Intravenous amiodarone for the rapid treatment of life-threatening ventricular arrhythmias in critically ill patients with coronary artery disease

Rhythm disturbances

Patients with cardiac rhythm disturbances may present in a variety of conditions. Patients may be unstable, requiring immediate interventions, or stable, allowing for a more deliberate approach. Rapid assessment of patient stability, underlying rhythm, and determination of appropriate interventions guides timely therapy. This article discusses the differential diagnosis and treatment of adult patients presenting with primary bradyarrhythmias and tachyarrhythmias, with the exception of atrial fibrillation and atrial flutter, covered elsewhere in this issue. A concise approach to diagnosis and determination of appropriate therapy is presented.

Pharmacology and Toxicology of a New Aqueous Formulation of Intravenous Amiodarone (Amio-Aqueous) Compared with Cordarone IV

Hypotension is the most frequent adverse event reported with intravenous amiodarone (Cordarone IV). The hypotension has been attributed to the vasoactive solvents of the formulation, polysorbate 80 and benzyl alcohol, both known to exhibit negative inotropy and hypotensive effect. A new aqueous formulation of intravenous amiodarone (Amio-Aqueous) does not contain vasoactive excipients and may be less toxic and cause less hypotension than Cordarone IV. This hypothesis was tested in a series of animal studies with direct comparison of Amio-Aqueous and Cordarone IV. All studies were performed on Sprague-Dawley rats. The acute toxicology study showed that both LD50 and LD100 were 30% greater for Amio-Aqueous than for Cordarone. At the dose at which all animals expired on Cordarone, 50% of animals were still alive on Amio-Aqueous. The study on myocardial contractility showed that Amio-Aqueous was a far less negative inotropic than Cordarone IV (P < 0.001). Amio Aqueous did not have an effect on contractility at 5- and 10-mg/kg dose levels while Cordarone resulted in a 25% (P < 0.01) and 29% (P < 0.002) decrease, respectively. The study on arterial blood pressure showed that Cordarone caused a significant decrease in blood pressure at each of the 3, 5, 10, and 20 mg/kg doses (P < 0.05 to P < 0.001) while Amio-Aqueous did not. The study on the antiarrhythmic effects showed comparable efficacy for both formulations. In conclusion, Cordarone IV was more toxic and caused significant hypotension and negative inotropy while Amio-Aqueous lacked the hypotensive and cardiotoxic properties of Cordarone. Therefore, Amio-Aqueous is a safer alternative than the standard formulation.

Comparative Effects of Rapid Bolus Administration of Aqueous Amiodarone Versus 10-Minute Cordarone I.V. Infusion on Mean Arterial Blood Pressure in Conscious Dogs

OBJECTIVE

This study was designed to test the hypothesis that rapid bolus administration of an aqueous formulation of intravenous amiodarone causes less hypotension than a 10-minute infusion of the standard formulation, Cordarone IV. Hypotension was the most common adverse event reported with Cordarone IV. The hypotension was not dose related, but related to the rate of infusion. Therefore, product labeling calls Cordarone and its generic formulations to be administered over 10 minutes. Cordarone IV contains polysorbate 80 and benzyl alcohol, each causes hypotension. A new aqueous formulation of amiodarone (Amio-Aqueous) does not contain these agents and therefore may cause less hypotension.

METHODS

Six conscious beagle dogs were instrumented with a telemetric device for blood pressure monitoring. The study was conducted on 5 days. On the first 2 days, a 10-min infusion or a bolus of D(5)W was administered (placebo). Over the following 3 days, the dogs received (in randomized order, one per day) a 10-min infusion of 2.5 mg/kg Cordarone IV and boluses of 2.5 mg/kg and 5.0 mg/kg Amio-Aqueous injected over 2 to 5 sec. The dogs were monitored for 2 hrs after dosing.

RESULTS

Compared to placebo, boluses of aqueous amiodarone produced no significant changes in the mean arterial blood pressure (MABP). In contrast, Cordarone infusion produced significant decreases in MABP that lasted for at least 2 hrs (p < 0.001).

CONCLUSION

Amio-Aqueous had significantly better hemodynamic profile permitting rapid intravenous administration. This is a significant advantage over the standard formulation, because Cordarone cannot be administered by rapid bolus due to excipient-related hypotension.

