Electrophysiologic effects of chronic amiodarone therapy in patients with ventricular arrhythmias

Noninvasive evidence of shortened atrial refractoriness during sinus rhythm in patients with paroxysmal atrial fibrillation

BACKGROUND

Shortening of the atrial refractory period is the key feature of atrial electrical remodeling during atrial fibrillation (AF). During sinus rhythm (SR), assessment of the atrial refractoriness is hampered by the fact that the atrial repolarization wave (Ta wave) is largely obscured by the following QRST complex. The purpose of this study was to study the Ta wave in subjects with paroxysmal AF during SR with third-degree atrioventricular (AV) block, and in matched controls.

METHODS

Fifteen patients (mean age 70 +/- 10 years, five males) with paroxysmal AF undergoing AV-nodal ablation were studied. Fifteen age- and gender-matched subjects (mean age 71 +/- 9 years, five males) with third-degree AV block, without a history of heart disease, were used as controls. Standard 12-lead electrocardiograms (ECGs) were recorded and transformed to orthogonal leads and studied using P-wave signal averaging technique.

RESULTS

The P to Ta interval was shorter (408 +/- 47 ms vs 451 +/- 53 ms, P = 0.017) and in Lead Y the Ta peak location was earlier (156 +/- 31 ms vs 187 +/- 34 ms, P = 0.002) in subjects with paroxysmal AF than in the controls. The P-wave duration (126 +/- 15 ms vs 129 +/- 17 ms, P = 0.59) and morphology was similar in AF patients and controls.

CONCLUSIONS

In this study, the ECG signs of shorter atrial refractoriness associated with a history of AF are visualized for the first time during SR. The finding of the earlier location of the PTa peak in AF subjects implies that a possible indicator of increased arrhythmia susceptibility may be visible already in the unprocessed ECG.

Clinical electrophysiologic effects of a single high oral dose of amiodarone

Several recent reports have described the antiarrhythmic effects of a single high oral dose of amiodarone but clinical electrophysiologic effects have not been reported. The present study was performed to assess electrophysiologic effects in 12 patients. After baseline electrophysiologic studies (EPS) patients were administered a single oral dose of 30 mg/kg of amiodarone. EPS was repeated 7.5 +/- 0.5 hours later. Plasma levels of amiodarone and its metabolite desethylamiodarone were determined at the time of the second EPS, Holter monitoring was performed for 24 hours after amiodarone administration. Amiodarone significantly increased the following parameters: corrected QT interval (+4.5%), functional refractory period of the right atrium (+7%); AH interval (+12.3%), effective refractory period of the atrioventricular node (+18.5%), and cycle length of Wenckebach block (+8.4%). These effects were not correlated with plasma levels of amiodarone and desethylamiodarone. Holter monitoring detected no significant bradycardia or arrhythmia. These findings indicate that the effects of a single high oral dose of amiodarone are the same as those known to be induced by acute intravenous administration.

Additive cardiac depression by volatile anesthetics in isolated hearts after chronic amiodarone treatment

Some patients undergoing general anesthesia may be chronically receiving the antidysrhythmic drug amiodarone. The half-life of this drug is very long and it may not be advisable or possible to discontinue its administration prior to anesthesia. We examined depressant effects of three volatile anesthetics in hearts isolated from guinea pigs chronically treated with amiodarone. Hearts were isolated and perfused retrogradely through the aorta with oxygenated Krebs-Ringer solution at 37 degrees C at constant pressure. Variables measured in 26 hearts were heart rate (HR), atrioventricular, intraatrial, and intraventricular conduction times (AVCT, IACT, IVCT) during pacing at 240 bpm, coronary flow, and left ventricular pressure (LVP). Amiodarone (20 mg intraperitoneally) or placebo (Group 1) was given once daily for 1 (Group 2) or 4 (Group 3) wk. Cardiac tissue concentrations of amiodarone were similar (12.1 micrograms/g wet weight) in hearts in Groups 2 and 3 but serum levels were twice as high in hearts in Group 3 as in Group 2 (0.33 vs 0.17 microgram/mL). Before anesthetic exposure, all variables for hearts in Group 2 were not significantly different from those in Group 1. Significantly, for hearts in Group 3, compared to those in Group 1, HR was slower (-14%), conduction times were longer (IACT + 5 ms, IVCT + 4 ms, AVCT + 9 ms), coronary flow was higher (+23%), and LVP was lower (-12%). After control measurements, hearts were exposed to 0.5 and 1 minimum alveolar anesthetic concentration (MAC) halothane, enflurane, and isoflurane in random order.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of electrophysiologic study results in patients treated with amiodarone

