Programmed electrical stimulation in patients with high-grade ventricular ectopy: electrophysiologic findings and prognosis for survival

Analytic Reviews: Electrophysiologic Testing in the Intensive Care Unit

The role of electrophysiologic concepts and procedures in managing patients with potentially life-threatening ar rhythmias in the intensive care unit is discussed. These patients may be survivors of sudden cardiac arrest or myocardial infarction or may be admitted for syncope or sustained or nonsustained ventricular tachycardia. The value of electrophysiologic testing is discussed in terms of the distinction between wide QRS complex tachycardias that are supraventricular or ventricular in origin and those in which preexcitation syndromes may be important. Drug-induced ventricular arrhythmias are discussed, with specific emphasis on torsades de pointes. Finally, the use of His bundle recordings in pa tients with atrioventricular conduction disturbances is discussed. The methodology of electrophysiologic test ing, including stimulation protocols and interpretation of results, is described.

Prompt and accurate diagnosis of ventricular arrhythmias with a novel index based on phase space reconstruction of ECG

AIM

To develop a statistical index based on the phase space reconstruction (PSR) of the electrocardiogram (ECG) for the accurate and timely diagnosis of ventricular tachycardia (VT) and ventricular fibrillation (VF).

METHODS

Thirty-two ECGs with sinus rhythm (SR) and 32 ECGs with VT/VF were analyzed using the PSR technique. Firstly, the method of time delay embedding were employed with the insertion of delay "τ" in the original time-series X(t), which produces the Y(t)=X(t-τ). Afterwards, a PSR diagram was reconstructed by plotting Y(t) against X(t). The method of box counting was applied to analyze the behavior of the PSR trajectories. Measures as mean (μ), standard deviation (σ) and coefficient of variation (CV=σ/μ), kurtosis (β) for the box counting of PSR diagrams were reported.

RESULTS

During SR, CV was always <0.05, while with the onset of arrhythmia CV increased >0.05. A similar pattern was observed with β, where <6 was considered as the cut-off point between SR and VT/VF. Therefore, the upper threshold for SR was considered CVth=0.05 and βth<6. For optimisation of the accuracy, a new index (J) was proposed: J=wCVCVth+1-wββth. During SR the upper limit of J was the value of 1. Furthermore CV, β and J crossed the cut-off point timely before the onset of arrhythmia (average time: 4min 31s; SD: 2min 30s); allowing sufficient time for preventive therapy.

CONCLUSION

The J index improved ECG utility for arrhythmia monitoring and detection utility, allowing the prompt and accurate diagnosis of ventricular arrhythmias.

Sustained Polymorphic Arrhythmias Induced by Programmed Ventricular Stimulation have Prognostic Value in Patients Receiving Defibrillators

BACKGROUND

Patients with ischemic cardiomyopathy (ICM) who have monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation (PVS) are at increased risk of sudden cardiac death (SCD). Among a primary prevention population, the prognostic significance of induced polymorphic ventricular arrhythmias is unknown.

METHODS

A total of 105 consecutive patients who received an implantable cardioverter-defibrillator (ICD) for primary prevention of SCD in the setting of ICM and non-sustained VT were retrospectively evaluated. Seventy-five patients (group I) had induction of monomorphic VT and 30 patients (group II) had a sustained ventricular arrhythmia other than monomorphic VT (ventricular flutter, ventricular fibrillation, and polymorphic VT) induced during PVS.

RESULTS

Baseline characteristics were similar between group I and group II except for ejection fraction (25% vs. 31%, P = 0.0001) and QRS duration (123 milliseconds vs. 109 milliseconds, P = 0.04). Sixteen of 75 (21.3%) patients in group I and 6 of 30 (20%) patients in group II received appropriate ICD therapy (P = 0.88). Survival free from ICD therapy was similar between groups (P = 0.54). There was a trend toward increased all-cause mortality among patients in group I by Kaplan-Meier analysis (P = 0.08). However, when adjusted for age, EF, and QRS duration mortality was similar (P = 0.45).

CONCLUSIONS

There is no difference in rates of appropriate ICD discharge or mortality between patients dichotomized by type of rhythm induced during PVS. These results suggest that patients in this population who have inducible VF or sustained polymorphic VT have similar rates of subsequent clinical ventricular tachyarrhythmias as those with inducible monomorphic VT.

Long-Term Incidence of Malignant Ventricular Arrhythmia and Shock Therapy in Patients with Primary Defibrillator Implantation Does Not Differ from Event Rates in Patients Treated for Survived Cardiac Arrest

INTRODUCTION

Recent trials have demonstrated benefit of prophylactic defibrillator (ICD) implantation compared to conventional treatment in high-risk patients. However, many patients have rare or no sustained arrhythmias following implantation. Our study addresses the question, whether patients with prophylactic defibrillator implantation have a lower risk for life-threatening ventricular tachycardia (VT) or ventricular fibrillation (VF) compared to sudden cardiac death (SCD) survivors.

