Proarrhythmic effects of antiarrhythmic drugs during programmed ventricular stimulation in patients without ventricular tachycardia

Usefulness of procainamide challenge for electrophysiologic arrhythmia risk stratification

Among 58 consecutive patients who underwent electrophysiologic testing for risk assessment and who subsequently received a third-generation implantable cardioverter-defibrillator, 39 had ventricular tachycardia induced in the baseline state and 19 had ventricular tachycardia induced only after administration of intravenous procainamide, increasing the yield of electrophysiologic risk assessment by 49%. At follow-up, ventricular arrhythmias requiring implantable cardioverter-defibrillator termination occurred in 14 of 39 patients inducible in the baseline state and in 7 of 19 patients inducible only with intravenous procainamide. The provocative use of intravenous procainamide during electrophysiologic risk assessment increases the detection rate for risk of sustained ventricular arrhythmias with no loss of positive predictive value.

Proarrhythmia

Proarrhythmia is defined as the aggravation of an existing arrhythmia or the development of a new arrhythmia secondary to antiarrhythmic drug. Proarrhythmic events include drug-induced bradyarrhythmias, atrial and ventricular proarrhythmias. New onset sustained or incessant ventricular tachycardia and torsade de pointes can be life threatening. This article reviews the incidence, aggravating factors, and treatment of proarrhythmia.

Proarrhythmia, a serious complication of antiarrhythmic drugs

Aggravation of arrhythmia with antiarrhythmic drugs is not an infrequent side effect associated with antiarrhythmic drugs. Defined as the provocation of a new arrhythmia or a significant increase in the frequency of a preexisting arrhythmia, it occurs with all antiarrhythmic agents, although the incidence varies from 6% to 23% with the different drugs. In general, arrhythmia aggravation is an early event, occurring within the first several days of initiating drugs therapy. It has been found, however, that this complication can also occur as a late event, particularly in patients who have evidence of ongoing ischemia that may be overt or silent. Although there is no good way to predict the patient who is likely to experience this complication, it has been observed that there several predictors of an increased risk for experiencing arrhythmia aggravation including significant underlying heart disease, congestive heart failure, evidence of active or potentially active ischemia, and electrolyte abnormalities, particularly hypokalemia.

Electrophysiologic mechanisms of adverse effects of class I antiarrhythmic drugs (cibenzoline, pilsicainide, disopyramide, procainamide) in induction of atrioventricular re-entrant tachycardia

We evaluated the electrophysiological mechanisms of adverse effects of class I antiarrhythmic drugs (cibenzoline in seven patients, pilsicainide in two, and disopyramide in two, and procainamide in three) in the induction of orthodromic atrioventricular re-entrant tachycardia (AVRT). In 14 patients (10 males, 4 females; mean age 37 +/- 18 years) who had inducible AVRT despite the administration of class I drugs, electrophysiological effects of class I antiarrhythmic drugs were evaluated using programmed electrical stimulation techniques. In 4 out of 6 patients with a manifest accessory pathway, class I drugs induced unidirectional conduction block of the accessory pathway (antegrade conduction block associated with preserved retrograde conduction) and enhanced the induction of AVRT with atrial extrastimulation. In eight patients with a concealed accessory pathway, the outward or inward expansion of the tachycardia induction zone was observed in patients who had greater prolongation of the conduction time than the refractory period of the retrograde accessory pathway after class I drugs. During ventricular extrastimulation, the induction of bundle branch re-entry after class I drugs initiated the AVRT in patients with either manifest or concealed accessory pathways. We conclude that the adverse effects of class I drugs are mainly due to induction of unidirectional retrograde conduction of the manifest accessory pathway and the greater prolongation of the retrograde conduction time of the concealed accessory pathway than the refractory period, regardless of the sub-classification of class I drugs.

