Determinants of tachycardia induction using ventricular stimulation in dual pathway atrioventricular nodal reentrant tachycardia

Retrograde slow pathway conduction in patients with atrioventricular nodal re-entrant tachycardia

AIMS

To study retrograde slow pathway conduction by means of right- and left-sided septal mapping.

METHODS AND RESULTS

Nineteen patients with slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) were studied before and after slow pathway ablation. Simultaneous His bundle recordings from right and left sides of the septum, using trans-aortic and trans-septal electrodes, were made during right ventricular pacing. Pre-ablation, decremental retrograde ventriculo-atrial (VA) conduction without jumps or discontinuities was recorded in eight patients (group 1). In six patients, retrograde conduction jumps were demonstrated (group 2) and in the remaining four patients, there was minimal prolongation of stimulus to atrium (St-A) intervals (group 3). The maximal difference (Delta St-A) between St-A intervals obtained with pacing at a constant cycle length of 500 ms and at the cycle length with maximal retrograde VA prolongation was significantly longer measured from the right His compared with the left His (122 +/- 25 vs. 110 +/- 33 ms, P = 0.02, respectively) in group 1 and group 2 (140 +/- 23 vs. 110 +/- 35 ms, P = 0.03), but not in group 3 (10 +/- 4 vs. 13 +/- 8 ms, P = 0.35). Post-ablation, Delta St-A intervals were similar between right and left His recordings (77 +/- 37 vs. 76 +/- 33 ms, P = 0.53, respectively) in group 1, (100 +/- 24 vs. 103 +/- 21 ms, P = 0.35) group 2, and (63 +/- 32 vs. 66 +/- 33 ms, P = 0.35) group 3.

CONCLUSION

In patients with typical AVNRT, retrograde conduction through the slow pathway results in earliest retrograde atrial activation on the left side of the septum and catheter ablation in the right inferoparaseptal area abolishes this pattern. These findings are compatible with the concept of slow pathway conduction by means of the inferior AV nodal extensions.

The Electrophysiologic Characteristics in Patients with Only Ventricular-Pacing Inducible Slow–Fast Form Atrioventricular Nodal Reentrant Tachycardia

BACKGROUND

Atrioventricular nodal reentrant tachycardia (AVNRT) can be usually induced by atrial pacing or extrastimulation. However, it is less commonly induced only by ventricular pacing or extrastimulation.

OBJECTIVE

The purpose of this retrospective study was to investigate the electrophysiologic characteristics in patients with slow-fast form AVNRT that could be induced only by ventricular pacing or extrastimulation.

METHODS

The total population was 1497 patients associated with AVNRT. There were 1373 (91.7%) patients who had slow-fast form AVNRT included in our study. Group 1 (n = 45) could be induced only by ventricular pacing or extrastimulation, and Group 2 (n = 1328) could be induced by only atrial stimulation or both atrial and ventricular stimulation. The electrophysiologic characteristics of the group 1 and group 2 patients were compared.

RESULTS

Group 1 patients had a significantly lower incidence of both antegrade and retrograde dual AV nodal pathways. The pacing cycle length (CL) of the antegrade 1:1 fast pathway (FP) and antegrade ERP of the FP were both significantly shorter in Group 1 patients. Mean antegrade FRP of the fast and slow pathways were significantly shorter in Group 1 patients. The differences of pacing CL of 1:1 antegrade conduction, antegrade ERP and FRP were much longer in Group 2 patients.

CONCLUSION

This study demonstrated the patients with slow-fast form AVNRT that could be induced only by ventricular stimulation had a lower incidence of dual AV nodal pathways and the different electrophysiologic characteristics (shorter pacing CL of the antegrade 1:1 FP, antegrade ERP of the FP and the differences of pacing CL of 1:1 antegrade conduction, antegrade ERP and FRP) from the other patients. The specific electrophysiologic characteristics in such patients could be the reason that could be induced only by ventricular stimulation.

Standard Right Atrial Ablation is Effective for Atrioventricular Nodal Reentry with Earliest Activation in the Coronary Sinus

INTRODUCTION

Reports suggest that coronary sinus (CS) or left atrial ablations may be necessary for treatment of AV nodal reentrant tachycardia (AVNRT) with earliest retrograde atrial activation in the CS. We assessed the efficacy of standard right atrial catheter ablation approaches in these tachycardias and determined the incidence of earliest activation in the CS in AVNRT.