Lack of a hypotensive effect with rapid administration of a new aqueous formulation of intravenous amiodarone

Hypotension is the most frequent adverse event reported with intravenous amiodarone. Hypotension has been attributed to the vasoactive solvents of the standard formulation (Cordarone IV) and is not dose related, but related to the rate of infusion. Drug labeling calls for intravenous amiodarone to be administered over 10 minutes. A new aqueous formulation of amiodarone (Amio-Aqueous) does not contain vasoactive excipients and may be administered safely by rapid administration without hypotension. This hypothesis was tested using combined data of 4 clinical trials; each assessed the development of hypotension prospectively. Hypotension was defined as a 25% decrease in systolic blood pressure (BP), with the development of a systolic BP of <90 mm Hg or a systolic BP that decreased to <80 mm Hg. In all, 358 Amio-Aqueous and 225 lidocaine boluses were administered to 278 patients; 246 had ventricular tachycardia (VT) during drug administration. Hypotension developed in 11% of patients on Amio-Aqueous versus 19% on lidocaine (p = NS), all during VT; most resolved spontaneously with VT termination. With both drugs, hypotension persisted after VT termination in 1% of patients; the incidence of drug-related hypotension occurred in 2% of patients (1% had hypotension requiring treatment). The Amio-Aqueous was discontinued in 1% of patients, and lidocaine was discontinued in 2% of patients because of hypotension. We conclude that Amio-Aqueous is at least as safe as lidocaine in terms of causing hypotension when administered rapidly. This is a significant advantage over the standard amiodarone formulation, because Cordarone cannot be administered by rapid bolus owing to excipient-related hypotension.

Intravenous lidocaine versus intravenous amiodarone (in a new aqueous formulation) for incessant ventricular tachycardia

The effectiveness of intravenous amiodarone for the treatment of incessant (shock resistant) ventricular tachycardia (VT) has not been established. This study evaluated the efficacy of a water-soluble amiodarone preparation or lidocaine for the treatment of shock-resistant VT. The trial was a double-blinded parallel design. Patients were randomized to receive up to 2 boluses of either 150 mg intravenous amiodarone or 2 boluses of 100 mg lidocaine followed by a 24-hour infusion. If the first assigned medication failed to terminate VT, the patient was crossed over to the alternative therapy. Twenty-nine patients were randomized to the study (18 received amiodarone and 11 received lidocaine). There were no significant differences between groups with regard to baseline characteristics. Immediate VT termination was achieved in 14 patients (78%) with amiodarone versus 3 patients (27%) on lidocaine (p <0.05). After 1 hour, 12 patients (67%) on amiodarone and 1 patient (9%) on lidocaine were alive and free of VT (p <0.01). Amiodarone had a 33% drug failure rate, whereas there was a 91% drug failure rate for lidocaine. The 24-hour survival was 39% on amiodarone and 9% on lidocaine (p <0.01). Drug-related hypotension with aqueous amiodarone was less frequent than with lidocaine. This study found that amiodarone is more effective than lidocaine in the treatment of shock-resistant VT.

Wide QRS complex tachycardias

Wide QRS complex tachycardia is a common clinical occurrence and presents a diagnostic challenge for the physician. History, physical examination, chest radiographs, and electrocardiographic analysis are important in making the correct diagnosis. Diagnosis of ventricular tachycardia is supported by history of prior myocardial infarction or congestive heart failure, physical examination showing cannon A-waves in the jugular venous pulsation or variable heart sounds, chest radiograph showing cardiomegaly or evidence of prior cardiac surgery, and characteristic ECG features: AV dissociation, fusion/capture beats, QRS concordance or typical morphologic features in leads V1 and V6. In this article, a clinical approach to wide QRS complex tachycardias is presented.

Innovative pharmacologic approaches to cardiopulmonary resuscitation

The survival rate of patients undergoing cardiopulmonary resuscitation is 5 to 15%. New cardiopulmonary resuscitation treatment approaches under investigation include the use of vasopressin as a vasopressor, amiodarone for the treatment of ventricular tachyarrhythmias, and adenosine antagonists (i.e., theophylline) for bradyasystolic rhythms. More innovative approaches include the use of thyroid hormone and endothelin.

Intravenous amiodarone for ventricular arrhythmias: overview and clinical use

Numerous pharmacological agents with varying cellular electrophysiological effects are available to treat cardiac arrhythmias. Amiodarone is predominantly a Vaughan Williams Class III agent, but also possesses electrophysiological characteristics of the other three Vaughan Williams classes (Class I and IV and minor Class II effects). Amiodarone's primary mechanism is to prolong the cardiac action potential and repolarization time leading to an increased refractory period and reduced membrane excitability. The efficacy and tolerability of intravenous (IV) amiodarone for acute treatment of recurrent and refractory ventricular tachycardia and ventricular fibrillation has been demonstrated in clinical trials. The ARREST trial, a randomized trial comparing IV amiodarone to placebo, found a significant improvement in the proportion of patients surviving to the emergency department following out-of-hospital cardiac arrest in amiodarone-treated patients. Intravenous amiodarone is an effective anti-arrhythmic agent for the acute treatment of life-threatening ventricular arrhythmias and represents an important treatment option for emergency anti-arrhythmic therapy for patients suffering from cardiac arrest.