METHODS AND RESULTS

Over 7 years we enrolled 245 patients. Occurrence of spontaneous sustained VT/VF resulting in adequate ICD treatment was the endpoint. Incidence, type, and treatment of sustained arrhythmia in 43 previously asymptomatic ICD recipients (group B) were compared to data of 202 survivors of imminent SCD (group A). All patients had severely impaired left ventricular ejection fraction (<45%). Group B patients had long runs (>6 cycles, <30 s) of VT during Holter monitoring and inducible sustained arrhythmia. Incidence of rapid VT and VF (cycle length <240 ms/heart rate >250 bpm) after 4 years (35% in both groups, P = ns) and adequate defibrillator therapies (57% vs 55%, P = ns) were similar in both groups after univariate and multivariate analysis. Cumulative mortality tended to be lower in group B compared to group A, but the difference was not statistically significant.

CONCLUSION

During long-term follow-up, incidence of sustained rapid ventricular arrhythmia in prophylactically treated patients is as high as that of SCD survivors. Benefit from defibrillator implantation for primary prevention (group B) appears to be comparable to that for survived cardiac arrest (group A).

Long-term prognosis of inducible ventricular flutter: not an innocent finding

BACKGROUND

The prognostic significance of ventricular flutter (VFL) induced during programmed electrical stimulation (PES) is currently unknown.

METHODS

This study examined patients who had PES-induced VFL and assessed their long-term prognosis compared with patients who had inducible sustained monomorphic ventricular tachycardia (SMVT).

RESULTS

Of 3414 patients undergoing PES, 74 (2%) had sustained VFL. They were compared with a group of 71 patients undergoing PES in the same time frame who had inducible SMVT. Patients with inducible VFL had a higher ejection fraction than patients with SMVT (0.39 vs 0.33; P =.05). More aggressive pacing was required for arrhythmia induction in patients with VFL, with more stimuli (2.7 +/- 0.5 vs 2.2 +/- 0.6; P <.01) and tighter S(2), S(3), and S(4) intervals. After a mean follow-up of 30 +/- 31 months, the mortality rate was 34% in patients with VFL and 30% in patients with SMVT (P =.41). No difference in the 2 groups in overall survival or a combined end point of sudden death or appropriate implantable cardioverter defibrillator shock was revealed with Kaplan-Meier analysis.

CONCLUSION

The long-term prognosis of patients with inducible VFL is similar to that of patients with inducible SMVT, even when VFL is induced with a relatively aggressive protocol.

Limited predictive value of inducible sustained ventricular tachycardia for future occurrence of spontaneous ventricular tachycardia in patients with coronary artery disease and relatively preserved cardiac function

To evaluate the significance of inducible sustained ventricular tachycardia (VT) in patients with coronary artery disease and relatively preserved cardiac function, 33 patients who met the following criteria were studied; documented nonsustained VT but no history of life-threatening arrhythmia, inducible sustained VT at electrophysiologic study, and implantation of a cardioverter-defibrillator. Eighteen patients developed clinical sustained VT within 2 years. By univariate analysis, left ventricular ejection fraction (EF) and the cycle length of induced VT were associated with clinical VT occurrence. By multivariate analysis, however, EF was the only independent predictor. Among 23 patients with EF <or=40%, 16 patients developed clinical sustained VT compared to 2 of 10 patients with EF >40% (P <.01). In coronary artery disease patients with relatively preserved EF, the incidence of clinical VT is considerably low even though sustained VT is inducible. Inducible VT is therefore not appropriate for risk stratification in this patient population.

Differences in inducibility and prognosis of in-hospital versus out-of-hospital identified nonsustained ventricular tachycardia in patients with coronary artery disease: clinical and trial design implications

OBJECTIVES

The goal of this study was to describe the influence of the clinical setting (in-hospital vs. out-of-hospital) in which nonsustained ventricular tachycardia (NSVT) is discovered on the rate of inducibility of sustained ventricular tachycardia (VT), arrhythmic events and survival in patients with coronary artery disease (CAD) and left ventricular (LV) dysfunction.

BACKGROUND

In-hospital presentation of sustained VT is independently associated with lower long-term overall survival. The impact of the clinical setting in which NSVT is documented is unknown.

METHODS

In the Multicenter Unsustained Tachycardia Trial (MUSTT), designed to assess the benefit of randomized antiarrhythmic therapy guided by electrophysiologic testing in patients with asymptomatic NSVT, CAD and LV dysfunction, eligible patients were enrolled irrespective of the setting in which the index arrhythmia was discovered. In this retrospective analysis, we compared the rate of VT inducibility and outcome of MUSTT-enrolled patients with in-hospital versus out-of-hospital presentation of NSVT.

