Treatment of atrioventricular node reentrant tachycardia with encainide: reversal of drug effect with isoproterenol

Clinical and electrophysiological characteristics, and relatively benign outcome, of typical atrioventricular nodal reentrant tachycardia in children and adolescents

BACKGROUND

Atrioventricular nodal re-entrant tachycardia is an uncommon arrhythmia in children. The natural history of this disturbance is poorly known in young patients.

METHODS

We analyzed the clinical and electrophysiological features, and the final outcome, in 19 children affected by typical atrioventricular nodal re-entrant tachycardia diagnosed by a transoesophageal electrophysiological study.

RESULTS

Of the cohort, 12 patients were female and 7 male, with a mean age of 11 years. Dual atrioventricular nodal physiology was demonstrated in 14 children (73%). The mean length of the tachycardia cycle was 297 milliseconds, with periods of 2 to 1 atrioventricular block during tachycardia noted in 5 children (26%). The mean cycle length was significantly shorter in the children who presented episodes of 2 to 1 atrioventricular block than in those who did not. After diagnosis, 12 children were not treated, 6 were treated with medical therapy, and 1 was submitted to radiofrequency transcatheter ablation. During a mean follow-up period of 41 months, 2 children with rare, but sustained, episodes of tachycardia that initially had not been treated were submitted to radiofrequency transcatheter ablation. Among children treated pharmacologically, 1 teenager was submitted to radiofrequency transcatheter ablation on the basis of parental choice, 3 children have discontinued medical therapy recording only sporadic episodes of tachycardia, and 2 children are still treated with antiarrhythmic drugs. At the last follow-up visit, 13 children (68%) were without any treatment, 4 had been successfully ablated, and 2 were still on medical treatment.

CONCLUSIONS

Our data indicates a relatively benign outcome in this group of children and adolescents with atrioventricular nodal re-entrant tachycardia.

Effects of cardioactive medications on retrograde conduction: Continuing relevance for current devices

INTRODUCTION

Retroconduction (ventriculo-atrial conduction) remains a problem for patients with implanted cardiac rhythm devices. Pacemaker algorithms can detect and terminate endless loop tachycardia (ELT), but actual prevention of ELT may require anti-arrhythmic drugs (AADs). Similarly, AADs can affect ICD rhythm discrimination algorithms that depend on atrio-ventricular ratios. There is concern whether these drugs remain effective during stress situations.

METHODS

Electrophysiologic studies that included retroconduction testing using slow ramp pacing were done in 1332 patients. The presence or absence of retroconduction at baseline and with drug was recorded, as was the rate at block. As a stress surrogate, isoproterenol was used to test retroconduction and reversal of drug-induced block.

RESULTS

Procainamide, mexiletine, phenytoin, disopyramide, quinidine, beta-blockers, encainide, and amiodarone caused complete retrograde block or decreased the rate at which block occurred (mean 76% of patients, p < 0.008), whereas digoxin, lidocaine, diltiazem, and verapamil did not. Isoproterenol (in the absence of AADs) increased the rate at block in 82% of 404 patients with retroconduction at baseline (p < 0.005). Of 319 patients without retroconduction at baseline, 134 (42%) developed retroconduction after isoproterenol. Isoproterenol reversed retrograde block in 39% of patients with block on an AAD. Amiodarone, digoxin, and the combination of digoxin plus a beta-blocker were most effective at resisting this reversal of ventriculo-atrial block (80%, 68%, and 75% respectively).

CONCLUSION

Most of the AADs reviewed increase the cycle length at block or abolish retroconduction, while isoproterenol has the opposite effect. Anti-arrhythmic medications, particularly amiodarone, digoxin, and the combination of digoxin plus a beta-blocker may be considered for a patient with multiple ELT episodes or certain ICD detection problems.

Cardiac electrophysiologic effects of norepinephrine in human beings

BACKGROUND

The electrophysiologic effects of norepinephrine (NE) in human beings have not been previously described.

METHODS

The electrophysiologic effects of NE infused at a rate of 25 ng/kg/min were determined in 21 patients with a mean age of 41 +/- 11 years and without structural heart disease who underwent an electrophysiology procedure. In a subgroup of 10 patients electrophysiologic parameters were measured at baseline, after the infusion of NE, and after administration of beta-blockade while in continuous NE infusion.

