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

Prognosis of patients with sustained ventricular tachycardia and of survivors of cardiac arrest not inducible by programmed stimulation

The aim of this study was to analyze the long-term clinical outcome of 60 prospectively studied patients with documented sustained ventricular tachyarrhythmia that was not inducible during baseline programmed ventricular stimulation: 39 with cardiac arrest due to noninfarction ventricular fibrillation (VF) and 21 with mild hemodynamically compromising sustained ventricular tachycardia (VT). Left ventricular ejection fraction was 55 +/- 14% in the VF group and 50 +/- 13% in the VT group (difference not significant). Patients were discharged without conventional antiarrhythmic drugs and received only empirical beta-blocker therapy. During a mean follow-up period of 21 +/- 16 months (mean +/- SD), 10 of 60 patients (17%) died suddenly. The actuarial incidence of sudden death at 1 and 4 years was similar in both groups (VF group, 10 and 20%; VT group, 16 and 16%) (p = 0.48). The actuarial incidence of sudden cardiac death was significantly higher in patients with left ventricular ejection fraction < or = 40% than in those with > 40% (1-year incidence in VF group, 40 vs 0%; VT group, 50 vs 0%) (p = 0.005 and p = 0.01, respectively). Multivariate regression analysis identified left ventricular ejection fraction < or = 40% and previous myocardial infarction as the only independent predictor of sudden cardiac death. The occurrence of frequent ventricular pairs during Holter monitoring was the only independent predictor of sustained VT recurrences. It is concluded that patients with sustained ventricular tachyarrhythmia in whom arrhythmia was non-inducible during baseline ventricular stimulation and not treated with antiarrhythmic therapy have a favorable outcome if left ventricular ejection fraction is high.(ABSTRACT TRUNCATED AT 250 WORDS)

Survival after a first episode of ventricular tachycardia or fibrillation

Recent outcome analyses in ventricular tachycardia (VT) and ventricular fibrillation (VF) have included patients undergoing electrophysiological study (EPS) at tertiary care centers. The selection process involved could introduce bias in the reported populations. We analyzed the outcome of 42 consecutive patients (aged 63 +/- 11 years) admitted to a coronary care unit within 48 hours of a first episode of VT/VF not associated with reversible causes. All patients recovered neurologically and were candidates for EPS. Nine patients (21%) died during the initial hospitalization (none had EPS), and another nine died during a follow-up of 17 +/- 12 months. Actuarial survival at 1 and 2 years was 64% and 62%, respectively. By Cox's model, congestive heart failure functional Class III-IV (P = 0.008; hazard ratio = 3.7) was the only independent prognostic factor. Among patients discharged, subsequent survival did not depend on the performance of EPS or on the antiarrhythmic therapeutic modalities used. Mortality after a first episode of VT/VF is high. Severe congestive heart failure is the most powerful prognostic factor. Studies including successfully referred patients undergoing EPS may not reflect the true natural history of patients with VT/VF.

A comparison of electrophysiologically guided antiarrhythmic drug therapy with beta-blocker therapy in patients with symptomatic, sustained ventricular tachyarrhythmias

BACKGROUND

Antiarrhythmic drug therapy guided by invasive electrophysiologic testing is now widely used in patients with symptomatic, sustained ventricular tachyarrhythmias.

METHODS

We conducted a prospective, randomized trial in 170 patients to investigate whether this approach would improve long-term outcome. Patients whose arrhythmia was inducible by programmed electrical stimulation were assigned to treatment with electrophysiologically guided drug therapy based on serial testing (61 patients) or with metoprolol (54 patients). Electrophysiologically guided therapy consisted of serial testing of antiarrhythmic agents to identify the first one that rendered the arrhythmia noninducible. The 55 patients whose arrhythmia was noninducible during the initial electrophysiologic test were also treated with metoprolol.

RESULTS

During a mean (+/- SD) follow-up period of 23 +/- 17 months, recurrent, nonfatal arrhythmia occurred in 44 patients and sudden death due to cardiac factors in 27. The incidence of symptomatic arrhythmia and sudden death combined was virtually the same in the two groups with inducible arrhythmia after two years of observation (electrophysiologically guided therapy vs. metoprolol therapy, 46 percent vs. 48 percent). The outcome was more favorable in the patients with noninducible arrhythmia at base line (75 percent had neither adverse event) than in those with inducible arrhythmia who were assigned to metoprolol therapy (P = 0.009 by log-rank test). Only 6 of the 29 patients (21 percent) with inducible arrhythmia that became noninducible during drug therapy had recurrent arrhythmia or sudden death, as compared with 21 of the 32 patients (66 percent) with arrhythmia that continued to be inducible (P less than 0.001). A multivariate regression analysis identified continued inducibility of the arrhythmia as an independent predictor of recurrent arrhythmia or sudden death (relative risk, 7.3; 95 percent confidence interval, 2.3 to 23.2; P less than 0.001).

CONCLUSIONS

As compared with metoprolol therapy, electrophysiologically guided antiarrhythmic drug therapy did not improve the overall outcome of patients with sustained ventricular tachyarrhythmias. However, effective suppression of inducible arrhythmia by antiarrhythmic drugs was associated with a better outcome than was lack of suppression.

Sudden death in idiopathic dilated cardiomyopathy

Approximately 30% of deaths among patients with IDCM are sudden. Although ventricular tachyarrhythmias are responsible for many of these deaths, bradyarrhythmias may also play a significant role. Patients with a previous history of sustained ventricular arrhythmias are at high risk for sudden death. In patients without prior symptomatic ventricular arrhythmias a history of unexplained syncope, severely impaired right ventricular hemodynamics, frequent spontaneous ventricular ectopy or NSVT, and inducible SMVT may help identify those at greatest risk of dying suddenly. With the exception of angiotensin-converting enzyme inhibitor therapy, attempts at pharmacologic prevention of sudden death have had limited efficacy. The implantable defibrillator offers promising results in survivors of previous sustained ventricular arrhythmias; its prophylactic use in other high-risk subgroups is the subject of active investigation.

Prevention of sudden cardiac death: the ICD, or an electrical end-point with preceding opportunities for intervention?

