Amiodarone and post-MI patients

A nontrivial differential diagnosis in COVID-19 pandemic: a case report and literary review of amiodarone-induced interstitial pneumonia

Amiodarone is a drug commonly used to treat and prevent cardiac arrhythmias, but it is often associated with several adverse effects, the most serious of which is pulmonary toxicity. A 79-year-old man presented with respiratory failure due to interstitial pneumonia during the COVID-19 pandemic. The viral etiology was nevertheless excluded by repeated nasopharyngeal swabs and serological tests and the final diagnosis was amiodarone-induced organizing pneumonia. The clinical and computed tomography findings improved after amiodarone interruption and steroid therapy. Even during a pandemic, differential diagnosis should always be considered and pulmonary toxicity has to be taken into account in any patient taking amiodarone and who has new respiratory symptoms.

Efficacy and Safety of Low-Dose Amiodarone Therapy for Tachyarrhythmia in Congenital Heart Disease

Amiodarone (AMD) is a class III anti-arrhythmic drug that is highly effective for tachyarrhythmia treatment. AMD is widely used in adults with congenital heart disease (CHD); however, higher doses of AMD (> 200 mg/day) can cause various non-cardiac side effects. The purpose of this study was to assess the efficacy, safety, and adverse events of low-dose AMD (≤ 200 mg/day) for tachyarrhythmia in patients with CHD. We retrospectively studied 80 patients with CHD and tachyarrhythmia who received oral low-dose AMD (≤ 200 mg/day) from January 2004 to March 2016. Low-dose AMD therapy was used to treat supraventricular tachycardia (SVT) in 51 patients and ventricular tachycardia (VT) in 29 patients. After a mean follow-up of 2.9 years for SVT and 3.2 years for VT, 36% and 65% of the patients with SVT and VT, respectively, were free from a first tachyarrhythmia recurrence for 3 years. The incidence of AMD-induced side effects was 23%, and all these cases consisted of thyroid dysfunction. Low-dose AMD was effective for the treatment of tachyarrhythmia in patients with CHD and had a relatively low incidence of side effects. These findings suggest that low-dose AMD is useful and effective for decreasing the frequency of tachyarrhythmia in patients with CHD and has a low incidence of side effects.

Amiodarone inhibits tissue factor expression in monocytic THP-1 cells

There is a possibility thrombus formation is closely involved in sudden cardiac death. Amiodarone, a potassium channel inhibitor, is known to reduce mortality in patients with coronary artery disease or low ejection fraction, having antithrombotic actions. Using human monocytic THP-1 cells, we investigated the effects of amiodarone on tissue factor mRNA and protein expression. The involvement of the two main potassium channels existing in THP-1 cells was also investigated. Amiodarone (10μM) significantly and almost completely inhibited the increase of tissue factor mRNA and protein expression induced by tumor necrosis factor-α (100ng/ml). The inhibitory effects of amiodarone on tissue factor mRNA expression showed dose-dependency. Margatoxin (1nM), a selective blocker of voltage-dependent potassium channel Kv1.3, also inhibited tissue factor protein expression, but didn't significantly inhibit mRNA expression. Ba(2+), a blocker of inwardly rectifying potassium channel Kir2.1, partly inhibited the increase of tissue factor mRNA and protein expression. This is the first study that shows amiodarone inhibits tissue factor expression in monocytic cells, by inhibiting mRNA transcription. The result may correlate with the facts amiodarone has antithrombotic actions in patients under extraordinary conditions where thrombus formation is enhanced. The inhibitory effects of amiodarone on tissue factor expression are drastic, different from those of margatoxin and Ba(2+). The result suggests amiodarone has an underlying mechanism to intensely inhibit tissue factor expression other than blocking Kv1.3 and Kir2.1.

Pathophysiologic bases for adjunctive therapies in the treatment and secondary prevention of acute myocardial infarction

Postmyocardial infarction (MI) survival has been steadily improving. This improvement has been due, in part, to the actions of the adjunctive medical therapies for the treatment of MI. Aspirin, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and lipid-lowering agents have been shown to improve survival in the treatment and secondary prevention of MI. Nitrates have beneficial effects as well. These medications complement the reperfusion strategies through different mechanisms. Other adjunctive medical therapies, namely magnesium, antiarrhythmic agents, and calcium-channel blockers, have not been shown to improve mortality with routine post-MI use despite their theoretical benefits.

Incidence and Predictors of Pulmonary Toxicity in Japanese Patients Receiving Low-Dose Amiodarone

BACKGROUND

Amiodarone-induced pulmonary toxicity (APT) is the most serious side-effect of amiodarone, and its detection and prevention are extremely important. This study was designed to evaluate the incidence and clinical risk factors of APT, and the utility of a pulmonary function test or serum KL-6 assay to predict pulmonary toxicity in Japanese patients receiving low-dose amiodarone.

