Acute hemodynamic effects of intravenous encainide in patients with heart disease

Development, calibration, and validation of a novel human ventricular myocyte model in health, disease, and drug block

Human-based modelling and simulations are becoming ubiquitous in biomedical science due to their ability to augment experimental and clinical investigations. Cardiac electrophysiology is one of the most advanced areas, with cardiac modelling and simulation being considered for virtual testing of pharmacological therapies and medical devices. Current models present inconsistencies with experimental data, which limit further progress. In this study, we present the design, development, calibration and independent validation of a human-based ventricular model (ToR-ORd) for simulations of electrophysiology and excitation-contraction coupling, from ionic to whole-organ dynamics, including the electrocardiogram. Validation based on substantial multiscale simulations supports the credibility of the ToR-ORd model under healthy and key disease conditions, as well as drug blockade. In addition, the process uncovers new theoretical insights into the biophysical properties of the L-type calcium current, which are critical for sodium and calcium dynamics. These insights enable the reformulation of L-type calcium current, as well as replacement of the hERG current model.

Pharmacokinetic and tolerance evaluation of actisomide, a new antiarrhythmic agent, in healthy volunteers

The pharmacokinetics and tolerance of actisomide (SC-36602) were determined following intravenous doses of 2.1, 4.2, and 8.4 mg/kg infused over five hours. Plasma concentrations observed in the low-dose group (2.1 mg/kg) were below the assay's limit of detection and were not included in the pharmacokinetic analysis. The following pharmacokinetic parameters were obtained in the medium-dose (4.2 mg/kg) and high-dose (8.4 mg/kg) groups, respectively: peak plasma concentration 4.25 +/- 0.26 and 7.81 +/- 0.31 micrograms/mL; area under the plasma concentration versus time curve 19.79 +/- 2.96 and 39.81 +/- 7.05 h.micrograms/mL; elimination rate constant of the beta phase 0.105 +/- 0.77 and 0.093 +/- 0.009 h(-1), and half-life 8.85 +/- 4.61 and 7.51 +/- 0.69 h. Left ventricular ejection fraction decreased by 10, 11, and 16 percent in the low-, medium-, and high-dose groups, respectively. Heart rate was not altered during the low-dose infusion. At the medium- and high-dose levels, resting peak heart rate increased by 18 and 27 percent, respectively. Systolic and diastolic blood pressures were not significantly changed in any of the dose groups. Changes in electrocardiographic intervals for the three dose groups were not significant except at the highest dose where an average 20 percent increase in the QRS interval was seen. Mild subjective adverse effects (dizziness, taste perversion, and circumoral paresthesia) which did not necessitate discontinuing the infusion occurred in the highest dosage group. Further studies are warranted to more fully characterize the pharmacokinetic profile and therapeutic potential of actisomide.

Comparative hemodynamics of antiarrhythmic drugs

It is important to consider the hemodynamic effects of antiarrhythmic drugs, because the majority of patients who require these drugs already have compromised cardiac function. The presently available antiarrhythmic agents vary in their potential for producing negative inotropic effects on the myocardium; they vary, as well, as to the mechanisms by which these effects are produced. The drugs in each of the Vaughan-Williams' classes are discussed in terms of the extent to which they affect cardiac output and the mechanisms by which they may depress cardiac function. Practically all antiarrhythmic agents can decrease cardiac output when administered intravenously. However, when given orally to patients with congestive heart failure, amongst Class I agents, encainide and mexilitine appear to have a reasonably good safety record with respect to the worsening of congestive heart failure. Class III antiarrhythmics also appear to be well tolerated in patients with severe LV dysfunction.

Comparative hemodynamic effects of procainamide, tocainide, and encainide in severe chronic heart failure

