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New perspectives in cardiology: pharmacodynamic classification of antiarrhythmic drugs.

Recent advancements in cardiac pharmacology and physiology have led to the identification of many new antiarrhythmic drugs and a better understanding of basic arrhythmogenic mechanisms. These parallel developments prompted a new nomenclature system for classifying the clinically important antiarrhythmic drugs according to their predominant electrophysiologic actions in cardiac cells. Antiarrhythmic drugs are now grouped into 4 main classes: classes I through IV. Class I agents comprise the standard membrane-stabilizing drugs such as lidocaine, quinidine, and procainamide; newer class I agents include disopyramide, aprindine, tocainide, and flecainide. Class II agents decrease sympathoadrenal excitation of the heart, and the clinically relevant members of this type act through blockade of the cardiac beta 1-adrenergic receptors; propranolol is the prototype. Class III agents selectively prolong the cardiac action potential and refractory period, and bretylium and amiodarone represent this group. Class IV agents are the calcium entry blocking drugs such as verapamil. An understanding of this classification system is essential to the internist and cardiologist who are beset with an emerging array of new antiarrhythmic drugs and affiliated pharmacodynamic terminologies.

Action Potentials↗

New perspectives in cardiology: recent advances in antiarrhythmic drug therapy.

During the past decade, advances in basic and applied cardiology have led to the introduction of several new antiarrhythmic drugs that have distinct clinical advantages over their older counterparts. These therapeutic advantages comprise either a more favorable pharmacokinetic disposition in the patient or new and perhaps novel mechanisms of antiarrhythmic actions. The class IV agent verapamil, for example, selectively blocks the slow inward Ca++ current in excitable tissues and this action is proving to be quite effective in controlling supraventricular tachyarrhythmias. Tocainide is a newly approved class I agent that exerts lidocaine-like effectiveness in treating serious ventricular arrhythmias. Unlike lidocaine, however, tocainide is not restricted to intensive care because it is effective after oral administration and has comparatively longer duration of antiarrhythmic action. Other recently approved or investigational agents include bretylium and amiodarone (class III), and aprindine, mexiletine, and disopyramide (class I). Along with clinical advantages, however, each drug has a characteristic pharmacologic-toxicologic profile and resulting spectrum of therapeutic application for only particular cardiac dysrhythmias. The advantages and disadvantages of each compound should be weighed equally when the new antiarrhythmic drugs are assessed as therapeutic alternatives for the older ones.

Adrenergic beta-Antagonists↗

Antiarrhythmic activity of alpha-tocopherol nicotinate and related compounds and their physico-chemical properties.

The effect of alpha-tocopherol nicotinate (Renascin), alpha-tocopherol and dodecanoic acid (lauric acid) on the positive inotropic action of ouabain and digoxin and on cardiac glycoside induced arrhythmias has been tested in isolated guinea-pig left atria and in anaesthetized guinea-pigs. alpha-Tocopherol nicotinate and dodecanoic acid significantly decrease the positive inotropic action of digoxin, but not that of ouabain in isolated guinea-pig atria. Ouabain and digoxin induced arrhythmias are suppressed by the three compounds in isolated guinea-pig atria and in anaesthetized guinea-pigs: alpha-tocopherol nicotinate has the highest antiarrhythmic activity followed by dodecanoic acid and alpha-tocopherol. These results are further evidence for the dissociation between the positive inotropic and arrhythmogenic action of cardiac glycosides. The antiarrhythmic activity of the three compounds and the physico-chemical properties, as measured in liposomes, are compared with that of quinidine and aprindine. As nicotinic acid does not show any effect on cardiac glycoside induced arrhythmias, the ester linkage in alpha-tocopherol nicotinate seems to be of particular importance for its antiarrhythmic activity.

Anesthesia↗

Poisoning with oral antiarrhythmic drugs.

The incidence of poisoning with antiarrhythmic drugs (AAD) is low, but frequently cardiac disturbances cause a high mortality. Clinical and toxicological data on verapamil, quinidine, ajmaline, prajmaliumbitartrate, mexiletine and aprindine as collected by the Austrian Poison Information Center (PIC) are presented in this paper. The drug concentrations of verapamil, mexiletine and quinidine detected in post-mortem specimens are discussed and compared with correspondent data from literature. Clinical experiences with this kind of intoxication are rather poor and therapeutical principles are very inconsistent. To avoid life-threatening symptoms, gastric lavage has to be performed irrespective of the latency period, accompanied by continuous cardiac monitoring. Cardiocirculatory disorders respond well to sympathomimetic drugs. Immediate and adequate cardiopulmonary resuscitation decisively determines the therapeutical success in critical cases.