RESULTS

The baseline NE plasma concentration of 298 +/- 153 pg/ml increased to 708 +/- 419 pg/ml after the infusion of NE. NE significantly increased the mean blood pressure, sinus cycle length, corrected sinus node recovery time, ventriculoatrial block cycle length, and the atrial and ventricular effective refractory periods. In a subset of 10 patients 0.2 mg/kg propranolol administered during continued infusion of NE resulted in a further increase in sinus cycle length, atrial-His interval, and ventricular refractoriness.

CONCLUSION

A physiologic elevation in the plasma NE concentration results in a depression of sinus node function and atrioventricular conduction and in prolongation of atrial and ventricular refractoriness. Some of NE's effects are partially offset by beta-adrenergic stimulation.

Beta-adrenergic augmentation of flecainide-induced conduction slowing in canine Purkinje fibers

BACKGROUND

This study was undertaken to test the hypothesis that beta-adrenergic stimulation in the setting of membrane depolarization will potentiate flecainide-induced conduction slowing.

METHODS AND RESULTS

To elucidate the potential mechanism for the flecainide proarrhythmia observed in CAST, the voltage dependence of beta-adrenergic modulation of impulse propagation in eight flecainide-superfused canine Purkinje fibers was examined with a dual-microelectrode technique. At physiological membrane potentials (Vm) ([K+]o=5.4 micromol), 1 micromol flecainide decreased Vmax from 698+/-55 to 610+/-72 V/s (P=.003) and squared conduction velocity (theta2) from 2.11+/-1.1 to 1.72+/-0.9 (m/s)2 (P=.001). With K+ depolarization to Vm=-70 mV, flecainide further reduced Vmax from 306+/-101 to 245+/-65 V/s and theta2 from 1.12+/-0.4 to 0.99+/-0.6 (m/s)2, producing a 2.0-mV hyperpolarizing shift of apparent Na+ channel availability curves derived from theta2. The addition of 1 micromol isoproterenol to flecainide-superfused fibers at physiological Vm increased theta2 by 8% to 1.84+/-0.6 (m/s)2 (P<.01) without altering Vmax. At -70 mV, the addition of isoproterenol magnified the flecainide-induced reduction of Vmax an additional 24% to 185+/-52 V/s (P<.01) and theta2 by 17% to 0.82+/-0.5 (m/s)2 (P=.04), producing an additional 1.8-mV (P=.002) and 1.9-mV (P=.002) hyperpolarizing shift in the apparent Na+ channel inactivation curves generated from Vmax and theta2, respectively. At physiological Vm, the action potential duration (APD95) was reduced from 307+/-35 to 269+/-27 ms (P<.001) by flecainide and subsequently to 217+/-4 ms (P<.001) with isoproterenol addition. With 12 mmol/L K+, APD95 decreased from 198+/-23 to 182+/-17 ms (P=.005) with flecainide and to 164+/-10 ms (P=.004) with isoproterenol.

CONCLUSIONS

At depolarized Vm, isoproterenol amplified the flecainide-induced reduction of Vmax and theta2, suggesting a further adrenergic-mediated reduction of Na+ current. Consequently, the synergy between catecholamines and flecainide at depolarized Vm and the shortened APD95 could facilitate arrhythmogenesis in the presence of underlying ischemia.

Mechanism of lethal proarrhythmia observed in the Cardiac Arrhythmia Suppression Trial: role of adrenergic modulation of drug binding

