Mechanism of Action of Antiarrhythmic Agents: Focus on Propafenone

Atrioventricular block in patients undergoing treatment with bradycardic drugs. Predictors of pacemaker requirement

INTRODUCTION AND OBJECTIVES

Atrioventricular block (AVB) in the presence of bradycardic drugs (BD) can be reversible, and pacemaker implantation is controversial. Our objective was to analyze the pacemaker implantation rate in the mid-term, after BD suspension, and to identify predictive factors.

METHODS

We performed a cohort study that included patients attending the emergency department with high-grade AVB in the context of BD. We studied the persistence of AVB after BD discontinuation, recurrence in patients with AVB resolution, and the predictive variables associated with pacemaker requirement at 3 years.

RESULTS

Of 127 patients included (age, 79 [71-83] years), BAV resolved in 60 (47.2%); among these patients, recurrence occurred during the 24-month median follow-up in 40 (66.6%). Pacemaker implantation was required in 107 patients (84.3%), despite BD discontinuation. On multivariable analysis, the variables associated with pacemaker need at 3 years were heart rate <35 bpm (OR, 8.12; 95%CI, 1.82-36.17), symptoms other than syncope (OR, 4.09; 95%CI, 1.18-14.13), and wide QRS (OR, 5.65; 95%CI, 1.77-18.04). Concomitant antiarrhythmic treatment was associated with AVB resolution (OR, 0.12; 95%CI, 0.02-0.66).

CONCLUSIONS

More than 80% of patients with AVB secondary to BD require pacemaker implantation despite drug discontinuation. Predictive variables were wide QRS, heart rate <35 bpm, and clinical presentation other than syncope.

Propafenone-Induced Liver Injury

OBJECTIVE:

To describe propafenone-induced liver injury.

DESIGN:

Retrospective case report.

SETTING:

Referred care in a large tertiary care center. Laboratory tests were performed at the auxiliary site and the tertiary care center.

PATIENT:

A 71-year-old woman with atrial fibrillation developed elevations of greater than two times the upper limit of normal in alkaline phosphatase (ALK), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma glutamyltransferase (GGT) after initiation of propafenone therapy.

INTERVENTIONS:

Studies included serial measurements of ALK, ALT, AST, and GGT.

RESULTS:

The patient developed elevations of greater than two times the upper limit of normal in ALK, ALT, and AST, one month after initiating propafenone therapy. The propafenone dose was decreased from 900 to 675 mg/d and, ten days later, the ALK, ALT, and AST were decreased slightly, but still above the upper limit of normal. One month later, serum transaminases had returned to baseline, but propafenone therapy was discontinued because of recurrent atrial fibrillation, persistent elevation in ALK, and elevation in GGT. Two months after discontinuing propafenone, serum aminotransaminase and ALK concentrations had normalized and GGT had decreased and remained only slightly elevated.

CONCLUSIONS:

The occurrence of liver injury secondary to propafenone therapy is rare. Reported cases appear to be secondary to hepatocellular injury, cholestasis, or a combination of the two. In this case, the pattern demonstrated by elevations in liver enzymes may be classified as acute cholestatic liver injury. Because the reported incidence is 0.1–0.2 percent and there are no known fatalities secondary to propafenone liver injury, routine monitoring of liver function tests in all patients receiving propafenone cannot be recommended at this time. Baseline liver function tests prior to initiating propafenone therapy with follow-up laboratory studies one month later are recommended in patients with known liver dysfunction. If elevations are noted, a reduction in dose may result in lower liver enzyme concentrations, although discontinuation of therapy may be required in some cases.

Effectiveness of intravenous propafenone for conversion of recent-onset atrial fibrillation: a placebo-controlled study

To evaluate the efficacy of propafenone in converting recent-onset atrial fibrillation (AF) lasting < 7 days, 182 patients were treated intravenously with propafenone (Group 1, n = 98) and with placebo 0.9% saline solution (Group 2, n = 84) in a double blind study. The treatment was continued until sinus rhythm (SR) was restored, but for no more than 24 h. Eighty-nine patients treated with propafenone (90.8%) and 27 patients treated with placebo (32.1%) responded to the treatment and SR was restored (p < 0.0005). The mean time for SR restoration was 2.51 +/- 2.77 h in Group 1, and 17.15 +/- 7.8 h in Group 2 (p < 0.0005). In both groups the patients in whom SR was not restored (nonresponders) had larger left atrial size and longer duration of AF than responders at the onset of the arrhythmia. Nonresponders in Group 1 showed a decrease in mean ventricular rate (MVR) from 143 +/- 16 to 101 +/- 18 (p < 0.0005), while in the nonresponders in Group 2 no reduction of MVR was observed. Two patients whose SR was restored with propafenone had sinus standstill lasting 3.4 and 3.8 s, respectively. Propafenone used intravenously is an effective, quick, and safe drug for treating AF. Moreover, it significantly reduces MVR in nonresponders.

