Ventricular flutter during treatment with amiodarone

Value of electrophysiologic studies in hypertrophic cardiomyopathy treated with amiodarone

The relation of electrophysiologic effects of amiodarone to long-term outcome was studied in 35 patients with hypertrophic cardiomyopathy (HC). Indications for electrophysiologic studies were: cardiac arrest (n = 3), syncope/presyncope (n = 27) and asymptomatic ventricular tachycardia (VT) (n = 5). Twenty-eight patients (80%) had VT, 3 (9%) atrial tachycardia and 3 (9%) paroxysmal atrial fibrillation during 24-hour Holter monitoring. The studies were repeated after a total amiodarone dose of 58 +/- 122 g and during a maintenance median daily dose of 400 mg. Amiodarone abolished paroxysmal atrial arrhythmias in all 6 patients. However, it caused marked atrioventricular nodal conduction abnormality in 3 patients and heart block or marked HV interval prolongation (to greater than or equal to 100 ms) in 4 patients. Sustained VT was induced in 26 patients (74%) at baseline study and in 23 patients (66%) taking amiodarone therapy. With amiodarone, VT was no longer inducible or was more difficult to induce in 11 patients (31%), and the drug abolished VT during Holter monitoring in all patients. However, VT was easier to induce with amiodarone or was induced only with amiodarone in 18 (51%) patients. Amiodarone significantly slowed the rate of induced VT (from 248 +/- 29 to 214 +/- 37 beats/min, p less than 0.001). This was associated with a change in its morphology from polymorphic to monomorphic VT in 7 patients. During a follow up of 18 +/- 14 months (range 2 to 56), amiodarone was discontinued because of adverse effects in 8 patients (23%).(ABSTRACT TRUNCATED AT 250 WORDS)

Side effects from amiodarone

Amiodarone causes many side effects involving all organ systems. Although most of the side effects are mild and do not limit the use of the drug, there are several that are serious. Since many of these toxic reactions develop only after a prolonged period of therapy, careful follow-up on a regular basis is essential.

Arrhythmogenic effects of antiarrhythmic drugs: a study of 506 patients treated for ventricular tachycardia or fibrillation

Antiarrhythmic therapy in 506 consecutive patients undergoing 1,268 antiarrhythmic drug trials for ventricular tachycardia or ventricular fibrillation was reviewed for evidence of arrhythmogenic drug effect defined as the occurrence of a new form of ventricular tachyarrhythmia temporally associated with initiation of drug therapy or dosage increase. Arrhythmogenic effects occurred in 6.9% of patients and 3.4% of drug trials. This ranged from a high of 11.8% caused by encainide to none occurring with procainamide, tocainide or beta-adrenergic blocking drugs. The incidence of arrhythmogenesis was significantly greater in patients whose presenting arrhythmia was sustained ventricular tachycardia than it was in those who presented with nonsustained ventricular tachycardia or ventricular fibrillation (p = 0.02). Decreased systolic function measured echocardiographically at the base of the left ventricle was associated with an increased incidence of arrhythmogenic effects (p = 0.006) whereas global left ventricular ejection fraction was not. Age, gender, cardiac diagnosis, location of prior myocardial infarction and New York Heart Association functional class for heart failure were not related to the occurrence of drug-induced arrhythmias. These findings emphasize the need for in-hospital cardiac monitoring during initiation of antiarrhythmic drug therapy for ventricular tachyarrhythmias.

A general overview of amiodarone toxicity: its prevention, detection, and management