A variety of recent in vivo studies have sought to clarify the mechanism underlying the proarrhythmic response of flecainide in the Cardiac Arrhythmia Suppression Trial (CAST). Increased inducibility of relatively stable ventricular arrhythmias in subacute and chronic postinfarction models has been universally observed. The arrhythmogenesis has been explained in part by drug induced modulation of anisotropic conduction in persistently ischemic tissue, increased durations of vulnerable windows, enhanced generation of unidirectional block with the introduction of extrastimuli, variability of repolarization within the ventricular wall, and the creation of stable reentrant circuits with narrow central zones of propagation. While these data explain arrhythmogenesis in general, malignant ventricular arrhythmia capable of producing the excess sudden or arrhythmic death mortality in the CAST trial have not been universally observed, nor have the proported beneficial effects of beta-blockade seen in the CAST trial and other studies been explained. Additional studies examining the adrenergic modulation of flecainide binding have shown reversal of flecainide effects in normal tissue, but paradoxical amplification of flecainide induced conduction slowing in depolarized tissue. This variable effect in normal versus abnormal tissue produces significant dispersions of conduction with an expected increased propensity for conduction failure in response to ectopy, increased liminal length for impulse propagation, enhanced vulnerability to premature extrastimuli, and completed reentrant circuits in regions of depressed membrane potentials. This, along with the decrease in action potential duration and accompanying refractoriness in the setting of adrenergic modulation may favor more malignant double wavelet or unstable ventricular arrhythmias.

Differential effect of esmolol on the fast and slow AV nodal pathways in patients with AV nodal reentrant tachycardia

INTRODUCTION

AV nodal reentrant tachycardia (AVNRT) usually involves anterograde conduction over a slowly conducting ("slow") pathway and retrograde conduction over a rapidly conducting ("fast") pathway. A variety of drugs, such as beta blockers, digitalis, and calcium channel blockers, have been reported to prolong AV nodal refractoriness in both the anterograde and retrograde limbs of the circuit. However, few data are available that address whether the fast and slow pathways respond in a quantitatively different manner to drugs such as beta-adrenergic antagonists. In addition, it is not known whether the effects of these agents on refractoriness parallel the effects on conduction in the fast and slow pathways. The present study was performed to measure the effect of the intravenous beta-adrenergic agent, esmolol, on refractoriness and conduction in both the fast and slow AV nodal pathways in patients with AVNRT.

METHODS AND RESULTS

Thirteen patients with discontinuous AV nodal conduction properties and typical AVNRT were studied. Anterograde and retrograde AV nodal functional assessment was performed at baseline and following steady-state drug infusion of intravenous esmolol at a dose of 500 micrograms/kg for 1 minute, 150 micrograms/kg per minute for the next 4 minutes, followed by a continuous maintenance infusion of 50 to 100 micrograms/kg per minute. The anterograde effective refractory period of the fast pathway increased from 381 +/- 75 msec at baseline to 453 +/- 92 msec during the infusion of esmolol (P = 0.003). The anterograde effective refractory period of the slow pathway was also prolonged by esmolol, from 289 +/- 26 msec to 310 +/- 17 msec (P = 0.005). However, the absolute magnitude of the change in the anterograde effective refractory period of the fast pathway (+72 +/- 59 msec) was significantly greater than the change in anterograde effective refractory period of the slow pathway (+21 +/- 16 msec, P = 0.01). The mean retrograde effective refractory period of the fast pathway increased from 276 +/- 46 msec to 376 +/- 61 msec during esmolol infusion (P = 0.03). Retrograde slow pathway conduction that could not be demonstrated at baseline became manifest in three patients during esmolol infusion. In contrast to the effects of esmolol on refractoriness, the AH interval during anterograde slow pathway conduction prolonged to a far greater extent (+84 msec) than the HA interval associated with retrograde fast pathway conduction (+5 msec, P = 0.04).

CONCLUSION

The beta-adrenergic antagonist, esmolol, has a quantitatively greater effect on anterograde refractoriness of the fast than the slow AV nodal pathway. However, the effects on conduction intervals during AVNRT are greater in the anterograde slow pathway than in the retrograde fast pathway. These observations suggest that the fast and slow pathways may have differential sensitivities to autonomic influences. This difference in the response to beta-adrenergic antagonists may be exploited as a clinically useful method for demonstrating slow pathway conduction in some individuals with AVNRT.

The effects of beta-adrenergic stimulation on the frequency-dependent electrophysiologic actions of amiodarone and sematilide in humans

BACKGROUND

The autonomic nervous system appears to play an important role in the development of clinical ventricular arrhythmias, and beta-adrenergic sympathetic stimulation may be important in modulating the electrophysiologic effects of class III antiarrhythmic agents. This study prospectively determined the effects of isoproterenol on the frequency-dependent actions of sematilide (a pure class III agent that selectively blocks the delayed rectifier potassium current) and amiodarone (a class III agent with a complex pharmacologic profile) on ventricular repolarization, refractoriness, and conduction.

