant impulse circulated or was caused by wave fronts originating outside the reentrant circuit. In only one episode were oscillations of cycle length associated with termination.

CONCLUSIONS

The mechanisms for termination of reentry in functional circuits causing VT are different from those in anatomic circuits where oscillatory behavior precedes termination.

Hyperpolarization-activated inward current in ventricular myocytes from normal and failing human hearts

BACKGROUND

The hyperpolarization-activated inward current (I[f]) was found to be overexpressed in hypertrophied rat ventricular myocytes, indicating that I(f) might favor arrhythmias in hypertrophied or failing ventricular myocardium. In the present study, we evaluated whether I(f) is expressed in human ventricular myocardium, if it may be increased in human heart failure, and if its autonomic modulation may be altered.

METHODS AND RESULTS

The whole-cell patch-clamp technique was used to record I(f) in isolated ventricular myocytes from 34 failing (dilated [DCM] or ischemic [ICM] cardiomyopathy) and 13 donor hearts (NF). I(f) was observed in all myocytes showing typical current properties, ie, time and voltage dependence, block by [Cs+]o, permeability for K+ and Na+, and current increase with raising [K+]o. There was a trend toward larger current densities in myopathic (at -130 mV in [K+]o 25 mmol/L; DCM: -1.37 +/- 0.12 pA/pF, n = 50; ICM: -1.39 +/- 0.24 pA/pF, n = 30) than in nonfailing cells (-1.18 +/- 0.21 pA/pF, n = 24), although this difference did not reach statistical significance (P=.23). Boltzmann distributions yielded an activation threshold of -80 mV and half-maximal activation at -110.96 +/- 0.06 mV in myopathic and normal myocytes. Isoproterenol (10(-5) mol/L) shifted the current activation by 10 mV (31 myopathic, 5 NF). Carbachol and adenosine had no direct effect on I(f) (6 and 12 myopathic, 3 and 3 NF, respectively) but reversibly antagonized beta-adrenergic stimulation (5 and 7 myopathic, 2 and 2 NF, respectively). Autonomic modulation was similar in failing and nonfailing cells.

CONCLUSIONS

In end-stage heart failure, no significant change of I(f) could be found, although there was a trend toward increased I(f). Together with an elevated plasma norepinephrine concentration and a previously reported reduction in I(K1) in human heart failure, I(f) might favor diastolic depolarization in individual myopathic cells.

[Holter monitoring and programmed ventricular stimulation]

Long-term ECG recordings are the method of choice to evaluate quantity and quality of spontaneous rhythm disturbances. However, this method is limited by the variability of the arrhythmias. Invasive procedures such as programmed stimulation allow the provocation of tachyarrhythmias. Indications for both methods are diagnostic clarification of clinical symptoms, risk stratification with respect to arrhythmogenic sudden cardiac death as well as the control of antiarrhythmic therapy.Due to the high variability of spontaneous complex ventricular arrhythmias, Holter monitoring often fails to document the cause of severe symptoms such as syncope or sudden cardiac death. In these patients, invasive electrophysiological testing is required to provoke the arrhythmia.The prognostic significance of spontaneous ventricular arrhythmias recorded during ambulatory monitoring depends on the underlying cardiac disease. In patients with coronary artery disease and a history of myocardial infarction there is evidence that frequent single and/or complex ventricular extrasystoles indicate an increased risk of sudden cardiac death, especially in the presence of a reduced left ventricular function. In these patients, programmed ventricular stimulation can further characterize a highrisk group.For the management of antiarrhythmic therapy in symptomatic patients, under certain conditions both methods appear to be helpful. For the majority of these patients, however, the invasive electrophysiologic study should be preferred.Thus, long-term ECG recordings and programmed electrical stimulation are no competing, but complementary methods in clinical cardiology.

General principles of antiarrhythmic therapy for ventricular tachyarrhythmias

Sudden cardiac death due to ventricular arrhythmias is a significant cause of mortality in patients with structural heart disease. Over the past several decades, the introduction of new pharmacologic and nonpharmacologic therapy has expanded the treatment options available. This article will focus on the use of antiarrhythmic medication for the treatment of ventricular arrhythmias and will review the following: (1) treatment goals for various clinical populations, (2) the mechanisms of antiarrhythmic and proarrhythmic actions of antiarrhythmic medications, and (3) empiric versus guided pharmacologic therapy.