RESULTS

Monomorphic sustained VT was induced in 35% and 28% of the patients whose index NSVT occurred in-hospital and out-of-hospital, respectively (adjusted p = 0.006). Cardiac arrest or death due to arrhythmia at two- and five-year follow-ups were 14% and 28% for untreated patients with in-hospital-identified NSVT and 11% and 21% for the out-of-hospital group (adjusted p = 0.10). Overall mortality rates at two- and five-year follow-ups were 24% and 48% for inpatients and 18% and 38% for outpatients (adjusted p = 0.018). In patients randomized to antiarrhythmic therapy, there was no significant interaction between patient status (in-hospital vs. out-of-hospital) and treatment impact on the rates of total mortality (p = 0.98) and arrhythmic events (p = 0.08).

CONCLUSIONS

In patients with CAD and impaired LV function, asymptomatic NSVT identified in-hospital, compared with that identified out-of-hospital, is associated with a higher rate of induction of sustained VT and overall mortality. Therefore, in similar patients, the clinical setting in which NSVT is discovered should be taken into account when formulating patient risk, treatment and clinical trial design.

Nonsustained ventricular tachycardia. A guide to the clinical significance and management

The patient with nonsustained ventricular tachycardia represents a common management problem for the cardiologists and internists. Treatment is sometimes needed for the suppression of symptoms. More commonly, nonsustained ventricular tachycardia is asymptomatic, and the clinician must determine the prognostic importance. The prognostic implications, the role of electrophysiologic study, and the potential role of pharmacologic and defibrillator intervention depend on the underlying cardiac substrate present in the individual patient.

Management of arrythmias

The management of arrhythmias in elderly patients with congestive heart failure, including atrial fibrillation, ventricular tachyarrhythmias, and bradyarrhythmias, is described. Patients with atrial fibrillation can be treated with rate control anticoagulation for stroke prevention or by attempt at cardioversion and maintenance of sinus rhythm. Elderly patients remaining in atrial fibrillation benefit from anticoagulation provided that no contraindication exists. In patients surviving malignant ventricular arrhythmias, defibrillator implantation is beneficial in elderly patients with heart failure. Prognosis and treatment of nonsustained arrhythmias depends on the presence of underlying cardiac abnormalities. In the healthy elderly population, treatment is not indicated. In patients with coronary artery disease, decreased ejection fraction, and nonsustained ventricular tachycardia, electrophysiology can further stratify risk, and defibrillator implantation can improve survival if arrhythmias are induced. This benefit is as great in elderly patients as in younger patients. Symptomatic bradycardias are increasingly common with advancing age. Symptoms are improved with pacing, with maximum benefit from physiologic rather than ventricular pacing. Although the elderly population poses a unique challenge when faced with arrhythmias, an active approach not only saves lives but also reduces morbidity.

Electrophysiologic testing to identify patients with coronary artery disease who are at risk for sudden death. Multicenter Unsustained Tachycardia Trial Investigators

BACKGROUND

The mortality rate among patients with coronary artery disease, abnormal ventricular function, and unsustained ventricular tachycardia is high. The usefulness of electrophysiologic testing for risk stratification in these patients is unclear.

METHODS

We performed electrophysiologic testing in patients who had coronary artery disease, a left ventricular ejection fraction of 40 percent or less, and asymptomatic, unsustained ventricular tachycardia. Patients in whom sustained ventricular tachyarrhythmias could be induced were randomly assigned to receive either antiarrhythmic therapy guided by electrophysiologic testing or no antiarrhythmic therapy. The primary end point was cardiac arrest or death from arrhythmia. Patients without inducible tachyarrhythmias were followed in a registry. We compared the outcomes of 1397 patients in the registry with those of 353 patients with inducible tachyarrhythmias who were randomly assigned to receive no antiarrhythmic therapy in order to assess the prognostic value of electrophysiologic testing.

RESULTS

Patients were followed for a median of 39 months. In a Kaplan-Meier analysis, two-year and five-year rates of cardiac arrest or death due to arrhythmia were 12 and 24 percent, respectively, among the patients in the registry, as compared with 18 and 32 percent among the patients with inducible tachyarrhythmias who were assigned to no antiarrhythmic therapy (adjusted P<0.001). Overall mortality after five years was 48 percent among the patients with inducible tachyarrhythmias, as compared with 44 percent among the patients in the registry (adjusted P=0.005). Deaths among patients without inducible tachyarrhythmias were less likely to be classified as due to arrhythmia than those among patients with inducible tachyarrhythmias (45 and 54 percent, respectively; P=0.06).

CONCLUSIONS

Patients with coronary artery disease, left ventricular dysfunction, and asymptomatic, unsustained ventricular tachycardia in whom sustained ventricular tachyarrhythmias cannot be induced have a significantly lower risk of sudden death or cardiac arrest and lower overall mortality than similar patients with inducible sustained tachyarrhythmias.