Administration, Oral↗

Electrophysiological actions of mexiletine (Kö1173) on canine Purkinje fibres and ventricular muscle.

1 The effects of mexiletine (Kö1173) were investigated in canine isolated cardiac Purkinje fibres and ventricular muscle with microelectrodes. Some Purkinje fibres were depolarized by mechanical stretch to induce spontaneous activity with slow upstroke velocity. The preparations were stimulated at rates of 1, 2, 3 and 4 Hz. The drug concentrations tested were 0.4, 2 and 10 mug/ml in Tyrode solution (KCl = 5.4 mM).2 The ;therapeutic' drug concentration (2 mug/ml) shortened action potential duration and effective refractory period of Purkinje fibres, the effect being pronounced at lower stimulation rates. In ventricular fibres, action potential duration changes were not consistent while the effective refractory period was prolonged.3 In depolarized Purkinje fibres showing automatic activity, the drug (0.4 or 2 mug/ml) depressed phase 4 depolarization and reduced the firing rate without changing maximum diastolic potential. However, when depolarized Purkinje fibres were electrically driven at a constant rate, the maximum diastolic potential became more negative with a concomitant decrease of pacemaker slope and increase of maximum rate of rise (V(max)) of action potentials.4 Moderate (2 mug/ml) to high (10 mug/ml) concentrations of the drug depressed V(max) in Purkinje fibres stimulated at 2 Hz by 12 and 42% respectively and depressed ;membrane responsiveness'. The decrease in V(max) depended upon the stimulation rate, being minimum at the lowest (1 Hz) and maximum at the highest (4 Hz) stimulation rate.5 The drug (2 mug/ml) improved V(max) of the earliest propagated premature action potentials by shifting the takeoff potential to more negative levels in both Purkinje and ventricular fibres.6 Membrane conductance in fibres mounted in a single sucrose gap chamber was increased by the drug (2 mug/ml) in both fibre types in normal and in Na(+)-deficient solutions. This increase was attributed to an increase in membrane K(+) permeability produced by the drug.7 All these effects are similar to those of lignocaine, diphenylhydantoin or aprindine, and can explain the antiarrhythmic action of mexiletine.

Animals↗

Secondary prevention of myocardial infarction with drugs.

Clinical trials in the field of secondary prevention of myocardial infarctions are reviewed, with emphasis on those studies that were randomized and included at least 100 patients. Standardized total mortality data, when available, are provided. Five groups of drugs are reviewed: 1) antiarrhythmic drugs, including studies of phenytoin, tocainide, mexiletine and aprindine. Important, commonly used drugs in this group, which apparently have not been submitted to clinical trials, include procainamide and lidocaine; 2) lipid-lowering drugs, including estradiol, conjugated equine estrogen, dextrothyroxine, clofibrate and nicotinic acid; 3) anticoagulant drugs, the oldest and most controversial preventive drug measure. In this group, only the oral drug derivatives of indandione or coumarin have been tested, and no appropriate studies of parenteral heparin were found; 4) platelet-active drugs--six studies dealing with aspirin alone, one combining aspirin and dipyridamole, and one study of sulfinpyrazone are reviewed; and 5) beta-adrenergic blocking drugs, including practolol and timolol.

Adrenergic beta-Antagonists↗

Pirmenol hydrochloride (CI-845): antiarrhythmic profile in coronary artery ligated conscious dogs.

The antiarrhythmic profile of CI-845 (pirmenol hydrochloride) was assessed in conscious, coronary artery ligated dogs. In single-dose studies in these arrhythmic dogs, CI-845 administered by the intravenous, intranuscular, and oral routes was highly effective in restoring normal sinus rhythm. A 2.5 mg/kg dose was effective against the arrhythmias occurring on the second day after ligation, while 5 mg/kg was effective against the higher-rate arhythmias of the first day after ligation. The reference agents ajmaline, aprindine, disopyramide, lidocaine, mexiletine, procainamide, and quinidine were also tested, and in this model, CI-845 had greater efficacy, a longer duration of activity, and/or a wider safety margin. In slow rate intravenous infusion studies, 1-2 mg/kg/hr of CI-845 maintained near total arrhythmia conversion in first-day postligation dogs. Rapid rate intravenous infusion studies (10 mg/kg/hr) demonstrated a good correlation between the CI-845 dose, plasma level, and arrhythmia conversion, as well as a wide margin of safety. Mean conversions to 80% normal rhythm were achieved at 2.5 mg/kg, with associated plasma levels of 0.8 +/- 0.1 micron/ml, while first sings or gross toxicity occurred at 21.7 +/- 2.4 mg/kg at plasma levels of 6.2 +/- 0.4 micron/ml. There were minimal effects on cardiac conduction and blood pressure even at large doses. In drug interaction studies, CI-845 was safe and effective in combination with disopyramide, lidocaine, procainamide, propranolol, and quinidine. The results clearly show CI-845 to be an orally effective, long-acting antiarrhythmic agent with a favorable margin of safety in the coronary artery ligated dog model.