Many of the newer antiarrhythmic agents are said to cause minimal myocardial depression, but their hemodynamic effects have not been invasively evaluated and compared in patients with severe chronic heart failure. In a randomized, crossover study, the hemodynamic responses to single oral doses of procainamide (750 mg), tocainide (600 mg), and encainide (50 mg) given to 21 patients with severe chronic heart failure were compared. Cardiac performance decreased with all three drugs, but the magnitude of deterioration differed among the three agents. Stroke volume index decreased with procainamide (-5 +/- 1 ml/m2, p less than 0.001), tocainide (-7 +/- 1 ml/m2, p less than 0.001), and encainide (-8 +/- 1 ml/m2, p less than 0.001), but the decline was significantly greater with encainide than with procainamide (p less than 0.05). Similarly, left ventricular filling pressure increased with tocainide and encainide (+4 +/- 1 and +5 +/- 2 mm Hg, respectively; both p less than 0.05), but not with procainamide; the increase was significantly greater with tocainide and encainide than with procainamide (p less than 0.001). These deleterious hemodynamic effects were accompanied by worsening symptoms of heart failure in six patients with encainide and seven patients with tocainide but in only two patients with procainamide. Serum levels for all drugs were in the therapeutic range. In conclusion, although the three type I antiarrhythmic agents tested may all adversely affect left ventricular function in patients with heart failure, encainide and tocainide are more likely than procainamide to cause hemodynamic and clinical deterioration.

Encainide

Encainide is a class IC antiarrhythmic agent having little or no effect on action-potential duration or maximum diastolic potential but decreasing the maximum rate of phase O depolarization as well as increasing atrial and ventricular effective refractory periods. In intact animals or humans, encainide increases the AH, PR, QRS, and H-V intervals while not affecting the sinus node cycle length or JT interval. QT interval increases only by the concomitant increase in the QRS interval. Encainide is metabolized to O-demethyl encainide (ODE) and 3-methoxy-ODE (MODE), both of which are also antiarrhythmics with similar pharmacology to encainide. Encainide and its metabolites have little negative inotropic activity and ancillary pharmacology. Consequently, encainide has little or no effect on hemodynamic variables in patients with either normal or compromised cardiac function. The drug is well tolerated, with side effects being mainly those associated with its local anesthetic activity such as blurred vision and dizziness. Encainide is particularly effective in patients with excessive premature ventricular complexes (PVCs) and less so in patients with sustained ventricular tachycardia (VT). Like all antiarrhythmics, encainide may aggravate or precipitate new arrhythmias (proarrhythmia). The overall incidence of proarrhythmia is about 10%, with less occurring in patients with PVCs and more in those with sustained VT; also, the incidence of proarrhythmia is higher in patients with underlying heart disease. Encainide is also effective for the treatment of supra-ventricular arrhythmias, including atrial fibrillation, PSVT (both PAF as well as reentry of the nodal or W-P-W type), and ectopic atrial tachycardia. Its dosage and role in antiarrhythmic therapy are discussed.

New antiarrhythmic drugs

While controversy still exists as to the precise indications for the treatment of all forms of ventricular arrhythmia, advances in the number and, more importantly, type of antiarrhythmic drugs can provide the clinician with a rational basis for selecting antiarrhythmic drug therapy. A host of new agents with different pharmacokinetic and electrophysiological actions are now available, and can be compared or contrasted to conventional antiarrhythmic agents such as quinidine, procainamide, disopyramide, lignocaine (lidocaine) and bretylium. This review summarises the electrophysiological, haemodynamic, pharmacokinetic, and efficacy and safety data of mexiletine, tocainide, flecainide, encainide, propafenone, amiodarone, sotalol, pirmenol, cibenzoline (cifenline) and ethmozine (moracizine, moricizine), and aims to provide a basis on which clinicians can compare and contrast these agents and form an algorithm for selection of antiarrhythmic drug therapy in the treatment of patients with ventricular arrhythmias.

Newer antiarrhythmic drugs

The effective management of cardiac arrhythmias remains a major challenge in cardiovascular therapeutics. The management of arrhythmias encompasses a wide spectrum of supraventricular and ventricular tachyarrhythmias occurring in patients with various cardiac diagnoses and different degrees of myocardial dysfunction. A number of the newer antiarrhythmic drugs that have either recently been released or appear promising are reviewed in this article. Drugs are described with respect to their basic pharmacology, electrophysiologic actions, pharmacokinetics and metabolism, hemodynamics, antiarrhythmic effects, side effects, interactions, indications, and dosage.