[Proarrhythmic effects of anti-arrhythmia agents]

Antiarrhythmic medications are widely used either at the ventricular or supraventricular level. However, those drugs can induce severe side effects. Actually, antiarrhythmic drugs are paradoxically able to favour the occurrence of new arrhythmias or aggravate the preexisting arrhythmia for which they were indicated. These proarrhythmic effects have been found in 10 to 20% of patients, as evidenced by literature. Moreover, the CAST study showed a significant increase in mortality in patients with non sustained ventricular arrhythmias after myocardial infarction who were treated with either flecainide or encainide, compared to the placebo group. This overmortality seems to be due, in large, to the proarrhythmic effects of antiarrhythmic drugs. Several mechanisms have been evoked, related to the type of antiarrhythmic drug and to the presenting arrhythmia: early post-depolarization due to slow calcium and sodium inward currents in the case of torsades de pointes, facilitation of intraventricular reentries in the case of class 1c antiarrhythmic drugs, facilitation of the ventricular response of atrial arrhythmias. These deleterious effects, that can be very serious, are unpredictable, not toxicity-related and all antiarrhythmic drugs are involved. Their detection appears to be difficult and is based upon ECG, Holter monitoring, treadmill test and possibly electrophysiologic study. The use of antiarrhythmic drugs requires the knowledge of their proarrhythmic effects, the analysis of the benefit-risk ratio--particularly if left ventricular function is impaired--and careful monitoring.

Con: antiarrhythmic drugs should not be used to suppress ventricular ectopy in the perioperative period

The alterations in autonomic tone imposed by the conduct of anesthesia and surgery predispose patients to ventricular ectopy. It is important to initially view any ectopy as a warning sign and promptly check the adequacy of ventilation and oxygenation. Most commonly an inadequate depth of anesthesia, surgical manipulation or electrolyte abnormality will be causative. Treatment of this underlying problem will usually suffice to terminate the ectopy. Importantly, many patients have preexisting, chronic, complex ventricular ectopy that gets revealed because of perioperative electrocardiographic monitoring. All available pharmacologic agents have significant adverse side effects. To date, all investigations examining outcome of suppression of ventricular ectopy show that successful suppression of ventricular ectopy was associated with an increased mortality. Although the prognosis for patients is worse when complex ventricular ectopy is associated with cardiac structural abnormalities, the optimal therapeutic approach to such patients remains undefined. Unless new data supporting the use of antiarrhythmic drugs in the perioperative setting become available, the risk to benefit ratio is considered unfavorable.

The patient with an automatic implantable cardioverter defibrillator

Sudden cardiac death is the leading cause of death in the United States. A relatively new technology used to treat ventricular dysrhythmias that lead to sudden cardiac death is the automatic implantable cardioverter defibrillator. This device uses patches on the heart to deliver an energy current to convert lethal dysrhythmias. The nurse practitioner can expect to encounter these devices when seeing patients for a variety of diagnoses. This article will serve as a resource for clinical management and patient education.

Polymorphic ventricular tachycardia induced by programmed stimulation: response to procainamide

OBJECTIVES

This study was designed to evaluate the effects of procainamide on polymorphic ventricular tachycardia induced by programmed stimulation and to correlate the responses with heart disease, left ventricular endocardial activation abnormalities and the signal-averaged electrocardiogram (ECG).

BACKGROUND

Polymorphic ventricular tachycardia is induced frequently during electrophysiologic studies. In many patients this response is an artifact of programmed stimulation; in others, it appears to be clinically relevant. Previous observations have suggested that in some patients type IA antiarrhythmic agents can change the response to programmed stimulation from polymorphic to uniform ventricular tachycardia.

METHODS

Programmed right ventricular stimulation was performed in the absence of antiarrhythmic drugs and after procainamide. Signal-averaged ECGs and left ventricular maps were performed during sinus rhythm in the absence of antiarrhythmic drugs.

RESULTS

We evaluated 79 consecutive patients undergoing clinical electrophysiologic studies, in whom polymorphic ventricular tachycardia was the only arrhythmia induced in the absence of antiarrhythmic drugs. After procainamide administration, uniform monomorphic ventricular tachycardia was induced in 24 patients (Group 1), inducible polymorphic ventricular tachycardia persisted in 30 patients (Group 2) and no ventricular tachycardia could be induced in the remaining 25 patients (Group 3). Twenty-three (96%) of 24 patients developing uniform ventricular tachycardia after procainamide administration had coronary artery disease compared with 63% of Group 2 and 48% of Group 3 patients (p = 0.003). Left ventricular aneurysms were also found more frequently (46%) in the patients developing uniform ventricular tachycardia after procainamide than in either Group 2 or Group 3 (13% and 0%, respectively, p < 0.008). Abnormalities of the signal-averaged ECG typically seen in patients with spontaneous reentrant sustained ventricular tachycardia were significantly more frequent in patients who developed inducible uniform ventricular tachycardia after procainamide than in those who did not. Similarly, patients developing uniform ventricular tachycardia after procainamide had more extensive abnormalities of left ventricular endocardial activation revealed by catheter maps during sinus rhythm.