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

Amiodarone. An overview of its pharmacological properties, and review of its therapeutic use in cardiac arrhythmias

Amiodarone, originally developed over 20 years ago, is a potent antiarrhythmic drug with the actions of all antiarrhythmic drug classes. It has been successfully used in the treatment of symptomatic and life-threatening ventricular arrhythmias and symptomatic supraventricular arrhythmias. In patients with left ventricular dysfunction amiodarone does not usually produce any clinically significant cardiodepression and the drug has relatively high antiarrhythmic efficacy. Preliminary studies indicate that amiodarone may have a beneficial effect on mortality and survival in certain groups of patients with ventricular arrhythmias, an action probably related to both its antiarrhythmic and antifibrillatory effects. The adverse effect profile of amiodarone is diverse, involving the cardiac, thyroid, pulmonary, hepatic, gastrointestinal, ocular, neurological and dermatological systems. Interstitial pneumonitis and hepatitis are potentially fatal, but the vast majority of adverse events are less serious, and some may be dose dependent. Pretreatment monitoring, regular assessments and the use of minimum effective doses are, therefore, necessary. Thus, with appropriate monitoring to control its well recognised adverse effects amiodarone has an important place as an effective 'broad spectrum' antiarrhythmic drug which has, so far, been used when other treatments have proved ineffective. More recent preliminary data also suggest that it may also have a beneficial effect in the prevention of sudden death in some patients.

New antiarrhythmic agents in pediatrics

This article reviews recent developments in the pharmacologic management of arrhythmias in children and provides specific information about six newer antiarrhythmic agents. With the current increase in recognition, frequency, and complexity of rhythm disturbances in children, pediatricians can expect to encounter children on these antiarrhythmic medications in their practices with increasing frequency.

The effect of intravenous amiodarone on heart rate in patients with acute myocardial infarction or ischemia and sinus tachycardia

The effect of intravenous (IV) amiodarone (300 mg) on heart rate was investigated in 22 patients with acute myocardial infarction (18) or ischemia (4) and sinus tachycardia. There were 11 men and 11 women (age range, 48 to 83 years; mean, 63.5). Amiodarone IV slowed the mean heart rate from 109 +/- 14 beats/min to 94 +/- 15 beats/min (p less than 0.0005). There was a linear correlation between the initial heart rate (preamiodarone) and the final heart rate (postamiodarone), (r = 0.6930, p less than 0.0005). Most of the patients with initial heart rates higher than the mean maintained relatively high heart rates (above the mean), while most patients with lower initial heart rates showed low heart rates (below the mean) after amiodarone administration. Patients in Killip class 1 showed a significant reduction in heart rate after receiving amiodarone, from a mean of 105 +/- 10 to 88 +/- 11 beats/min (p less than 0.01). Patients in Killip class 2 also had reduced heart rates (118 +/- 14 to 81 +/- 39 beats/min), but these changes were not statistically significant. Of the three patients in Killip class 3 to 4, the heart rate slowed by 10 beats/min in one, while in the remaining two no changes were observed. There were no significant side effects from the administration of amiodarone.

New antiarrhythmic drugs

While controversy still exists as to the precise indications for the treatment of all forms of ventricular arrhythmia, advances in the number and, more importantly, type of antiarrhythmic drugs can provide the clinician with a rational basis for selecting antiarrhythmic drug therapy. A host of new agents with different pharmacokinetic and electrophysiological actions are now available, and can be compared or contrasted to conventional antiarrhythmic agents such as quinidine, procainamide, disopyramide, lignocaine (lidocaine) and bretylium. This review summarises the electrophysiological, haemodynamic, pharmacokinetic, and efficacy and safety data of mexiletine, tocainide, flecainide, encainide, propafenone, amiodarone, sotalol, pirmenol, cibenzoline (cifenline) and ethmozine (moracizine, moricizine), and aims to provide a basis on which clinicians can compare and contrast these agents and form an algorithm for selection of antiarrhythmic drug therapy in the treatment of patients with ventricular arrhythmias.