Clinical approach to wide QRS complex tachycardias

Wide QRS complex tachycardia is a frequently encountered arrhythmia in the emergency department and presents a diagnostic challenge to the emergency physician. The history, physical examination, chest radiograph, and electrocardiogram analysis are important in making the correct diagnosis. The diagnosis of ventricular tachycardia is supported by, 1) a history of prior myocardial infarction or congestive heart failure; 2) a physical examination showing cannon A-waves in the jugular venous pulsation or variable heart sounds; 3) a chest radiograph showing cardiomegaly or evidence of prior cardiac surgery; and 4) characteristic ECG features that include AV dissociation, fusion-capture beats, QRS concordance, or, typical morphologic features in leads V1 and V6. This article presents the diagnostic and therapeutic approaches to wide QRS tachycardias.

Cardiopulmonary resuscitation: a review for clinicians

Attempts at cardiopulmonary resuscitation (CPR) date from antiquity, but it is only in the last 50 years that a scientifically-based methodology has been developed. External chest compressions is the standard method for managing circulatory arrest, however, numerous alterations of this technique have been proposed in attempts to improve outcome from CPR. Defibrillation is the single most important therapy for the management of ventricular fibrillation or pulseless ventricular tachycardia. Adrenergic agents used to improve myocardial and cerebral perfusion are also the subject of considerable investigation with new agents entering clinical study. This paper reviews the history, current techniques and pharmacotherapy as well as controversial issues in the management of patients with cardiac arrest.

Intravenous amiodarone

Intravenous amiodarone was approved in 1995 for the treatment of malignant and resistant ventricular arrhythmia. Although it is an "old drug," much has been learned recently about this complex drug and its application in a variety of cardiac arrhythmias. The objectives of this review were to summarize what is known about intravenous amiodarone, including its pharmacologic and electrophysiologic effects, to review its efficacy for the treatment of patients with highly malignant ventricular arrhythmia and to provide specific information about its clinical use for this and other indications. The studies that were reviewed were selected on the basis of time published (from 1983 to 1995) and the completeness of information provided regarding patient clinical characteristics, drug dosing and methods of evaluation, efficacy analyses, long-term follow-up and complications. The full data from the three controlled trials that formed the basis of the drug's approval are contained in published reports that were also extensively reviewed. Intravenous amiodarone has demonstrable efficacy for the treatment of frequently recurrent destabilizing ventricular tachycardia and ventricular fibrillation, with suppression rates of 63% to 91% in uncontrolled trials. The three pivotal trials confirmed these findings and demonstrated a dose-response relation, with at least comparable efficacy to bretylium, a drug with a similar indication. The safety profile has also been well described; cardiovascular adverse effects are the most frequent, especially hypotension. Intravenous amiodarone is a useful addition to the drugs available for the treatment of patients with very severe ventricular arrhythmia. Its use in patients with other rhythm disorders appears promising, but final recommendations must await development of definitive data from ongoing clinical trials.

Pharmacokinetics of intravenous amiodarone in patients with impaired left ventricular function

To evaluate the potential need for modification of dose regimens of intravenous amiodarone in patients with left ventricular dysfunction, the pharmacokinetics of amiodarone and its active metabolite, desethylamiodarone (DEA), were examined after a single 15-minute intravenous infusion of amiodarone 5 mg/kg. Three parallel groups of otherwise healthy volunteers with normal (n = 12), moderately impaired (ejection fraction > 30 but < or = 45%; n = 6), or severely impaired (ejection fraction < or = 30%; n = 6) left ventricular function were enrolled in the study. Serial blood samples were obtained over a 76-day period for estimation of pharmacokinetic parameters. With the exception of the half-life (t1/2) of DEA, statistical comparisons revealed no significant between-group differences in pharmacokinetic parameters or correlations between pharmacokinetic parameters and ejection fractions. The t1/2 of DEA was increased by approximately 60% in patients with severe left ventricular dysfunction compared with that in patients with moderately impaired and normal left ventricular function. The rate of DEA formation is slow, however, and its concentration relative to amiodarone is low. Therefore, it is unlikely that concentrations of DEA in serum would reach levels that contribute significantly to the pharmacologic activity of amiodarone during short-term (up to 2 weeks) intravenous amiodarone therapy. Single doses of amiodarone were well tolerated. The results of this study suggest that intravenous amiodarone can be used with appropriate observation to control arrhythmias, regardless of the degree of left ventricular dysfunction.

Intravenous amiodarone: pharmacology, pharmacokinetics, and clinical use

OBJECTIVE

To review the clinical pharmacology, pharmacokinetics, and clinical efficacy and safety of intravenous amiodarone.