CONCLUSIONS

The conversion of inducible polymorphic ventricular tachycardia to uniform ventricular tachycardia after procainamide administration occurs almost exclusively in patients with coronary disease, previous myocardial infarction and abnormal left ventricular function. This response may permit activation mapping of tachycardias, allowing the application of surgical or catheter ablation techniques that would otherwise not be possible in such patients.

Relation between ventricular repolarization duration and cardiac cycle length during 24-hour Holter recordings. Findings in normal patients and patients with long QT syndrome

BACKGROUND

The interval from the R wave to the maximum amplitude of the T wave (RTm) contains the heart rate dependency of ventricular repolarization.

METHODS AND RESULTS

A computer algorithm was developed to quantify the RTm and preceding RR intervals for each of more than 50,000 beats on 24-hour ambulatory electrocardiographic (Holter) recordings to evaluate the dynamic relation between repolarization duration and cycle length. The relation of RTm to the preceding RR interval (RTm/RR slope) was determined by the best-fit linear regression equation between these two parameters. Eleven normal subjects and 16 patients with long QT syndrome (LQTS) were investigated. Six of the normal subjects had Holter recordings obtained before and after beta-blocker therapy. beta-Blockers were associated with a significant (p = 0.005) reduction in the RTm/RR slope from 0.13 +/- 0.02 to 0.10 +/- 0.02. The mean value of the RTm/RR slope was significantly (p = 0.003) larger in the LQTS patients (0.21 +/- 0.08) than in normal subjects (0.14 +/- 0.03).

CONCLUSIONS

These findings indicate that 1) quantification of the dynamic relation between ventricular repolarization and RR cycle length can be obtained on a large number of Holter-recorded heart beats; 2) beta-blockers reduce the RTm/RR slope in normal patients; and 3) LQTS patients have an exaggerated delay in repolarization at long RR cycle lengths.

Antiarrhythmic drug exacerbation of ventricular tachycardia inducibility during electrophysiologic study

Most studies examining antiarrhythmic drug exacerbation of ventricular arrhythmias have been performed in patients in whom clinical proarrhythmia developed. The clinical significance and predictors of antiarrhythmic drug exacerbation of inducible ventricular arrhythmias during electrophysiologic study have received less attention. Accordingly, a consecutive number of patients undergoing electrophysiologic study for evaluation of ventricular arrhythmias (but who had no history of clinical proarrhythmia) were prospectively examined. Drug-induced exacerbation was defined as no inducible ventricular tachycardia in the baseline drug-free state that increased to inducible nonsustained or sustained ventricular tachycardia, or inducible nonsustained ventricular tachycardia at baseline that increased to inducible sustained ventricular tachycardia. After administration of primarily type IA antiarrhythmic agents (procainamide and quinidine in 97% of the patients), patients were considered drug test negative (n = 80) when they had no increase in inducible ventricular tachycardia, and patients were considered drug test positive (n = 16) when they had exacerbation of inducible arrhythmias. The drug test-positive group's clinical characteristics differed markedly from those of the drug test-negative group. Compared with the drug test-negative group, the drug test-positive group had reduced (less than 40%) left ventricular ejection fractions (80% vs 39%, p = 0.005) and higher prevalences of myocardial infarctions (81% vs 35%, p = 0.027), left ventricular aneurysms (27% vs 5%, p = 0.026), and bundle branch blocks (53% vs 16%, p = 0.005). Thus exacerbation of ventricular tachycardia induction after antiarrhythmic agent administration was most common in patients with significant organic heart disease. The drug test-positive group was more frequently treated with antiarrhythmic therapy than was the drug test-negative group.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Antiarrhythmic drug treatment: need for continuous vigilance

Any physician treating cardiac arrhythmias should be aware of a possible worsening of the arrhythmia (so-called arrhythmogenesis) after the start of antiarrhythmic drug treatment. To facilitate the recognition of that complication the type and possible mechanisms of arrhythmogenesis are reviewed. Recognition also requires an understanding of (a) the time of appearance of arrhythmogenic effects after different drugs, (b) the value of non-invasive and invasive tests, and (c) the profile of the patient most likely to develop this problem. Guidelines are given to reduce the incidence of the arrhythmogenic effects of antiarrhythmic drugs and a plea is made that the physician should be always on the alert for this complication.