METHODS AND RESULTS

We retrospectively evaluated intracardiac recordings from 225 consecutive patients who underwent electrophysiologic studies and radiofrequency (RF) ablation for AVNRT in two institutions. Atrial activation during AVNRT was evaluated using multiple catheters according to standard protocol used in our laboratories. RF ablations in the triangle of Koch were performed in all patients. Eighteen of 225 patients (8%) had earliest activation in one of the CS poles. The demographics and AVNRT characteristics of these 18 patients were similar to those of the other 207 patients who did not have CS as earliest activation site and included both typical and atypical AVNRT. Following RF ablation, none of the 18 patients had inducible AVNRT.

CONCLUSION

Successful RF ablation can be performed at standard sites in the triangle of Koch regardless of earliest site of atrial activation. The incidence of CS as earliest retrograde atrial activation site in AVNRT is 8%.

Coronary sinus pacing initiates counterclockwise atrial flutter while pacing from the low lateral right atrium initiates clockwise atrial flutter. Analysis of episodes of direct initiation of atrial flutter

INTRODUCTION

Rapid atrial pacing in sinus rhythm may directly induce atrial flutter without provoking intervening atrial fibrillation, or initiate atrial flutter indirectly, by a conversion from an episode of transient atrial fibrillation provoked by rapid atrial pacing. The present study was performed to examine whether or not the direct induction of clockwise or counterclockwise atrial flutter was pacing-site (right or left atrium) dependent.

METHODS AND RESULTS

We analyzed the mode of direct induction of atrial flutter by rapid atrial pacing. In 46 patients with a history of atrial flutter, rapid atrial pacing with 3 to 20 stimuli (cycle length = 500 - 170 ms) was performed in sinus rhythm to induce atrial flutter from 3 atrial sites, including the high right atrium, the low lateral right atrium, and the proximal coronary sinus, while recording multiple intracardiac electrograms of the atria. Direct induction of atrial flutter by rapid atrial pacing was a rare phenomenon and was documented only 22 times in 15 patients: 3, 11, and 8 times during stimulation, respectively, from the high right atrium, low lateral right atrium, and the proximal coronary sinus. Counterclockwise atrial flutter (12 times) was more frequently induced with stimulation from the proximal coronary sinus than from the low lateral right atrium (8 vs 1, P = .0001); clockwise atrial flutter (10 times) was induced exclusively from the low lateral right atrium (P = .0001 for low lateral right atrium vs proximal coronary sinus, P = .011 for low lateral right atrium vs high right atrium).

CONCLUSIONS

Direct induction of either counterclockwise or clockwise atrial flutter was definitively pacing-site dependent; low lateral right atrial pacing induced clockwise, while proximal coronary sinus pacing induced counterclockwise atrial flutter. Anatomic correlation between the flutter circuit and the atrial pacing site may play an important role in the inducibility of counterclockwise or clockwise atrial flutter.

Initial onset of accessory pathway-mediated and atrioventricular node reentrant tachycardia after age 65: clinical features, electrophysiologic characteristics, and possible facilitating factors

OBJECTIVE

To evaluate the clinical features electrophysiologic characteristics, and possible facilitating factors in older patients (> or = 65 years) with initial onset of accessory pathway-mediated and atrioventricular (AV) node reentrant tachycardia.

DESIGN

Of the patients undergoing electrophysiologic study and radiofrequency catheter ablation of accessory pathway-mediated and AV node reentrant tachycardia at this institution, patients with initial tachyarrhythmia after age 65 years were compared with those presenting initially before age 30.

SETTING

A tertiary medical center for the general public.

PARTICIPANTS

Sixty-six patients had their initial symptoms after age 65: Group I, 32 patients with accessory pathway-mediated tachycardia, and Group II, 34 patients with AV node reentrant tachycardia. Four-hundred forty patients had their initial symptoms before age 30: Group III, 283 with accessory pathway mediated tachyarrhythmia, and Group IV, 157 with AV node reentrant tachycardia.

INTERVENTION

All patients underwent electrophysiological study to determine the mechanisms of tachyarrhythmia, and radiofrequency catheter ablation for treatment of tachycardia.

