Oral mexiletine in the treatment of refractory ventricular arrhythmias: the role of electrophysiologic techniques

Anti-arrhythmic drug therapy in implantable cardioverter-defibrillator recipients

Implantable cardioverter-defibrillators (ICDs) have revolutionized the primary and secondary prevention of patients with ventricular arrhythmias. However, the adverse effects of appropriate or inappropriate shocks may require the adjunctive use of anti-arrhythmic drugs (AADs). Beta blockers are the cornerstone of pharmacological primary and secondary prevention of ventricular arrhythmias. In addition to their established efficacy at reducing the incidence of ventricular arrhythmias, beta-blockers are safe with few side effects. Amiodarone is superior to beta blockers and sotalol for the prevention of ventricular arrhythmia recurrence. However, long-term amiodarone use is associated with significant side effects that limit its utility. Sotalol and mexiletine are the main alternatives to amiodarone with a better side effect profile though they are less efficacious at preventing ventricular arrhythmia recurrence. Dofetilide, azimilide and ranolazine are emerging as therapeutic options for secondary prevention; more studies are needed to assess efficacy and safety in comparison to currently used agents. Beta blockers and amiodarone are the mainstay of therapy in patients experiencing electrical storm; their use reduces the frequency of ventricular arrhythmias and ICD intervention as well as affording time until catheter ablation can be considered.

Efficacy of class 1C antiarrhythmic agents in patients with inducible ventricular tachycardia refractory to therapy with class 1A antiarrhythmic drugs

The efficacy of class 1C antiarrhythmic agents was determined in 36 patients with inducible sustained monomorphic ventricular tachycardia during baseline electrophysiology study (EPS), who continued to have inducible monomorphic ventricular tachycardia during EPS on class 1A antiarrhythmic therapy. Of 12 patients who partially responded to class 1A drugs, 11 (91.7%) continued to have a partial response during EPS on class 1C therapy, whereas one patient did not respond. Of 24 nonresponders to class 1A therapy, 2 (8.3%) responded during EPS on class 1C therapy, 7 (29.2%) partially responded, and 15 (62.5%) did not respond. In the 24 nonresponders to class 1A therapy, 9 of 17 patients (53%) with left ventricular ejection fraction (EF) > or = 30% responded or partially responded to class 1C therapy, compared with none of 7 patients with EF < 30% (P < .05). The EPS on class 1C agents in patients who fail to respond to class 1A therapy may be warranted only in those with EF > or = 30%.

Role of combination drug therapy with a class IC antiarrhythmic agent and mexiletine for ventricular tachycardia

The combination of mexiletine and a class IC antiarrhythmic agent (encainide, propafenone or flecainide) was evaluated by electrophysiologic testing in 14 patients with a history of sustained ventricular tachycardia whose tachycardia remained inducible during therapy with the class IC drug alone. During the control drug-free state, all patients had inducible ventricular tachycardia, with a mean cycle length of 260 ms (range 190 to 400). During monotherapy with the IC agent the tachycardia remained inducible in each patient, but there was a significant increase in the cycle length to 340 ms (240 to 500) (p less than 0.001). The effective refractory period of the ventricle was not altered. Treatment with mexiletine (oral in 13 and intravenous in 1) was begun and electrophysiologic testing was repeated. Ventricular tachycardia in one patient was rendered noninducible and one patient had arrhythmia aggravation. The tachycardia in the remaining 12 patients remained inducible but its average cycle length increased further to 392 ms (340 to 460) (p = NS). Nine patients had rate slowing and the average cycle length of the ventricular tachycardia in this group was significantly increased (302 to 388 ms, p less than 0.05). The average effective refractory period was significantly increased during combination therapy (267 ms) compared with no drug therapy (235 ms) and therapy with the class IC drug alone (247 ms) (p less than 0.05). After a mean follow-up interval of 22 months, seven patients continue on the combined treatment and have no ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of combination therapy with mexiletine and procainamide in patients with inducible sustained ventricular tachycardia refractory to intravenous procainamide