Nonsustained ventricular tachycardia

The patient with nonsustained ventricular tachycardia represents a common management problem for the cardiologist. The challenges posed by this type of arrhythmia differs from those posed by other arrhythmias, because most instances of nonsustained ventricular tachycardia do not cause symptoms. This article reviews common situations in which nonsustained ventricular tachycardia occurs and their appropriate management.

Arrhythmias in heart failure: current concepts of mechanisms and therapy

About one half of deaths in patients with heart failure are sudden, mostly due to ventricular tachycardia (VT) degenerating to ventricular fibrillation or immediate ventricular fibrillation. In severe heart failure, sudden cardiac death also may occur due to bradyarrhythmias. Other dysrhythmias complicating heart failure include atrial and ventricular extrasystoles, atrial fibrillation (AF), and sustained and nonsustained ventricular tachyarrhythmias. The exact mechanism of the increased vulnerability to arrhythmias is not known. Depending on the etiology of heart failure, different preconditions, including ischemia or structural alterations such as fibrosis or myocardial scarring, may be prominent. Reentrant mechanisms around scar tissue, afterdepolarizations, and triggered activity due to changes in calcium metabolism significantly contribute to arrhythmogenesis. Furthermore, alterations in potassium currents leading to action potential prolongation and an increase in dispersion of repolarization play a significant role. Treatment of arrhythmias is necessary either because patients are symptomatic or to reduce the risk for sudden cardiac death. The individual history, left ventricular function, electrophysiologic testing, and the signal-averaged ECG give useful information for identifying patients at risk for sudden cardiac death. The implantable cardioverter defibrillator (ICD) has evolved as a promising therapy for life-threatening arrhythmias. A potential role may exist for antiarrhythmic drugs, mainly amiodarone. There is growing evidence that patients with sustained VT or a history of resuscitation have the best outcome with ICD therapy regardless of the degree of heart failure. Many of these patients require additional antiarrhythmic therapy because of AF or nonsustained VTs that may activate the device. Catheter ablation or map-guided endocardial resection are additional options in selected patients but seldom represent the only therapeutic strategy.

A randomized study of the prevention of sudden death in patients with coronary artery disease. Multicenter Unsustained Tachycardia Trial Investigators

BACKGROUND

Empirical antiarrhythmic therapy has not reduced mortality among patients with coronary artery disease and asymptomatic ventricular arrhythmias. Previous studies have suggested that antiarrhythmic therapy guided by electrophysiologic testing might reduce the risk of sudden death.

METHODS

We conducted a randomized, controlled trial to test the hypothesis that electrophysiologically guided antiarrhythmic therapy would reduce the risk of sudden death among patients with coronary artery disease, a left ventricular ejection fraction of 40 percent or less, and asymptomatic, unsustained ventricular tachycardia. Patients in whom sustained ventricular tachyarrhythmias were induced by programmed stimulation were randomly assigned to receive either antiarrhythmic therapy, including drugs and implantable defibrillators, as indicated by the results of electrophysiologic testing, or no antiarrhythmic therapy. Angiotensin-converting-enzyme inhibitors and beta-adrenergic-blocking agents were administered if the patients could tolerate them.

RESULTS

A total of 704 patients with inducible, sustained ventricular tachyarrhythmias were randomly assigned to treatment groups. Five-year Kaplan-Meier estimates of the incidence of the primary end point of cardiac arrest or death from arrhythmia were 25 percent among those receiving electrophysiologically guided therapy and 32 percent among the patients assigned to no antiarrhythmic therapy (relative risk, 0.73; 95 percent confidence interval, 0.53 to 0.99), representing a reduction in risk of 27 percent). The five-year estimates of overall mortality were 42 percent and 48 percent, respectively (relative risk, 0.80; 95 percent confidence interval, 0.64 to 1.01). The risk of cardiac arrest or death from arrhythmia among the patients who received treatment with defibrillators was significantly lower than that among the patients discharged without receiving defibrillator treatment (relative risk, 0.24; 95 percent confidence interval, 0.13 to 0.45; P<0.001). Neither the rate of cardiac arrest or death from arrhythmia nor the overall mortality rate was lower among the patients assigned to electrophysiologically guided therapy and treated with antiarrhythmic drugs than among the patients assigned to no antiarrhythmic therapy.

CONCLUSIONS

Electrophysiologically guided antiarrhythmic therapy with implantable defibrillators, but not with antiarrhythmic drugs, reduces the risk of sudden death in high-risk patients with coronary disease.

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.