METHODS AND RESULTS

Five hundred consecutive patients receiving amiodarone were retrospectively evaluated. Mean follow-up period was 48 months and mean maintenance dose was 141 mg daily. Cumulative incidence of APT was 4.2%, 7.8%, and 10.6% at 1, 3, and 5 years, respectively. On multivariate analysis, age at the start (hazard ratio (HR) =1.48, 95% confidence interval (CI) 1.13 to 1.93) was a significant pretreatment risk factor. Age (HR =1.64, 95% CI 1.29 to 2.09), maintenance dose (HR =1.90, 95% CI 1.45 to 2.49) and plasma monodesethylamiodarone concentration (HR =1.30, 95%CI 1.08 to 1.58) were risk factors. Sensitivity and specificity in screening with measurement of percent predicted diffusion capacity of carbon monoxide, > or =15% individual decrease, were 68% and 69%, and for > or =20% individual decrease, were 59% and 74%, whereas those in screening with serum KL-6 assay, > or =500 U/ml, were 25% and 91%, respectively.

CONCLUSIONS

Even at low dose, amiodarone shows substantial pulmonary toxicity. Higher age and higher maintenance dose are risk factors. Further decreasing the maintenance dose of amiodarone should be considered in order to reduce the incidence of pulmonary toxicity, at least in Japanese patients.

Amiodarone: ionic and cellular mechanisms of action of the most promising class III agent

Amiodarone is the most promising drug in the treatment of life-threatening ventricular tachyarrhythmias in patients with significant structural heart disease. The pharmacologic profile of amiodarone is complex and much remains to be clarified about its short- and long-term actions on multiple molecular targets. This article reviews electrophysiologic effects of amiodarone based on previous reports and our own experiments in single cells and multicellular tissue preparations of mammalian hearts. As acute effects, amiodarone inhibits both inward and outward currents. The inhibition of inward sodium and calcium currents (I(Na), I(Ca)) is enhanced in a use- and voltage-dependent manner, resulting in suppression of excitability and conductivity of cardiac tissues especially when stimulated at higher frequencies and in those with less-negative membrane potential. Both voltage- and ligand-gated potassium channel currents (I(K), I(K,Na), I(K,ACh)) are also inhibited at therapeutic levels of drug concentrations. Acutely-administered amiodarone has no consistent effect on the action potential duration (APD). The major and consistent long-term effect of the drug is a moderate APD prolongation with minimal frequency dependence. This prolongation is most likely due to a decrease in the current density of I(K) and I(to). Chronic amiodarone was shown to cause a down-regulation of Kv1.5 messenger ribonucleic acid (mRNA) in rat hearts, suggesting a drug-induced modulation of potassium-channel gene expression. Tissue accumulation of amiodarone and its active metabolite (desethylamiodarone) may modulate the chronic effects, causing variable suppression of excitability and conductivity of the heart through the direct effects of the compounds retained at the sites of action. Amiodarone and desethylamiodarone could antagonize triiodothyronine (T3) action on the heart at cellular or subcellular levels, leading to phenotypic resemblance of long-term amiodarone treatment and hypothyroidism.

Sudden cardiac death

SCD continues to be an important cause of death and morbidity. Despite expanding insight into the mechanisms causing SCD, the population at high risk is not being effectively identified. Although there is still much to do in the management phase of SCD (predicting the efficacy of various therapies), recent clinical trials have helped define the relative risks and benefits of therapies in preventing SCD. Trials are underway to determine whether treating other patient populations, including asymptomatic patients after MI, will improve survival rate. The approach to reducing mortality rate will always be multifaceted; primary prevention of coronary artery disease and prompt salvage of jeopardized myocardium are 2 important aspects of this approach. In addition to interventions for MI, such as myocardial revascularization when indicated, simple and easily administered therapies that are likely to remain the most effective prophylactic interventions are aspirin, ACE inhibitors, beta-blockers, and cholesterol-lowering agents. However, the MADIT and AVID data clearly demonstrate a role for ICD therapy in a subgroup of patients who have VT/VF and are at risk of cardiac arrest. Even though the absolute magnitude of benefit associated with ICDs is still to be determined, the AVID study and other recent reports provide convincing evidence that patients who have VT/VF fare better with ICDs than with antiarrhythmic drug therapy. For the high-risk population described in this article, in addition to aggressive anti-ischemic and heart failure therapy, ICDs are now a mainstay of life-saving treatment. Still to be surmounted is the challenge of identifying patients who have nonischemic substrates and of providing them with the appropriate therapy. Guided by genetic studies and new insight into the mechanisms of such problems as congenital long QT syndrome, life-saving and life-enhancing therapies may soon be available for the management of SCD.

Is hospital admission for initiation of antiarrhythmic therapy with sotalol for atrial arrhythmias required? Yield of in-hospital monitoring and prediction of risk for significant arrhythmia complications

OBJECTIVES

We sought to determine the yield of in-hospital monitoring for detection of significant arrhythmia complications in patients starting sotalol therapy for atrial arrhythmias and to identify factors that might predict safe outpatient initiation.