Sudden cardiac death (SCD) is usually due to monomorphic ventricular tachycardia and/or ventricular fibrillation. However, in the vast majority of patients these arrhythmias are associated with advanced structural disease. In our society, this is usually due to coronary artery disease (CAD). The implantable cardioverter--defibrillator is the logical approach to management in survivors of SCD. Its rational use must be guided by electrophysiology study. However, a realistic and cost-effective approach to the prevention of a first cardiac arrest must be multifaceted and take cognisance of other aspects including primary prevention. Limitation of the size of myocardial infarction (MI) is vital. Trials already suggests that effective thrombolysis may impinge long-term on arrhythmic end-points. Following infarction, ventricular arrhythmias and sudden death may also be decreased by aspirin, beta-blockers, and possibly angiotensin converting enzyme inhibitors and amiodarone. Many post-infarction studies employ a combined end-point of death and clinical arrhythmias. However, death is usually confined to those with an ejection fraction < 35%. In them, treatment of associated heart failure is often a consideration and if the ejection fraction < 15-20%, depending on donor availability, transplantation may even be the preferred therapeutic option to the cardioverter-defibrillator.

Reproducibility of programmed electrical stimulation responses in patients with ventricular tachycardia or fibrillation associated with coronary artery disease

Invasive electrophysiologic studies were performed in 102 patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) using an aggressive programmed electrical stimulation (PES) protocol. The study was repeated after 2.0 +/- 2.9 days in all patients with no intercurrent changes in antiarrhythmic therapy. Patients with coronary artery disease (n = 72) were identified and PES results of these patients were analyzed and compared with results of patients without coronary artery disease. Multiple clinical and electrophysiologic factors were analyzed to determine any association with concordance of PES responses. No significant difference in concordance of PES responses was found in the 2 groups of patients. PES responses were groups into 3 categories: (1) noninducible, (2) nonsustained VT, and (3) sustained VT. Kappa values of PES responses of noninducible and sustained VT in both groups were higher and therefore the PES responses were more reproducible than nonsustained VT. The induction of sustained monomorphic VT was more reproducible than a PES response of nonsustained or sustained polymorphic VT. Inducible sustained VT with a rate of greater than or equal to 250 beats/min was less reproducible than induction of sustained VT with a rate less than 250 beats/min. Induction of VT by 3 extrastimuli was less reproducible than with any other mode. This short-term variability may account for false negatives associated with PES-directed antiarrhythmic therapy. Because of these findings, it is recommended that nonsustained VT and sustained polymorphic or rapid polymorphic VT should not be used as PES end points to guide antiarrhythmic therapy.

Adjuvant metoprolol improves efficacy of class I antiarrhythmic drugs in patients with inducible sustained monomorphic ventricular tachycardia

Inducible ventricular tachycardia frequently persists despite solitary class I antiarrhythmic drug therapy. To determine the effect of metoprolol as adjuvant therapy, 19 patients with clinical ventricular tachycardia with baseline inducible sustained monomorphic ventricular tachycardia and persistently inducible ventricular tachycardia despite class I drugs were evaluated. Eight of 19 patients (42%) became noninducible when metoprolol was added to class I drug therapy. Sixteen of 19 patients (84%) were harder to induce or noninducible on a regimen of adjuvant metoprolol therapy. In evaluating the clinical characteristics of the 19 patients, no significant differences were found between patients who were persistently inducible and those rendered noninducible. In evaluating the electrophysiologic characteristics, the group eventually rendered noninducible had a significantly shorter baseline induced cycle length (259 +/- 27 vs 305 +/- 53 msec). Combination class I drug and metoprolol therapy significantly lengthened the ventricular effective refractory period in both groups compared with baseline. The long-term follow-up was excellent in all patients remaining on metoprolol in the noninducible group. Therefore adjuvant metoprolol therapy creates a significant improvement in a number of patients with persistently inducible ventricular tachycardia despite class I drug therapy.

Selection of patients for programmed ventricular stimulation: a clinical decision-making model based on multivariate analysis of clinical variables

OBJECTIVE

This study was conducted to assess the utility of clinical variables in predicting the inducibility of sustained ventricular arrhythmias in a heterogeneous group of patients undergoing programmed ventricular stimulation.

METHODS

Variables were considered in a simulated chronologic order to determine the incremental information added by the signal-averaged electrocardiogram (ECG) and left ventricular ejection fraction. All patients undergoing baseline programmed ventricular stimulation for induction of ventricular tachyarrhythmia during a 30-month period were included in the study. Fourteen historical, ECG, signal-averaged ECG and left ventricular wall motion variables were evaluated for their ability in predicting inducibility of a sustained ventricular arrhythmia, a "positive" event, at programmed ventricular stimulation.

RESULTS

On univariate analysis of the clinical variables, comparison between patients with positive or negative results showed significant differences in 10 of the 14 clinical variables: major cardiac diagnosis, history of ventricular tachycardia, myocardial infarction by history or ECG, all five signal-averaged ECG variables, left ventricular ejection fraction and presence of left ventricular aneurysm. On multivariate analysis, five independent variables were determined to be important: history of ventricular tachycardia, historical or ECG evidence of myocardial infarction, history of loss of consciousness, filtered QRS duration on the signal-averaged ECG and left ventricular ejection fraction. However, with sequential multivariate analysis, a model based only on historical and conventional ECG data was found to do as well as a model that included signal-averaged ECG and left ventricular ejection fraction data.

CONCLUSIONS

Routinely available noninvasive historical, ECG, signal-averaged ECG and left ventricular wall motion variables can be used to accurately predict the outcome of programmed ventricular stimulation. The majority of the predictive power was obtained with the routine model, using only historical and ECG data. The signal-averaged ECG and left ventricular wall motion analysis added no significant incremental information.

Effect of the antiarrhythmic agent moricizine on survival after myocardial infarction

BACKGROUND

The Cardiac Arrhythmia Suppression Trial (CAST) tested the hypothesis that the suppression of asymptomatic or mildly symptomatic ventricular premature depolarizations in survivors of myocardial infarction would decrease the number of deaths from ventricular arrhythmias and improve overall survival. The second CAST study (CAST-II) tested this hypothesis with a comparison of moricizine and placebo.

METHODS

CAST-II was divided into two blinded, randomized phases: an early, 14-day exposure phase that evaluated the risk of starting treatment with moricizine after myocardial infarction (1325 patients), and a long-term phase that evaluated the effect of moricizine on survival after myocardial infarction in patients whose ventricular premature depolarizations were either adequately suppressed by moricizine (1155 patients) or only partially suppressed (219 patients).