This study evaluated the role of serial electropharmacological testing on combination therapy with mexiletine and procainamide in 20 patients with inducible sustained ventricular tachycardia (VT) refractory to intravenous procainamide. The clinical arrhythmias were cardiac arrest in five patients, sustained VT in 11 patients, and recurrent syncope of presumably arrhythmic origin in four patients. The mean left ventricular ejection fraction (LVEF) was 0.40 +/- 0.12 (mean +/- SD). All patients had inducible sustained VT at baseline and after administration of intravenous procainamide. All 20 patients underwent electropharmacological testing on combination therapy with mexiletine and procainamide. The mean cycle length of inducible sustained VT was 251 +/- 48 ms at baseline, 324 +/- 81 ms on intravenous procainamide (P less than 0.014 vs baseline), and 365 +/- 82 ms on combination therapy (P less than 0.0001 vs baseline, P = NS vs intravenous procainamide). Combination therapy did not suppress VT inducibility, nor did it make VT more difficult to induce in 19 of 20 patients. The remaining one patient had a partial response (runs of nonsustained VT, longest 10 seconds). Furthermore, combination therapy did not significantly prolong the VT cycle length over and above that observed during testing with intravenous procainamide. Therefore, in patients with inducible sustained VT refractory to procainamide during initial electropharmacological testing, mexiletine in combination with procainamide appears to be of little or no value and serial electropharmacological testing on these drugs is of limited usefulness. Early initiation of alternative therapy may be the preferred clinical option.

Mexiletine versus quinidine as first-line antiarrhythmia therapy: results from consecutive trials

The efficacy of mexiletine and quinidine in controlling ventricular couplets (VC) and ventricular tachycardia (VT) was compared in 156 trials (78 for each drug) in 114 consecutive patients. Forty-two patients received both drugs, whereas 36 patients were given mexiletine, and 36 patients received quinidine only. During acute drug testing, mexiletine was more effective than quinidine in controlling VC and VT (54 vs. 32 patients, respectively, P less than .001) and resulted in fewer proarrhythmic events (4 vs. 13, respectively, P less than .05). Mean duration of follow-up for mexiletine (27 +/- 14 mo) and quinidine (21 +/- 14 mo) did not differ. Long-term success was more frequent with mexiletine administration than quinidine administration (33/47 vs. 10/30 patients, respectively, P less than .01). The incidence of sudden death during follow-up with the two drugs did not differ overall, but more patients with ejection fraction greater than or equal to 40% died suddenly while taking quinidine than while receiving mexiletine (4/17 vs. 0/24, P less than .02). Mexiletine is as effective as quinidine for treating VC and VT and appears to be less proarrhythmic. It should be considered as an initial choice in the management of VC and VT.

Treatment of ventricular tachycardia induced cardiogenic shock by percoronary chemical ablation

Incessant ventricular arrhythmias pose an especially challenging therapeutic dilemma. We describe the successful treatment and follow-up of a patient with refractory ventricular tachycardia-induced cardiogenic shock with percoronary chemical ablation. After endocardial mapping was used to identify the "tachycardia-related" coronary artery, temporary termination of the arrhythmia with balloon occlusion and subselective intracoronary installation of iced saline as previously advocated was unsuccessful. This was probably due to a dual arterial blood supply to the arrhythmogenic focus. However, infusion of 2 cc ethanol (99%) permanently terminated the arrhythmia. Contrary to previous experience, ethanol-induced arrhythmia termination did not result in arterial occlusion, further supporting a direct toxic effect on the myocardium as its mode of action. Use of standard angioplasty balloon inflation prevents "backwash" of distally infused ethanol and more generalized cell death. The only complication of this procedure was temporary third-degree AV block, requiring permanent pacemaker implantation.

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.

Mexiletine: pharmacology and therapeutic use

Mexiletine is a Class IB antiarrhythmic which has basic and clinical electrophysiologic properties similar to lidocaine. Like other Class I antiarrhythmic agents, mexiletine blocks the rapid inward sodium current responsible for phase 0 of the action potential. It has been noted in the clinical electrophysiology laboratory to have minimal effect on sinus node function and AV nodal and His-Purkinje system conduction. Pharmacokinetic studies have shown that oral absorption is rapid with bioavailability of 80-90%. Mexiletine is predominantly metabolized by the liver with elimination half-life of 9 to 12 hours. The antiarrhythmic effects of the primary drug's metabolites remain to be defined. Hemodynamic studies have shown mexiletine to have a lesser negative inotropic effect than procainamide or disopyramide. Although mexiletine as a single agent successfully suppresses 60 to 80% of spontaneous ventricular arrhythmias, it has lower efficacy in suppression of induced ventricular arrhythmias. Multiple studies have shown that as monotherapy mexiletine is effective in preventing the induction of ventricular tachycardia in approximately 20% of patients. When used in combination with a Class IA antiarrhythmic drug for suppression of induced ventricular arrhythmias, multiple investigators have reported greater efficacy. Neurological side effects (tremor, dizziness, memory loss) occur in approximately 10% of patients while gastrointestinal side effects (nausea, anorexia, gastric irritation) occur in up to 40% of patients. Proarrhythmia or other serious toxicity from the drug is uncommon.