BACKGROUND

The need for hospital admission during initiation of antiarrhythmic therapy has been questioned, particularly for sotalol, with which proarrhythmia may be dose related.

METHODS

The records of 120 patients admitted to the hospital for initiation of sotalol therapy were retrospectively reviewed to determine the incidence of significant arrhythmia complications, defined as new or increased ventricular arrhythmias, significant bradycardia or excessive corrected QT (QTc) interval prolongation.

RESULTS

Twenty-five patients (20.8%) experienced 35 complications, triggering therapy changes during the hospital period in 21 (17.5%). New or increased ventricular arrhythmias developed in 7 patients (5.8%) (torsade de pointes in 2), significant bradycardia in 20 (16.7%) (rate <40 beats/min in 13, pause >3.0 s in 4, third-degree atrioventricular block in 1, permanent pacemaker implantation in 3) and excessively prolonged QTc intervals in 8 (6.7%) (dosage reduced or discontinued in 6). Time to the earliest detection of complications was 2.1 +/- 2.5 (mean +/- SD) days after initiation of sotalol, with 22 of 25 patients meeting criteria for complications within 3 days of monitoring. Baseline electrocardiographic intervals or absence of heart disease failed to distinguish a low risk group. Multivariate analysis identified absence of a pacemaker as the only significant predictor of arrhythmia complications (p = 0.022).

CONCLUSIONS

Because clinically significant complications can be detected with in-hospital monitoring in one of five patients starting sotalol therapy, hospital admission is warranted for initiation of sotalol. Patients without pacemakers are at higher risk for these complications.

Controlling cardiac arrhythmias: an overview with a historical perspective

During the past decade, several developments in our knowledge of antiarrhythmic drugs have had a major influence on our approach to their use. These developments may be summarized as follows: (1) it has become clear that arrhythmias merit treatment only for the relief of symptoms, with improved quality of life, and for prolongation of survival by reducing arrhythmic deaths; (2) suppression of arrhythmias--symptomatic or asymptomatic--may not necessarily decrease mortality, the net impact on mortality being agent-specific; (3) antiarrhythmic drugs have the propensity to decrease as well as to increase cardiac arrhythmias (producing proarrhythmias); (4) the most important determinant of arrhythmia mortality is the degree and nature of ventricular dysfunction; and (5) only controlled trials have the potential to establish the effect of treatment on mortality in patients with cardiac arrhythmias. To these considerations must be added the advances in nonpharmacologic approaches to controlling cardiac arrhythmias. These include catheter ablation of cardiac arrhythmias, certain surgical techniques that in selected patients offer prospects of cure, and the development of implantable ventricular and atrial cardioverter defibrillators, which allow the evaluation of drugs versus placebo against the background of the defibrillator. This is particularly germane in the case of life-threatening symptomatic ventricular arrhythmias such as sustained ventricular tachycardia and ventricular fibrillation. Antiarrhythmic drugs and implantable devices in the control of arrhythmias cannot be considered in isolation. Their role in mortality reduction needs to be defined alone as well as in combination by controlled clinical trials.

What can we expect from prophylactic implantable defibrillators?

Death due to ventricular tachyarrhythmia (VT) remains an important public health problem; patients with prior myocardial infarction (MI) constitute the largest identifiable population for prophylactic interventions. Targeting of progressively higher-risk subgroups of post-MI survivors carries inevitable tradeoffs with respect to the global impact of interventions on overall mortality. Therapy with aspirin, beta blockers, and angiotensin-converting enzyme (ACE) inhibitors comprise the benchmark against which all additional interventions, including implantable defibrillators, must be measured. Initial enthusiasm for empiric amiodarone therapy has been tempered by the limited benefit demonstrated in recent randomized trials. Trials of other class III antiarrhythmic drugs, including both d,l-sotalol and d-sotalol, have also failed to demonstrate survival benefit. The Multicenter Automatic Defibrillator Implantation Trial (MADIT) demonstrated significantly improved survival associated with defibrillators in a small subgroup of post-MI survivors with a high short-term risk of death. The ultimate number and optimal criteria for selection of patients who may benefit from prophylactic defibrillator therapy after MI will undergo continued evolution as new data from current and ongoing trials become available.