Although amiodarone is a highly effective antiarrhythmic agent, it has a high incidence of side effects, some of which can be serious or even lethal. With close monitoring, side effects can be found in essentially all patients, but fortunately most of these are mild and well tolerated. Furthermore, many will respond to dosage reduction in a relatively short period of time, ie, days to weeks, which is remarkable considering the long period of time amiodarone has been shown to persist in tissues. There is reasonable evidence that toxicity, particularly the early toxic manifestations with large loading dosages, can be favorably modified by reducing the dosage. Similarly, reducing the maintenance dosage will, in most instances, reduce or eliminate most toxic manifestations. The mechanisms of toxic effects are uncertain, but suggestive evidence exists for and against both an immunologic reaction and an intracellular lysosomal lipoidosis. Principles of use of amiodarone should include individualizing administration of dosages for each patient due to the unusual pharmacokinetic properties of this drug and continuous long-term attempts at using the lowest effective dosage. There are no definite tests that predict amiodarone efficacy or toxicity, but the serum level can be used as a rough guide of absorption and distribution in the attempt to minimize the maintenance dosage. No guidelines regarding screening tests for toxicity can be made at this time since great variability in these tests has been reported, and no evidence exists for their benefit in preventing adverse effects to amiodarone. However, follow-up testing at the intervals noted in the package insert are reasonable and important. The possibility of interactions with drugs already reported and with others not yet reported should always be kept in mind, and appropriate monitoring for clinical evidence of toxicity due to the concomitantly used drugs should be undertaken. Amiodarone can have a tremendous beneficial effect in the proper circumstances, but it is a drug that should command utmost respect because of its side effects and requires constant vigilance from any physician wishing to use it.

Worsening of ventricular tachycardia by amiodarone

The details of worsening of ventricular tachycardia in 8 (4.1%) of 194 patients receiving treatment with amiodarone are reported. Two forms of amiodarone-induced tachycardia were recognized: first, the development of new tachycardias (three patients) and second, a change in the pattern of recurrence of clinical tachycardia (five patients). In retrospect, the time from the initiation of amiodarone to the initial documentation of worsening ranged from 1 to 23 days (mean +/- SD, 9.4 +/- 8.2 days) and the time from the initiation of therapy to the recognition of worsening ranged from 6 to 26 days (14.6 +/- 10.1 days). Seven patients survived the worsening of tachycardia and one died. The total dose of amiodarone received and the duration of administration did not correlate with time to manifestation or time to resolution of worsening. This report emphasizes that worsening of ventricular tachycardia as a result of amiodarone is often difficult to differentiate from inadequate drug loading or early recurrence of 2 patient's clinical tachycardia. Further, because of the pharmacokinetics of the drug, the manifestations of worsening may be prolonged. In the cases reported, it ranged from 2 to 26 days (7.9 +/- 8.3 days), which is longer than previously reported. Because of the potential for amiodarone to cause life-threatening worsening of ventricular tachycardia and in accordance with current results, a period of in-hospital monitoring of at least 10 days at the start of therapy with amiodarone is recommended.

Amiodarone in the management of cardiac arrhythmias: current concepts

This article reviews current information on the clinical pharmacology, therapeutic utility, and adverse reactions of amiodarone, with emphasis on guidelines for its rational use.

Effects of acute intravenous and chronic oral amiodarone on defibrillation energy requirements

Amiodarone is commonly used with the automatic implantable defibrillator to treat recurrent ventricular tachyarrhythmias. The effects of acute intravenous and chronic oral amiodarone on the energy requirements for successful defibrillation were evaluated in 12 dogs chronically instrumented with right atrial spring and left ventricular patch defibrillation electrodes. Multiple shocks of varying energy were applied in balanced random order to construct curves of percent successful defibrillation vs energy (DF curves) on each test day. Dogs were studied on days 1, 11, 18, 25, and 32. On day 11, DF curves were determined before and after infusing saline (n = 6) or amiodarone (n = 6), 10 mg/kg loading and 0.33 mg/kg/min maintenance doses. Dogs administered intravenous amiodarone were continued on oral drug (300 mg twice daily) for the remainder of the study. Data were analyzed by logistic regression and the energy required for 50% (E50) and 80% (E80) successful defibrillation were compared. Differences between controls and animals receiving chronic oral amiodarone were not significant on any day. After acute intravenous infusion, dogs given amiodarone had a 21.7 +/- 12.8% decrease in E50 (p less than 0.01) and a 19.7 +/- 17.8% decrease in E80 (p less than 0.05), while controls had an 11.4 +/- 30.5% increase (p = NS) in E50 and 6.30 +/- 30.5 increase in E80 (p = NS). It is concluded that the energy required for successful defibrillation is decreased by acute intravenous amiodarone, while chronic oral administration has no significant effect.