Electrophysiologic evaluation of antiarrhythmic therapy for ventricular tachyarrhythmias

The use of electrophysiologic studies has contributed significantly to our understanding of the mechanisms of ventricular tachyarrhythmias and enhanced our ability to assess objectively the efficacy of various therapeutic interventions in modifying or preventing their recurrence. The basis on which electrophysiologic testing techniques is founded is the ability reproducibility to initiate ventricular arrhythmias by programmed electrical stimulation in patients with a history of recurrent ventricular tachycardia or fibrillation. Ventricular tachycardia can be initiated by electrophysiologic studies in approximately 90% of patients with clinically documented recurrent, sustained ventricular tachycardia related to coronary artery disease and in 60% of patients with nonsustained ventricular tachycardia. Reports indicate that electrophysiologic testing is highly specific as well (99% for sustained monomorphic ventricular tachycardia). Studies in patients with recurrent ventricular tachycardia demonstrate that prevention by antiarrhythmic drugs of the ability to initiate tachycardias that were previously inducible by comparable stimulation techniques in the absence of therapy is highly predictive of freedom from recurrent episodes of spontaneous ventricular tachycardia and ventricular fibrillation. This end point can be achieved in 35 to 75% of patients. This wide range of success rates results from differences in the patient populations studied, as well as major differences in the programmed stimulation and antiarrhythmic drug protocols used among laboratories. The positive predictive value of this technique (defined as the percentage of patients in whom complete suppression of inducible ventricular tachycardia or ventricular fibrillation is achieved during electrophysiologic testing with antiarrhythmic drugs and in whom no spontaneous arrhythmia occurs at 1- to 2-year follow-up) ranges between 80 and 95%.

Long-term efficacy of mexiletine alone and in combination with class Ia antiarrhythmic drugs for refractory ventricular arrhythmias

The efficacy of mexiletine used alone, and in combination with a class Ia antiarrhythmic drug, was assessed in 159 previously drug-refractory patients with ventricular tachycardia (VT) during serial electrophysiologic studies and during long-term (5-year) clinical follow-up. Electrically-inducible ventricular tachycardia was suppressed by mexiletine alone in 23% of patients tested, and a combined antiarrhythmic drug regimen was effective in 29% of the trials performed. Mexiletine was much more likely to be effective in patients presenting with nonsustained VT or ventricular fibrillation than in patients with sustained VT (p less than 0.005). After 1 and 4 years of treatment, 18% and 42% of the patients treated with mexiletine alone had died suddenly or suffered recurrent symptomatic VT, compared to 11% and 25% of patients treated with the combined antiarrhythmic drug regimens (p = NS). Mexiletine therapy was associated with frequent, though readily reversible, adverse reactions. However, mexiletine treatment had to be discontinued permanently in 8 of 92 patients (9%) because of intolerable side effects. We conclude that the added efficacy and possible improved arrhythmia-free survival associated with combining mexiletine with a class Ia agent should be further investigated.

New antiarrhythmic drugs: tocainide, mexiletine, flecainide, encainide, and amiodarone

Tocainide, mexiletine, flecainide, encainide, and amiodarone are antiarrhythmic agents that have recently been approved by the Food and Drug Administration for general use in the treatment of ventricular arrhythmias. All five agents are effective in the treatment of patients with ventricular arrhythmias, whereas encainide, flecainide, and amiodarone are also useful in patients with supraventricular arrhythmias and the Wolff-Parkinson-White syndrome (although not yet approved for these indications). Tocainide and mexiletine are similar to lidocaine and are as effective as quinidine in patients with ventricular arrhythmias. Encainide and flecainide are superior to quinidine for the control of ventricular ectopic beats and as effective as quinidine for patients with ventricular tachycardia. Amiodarone is the most effective agent available for treating patients with ventricular tachycardia, but it is also the most toxic antiarrhythmic agent and should be used only when other antiarrhythmic drugs have not been effective or tolerated.