Arrhythmias and sudden death in heart failure

Survival of patients with heart failure has improved over the past decade due to advances in medical therapy. Sudden death continues to cause 20 to 50% of deaths. Ventricular arrhythmias are common in patients with heart failure. Ventricular hypertrophy, scars from prior myocardial infarction, sympathetic activation, and electrolyte abnormalities contribute. Some sudden deaths are due to bradyarrhythmias and electromechanical dissociation rather than ventricular arrhythmias. The risks and benefits of antiarrhythmic therapies continue to be defined. Class I antiarrhythmic drugs should be avoided due to proarrhythmic and negative inotropic effects that may increase mortality. For patients resuscitated from sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) amiodarone or an implantable cardioverter defibrillator (ICD) should be considered. ICDs markedly reduce sudden death in VT/VF survivors, but in advanced heart failure, this may not markedly extend survival. Catheter or surgical ablation can be considered for selected patients with bundle branch reentry VT or difficult to control monomorphic VT. For patients who have not had sustained VT/VF antiarrhythmic therapy should generally be avoided, but may benefit some high risk patients. Amiodarone may be beneficial in patients with advanced heart failure and rapid resting heart rates. ICDs may improve survival in selected survivors of myocardial infarction who have inducible VT.

Amiodarone: the expanding antiarrhythmic role and how to follow a patient on chronic therapy

Amiodarone was introduced as an antiarrhythmic compound in the early 1970s and was approved in the U.S. for the treatment of refractory ventricular arrhythmias in late 1984. Since that time the drug has become the most widely studied antiarrhythmic compound with expanding potential indications, including maintaining stability of sinus rhythm, secondary prevention in the survivors of myocardial infarction, and prolongation of survival in certain subsets of patients with congestive heart failure. Intravenous amiodarone was introduced in the U.S. in 1995 for the control of recurrent destabilizing ventricular tachycardia or ventricular fibrillation resistant to conventional therapy. The level of comfort in its use has risen considerably in the recent past. This has stemmed from the reasonably decisive evidence that class I agents increase mortality in patients with structural heart disease. In contrast, amiodarone either reduces mortality or its effect is neutral; this is consistent with its low to negligible proarrhythmic actions. The drug does not aggravate heart failure and it may even increase left ventricular ejection fraction and improve exercise capacity. Above all, it is becoming increasingly evident from wider experience and from controlled clinical trials that the side-effect profile of the drug is not as compelling an issue as it appeared to be when first used in much higher doses. Therefore, the overall objective of amiodarone therapy is to use the lowest dose that produces a defined therapeutic end point without causing serious side effects. Careful clinical surveillance in conjunction with monitoring of certain laboratory parameters and indices of efficacy at regular intervals permits the drug to be used effectively in a large number of patients who fail to respond to, or are intolerant of other antiarrhythmic compounds. Many experienced clinicians have begun to consider the use of amiodarone as first-line therapy in certain disorders of rhythm, especially in patients with severely compromised ventricular function.

Ion channel blockers in the treatment of chronic heart failure

Strategies for pharmacological treatment of chronic congestive heart failure (CHF) are discussed from the viewpoint of cardiac ion channel modulations. It remains controversial as to whether Na channel blockers, which are the most effective drugs to suppress ventricular arrhythmias, can improve the prognosis of chronic CHF. As far as recent knowledge of interactions between the Na channel and its blocker is concerned, lidocaine-like agents such as mexiletine, which inhibit the Na channel current by binding to the channel in the inactivated state, are recommended because they can suppress premature ventricular contractions without prolongation of QRS complexes of sinus beats. To develop a new agent for the treatment of chronic CHF, we extracted the common features of electropharmacologic actions shared by amiodarone and vesnarinone, both of which have been reported to reduce the mortality of patients with chronic CHF. It is concluded that increases in the action potential duration (APD) of ventricular muscle mediated through an inhibition of the delayed rectifier K channel (IK channel) and a reduction of sinus node firing through an inhibition of L type Ca channel in addition to IK channel inhibition, are essential for the treatment of chronic CHF.

Controlling Paroxysmal Atrial Fibrillation by a Combination of Amiodarone and Flecainide: Description of a Case With 15-Year Follow-up

A 77-year-old man with no known cardiac disease has had paroxysmal atrial fibrillation for 35 years with disabling symptoms and poor exercise tolerance when not in sinus rhythm, and he did not respond to conventional therapy. Fifteen years ago he was placed on amiodarone. His arrhythmia converted to atrial flutter with a flutter rate below 200 beats/min; DC cardioversion at 3 months led to transient sinus rhythm. At 5 months he converted spontaneously to sinus rhythm and had very few recurrences until 4 years later when he began to experience further frequent recurrences when the dose was reduced from 400 mg/day to 200 mg/day. Redosing at the higher dose led to skin discoloration; amiodarone was then replaced with sotalol, which the patient did not tolerate. After 9 months with efforts to rate control with various agents, amiodarone was reintroduced at 400 mg/day, which achieved full control, but to obviate the development of skin changes, flecainide was added at a dose of 100 mg twice a day, and the dose of amiodarone was gradually reduced to 200 mg/day. This combination regimen has produced no side effects or organ toxicity, although a degree of hypogonadism developed. It responded well to testosterone replacement. On the combination regimen, there have been no symptomatic arrhythmia recurrences over 8 years. Amiodarone and flecainide may have additive or synergistic effects in maintaining sinus rhythm in atrial fibrillation; the antiarrhythmic property of amiodarone is likely to minimize or nullify the proarryhthmic reactions of flecainide during combination therapy. This combination regimen may allow the extension of the use of flecainide in controlling refractory atrial flutter and fibrillation in patients with structural cardiac disease. The efficacy and safety of the combination regimen of the two drugs should be addressed in controlled clinical trials.