Administration, Oral↗

[Electrocardiographical changes and rhythm disorders in Barlow's syndrome].

Mitral valve prolapse ( MVP ) , responsible for most of the symptoms which had previously been interpreted as being due to neurocirculatory disorders or cardiac neurosis , is being recognised more often and has an incidence of about 6-8 % in an unselected population . Although this condition was considered for a long time to be a benign auscultatory abnormality , it may be the cause of serious cardiac complication . Arrhythmias predominate with an incidence of 60 to 80 % on continuous electrocardiography . In a series of 245 patients with mitral valve prolapse confirmed on echocardiography , 52 patients chosen at random were studied to determine the incidence pf ST changes , disturbances of heart rate , QT interval , changes of QRS , arrhythmias with resting , exercise and continuous ECG over 24 hours ( HMS = Holter Monitoring System ) . Abnormalities of ventricular repolarisation , especially flattening of the T wave and , less commonly , St depression were observed in about one third of the patients . These changes were more common in the inferior but were also found in the left precordial leads . 73 % of the 52 patients had a heart rate of 75/mn and their QT intervals showed the following changes : 30.7 % Had a duration greater than the 120 th percentile ; 19.2 % had a duration greater than the upper limit of normal . The other 50 % had a QT interval of around the 100 th percentile . None had a duration of less than the 90 th percentile . In 22.5 % patients , QRS changes due to conduction defects were recorded ( 15 % right bundle branch block - RBBB - , 7.5 % incomplete RBBB ) . HMS is the method of choice for detection of arrhythmias . Resting ECG only showed premature ventricular contractions ( PVCs ) in 12.5 % , compared to 32.5 % on exercise ECG and 62.5 % on HMS . 50 % PVCs were monomorphic , 5 % polymorphic , 7.5 % in salvos and 7.4 % supraventricular in origin . The circadian variation of PVC was striking with a high incidence during periods of activity . There was no statistical correlation between the incidence of PVCs , age , sex , type of MVP and the symptoms and auscultatory findings . The theories on the pathogenesis of the arrhythmias are divided between that based on an underlying cardiomyopathy ( confirmed by the presence of degenerated myocytes on electron microscopy ) and the mechanical hypothesis ( chordae tendinae irritating the endocardium or traction on the papillary muscle with resulting ischaemia ) which provide a better explanation of the clear predominance of monomorphic PVCs . The treatment of Barlow's syndrome is discussed . In our opininon , therapy is only required for ventricular arrhythmias detected by a sufficiently sensitive method such as HMS . Most authors use beta blockers , eventually in association with quinidine Therapeutic successes have also been observed with mexiletine , amiodarone , aprindine and less commonly with disopyramide .

Adolescent↗

[Antiarrhythmic effect of disopyramide in ventricular extrasystole and auricular fibrillation].

Disopyramide (B 712) was tested in 39 patients with chronic arrhythmias of different kind: 23 cases with atrial fibrillation, 16 cases with ventricular ectopic beats, two cases with supraventricular tachycardias. The effect of disopyramide was compared to a pretreatment with one or several antiarrhythmic drugs (quinidine, beta-blocking agents, verapamil, ajmalin-bitartrat, aprindine, propafenone, diphenylhydantoin) which had been discontinued either due to ineffectiveness or the occurrence of intolerable side effects. Therapeutical effectiveness was controlled by on-line arrhythmia computers in the CCU or Holter monitoring. 15 patients were treated longer than 4 weeks up to 16 months (mean 35+/-22,6 weeks). The following results were achieved: 1 atrial fibrillation, abolition or significant reduction of the rate of recurrence in 10 out of 23 patients; slight reduction or no effect in 13 patients; 2. ventricular ectopic beats: abolition or significant reduction in 6 out of 16 patients, slight reduction or no effect in the remaining 10 patients. Patients who were treated successfully received the same dosis as those without therapeutical success. In cases with atrial fibrillation, the success was dependent on the duration of this arrhythmia prior to treatment. In comparison to the pretreatment with one or several of the above-mentioned anti-arrhythmic drugs, disopyramide was as effective as the drug given before. The analysis of the Ecg revealed a slight but insignificant prolongation of the time intervals. In 22 patients reversible dosage-dependent side effects were observed which are due to the vagolytic action of the drug: dry mouth, blurred vision, urinary hesitancy, nausea, headache. These side effects occurred at daily dosages between 400 to 800 mg increasing markedly in patients on 800 mg a day. The drug had to be discontinued in 4 cases because of side effects. During long-term treatment no severe side effects were observed. Thus, disopyramide may serve as an alternative to quinidine, especially if the latter has to be stopped because of side effects.