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.

Resting, and rate-dependent depression of Vmax of guinea-pig ventricular action potentials by amiodarone and desethylamiodarone

1 The cellular electrophysiological effects of amiodarone and its metabolite desethylamiodarone (DEA) were studied in guinea-pig ventricular myocardium by use of standard microelectrode techniques. 2 Both compounds produced significant increases in action potential duration (Class III antiarrhythmic effect) and decreases in maximum rate of depolarization (Class I effect), at clinically relevant concentrations. 3 The Class I effects were rate-dependent, with small (0-16%) falls in maximum depolarization rate in the absence of stimulation ('resting block') and progressively larger effects at decreasing interstimulus intervals (range 1200-300 ms). 4 The kinetics of onset and offset of the Class I effect in response to a step change in driving rate were quite fast for both drugs (comparable to those reported for Class Ib agents). 5 It is concluded that this unique combination of Class III action plus Class I effects with fast onset and offset kinetics may help explain the great efficacy of amiodarone in antiarrhythmic therapy.

Effect of amiodarone on sinus node function in patients with sick sinus syndrome

The effect of amiodarone on sinus node function has been studied in 9 patients with symptomatic sick sinus node as documented by Holter-ECG. All patients had programmable dual-chamber pacemakers. Sinus node activity was assessed by intermittently inhibiting the pacemakers before and after four weeks of oral amiodarone treatment. Sinus node function was not altered by amiodarone in 5 patients but was severely depressed in 4 patients. Thus, it is concluded that amiodarone cannot be used safely in all patients with the tachybrady syndrome for the treatment of symptomatic tachyarrhythmias without concomitant pacing.

The effect of fascicular block on ventriculoatrial conduction during AV reentrant tachycardia

Two patients with Wolff-Parkinson-White syndrome and surgically mapped anterior left free wall atrioventricular bypass tracts had orthodromic atrioventricular reentry tachycardia conducted with complete left bundle branch block (CLBBB), complete right bundle block (CRBBB), left anterior fascicular block (LAFB), and a narrow QRS. Ventriculoatrial conduction increased by 35 and 85 ms with CLBBB compatible with the left free wall location of the bypass tracts. In one patient, resolution of CLBBB occurred in two stages. Initially, left posterior fascicular block (LPFB) resolved, decreasing VA conduction by 20 ms. With resolution of the remaining LAFB, there was a further 15 ms decrease in VA conduction. In the other patient, the isolated occurrence of LAFB increased ventriculoatrial conduction by 30 ms. These changes confirmed the location of the bypass tracts in the anterior portion of the left ventricular free wall. Changes in VA conduction with fascicular block can help localize the ventricular insertion of atrioventricular bypass tracts.

Relation between amiodarone and desethylamiodarone plasma concentrations and electrophysiologic effects, efficacy and toxicity

Because the value of monitoring amiodarone plasma concentrations remains undefined, this study was performed to evaluate its role during the management of patients receiving amiodarone. The early electrophysiologic effects of amiodarone were assessed in 40 consecutive patients with coronary artery disease and sustained ventricular tachycardia or fibrillation who underwent electrophysiologic studies and measurement of amiodarone plasma concentration before and 29 +/- 15 (mean +/- SD) days after initiation of therapy. Amiodarone and desethylamiodarone plasma levels did not correlate with changes in either sinus cycle length, QTc interval, ventricular effective refractory period, AH and HV intervals or ventricular tachycardia cycle length. Amiodarone and desethylamiodarone plasma concentrations and the effects of the drug on conduction intervals or right ventricular effective refractory periods were not related to suppression of arrhythmia induction by ventricular stimulation after 1 month of therapy. The relation between amiodarone plasma concentrations and both toxicity and efficacy during long-term therapy were prospectively assessed in a larger series of 114 consecutive patients with either symptomatic supraventricular or ventricular arrhythmias who were followed up on long-term amiodarone therapy for 26 +/- 15 months. Sixty-three patients (55%) had one or more adverse effects attributed to amiodarone. By life-table analysis, 40, 69 and 80% of patients had experienced an adverse reaction after 1, 2 and 3 years of therapy, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical, haemodynamic, and antiarrhythmic effects of long term treatment with amiodarone of patients in heart failure