Encainide: its electrophysiologic and antiarrhythmic effects, pharmacokinetics, and safety

Encainide is a class IC antiarrhythmic agent that has been under clinical investigation for the last decade. Laboratory and clinical studies have demonstrated it to be a potent suppressor of ventricular extrasystoles. It is effective in approximately one-half of patients with malignant ventricular arrhythmias. The preliminary experience in patients with supraventricular arrhythmias indicates that the drug is particularly effective in arrhythmias associated with an accessory pathway. Side effects most commonly include blurred vision, nausea, heart block, and proarrhythmic effects. The hemodynamic effect of oral encainide are insignificant in patients with well-preserved left ventricular function. Despite minimal myocardial depression in patients with left ventricular dysfunction, there is the potential for worsening of heart failure. Encainide has a short half-life of 3 hours, but has 2 active metabolites with longer half-lives. No clinically significant drug interaction has been demonstrated with encainide therapy.

Hemodynamic effects of pirmenol and lidocaine: a placebo-controlled, double-blind, comparative study

The acute hemodynamic effects of pirmenol and lidocaine were studied in a double-blind, placebo-controlled investigation. Thirty patients undergoing catheterization received one of the following: pirmenol as a 50-mg intravenous bolus injection followed by a 2.5 mg/min infusion, lidocaine as a 75-mg intravenous bolus injection followed by a 3 mg/min infusion or placebo administered in a similar fashion. Mean plasma pirmenol concentrations during steady infusion were 2.3 to 2.4 mg/liter, and mean plasma lidocaine concentrations were 16 to 24 mumol/liter. Pirmenol increased heart rate from baseline by 10 beats/min (p less than 0.001) and mean arterial pressure by 5 mm Hg (p less than 0.001), with similar increases in systemic (p less than 0.05) and pulmonary vascular resistance (p less than 0.01). Lidocaine induced a comparable increase in mean arterial pressure (6 mm Hg, p less than 0.001), but unlike pirmenol, it increased left ventricular and diastolic pressure by 2.8 mm Hg (p less than 0.05). Indexes of left ventricular work were not affected by either drug. Echocardiographic ejection fraction was reduced more by pirmenol (-0.05, p less than 0.0001) than by lidocaine (-0.03, p less than 0.05), a difference that may be related to the changes in heart rate. Side effects were not observed in any patient. The myocardial depressant effect of pirmenol is relatively slight and comparable to that of lidocaine.

Acute intravenous and long-term oral hemodynamic effects of encainide

The short- and long-term hemodynamic effects of encainide, a new class IC antiarrhythmic agent, were studied in 25 patients (mean age 61 +/- 11) with complex symptomatic ventricular arrhythmia and left ventricular dysfunction. Ninety-two percent had previous myocardial infarction and 8% had dilated cardiomyopathy. Seventy-five percent had congestive heart failure, class III or IV, according to the New York Heart Association. All patients underwent a nuclear ventriculogram performed at least 3 days after discontinuing previous antiarrhythmic drugs. Nuclear ventriculograms were repeated 1 to 6 weeks later while the patients were receiving therapeutic doses of encainide ranging from 75 to 300 [corrected] mg/day. Nuclear ventriculograms were also repeated after 6 months or 1 year of encainide therapy in 16 of these patients. Encainide did not have significant effects on heart rate, blood pressure, left ventricular ejection fraction, systolic or end-diastolic volumes. None of the patients showed a worsening of congestive heart failure during encainide therapy. These results compare favorably with those of other class I antiarrhythmic agents. A review of published reports on the hemodynamic effects of intravenous encainide shows it to have a mild but statistically significant dose-related depressant effect on cardiac function. This effect, however, appears to be no different from that of other newer class I agents.

Hemodynamic effects of moricizine at rest and during supine bicycle exercise: results in patients with ventricular tachycardia and left ventricular dysfunction

To evaluate the hemodynamic effects of moricizine, 20 patients with frequent nonsustained ventricular tachycardia (VT) with a mean left ventricular ejection fraction (EF) of 39 +/- 14% were enrolled in a prospective single-blind, placebo-controlled study. Hemodynamic measurements were performed at rest and during supine bicycle exercise on placebo and moricizine therapy (10 mg/kg/day). Although 16 of 19 patients experienced no rest or exercise deterioration in hemodynamic parameters during drug dosing, three patients had acute deterioration of pulmonary capillary wedge pressure and cardiac index (CI) on moricizine. During follow-up of 6 +/- 3 months, two subgroups were identified: 10 of 19 patients had effective long-term reduction in VT, whereas 9 of 19 patients had poor control of ventricular arrhythmia or congestive heart failure and were discontinued from the trial. Baseline EF and hemodynamic parameters at rest were similar in both patient subgroups. However, protocol dropouts had a hemodynamic response to exercise on moricizine that was significantly depressed as compared to patients with a favorable antiarrhythmic outcome (p less than 0.02). The following hemodynamic profile characterizes patients unlikely to have an antiarrhythmic response to moricizine: an increase in CI of less than 1.0 L/min/m2 and no increase in left ventricular stroke work index during supine exercise.

