Electrophysiologic effects of procainamide in subtherapeutic to therapeutic doses on human atrioventricular conduction system

Accelerated AV nodal conduction with use of procainamide in atrial fibrillation

BACKGROUND

Atrial fibrillation is a common dysrhythmia seen in the emergency department (ED). Chemical or electrical cardioversion may be performed on patients who have had atrial fibrillation for < 48 h duration and who are at low risk for thromboembolic events. Multiple studies suggest that intravenous procainamide is an appropriate agent in the treatment of acute atrial fibrillation due to its relatively low risk profile and high conversion rate.

OBJECTIVES

A case is presented that demonstrates an adverse reaction to the use of intravenous procainamide for chemical cardioversion of atrial fibrillation in an otherwise hemodynamically stable patient.

CASE REPORT

We report a case of lone paroxysmal atrial fibrillation in a patient with a structurally normal heart who suffered paradoxical accelerated atrioventricular nodal conduction and secondary hypotension in response to procainamide administration.

CONCLUSION

When administering procainamide for chemical cardioversion of atrial fibrillation, a low threshold should be maintained for administration of a complementary rate-controlling agent, and facilities for immediate electrical cardioversion always must be available.

The effect of intravenous procainamide on the HV interval at electrophysiologic study

The His bundle electrogram recorded at electrophysiologic study clearly differentiates atrioventricular (AV) node disease from distal conduction system disease. The distal conduction system may be tested further by infusing procainamide (10-15 mg/kg) intravenously. High-grade distal AV block or prolongation of the HV interval <80 ms was defined as an abnormal response to this test. We retrospectively reviewed the medical records of 79 patients who underwent electrophysiologic study with intravenous procainamide. An abnormal response to procainamide was observed in only 3% of 37 patients with a normal baseline HV (</= ms), in 48% of 27 patients with mild HV prolongation (56 to 70 ms), and in all 15 patients with moderate HV prolongation (<70 ms) (P <0.0001 for the trend). Procainamide induced high-grade AV block in 4 of 28 patients (14%) studied for syncope and in 1 of 51 patients (2%) studied for ventricular tachycardia. Syncope as the indication for electrophysiologic study (P = 0.05) and left bundle branch block morphology (P = 0.03) were predictors of high-grade AV block; baseline HV and QTc intervals were significantly prolonged in patients who developed AV block with procainamide. We identified a strong linear correlation (R = 0.85) between post-drug and baseline HV intervals, with a regression slope of 1.17 +/- 0.09 and an intercept (+/- standard error) of 5.8 +/- 5.0 ms. This linear response to procainamide and published prospective studies support pacing syncope patients with baseline HV <70 ms. Therefore, procainamide infusion during the electrophysiologic study of patients with undifferentiated syncope should be reserved for those with mild HV prolongation from approximately 55 to 70 ms.

Pharmacological stress testing of the His-Purkinje system in patients with bifascicular block

This literature review, based mainly on the English-language literature, focuses on pharmacological stress testing of the His-Purkinje system as part of an invasive electrophysiological study. The main target group for this investigation is patients with bifascicular block and syncope in which intermittent high grade AV block is suspected. Several drugs have been used for this purpose, mainly Class I antiarrhythmic agents such as ajmaline, procainamide, disopyramide, and flecainide. Most studies, unfortunately, suffer from limited patient numbers, lack of adequate control groups, and/or adequate follow-up. The sensitivity of the disopyramide stress test has been shown to be 75%-100% for prediction of impending high grade AV block. The specificity was > 90%. Studies on procainamide have shown a sensitivity of 60% but the specificity has not been assessed. There are no studies allowing a strict comparison of the diagnostic value of pharmacological provocation with different drugs. Based on the similarities of the electrophysiological effects on the His-Purkinje system of the above Class I agents, it is reasonable to assume that all of them might be of diagnostic value in the present clinical context, provided atrial and ventricular stimulation after drug is included in the protocol.