The coming of age of the class III antiarrhythmic principle: retrospective and future trends

Antiarrhythmic drug therapy is in a state of continuous flux. In the last decade or so, numerous experimental and clinical studies have revealed that drugs that act by delaying conduction, while markedly suppressing ventricular arrhythmias, have the proclivity to increase mortality in subsets of patients with significant cardiac disease. The adverse impact on mortality was confirmed by placebo-controlled randomized trials as well as meta-analysis of smaller randomized clinical trials. The latter indicated that beta blockers exert a beneficial effect on mortality. Benefit from drugs that lengthen repolarization, especially drugs that have the additional property of blocking sympathetic excitation, was also seen in relatively small numbers of patients. Sotalol and amiodarone fell into this category of antiarrhythmic drugs. There were 2 major consequences that stemmed from the results of these trials. First, the endpoint of clinical trials shifted to total mortality from surrogates such as defined degree of suppression of ventricular arrhythmias. Second, concern regarding increases in mortality produced by class I drugs engendered a shift in favor of drugs that prolong repolarization. Such a shift was bolstered by the growing body of data that established the efficacy of sotalol and amiodarone as potent agents for the control of life-threatening ventricular arrhythmias. They were both found to be superior to class I agents. The perception that the critical factor that mediates their efficacy is the homogeneous prolongation of repolarization has led to the synthesis and characterization of so-called pure class III agents, which include d-sotalol and other lKr blockers such as dofetilide, sematilide, E-4031, and almokalant, among numerous others. The increase in mortality produced by d-sotalol in patients with myocardial infarction and lowered ejection fraction and in patients with and without heart failure has led researchers to question how to design future antiarrhythmic molecules. In the search for an ideal antifibrillatory agent, should emphasis be placed on simple molecules such as pure class III agents or on those with more complex profiles, such as sotalol and amiodarone, which exhibit antiadrenergic actions and the ability to prolong cardiac repolarization? The available data are in favor of the latter approach.

Antiarrhythmic actions of amiodarone: a profile of a paradoxical agent

Amiodarone, a complex compound with variegated electropharmacologic and pharmacokinetic properties and an equally complex side-effect profile, continues to have a critical role in the control of ventricular and supraventricular tachyarrhythmias as the use of class I agents has declined. Such is also the case with sotalol. Unlike other so-called class III agents, amiodarone non-competitively blocks sympathetic stimulation, and its effects on repolarization are not associated with reverse use dependency. Rarely does it produce torsades de pointes despite its propensity to induce significant bradycardia and marked prolongation of the QT interval. During long-term therapy with the drug, there is no impairment of ventricular function; in fact, there are significant increases in the left ventricular ejection fraction during protracted amiodarone therapy in patients with heart failure. Long-term amiodarone administration consistently demonstrates marked efficacy in a wide spectrum of arrhythmias. The major limitation of amiodarone during long-term therapy is its unusual side-effect profile, although the increasing trend for low-dose drug therapy has demonstrated a major decline in the overall incidence of serious adverse reactions. Amiodarone is effective in controlling symptomatic ventricular tachycardia and fibrillation (VT/VF) in > 60-70% of patients when conventional agents (especially class I) are ineffective or not well tolerated. The efficacy of amiodarone compared with that of an implantable cardioverter-defibrillator in patients with VT/VF and in survivors of cardiac arrest remains uncertain when total mortality is used as the primary endpoint of comparison. Amiodarone suppresses ventricular ectopy and markedly suppresses nonsustained VT. It prevents inducible VT/VF in a small number of patients, but slows VT rate in a larger number. The role of the drug in prolonging survival in the postmyocardial infarction patient is unclear, although preliminary data from blinded studies suggest that the drug decreases arrhythmia-related mortality. Similarly, in heart failure, amiodarone has the potential to reduce total mortality but appears to be selectively effective in nonischemic rather than in ischemic cardiomyopathy. Intravenous amiodarone was recently introduced in the United States for the control of recurrent destabilizing VT or VF resistant to conventional therapy. There is also evolving data indicating that the drug might be the most potent agent in maintaining sinus rhythm in patients with atrial fibrillation or flutter converted chemically or electrically to sinus rhythm. However, blinded controlled comparative studies involving sotalol, quinidine, or pure class III drugs have not been carried out. The available data nevertheless suggest that, barring its side-effect profile, amiodarone is a desirable prototype of a broad-spectrum antifibrillatory and antiarrhythmic compound.

