Combination antiarrhythmic therapy for management of malignant ventricular arrhythmia

Mexiletine overdose producing status epilepticus without cardiovascular abnormalities

Few cases of mexiletine overdose have been reported in the literature. The available case reports have invariably noted significant hemodynamic or electrocardiographic abnormalities. A 41-year-old woman, on mexiletine for arrhythmia control, ingested up to 90 of her 200 mg mexiletine tablets in a suicide attempt. She presented to the emergency department awake with a normal blood pressure and pulse. Shortly afterwards, the patient had a generalized motor seizure, which responded after 40 minutes to intravenous diazepam 100 mg, phenobarbital 1 g and pyridoxine 5 g. Recurrent status epilepticus at one hour required an additional 40 mg of diazepam and a loading dose of pentobarbital. During the entire episode, her electrocardiogram remained normal. The patient's mexiletine level was 20 micrograms/mL (therapeutic 1-2 micrograms/mL) and the patient's urine screen was negative for cocaine. Mexiletine is a group Ib antidysrhythmic agent with electrophysiologic effects similar to lidocaine. Mexiletine has a little first pass hepatic metabolism and a large volume of distribution along with a high lipid solubility, and prolonged central nervous system toxicity may be expected. As with lidocaine, the toxic deaths from mexiletine have resulted from hypotension and bradycardia. The patient reported had a significant mexiletine overdose which resulted in convulsive status epilepticus, but was devoid of hemodynamic or electrocardiographic abnormalities.

Efficacy of antiarrhythmic drugs in patients with arrhythmogenic right ventricular disease. Results in patients with inducible and noninducible ventricular tachycardia

BACKGROUND

Ventricular tachyarrhythmias are the major clinical manifestation of arrhythmogenic right ventricular disease. Although antiarrhythmic therapy has been widely advocated, there is only limited information available on the efficacy of antiarrhythmic drugs in these patients.

METHODS AND RESULTS

The short- and long-term efficacies of various antiarrhythmic agents were retrospectively and prospectively analyzed in 81 patients (mean age, 39 +/- 14 years; range, 16-68 years; 61.7% males) with arrhythmogenic right ventricular disease. In 42 patients with inducible ventricular tachycardia during programmed ventricular stimulation, the following efficacy rates were obtained: class Ia and Ib drugs (n = 18), 5.6%; class Ic drugs (n = 25), 12%; beta-blockers (n = 8), 0%; sotalol (n = 38), 68.4%; amiodarone (n = 13), 15.4%; verapamil (n = 5), 0%; and drug combinations (n = 26), 15.4%. Only one of the 10 patients not responding to sotalol was treated effectively by amiodarone, whereas the remaining nine patients proved to be drug refractory toward all other drugs tested (3.8 +/- 2.3 drugs, including amiodarone in five cases) and underwent nonpharmacological therapy. During a follow-up of 34 +/- 25 months, three of the 31 patients (9.7%) discharged on pharmacological therapy had nonfatal recurrences of ventricular tachycardia after 0.5, 51, and 63 months, respectively. In 39 patients with noninducible ventricular tachycardia during programmed ventricular stimulation, the following efficacy rates were observed: class Ia and Ib drugs (n = 16), 0%; class Ic agents (n = 23), 17.4%; beta-blockers (n = 7), 28.6%; sotalol (n = 35), 82.8%; amiodarone (n = 4), 25%; verapamil (n = 24), 50%; and drug combinations (n = 11), 9.1%. During a follow-up of 14 +/- 13 months, four of 33 patients (12.1%) discharged on antiarrhythmic drugs had nonfatal relapses of their clinical ventricular arrhythmia.

CONCLUSIONS

Thus, in arrhythmogenic right ventricular disease, sotalol proved to be highly effective in patients with inducible as well as noninducible ventricular tachycardia. Patients with inducible ventricular tachycardia not responding to sotalol are likely to not respond to other antiarrhythmic drugs and should be considered for nonpharmacological therapy without further drug testing. Amiodarone did not prove to be more effective than sotalol and may not be an alternative because of frequent side effects during long-term therapy, especially in young patients. Verapamil and beta-blockers were effective in a considerable number of patients with noninducible ventricular tachycardia and may be a therapeutic alternative in this subgroup. Class I agents appear to be rarely effective in the treatment of both inducible and noninducible ventricular tachycardia in arrhythmogenic right ventricular disease.