The effect of metal detector gates on implanted permanent pacemakers

The effect of metal detector security gates, such as are used in airports, was tested in 103 nonselected pacemaker patients. Various types of single and dual chamber units were examined, using telemetry during the test. Pulse rate and duration were measured immediately before and after the procedure. No ill effect was seen on any of the units tested, pacemaker inhibition was not observed, and programmability was not affected. Metal detector security gates have no effect on implanted permanent pacemakers.

Effects of procainamide on intra-atrial [corrected] electrograms during atrial fibrillation: implications [corrected] for detection algorithms

The effects of antiarrhythmic drugs on electrograms have implications for arrhythmia-detection algorithms in implantable antitachycardia devices. Filtered and unfiltered intra-atrial electrograms were analyzed in eight patients who received procainamide (50 mg/min iv, up to 1000 mg) during 11 episodes of atrial fibrillation. Continuous recordings were made before, during, and after the infusion. The recordings were digitized, divided into 4.27 sec segments, and analyzed for atrial rate, median frequency and amplitude probability density function. Significant differences were noted before and after infusion of procainamide for atrial rate (498 +/- 97 vs 356 +/- 146 beats/min; p less than .005), median frequency (5.50 +/- 1.22 vs 4.24 +/- 0.99 Hz; p less than .0005), and density (58.3 +/- 13.9% vs 69.1 +/- 15.0%; p less than .005). Pre- and postprocainamide values were compared with published criteria for detection of atrial fibrillation. Before procainamide, only 2.3%, 5.7%, and 3.4% of the data segments failed to meet criteria for atrial fibrillation by rate, frequency content, and density, respectively. In contrast, after procainamide, 50%, 36.4%, and 28.4% of the data segments failed to meet these same criteria, despite electrograms still meeting morphologic criteria for atrial fibrillation. Thus procainamide resulted in changes sufficient to cause failure of published criteria for detection of atrial fibrillation. These findings have broad implications for the function of antitachycardia devices in patients receiving antiarrhythmic drug therapy.

Rate-dependent effects of procainamide on His-Purkinje conduction in man

Microelectrode studies in isolated cardiac tissues have shown that the depressant effect of several antiarrhythmic drugs on the maximal upstroke velocity of the cardiac action potential is rate-dependent. To determine whether this effect of antiarrhythmic drugs is seen in humans, 14 patients undergoing atrial pacing at several rates were prospectively studied before and after the infusion of procainamide (15 mg/kg). The HV interval (His-Purkinje conduction rate) and the QRS duration (intraventricular conduction rate) were measured. Before procainamide infusion, atrial pacing did not significantly prolong the maximal HV interval (from 54 +/- 15 to 58 +/- 13 ms). After procainamide infusion (mean serum level 10.0 +/- 3 micrograms/ml) atrial pacing at an average of 5 pacing rates significantly prolonged the HV interval (from 67 +/- 18 to 80 +/- 20 ms, p less than 0.001). The extent of HV prolongation with atrial pacing after procainamide infusion was independent of the HV interval at rest before procainamide. The duration of the QRS complex also tended to prolong with atrial pacing after procainamide infusion, but this prolongation was not statistically significant. Thus, procainamide produces a rate-dependent depressant effect on His-Purkinje and intraventricular conduction, confirming observations made in isolated tissue preparations.

Electrophysiologic properties and antiarrhythmic mechanisms of intravenous N-acetylprocainamide in patients with ventricular dysrhythmias