Effects of hypothyroidism on the vulnerability to ventricular fibrillation in dogs: a comparative study with amiodarone

It has been shown that thyroid hormone has a significant effect on the heart and that suppression of thyroid function may contribute to the antiarrhythmic effect of amiodarone. The study was aimed at investigating the effects of hypothyroidism, compared with those of amiodarone, on vulnerability to ventricular fibrillation in dogs. In this study, 25 adult dogs were randomly divided into three groups: a hypothyroid group following total thyroidectomy (n = 9), an amiodarone group (n = 8, 400 mg per day, 4 weeks), and a control group (n = 8). Both amiodarone and control groups were subjected to sham surgery. Five to 8 weeks after surgery, ventricular fibrillation threshold and other electrophysiological parameters were determined. Right ventricular effective refractory period, monophasic action potential duration, and ventricular fibrillation threshold were significantly increased in both the thyroidectomized and amiodarone-treated animals. There was no significant change in monophasic action potential duration dispersion. The incidence of ventricular fibrillation during ischemia and reperfusion was significantly reduced in both treated groups compared with the sham-operated euthyroid controls. These observations suggest that hypothyroidism has a significant antifibrillatory effect in dogs. Homogeneous prolongation of repolarization and refractoriness may contribute to the antifibrillatory action of hypothyroidism.

The cardiac ion channels: relevance to management of arrhythmias

The electrical activity of cardiac tissue is determined by the highly regulated flow of ions across the cell membrane during the cardiac action potential. Ion channels are pore-forming proteins through which these electric currents flow. In this review, the ion currents that underlie the action potential are first described. Then, the way in which expression of individual ion-channel genes results in such ion currents is discussed. Finally, the concept that arrhythmias may be due to abnormalities of structure, function, or number of ion channels, or the way in which they respond to abnormalities in their environment (such as acute ischemia), is reviewed. Further understanding of the molecular mechanisms underlying normal and abnormal cardiac electrophysiologic behavior should allow the development of safer and more effective antiarrhythmic interventions.

Expanding indications for the use of Class III agents in patients at high risk for sudden death

The evidence that antiarrhythmic compounds that act by slowing conduction velocity increase mortality in patients with cardiac disease is now compelling. Emphasis is now shifting to agents that act by lengthening repolarization and have additional antiadrenergic properties. There is preliminary evidence that pure Class III agents devoid of antisympathetic activity may also increase rather than decrease mortality in certain patients. Thus, in recent years, sotalol and amiodarone have emerged as the preferred agents for the control of most ventricular arrhythmias occurring in the setting of significant heart disease. Sotalol has not been widely studied in postinfarct patients; one trial indicated that the drug did reduce total mortality but the difference did not reach statistical significance. A number of studies with amiodarone in the postmyocardial infarction patients have revealed benefit, but these were from nonblinded studies. Two blinded, placebo-controlled studies are currently ongoing. A potential new indication of amiodarone is in patients with arrhythmias in heart failure in whom amiodarone markedly increased left ventricular ejection fraction, with a pronounced suppressant effect on premature ventricular complexes and nonsustained ventricular tachycardia and a trend for a decrease in mortality in patients with nonischemic cardiomyopathy. The most promising indication of amiodarone in low doses is in the maintenance of sinus rhythm in patients with atrial flutter and fibrillation. For the present, amiodarone appears to be the best prototype of a desirable complex antiarrhythmic compound, if its variegated side effect profile can be favorably modified from knowledge of structure-activity relationships.

Amiodarone and torsades de pointes in patients with advanced heart failure

Amiodarone is considered to be safe in patients with prior QT prolongation and torsades de pointes taking class I antiarrhythmic agents who require continued antiarrhythmic drug therapy. However, the safety of amiodarone in advanced heart failure patients with a history of drug-induced torsades de pointes, who may be more susceptible to proarrhythmia, is unknown. Therefore, the objective of this study was to assess amiodarone safety and efficacy in heart failure patients with prior antiarrhythmic drug-induced torsades de pointes. We determined the history of torsades de pointes in 205 patients with heart failure treated with amiodarone, and compared the risk of sudden death in patients with and without such a history. To evaluate the possibility that all patients with a history of torsades de pointes would be at high risk for sudden death regardless of amiodarone treatment, we compared this risk in patients with a history of torsades de pointes who were and were not subsequently treated with amiodarone. Of 205 patients with advanced heart failure, 8 (4%) treated with amiodarone had prior drug-induced torsades de pointes. Despite similar severity of heart failure, the 1-year actuarial sudden death risk was markedly increased in amiodarone patients with than without prior torsades de pointes (55% vs 15%, p = 0.0001). Similarly, the incidence of 1-year sudden death was markedly increased in patients with prior torsades de pointes taking amiodarone compared with such patients who were not subsequently treated with amiodarone (55% vs 0%, p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic effects of procainamide, mexiletine, and amiodarone on the transplanted heart. Experimental study