Twenty two patients with heart failure were studied in a double blind crossover trial to compare amiodarone (200 mg/day) with placebo. Each agent was given for three months. Extrasystoles and complex ventricular arrhythmias were common during ambulatory electrocardiographic monitoring and during exercise testing at entry to the study. Breathlessness and tiredness as assessed by visual analogue scores and duration of treadmill exercise did not become worse during amiodarone treatment. During the placebo and amiodarone phases of the study left ventricular ejection fraction and cardiac index determined by first pass radionuclide ventriculography were similar, both at rest and during upright bicycle exercise. Exercise induced ventricular tachycardia was abolished and simple and complex ventricular arrhythmias observed on 24 hour ambulatory monitoring were greatly diminished during amiodarone treatment. Three patients died, all suddenly, during the placebo phase. In two patients amiodarone was withdrawn after a further myocardial infarction in one and a worsening of symptoms of ventricular arrhythmia in the other. In contrast with other antiarrhythmic agents amiodarone is effective in suppressing ventricular arrhythmias in heart failure without causing adverse haemodynamic effects. Because frequent ventricular arrhythmias are known to be associated with a poor prognosis in heart failure, these data suggest that amiodarone may improve the poor prognosis in patients with heart failure.

Amiodarone for refractory atrial fibrillation

Atrial fibrillation (AF) is a difficult arrhythmia to manage with antiarrhythmic agents. Amiodarone is highly effective in restoring and maintaining normal sinus rhythm in patients with AF. However, the mechanism and predictors of efficacy for amiodarone in treating AF have not been adequately addressed. Various measures of success or failure of amiodarone therapy were examined in 68 patients who had paroxysmal or chronic, established AF refractory to conventional antiarrhythmic agents. The patients were 25 to 75 years old (mean 59) and mean follow-up was 21 months (range 3 to 56). Maintenance amiodarone dosages were 200 to 400 mg/day. Overall, amiodarone therapy was effective long term in 54 of the 68 patients (79%). Left atrial diameter, age, gender and origin of AF were not helpful in predicting success or failure of amiodarone therapy. The presence of chronic AF for longer than 1 year was an adverse factor in maintaining normal sinus rhythm (p = 0.007), although the success rate even in this group was relatively high (57%). Thirty-five percent of the patients had adverse effects, which precluded long-term therapy with amiodarone in 10%.

The effect of cordarone on isoproterenol-induced damage to the myocardium in rats

In this experimental work we evaluated the effect of preventively administered Cordarone on the myocardial damage of rats, caused by isoproterenol. Cordarone had prevented the early mortality of rats up to 1 h, however, after the administration of high doses of Cordarone the late mortality of experimental animals was increased. In the group of rats, which were treated by Cordarone there were almost no small necroses of myocardium, which were, however, contrary--very often found in the control animals. We guess that this effect of Cordarone is caused by its influence on the heart rate, which is slowing down, by its antiarrhythmic effect and by its efficiency to improve the perfusion of myocardium by its power to decrease the resistance of coronary vessels.