Side effects and complications of amiodarone therapy

To assess the incidence of adverse effects associated with long-term amiodarone therapy, we reviewed the records of 217 consecutive patients who were treated for refractory arrhythmia. After an average of 11.8 months of therapy, one or more side effects occurred in 113 patients (52%). These were considered clinically significant in 42 patients (19.3%), mandating discontinuation of amiodarone in 18 (8.3%). The untoward reactions requiring discontinuation of amiodarone included thyroid dysfunction, visual disturbances, pulmonary infiltrates, ataxia, cardiac conduction abnormalities, and drug interactions. The mild side effects included corneal microdeposits, skin rashes, and gastrointestinal symptoms. There was a weak correlation between blood levels of amiodarone, the daily dose, and the cumulative dose (r = 0.23, p = 0.015). Drug levels were higher in symptomatic patients (p less than 0.03), although they received lower doses of amiodarone. While amiodarone is associated with frequent side effects, they are generally mild and do not necessitate drug discontinuation. Careful monitoring of therapy is essential to detect the potentially serious adverse reactions which are encountered in nearly 20% of patients.

Clinical use and pharmacology of amiodarone

Amiodarone, an investigational drug in the United States, has had considerable use in this country and worldwide in the treatment of cardiac arrhythmias. This article reviews the clinical pharmacology of this potentially useful antiarrhythmic agent.

Long QT: good, bad or indifferent?

A survey of current literature suggests an increasing interest in both the desirable and undesirable implications of a prolonged QT interval, the former perceived to be the beneficial effect of antiarrhythmic drugs that prolong the duration of ventricular action potential, and the latter considered to be a potential marker for sudden cardiac death in patients with ischemic heart disease. In addition, there has been an increasing interest in the congenital long QT syndrome associated with an apparent dysfunction of the autonomic nervous system and serious, potentially lethal ventricular arrhythmias. Circumstantial evidence suggests that these arrhythmias are due to increased dispersion of repolarization which may be aggravated by psychologic and emotional perturbations. In this review, the associations between the long QT interval, autonomic nervous system, dispersion of repolarization, antiarrhythmic drugs and ventricular arrhythmias are examined. Attention is directed to the difficulties of accurate QT measurement, problems related to the correction of the QT interval for heart rate and sex (QTc), the wide range of normal values and the modest QT alterations after various manipulations of the autonomic nervous system. Clinical conditions associated with marked, moderate and occasional QT lengthening are listed and discussed briefly in relation to the disturbances of nervous system, dispersion of ventricular repolarization and ventricular arrhythmias. It is proposed that the absence of relevant animal models of neurogenic or psychogenic QT prolongation hinders the investigation of the neurogenic factors associated with QT lengthening. QT prolongation is most often induced by antiarrhythmic drugs and ischemic heart disease. However, it is not known whether the occurrence of torsade de pointes type of ventricular tachycardia in patients treated with antiarrhythmic drugs is related to a critical drug dose or a critical degree of QTc prolongation. There is no conclusive evidence that QT lengthening has any predictive value either during the acute phase or during convalescence after myocardial infarction. Also, a serious deficiency in current knowledge is the lack of an established relation between the prolonged QT interval and the dispersion of ventricular repolarization. It is concluded that the number of unanswered questions discussed in this review still makes it difficult to judge when a prolonged QT interval is good, bad or indifferent.

Amiodarone-induced intra-His block

Two patients, one with and one without preexisting conduction system abnormalities, were treated with amiodarone for refractory ventricular arrhythmias. Electrophysiologic testing before and during amiodarone therapy revealed amiodarone-induced HV interval prolongation and second degree intra-His Wenckebach block with no change in QRS configuration during atrial pacing at relatively long cycle lengths. The mechanism responsible for this phenomenon is unclear. These cases illustrate that amiodarone can induce distal conduction system block even in the absence of clinical conduction system disease in a pattern that mimics atrioventricular nodal block.

