Selective blockade of retrograde fast pathway by intravenous disopyramide in paroxysmal supraventricular tachycardia mediated by dual atrioventricular nodal pathways

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.

Variable responsiveness of anterograde and retrograde fast pathway conduction to adenosine in patients with typical AV-nodal reentry tachycardia

Adenosine is known as a substance which depresses predominantly the slow pathway of the av-node. However, the effect of adenosine on the anterograde and retrograde fast pathway (FP) has not been studied in a large patient population. Ninety-one patients with inducible typical av-nodal reentrant tachycardias (AVNRT) were included. The clinically used dosage of 12 mg adenosine was administered subsequently as bolus injection during a constant atrial and ventricular pacing (500 ms) in all patients. Electrophysiological av-nodal parameters were determined. A higher responsiveness of the anterograde compared to the retrograde FP was observed: the majority of patients (76%) blocked anterogradely and 55% blocked retrogradely within the FP after the administration of 12 mg adenosine. Thirty-six percent of all patients revealed a differential behaviour to adenosine. Sixteen percent of all patients were completely resistant to adenosine (P=0.012). Electrophysiological parameters did not predict the responsiveness of the FP to adenosine. In patients with typical AVNRT the anterograde FP shows a higher sensitivity than the retrograde FP to adenosine. This might reflect an anatomical and/or functional distinction between anterograde and retrograde FP. The variable response to adenosine could be due to individual anatomical and electrophysiological heterogenity of the perinodal tissue and the av-node.

Atrioventricular nodal reentry tachycardia in patients with sinus node dysfunction: electrophysiologic characteristics, clinical presentation, and results of slow pathway ablation

INTRODUCTION

Sinus node dysfunction (SND) is frequently associated with impaired AV conduction. This study investigated the electrophysiologic properties of dual AV nodal pathways in patients suffering from both SND and AV nodal reentrant tachycardia (AVNRT).

METHODS AND RESULTS

Two groups of patients with slow-fast AVNRT underwent invasive electrophysiologic testing and catheter ablation of the slow pathway. Group A comprised 10 patients with SND (age 70 +/- 8 years). Group B included 10 age-matched patients without SND (age 69 +/- 7 years; P = NS) who served as controls. Patients of group A exhibited prolongation of the anterograde Wenckebach cycle lengths (WBCLs) of both the fast pathway (559 +/- 96 vs 361 +/- 38 msec; P < 0.01) and the slow pathway (409 +/- 57 vs 339 +/- 32 ms; P < 0.01). However, the delta between the WBCLs of the fast and the slow pathways was larger in patients of group A (150 +/- 80 vs 22 +/- 20 msec; P < 0.01). Retrograde fast pathway conduction was well preserved with no difference in WBCLs (356 +/- 42 vs 330 +/- 47 msec; P = NS). Cycle lengths of AVNRT were longer in group A (468 +/- 46 vs 363 +/- 37 msec; P < 0.01). Clinically, all patients of group A suffered from multiple episodes of AVNRT per week, which was not the case in any patient of group B (P < 0.01). Catheter ablation of the slow pathway eliminated AVNRT in all patients without complications.

CONCLUSIONS

Patients with AVNRT and SND exhibit characteristic electrophysiologic alterations of both AV nodal pathways. Clinically, this results in significantly more frequent episodes of tachycardia. Slow pathway ablation appears to be safe and effective in these patients.

Differential effects of adenosine on antegrade and retrograde fast pathway conduction in atrioventricular nodal reentry

Although adenosine depresses antegrade atrioventricular (AV) nodal conduction, the effects of adenosine on antegrade and retrograde fast pathway conduction in AV nodal reentry have not been determined. In 17 patients (five men, 12 women, mean age 49 +/- 12 years) with common slow-fast AV nodal reentrant tachycardia, the antegrade slow pathway conduction was selectively and completely ablated by radiofrequency catheter ablation while the antegrade and retrograde fast pathway conduction remained intact. During high right atrial pacing at a mean pacing cycle length of 474 +/- 36 msec, adenosine was rapidly injected intravenously at an initial dose of 0.5 mg followed by stepwise increases of 0.5 mg or 1.0 mg given at 5-minute intervals until second-degree AV block developed. During right ventricular apical pacing at the same pacing cycle lengths (mean 474 +/- 36 msec) as those in the study of antegrade conduction, intravenous injection of incremental doses of adenosine was repeated until ventriculoatrial (VA) block occurred. The adenosine-induced prolongation of VA conduction was also determined in the presence of verapamil (loading dose 0.15 mg/kg, maintenance dose 0.005 mg/kg/min) in seven of 17 patients. The dose of adenosine required to produce AV block, the increase in the atrio-His interval by 50% and the maximal response were 3.4 +/- 1.4 mg, 1.8 +/- 0.6 mg, and 58% +/- 5%, respectively. On the other hand, the dose of adenosine required to produce VA block, the increase in the VA interval by 50%, and the maximal response were 8.2 +/- 2.9 mg, 3.4 +/- 0.6 mg, and 20% +/- 5%, respectively, in the control and 3.7 +/- 0.5 mg, 3.5 +/- 0.7 mg, and 23% +/- 5%, respectively, in the presence of verapamil. In conclusion, adenosine has a differential potency to depress AV and VA conduction in patients with AV nodal reentry, with greater potency for slowing antegrade fast than retrograde fast pathway conduction. Verapamil had an additive effect to adenosine on slowing retrograde VA conduction, which further supports the evidence that the retrograde fast pathway in part involves an AV nodal-like structure.