RESULTS

CAST-II was stopped early because the first 14-day period of treatment with moricizine after a myocardial infarction was associated with excess mortality (17 of 665 patients died or had cardiac arrests), as compared with no treatment or placebo (3 of 660 patients died or had cardiac arrests); and estimates of conditional power indicated that it was highly unlikely (less than 8 percent chance) that a survival benefit from moricizine could be observed if the trial were completed. At the completion of the long-term phase, there were 49 deaths or cardiac arrests due to arrhythmias in patients assigned to moricizine, and 42 in patients assigned to placebo (adjusted P = 0.40).

CONCLUSIONS

As with the antiarrhythmic agents used in CAST-I (flecainide and encainide), the use of moricizine in CAST-II to suppress asymptomatic or mildly symptomatic ventricular premature depolarizations to try to reduce mortality after myocardial infarction is not only ineffective but also harmful.

Significance of aborted cardiac arrest and sustained ventricular tachycardia in patients referred for treatment therapy of advanced heart failure

Cardiac arrest in patients with heart failure may be the result of remediable factors such as pulmonary edema, drug toxicity, or electrolyte abnormalities, or it may be due to primary arrhythmias. The relation of prior aborted cardiac arrest or sustained ventricular tachycardia to subsequent prognosis was assessed in 458 consecutive patients referred for management of advanced heart failure (left ventricular ejection fraction 0.2 +/- 0.07). All patients received tailored vasodilator and diuretic therapy and were then followed as outpatients. Patients were divided into four groups: 388 patients (85%) with no prior cardiac arrest or sustained ventricular tachycardia, 31 patients (7%) with a primary arrhythmia cardiac arrest, 22 patients (5%) with a secondary cardiac arrest, and 17 patients (4%) with sustained ventricular tachycardia without cardiac arrest. Patients with cardiac arrest resulting from a primary arrhythmia were usually treated with antiarrhythmic drugs (25 patients), and five patients received an implantable defibrillator. After hospital discharge actuarial 1-year sudden death risk (17%) and total mortality (24%) rates for the group with primary arrhythmia were similar to corresponding values in patients with no history of cardiac arrest or sustained ventricular tachycardia (17% and 30%, respectively). In patients with a secondary cardiac arrest as a result of exacerbation of heart failure (11 patients), torsade de pointes (10 patients), or hypokalemia (one patient), therapy focused on removal of aggravating factors. Actuarial 1-year sudden death (39%) and total mortality (54%) rates for the group with secondary arrest were higher than for patients without a history of cardiac arrest (p = 0.003 and 0.005, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Incidence and timing of recurrences of sudden death and ventricular tachycardia during antiarrhythmic drug treatment after myocardial infarction

Incidence and timing of recurrences of sustained ventricular tachycardia (VT) or sudden death were studied in 206 patients who survived their first episode of ventricular fibrillation (VF; n = 52) or sustained VT (n = 154) after myocardial infarction. All patients were treated with (empirically selected) antiarrhythmic drugs; 49% received amiodarone. After a mean follow-up of 36 months, 64 patients (41%) in the VT group and 10 (19%) in the VF group had nonfatal VT recurrences. Sudden death occurred in 22 (14%) and 9 (17%) patients in the VT and VF groups, respectively. Incidence of sudden death had 2 peaks at approximately 3 and 12 months. Nonfatal VT recurrences were more frequent (most often occurring in first 6 months) in the VT than in the VF group. Sudden death occurred during the following 3 years in only 10% of patients who survived 1 year. There was a much higher incidence of sudden death in patients with left ventricular ejection fraction (LVEF) less than or equal to 40% than in those with LVEF greater than 40% (28 of 65 vs 3 of 141; p less than 0.0001), but no relation between LVEF and nonfatal VT recurrences.

Time to first pulse after automatic implantable cardioverter defibrillator implantation

Should automatic implantable cardioverter defibrillator (AICD) power sources be explanted and discontinued if they have not pulsed during the first generator life? We have followed 59 patients an average of 23 months (range, 3 days to 8.4 years) after AICD implantation. The indication for AICD implantation was based on clinical dysrhythmia, history of sudden death, and findings at electrophysiologic study. Thirty-eight of 59 patients (64%) had experienced sudden death and 52/58 (90%) were inducible at electrophysiologic study. Excluding 5 inappropriate pulsing episodes, 31 of 59 patients (53%) had 235 pulses (range, 1 to 36; median, 2 pulses). The time to first pulse after implantation ranged from 1 day to 3.5 years with a median time of 2 months. In 6 patients, the first pulsing occurred later than 1 year after AICD implantation. Fifteen generators demonstrating impending power source failure have been replaced in 11 patients. Power source depletion occurred at an average of 24.1 months (range, 8 to 40 months). In 3 patients, the first pulsing occurred after generator depletion and replacement. By univariate analysis, none of 13 variables (sex, age, cardiac disease process, functional class, previous myocardial infarction, sudden death history, ejection fraction, type of dysrhythmia, inducibility with electrophysiologic testing, number of extra stimuli required for induction, left ventricular aneurysm resection, endocardial resection, or concomitant operation) was found to be a predictor of pulsing (p greater than 0.05). We conclude that the majority of patients with pulses after AICD implantation will have them during the first 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

A critical appraisal of indications for the implantable cardioverter defibrillator (ICD)

The implantable cardioverter defibrillator (ICD) is a remarkably effective therapy for reducing sudden cardiac death in patients with malignant ventricular arrhythmias. The indications for implantation of the ICD were approved in 1985 by the United States Food and Drug Administration; it could be implanted in patients who have experienced cardiac arrest or in those with recurrent ventricular arrhythmias which are not suppressed by anti-arrhythmic drugs in the electrophysiology laboratory. These established indications have not changed in the last seven years. In the near future, the release of third-generation ICDs (with antitachycardia pacing) will likely further expand indications for the device. Many patients with stable ventricular tachycardia who have not had syncope or cardiac arrest will receive a third-generation defibrillator. Also, three clinical trials now in progress--CABG-PATCH, Multicenter Automatic Defibrillator Implantation Trial (MADIT) and Multicenter Unsustained Tachycardia Trial (MUSTT)--are studying "pre-event" patients with low ejection fraction and electrical instability; some of the patients in each trial are being prospectively randomized to the ICD. Within the next five years we will have a better understanding of the role of ICD therapy in such patients. Until these studies are completed, it is important that the indications for the ICD not be expanded.