DATA IDENTIFICATION

Articles were identified through a computer search of the English-language literature using MEDLINE (KR Information OnDisc) and the search term amiodarone. Additional articles were identified through examination of the bibliographies of the articles initially retrieved.

STUDY SELECTION

Relevant or representative animal studies, clinical trials, and case reports were selected for evaluation. Particular emphasis was placed on studies pertaining to the use of intravenous amiodarone in treatment-refractory ventricular fibrillation (VF) and hemodynamically unstable ventricular tachycardia (VT).

DATA EXTRACTION

The literature was assessed for adequate description of patients, study methodologies (e.g., study design, number of patients), and outcomes.

DATA SYNTHESIS

Amiodarone is an unusual class III antiarrhythmic that produces each of the four main types of antiarrhythmic action in addition to other effects, such as vasodilatory, selective antithyroid, and other activities that may be therapeutically relevant. Amiodarone pharmacokinetics demonstrate extensive interpatient variability and are characterized by wide tissue distribution (steady-state volume of distribution 40-84 L/kg), slow total body clearance (90-158 mL/h/kg), long terminal elimination half-life (20-47 d), and extensive hepatic metabolism. The onset of maximal antiarrhythmic effect is a function of both amiodarone dosage and time. The high plasma concentrations achieved with intravenous dosing do not fully replicate the electrophysiologic effects observed following long-term oral administration, particularly with respect to class III activity. Available data suggest that intravenous amiodarone is associated with an efficacy rate of 50% or more in treatment-refractory VT/VF, and has a relatively rapid (2-24 h) onset of action. The drug is relatively well tolerated, but close hemodynamic, electrocardiographic, and hepatic function monitoring are required. The value of using amiodarone serum concentrations to guide therapy remains uncertain.

CONCLUSIONS

Intravenous amiodarone is an effective, relatively safe antiarrhythmic for the treatment of recurrent, hemodynamically unstable VT/VF refractory to other drug therapy in the acute care setting.

Randomized, double-blind comparison of intravenous amiodarone and bretylium in the treatment of patients with recurrent, hemodynamically destabilizing ventricular tachycardia or fibrillation. The Intravenous Amiodarone Multicenter Investigators Group

BACKGROUND

After several days of loading, oral amiodarone, a class III antiarrhythmic, is highly effective in controlling ventricular tachyarrhythmias; however, the delay in onset of activity is not acceptable in patients with immediately life-threatening arrhythmias. Therefore, an intravenous form of therapy is advantageous. This study was designed to compare the safety and efficacy of a high and a low dose of intravenous amiodarone with bretylium, the only approved class III antiarrhythmic agent.

METHODS AND RESULTS

A total of 302 patients with refractory, hemodynamically destabilizing ventricular tachycardia or ventricular fibrillation were enrolled in this double-blind trial at 82 medical centers in the United States. They were randomly assigned to therapy with intravenous bretylium (4.7 g) or intravenous amiodarone administered in a high dose (1.8 g) or a low dose (0.2 g). The primary analysis, arrhythmia event rate during the first 48 hours of therapy, showed comparable efficacy between the bretylium group and the high-dose (1000 mg/24 h) amiodarone group that was greater than that of the low-dose (125 mg/24 h) amiodarone group. Similar results were obtained in the secondary analyses of time to first event and the proportion of patients requiring supplemental infusions. Overall mortality in the 48-hour double-blind period was 13.6% and was not significantly different among the three treatment groups. Significantly more patients treated with bretylium had hypotension compared with the two amiodarone groups. More patients remained on the 1000-mg amiodarone regimen than on the other regimens.

CONCLUSIONS

Bretylium and amiodarone appear to have comparable efficacies for the treatment of highly malignant ventricular arrhythmias. Bretylium use, however, may be limited by a high incidence of hypotension.

Dose-ranging study of intravenous amiodarone in patients with life-threatening ventricular tachyarrhythmias. The Intravenous Amiodarone Multicenter Investigators Group

BACKGROUND

Oral amiodarone effectively suppresses ventricular arrhythmias; however, full activity may take days or weeks. In patients with frequent, life-threatening ventricular arrhythmias, this delay is not acceptable. Thus, in these patients, the speed and dosing accuracy of an intravenous formulation would be beneficial. The goal of this study was to demonstrate the efficacy of intravenous amiodarone in patients with refractory, recurrent hemodynamically destabilizing ventricular tachycardia or ventricular fibrillation by determining a dose response among three regimens.