Effects of congestive heart failure on the pharmacokinetics and pharmacodynamics of antiarrhythmic agents

Changes in the pharmacokinetics of antiarrhythmic agents should be expected in patients with congestive heart failure (CHF). The direction of the changes, however, is not always predictable. The volume of distribution is often decreased by as much as 40%, and loading doses should, therefore, be appropriately reduced. Drug clearance may also be diminished due to decreased blood flow to the liver and kidneys, as well as decreased hepatic drug-metabolizing activity. Infusion rates should similarly be lowered to avoid toxicity. However, decreases in both volume of distribution and clearance may result in little, if any, change in elimination half-life, despite higher plasma concentrations. On the other hand, the elimination half-life of antiarrhythmic agents that have a large volume of distribution and are highly cleared by the liver may be twice as long in patients with CHF compared with normal subjects. Thus, the total daily dose of drug should also be lower in these patients. In addition, the time necessary to reach steady state is longer, so that premature dose escalation may lead to excessive drug accumulation. In terms of their pharmacodynamic effects, all antiarrhythmic agents have the potential to manifest a degree of negative inotropy, which must be anticipated as a possible side effect in patients with CHF. Some of the newer agents, such as tocainide and encainide, appear to cause only minimal myocardial depression. Other potential complications of all antiarrhythmic therapy include proarrhythmia and possible drug interactions with digitalis and diuretics.

Therapy with investigational antiarrhythmic drugs

The investigational antiarrhythmic agents available for use in this country are predominantly class I drugs with local anesthetic membrane effects. These drugs are often used successfully to control arrhythmias refractory to treatment with the standard antiarrhythmic drugs. Side effects often limit their use, and particular attention needs to be paid to their cardiac side effects, such as exacerbation of arrhythmia or enhanced conduction defects.

Clinical profiles of newer class I antiarrhythmic agents--tocainide, mexiletine, encainide, flecainide and lorcainide

New class I antiarrhythmic drugs differ in potency, adverse effects and pharmacokinetics. Encainide and flecainide can totally suppress arrhythmias in some patients, but arrhythmia induction can also occur. At effective dose levels, neurologic and gastrointestinal adverse effects are uncommon. Flecainide pharmacokinetics are suitable for oral use but encainide disposition is complex with variable bioavailability and active metabolites that contribute substantially to activity. Lorcainide is also potent, but neurologic adverse effects are common and dose-dependent bioavailability and an active metabolite may complicate long-term oral therapy. Tocainide and mexiletine can suppress arrhythmias in acute myocardial infarction, during convalescence from myocardial infarction and in patients with arrhythmias resistant to other therapy. Dose-related neurologic and gastrointestinal adverse effects are common, but hemodynamic effects are minor and arrhythmia induction is rare. Tocainide disposition is reasonably predictable and stable in patients, but mexiletine disposition is less so because of variation in distribution and clearance. Although all of the newer agents have some disadvantages, their availability should increase the likelihood of success in the high-risk patient.

Hemodynamic effects of antiarrhythmic drugs

In order to use antiarrhythmic drugs safely, one must understand their hemodynamic effects. Quinidine and the calcium antagonists have direct cardiac effects and frequently opposing autonomically mediated or indirect cardiac effects. Lidocaine is exceptionally well tolerated, even by patients with severe left ventricular dysfunction. Phenytoin and procainamide have the potential for serious adverse effects, but are generally well tolerated at usual doses. Disopyramide causes serious depression of left ventricular function in many patients because of its direct myocardial depressant and peripheral vasoconstricting actions. Although bretylium causes an immediate increase in contractility, it can ultimately result in important hypotension. In this review the in vitro and in vivo hemodynamic effects of these and other antiarrhythmic drugs are discussed to provide information that will assist the clinician in using these drugs properly.