Cost-effectiveness of the implantable cardioverter-defibrillator: effect of improved battery life and comparison with amiodarone therapy

The implantable cardioverter-defibrillator (ICD) greatly reduces the incidence of sudden cardiac death among patients with recurrent sustained ventricular tachycardia and fibrillation who do not respond to conventional antiarrhythmic therapy. A cost-effectiveness analysis was performed, comparing the ICD, amiodarone and conventional agents. Actual variable costs of hospitalization and follow-up care were used for 21 ICD- and 43 amiodarone-treated patients. Life expectancy and total variable costs were predicted with use of a Markov decision analytic model. Clinical event rates and probabilities were based on published reports or expert opinion. Life expectancy with an ICD (6.1 years) was 50% greater than that associated with treatment with amiodarone (3.9 years) and 2.5 times that associated with conventional treatment (2.5 years). Assuming replacement every 24 months, ICD lifetime treatment costs (in 1989 dollars) for a 55-year old patient are expected to be $89,600 compared with $24,800 for amiodarone and $16,100 for conventional therapy, yielding a marginal cost/effectiveness ratio for ICD versus amiodarone therapy of 1f429,200/year of life saved, which is comparable to that of other accepted medical treatments. If technologic improvements extend average battery life to 36 months, the marginal cost/effectiveness ratio would be $21,800/year of life saved, and at 96 months it would be $13,800/year of life saved. Patient age at implantation did not significantly affect these results. If quality of life on amiodarone therapy is 30% lower than that with the ICD, the marginal cost/effectiveness ratio decreases by 35%. If the quality of life for patients receiving drugs is 40% lower than that of patients treated with an ICD, use of the defibrillator becomes the dominant strategy.

Continuing experience with the automatic implantable cardioverter defibrillator

The automatic implantable cardioverter defibrillator (AICD) is now used commonly in the management of malignant ventricular arrhythmias. Its use may obviate the need for antiarrhythmic drugs or endocardial resection. We reviewed our continuing experience with the AICD to determine its safety and efficacy. Since June 1987, 102 patients (mean age: 63 years) who survived out-of-hospital ventricular fibrillation or hemodynamically unstable ventricular tachycardia not associated with acute myocardial infarction underwent implantation of an AICD. There were three operative deaths and nine complications. Eighty-nine patients are alive. No patient has experienced sudden cardiac death. Forty-two patients (43%) have had 1 or more AICD discharges associated with symptoms of cardiac arrest. During AICD implantation, it appears preferable to configure lead placement by individual patient characteristics rather than by a rigid protocol. The relative safety and efficacy of the AICD support its use as an alternative to toxic medications or more dangerous endocardial resection in suboptimal candidates.

Influence of left ventricular function on outcome of patients treated with implantable defibrillators

BACKGROUND

The outcomes of patients treated with implantable defibrillators were compared between patients with left ventricular ejection fraction greater than or equal to 30% and less than 30%.

METHODS AND RESULTS

Of 68 consecutive patients treated with implantable defibrillators, 40 patients (group 1) had left ventricular ejection fraction greater than or equal to 30%, and 28 patients (group 2) had left ventricular ejection fraction less than 30%. Sudden death, surgical mortality, nonsudden arrhythmia-related death (death within 24 hours after an arrhythmic event despite initial termination of the arrhythmia by the implantable defibrillator), total arrhythmia-related death (including sudden death, surgical death, and nonsudden arrhythmia-related death), and total cardiac death were compared between the two groups. Surgical mortality was 4.4% (0% in group 1, 11% in group 2). During the follow-up of 31 +/- 27 months, actuarial survival rates free of events were 97%, 97%, and 97% in group 1 and 96%, 91%, and 82% in group 2 at 12, 24, and 36 months, respectively, for sudden death (p = NS); 97%, 97%, and 97% in group 1 and 85%, 81%, and 72% in group 2 at 12, 24, and 36 months, respectively, for sudden death and surgical mortality (p less than 0.05); 97%, 97%, and 97% in group 1 and 82%, 78%, and 70% in group 2 at 12, 24, and 36 months, respectively, for total arrhythmia-related death (p less than 0.05); and 95%, 95%, and 95% in group 1 and 82%, 69%, and 57% in group 2 at 12, 24, and 36 months, respectively, for total cardiac death (p less than 0.05). Four (57%) of seven nonsudden cardiac deaths during the initial 36-month follow-up period were causally related to arrhythmia (three surgical deaths and one arrhythmia-related nonsudden death).

CONCLUSIONS

The outcome of patients treated with implantable defibrillators is strongly influenced by the degree of left ventricular dysfunction. In group 1 patients, surgical mortality, sudden death, and total cardiac death are rare. In group 2, sudden death rate may not be markedly different from that of group 1 patients. However, the risk of therapy (surgical mortality) is high. Many nonsudden cardiac deaths are causally related to arrhythmia (surgical mortality or nonsudden arrhythmia-related death). Therefore, the survival rate free of total arrhythmia-related death is significantly lower in group 2 (70% versus 97% in group 1 at 3 years). Further studies are needed to determine the roles of defibrillator therapy and other therapies in various clinical settings.

Long-term outcome of survivors of cardiac arrest whose therapy is guided by electrophysiologic testing

The long-term outcome of 217 consecutive survivors of cardiac arrest whose therapy was guided by electrophysiologic testing was analyzed. After electrophysiologic testing, 81 patients (37%) were classified as having no inducible arrhythmia and were treated without antiarrhythmic drugs; 23 received an implantable defibrillator. Of the 136 patients with inducible arrhythmia, the 51 (38%) who responded to serial drug testing were treated with the successful drug and the 85 (62%) with unsuccessful drug testing were treated with an implantable defibrillator (47 patients), amiodarone (36 patients) or drugs that were unsuccessful during testing (2 patients). The mean follow-up interval for all patients was 35 +/- 23 months. The actuarial incidence of sudden death and overall death was similar for patients whose arrhythmias were not inducible, drug responders and nonresponders. The actuarial incidence rate of recurrent arrhythmic events in nonresponders was 35 +/- 5% and 53 +/- 7% at 2 and 5 years, respectively. These values were significantly lower (and statistically similar to each other) in the other two patient groups: patients with noninducible arrhythmia (19 +/- 5% and 31 +/- 7%, respectively, p less than 0.05) and drug responders (13 +/- 5% and 23 +/- 8%, respectively, p less than 0.01). Patients with an implantable defibrillator who had recurrent arrhythmic events were significantly less likely to die suddenly than were patients without a defibrillator who had recurrent events (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Implantable cardioverter defibrillators: current status and future directions