METHODS AND RESULTS

A total of 342 patients were enrolled at 46 medical centers in the United States. Patients received one of three randomized, double-blind dose regimens delivering 125, 500, or 1000 mg during the first 24 hours. Supplemental infusions (150 mg) of intravenous amiodarone could be given to treat breakthrough ventricular arrhythmias. The key efficacy end points were the arrhythmia event rate, time to first arrhythmic event, and number of supplemental infusions administered. The event rate decreased with increasing doses: median values were 0.07, 0.04, and 0.02 events per hour for the 125-, 500-, and 1000-mg dose groups, respectively, representing a significant decrease from baseline event rates (P = .043), and approached significance in the overall test for trend (P = .067). There was a significant dose-related increase in the time to first event (trend test P = .025) and a significant dose-related decrease in the number of supplemental boluses per hour (trend test P = .043). Hypotension was the most common (26%) treatment-emergent adverse event during intravenous amiodarone therapy; there was no dose-response relationship. Seventy-eight percent of the patients survived to at least 48 hours.

CONCLUSIONS

Intravenous amiodarone is effective for the treatment of recurrent, life-threatening ventricular tachyarrhythmias.

Parenteral magnesium sulfate versus amiodarone in the therapy of atrial tachyarrhythmias: a prospective, randomized study

OBJECTIVE

To compare the efficacy of parenteral magnesium sulfate vs. amiodarone in the therapy of atrial tachyarrhythmias in critically ill patients.

DESIGN

Prospective, randomized study.

SETTING

Multidisciplinary intensive care unit (ICU) at a university teaching hospital.

PATIENTS

Forty-two patients, 21 medical and 21 surgical, of mean (SD) age 67 +/- 15 yrs and mean Acute Physiology and Chronic Health Evaluation II score of 22 +/- 6, with atrial tachyarrhythmias (ventricular response rate of > or = 120 beats/min) sustained for > or = 1 hr.

INTERVENTIONS

After correction of the plasma potassium concentration to > or = 4.0 mmol/L, patients were randomly allocated to treatment with either a) magnesium sulfate 0.037 g/kg (37 mg/kg) bolus followed by 0.025 g/kg/hr (25 mg/kg/hr); or b) amiodarone 5 mg/kg bolus and 10 mg/kg/24-hr infusion. Therapeutic plasma magnesium concentration in the magnesium sulfate group was 1.4 to 2.0 mmol/L. Therapeutic end point was conversion to sinus rhythm over 24 hrs.

MEASUREMENTS AND MAIN RESULTS

At study entry (time 0), initial mean ventricular response rate and systolic blood pressure were 151 +/- 16 (SD) beats/min and 127 +/- 30 mm Hg in the magnesium sulfate group vs. 153 +/- 23 beats/min and 123 +/- 23 mm Hg in the amiodarone group, respectively (p = .8 and .65). Plasma magnesium (time 0) was 0.84 +/- 0.20 vs. 1.02 +/- 0.22 mmol/L in the magnesium and amiodarone group, respectively (p = .1). Eight patients had chronic dysrhythmias (magnesium 3, amiodarone 5). Excluding the two patient deaths (amiodarone group, time 0 + 12 to 24 hrs), no significant change in systolic blood pressure subsequently occurred in either group. In the magnesium group, mean plasma magnesium concentrations were 1.48 +/- 0.36, 1.82 +/- 0.41, 2.16 +/- 0.45, and 1.92 +/- 0.49 mmol/L at time 0 + 1, 4, 12 and 24 hrs, respectively. By logistic regression, the probability of conversion to sinus rhythm was significantly better for magnesium than for amiodarone at time 0 + 4 (0.6 vs. 0.44), 12 (0.72 vs. 0.5), and 24 (0.78 vs. 0.5) hrs. In patients not converting to sinus rhythm, a significant decrease in ventricular response rate occurred at time 0 + to 0.5 hrs (mean decrease 19 beats/min, p = .0001), but there was no specific treatment effect between the magnesium and the amiodarone groups; thereafter, there was no significant reduction in ventricular response rate over time in either group.

CONCLUSIONS

Intravenous magnesium sulfate is superior to amiodarone in the conversion of acute atrial tachyarrhythmias, while initial slowing of ventricular response rate in nonconverters appears equally efficacious with both agents.

Parenteral antiarrhythmic drug therapy in ventricular tachycardia/ventricular fibrillation: evolving role of class III agents--focus on amiodarone

More effective intravenous antiarrhythmic agents are required for treatment of patients with refractory malignant ventricular arrhythmias. More recently, a great deal of interest has been focused on use of intravenous amiodarone for these patients. Uncontrolled early studies showed that intravenous amiodarone was effective in 42% to 81% of treated patients. Recent large cooperative trials have documented the efficacy of intravenous amiodarone in these patients and have shown an efficacy comparable to bretylium in patients with refractory sustained ventricular tachycardia or fibrillation.