Adolescent↗

[Lorcainid--electrophysiologic examinations of a new anti-arrhythmia agent].

The electrophysiologic properties of Lorcainide (1.25 and 2.5 mg/kg) were studied on 21 patients by intracardiac electrograms and atrial stimulation. A prolongation of the H-V interval, widening of QRS duration but only minor changes in A-H interval were found. The effective refractory period of the atria increased, the effective and functional refractory periods of the A-V node changed variable following Lorcainide. There was a slight increase in heart rate and the sinus node recovery time was longer after 2.5 mg/kg of the drug. The major site of action of Lorcainide in man appears to be the His-Purkinje system. In electrophysiologic terms the new antiarrhythmic agent closely resembles Aprindine.

Acetanilides↗

[Prophylaxis of supraventricular paroxysmal tachycardias on the basis of electrophysiologic examinations].

Paroxysmal supraventricular tachycardias (PSVT) were classified with regard to electrophysiologic criteria in 12 cases. In 6 patients the reentry circuit of the PSVT involved a concealed accessory connection, in 6 patients the reentry circuit was confined to the A-V node. Different antiarrhythmic drugs were administered orally over a 4 week period, the frequency of attacks and possible side effects were recorded. In patients with accessory pathway metoprolol (n = 3), ajmalin (n = 3), Aprindine (n = 1) and verapamil (n = 1) prevented the occurrence of PSVT. Verapamil, Ro 11-1781, metoprolol and digitalis were effective in A-V nodal reentry. PSVT could be prevented in all but one patient by at least one drug.

Adult↗

A model study of time- and voltage-dependent effects of class I antiarrhythmic drugs in guinea-pig papillary muscles as related to external potassium concentration.

1. A piecewise exponential three-state model previously introduced by the authors in 5.4 mmol/l was intended to apply to states with different [K+]o and with a different drug. Using the conventional microelectrode technique the effects of 20 mumol/l mexiletine (MEX), 5 mumol/l aprindine (APR), 20 mumol/l quinidine (QUI), 5 mumol/l flecainide (FLE), 5 mumol/l E-0747 (dl-6-chloro-2,2'-dimethyl-1'-[3-(4-hydroxypiperizino)propyl]spiro [chroman-4,4'-imidazolidine]-2',5'-dione hydrochloride and 100 mumol/l QX-222, a quaternary derivative of lidocaine, on action potentials (APs) in guinea-pig papillary muscles were studied. Specific objects of the study were (1) steady state Vmax values at various frequencies (all drugs), (2) the recovery process of Vmax in premature responses (MEX) and (3) Vmax changes during a train of stimulation at 1 Hz after a rest period (all other drugs) in 2.7 and 10 mmol/l [K+]o. Further, those of APR alone and APR plus 1 mmol/l nicorandil (NIC), which shortened action potential durations (APDs) specifically, were investigated on the above items (1) and (3) in 5.4 mmol/l [K+]o. 2. All the drugs reduced the Vmax of APs frequency-dependently and, except QX-222, more markedly in 10 mmol/l [K+]o than in 2.7 mmol/l [K+]o at 1 Hz. 3. The rate constants estimated from the model fitting characterized MEX and APR and the other drugs as predominantly inactivated and activated channel blockers, respectively. The calculated rate of onset of block, lambda T, does not differ much between the three [K+]o levels. lambda T shows that APR belongs to class Ia rather than class Ib.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

[Epidural anesthesia for herniorrhaphy in a patient with severe dilated cardiomyopathy (DCM) under pimobendan control].