The role of antiarrhythmic therapy in the management of nonsustained ventricular tachycardia

The incidence of nonsustained ventricular tachycardia (NSVT) after myocardial infarction (MI), has decreased significantly in the thrombolytic era and may not have a high enough power to predict sudden cardiac death or all-cause mortality post-MI. Nonetheless, noninvasive algorithms that utilize the combination of NSVT with left ventricular dysfunction, abnormal signal-averaged electrocardiogram, and heart rate variability can be used for better risk assessment. Recent multicenter studies have provided strong evidence for the use of an implantable cardioverter defibrillator in patients with NSVT and inducible sustained ventricual tachycardia. On the other hand anti-arrhythmic drugs have no role and most are harmful in asymptomatic patients post-MI with NSVT.

Management of ventricular arrhythmias: a trial-based approach

Sudden cardiac death accounts for approximately 300,000 deaths annually in the U.S., and most of these are secondary to ventricular tachycardia (VT) and fibrillation in patients with coronary artery disease. Most patients with cardiac death die before reaching the hospital, which brought about a tremendous amount of research focused at identifying patients at high risk. Several trials were initiated to test the effectiveness of various therapeutic measures in these high-risk patients. A history of myocardial infarction, depressed left ventricular function and nonsustained VT have all been identified as independent risk factors for future arrhythmic death. Similarly, patients with a history of sustained VT or a history of sudden cardiac death are a high-risk group and should be aggressively evaluated and treated. The purpose of this article is to discuss risk stratification and primary prevention of sustained ventricular arrhythmias. We also review the recent secondary prevention trials and discuss the options available in the management of patients with sustained ventricular arrhythmias.

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.

Sex differences in ventricular function in patients with right bundle branch block

BACKGROUND

Left ventricular function in patients with right bundle branch block is variable and depends on the population under study. This study assessed the implications of right bundle branch block for the estimation of resting left ventricular function in patients with right bundle branch and suspected coronary artery disease.

METHODS AND RESULTS

Seventy-four patients with right bundle branch block, symptoms suggestive of coronary artery disease, and no electrocardiographic Q waves were compared with 649 patients with entirely normal electrocardiograms to assess the implications of right bundle branch block on resting left ventricular function. Resting ejection fraction was determined by radionuclide ventriculography. Patients with right bundle branch block were older (mean 65.0+/-10.2 years vs 53.8+/-11.1; P< .001) and had a lower mean ejection fraction (60%+/-11% vs 63%+/-9%; P< .005) compared with patients with normal electrocardiograms. There was a highly significant interaction between right bundle branch block and sex with respect to resting ejection fraction (P< .001). The mean ejection fraction for men with right bundle branch block was 57%+/-10% (17% with abnormal resting ejection fraction) compared with 62%+/-8% (7% with abnormal resting ejection fraction) for normal men. In contrast, the mean ejection fraction for women with right bundle branch block was 68%+/-9% (0% with abnormal resting ejection fraction) compared with 65%+/-9% (5% with abnormal resting ejection fraction) for normal women.

CONCLUSIONS

Male patients with right bundle branch block and symptoms suggestive of coronary artery disease have a lower resting ejection fraction than mole patients with normal electrocardiograms. This difference is not seen in female patients.

Ventricular arrhythmias in the elderly

Sudden cardiac death (SCD) remains a significant medical problem in the United States. The incidence of SCD increases with advancing age because cardiovascular disease is more prevalent in the elderly. Management of ventricular arrhythmias in the elderly patient is especially challenging because of increased risk of interventional and pharmacologic therapies, altered pharmacokinetics of drugs, and sometimes unclear long-term benefits.

Age-related electrophysiological and histological changes in rabbit hearts: age-related changes in electrophysiology

Because of the known higher incidence of cardiac arrhythmia in aged patients we tried to define the underlying arrhythmogenic substrate by quantifying those electrophysiological alterations in aged rabbit hearts, which are commonly believed to be arrhythmogenic, relating them to histological findings in the same hearts. This is the first investigation that analyses the effect of ageing on the epicardial excitation spreading. Isolated hearts from young (ten weeks) and old (1.5-2 years) white New Zealand rabbits were perfused according to the Langendorff-technique, submitted to epicardial potential mapping for 60 min and investigated histologically. Electrophysiological data in aged hearts showed a) a higher variability of the activation pattern, b) an increased dispersion of the epicardial potential duration; c) a prolongation of the AV-conduction time and of the duration of the epicardial activation signal, which was fractionated in aged hearts. Histological findings showed extensive incorporation of fat cells and connective tissue in ventricular and AV-node tissues, which may explain the prolonged conduction time, and a marked hypertrophy of the ventricular myocytes. The observed high dispersion, the broadened and fractionated epicardial activation signal and the enhanced variability of the activation patterns may be due to the observed long strands of collageneous tissue separating ventricular muscle fibres in aged hearts. These changes help to explain the enhanced susceptibility to arrhythmogenic stimuli with age.

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.

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.