Sympatholytic action of intravenous amiodarone in the rat heart

BACKGROUND

Amiodarone is a commonly used antiarrhythmic agent with complex pharmacological effects. Although ventricular arrhythmias can be suppressed soon after intravenous amiodarone, the mechanisms responsible for this action are unclear. We studied the effects of acute treatment with amiodarone on the metabolism and release of norepinephrine (NE) in intact rats and in perfused rat hearts.

METHODS AND RESULTS

Experiments were performed in anesthetized rats and in perfused, innervated hearts with amiodarone administered intravascularly. NE release was induced by electrical stimulation of the sympathetic ganglion. Concentrations of NE and its intraneuronal metabolite dihydroxyphenylglycol (DHPG) in hearts, plasma, and coronary venous effluent were measured by high-performance liquid chromatography. Acute administration of amiodarone induced dose-dependent increases in DHPG concentrations in plasma (5 mg/kg, +48%; 15 mg/kg, +84%; and 50 mg/kg, +467%) and in coronary venous effluent (1 mumol/L, +37%; 3 mumol/L, +510%; and 10 mumol/L, +1100%) together with an unchanged basal overflow of NE. In perfused hearts, NE release evoked by nerve stimulation was inhibited by infusion of amiodarone (1 mumol/L, -16%; 3 mumol/L, -24%; and 10 mumol/L, -64%) or by intravenous amiodarone (50 mg/kg) given 1 hour before heart perfusion (-70%), and the extent of this suppression correlated well with levels of DHPG overflow present immediately before nerve stimulation. When given in vitro and in vivo, amiodarone also significantly reduced NE and increased DHPG content in the heart, leading to a raised DHPG/NE ratio. All these effects of amiodarone were similar to those found with reserpine but less potent. In contrast, oral amiodarone produced none of these effects.

CONCLUSIONS

Acute administration of amiodarone in perfused hearts or intact rats induces partial NE depletion in the heart by interfering with vesicular NE storage and enhancing intraneuronal NE metabolism, effects associated with an impaired NE release during sympathetic activation. Oral dosing with amiodarone has no such effect. Further study is required to test whether this novel sympatholytic effect of amiodarone contributes to its antiarrhythmic action after intravenous administration.

Oral amiodarone loading for the rapid treatment of frequent, refractory, sustained ventricular arrhythmias associated with coronary artery disease

To evaluate the efficacy and safety of oral amiodarone in the treatment of recurrent, sustained, refractory ventricular arrhythmias, rapid high-dose oral loading was used to treat 12 critically ill patients with frequent, sometimes incessant, sustained ventricular arrhythmias refractory to 2 to 6 antiarrhythmic agents. Presenting arrhythmias included sustained monomorphic ventricular tachycardia and ventricular fibrillation associated with cardiac arrests in 6 patients. Patients experienced 2 to 10 episodes (mean 5 +/- 2) of sustained ventricular arrhythmias over a mean period of 6.2 +/- 5.0 days (range 1 to 14) before oral amiodarone was initiated at 1,200 to 1,400 mg/day. This included at least 1 to 4 episodes (mean 2.2 +/- 1.1) within 24 hours before amiodarone. One to 4 antiarrhythmic drugs were administered concurrently during amiodarone loading. Sustained ventricular arrhythmias no longer occurred after a mean of 5.2 days (range 1 to 22) with amiodarone. Arrhythmias were controlled in 4 patients within 24 hours, 5 patients within 48 hours, 7 patients within 4 days and 10 patients within 6 days. Patients experienced a mean of 0.6 +/- 0.8 episodes within 24 hours after amiodarone. Nine patients survived to hospital discharge. No patient had significant adverse effects during high-dose loading. In conclusion, high-dose oral amiodarone loading, when added to previously unsuccessful conventional antiarrhythmic therapy, is safe and often rapidly effective for at least short-term control of frequent, refractory, sustained ventricular arrhythmias.

Classification of death in patients under antiarrhythmic treatment

In the evaluation of antiarrhythmic treatment, total mortality and total cardiac mortality are the only endpoints difficult to misclassify. End-stage cardiac failure competes with "suddenness" in many instances of sudden arrhythmic death. This observational study reports on 23 deaths in a group of 129 patients under antiarrhythmic treatment. In the 21 cases of cardiac death, with respect to the notion "sudden arrhythmic death," classification was problematic in 6 patients. According to different interpretations, the number of deaths listed as "sudden" could vary between one and six. A concise description of cause and circumstances of death, is presented.

Prospective, randomized comparison of conventional and high dose loading regimens of amiodarone in the treatment of ventricular tachycardia

OBJECTIVES

The purpose of this prospective randomized study was to compare the electrophysiologic effects of conventional and high dose loading regimens of amiodarone in patients with sustained ventricular tachycardia.