To define electrophysiologic properties and antiarrhythmic mechanisms of N-acetylprocainamide (NAPA), we studied 16 patients with symptomatic ventricular dysrhythmias. Electrophysiologic studies were performed before and after intravenous infusion of NAPA at 20 mg/kg over 20 minutes, achieving plasma concentrations of 24 +/- 3.2 to 35.5 +/- 4.5 micrograms/ml. NAPA did not significantly change sinus cycle length or atrioventricular (AV) conduction times (PA, AH, HV, and QRS), but it lengthened the QTc interval (p less than 0.001) during sinus rhythm. Programmed atrial stimulation revealed that NAPA had no discernible effects on AV nodal conduction; however, it exerted depressive effects on the His-Purkinje system in 9 of 16 patients. In 7 of 16 patients who manifested frequent ventricular premature beats (VPBs), NAPA abolished VPBs in only three of them; NAPA induced progressive prolongation of the premature coupling interval before complete abolition of VPBs. In 8 of 16 patients who had inducible repetitive ventricular response (RVR) because of reentry within the His-Purkinje system, NAPA narrowed or abolished the RVR zone in 3 patients and slowed the RVR rate with widening of the RVR zone in the remaining 5 patients. In 2 of 16 patients with slow ventricular tachycardia (VT), NAPA had no antiarrhythmic effects. By contrast, in the other 2 of 16 patients in whom sustained VT could be reproducibly elicited with programmed ventricular stimulation, NAPA slowed the rate of VT and suppressed VT inducibility. We conclude that electrophysiologic properties of NAPA are slightly different from those of procainamide and that NAPA is not uniformly effective for suppressing ventricular dysrhythmias, but its antiarrhythmic mechanisms are similar to those of procainamide.

Antiarrhythmic drug combinations in the treatment of ventricular tachycardia

Combinations of antiarrhythmic drugs are frequently used to treat refractory ventricular tachycardia (VT), but few scientific data support this practice. We examined the efficacy and electrophysiology of 110 antiarrhythmic drug combination trials at electrophysiologic study in 74 patients with recurrent ventricular tachycardia. Lidocaine was combined with quinidine in 33 trials, procainamide in 22 and encainide in 20. Propranolol was combined with quinidine in 17 trials, procainamide in 12 and encainide in six. All individual drugs tested (except propranolol, which was usually not tested individually) had failed at electrophysiologic study or clinically in the presence of usually accepted plasma concentrations. Lidocaine in combination with quinidine was effective in 3% of the trials, with procanamide in 5% and with encainide in none of the trials. Propranolol in combination with quinidine was effective in 18% of the trials, with procainamide in 17% and with encainide in none of the trials. The electrophysiologic effects of the tested drug combinations were dominated by the individual effects of the type 1 antiarrhythmic agents. We conclude that the tested antiarrhythmic drug combinations are infrequently effective in preventing VT induction at electrophysiologic study when each agent has failed individually. The addition of lidocaine or propranolol to quinidine, procainamide or encainide does not produce significant synergistic or new effects on the electrophysiologic variables analyzed.

Electrophysiologic effects of N-acetylprocainamide in human beings

The electrophysiologic properties of N-acetylprocainamide (NAPA) were studied in 10 patients undergoing cardiac catheterization. Each patient received two successive intravenous infusions: one loading infusion over 15 minutes and one maintenance infusion at a slower rate for 30 minutes. Eight patients received 10.5 mg/kg body weight and two received larger doses (16 and 21 mg/kg, respectively). NAPA plasma concentration was measured at 5 minute intervals from 0 to 25 minutes, and then at 15 and 30 minutes of the second infusion. Mean blood pressure and electrophysiologic data obtained by programmed stimulation were recorded before drug administration and at 15 and 30 minutes of the infusion when the concentration of NAPA was nearly constant in each patient (range 12 to 35 microgram/ml). NAPA decreased blood pressure (p less than 0.005), increased corrected Q-T interval (p less than 0.01) and increased the atrial and ventricular effective refractory periods from 267 +/- 40 to 307 +/- 41 ms (p less than 0.01) and from 278 +/- 37 to 301 +/- 32.8 ms (p less than 0.05), respectively. NAPA did not significantly change sinus cycle length or sinus nodal recovery time, conduction intervals (A-H, H-V, P-R, QRS), atrioventricular nodal functional refractory period or nodal Wenckebach cycle length. The patient receiving the largest dose experienced mild nausea when the plasma concentration was above 35 microgram/ml. These data show that the electrophysiology of NAPA in human beings is different from that reported for procainamide. At the plasma concentrations studied NAPA increases atrial and ventricular refractory periods without increasing cardiac conduction times

The effectiveness of antiarrhythmic agents on early-cycle premature ventricular complexes