Prediction of electrophysiologic study results in patients treated with amiodarone

To identify whether electrophysiologic study results during early-phase amiodarone therapy can be predicted by previous electrophysiologic study, we reviewed the electrophysiologic data of 50 patients with inducible sustained ventricular arrhythmias who underwent 4.3 +/- 1.3 drug trials before being given amiodarone. Study results during testing with agents of the modified Vaughan Williams Ia classification were compared with data obtained after 2 weeks of amiodarone therapy. Partial response by electrophysiologic study was defined as well-tolerated ventricular tachycardia < 150 beats/min associated with a blood pressure > or = 90 mm Hg. Significant slowing in the rate of induced ventricular tachycardia was seen during therapy with both Ia agents and amiodarone, although there was a trend toward greater slowing during amiodarone treatment (180 +/- 45 beats/min vs 164 +/- 65 beats/min; p = 0.09). Two of three patients with noninducible ventricular tachycardia during amiodarone showed profound ventricular tachycardia slowing during Ia therapy. Thirty-eight of 50 patients demonstrated concordance of electrophysiologic study results with regard to achieving partial response criteria. Twenty patients died during a mean follow-up period of 37 +/- 29 months; 7 of the 10 sudden deaths occurred in patients who did not meet partial response criteria. We conclude that patients with inducible sustained ventricular arrhythmias failing serial drug testing with Ia agents only rarely have their ventricular tachycardia suppressed during amiodarone therapy. Partial response criteria are often concordant between testing on agents of the Ia classification and amiodarone, and there was no significant difference in survival in patients based on their partial response status.

Use of electrophysiological studies in the diagnosis and treatment of cardiac patients with left ventricular dysfunction and high grade ventricular ectopy

We studied the sudden death occurrence in 28 patients (23 males, age 59.2 +/- 15.6 years) who had a documented cardiac disease with left ventricular dysfunction (ejection fraction < or = 0.4) and high grade ventricular ectopy. None had suffered from spontaneous sustained ventricular arrhythmia and/or syncope. Their diagnosis and treatment were guided by electrophysiological studies. Electrophysiological studies were performed in the antiarrhythmic drug-free state. In cases when sustained ventricular arrhythmias could be induced, antiarrhythmic treatment was prescribed according to the results of the electrophysiological studies. In cases of non-inducibility, no antiarrhythmic treatment was prescribed. The patients were followed up for a period of 20.6 +/- 11.2 months. The end points were occurrence of documented spontaneous sustained ventricular arrhythmia and sudden death. None of the 19 non-inducible patients experienced sudden death or spontaneous sustained ventricular arrhythmia. Two of the nine inducible patients died suddenly (P = 0.1). The 3-year sudden death mortality rate of the whole group was 7.5%. We conclude that when cardiac patients with high grade ventricular ectopy and left ventricular systolic dysfunction are treated according to the results of electrophysiological studies, it can be expected that their 3-year mortality rate will be low and significantly inferior to that reported for conventionally treated patients.

Inherited ventricular arrhythmias and sudden death in German shepherd dogs

OBJECTIVES

This report describes a unique group of German shepherd dogs with inherited ventricular arrhythmias and sudden death. Before death, these dogs have no evidence of cardiovascular failure.

BACKGROUND

There are few spontaneous animal models of sudden death that permit intensive investigation.

METHODS

To determine the temporal evolution of ventricular arrhythmias and to characterize the syndrome of sudden cardiac death in these dogs, 24-h ambulatory electrocardiographic (ECG) monitoring, echocardiograms, electrophysiologic testing and breeding studies were conducted.

RESULTS

The 24-h ambulatory ECGs from dogs that died showed frequent ventricular arrhythmias with rapid polymorphic ventricular tachycardia (rates > 480 beats/min). Affected dogs had a window of vulnerability for arrhythmias, with the highest incidence and severity of arrhythmias between 20 to 30 and 40 to 50 weeks of age. Affected dogs that died did not have prolongation of the QT interval over a spectrum of heart rates compared with unaffected dogs. The clinical arrhythmia was not induced in dogs during programmed electrical stimulation. Severely affected dogs monitored > 5 years did not develop any evidence of heart failure or cardiomyopathy, and no histopathologic abnormalities existed. Seventeen dogs died suddenly (age 4 to 30 months) and were either 1) found dead at first observation in the morning (n = 8), 2) observed to die during sleep (n = 4), 3) observed to die while resting after exercise (n = 3), or 4) observed to die during exercise (n = 2). All sudden deaths occurred between the end of September and April, with most (n = 11) during January and February.

CONCLUSIONS

The cause of the inherited severe ventricular arrhythmias and sudden death in these young German shepherd dogs is still undetermined. A purely arrhythmic disorder is supported by the lack of cardiac pathology. Moreover, the window of vulnerability to ventricular arrhythmias and the age and circumstances of death invite speculation about the role of the autonomic nervous system.