Usefulness of the electrophysiology laboratory for evaluation of proarrhythmic drug response in coronary artery disease

Two potential manifestations of proarrhythmic responses to type IA antiarrhythmic agents in the electrophysiology laboratory were evaluated in 122 patients with chronic coronary artery disease and previous myocardial infarction: (1) conversion of uniform nonsustained ventricular tachycardia (VT) into sustained VT after drug administration, and (2) induction of sustained VT by fewer extrastimuli after drug administration. Forty-two patients were evaluated for nonsustained VT. Eighty patients were evaluated for sustained VT: 30 of these had spontaneous sustained VT only while receiving empiric therapy with quinidine or procainamide, whereas the remaining 50 developed spontaneous VT in the absence of antiarrhythmic drugs. All patients underwent programmed stimulation in the baseline state and after procainamide. Four patients had conversion of induced uniform nonsustained VT into the same morphology, but sustained VT after procainamide administration. These responses only occurred in patients evaluated for nonsustained VT. Over 90% of patients presenting with sustained VT had uniform sustained VT induced at the baseline study and after procainamide, regardless of whether the spontaneous arrhythmia occurred only in the presence or absence of antiarrhythmic drugs. There was no significant difference in the change in mode of induction from baseline to procainamide study, regardless of whether patients had developed spontaneous VT only in the presence or absence of antiarrhythmic drugs. One patient with no inducible VT at the baseline study had inducible uniform sustained VT after procainamide administration, and 1 patient with inducible VT at baseline developed spontaneous sustained uniform VT after procainamide administration. Both patients had developed spontaneous sustained VT only while receiving therapy with type IA agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Syncope of unknown origin: clinical, noninvasive, and electrophysiologic determinants of arrhythmia induction and symptom recurrence during long-term follow-up

Ninety-one consecutive patients with syncope of unknown origin underwent electrophysiologic studies (EPS). Univariate analysis identified the following variables: age, + signal-averaged ECG (SAECG), left ventricular ejection fraction (LVEF), history of myocardial infarction, coronary artery disease, left ventricular aneurysm, and history of sustained monomorphic ventricular tachycardia (SMVT) on Holter; multivariate analysis identified +SAECG, LVEF, and history of SMVT as risk factors for induction of SMVT at EPS. All patients were followed up for 19.0 +/- 8.3 months and 17 had recurrence of syncope. Patients were divided into empiric, EP-guided, and no therapy groups. The EP-guided therapy group included all patients with SMVT at EPS. Recurrence rates among all three groups were similar. We conclude that: (1) Patients who have inducible SMVT at EPS can be identified using certain clinical and noninvasive variables. When these patients undergo EP-guided therapy, their rate of recurrence of syncope becomes compatible with that of patients who had no arrhythmia induced at EPS. (2) Empiric therapy does not offer any benefit over no therapy in reducing the rate of recurrent of scope.

Poisoning due to class IA antiarrhythmic drugs. Quinidine, procainamide and disopyramide