New antiarrhythmic drugs in pediatric use: propafenone

Propafenone hydrochloride, a class 1C antiarrhythmic agent, combines sodium channel-blocking effects with beta-blocking capacities and a weak calcium antagonism. The drug exerts marked electrophysiologic effects on accessory atrioventricular pathways. In patients with atrioventricular nodal reentry tachycardia, propafenone is able to block conduction in the fast conducting pathway. In addition, propafenone is very effective in young patients with supraventricular tachycardia based on enhanced abnormal automaticity. In pediatric patients, left ventricular performance remains unimpaired. Proarrhythmic events have been noted in children only occasionally. In accordance with the electrophysiologic profile, intravenous and oral propafenone is an effective agent for treatment of supraventricular tachycardia based on a reentry mechanism and due to abnormal automaticity (i.e., supraventricular tachycardia based on an accessory atrioventricular pathway, atrioventricular nodal reentry tachycardia, junctional ectopic tachycardia, and atrial ectopic tachycardia). In children with ventricular dysrhythmias, efficacy seems to be related to the underlying cardiac diagnosis. Propafenone is well tolerated in the majority of young patients. Incidence of proarrhythmic events seems to be lower with propafenone than with other class 1C agents. However, the risk of these serious adverse events should be taken into account when therapy with propafenone is considered, particularly in patients with structural heart disease.

Direct enantiomeric high performance liquid chromatographic separation of propafenone and its major metabolite in serum on a cellulose tris-3,5-dimethylphenyl carbamate chiral stationary phase

A direct, isocratic and simple liquid chromatographic method is described for the enantiomeric separation of propafenone (PRO) and its major metabolite, 5-hydroxypropafenone, using a cellulose tris-3,5-dimethylphenyl carbamate (Chiralcel ODS) column. The stereochemical separation factor (alpha) obtained was 1.14 and the maximum stereochemical resolution factor (R) was 0.80 when using a mobile phase consisting of hexane: 2-propanol:diethylamine (90:10:0.4) at 23 degrees C. The hydroxy metabolite could not be successfully separated into its corresponding enantiomers under these chromatographic conditions. The method has been used to determine and identify the enantiomers of PRO and its hydroxy metabolite in a serum sample.

Stereoselective electrophysiological effects of propafenone in Langendorff perfused guinea pig hearts

The present study was focused on the stereoselective electrophysiological effects of (R)- and (S)-propafenone.HCl evaluated in isolated Langendorff perfused guinea pig hearts. Conduction intervals were measured using an ECG-recording method of high resolution. Refractory periods of the different parts of the myocardium were determined by stimulation with premature stimuli, as well as by stimulation with increasing pacing rate (rate-dependent/refractory periods). Drug concentrations of 0.1, 1 and 3 microM were tested. Both compounds induced a dose-dependent increase in AV-nodal, His-bundle, and intraventricular conduction time which reached significance (p less than 0.01) following 3 microM of either compound. Sinus rate was also dose-dependently and significantly reduced. (R)- and (S)-propafenone.HCl induced a marked prolongation of the rate-dependent refractory period of sino-atrial (by 140 +/- 22%, p less than 0.01 and by 141 +/- 14%, p less than 0.01, respectively) and AV-nodal (by 34 +/- 22%, p less than 0.01 and by 42 +/- 15%, p less than 0.01, respectively) conduction and of the atrial (by 182 +/- 21%, p less than 0.01 and by 195 +/- 15%, p less than 0.01, respectively) and ventricular (by 93 +/- 16%, p less than 0.01 and by 88 +/- 16%, p less than 0.01, respectively) myocardium. The effective refractory periods evaluated by stimulation with premature stimuli were also significantly prolonged under the influence of (R)- and (S)-propafenone.HCl, except the ventricular myocardial refractoriness by (R)-propafenone.HCl (increase to 114 +/- 23%, n.s.). Both compounds showed a strong rate-dependence of their effects and, thus, the refractory periods evaluated by stimulation with increasing pacing rate were significantly more prolonged than the refractory periods evaluated by stimulation with premature stimuli. The main difference between the effects of (R)- and (S)-propafenone.HCl on the cardiac electrical activity is the lack of effect of (R)-propafenone.HCl on the ventricular myocardial refractoriness evaluated by stimulation with premature stimuli.

Effectiveness of intravenous propafenone for conversion of atrial fibrillation and flutter of recent onset

The efficacy of intravenous propafenone (2 mg/kg) was assessed in 83 consecutive patients: 68 with atrial fibrillation (AF) and 15 with atrial flutter lasting less than 15 days. Conversion to sinus rhythm occurred in 47 patients (57%), including 42 (62%) of those with AF and 5 (33%) of those with atrial flutter (p less than 0.05). The mean time to conversion was 29 +/- 24 minutes. The success rate was strongly affected by arrhythmia duration. Thus, conversion occurred in 40 patients (71%) among the 56 with arrhythmia lasting less than 48 hours but in 7 patients (26%) among the 27 with a longer lasting arrhythmia (p less than 0.0005). Left atrial size (determined echocardiographically in 56 patients) was significantly larger in nonconverters (49 +/- 12 vs 39 +/- 7 mm, p less than 0.0005). In nonconverters the mean ventricular rate decreased from 141 +/- 26 to 104 +/- 22 beats/min (p less than 0.0005). Except for reversible low output state in 3 patients already hemodynamically compromised, no significant side effects were observed. In conclusion, (1) intravenous propafenone allows a quick restoration of sinus rhythm in the majority of patients with AF of recent onset, whereas it seems less effective in atrial flutter; (2) its efficacy is influenced by the duration of the arrhythmia and by left atrial dimensions; (3) the drug allows control of ventricular rate; and (4) its use seems to be safe except in patients with severe cardiac failure.