METHODS AND RESULTS

The frequency-dependent electrophysiologic effects of sematilide (n = 11) and amiodarone (n = 22) were determined at (1) drug-free baseline, (2) during steady-state (> 48 hours) dosing with sematilide (455 +/- 5 mg/d [mean +/- SEM]) or after 10.5 days of amiodarone loading (1618 +/- 32 mg/d), and (3) during isoproterenol administration (35 ng/kg per minute) to patients receiving sematilide or amiodarone. Electrophysiologic determinations were made at paced cycle lengths of 300 to 500 ms. The two groups were similar in all clinical characteristics. The ventricular action potential duration at 90% repolarization (APD90) was significantly prolonged by sematilide (mean increase, 7 +/- 1%, P < .01 by ANOVA) and amiodarone (mean increase, 12 +/- 1%, P < .001). However, while sematilide-induced APD90 prolongation was fully reversed to baseline values during isoproterenol infusion, the APD90 in patients receiving amiodarone remained significantly prolonged by a mean of 6 +/- 1% compared with baseline (P = .005). The reduction in the APD90 was frequency dependent for both agents, with a greater reduction at longer than shorter paced cycle lengths (P < .02). During isoproterenol infusion the right ventricular effective refractory period (RVERP) in patients receiving sematilide was significantly reduced to mean values of 8 +/- 2% below baseline (P < .05), whereas the RVERP in patients receiving amiodarone remained significantly prolonged by a mean of 7 +/- 1% above baseline values (P = .01). Sematilide and sematilide/isoproterenol had no effect on ventricular conduction. Amiodarone increased the QRS duration by 14 +/- 4% (paced cycle length, 500 ms) to 32 +/- 5% (paced cycle length, 300 ms) compared with baseline values. Isoproterenol attenuated amiodarone-induced QRS prolongation by a mean of 5 +/- 1% (P = .005), without frequency-dependent effects, consistent with isoproterenol-induced increases in the sodium current. During isoproterenol infusion there was a trend for the sustained VT cycle length to be reduced below baseline in patients receiving sematilide (275 +/- 16 versus 298 +/- 55 ms, P = .06), whereas it remained significantly prolonged compared with baseline in patients receiving amiodarone (327 +/- 17 versus 257 +/- 12 ms, P < .001).

CONCLUSIONS

Isoproterenol fully reversed the effects of selective potassium channel block with sematilide on the APD90 and further reduced the RVERP to values significantly below baseline; it partially attenuated but did not fully reverse amiodarone-induced prolongation of the APD90 and RVERP, which remained significantly prolonged beyond baseline values. Isoproterenol exerted frequency-dependent effects in both patient groups on the APD90; it modestly attenuated amiodarone-induced conduction slowing without frequency-dependent actions; and the sustained VT cycle length remained significantly prolonged during isoproterenol administration to patients receiving amiodarone but not in those receiving sematilide. These findings may have important clinical implications regarding protection from arrhythmia development in patients receiving pure class III agents or amiodarone.

Sotalol. An updated review of its pharmacological properties and therapeutic use in cardiac arrhythmias