BACKGROUND

Uncontrolled studies in which patients have been treated with an oral loading dose of 2 to 4 g/day of amiodarone have suggested that, compared with a conventional loading dose, this dosing regimen results in more rapid control of spontaneous ventricular tachycardia and ventricular tachycardia induced by programmed stimulation.

METHODS

Patients in whom sustained monomorphic ventricular tachycardia was inducible by programmed stimulation and who were refractory to class I antiarrhythmic medications were randomly assigned to receive either a conventional (n = 15) or a high (n = 17) loading dose of amiodarone. The conventional dose consisted of 600 mg twice a day for 10 days. The high dose regimen consisted of 50 mg/kg body weight per day on days 1 to 3, 30 mg/kg per day on days 4 and 5 and 600 mg twice a day on days 6 to 10. An electrophysiologic test was performed in the baseline state and after 3 and 10 days of therapy. An adequate response to amiodarone was defined as the inability to induce ventricular tachycardia or the ability to induce only relatively slow (cycle length > or = 350 ms) hemodynamically stable ventricular tachycardia.

RESULTS

After 3 days of therapy, 2 of 14 patients who received the conventional loading dose and 6 of 15 patients who received the high dose loading regimen had an adequate response to amiodarone (p = 0.08). After 10 days of therapy, four patients in each group had an adequate response to amiodarone (p = NS). Three patients who received the high dose and one patient who received the conventional dose of amiodarone had an adequate response after 3 days of therapy but not after 10 days of therapy. There were significant increases in the sinus cycle length, atrioventricular block cycle length, ventricular effective refractory period and ventricular tachycardia cycle length after 3 and 10 days of therapy compared with baseline values regardless of the dosing regimen. The extent of the effects of amiodarone on these variables after 3 and 10 days of therapy was similar with both dosing regimens.

CONCLUSIONS

The therapeutic and electrophysiologic effects of conventional and high dose loading regimens of amiodarone do not differ significantly after 3 or 10 days of therapy. High oral loading doses of amiodarone do not offer any significant clinical advantage over a conventional loading dose of amiodarone for controlling ventricular tachycardia induced by programmed stimulation.

Electrophysiologic testing in patients who respond acutely to intravenous amiodarone for incessant ventricular tachyarrhythmias

The outcome of patients who receive intravenous amiodarone for suppression of incessant ventricular tachyarrhythmia has not been studied conclusively. We conducted a prospective study in which all patients who responded acutely to intravenous amiodarone and went on to receive a subsequent oral loading dose were subjected to electrophysiologic testing before hospital discharge to determine whether additional or alternative therapy would be required. Among 18 patients (17 with ischemic heart disease) who entered the protocol, 16 had a clinical response to intravenous amiodarone alone (12 patients) or in combination with another antiarrhythmic drug (4 patients) and survived to study. Of these, 10 had monomorphic ventricular tachycardia (VT) when first seen, five had polymorphous VT or ventricular fibrillation (VF), and three had both. In seven patients sustained monomorphic VT was inducible (group 1), and in nine it was not (group 2). The only clinical factor that distinguished group 1 from group 2 was age (group 1 > group 2). Five patients in group 1 and one in group 2 received an implantable cardioverter defibrillator; one patient in group 1 had a successful endocardial resection. During a mean follow-up period of 11 months, four patients in group 1 have had appropriate implantable cardioverter defibrillator discharges, whereas only one patient in group 2 has had a clinical event (sudden death). We conclude that intravenous amiodarone is a highly effective drug used alone or in combination to suppress spontaneous incessant VT/VF. Predischarge electrophysiologic testing, even in patients who have polymorphous VT, has predictive value over and above the observed clinical response. These preliminary results favor predischarge testing and aggressive device treatment in this cohort.

The use of antiarrhythmics in advanced cardiac life support

Antiarrhythmic agents have been used to treat malignant ventricular arrhythmias in the setting of acute myocardial ischemia with proven efficacy for many years. Thus, it has been presumed that these agents would be efficacious for the treatment of cardiac arrest. Unfortunately, hard data supporting this contention are unavailable to date. Furthermore, some of the experimental data in this area are conflicting, especially regarding the relative effects of lidocaine and bretylium. Thus, little definitive can be said based on experimental information. In two randomized patient studies, lidocaine and bretylium performed comparably. Because of the frequent use of lidocaine and thus the familiarity of most health care professionals with its use, it makes educational sense to utilize lidocaine as the antiarrhythmic drug of first choice during the cardiac arrest sequence. Recent data suggesting that amiodarone may be efficacious in patients with recurrent arrhythmias require additional confirmation. Although antiarrhythmic agents have been shown to be effective in the treatment of malignant arrhythmias in patients with acute myocardial infarction, their use prophylactically for patients with suspected infarction (advocated in the past) has recently undergone reevaluation. It is now clear that despite a reduction in ventricular fibrillation, overall mortality may be increased. This may be because the prophylactic treatment of patients with suspected infarction includes a large number of patients not at risk for ventricular fibrillation who still may be at risk for drug toxicity. Thus, prophylactic administration of lidocaine to all patients with suspected acute myocardial infarction can no longer be recommended. There are inadequate data upon which to base a recommendation concerning the use of lidocaine in patients receiving thrombolytic therapy. The group most likely to benefit from lidocaine are patients with ST segment elevation who present early after the onset of acute myocardial infarction. The use of lidocaine in this group requires additional study. At present, despite enthusiasm for the prophylactic use of magnesium for the treatment of arrhythmias, data are inadequate to support its routine administration. However, given the importance of magnesium and potassium levels in the genesis of malignant arrhythmias, their levels in plasma should be assessed, and abnormalities should be promptly corrected. The potential uses of antiarrhythmic agents during advanced cardiac life support span a remarkably diverse number of applications. For the purpose of this review, only the use of these agents during CPR and during the early hours of acute or suspected acute myocardial infarction will be considered.