Quinidine, procainamide and disopyramide are antiarrhythmic drugs in the class 1A category. These drugs have a low toxic to therapeutic ratio, and their use is associated with a number of serious adverse effects during long term therapy and life-threatening sequelae following acute overdose. Class 1A agents inhibit the fast inward sodium current and decrease the maximum rate of rise and amplitude of the cardiac action potential. Prolonged Q-T interval and, to a lesser extent, QRS duration may be observed at therapeutic concentrations of quinidine. With increasing plasma concentrations, progressive depression of automaticity and conduction velocity occur. 'Quinidine syncope' (a transient loss of consciousness due to paroxysmal ventricular tachycardia, frequently of the torsade de pointes type) occurs with therapeutic dosing, often in the first few days of therapy. Extracardiac adverse effects of quinidine include potentially intolerable gastrointestinal effects and hypersensitivity reactions such as fever, rash, blood dyscrasias and hepatitis. Procainamide produces electrophysiological changes that are similar to those of quinidine, although Q-T interval prolongation with the former is less pronounced at therapeutic concentrations. Hypersensitivity reactions including fever, rash and (more seriously) agranulocytosis are associated with procainamide, and a frequent adverse effect requiring cessation of therapy is the development of systemic lupus erythematosus. Of the 3 drugs, disopyramide has the most pronounced negative inotropic effects, which are especially significant in patients with pre-existing left ventricular dysfunction. As with quinidine, unexpected 'disopyramide syncope' at therapeutic concentrations has been described. Anticholinergic side effects are common with this drug and may require cessation of therapy. Disopyramide therapy may unpredictably induce severe hypoglycaemia. Severe intoxication with the class 1A agents may result from acute accidental or intentional overdose, or from accumulation of the drugs during long term therapy. Acute overdose can result in severe disturbances of cardiac conduction and hypotension, frequently accompanied by central nervous system toxicity. Decreased renal function can cause significant accumulation of procainamide and its active metabolite acecainide (N-acetyl-procainamide), resulting in severe intoxication. Mild to moderate renal dysfunction is less likely to lead to quinidine or disopyramide intoxication, unless renal failure is severe or concurrent hepatic dysfunction is present. Management of acute intoxication with class 1A drugs includes gut decontamination with provision of respiratory support and treatment of seizures as needed. Hypertonic sodium bicarbonate, by antagonising the inhibitory effect of quinidine on sodium conductance, may reverse many or all manifestations of cardiovascular toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

H2-receptor antagonism is not pro-arrhythmic in a chronic canine model

Seven to 28 days after coronary artery ligation, programmed electrical stimulation was performed in conscious dogs. Groups of 6 previously inducible dogs in which no arrhythmia could presently be achieved were randomly allocated to receive quinidine, cimetidine, ranitidine or placebo. Results were assessed for the drugs' ability to induce ventricular tachycardia or fibrillation, and compared with placebo using Fisher's Exact Test. In the placebo group 4/6 dogs remained unchanged, one developed an arrhythmia, and one died. With quinidine, 3/6 dogs developed an arrhythmia (0.5 mg/kg, 4.0 mg/kg, 4.0 mg/kg) and three died (4 mg/kg, 8 mg/kg, 16 mg/kg) (p less than 0.05 compared with placebo). With cimetidine, 4/6 dogs remained unchanged, one developed an arrhythmia after 4 mg/kg, and one died after 0.5 mg/kg. After ranitidine 3/6 dogs remained unchanged and three died (1.0 mg/kg, 4.0 mg/kg, 16.0 mg/kg). PR, QTc, QRS, refractory periods, and mean systolic pressure remained unchanged after placebo, cimetidine, and ranitidine, but QTc increased (p less than 0.05) and mean systolic pressure fell (p less than 0.01) after quinidine. Heart rate did not change following placebo, but increased (p less than 0.05) after each of the three drug treatments. These results fail to show a significant arrhythmogenic effect of cimetidine or ranitidine in a model validated by the significant pro-arrhythmic effects of quinidine. The cause of death in all cases was ventricular fibrillation.

Paradoxical effects of exercise on the QT interval in patients with polymorphic ventricular tachycardia receiving type Ia antiarrhythmic agents