Sotalol is a nonselective beta-adrenoceptor antagonist which prolongs cardiac repolarisation independently of its antiadrenergic action (class III antiarrhythmic properties). The antiarrhythmic action of sotalol appears to arise predominantly from its class III properties, and the drug exhibits a broader antiarrhythmic profile than the conventional beta-blockers. Sotalol is effective in controlling paroxysmal supraventricular tachycardias and the ventricular response to atrial fibrillation/flutter in Wolff-Parkinson-White syndrome, in maintaining sinus rhythm after cardioversion of atrial fibrillation/flutter, and in preventing initiation of supraventricular tachyarrhythmias following coronary artery bypass surgery. Sotalol shows promise in the control of nonmalignant and life-threatening ventricular arrhythmias, particularly those associated with ischaemic heart disease. It is effective in suppressing complex forms of ventricular ectopy, displaying superior antiectopic activity to propranolol and metoprolol. The acute efficacy of sotalol in preventing reinduction of sustained ventricular tachyarrhythmias and suppressing spontaneous episodes of these arrhythmias on Holter monitoring is translated into long term prophylactic efficacy against arrhythmia recurrence in approximately 55 to 85% of patients with refractory life-threatening ventricular arrhythmias. In addition, sotalol offers the advantage over the class I agents of reducing cardiac and all-cause mortality in the high risk population with life-threatening ventricular arrhythmias. The adverse effects of sotalol are primarily related to its beta-blocking activity and its class III property of prolonging cardiac repolarisation. Sotalol is devoid of overt cardiodepressant activity in patients with mild or moderate left ventricular dysfunction. The overall arrhythmogenic potential is moderately low, but torsade de pointes may develop in conjunction with excessive prolongation of the QT interval due to bradycardia, hypokalaemia or high plasma concentrations of the drug. In summary, sotalol displays a broad spectrum of antiarrhythmic activity, is haemodynamically well tolerated, and confers a relatively low proarrhythmic risk. It is likely to prove particularly appropriate in the treatment and prophylaxis of life-threatening ventricular tachyarrhythmias.

Atrioventricular nodal reentry. Clinical, electrophysiological, and therapeutic considerations

BACKGROUND

Atrioventricular (AV) nodal reentry is a relatively common cause of regular, narrow QRS tachycardia. The underlying basis for this arrhythmia is functional (and anatomic) duality of pathways in the region of the AV node, although the exact boundaries of the reentrant circuit have not been convincingly defined. During the more common type of AV nodal reentry (seen in approximately 90% of cases), a slow conducting pathway is used in the anterograde direction, and a fast pathway is operative in the retrograde direction. In the uncommon form, the direction of impulse propagation within the reentrant circuit is reversed. In this article, the clinical, ECG, and electrophysiological features of AV nodal reentry as well as approaches to therapy are discussed.

METHODS AND RESULTS

Clinical diagnosis may be made from the surface ECG. In the common type of AV nodal reentry, the P wave is obscured by the QRS or may be present in its terminal portion. The P wave in the uncommon form occurs late (i.e., in or after the T wave), producing a pattern of long RP and short PR. Both forms of AV nodal reentry are controllable with various therapeutic modalities. For acute termination, adenosine is probably the ideal agent. Prevention of recurrences can be achieved with several pharmacological agents, including beta-blockers, calcium channel blockers, and class Ia, Ic, and III antiarrhythmic agents. Curative therapy is now available with a variety of nonpharmacological methods. However, the most promising therapy at the present time is catheter modification of the AV node by ablation of either the fast or slow pathway, using radiofrequency energy. Ablation of the fast pathway carries a higher risk of second- or third-degree AV block. Slow pathway ablation, by providing a high rate of success and minimal risk of AV block, seems to be a more acceptable initial approach.

CONCLUSIONS

AV nodal reentry is a common cause of paroxysmal supraventricular tachycardia, and a precise diagnosis can be made with intracardiac electrophysiological evaluation. Although the arrhythmia responds to a variety of antiarrhythmic agents, curative therapy can now be offered with catheter modification of the AV node using radiofrequency energy. At the time of this writing, it seems that catheter modification of the AV node is rapidly becoming the therapy of initial choice in patients with symptomatic AV nodal reentrant tachycardia requiring treatment.

Should radiofrequency therapy be performed in every symptomatic patient with supraventricular tachycardia? (Pro drug position)

The indication for treatment of paroxysmal supraventricular tachycardia depends on the frequency and severity of the tachycardia attacks. If the tachycardia attacks are mildly symptomatic and occur only once or twice a year, there is no indication for either continuous drug therapy or radiofrequency ablation. The only therapeutic measure required is termination of each acute event. If symptoms occur frequently, long-term antiarrhythmic drug therapy is then indicated and will be effective for chronic prophylaxis in most individuals with a low risk of proarrhythmic events. Only in patients with severe or life-threatening symptoms or cases refractory to drug therapy would radiofrequency ablation possibly be justified.