The effects of procainamide, mexiletine, and amiodarone on automaticity, conduction, and refractoriness were studied in a model of heterotopic heart transplantation in dogs that combined an innervated heart (recipient) and a denervated transplanted heart (donor). After the surgical procedure, 500 mg procainamide (n = 13), 200 mg plus 0.1 mg/kg per minute mexiletine (n = 10), or 150 mg amiodarone (n = 10) was administered intravenously. During a baseline period and after drug administration, each heart was assessed for atrioventricular interval; cycle length; sinoatrial conduction time; atrioventricular node anterograde and retrograde block points; atrioventricular node and ventricular antegrade effective refractory periods; PR, QRS, and QT intervals on electrocardiogram; systemic arterial, pulmonary arterial, central venous, and pulmonary capillary wedge pressures; and cardiac output. In recipients, procainamide reduced cardiac output, depressed sinus automaticity, slowed conduction time without affecting the QRS interval, and prolonged the nodal and ventricular refractoriness; in donor hearts, it depressed automaticity and prolonged nodal refractoriness, but did not modify conduction or ventricular refractoriness. Mexiletine only moderately depressed sinus automaticity in recipient hearts; it did not affect the other parameters either in recipient or transplanted hearts, nor did it alter the hemodynamic situation. Amiodarone produced hypotension, reduced cardiac output, and prolonged all the electrophysiologic intervals except the QRS interval in recipient hearts. These changes were even more pronounced in the transplanted hearts and led to extreme sinus bradycardia in four cases. Of these three drugs, mexiletine appears to be the safest should treatment for arrhythmias be necessary in transplant recipients.

Diazoxide blocks the morphine induced lengthening of action potential duration on guinea-pig papillary muscle

1. Intracellular microelectrodes were used to evaluate the possible involvement of potassium currents in the action potential prolongation induced by morphine. To this purpose we investigated the electrophysiological effect of morphine on the isolated guinea pig right ventricular papillary muscle in the presence of the potassium channel opener and inhibitor diazoxide and glibenclamide respectively. 2. Diazoxide (1 microM), which is devoid of effect on its own, blocks the lengthening of action potential duration (APD) induced by morphine (5 mM). 3. However, in the presence of glibenclamide (1 microM), morphine (5 mM) prolonged APD in approximately the same proportion as that observed when used alone. 4. These results suggest that diazoxide but not glibenclamide sensitive potassium channels could mediate the APD prolongation induced by morphine.

Pharmacodynamic, pharmacokinetic and antiarrhythmic properties of d-sotalol, the dextro-isomer of sotalol

In recent years, there has been a major shift from the use of antiarrhythmic drugs that act by slowing conduction to those that exert their beneficial actions by lengthening cardiac repolarisation. Such a shift is occurring because sodium channel blockers may increase mortality, especially in patients with structural heart disease, and because drugs such as sotalol and amiodarone are effective, with a potential for decreasing arrhythmic mortality. In this context, the electrophysiological and antiarrhythmic properties of d-sotalol, the dextro-isomer of sotalol, are of major importance. d-Sotalol is essentially devoid of beta-blocking actions and may be considered a pure class III compound. It has been assumed that its clinical efficacy would approximate that of amiodarone and sotalol, but without the complex adverse effect profile of amiodarone and the adverse beta-blocker effects of racemic sotalol. d-Sotalol has pharmacokinetic properties that resemble those of the racemate. It lengthens the QT/QTc interval but does not affect other electrocardiographic (ECG) intervals. It increases the refractory period in the atria, ventricles, bypass tracts and the His-Purkinje system while minimally slowing the heart rate. In preliminary studies, it had a weak suppressant effect on premature ventricular contractions, prevented inducibility of ventricular tachycardia or fibrillation in about 40% of patients, and demonstrated the potential to terminate atrial flutter and fibrillation and maintain stability of sinus rhythm during prophylactic administration. The drug exhibits little or no negative inotropic actions. Thus, it is likely to be better tolerated in patients with congestive heart failure dependent on sympathetic stimulation for compensation. Because it produces less bradycardic effect than the racemate, it is believed that the drug might induce a lower rate of torsade de pointes. The role of d-sotalol in controlling cardiac arrhythmias is being addressed in a number controlled clinical trials. However, one such double-blind, placebo-controlled trial, Survival With Oral d-Sotalol (or SWORD), in survivors of myocardial infarction with depressed ventricular function was recently terminated prematurely because of a strikingly greater all-cause mortality compared with placebo (4.6 versus 2.6%). These preliminary findings, still to be fully analysed and interpreted for clinical significance, nevertheless raise valid concerns regarding the currently popular concept of controlling cardiac arrhythmias by the selective or isolated prolongation of repolarisation ('pure' class III action) as an antiarrhythmic principle.