The cellular electropharmacology of the simultaneous administration of propranolol and mexiletine: a class I and II antiarrhythmic drug combination

The addition of propranolol to mexiletine may reduce the adverse effects of mexiletine and possibly increase its efficacy. We compared the cellular electrophysiologic effects of this combination with mexiletine and propranolol alone, over concentration ranges of 3.2 to 100 microM mexiletine and 0.80 to 25.0 microM propranolol, using standard microelectrode techniques and a stimulation frequency of 1.5 Hz. Mexiletine and propranolol both depressed the rate of rise of phase 0 (Vmax) with concentration-response curves of similar slope and a relative potency of 8:1, propranolol to mexiletine. Thus, combinations of 8:1 molar ratios of mexiletine to propranolol were assessed. The combination depressed Vmax to the same extent as mexiletine or propranolol alone. Mexiletine, propranolol and the combination all shortened action potential duration (APD) to the same extent. At low concentration mexiletine, propranolol and the combination shortened effective refractory period (ERP). At 25 microM mexiletine, this effect reversed and ERP began lengthening. The effect of the combination paralleled mexiletine while with propranolol alone the reversal did not occur until the highest concentration was reached. Mexiletine prolonged ERP relative to APD, an effect not shared by propranolol and attenuated with the combination (P less than 0.05). We conclude that combining propranolol with mexiletine does not alter any of the cellular electrophysiologic effects of mexiletine except the prolongation of ERP relative to APD. Although this may be an important antiarrhythmic effect, the extent by which in vivo concentrations of propranolol may reduce the clinical antiarrhythmic efficacy of mexiletine is likely to be negligible.

Arrhythmogenesis--a European perspective

Arrhythmogenesis as an effect of antiarrhythmic therapy is a relatively recent concern. Satisfactory definitions are lacking, but 2 categories, clinical and technical, can be recognized. Although arrhythmogenesis is an international problem and multifactorial, its expression depends on variables that differ according to geographic location. In Europe, use of antiarrhythmic therapy is more conservative than it is in the U.S. In the U.S., many antiarrhythmic drugs commonly used in Europe are either recently released, are on limited release or are available only in investigational protocols. Mexiletine, class IC agents and sotalol are agents in routine use in Europe. All have arrhythmogenic potential, although this appears lowest with mexiletine.

Newer antiarrhythmic drugs in children

Our experience with the use of five new antiarrhythmic drugs for treating life-threatening arrhythmias in children will be briefly reviewed. Prevention of recurrent episodes of atrial flutter with digoxin and local anesthetic antiarrhythmic drugs often is only moderately successful, benefiting 65% of patients. Amiodarone is particularly useful for those patients who cannot be controlled on this regimen. We caution that the heart rate be monitored carefully when therapy with amiodarone is initiated in patients likely to have sick sinus syndrome. We have found mexiletine useful for controlling significant ventricular arrhythmias in patients with congenital heart disease. Likewise, 79% (11 of 14) of patients with ventricular tachycardia treated with amiodarone were well controlled. However, the range of disease categories (congenital heart disease, myocarditis, cardiomyopathy) in which amiodarone is effective is much broader than for mexiletine. Although other investigators have used amiodarone successfully for controlling supraventricular tachycardia in the Wolff-Parkinson-White syndrome or secondary to concealed accessory AV connections, we recommend surgical ablation. Propafenone has significantly improved our ability to control postoperative JET. Although JET is self-limited in duration and spontaneously remits, it frequently produces life-threatening hemodynamic compromise in the postoperative setting. Propafenone slows the ventricular rate into a range in which AV sequential pacing may be instituted. Generally, after 24 to 72 hours, the patient may be quickly weaned from propafenone. Chronic incessant supraventricular tachycardia (SVT) is frequently associated with a dilated cardiomyopathy. The two most common mechanisms of incessant SVT are PJRT and AET. We have found encainide and ethmozine extremely effective in suppressing tachycardia episodes in PJRT and AET, respectively. Medical therapy has been associated with few side effects.

Safety and efficacy of encainide for malignant ventricular arrhythmias

The antiarrhythmic effect of encainide was evaluated in 140 patients with documented symptomatic ventricular tachycardia or ventricular fibrillation refractory to conventional agents. In 102 patients with reproducible spontaneous arrhythmia, noninvasive methods, including ambulatory monitoring and exercise testing, were used to evaluate drug efficacy, while in the remaining 38 patients electrophysiologic testing was performed. Side effects necessitated drug discontinuation in 10 patients before noninvasive evaluation. Of the remaining 92 patients 44 (48%) responded to encainide. Of the 38 patients who underwent electrophysiologic study, 1 discontinued encainide because of side effects and in 4 patients the spontaneous occurrence of sustained ventricular tachycardia precluded repeat study. Of the remaining 33 patients, 10 (30%) were rendered noninducible with encainide. The drug was more effective in those with a left ventricular ejection fraction greater than 35% (p less than 0.03) and in those presenting with nonsustained ventricular tachycardia. Side effects were reported in 53 of 140 patients (38%) and were primarily nausea, vomiting, headaches and tremors. Aggravation of arrhythmia occurred in 4% of patients with a history of nonsustained arrhythmia and in 25% of those with a history of sustained ventricular tachycardia or ventricular fibrillation. Worsening of arrhythmia was not related to mean dose of drug, mean blood level or electrocardiographic changes; it was more likely to occur in patients with a markedly reduced left ventricular ejection fraction (average 32%) and in those with a history of sustained ventricular tachyarrhythmia (p less than 0.05). Long-term encainide therapy was continued in 48 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Intolerance and ineffectiveness of mexiletine in patients with serious ventricular arrhythmias