A 60-year-old man with severe DCM was scheduled for a herniorrhaphy under epidural anesthesia using fentanyl. Three months prior to operation, the patient suffered heart failure associated with life-threatening ventricular arrhythmia. The former was successfully treated with pimobendan as the main constituent of medication, but the latter was not responsive to various antiarrhythmic drugs with the exception of aprindine. On the day of operation and for two days postoperatively, pimobendan was administered daily. A sudden drop in systemic blood pressure and central venous pressure (CVP) during anesthesia, as well as the tendency to hypotensive status in the postoperative period were well regulated with continuous infusion of dopamine and dobutamine via CVP catheter probably due to the effect of up-regulation of pimobendan, together with adjustment of the volume of intravenous fluids. No dangerous ventricular arrhythmia were observed. Thereafter the patient made uneventful progress and was discharged on the 8th postoperative day.

Anesthesia, Epidural↗

[Medical management of tachycardias (author's transl)].

Guidelines for a step-wise plan of treatment of tachycardias have been compiled based on clinical empirical experience and with the aid of surface electrocardiograms, intracardial electrograms and stimulation techniques. The plan is primarily with the aid of surface electrocardiograms, intracardial electrograms and stimulation techniques. The plan is primarily oriented with respect to the antiarrhythmic efficacy, the adverse reactions and the practicability of the respective agents. Any type of tachycardia, including premature atrial or ventricular contractions, may be regarded as indication for treatment. Treatment is not indicated only in those asymptomatic patients with rare and evanescent tachycardias and in those with less than 300 premature contractions per hour. Beta-adrenergic blockers are the drugs of choice for the persistent sinus tachycardia. Should the latter agents be contraindicated, propafenon, amiodarone or aprindine may be administered. Verapamil and/or digitalis are indicated only for suppression of paroxysmal sinus tachycardias. Atrial premature contractions are best managed with guinidine or disopyramid. An acute reduction of rapid ventricular rates associated with atrial tachycardias, atrial flutter or fibrillation can best be attained through the administration of verapamil prior to digitalis or beta-adrenergic blockers. Re-establishment of sinus rhythm and prophylactic suppression of the latter should be undertaken with quinidine or disopyramid in combination with digitalis and/or either a beta-adrenergic blocker or intravenously-administered verapamil. Verapamil is the drug of choice for initial management of AV-junctional tachycardia for which a combination with digitalis may be considered. An alternative combination is that of a beta-adrenergic blocker and digitalis. For the acute treatment of ventricular tachycardias, lidocain has proved most effective. Although ajmaline and/or propafenon may be given should no response be obtained, electrical cardioversion would be more appropriate. To prevent ventricular tachycardia or when treatment is indicated for ventricular premature beats, ajmaline, propafenon, quinidine, disopyramid or mexiletine, occasionally in combination with a beta-adrenergic blocker should be employed. Verapamil and/or ajmaline, are usually very effective for termination of reciprocal tachycardias. Ajmaline or propafenon in combination with a beta-adrenergic blocker is recommended for the prophylactic treatment of reciprocal tachycardia. In patients who additionally have bradycardia, prolonged QT-intervals or pre-excitation syndromes, the guidelines should be modified accordingly.

Anti-Arrhythmia Agents↗

Moxaprindine in the acute treatment of ventricular arrhythmias in patients with cardiovascular disease.

The antiarrhythmic activity of intravenous moxaprindine was evaluated in 26 patients with cardiovascular disease; the mean maximum dose was 2.5 +/- 0.12 mg/kg. Ventricular extopics were completely abolished in 19 patients and significantly reduced in four patients, but were not favourably affected in three patients. In one patient with numerous runs of ventricular tachycardia, normal sinus rhythm was restored. Coupled ventricular ectopic activity always completely disappeared. At the maximum dose, the PR-interval (+27.7 +/- 3.3%), the QRS-duration (+24.6 +/- 2.2%), the QT-interval (+17.0 +/- 1.5%) and the QTc-interval (+10.8 +/- 1.2%) were significantly prolonged. The QRS morphology essentially remained unchanged. Moxaprindine caused first degree atrioventricular block in eight patients. The sinus rate was slowed at every dosage level. Nevertheless, moxaprindine could safely be administered to patients with dysfunction of the specialized conduction system, or with a damaged myocardium. Serious side effects did not occur. Moxaprindine is a promising new antiarrhythmic drug for the treatment of ventricular arrhythmias, but its value and safely in the chronic oral treatment of these arrhythmias remain to be established.

Adult↗