Sudden cardiac death remains the most common mode of mortality in the United States, accounting for up to 450,000 deaths per year. Survivors of cardiac arrest and patients who have recurrent ventricular tachycardia have a high mortality rate with or without antiarrhythmic therapy. The implantable cardioverter defibrillator (ICD) was introduced in 1980 by Mirowski as a potential treatment for these patients. There are presently over 24,000 implants worldwide and the device has proved to be an effective means of preventing sudden death. The components of an ICD include a generator, defibrillation patches or leads, and pacing/sensing leads. The devices can be implanted with acceptable mortality and morbidity either by median sternotomy, left anterior thoracotomy, subxiphoid, or left subcostal approaches. The long-term results have been excellent with an actuarial incidence of sudden cardiac death of 3% at 5 years. Improvements in battery and capacitor technology, lead design, and tachycardia recognition, combined with the addition of hemodynamic sensors and a better understanding of the science of defibrillation, should lead to further improvements over the next several years in the ICD.

Biological risk factors for sudden death in patients with coronary artery disease and without heart failure

In a study of biological risk factors for sudden death in patients with coronary artery disease, 320 patients were, prospectively, recruited and followed-up over two years. None of the patients had heart failure or recent myocardial infarction. The following variables were recorded: previous acute myocardial infarction, hypertension, smoking habits, ventricular arrhythmia; the angiographic variables included: left ventricular ejection fraction, Jenkins' and mean atherosclerotic scores; lipid profile: cholesterol, triglycerides, high density lipoprotein cholesterol, low density lipoprotein cholesterol, apolipoproteins Al and B; hemostatic profile: fibrinogen, fibrinopeptide A, antithrombin III, factor VIII antigen, factor VIII coagulant, protein C, plasminogen, alpha 2-antiplasmin, euglobulin clot lysis time and tissue plasminogen activator before and after venous occlusion, tissue plasminogen activator inhibitor, platelet factor 4, beta-thromboglobulin. During the follow-up period, 12 of the patients died suddenly. In these patients, ejection fraction was lower: 49 +/- 16% versus 61 +/- 14% for the other patients (P less than 0.02), fibrinogen higher: 3.9 +/- 0.8 g/l versus 3.5 +/- 0.8 for the living patients (P less than 0.05) and protein C lower: 89 +/- 39% versus 111 +/- 39% (P = 0.06) for the other patients. In multivariate analysis: lower ejection fraction (P less than 0.008), older age (P less than 0.03) and lower protein C (P less than 0.01) were correlated with sudden death. Among the patients with coronary artery disease, the raised fibrinogen and the decreased protein C appeared to be risk factors for sudden cardiac death. These alterations reflected a prothrombotic state which might increase the ischemic risk, due to an acute thrombosis, leading to the fatal ventricular arrhythmia. Determination of these hemostatic variables might be a useful adjunct for assessment of the vital prognosis of patients with coronary artery disease, especially the risk of sudden death in addition to other known clinical, electrocardiographic, hemodynamic risk factors. This would also guide both the instigation of complementary investigations and appropriate therapy in such high risk group of patients.

Results of Electrophysiological Testing and Long-Term Follow-Up in Patients Sustaining Cardiac Arrest Only While Receiving Type IA Antiarrhythmic Agents

Therapeutic management of patients sustaining a cardiac arrest while receiving antiarrhythmic agents can be difficult since the role of the drug in possibly facilitating the arrhythmia is often difficult to define. To determine if the response to programmed stimulation could give insight into which patients may have experienced a drug-induced cardiac arrest, we studied 29 patients (61 +/- 9 years) with no prior history of sustained ventricular tachyarrhythmias (VT) who suffered a cardiac arrest only while receiving type Ia antiarrhythmic agents. Patients with documented myocardial infarction, acute ischemia, electrolyte abnormalities, or torsade de pointes were excluded from the study. Twenty-four patients had coronary artery disease with prior myocardial infarction (ejection fraction 28% +/- 9%) and five patients had idiopathic dilated cardiomyopathy (ejection fraction 31% +/- 6%). During baseline electrophysiological testing, 19 patients (66%) had inducible sustained ventricular arrhythmias: uniform VT, n = 14 (group I), polymorphic VT or ventricular fibrillation, n = 5 (group II). Ten patients (group III) had no inducible sustained ventricular arrhythmias. To determine if rechallenge with a type Ia agent could facilitate induction of a sustained ventricular arrhythmia in group III, eight patients underwent ten electrophysiological studies during therapy with either procainamide or quinidine. Only two patients developed sustained VT in response to programmed stimulation. Patients in groups I and II received therapy guided by electrophysiological testing, including antiarrhythmic agents alone (n = 8), subendocardial resection (n = 4), or an implantable cardioverter defibrillator (n = 7). Patients in group III received antiarrhythmic agents empirically (n = 3), or for treatment of atrial tachyarrhythmias (n = 2) or nonsustained VT (n = 1). In addition, four patients in group III received an implantable cardioverter defibrillator. During a mean follow-up of 28 +/- 27 months (range: 1 day-84 months) 13 patients died suddenly or received a defibrillator shock preceded by syncope or presyncope: group I: n = 5; group II: n = 2; group III: n = 6.

IN CONCLUSION

(1) most patients sustaining a cardiac arrest only in the presence of type Ia antiarrhythmic agents have inducible sustained VT in the absence of antiarrhythmic agents, and (2) the risk of recurrent VT persists in patients without inducible sustained arrhythmias in the drug-free state, regardless of whether they manifest inducible arrhythmias after rechallenge with a type Ia agent.

Reproducibility of Successful Drug Trials in Patients With Inducible Sustained Ventricular Tachycardia

Patients whose inducible sustained ventricular tachycardia is suppressed during serial electrophysiological testing have a small but gradually increasing actuarial incidence of recurrent arrhythmias despite therapy with the "successful" drug. In an effort to improve the predictive value of a drug response, in 1990 we began to require that our full stimulation protocol be repeated successfully several times before considering a drug to be effective. In 23 consecutive patients who had inducible sustained ventricular tachycardia which was suppressed by at least one drug during invasive serial drug testing using a standard stimulation protocol, the identical stimulation protocol was performed six times during therapy with the initially successful drug (three trials on Day 1 and three trials on Day 2). Repeat trials were completed (i.e., either all six trials were successfully finished or sustained tachycardia was induced) for 29 initially successful drugs in these 23 patients. With 18 of these 29 initially successful drugs (62%), sustained ventricular tachycardia was eventually induced during repeat trials. The eventual drug failures could not be correlated with specific drugs tested, subtherapeutic or falling serum drug levels, marked fluctuations in autonomic tone, or changes in anatomic substrate. The proportion of patients failing each repeat trial was relatively constant: 4/29 (14%) failed Trial 2, 2/25 (8%) failed Trial 3, 7/23 (30%) failed Trial 4, 2/16 (13%) failed Trial 5, and 3/14 (21%) failed Trial 6. The increase in the cumulative incidence of drug failure during repeat trials was nearly linear. Inducibility of ventricular tachycardia appears to be a probability function; a successful drug study should not be regarded as an absolute phenomenon.