Risk assessment and risk stratification in sudden cardiac death: a biostatistician's view

Determining individual probabilities of developing lethal arrhythmia over time (risk assessment) and grouping individuals by that probability (risk stratification) are similar to, yet differ in purpose from, screening, diagnosis, risk factor identification, and prognostic staging. Methods of handling bias, use of multiple predictors, and evaluation of results provide challenges. A key purpose of risk assessment and stratification is examined. The role of operational definitions of predictors and events and of methods that account for multiple predictors and known confounding factors is analyzed. Constructed examples illustrate potential pitfalls in assessment and how multivariate techniques can deal with multiple predictors. A trial design to evaluate risk stratification for the identified purpose is elaborated and potential results are interpreted. Bias from predictors regressing to the mean can be minimized either by averaging a number of measurements or by equalizing the bias in comparison groups. An analysis of two predictors and two risk strata illustrates how the discrimination of combined predictors may be greater than the sum of the individual variables' discrimination. Risk stratification can be evaluated in trials that randomize competing interventions within different risk strata. Results of such trials indicate whether the risk strata adequately distinguish individuals by their responsiveness to particular intervention. Potential pitfalls, not easily recognized in risk stratification, can be avoided in the methods and in studies for evaluating those methods. Multivariate techniques maximize the discrimination of multiple predictors, but may increase complexity. Randomized trials of treatment provide evidence for utility of risk stratification.

Management of patients with life-threatening ventricular tachyarrhythmias in the defibrillator era: the need to differentiate

Patients with a history of sustained ventricular tachyarrhythmias form an extremely inhomogeneous group with respect to presenting arrhythmia, underlying cardiac disease, and therefore, risk of dying suddenly. For subgroups such as ventricular tachycardia in the absence of underlying cardiac disease, radiofrequency catheter ablation offers cure. In others, implantation of a cardioverter defibrillator already appears to have gained the therapy of first choice, leaving only a secondary role to antiarrhythmic drugs. It must be emphasized however, that these new therapeutic strategies have their pros and cons like the older, seemingly out-fashioned approaches of noninvasively or invasively guided antiarrhythmic drug therapy or empiric amiodarone treatment. Until the advent of controlled randomized trials comparing the implantable cardioverter defibrillator (ICD) with the best other, usually medical form of treatment, physicians must continue to base their individual therapeutic decisions on circumstantial published and personal experience. In doing so, the recent achievements of catheter ablation and defibrillator implantation have definitely improved patient care, but have not made antiarrhythmic drugs jobless. With all the alternatives at hand, it remains a challenging task to weigh the benefits and risks of the various approaches against each other in an attempt to tailor the antiarrhythmic intervention to the very individual need of the patient.

Arrhythmia risk: electrophysiological studies and monophasic action potentials

Shortly after in the introduction of programmed electrical stimulation (PES) of the heart to study and localize cardiac arrhythmias in the intact human heart, the technique was used for risk stratification of the arrhythmia patient. Two decades later we have to conclude that especially in ventricular arrhythmias the technique of PES did not live up to our expectations and the left ventricular function is a better long-term predictor than the induction of ventricular arrhythmias or the ability to find an antiarrhythmic drug able to prevent the initiation of the classically documented ventricular arrhythmia. Another sobering finding came from the analysis of the characteristics of the patient dying suddenly out-of-hospital, which showed that most of those patients could not be classified before the event as being at high risk using noninvasive or invasive testing, not even in those with a previous cardiac history. Monomorphic action potential (MAP) recordings have been of importance in our understanding of torsade de pointe arrhythmias in congenital and acquired QT prolongation. A major problem in case of a less generalized electrophysiological abnormality is the identification of the appropriate place where to put the MAP-electrode.

Predictors of arrhythmic death and cardiac arrest in the ESVEM trial. Electrophysiologic Study Versus Electromagnetic Monitoring

BACKGROUND

The purpose of this study was to determine if the presenting ventricular arrhythmia (ventricular tachycardia or ventricular fibrillation/cardiac arrest) predicted the type of arrhythmia recurrence in patients treated with antiarrhythmic drugs.

METHODS AND RESULTS

In the previously reported Electrophysiologic Study Versus Electrocardiographic Monitoring (ESVEM) trial, there were 486 patients who were randomized to antiarrhythmic drug testing guided by electrophysiological study or by ambulatory ECG monitoring. Use of a defibrillator (implantable cardioverter-defibrillator, ICD) without stored electrograms among 81 patients precluded determination of the type of arrhythmia recurrence; thus these patients were censored at the time of ICD implantation. Of the 486 patients, 381 presented with ventricular tachycardia and 105 with cardiac arrest. Over a 6-year follow-up period, 285 of the 486 patients had an arrhythmia recurrence; of these, 97 had an arrhythmic death or cardiac arrest as a first recurrence. In the current analysis, all 129 arrhythmic deaths/cardiac arrests that occurred any time during follow-up were evaluated as end points.

CONCLUSIONS

Although univariate analysis suggested that there was an association between the presenting arrhythmia and outcome, multivariate analysis failed to substantiate the predictive value of the presenting arrhythmia. Left ventricular ejection fraction was the single most important predictor of arrhythmic death or cardiac arrest. This information may be an important factor in deciding whether to advise ICD therapy.