Twelve patients completed a double-blind, crossover antiarrhythmic drug trial in which 300 mg of quinidine, 500 mg of procainamide, 100 mg of phenytoin, or placebo was given four times daily on subsequent weeks. Analysis of 24-hour Holter tapes with a computerized analysis system (Argus/H) permitted accurate counting of premature ventricular complexes (PVCs) subclassified according to coupling interval. No antiarrhythmic agent demonstrated a significant overall reduction in the number of PVCs, but both quinidine and procainamide showed a statistically significant (p less than 0.05) reduction of PVCs with coupling intervals less than 400 msec. This effect was noted both in isolated PVCs (quinidine only) and in PVCs that were part of a couplet or run (both drugs). These findings demonstrate that clinically important effects of procainamide and quinidine can occur in the absence of an overall reduction in the number of PVCs.

Strength-interval relation in the human ventricle: effect of procainamide

The effects of procainamide on strength-interval relations were evaluated in 18 patients. At plasma concentrations of 4.3 to 13.6 micrograms/ml procainamide had minimal effects on threshold current in late diastole, but in early diastole it shifted the strength-interval curve to the right. The basic strength-interval relation (that is, decreasing refractory period as current is increased) was not altered. The control refractory period decreased by a mean of 44 ms as the current was increased from threshold to 10 mA, whereas a mean decrease of 42 ms was observed after procainamide. However, the steep portion of the strength-interval curve(absolute refractory period) was shifted to longer coupling intervals by a mean value of 24 ms. These findings suggest that procainamide may primarily affect active membrane properties, but exert little net effect on passive membrane properties late in diastole.

Temporary atrial standstill

Temporary atrial standstill is a relatively rare event requiring intraatrial electrogram recordings for its documentation. Previous reports have emphasized its relationship to drug intoxication, infarction, the immediate post open-heart surgery period, or the premorbid state; significant impairment of atrial excitability is usual. The occurrence of atrial standstill in the presence of intact atrial excitability suggests "electrical isolation" of the atria. The three patients we describe manifested temporary atrial standstill while maintaining atrial excitability. Diffuse conduction system disease and drug effects played a contributory role.

Intracardiac electrophysiological effects of lorcainide in man

The electrophysiological effects of lorcainide 1.25 or 2.5 mg/kg given iv over 2 or 4 min, were studied in 21 patients with normal and diseased impulse formation and conduction, by means of intracardiac recording and stimulation. Sinus rate and the effective atrial refractory period rose following both doses of lorcainide. The corrected sinus node recovery time rose only after lorcainide 2.5 mg/kg and then most markedly in patients with sinus node dysfunction. The P-A interval remained unchanged following the drug. The A-H interval during sinus rhythm, and the pooled A-H intervals during atrial pacing, increased slightly, and the functional and effective A-V nodal refactory period changed variably. Wenckebach periods above the bundle of His occurred at lower atrial pacing rates following both doses of lorcainide in 7 patients, at the same atrial pacing rate in 9 and at higher rates in 3. H-V intervals, pooled H-V intervals and QRS-width lengthened in all patients, most markedly in cases with a conduction delay below the His bundle, who had received lorcainide 2.5 mg/kg. Thus, lorcainide shares some electrophysiological properties with procainamide and aprindine. Higher doses should be used with caution in patients with pre-existing conduction delay below the bundle His.

Intermittent atrioventricular block: procainamide administration as a provocative test

Twelve patients with clinical features suggesting possible intermittent high degree atrioventricular block were studied. All 12 patients had basic 1:1 atrioventricular conduction but nine had an electrocardiographic pattern of bifascicular distal conduction disease (right bundle branch block with left anterior or posterior hemiblock, or left bundle branch block). Intracardiac conduction was assessed by recording of the His bundle electrocardiogram and atrial pacing techniques, before and 20 minutes after intravenous administration of procainamide, in a dose of up to 10 mg/kg. Before procainamide administration, seven of the 12 patients had a prolonged H-V interval (greater than 55 ms). Procainamide administration lengthened the H-V interval in all 12 patients by 5--40 ms. In five patients, procainamide induced second or third degree AV block below the level of the bundle of His. It was concluded that the administration of procainamide may be a useful provocative test of distal conduction in patients with possible intermittent AV block.