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.

Intravenous amiodarone for short-term treatment of refractory ventricular tachycardia or fibrillation

Intravenous amiodarone was administered to 22 patients with recurrent ventricular tachycardia failing an average of 3.0 prior antiarrhythmic agents after a mean of 14.6 cardioversions per patient. Patients received a mean bolus of 239 mg amiodarone, and a constant infusion of 0.5 to 1.0 mg/ml was administered over a mean of 50.7 hours. Hypotension requiring pressor agents was seen in nine patients and temporary pacing was needed in five patients. In the hospital, arrhythmic deaths occurred in two (9%) patients and nonarrhythmic deaths occurred in six (27%) patients. There were three late sudden deaths and three additional patients with appropriate automatic defibrillator discharges in follow-up. Intravenous amiodarone is very effective in preventing arrhythmic deaths in patients with refractory ventricular tachycardia and fibrillation.

Electrocardiographic and antiarrhythmic effects of intravenous amiodarone: results of a prospective, placebo-controlled study

The antiarrhythmic efficacy of intravenously administered amiodarone was examined in a prospective, randomized, placebo-controlled study that involved 77 patients after coronary artery bypass surgery. Amiodarone was given after surgery in a loading bolus of 300 mg for 2 hours followed by 1200 mg every 24 hours for 2 days and 900 mg every 24 hours for the next 2 days. Amiodarone suppressed both supraventricular and ventricular arrhythmias within 12 hours after the start of therapy. Particularly, the incidence of atrial fibrillation (5% vs 21% in the control group; p less than 0.05) and of nonsustained ventricular tachycardia (3% vs 16%; p less than 0.05) was reduced by amiodarone. Heart rate was slowed (p less than 0.001) and repolarization--as judged by JTc interval--was prolonged compared with the control group (p less than 0.01). In two patients, amiodarone infusion was stopped because of excessive QTc prolongation. No detrimental hemodynamic effects of the drug were observed. Thus the intravenous administration of amiodarone appears to be suitable for patients in whom rapid suppression of symptomatic supraventricular and ventricular arrhythmias is warranted in the presence of left ventricular dysfunction.

Efficacy and tolerance of high-dose intravenous amiodarone for recurrent, refractory ventricular tachycardia

High-dose intravenous amiodarone was given to 35 patients with recurrent life-threatening ventricular tachycardia (VT) refractory to conventional antiarrhythmic agents. Intravenous amiodarone was given as a 5 mg/kg dose over 30 minutes followed by 20 to 30 mg/kg/day as a constant infusion for 5 days. Twenty-two (63%) patients responded to intravenous amiodarone. All 22 responders received oral amiodarone. Thirteen (59%) continue to receive oral amiodarone after an average follow-up of 19 months, 4 (18%) had sudden cardiac death on oral amiodarone, 2 (9%) died while receiving amiodarone, secondary to left ventricular failure, and 3 (14%) discontinued amiodarone because of side effects. Of the 13 (37%) nonresponders, 10 died in the hospital while receiving intravenous amiodarone, secondary to lethal arrhythmia. Three nonresponders were discharged from the hospital; 2 with automatic cardioverter/defibrillators and 1 receiving a combination of antiarrhythmic agents. Serious adverse events occurred in 13 (37%) patients during intravenous amiodarone therapy. These included hypotension in 8 patients, symptomatic bradycardia in 4 patients and sinus arrest with bradycardia and hypotension in 1 patient. Minor side effects occurred in 23 (66%) patients. In conclusion, high dose intravenous amiodarone is effective in most patients with recurrent, sustained VT but is associated with an unacceptably high incidence of serious adverse events. The optimal dose and duration of intravenous amiodarone for patients with recurrent, refractory sustained VT remain unknown.