Identification of patients at high risk for recurrence of sustained ventricular tachycardia after healing of acute myocardial infarction

A prognostic index for nonfatal recurrences of ventricular tachycardia (VT) was developed using a retrospective analysis of a group of 206 patients with sustained monomorphic VT or ventricular fibrillation (VF) after healing of acute myocardial infarction. 74 patients (36%) (64 with VT and 10 with VF) had recurrences of sustained monomorphic VT during 3.4 +/- 9 years of follow-up. Three clinical variables were selected and weighted by stepwise logistic discriminant analysis of the study group. They were coded as follows: interval of myocardial infarction to arrhythmia (less than 2 months = 1; 2 to 6 months = 2; greater than 6 months = 3), drug therapy with or without sotalol (with = 1, without = 2), and VT or VF as the presenting arrhythmia (VT = 1, VF = 2). The prognostic index was: 3.41 - (0.56 x interval) - (1.94 x therapy) + (0.86 x arrhythmia). This index was validated prospectively in a test group of 158 consecutive patients with VT or VF after healing of acute myocardial infarction. Patients were allocated into different classes with decreasing prognostic index values associated with increasing risk for recurrences of VT. In the test group, 27 of 158 (17%) patients (22 with VT and 5 with VF) had recurrences of VT (follow-up of 2 +/- 2 years). Two risk classes of patients were identified: high risk for recurrences of VT (61%) corresponding to patients with a negative index; and low risk (4%) consisting of those with a positive index. Thus, using O as the cutoff point, the sensitivity, specificity, and positive and negative predictive values were 81, 89, 62 and 96%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of sudden death in survivors of myocardial infarction: a decision analysis approach

During the first year after myocardial infarction, 5% to 15% of patients die, and the majority of deaths occur suddenly. Highly efficacious therapy, such as the implantable cardioverter-defibrillator, may reduce the chance of sudden death, but broad application is limited by associated risks. Hence, attempts to identify patients at high risk so they can receive therapy are desirable. Subgroups with high or low sudden death risks can be identified based on left ventricular function. Further risk stratification using programmed electrical stimulation and the signal-averaged ECG has been advocated, but the best strategy is unknown. Using a decision analysis model, we compared the 1-year survival rates in survivors of myocardial infarction treated with the implantable cardioverter-defibrillator either empirically or based on screening with the signal-averaged ECG and programmed electrical stimulation. The best strategy for selecting patients for therapy depended on the pre-therapy sudden death risk. For patients at low risk, such as those with well-preserved ventricular function, antiarrhythmic therapy selected with screening tests or given empirically increased both the mortality rate resulting from the adverse effects of therapy and the excellent survival rate without therapy. In the moderate-risk population, both empiric and stratified approaches reduced mortality, but stratification substantially limited the number of patients receiving unnecessary therapy. In the high-risk population, empiric treatment achieved the best survival rate, and screening resulted in only a small reduction in the number of patients treated unnecessarily.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiarrhythmic drug therapy in congestive heart failure. Indications and complications

High-grade ventricular arrhythmias are common in congestive heart failure (CHF). However, antiarrhythmic drug therapy is indicated only for patients with symptomatic or hemodynamically significant sustained arrhythmias. Before such therapy is initiated, reversible causes of arrhythmias (eg, electrolyte imbalance, drug interactions and toxicity, decompensation of CHF, ongoing ischemia) should be sought out and corrected. Patients with poor ventricular function or a history of CHF should be hospitalized and monitored continuously during initiation and evaluation of antiarrhythmic therapy so that early detection of proarrhythmic response is possible. Therapy should be initiated with the smallest effective dose, which then is increased slowly to minimize the risk of side effects. Drug selection should be guided electrophysiologically or noninvasively, and empirical antiarrhythmic drug therapy must be avoided.

Patients with supraventricular tachycardia presenting with aborted sudden death: incidence, mechanism and long-term follow-up

A total of 13 (4.5%) of 290 patients with aborted sudden death had either documented (7; 54%) or strong presumptive evidence of supraventricular tachycardia that deteriorated into ventricular fibrillation. Six (46%) of the 13 had an accessory conduction pathway and either atrial fibrillation (5 patients) or paroxysmal atrioventricular (AV) reentrant tachycardia (1 patient) that deteriorated into ventricular fibrillation. Three patients with AV node reentrant tachycardia and four with atrial fibrillation and enhanced AV node conduction presented with supraventricular arrhythmias that deteriorated into ventricular fibrillation. Patients were treated with medical, surgical or catheter ablative procedures designed to prevent recurrences of supraventricular arrhythmias. Four patients received an implanted automatic defibrillator, but none had an appropriate device discharge. Over a follow-up period of 41.6 +/- 33.6 months, 12 patients are alive without symptomatic arrhythmias. One patient died because of severe chronic lung disease and heart failure. Supraventricular tachycardia was the cause of aborted sudden death in approximately 5% of patients referred for evaluation of sudden cardiac death. Treatment directed at prevention of supraventricular tachycardia was associated with an excellent prognosis. Current treatment techniques appear to obviate the need for automatic defibrillator therapy in these patients.