Should electrophysiological studies be performed in asymptomatic patients following myocardial infarction? A pragmatic approach

We analyze the arguments commonly afforded by advocates of electrophysiological evaluation for patients with recent myocardial infarction. These arguments are: (1) electrophysiological evaluation is useful for risk stratification of infarct survivors; and (2) it may be used for guiding drug therapy or to identify a group of asymptomatic patients who will benefit from implantation of an automatic cardioverter defibrillator. A positive electrophysiological study is apparently the single best predictor of future arrhythmic events in infarct survivors. However, several noninvasive tests combined may provide just as valuable information. Therefore, electrophysiological evaluation should not be advised, to the majority of infarct survivors, for the mere purpose of risk stratification. Nevertheless, electrophysiological evaluation may be proposed to patients with impaired left ventricular function or high grade ventricular arrhythmias. Patients without inducible arrhythmias have a good prognosis and may be spared the risk of long-term treatment with antiarrhythmic drugs. However, before proceeding with invasive electrophysiological evaluation, both physician and patient should ask themselves if they are willing to go ahead with defibrillator implantation in case sustained monomorphic ventricular tachycardia is induced.

Determinants of induction of ventricular tachycardia in nonsustained ventricular tachycardia after myocardial infarction and the usefulness of the signal-averaged electrocardiogram

Assessment of the implications of clinical and noninvasive variables, including the results of signal-averaged electrocardiography, was performed > or = 3 weeks after myocardial infarction in 57 patients with nonsustained ventricular tachycardia (VT) who underwent programmed ventricular stimulation to guide antiarrhythmic therapy. The clinical and noninvasive parameters assessed included ages, left ventricular ejection fractions, sites of infarction, presence of akinetic or dyskinetic left ventricular segments, history of syncope, history of coronary artery bypass surgery, and presence or absence of late potentials from signal-averaged electrocardiography. Other than the presence of late potentials, no clinical or noninvasive parameters identified such persons with a significantly higher likelihood of inducible VT. When assessed as positive if 1 or more variables were abnormal, 16 of 16 (100%) patients with versus 17 of 41 without inducible VT had late potentials (p < 0.002). With more stringent criteria required (defined as prolongation of the QRS vector complex duration and low root-mean-square voltage of the terminal 40 ms of the vector complex) 8 of 16 patients (50%) with and 4 of 41 (10%) without inducible VT had late potentials recorded (p < 0.002). Thus, the signal-averaged electrocardiogram may enable identification of persons with nonsustained VT after myocardial infarction who are most likely to have VT induced at programmed ventricular stimulation.

Prevention of sudden death in patients with coronary artery disease: the Multicenter Unsustained Tachycardia Trial (MUSTT)

This trial will significantly advance our understanding of the prognostic and therapeutic usefulness of electrophysiologic studies in patients with coronary artery disease. Several features of this trial are worth emphasizing. First, the protocol for performing programmed stimulation and serial drug testing is designed to mirror those currently in use by many practicing electrophysiologists. While practice patterns vary, the procedures used in the trial reflect what is considered "usual and standard" practice. Second, because half of the patients with inducible sustained ventricular tachycardia will be given no antiarrhythmic therapy, we will be able to ascertain the true risk of sudden death in this patient population without the influence of these agents. Third, this trial will assess the usefulness of a method of guiding antiarrhythmic therapy (electrophysiologic testing) to reduce mortality in this high-risk population. It will not evaluate the efficacy of a specific type of antiarrhythmic therapy.

The clinical significance of nonsustained ventricular tachycardia

Nonsustained ventricular tachycardia (NSVT) is an arrhythmia not often associated with symptoms; however, its occurrence in patients with structural heart disease is a prognostic indicator of an increased risk of mortality and sudden death. The management of asymptomatic patients with NSVT should first attempt to identify which patients are at highest risk for cardiac arrest, and second, devise a treatment that can reduce the incidence and/or mortality of cardiac arrest in this group. In patients with chronic coronary artery disease (CAD) and NSVT, programmed electrical stimulation identifies both a low and high risk group with respect to occurrence of ventricular arrhythmias. The negative predictive value of programmed electrical stimulation in patients with CAD and NSVT has been well established; however, uncertainty remains as to the optimal therapy for CAD patients with inducible ventricular arrhythmias. A number of reports suggest that patients whose inducible ventricular arrhythmias are rendered noninducible with antiarrhythmic drugs have a much lower risk of sudden death. It is yet to be resolved whether arrhythmias rendered noninducible identify a subgroup at low risk for cardiac arrest, independent of treatment. There is some evidence to suggest that the frequency of NSVT in patients with nonischemic dilated cardiomyopathy identifies a group at higher risk of sudden death. Programmed electrical stimulation adds little in helping to identify which of these patients are most likely to have cardiac arrest. The presence of NSVT in asymptomatic patients with hypertrophic cardiomyopathy may identify a group at higher risk for cardiac arrest.(ABSTRACT TRUNCATED AT 250 WORDS)