Fifty-one patients were treated with mexiletine over 10.4 +/- 16 months. The clinical arrhythmia in 25 (49%) was ventricular fibrillation (VF), 11 (22%) had sustained ventricular tachycardia (VT), and 15 (29%) had symptomatic nonsustained VT. Ischemic heart disease was present in 33 patients (66%), cardiomyopathy in nine (17%), and valvular or congenital heart disease in nine (17%). Only six (12%) remain on the drug. Arrhythmias recurred in 21 patients (41%): seven (14%) with VF, three (5%) with sustained VT, and 11 (22%) with symptomatic nonsustained VT. Intolerable side effects occurred in another 17 (33%). Seven patients (14%) died from nonarrhythmic-related deaths while taking mexiletine. Mexiletine was combined with a conventional type IA antiarrhythmic agent in 25 patients (49%). In 12 of these 25 patients (48%), ventricular arrhythmias recurred. These findings were not significantly different from those of the group treated with mexiletine alone, where arrhythmias recurred in 9 of 26 patients (35%) (p = NS). Thus mexiletine, alone or in combination with a type IA antiarrhythmic agent, has limited clinical utility in patients with life-threatening ventricular arrhythmias.

Relationship between ease of inducibility of arrhythmia with electrophysiologic testing and response to antiarrhythmic therapy

Electrophysiologic studies are an important tool for guiding the selection of an effective antiarrhythmic drug. The purpose of this study was to determine if there was a relationship between the number of extrastimuli necessary to induce arrhythmia and the response to antiarrhythmic drugs. A group of 56 patients with sustained ventricular tachycardia or ventricular fibrillation who were inducible underwent 235 single-drug studies (4.2 per patient). During the control study, one extrastimulus provoked an end point in 12 patients (group 1) and in only two patients (17%) was at least one drug effective. Of the 18 patients requiring two extrastimuli for induction during baseline (group 2), at least one drug was effective in 11 patients (61%). At least one drug was effective in 20 of 26 patients (77%) who required three extrastimuli (group 3). There were no significant differences among the three groups with respect to presenting arrhythmia, presence of coronary artery disease, or left ventricular ejection fraction. When single drugs or a combination of drugs were used, 58% of group 1, 72% of group 2, and 85% of group 3 were rendered noninducible. During a follow-up of 28 to 32 months, yearly recurrence of arrhythmia was 9.4%, 4.6%, and 1.7%, for the three groups, respectively.

Pharmacology and clinical use of mexiletine

Mexiletine is an antiarrhythmic agent with structural and electrophysiologic properties similar to those of lidocaine. Mexiletine decreases ventricular automaticity while shortening both action potential duration and effective refractory period. The drug may be administered orally or intravenously. Hepatic metabolism is the major route of elimination. The elimination half-life is approximately 10 hours, but longer in patients with acute myocardial infarction, chronic congestive heart failure or hepatic insufficiency. Mexiletine suppresses ventricular ectopy in the acute phase of myocardial infarction. The drug is effective for some patients in whom lidocaine has failed. It suppresses chronic ventricular ectopy and is well tolerated in approximately two-thirds of stable outpatients treated with this agent. In that population, mexiletine is comparable in efficacy to quinidine, procainamide and disopyramide. It is effective in 30-50% of patients with ventricular arrhythmias refractory to other antiarrhythmic drugs. In patients with refractory arrhythmias, the efficacy of mexiletine may be enhanced by combination with propranolol, quinidine or amiodarone. Adverse reactions limit use of mexiletine in approximately 20% of patients. Gastrointestinal and central nervous system side effects are the most common. Mexiletine does not depress myocardial function. Aggravation of arrhythmias is uncommonly observed. The usual intravenous dose of mexiletine is 150-250 mg over at least 10 minutes. Long-term oral dosages are usually 200-300 mg 3 or 4 times daily.