Efficacy of intravenous sotalol for suppressing inducibility of supraventricular tachycardias at rest and during isometric exercise

The efficacy of intravenous sotalol (1 mg/kg) for suppressing inducibility of supraventricular tachycardias (SVT) with different electrophysiologic mechanisms was studied in 30 consecutive patients referred for an electrophysiologic study because of paroxysmal SVT. Orthodromic SVT using accessory atrioventricular (AV) connection was inducible in 14 patients, AV nodal reentrant SVT in 8, and intraatrial SVT in 8 before administration of sotalol, Isometric handgrip exercise facilitated the inducibility of SVT in 8 patients who were noninducible at rest. After intravenous sotalol, 7 of 14 patients (50%) with orthodromic SVT, 8 of 8 (100%) with AV nodal reentrant SVT, and 8 of 8 (100%) with intraatrial reentrant SVT became noninducible into sustained SVT, Isometric exercise facilitated the inducibility of only 3 nonsustained SVT runs after sotalol infusion, and exercise did not reverse the prolongation of refractory periods of the atrium, AV node, accessory pathway and ventricle caused by sotalol. During a mean follow-up period of 18 +/- 7 months, none of the 14 patients who remained noninducible into sustained SVT during the stress test after intravenous sotalol and tolerated long-term oral sotalol therapy had recurrence of symptomatic SVT. Thus, sotalol is efficacious for suppressing SVT with AV nodal or intraatrial reentrant mechanism, but less efficacious in patients with accessory AV pathway. The beta-blocking and cellular antiarrhythmic effects of sotalol are not significantly reversed by exercise.

Reversal of antiarrhythmic drug effects by epinephrine: quinidine versus amiodarone

Although previous studies have demonstrated that the electrophysiologic effects of many antiarrhythmic agents can be reversed by catecholamines, the susceptibility of amiodarone to such reversal is unknown. The objective of this study was to compare the relative degree of reversal of the electrophysiologic effects of quinidine and amiodarone by epinephrine infusions that result in plasma epinephrine levels similar to those achieved during various physiologic stresses. Twenty-nine patients who had inducible sustained monomorphic ventricular tachycardia and underwent electropharmacologic testing with quinidine and amiodarone were enrolled in the study. The variables measured before and during an epinephrine infusion (25 or 50 ng/kg per min) included the sinus cycle length, mean arterial pressure, QT interval and effective refractory period at drive train cycle lengths of 600 and 400 ms. The effective refractory period measured at a drive train cycle length of 600 ms shortened less during amiodarone therapy (2 +/- 2%) than during quinidine therapy (6 +/- 4%) or than in the baseline state (6 +/- 4%; p less than 0.01). Similar results were obtained during evaluation of the effective refractory period at a cycle length of 400 ms. Epinephrine infusion, at both 25 and 50 ng/kg per min, completely reversed the effects of quinidine and partially reversed the effects of amiodarone on the effective refractory period. The effects of epinephrine on the sinus cycle length and QT interval were similar in the baseline state and in conjunction with quinidine and amiodarone. Twenty-four patients underwent programmed ventricular stimulation during amiodarone therapy alone and in conjunction with either a 25- or a 50-ng/kg per min infusion of epinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous 3-methoxy-O-desmethyl-encainide in reentrant supraventricular tachycardia: a randomized double-blind placebo-controlled trial in patients undergoing EP study

Encainide is an agent effective in atrioventricular and atrioventricular nodal reentrant tachycardia. The metabolites O-desmethyl encainide and 3-methoxy-O-desmethyl encainide (MODE) are responsible for the clinical effects of encainide in most patients. In this study, intravenous MODE was evaluated in eight patients with reentrant supraventricular tachycardia undergoing electrophysiological testing. After tachycardia was induced at least twice to ensure reproducibility, MODE (30 micrograms/kg/min x 15 min, then 7.5 micrograms/kg/min) or placebo was administered in a double-blind fashion. If tachycardia remained inducible, the infusion was unblinded; in nonresponding subjects who received placebo, MODE was then administered. Placebo was ineffective in 3/3 patients. MODE prevented tachycardia induction in 5/8 patients and increased the tachycardia cycle length from 302 +/- 38 to 413 +/- 67 msec in the other three. At a mean concentration of 774 +/- 229 ng/ml, MODE prolonged PR, AH, HV, QRS, and QT intervals, right ventricular and accessory pathway effective refractory periods, and slowed or blocked antegrade accessory pathway conduction. Changes in intracardiac conduction were rate independent between cycle lengths 400 to 600 msec, while changes in ventricular effective refractory periods were most pronounced at rapid pacing rates. No adverse effects, hemodynamic changes, or conduction disturbances occurred. Thus, MODE can modify or suppress induction of reentrant atrioventricular or atrioventricular nodal tachycardia. The study design used here is well suited for the evaluation of newer antiarrhythmic agents by electrophysiological testing.