Exacerbation of ventricular arrhythmias during the postoperative period after implantation of an automatic defibrillator

The postoperative course of 68 consecutive patients treated with an implantable defibrillator during the period from 1982 through 1990 was studied. In 46 patients (group 1), no concomitant surgery was performed during the implantation. In 22 patients (group 2), concomitant surgery (coronary artery bypass [n = 12], valve replacement [n = 3] or arrhythmia surgery [n = 7]) was performed. All patients in group 1 were clinically stable before surgery, receiving an antiarrhythmic regimen chosen by serial drug testings. The same regimen was continued postoperatively. Eight of the 46 patients in group 1 whose condition had been stable in the hospital for 19 +/- 25 days preoperatively developed multiple episodes of sustained ventricular tachycardia 4 +/- 9 days after implantation while receiving the same antiarrhythmic regimen. Although the exacerbation was transient in some patients, six required different antiarrhythmic therapy and one eventually died. Two additional patients had frequent and prolonged episodes of nonsustained ventricular tachycardia that could trigger the defibrillator, requiring changes in the antiarrhythmic regimen. Another patient had progressive cardiac failure and died on day 5. A marked (sevenfold) increase in asymptomatic ventricular arrhythmias was noted in 42% of the remaining 35 patients. In group 2 (combined surgery), one patient developed refractory ventricular tachycardia 3 days postoperatively and died on that day. Three patients developed frequent nonsustained ventricular tachycardia postoperatively, requiring changes in the antiarrhythmic regimen. The overall surgical mortality rate was 4.4% (4.3% in group 1 and 4.5% in group 2) and was due to refractory ventricular tachycardia in two patients and cardiac failure in one.(ABSTRACT TRUNCATED AT 250 WORDS)

Results of electrophysiologic testing and long-term prognosis in patients with coronary artery disease and aborted sudden death

The purpose of this study was to evaluate the results of electrophysiologic testing and the long-term prognosis of 56 patients with coronary artery disease who presented with aborted sudden death unrelated to acute myocardial infarction. The mean age of the patients was 62 +/- 8 years (+/- standard deviation) and 48 were men. The mean left ventricular ejection fraction was 0.34 +/- 0.16. During the baseline electrophysiology test, sustained monomorphic ventricular tachycardia (VT) was inducible in 22 patients who then underwent electropharmacologic testing: 11 patients were treated with antiarrhythmic drugs that suppressed the induction of VT or resulted in the VT becoming hemodynamically stable; 10 patients who failed drug testing received an automatic implantable cardioverter/defibrillator (AICD); one patient underwent endocardial resection. Among 34 patients who did not have inducible sustained VT, a precipitant of cardiac arrest (severe ischemia, proarrhythmia) was identified and was corrected in 9 of 34. An AICD was recommended in the remaining 25 patients; however, nine patients refused and were treated empirically with antiarrhythmic drugs. The mean follow-up was 22 +/- 12 months. The 2-year actuarial incidence of sudden death was 31% in patients who were treated with drugs based on the results of electropharmacologic testing, 26% in patients who were treated with antiarrhythmic drugs on an empiric basis, 0% among patients in whom a correctable etiology for the cardiac arrest was identified, and 9% among patients who underwent implantation of an AICD. The 3-year actuarial incidence of sudden death among the 20 patients treated with antiarrhythmic drugs was 53%, compared with 9% among the 26 patients who underwent AICD implantation (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Survivors of acute myocardial infarction: who is at risk for sudden cardiac death?

Coronary artery disease is the leading cause of death in the United States. Approximately half of the deaths attributable to coronary artery disease are sudden cardiac deaths. A logical approach to prevention of sudden death is to identify those who are at risk and then to initiate effective therapy. Left ventricular dysfunction, frequent ventricular ectopic activity, nonsustained ventricular tachycardia, and late potentials have been identified as markers for increased risk of sudden cardiac death. The sensitivity and specificity of these risk factors vary, and the positive predictive power is less than satisfactory. The value of invasive electrophysiologic testing for risk stratification in the general postinfarction patient population remains unclear. In addition to these diagnostic difficulties, prevention of sudden death also has been limited by imperfect efficacy and potential lethal effects of the currently available antiarrhythmic agents. Automatic implantable defibrillators are effective for aborting sudden death; however, the potential for more general use of automatic defibrillators in asymptomatic but high-risk postinfarction patients has not been evaluated.

Predictors of first discharge and subsequent survival in patients with automatic implantable cardioverter-defibrillators

BACKGROUND

Two hundred eighteen patients were evaluated in a two-phase approach (time to first appropriate discharge, survival after discharge) to identify factors that may be related to maximal benefit derived from use of an automatic implantable cardioverter-defibrillator (AICD).

METHODS AND RESULTS

One hundred ninety-seven patients survived implantation of AICD, with or without concomitant cardiac surgery. One hundred five patients had an AICD discharge associated with syncope, presyncope, documented sustained ventricular tachycardia or fibrillation, or sleep at 9.1 +/- 11.1 months after implantation. Patients survived 23.8 +/- 18.0 months after AICD discharge. Left ventricular dysfunction (p = 0.008 for ejection fraction less than 25%) was associated with earlier AICD discharge and shortened survival after AICD discharge (p = 0.008 for ejection fraction less than 25%; p = 0.01 for New York Heart Association functional class III and IV). beta-Blocker administration (p = 0.006) and coronary bypass surgery (p = 0.06) were associated with later AICD discharge. Coronary bypass surgery (p = 0.035) but not beta-blockers was associated with more prolonged survival after AICD discharge.

CONCLUSIONS

These data suggest that a relatively easy algorithm can be applied to predict which patient will benefit most from AICD implantation.

A survey of sudden death associated with the use of antipsychotic or antidepressant drugs: 49 cases in Finland

Phenothiazines have repeatedly been found to be associated with cases of sudden death, but the issue of causality has remained controversial. A survey of medicolegal autopsies performed in Finland over a 3-year period revealed that sudden unexpected deaths of 31 women (mean age 44 years, range 25-69) and 18 men (mean age 40 years, range 26-62) were associated with either the use of antipsychotic or antidepressant drugs. Therapeutic use of phenothiazines was documented in all but 3 of these 49 cases and thioridazine was involved in over half of them. Thus, whereas thioridazine was the only antipsychotic drug associated with 15 cases, only 5 cases were associated with any of the other antipsychotic or antidepressant drugs. The differences between the subgroups of psychotropic drugs remained clear after adjustment according to the respective data on drug use in the population. Although there are several uncontrolled confounding factors, the overrepresentation of phenothiazines, especially thioridazine, among psychiatric patients who died suddenly is striking and, taken together with their well-established arrhythmogenic effects, warrants further attention.