We analyzed the results of exercise testing performed in the absence of all antiarrhythmic drugs in 11 case patients with newly documented polymorphic ventricular tachycardia in response to type Ia antiarrhythmic agents. These results were compared with those found in 11 control patients matched for age, sex, and heart disease to determine whether the response of the QT interval to exercise testing was abnormal in patients who developed worsening of arrhythmia while taking antiarrhythmic drugs. QT, RR, and QTc intervals (by Bazett's method) were evaluated at rest and at 3 minutes of exercise in both groups. At rest, there was no significant difference in the QT interval (410 +/- 13 vs. 386 +/- 11 msec), RR interval (890 +/- 56 vs. 781 +/- 43 msec), or corrected QT interval (438 +/- 10 vs. 438 +/- 4 msec) in the case patients and the control patients. Both groups demonstrated a similar chronotropic response to exercise. The QT interval shortened in both groups with exercise (p less than 0.001), but the degree of shortening tended to be greater in the control patients (to 310 +/- 9 msec) than in the case patients (to 357 +/- 11 msec) (p = 0.06). Thus, there was a paradoxical increase in the QTc interval in the patients who experienced a proarrhythmic effect of type Ia drugs but not in the control patients (to 482 +/- 8 vs. 431 +/- 5 msec; p less than 0.001). Ten of 11 case patients but only one of 11 control patients had an increase in QTc interval of more than 10 msec with exercise (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Facilitation of ventricular tachycardia initiation by procainamide during programmed ventricular stimulation in patients with heart failure

Antiarrhythmic drugs occasionally facilitate, rather than prevent, ventricular tachycardia. The purpose of this study was to assess the incidence of procainamide facilitation of ventricular tachycardia initiation during programmed electrical stimulation in patients with no history of spontaneous sustained ventricular tachycardia but who are at high risk. Twenty patients with advanced heart failure (mean left ventricular ejection fraction 0.19 +/- 0.09) and nonsustained ventricular tachycardia and in whom sustained ventricular tachycardia was not inducible by programmed electrical stimulation in the basal state were studied. Six patients had coronary artery disease, 13 had idiopathic dilated cardiomyopathy, and 1 had valvular heart disease. All patients received programmed stimulation from the right ventricular apex with one to three extra-stimuli before and after the intravenous infusion of 10 mg/kg of procainamide (serum level 6.6 +/- 2.4 mcg/l). In two patients (10%) sustained monomorphic ventricular tachycardia was initiated only after the administration of procainamide. One of these patients later died in ventricular tachycardia during hyperkalemia. Of the noninducible patients, during a follow-up period of 6 +/- 5 months, two died suddenly and one developed symptomatic ventricular tachycardia. Thus, procainamide can unmask potential reentry circuits in some patients who have not had spontaneous sustained ventricular tachycardia. In patients with heart failure, this risk, as assessed by programmed stimulation after a single dose of procainamide, appears to be low.

New antiarrhythmic drugs: tocainide, mexiletine, flecainide, encainide, and amiodarone

Tocainide, mexiletine, flecainide, encainide, and amiodarone are antiarrhythmic agents that have recently been approved by the Food and Drug Administration for general use in the treatment of ventricular arrhythmias. All five agents are effective in the treatment of patients with ventricular arrhythmias, whereas encainide, flecainide, and amiodarone are also useful in patients with supraventricular arrhythmias and the Wolff-Parkinson-White syndrome (although not yet approved for these indications). Tocainide and mexiletine are similar to lidocaine and are as effective as quinidine in patients with ventricular arrhythmias. Encainide and flecainide are superior to quinidine for the control of ventricular ectopic beats and as effective as quinidine for patients with ventricular tachycardia. Amiodarone is the most effective agent available for treating patients with ventricular tachycardia, but it is also the most toxic antiarrhythmic agent and should be used only when other antiarrhythmic drugs have not been effective or tolerated.

Electrophysiologic study in the management of cardiac arrest survivors: a critical review

This review discusses the value and limitations of EPS in the management of cardiac arrest survivors. Uncertainties associated with EPS include a lack of consensus with respect to stimulation protocol, end points for VT suppression during drug testing, significance of induced polymorphic VT or VF, and timing of EPS after myocardial infarction. Despite methodologic shortcomings in most clinical studies, a useful body of knowledge has emerged. In cardiac arrest survivors, incidence of inducible sustained VT ranged from 35% to 75%. Where induced VT (sustained or nonsustained) was successfully suppressed, recurrent arrhythmic events occurred in 0% to 33% of patients over a 1- to 5-year follow-up period. Failed regimens correlated with a high risk of arrhythmic recurrence. EPS also helps to select patients for the implantable defibrillator or electrocardiac surgery. In conclusion, EPS appears empirically useful in the management of cardiac arrest survivors with coronary artery disease; its value in other disease entities is uncertain.