Kinetics of electrophysiologic changes during oral loading of amiodarone and after withdrawal of amiodarone in the unsedated dog

We examined the temporal kinetics of onset and offset of the cardiac electrophysiologic effects of orally administered amiodarone in chronically instrumented, unsedated adult dogs (n = 8). Right atrial (RA), atrioventricular nodal (AVN), and right ventricular (RV) effective refractory period (ERP), and AVN functional refractory period (FRP), were determined daily for 21 days during amiodarone loading (24 mg/kg/day) and for 21 days after cessation of amiodarone. Left ventricular (LV) ERP was assessed in four of eight animals. Group mean RA-ERP peaked and plateaued early during amiodarone loading (time to reach one-half observed peak change [t1/2 onset] = 1.2 +/- 0.5 days) and rapidly returned toward baseline after cessation of drug (decay time to one-half peak value [t1/2 offset] = 2.0 +/- 1.7 days). Group mean RV-ERP rose in a linear manner throughout the loading period (t1/2 onset = 9.3 +/- 2.1 days) and remained elevated after cessation of drug (t1/2 offset greater than 21.0 days). Group mean AVN-ERP and FRP exhibited temporal kinetics intermediate between those of the RA-ERP and RV-ERP, both during amiodarone loading and after cessation of the drug. Group mean LV-ERP onset kinetics (assessed in a limited number of animals, n = 4) appeared to differ from RV-ERP onset kinetics (t1/2 onset = 2.5 +/- 2.5 days), whereas LV-ERP and RV-ERP offset kinetics appeared similar (t1/2 offset greater than 21 days). In summary, our findings demonstrate that during oral loading, the temporal sequence of onset of amiodarone-induced electrophysiologic effects is site dependent. Similarly, after cessation of amiodarone, the persistence of drug-induced electrophysiologic effects is both variable and site dependent.

Evaluation by serial electrophysiologic studies of an abbreviated oral loading regimen of amiodarone

Optimal loading and maintenance regimens for amiodarone are undefined. Serial electrophysiologic testing was used in 25 patients with ventricular tachycardia to assess the adequacy of a 1-week oral loading regimen at 1,200 mg/day, to modify maintenance dosing at the conclusion of loading, and to evaluate the appropriateness of maintenance dosing after 2 months of therapy. During the loading period, highly significant (p less than 0.001) increases occurred in the AH interval (88 +/- 22 vs 120 +/- 31 ms), HV interval (49 +/- 10 vs 61 +/- 11 ms), AV nodal Wenckebach cycle length (390 +/- 92 vs 537 +/- 147 ms), ventricular refractory period (247 +/- 17 vs 276 +/- 23 ms), mean ventricular tachycardia cycle length (254 +/- 38 vs 298 +/- 52 ms) and return cycle length (294 +/- 55 vs 360 +/- 87 ms). Ventricular tachycardia inducibility decreased in only a minority of cases, and when observed in association with a more than 10% increase in ventricular refractory period, resulted in a lower maintenance dose. After 2 months of maintenance therapy no additional change occurred in any of these parameters except for an increase in ventricular tachycardia cycle length (298 +/- 52 vs 330 +/- 65 ms, p less than 0.017). Ventricular tachycardia inducibility again showed no consistent response. It is concluded that patients can be discharged after 1 week of therapy with oral amiodarone loading at 1,200 mg/day and that maintenance dosing modified by electrophysiologic assessment results in steady perpetuation of the cardiac amiodarone effect, as indicated by the time course of change in electrophysiologic variables consistently affected.

Amiodarone: pharmacology and antiarrhythmic and adverse effects

Amiodarone is a benzofuran derivative that has been effective for the treatment of both supraventricular and ventricular tachyarrhythmias. It has a large volume of distribution, moderate bioavailability and a long half-life. Its pharmacokinetics are not well understood and its tissue distribution is not typical of a 2-compartment model. Due to ocular, dermatologic, gastrointestinal, neurologic, cardiovascular, thyroid and pulmonary toxicity, amiodarone should be reserved for use in patients with refractory and/or life-threatening arrhythmias.

Value of hepatic computerized tomographic scanning during amiodarone therapy

Amiodarone therapy is difficult to monitor because of the poor correlation between plasma amiodarone levels and clinical efficacy or toxicity. Monitoring tissue levels may give a better measure of effectiveness, but tissue levels cannot be easily measured. The iodine-containing amiodarone and its major metabolite, desethylamiodarone (DA), are highly tissue-bound, and it has been shown that computerized tomographic (CT) scanning of the abdomen will detect drug deposition in the liver. Ten patients receiving chronic amiodarone therapy were studied by abdominal CT scanning. Liver CT density was increased in 6; 68 to 94 CT units (normal 50 to 65) and liver/spleen relative CT density increased in 5; 1.4 to 2.0 (normal 1.0 to 1.3). Estimates of liver drug levels (based on a calibration curve with inorganic iodide) gave values of up to 3 g of amiodarone and DA per kilogram weight of liver. Absolute and relative liver CT density correlated significantly with plasma levels of DA (r = 0.65, p less than 0.05), but not with amiodarone (r = 0.55, p less than 0.1). No significant correlation was found with QTc intervals. This indirect estimate of liver deposition of amiodarone and DA may prove useful in guiding antiarrhythmic therapy.