Toxic and therapeutic effects of amiodarone in the treatment of cardiac arrhythmias

Amiodarone was used to treat cardiac arrhythmias that had been refractory to conventional medical therapy. The first 70 consecutive patients treated with amiodarone in this study had at least 6 months of follow-up (range 6 to 24, mean 11) and form the basis for this report. Sixty-six patients were treated for ventricular arrhythmias and four for supraventricular tachycardias. Amiodarone therapy consisted of a loading dose of 600 mg orally twice a day for 7 days, and 600 mg daily thereafter. Doses were reduced only if side effects occurred. Because of frequent side effects, the dose was reduced from 572 +/- 283 mg per day (mean +/- standard deviation) at 45 days to 372 +/- 174 mg per day at 6 months. With a mean follow-up of 11 months in the 54 patients who continued to take amiodarone, only 4 patients had ventricular fibrillation. Three additional patients experienced recurrent sustained ventricular tachycardia in long-term follow-up. All 70 patients had extensive clinical and laboratory evaluation in follow-up. Side effects were common, occurring in 93% of patients. Thirteen patients (19%) had to discontinue the medication because of severe side effects. Fifty-six patients had gastrointestinal side effects, most commonly constipation. All patients but 1 eventually developed corneal microdeposits, and 43 patients were symptomatic. Cardiovascular side effects were uncommon. Symptomatic pulmonary side effects occurred in seven patients, with unequivocal pulmonary toxicity occurring in five. Neurologic side effects, most commonly tremor and ataxia, occurred in 52 patients. Thyroid dysfunction occurred in 3 patients, and 32 patients had cutaneous abnormalities. Miscellaneous other side effects occurred in 32 patients. Amiodarone appears to be useful in the management of refractory arrhythmias. Because virtually all patients develop side effects when given a maintenance daily dose of 600 mg, lower maintenance doses should be used. It is unknown if the more severe side effects are dose-related. Amiodarone is difficult to administer because of its narrow toxic-therapeutic range and prolonged loading phase. More importantly, the first sign of antiarrhythmic failure may be manifest as sudden cardiac death.

Clinical efficacy of amiodarone in treatment of recurrent ventricular tachycardia and ventricular fibrillation

The clinical antiarrhythmic efficacy of amiodarone treatment was examined in 196 patients with recurrent ventricular tachycardia (VT) or ventricular fibrillation (VF) resistant to other antiarrhythmic drugs. Patients had received a mean of 4.4 +/- 1.9 unsuccessful drug trials over a mean of 15.2 months prior to amiodarone treatment of recurrent VF in 57 patients; recurrent, sustained VT in 95 patients; and recurrent, nonsustained VT in 44 patients. Amiodarone dosage during the first 2 to 4 weeks of treatment was 800 to 1600 mg/day. During long-term follow-up, amiodarone dosage was reduced to 200 to 600 mg/day, based on the control of arrhythmia and patient tolerance. Electrophysiologic studies were performed prior to and after 2 or more weeks of amiodarone treatment. After a mean follow-up of 16.2 +/- 13.0 months, 126 (64%) of 196 patients continued successful treatment with amiodarone. At electrophysiologic study, amiodarone prevented VT induction in 13 patients, and although VT was induced in 101 patients, 80 patients continued treatment for 14.2 months without recurrence of spontaneous VT. Amiodarone treatment was discontinued because of recurrent VT in 22 patients, sudden cardiac death in 15 patients, adverse effects in 12 patients, and noncardiac death in 21 patients. In nine patients, recurrent VT/VF appeared related to amiodarone-induced exacerbation of arrhythmia. Pulmonary toxicity occurred in seven patients, and 19 patients developed blue skin discoloration. Other adverse effects were usually dosage related. In summary, amiodarone was a highly effective antiarrhythmic drug, but at the dosages employed, the risk of significant adverse effects warrants careful surveillance during treatment.