"AV nodal" reentry: Part II: AV nodal, AV junctional, or atrionodal reentry?

The classical model of "atrioventricular (AV) nodal" reentrant tachycardia suggests that the reentrant circuit is entirely within the compact AV node and that AV nodal tissue is present proximal and distal to the circuit. Recent evidence from mapping studies and from examination of the effects of curative procedures, however, suggests that the upper end of the circuit uses perinodal atrial or transitional tissue. Moreover, the anatomical substrate of dual "AV nodal" pathways is likely to be the multiple connections between compact AV node and atrium rather than discrete intranodal pathways. The antegrade slow pathway appears to be situated at the posteroinferior approaches to the AV node in the region between the coronary sinus orifice and the tricuspid annulus. The retrograde fast pathway appears to be situated in the anterior atrionodal connections at the apex of Koch's triangle, close to the His bundle. The lower turnaround point of the circuit is likely to be within the AV node.

Disopyramide. A reappraisal of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in cardiac arrhythmias

Disopyramide is a widely used class IA antiarrhythmic drug with a pharmacological profile of action similar to that of quinidine and procainamide. Over the past 10 years disopyramide has demonstrated its efficacy in ventricular and atrial arrhythmias. In therapeutic trials, usually involving small numbers of patients, the efficacy of disopyramide was comparable with that of mexiletine, perhexiline, tocainide, propafenone or prajmalium. Recent comparisons with quinidine have confirmed the similar efficacy and better tolerability of disopyramide. The suggestion from initial studies that disopyramide may be less effective than amiodarone or flecainide requires further investigation. In addition, studies have failed to demonstrate that the early administration of disopyramide after acute myocardial infarction decreases important arrhythmias or early mortality. Thus, disopyramide is now well established as an effective antiarrhythmic drug in ventricular and supraventricular arrhythmias although its role in therapy relative to that of recently introduced antiarrhythmic agents is not clear.

Slow inward current and cardiac arrhythmias

The slow inward current contributes to the normal electrical and contractile activity of several cardiac and vascular tissues and also may mediate the electrical abnormalities responsible for certain cardiac arrhythmias. The slow inward current differs from the fast inward sodium current in that it is carried primarily by calcium rather than sodium, requires a more positive level of membrane potential to be activated, has slower activation and inactivation kinetics, is responsible for normal depolarization in sinus and atrioventricular (AV) nodal cells and is blocked by a rather specific group of agents that includes verapamil, diltiazem and nifedipine. Recent data suggest that slow-channel openings occur in bursts, separated by silent periods, and that less negative membrane potentials and beta-adrenergic stimulation increase the probability that the channels will open. Inactivation of the channels is associated with a lower probability of channel opening. Slow-channel blocking agents such as verapamil, diltiazem and nifedipine appear to bind to activated, rather than rested, slow channels. Therefore, their effects are more prominent at faster pacing rates and at less negative membrane potentials. Clinically occurring cardiac arrhythmias dependent on the slow inward current include primarily sinus and AV nodal reentry and reciprocating tachycardia in the Wolff-Parkinson-White syndrome when one of the pathways incorporates the AV node. Damaged atrial, ventricular and specialized tissue also can generate slow response-mediated reentry or forms of automaticity that may be clinically important under certain circumstances.

Salutary effects of intravenous ajmaline in patients with paroxysmal supraventricular tachycardia mediated by dual atrioventricular nodal pathways: blockade of the retrograde fast pathway

Electrophysiologic effects of 50 mg iv ajmaline were evaluated in 10 patients with atrioventricular nodal reentrant paroxysmal supraventricular tachycardia (PSVT) utilizing the slow pathway for antegrade and the fast pathway for retrograde conduction. Ajmaline terminated the PSVT in all 10 patients in 17 to 165 sec (mean 94 +/- 49 sec): by ventriculoatrial block in eight, AH block in one, and intra-atrial reentry in one patient. The predrug mean PSVT cycle length of 289 +/- 44 msec (range 240 to 350) increased significantly to 373.5 +/- 60 msec (range 263 to 464; p less than .01) before the tachycardia was terminated. The increase in cycle length was a function of both AH and HA prolongation. In all 10 patients ajmaline depressed conduction through the retrograde fast pathway, as evidenced by the increase in mean ventricular paced cycle length producing ventriculoatrial block from less than or equal to 280 +/- 40 to 438 +/- 93 msec (p less than .001), and the increase in the effective refractory period of the ventriculoatrial conduction system from less than or equal to 241 +/- 42 to less than or equal to 298 +/- 62 msec (p less than .05); the drug abolished ventriculoatrial conduction in four cases. The effective refractory period of the antegrade fast pathway was unchanged after ajmaline (less than or equal to 281 +/- 31 vs less than or equal to 275 +/- 38 msec; p = NS), but conduction through the antegrade slow pathway was depressed (atrial paced cycle length producing AH block 269 +/- 30 msec before and 312 +/- 44 msec after drug; p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)