Amiodarone treatment in patients with ventricular arrhythmias

Amiodarone has been used in the therapy of supraventricular and ventricular tachycardia, and has often been categorised as a class III rather than a class I agent. However, in patients with ventricular arrhythmias, amiodarone 800mg daily for 14 days prolonged the right ventricular effective refractory period by a mean of 18.8 msec (p less than 0.05), and HV interval by a mean of 5.2 msec (p less than 0.05), these changes being similar to those noted with drugs such as quinidine, procainamide, disopyramide and encainide. The antiarrhythmic efficacy of amiodarone was evaluated in 196 patients with recurrent sustained ventricular tachycardia, recurrent ventricular fibrillation or recurrent nonsustained ventricular tachycardia. Coronary artery disease, dilated (congestive) cardiomyopathy, or other forms of heart disease were present in most patients. After 1 month of therapy, 177 patients continued to receive amiodarone and, during the remainder of the follow-up period, 139 patients had no recurrence of spontaneous ventricular tachycardia or ventricular fibrillation. Sudden cardiac death occurred in 15 patients after a mean treatment period of 10.4 months. Overall, amiodarone was an effective form of therapy in patients with ventricular tachycardia and ventricular fibrillation.

Therapy with investigational antiarrhythmic drugs

The investigational antiarrhythmic agents available for use in this country are predominantly class I drugs with local anesthetic membrane effects. These drugs are often used successfully to control arrhythmias refractory to treatment with the standard antiarrhythmic drugs. Side effects often limit their use, and particular attention needs to be paid to their cardiac side effects, such as exacerbation of arrhythmia or enhanced conduction defects.

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.

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.

Effect of amiodarone on retrograde conduction and refractoriness of the His-Purkinje system in man

The effects of long term treatment with oral amiodarone on retrograde conduction ( S2H2 interval) and refractoriness of the His-Purkinje system were studied in 11 patients using His bundle electrograms and the ventricular extrastimulus method. Ten patients had ventricular tachycardia and one supraventricular tachycardia. Electrophysiological studies were carried out before and after the patients had been taking their maintenance dose for a mean duration of 84 days. After amiodarone treatment the HV interval was prolonged in seven patients and unchanged in four. At comparable S1S2 intervals, the S2H2 intervals were longer after treatment with amiodarone in all patients than before. Similarly, the longest S2H2 intervals achieved after amiodarone were longer than the control values. Amiodarone significantly increased the relative, effective, and functional refractory periods of the His-Purkinje system. Thus amiodarone exerts important effects on the His-Purkinje system.

Alterations to the electrical activity of atrial muscle isolated from the rat heart, produced by exposure in vitro to amiodarone

Glass microelectrodes were used to record transmembrane electrical activity from cells located just beneath the endocardial surface of the left atrial free wall of rat hearts during superfusion and electrical stimulation in vitro at 37 degrees C. Availability of the fast sodium channel for current flow was inferred from the maximum rate of rise of membrane potential during phase O of the action potential (Vmax). Muscle exposed to polysorbate 80 (10 to 80 micrograms ml-1) showed a concentration-dependent lengthening of action potential duration (APD) but no detectable change in Vmax. Amiodarone (1 to 20 micrograms ml-1) was dissolved in physiological salt solution with the aid of polysorbate 80 (50 micrograms ml-1) and caused a concentration-dependent prolongation of APD and a decrease in Vmax, both of which were slow to develop and extremely slow to wash-out. The speed of onset of action of amiodarone varied with drug concentration and ranged from a few minutes with high concentrations to many hours with low concentrations.