Comparison of class Ia/Ib versus class III antiarrhythmic drugs for the suppression of inducible sustained ventricular tachycardia associated with coronary artery disease

Previous studies suggest that class Ia drugs are ineffective in suppression of sustained ventricular tachycardia by programmed stimulation. More favorable results have been described with combinations of Ia and Ib drugs and also with class III antiarrhythmic drugs, but there have been no direct comparisons between these 2 regimens. The present study was undertaken to compare the electrophysiologic efficacy and predictors of success of these 2 regimens in patients with ischemic heart disease and inducible sustained monomorphic ventricular tachycardia. The population consisted of 136 patients with documented coronary artery disease. All had sustained monomorphic ventricular tachycardia inducible during baseline electrophysiologic study and following intravenous procainamide. Follow-up studies were performed with a combination of oral class Ia and Ib or class III antiarrhythmic drugs. A positive response was the inability to induce a sustained ventricular arrhythmia with up to 3 extrastimuli at 2 right ventricular pacing sites. Response rates were 13% for Ia/Ib combination and 19% for class III agents (p = 0.40). Congestive heart failure differentially affected response rates. Only 8% of those responding to Ia/Ib therapy had heart failure compared with 59% of responders to class III (p <0.01). Multivariate analysis identified heart failure (RR 12.2, p = 0.03) as the only parameter with independent predictive value of response to Ia/Ib therapy. These results indicate that congestive heart failure is a potent predictor of a negative response to a combination of class Ia and Ib antiarrhythmic drugs. In this population, class III drugs or nonpharmacologic therapy should be considered as initial treatment.

QT dispersion as a risk factor for sudden cardiac death and fatal myocardial infarction in a coronary risk population

OBJECTIVE

To test in a prospective study the hypothesis that increased QT dispersion in resting 12-lead ECG is a predictor of sudden cardiac death.

DESIGN

A nested case-control study during a mean (SD) follow up time of 6.5 (2.8) years.

SETTING

A prospective, placebo controlled, coronary prevention trial with gemfibrozil among dyslipidaemic middle aged men in primary (occupational) health care units: the Helsinki heart study.

PATIENTS

24 victims of fatal myocardial infarction, 48 victims of sudden cardiac death without acute myocardial infarction, and their matched controls.

MAIN OUTCOME MEASURES

QT dispersion in baseline and pre-event electrocardiograms.

RESULTS

At study baseline, QT dispersion was similar in all victims and controls. When estimated from the pre-event ECG on average 14 months before death, the risk of sudden cardiac death in the highest QTPEAK (up to the peak of the T wave) dispersion tertile (> or = 50 ms) was 6.2-fold (95% confidence interval 1.7 to 23.5) compared with the risk in the lowest tertile (< or = 30 ms), and 4.9-fold (1.2 to 19.5) after adjustment for the presence of left ventricular hypertrophy, while QTPEAK dispersion could not predict fatal myocardial infarction. QTEND dispersion (up to the end of the T wave) in pre-event ECGs could not discriminate victims of either sudden cardiac death or fatal myocardial infarction from their matched controls.

CONCLUSIONS

In middle aged men with a normal conventional QT interval in 12-lead resting ECG, increased QTPEAK dispersion is an independent risk factor for sudden cardiac death, but not for fatal myocardial infarction.

Idiopathic ventricular fibrillation

Idiopathic ventricular fibrillation is defined as cardiac arrest in the absence of structural heart disease and other identifiable causes of ventricular fibrillation. It occurs in 1% to 9% of survivors of out-of-hospital cardiac arrest. The mean age of these patients is 35 to 40 years, and 70% to 75% are male. The pathogenesis is unknown; psychosocial factors may play a role. Baseline clinical characteristics have not been found to identify the 20% to 30% of patients who will have recurrent cardiac arrest. At present, implantation of an automatic defibrillator is the treatment of choice. Two registries have been established to enhance our knowledge of this unusual catastrophic entity.

Evaluation and treatment strategies in patients at high risk of sudden death post myocardial infarction

Over 50 percent of deaths in patients who survive an acute myocardial infarction are due to fatal ventricular tachyarrhythmias. Patients who survive an episode of sustained ventricular arrhythmia are at highest risk of recurrent cardiac arrest. Electrophysiologic studies have been found to be useful in guiding therapy and reducing mortality in these patients and in patients with syncope due to arrhythmic etiology. Evaluation and treatment of nonsustained ventricular tachycardia post infarction remains somewhat controversial. A recently published trial (MADIT), however, showed improved survival with an implanted defibrillator in patients with coronary disease and asymptomatic nonsustained ventricular tachycardia. Asymptomatic patients post infarction at high risk include those who have significant left ventricular dysfunction, late potentials, high-grade ventricular ectopy, and abnormal heart rate variability. These tests individually, however, have a low positive predictive accuracy. This, combined with the fact that antiarrhythmic drugs are frequently not effective and can be proarrhythmic, leaves the best treatment for these patients uncertain. It is known, however, that beta-adrenoreceptor blocking agents do reduce mortality after an acute myocardial infarction. Early studies have shown mixed results relating to sudden death and total mortality with amiodarone. To date, no other antiarrhythmic drug has shown benefit, while several have been shown to be harmful. Recent studies have also shown some beneficial effects of angiotensin-converting enzyme inhibitors, carvedilol, a third-generation beta-blocking agent with vasodilator properties, and the angiotensin II receptor antagonist losartan. However, their precise role in reducing sudden death needs to be defined further.