Management of nonsustained ventricular tachycardia guided by electrophysiological testing

Two hundred eighty patients with spontaneous nonsustained ventricular tachycardia were treated based on the results of electrophysiological testing. Seventy-nine patients had no evidence of structural heart disease, 134 had coronary artery disease, 43 had idiopathic dilated cardiomyopathy, and 24 patients had miscellaneous types of heart disease. Sustained monomorphic ventricular tachycardia was induced during electrophysiological testing in the drug free state in 52 of 280 patients (19%). Ventricular tachycardia was induced more frequently in patients with coronary artery disease (32%) than in any of the other groups (P < 0.001). The patients with inducible sustained monomorphic ventricular tachycardia underwent a mean of 1.9 +/- 1.3 drug trials. Twenty-five patients had the induction of ventricular tachycardia suppressed by pharmacological therapy and were treated with the drug judged to be effective during electropharmacological testing. Twenty-seven patients continued to have inducible sustained monomorphic ventricular tachycardia despite antiarrhythmic therapy and were discharged on the drug that made induced ventricular tachycardia best tolerated. Forty-five of 280 patients (16.1%) died during a mean follow-up period of 19.6 +/- 14.4 months. There were 15 sudden cardiac deaths, 21 nonsudden cardiac deaths, 6 noncardiac deaths, and 3 deaths that could not be classified. Sudden cardiac death mortality was lowest in the patients without structural heart disease (0% at 2 years), intermediate in the patients with coronary artery disease and miscellaneous heart disease (4% at 2 years), and highest in the patients with idiopathic dilated cardiomyopathy (13% at 2 years; P < 0.01 for pairwise comparisons). No patient treated with a drug that had suppressed the induction of sustained ventricular tachycardia died suddenly during the follow-up period whereas four of 27 patients who were discharged on "ineffective antiarrhythmic drugs" and 11 of 228 patients without inducible sustained ventricular tachycardia experienced sudden cardiac death during the follow-up period. By multivariate analysis, ejection fraction and inducible ventricular tachycardia during the predischarge electrophysiological test were independent predictors of sudden cardiac death. In conclusion, in patients with spontaneous non-sustained ventricular tachycardia: (1) Arrhythmia inducibility varies depending on the underlying heart disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Endocardial mapping during sinus rhythm in patients with coronary artery disease and nonsustained ventricular tachycardia

Programmed stimulation in patients with nonsustained ventricular tachycardia (VT) and coronary artery disease (CAD) induces sustained VT in 30 to 50% of patients. The presence of inducible, sustained VT identifies patients at high risk for sudden death. This study sought to determine whether patients with nonsustained VT who have inducible, sustained VT would have differences of left ventricular endocardial activation and conduction compared with those of patients without inducible, sustained VT. Thirty-six patients with CAD referred for evaluation of nonsustained VT underwent programmed ventricular stimulation and catheter mapping of left ventricular endocardial activation. Using previously validated methods, electrograms were classified as normal, abnormal or fractionated based on measurement of local electrogram duration and amplitude. Programmed stimulation induced sustained, uniform VT in 16 of 36 patients (44%). Patients with inducible, sustained, uniform VT had significantly more sites with abnormal (48%) and fractionated (5.5%) electrograms than did those without inducible VT (35% abnormal and 0.4% fractionated; p = 0.05 and 0.01, respectively). Patients with inducible VT had a mean of 15% of mapped sites displaying late electrograms versus only 3% in those without inducible VT (p < 0.01). The duration of the longest local electrogram in patients with inducible, sustained, uniform VT was 128 ms compared with 100 ms in those without inducible VT (p < 0.001). Thus, patients with CAD presenting with nonsustained VT who have inducible, sustained, uniform VT have significantly greater degrees of local conduction slowing and delayed activation than do those without inducible, sustained, uniform VT. These observations support reentry as the mechanism of the induced arrhythmias in these patients.

Lack of arrhythmogenicity of aminophylline in dogs

This study was designed to determine if doses of aminophylline up to 10 mg/kg given i.v. would produce ventricular arrhythmias in seven healthy dogs anaesthetized with fentanyl-droperidol-pentobarbital. Arrhythmias were sought by inspection of ECGs before and after attempts at provoking them with 5 micrograms/kg boluses of epinephrine given i.v., or by programmed electrical stimulation. After cumulative doses of 10 mg aminophylline/kg body weight, producing an estimated plasma concentration of greater than 30 micrograms/ml, no ventricular ectopia other than escape depolarizations were observed. We were unable to document an arrhythmogenic effect of aminophylline when given rapidly by the i.v. route. It is possible that the anaesthetic regimen reduced the arrhythmogenic property of aminophylline, or that arrhythmias might be produced in either obese or ill dogs; but it is unlikely that chronic administration of aminophylline would be more arrhythmogenic.