Amiodarone: electrophysiologic actions, pharmacokinetics and clinical effects

Interest in amiodarone has increased because of its remarkable efficacy as an antiarrhythmic agent. The purpose of this report is to review what is known about the electrophysiologic actions, hemodynamic effects, pharmacokinetics, alterations of thyroid function, response to treatment of supraventricular and ventricular tachyarrhythmias and adverse effects of amiodarone. Understanding the actions of amiodarone and its metabolism will provide more intelligent use of the drug and minimize the development of side effects. The mechanism by which amiodarone suppresses cardiac arrhythmias is not known and may relate to prolongation of refractoriness in all cardiac tissues, suppression of automaticity in some fibers, minimal slowing of conduction in fast channel-dependent tissue, or to interactions with the autonomic nervous system, alterations in thyroid metabolism or other factors. Amiodarone exerts definite but fairly minor negative inotropic effects that may be offset by its vasodilator actions. Amiodarone has a reduced clearance rate, large volume of distribution, low bioavailability and a long half-life that may last 2 months in patients receiving short-term therapy. Therapeutic serum concentrations range between 1.0 and 3.5 micrograms/ml. The drug suppresses recurrences of cardiac tachyarrhythmias in a high percent of patients, in the range of 80% or more for most supraventricular tachycardias and in about 66% of patients with ventricular tachyarrhythmias, sometimes requiring addition of a second antiarrhythmic agent. Side effects, particularly when high doses are used, may limit amiodarone's usefulness and include skin, corneal, thyroid, pulmonary, neurologic, gastrointestinal and hepatic dysfunction. Aggravation of cardiac arrhythmias occurs but serious arrhythmias are caused in less than 5% of patients. Amiodarone affects the metabolism of many other drugs and care must be used to reduce doses of agents combined with amiodarone.

Serious adverse effects of amiodarone

Amiodarone is an effective antiarrhythmic drug which has been used successfully to treat a variety of cardiac arrhythmias. Early reports emphasized both the striking efficacy of this agent and the relative paucity of side effects necessitating discontinuing treatment with this drug. As amiodarone has been used more widely and in more diverse patient populations, reports of serious thyroid, pulmonary, cardiovascular, and other adverse reactions have appeared in the literature. In this paper, we review the serious adverse effects that have been reported to date. The incidence of these reactions varies considerably in different series, and cannot be explained solely by different doses employed or by varying methods of drug administration. The final role of amiodarone in the therapy of cardiac arrhythmias cannot be determined until the long-term toxicity has been more thoroughly investigated.

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.

The electrophysiologic basis for the use of amiodarone for treatment of cardiac arrhythmias

The electrophysiologic basis for the use of amiodarone in the treatment of cardiac arrhythmias is outlined, with reference to studies in isolated cardiac tissues, whole animal, and human studies. Amiodarone appears to have the distinctive property of directly prolonging action potential duration (and hence refractory periods) in nearly all cardiac tissues. Independent of its effects on refractory periods, conduction may also be impaired in the His-Purkinje system, possibly due to depression of phase 0 of the action potential. Sinus node and atrial automaticity, as well as that arising from diseased Purkinje fibers, may be depressed. Normal ventricular escape pacemakers appear relatively unaffected, however. A nonspecific anti-adrenergic action may contribute to its observed effects. These electrophysiological effects are more obvious and predictable after several weeks of oral treatment than after intravenous administration, suggesting a time-dependent mechanism of action. The drug appears well suited to the prevention of enhanced automaticity in the ventricle and re-entry throughout the heart, and its frequent clinical success in a broad spectrum of cardiac arrhythmias attests to this. Unwanted side effects include sinus node depression, His-Purkinje conduction delay or block, and ventricular arrhythmias enhanced by QT prolongation. However, the frequency of clinically significant examples of unwanted arrhythmic effects appears to be acceptably low.

Acute overdosage of amiodarone in a suicide attempt

Clinical and biochemical variables and blood levels of amiodarone and its metabolite are reported after acute self-intoxication in a young woman. Despite the huge amount of drug ingested no clinical side effects were documented over the monitored period of 3 months.