Effect of the combination of low-dose mexiletine and metoprolol on ventricular arrhythmia

Antiarrhythmic drug therapy is often ineffective or poorly tolerated. Combining antiarrhythmic agents with different electrophysiologic properties may have a synergistic antiarrhythmic effect when compared with each drug alone. If a lower dose of each drug can be used, combination therapy may also result in lower incidence of side effects. The goal of our study was to assess the complementary effect of low-dose mexiletine and metoprolol, when compared with either drug alone. Ten patients with frequent ventricular arrhythmias including 7 patients with nonsustained ventricular tachycardia were evaluated in an open-label sequential study. The response to drug therapy was evaluated by 24-h continuous EKG monitoring, exercise stress testing, and echocardiogram after each treatment. Combination therapy effectively reduced ventricular arrhythmias in 8 patients (80%) in contrast to only 1 patient (10%) on metoprolol alone and 4 patients (40%) on mexiletine alone. In 5 patients (71%) ventricular tachycardia was abolished. The number of couplets was reduced from 51 +/- 39 to 1.9 +/- 2.4 (p less than 0.01) and total premature ventricular beats from 7790 +/- 9047 to 597 +/- 515 (p = 0.06). Combination therapy was well tolerated without proarrhythmia or precipitation of congestive heart failure. It is concluded that low-dose mexiletine combined with metoprolol is effective in suppressing ventricular arrhythmias in selected patients, and enhances the antiarrhythmic effect of either drug alone without significant side effects.

Combination of flecainide and mexiletine for the treatment of ventricular tachyarrhythmias

A combination of oral flecainide and mexiletine was given to 11 patients in whom monotherapy with one of these drugs was ineffective for the suppression of inducible ventricular tachycardia or fibrillation. In eight of 11 studies, combination therapy prevented inducibility of a sustained ventricular tachycardia or resulted in induction of only nonsustained tachycardia (P = 0.0003, when compared to monotherapy). In one patient, a slow ventricular tachycardia was induced. During exercise testing ventricular tachycardia occurred in two of these nine patients, and ventricular fibrillation in another patient. Seven patients received combination on the long term, for a mean of 18 months. One patient had recurrences of ventricular tachycardia which was well tolerated. Another patient had a recurrent episode of ventricular fibrillation, but was successfully resuscitated. Severe congestive heart failure occurred in two patients. ACE inhibitors were given to them and to another four patients. No other important unwanted effects occurred. The combination of mexiletine and flecainide is very effective in suppressing inducible sustained ventricular tachycardia. The efficacy of this combination to prevent recurrences of ventricular tachyarrhythmias is acceptable. Exercise testing is of importance to unmask proarrhythmic effects before discharge from hospital.

Mexiletine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in the treatment of arrhythmias

As a member of the class Ib antiarrhythmic drugs mexiletine's primary mechanism of action is blocking fast sodium channels, reducing the phase 0 maximal upstroke velocity of the action potential. It increases the ratio of effective refractory period to action potential duration, but has little effect on conductivity. Unlike quinidine it does not prolong QRS and QT (QTc) intervals. In the dosage range 600 to 900 mg daily mexiletine effectively suppresses premature ventricular contractions (PVCs) in 25% to 79% of patients, with or without underlying cardiac disease. In comparative studies the response rate was comparable to that with quinidine or disopyramide. However, the use of antiarrhythmic therapy in patients with asymptomatic arrhythmias is controversial. More importantly, mexiletine abolishes spontaneous or inducible ventricular tachycardia or fibrillation in the short term in 20% to 50% of patients with refractory arrhythmias. Arrhythmia suppression is maintained in 57% to over 80% of these early therapeutic successes in the long term, with mexiletine alone or in combination with another antiarrhythmic drug. As with other antiarrhythmic drugs, there is no substantial evidence that administration of mexiletine after acute myocardial infarction improves long term prognosis. Although the incidence of adverse effects associated with mexiletine is high, the majority are minor gastrointestinal or neurological effects which can be adequately controlled through dosage adjustment. Furthermore, mexiletine has minimal effects on haemodynamic variables, or on cardiac function in patients with or without pre-existing deterioration of left ventricular function, and it appears to have a low proarrhythmic potential. Thus, while the therapeutic efficacy of mexiletine for the prevention or suppression of symptomatic ventricular arrhythmias may be no greater than that of other antiarrhythmic drugs, and less than that of some (e.g. amiodarone), it is effective in a significant proportion of patients refractory to other treatments and can be administered without causing adverse haemodynamic effects to patients with complicating factors such as acute myocardial infarction or congestive heart failure.