Inability of the signal-averaged electrocardiogram to determine risk of arrhythmia recurrence in patients with implantable cardioverter defibrillators

Signal-averaged electrocardiography has been used to identify patients at risk for arrhythmic death after myocardial infarction. Since patients with implantable cardioverter defibrillators (ICDs) are at high risk for arrhythmic events, they should also be expected to have a high incidence of abnormal signal-averaged electrocardiograms (SAECGs). However, whether the SAECG can discriminate patients who will have arrhythmia recurrence and receive appropriate ICD shocks from those who will have no recurrence and no shocks is unknown. This study examines the usefulness of the SAECG to separate appropriate users from non-users of the ICD. Fifty patients with ICDs participated in this study. Those who received a shock preceded by symptoms, a shock without preceding symptoms but with electrocardiographic documentation of ventricular fibrillation or ventricular tachycardia, or a shock while asleep were classified as ICD users. All other patients were classified as nonusers. The SAECG was classified as normal if the QRS duration on the standard electrocardiogram was less than or equal to 110 msec and if the total filtered QRS duration was less than 120 msec, the root-mean square voltage of the terminal 40 msec was greater than 25 muV, and the terminal low amplitude signal duration measured less than 38 msec. The SAECG was classified as abnormal if the QRS duration on the standard electrocardiogram was less than or equal to 110 msec and any one of these three criteria were outside the "normal range." The SAECG was classified as indeterminate if the QRS duration on the standard 12-lead electrocardiogram was greater than 110 msec. For the entire group of 50 patients, 8 (16%), 12 (24%), and 30 (60%) had normal, abnormal, and indeterminate SAECGs, respectively. Of the 22 ICD users, 1 (5%), 5 (23%), and 16 (73%) patients had normal, abnormal, and indeterminate SAECGs, respectively. Of the 28 ICD nonusers, 7 (25%), 7 (25%), and 14 (50%) patients had normal, abnormal, and indeterminate SAECGs, respectively. ICD users had lower left ventricular ejection fractions (P = 0.0002), a higher incidence of ventricular tachycardia (P = 0.04), prior exposure to a greater number of antiarrhythmic drugs (P = 0.04), and a lower likelihood for survival (P = 0.02) compared to the ICD nonusers. There was no statistically significant difference between the ICD users and nonusers as stratified by SAECG classification regardless of whether or not the interminate studies were included or excluded from the analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Arrhythmogenic effects of graded coronary blood flow reductions superimposed on prior myocardial infarction in dogs

BACKGROUND

We studied arrhythmogenesis and its underlying pathophysiology during graded reductions of coronary blood flow, superimposed on prior myocardial infarction to test the hypothesis that spontaneous ventricular fibrillation and induced ventricular tachycardia are dependent on different patterns of coronary flow reduction in hearts with prior myocardial infarction.

METHODS AND RESULTS

In 10 sham-operated dogs (control group) and 24 dogs with 3-week-old experimental apical myocardial infarction, the left circumflex coronary artery was constricted to produce four grades of flow reduction: 25%, 50%, 75%, and 100%. Among the sham-operated control animals, only one of 10 (10%) developed spontaneous ventricular fibrillation and only two of nine (22%) were inducible into sustained ventricular tachycardia during 100% circumflex coronary artery flow reduction. No spontaneous ventricular fibrillation or inducible ventricular tachycardia occurred with lesser grades (25%, 50%, or 75%) of flow reduction among the control animals. In the myocardial infarction group, five of 24 dogs (21%) were inducible before flow reduction. However, 50% flow reduction in the myocardial infarction group resulted in inducibility of ventricular tachycardia in 12 of 24 dogs (50%); nine of 16 (56%) during 75% flow reduction; and six of 11 (55%) with 100% flow reduction. In addition, none of the dogs in the myocardial infarction group developed spontaneous ventricular fibrillation during 25% or 50% flow reduction, whereas six of 22 (27%) developed ventricular fibrillation during 75% flow reduction and 10 of 21 (48%) during 100% flow reduction. In dogs with spontaneous ventricular fibrillation during flow reduction, the total myocardial mass of the ischemic "risk" zone and infarcted zone was significantly greater than in those without spontaneous ventricular fibrillation (68 +/- 5% versus 56 +/- 6% [p less than 0.01]). There was no difference in the total myocardial mass of the ischemic risk zone and infarcted zone between dogs with and without inducible ventricular tachycardia during flow reduction.

CONCLUSIONS

In canine model of subacute myocardial infarction, superimposed ischemia increased the likelihood of inducible sustained ventricular tachycardia with lesser grades of coronary flow reduction compared with that necessary to allow spontaneous ventricular fibrillation. The underlying pathophysiology appears to differ between spontaneous ventricular fibrillation and electrically induced sustained ventricular tachycardia.

A prospective comparison of class IA, B, and C antiarrhythmic agents in combination with amiodarone in patients with inducible, sustained ventricular tachycardia

BACKGROUND

Clinical experience suggests that combinations of antiarrhythmic agents provide more effective control of ventricular tachyarrhythmias than does therapy with single agents.

METHODS AND RESULTS

Antiarrhythmic and electrophysiological effects of three class I antiarrhythmic agents, one from each subclass A, B, and C, were assessed in single use and in combination with amiodarone in patients with inducible, sustained ventricular tachycardia that was not suppressed by monotherapy with these agents. Thirty-one patients underwent an electrophysiology test on four occasions: at baseline; after 2-4 days of treatment with quinidine, mexiletine, or encainide; after 2 weeks of treatment with 1,200 mg/day amiodarone; and last, after 2-4 days of treatment with both amiodarone and the previously tested class I agent. The combination of a class I agent and amiodarone prevented the induction of sustained ventricular tachycardia in only one of 31 (3%) patients. Ventricular tachycardia became hemodynamically stable in 11 of 31 (34%) patients because of a marked prolongation in the tachycardia cycle length. It increased from 323 +/- 39 to 423 +/- 84 msec (n = 11, p less than 0.01) by adding encainide to amiodarone therapy, and it showed a tendency to lengthen when quinidine was added to amiodarone (from 373 +/- 77 to 425 +/- 58 msec; n = 10, NS). Each class I agent increased amiodarone-induced depression in myocardial conduction, but the extent of the additional depression seemed to differ among the three subclasses. Ventricular refractoriness was increased by all class I agents when used in combination with amiodarone, although not by mexiletine or encainide when used alone.

CONCLUSIONS

Class I antiarrhythmic agents slow ventricular conduction and increase ventricular refractoriness when used in combination with amiodarone. When amiodarone and class I drugs by themselves do not suppress the induction of ventricular tachycardia, the combination of amiodarone and a class I agent seldom results in noninducibility; however, it often lengthens the ventricular tachycardia cycle length and may render the ventricular tachycardia hemodynamically stable.