Acute effects of amiodarone on membrane properties, refractoriness, and conduction in guinea pig papillary muscles

Amiodarone has potent and complex antiarrhythmic effects associated with a rare incidence of proarrhythmia. For a comprehensive understanding of its antiarrhythmic mechanisms in the same preparations, amiodarone (50 microM) was employed as it would be in the clinical setting and applied to guinea pig papillary muscles impaled by microelectrodes, paced at different rates, and superfused with various concentrations of potassium ([K]e). Amiodarone exerted complex actions, as follows: (1) The maximum rate of rise (Vmax) of the fast action potential (i.e., [K]e = 5.4-9.0 mM) as well as that of the slow action potential (i.e., [K]e = 15.0 mM in the presence of 1.0 microM isoproterenol) was suppressed in a rate-dependent manner. (2) Amiodarone exhibited a rate- and [K]e-dependent increase in the ratio of effective refractory period vs action potential duration at 90% repolarization (ERP/APD90), disclosing post-repolarization refractoriness. (3) Amiodarone had no effect on passive cable factors, such as threshold current and tissue resistance, during propagation. These versatile electrophysiological effects of amiodarone may contribute to its unique antiarrhythmic effects, as well as the low incidence of proarrhythmia with this drug.

Divergent effects of chronic amiodarone administration on systolic and diastolic function in patients with heart disease

The purpose of this study was to determine the effects of chronic amiodarone treatment on systolic and diastolic function in patients with cardiac disease undergoing treatment for resistant ventricular arrhythmias. Previous studies have shown that chronic amiodarone treatment either has no effect or increases left ventricular ejection fraction, but the effects on diastolic properties of the ventricle have not been defined. Twelve male patients were given loading doses of amiodarone followed by a maintenance regimen. Serial measurements of heart rate, blood pressure, and indexes of systolic and diastolic function were measured by Doppler echocardiographic techniques at baseline conditions and at 2, 8, and 12 weeks of drug therapy. Changes in altered thyroid state were excluded by serial determinations of thyroid function. Amiodarone increased left ventricular ejection fraction (+16%, p < 0.01 by 8 weeks), decreased presystolic ejection period/left ventricular ejection time (-12%, p < 0.01 by 8 weeks), and increased velocity of circumferential fiber shortening (+22%, p < 0.05 by 8 weeks). Amiodarone decreased mitral inflow velocity peak E/peak A (-7%, p < 0.01 by 12 weeks), and increased deceleration and isovolumic relaxation times incrementally (+36% [p < 0.001] and +23% [p < 0.001], respectively, at 12 weeks). Chronically administered amiodarone can improve systolic function and exert a negative lusitropic action in patients with heart disease.

Choice and chance in drug therapy of cardiac arrhythmias: technique versus drug-specific responses in evaluation of efficacy

Numerous recent advances in pharmacotherapy for arrhythmia have necessitated a reorientation in terms of choice of specific agents, techniques for predicting drug effects, and the endpoints for judging therapeutic efficacy. For the management of ventricular arrhythmias and preventing mortality, several trends are becoming clear. It is unlikely that sodium channel blockers will continue to play a major role, except in patients with structurally normal hearts. Emphasis is shifting way from class I agents to those that act by prolonging repolarization without effect on conduction. These latter agents have been termed pure class III agents and have been developed because of the clinical experience with sotalol and amiodarone. On the other hand, there is compelling evidence that sympathetic inhibition per se (as exemplified by beta blockers) or as an integral component of more complex molecules (e.g., sotalol, amiodarone) is a critical feature of desirable antifibrillatory agents. Thus, compared with D,L-sotalol or amiodarone, pure class III agents are likely to be much less effective and may need to be used in combination with antiadrenergic compounds. Compared with amiodarone, they are likely to induce a higher incidence of torsades de pointes, especially in the case of concomitant diuretic therapy. Therapy guided by programmed electrical stimulation or Holter monitoring is likely to play a diminishing role in the development of antiarrhythmic drug regimens, and thus an antiarrhythmic agent's effectiveness may need to be evaluated against the background of implantable cardioverter-defibrillators or against amiodarone therapy. There is increasing evidence that "guided" therapy may simply identify responders from nonresponders and objective endpoints of therapy may be influenced more by drug-specific responses than by the techniques used for their selection. The data raise the issue whether in the future, therapy for ventricular tachycardia or fibrillation might be chosen empirically but from a limited range of compounds, such as beta blockers, amiodarone, sotalol, and possibly certain pure class III agents that are presently under development. Although it is reasonably certain that there is a need to shift from delaying conduction as a means for treating arrhythmias to one that entails prolongation of repolarization, it remains to be determined what might be the characteristics of an ideal antifibrillatory compound. The greatest promise is the area of complex molecules with a diversity of electrophysiologic actions, as exemplified by amiodarone and similar compounds that have the property of blunting sympathetic excitation. The complexity of their electrophysiologic and pharmacodynamic properties might provide a more favorable match with the vulnerable substrate for reducing electrical instability, thereby preventing ventricular fibrillation.