Electrophysiologic effects of isoproterenol in patients with atrioventricular reentrant tachycardia treated with flecainide

The electrophysiologic effects of isoproterenol in patients treated with flecainide for atrioventricular (AV) reentrant tachycardia were studied to evaluate the mechanism of tachycardia inducibility after isoproterenol and the value of isoproterenol challenge as a predictor of spontaneous arrhythmia recurrence. Seventeen patients underwent electrophysiologic study before and after oral flecainide administration and after the addition of isoproterenol to flecainide. No patient had inducible sustained supraventricular tachycardia after flecainide alone. Two patients had inducible sustained and six had inducible nonsustained tachycardia after isoproterenol was added to flecainide. The patients were then followed up on the same flecainide dose they received at the time of the electrophysiologic study.

FINDINGS

1) Flecainide treatment prolonged HV and VA intervals, and the addition of isoproterenol did not affect these variables. 2) Isoproterenol shortened anterograde and retrograde block cycle length and the refractory period of the accessory pathway and the AV node. It also decreased the tachycardia cycle length, an effect that was due solely to shortening of AV node conduction time. 3) Flecainide treatment prevented tachycardia induction by affecting retrograde conduction over the accessory pathway. Isoproterenol allowed for tachycardia induction and for more sustained episodes of tachycardia by reversing the effect of flecainide on retrograde accessory pathway conduction. 4) Tachycardia recurred during follow-up in all three patients in whom tachycardia of greater than or equal to 10 s duration was induced after isoproterenol but in no patient who had no or shorter episodes of induced tachycardia (and who did not have a change in medical regimen).

CONCLUSIONS

1) Isoproterenol reverses flecainide-induced prolongation of block cycle length and refractory periods of the accessory pathway and AV node. 2) Isoproterenol reverses flecainide-induced prevention of tachycardia induction through reversal of the effects of flecainide on the retrograde accessory pathway. 3) The addition of isoproterenol during flecainide restudy is valuable in predicting long-term drug efficacy.

Isoproterenol reversal of antiarrhythmic effects in patients with inducible sustained ventricular tachyarrhythmias

Seventeen patients (16 men and 1 woman) were challenged with isoproterenol after their initially inducible sustained ventricular tachyarrhythmia (monomorphic tachycardia in 14 patients and fibrillation in 3) was completely suppressed by class I antiarrhythmic drugs. Coronary artery disease was documented in 11 patients, dilated cardiomyopathy in 2 and no structural heart disease in the remaining 4 patients. The initial presentation was aborted sudden cardiac death (five patients), syncope (eight patients) and symptomatic nonsustained ventricular tachycardia (four patients). The antiarrhythmic drug that rendered the initial ventricular tachyarrhythmias noninducible was class IA in 11 cases, class IC in 5 and combined class IA and IB in 1. The original ventricular tachyarrhythmia became reinducible in 10 patients (group A) and remained noninducible in 7 patients (group B) after isoproterenol infusion at a rate necessary to achieve a 20% increase in heart rate. Despite the results of isoproterenol challenge, all patients were maintained on their electrophysiologically guided antiarrhythmic regimen. During a mean follow-up period of 13 +/- 9 months, 3 of the 10 patients in group A experienced clinical recurrence of tachyarrhythmia; no recurrence was noted in group B. In conclusion, reinducibility of ventricular tachyarrhythmia after beta-adrenergic stimulation seems to identify a subgroup of patients at high risk of subsequent arrhythmic events. Beta-adrenergic blockade or surgical therapy may be indicated in some patients with a positive isoproterenol challenge.