RESULTS

(1) Older patients with initial arrhythmia had incidence of critical clinical manifestations, including tachyarrhythmia-related syncope and cardioversion, similar to those with initial arrhythmia at a younger age. (2) Patients in Group III, showed anterograde effective refractory period (ERP) of the AV node (P = .432), longer anterograde ERP of the accessory pathway (P = .004), and greater difference of the anterograde ERP between the AV node and the accessory pathway (D-ERP) (P = .003) similar to patients in group I. In Group II, the ERP and Wenckebach cycle length of the retrograde fast pathway was significantly longer than in Group IV (P = .037 and P < .001, respectively), and a greater percentage of patients in Group II than in Group IV AV node reentrant tachycardia needed isoproteronol to facilitate the induction of reentrant tachycardia (P = .034). (3) Patients in Group I and Group II had a higher incidence of supraventricular and ventricular ectopic activity than those in Group III (P = .002 and P = .005, respectively) and Group IV (P = .024 and P = .012, respectively) in 24-hour ambulatory electrocardiograms.

CONCLUSION

The initial onset of accessory pathway-mediated tachycardia after age 65 may be caused by changes of electrophysiologic properties (greater D-ERP) as well as increased supraventricular and ventricular ectopic activity. Influence of the autonomic nervous system, rather than changes of conduction properties in the AV node, and increase in ectopic activity may contribute to the new onset of AV node reentrant tachycardia in older adults. The choice of antiarrhythmic drugs and radiofrequency ablation require attention to the clinical profile and facilitating factors of reentrant tachycardia in this group of patients.

NASPE Young Investigator Awardee-1993. Computer model of the atrioventricular node predicts reentrant arrhythmias

INTRODUCTION

Following atrial premature beats, the AV node may exhibit sustained reentrant tachyarrhythmias, isolated echo beats, or discontinuities in the recovery curve (the plot of conduction time versus atrial cycle length). A computer model was used to examine the hypothesis that spatial variation of AV nodal passive electrical resistance may account for these phenomena.

METHODS AND RESULTS

A computer model of a rectangular lattice of electrotonically linked elements whose ionic kinetics simulated nodal ionic flux was developed. The model showed that there exists a resistance value that minimizes the effective refractory period, because high resistance prevents depolarization of distal elements, while low resistance allows leakage of depolarizing current by electrotonic transmission, preventing activation of proximal elements. High resistances stabilized reentry by slowing conduction. Simulations incorporating equal resistance values between elements predicted increased AV nodal conduction times with increasing prematurity of atrial impulses. A model with a gradual change in resistance between fibers produced discontinuities and tachycardia, but not both simultaneously. Uniform anisotropy produced preferential transverse block, leading to echo beats and "fast-slow" tachycardia, but not recovery curve discontinuities. Nonuniform anisotropy could produce reentry, but tachycardia often occurred without discontinuities. Dividing the lattice into two electrotonically linked parallel pathways with different resistance values ("dual pathway model") predicted recovery curve discontinuities, echo beats, and tachycardia. At critical atrial cycle lengths, only the (high resistance) slow pathway conducted antegradely, while the fast pathway conducted retrogradely, to generate the typical "slow-fast" tachycardia. Responses of the dual pathway model to ablation were consistent with clinical data, including the previous observation of a decrease in fast pathway effective refractory period after slow pathway ablation.

CONCLUSION

Differences in passive electrical resistance of electronically linked dual pathways within the AV node may account for functional longitudinal dissociation, reentrant arrhythmias, and responses to catheter ablation therapy.

Determinants of simultaneous fast and slow pathway conduction in patients with dual atrioventricular nodal pathways

Double His bundle and ventricular responses to a single atrial impulse caused by a simultaneous fast and slow pathway conduction was observed during electrophysiologic study in three patients with dual-pathway atrioventricular nodal reentrant paroxysmal supraventricular tachycardia. In patient No. 1 this phenomenon occurred during rapid atrial pacing, in patient No. 2 during both rapid atrial pacing and delivery of a single atrial extrastimulus, and in patient No. 3 during delivery of double atrial extrastimuli. Retrograde unidirectional block in the slow pathway was suggested by retrograde induction of tachycardia at a long ventricular paced cycle length and/or long ventricular coupling interval in all three patients. Our findings suggest that major determinants of this phenomenon include: a sufficient conduction delay in the slow pathway so that the distal tissue is able to respond for the second time, and a retrograde unidirectional block in the slow pathway so that the fast pathway impulse will not enter and collide with the oncoming slow pathway impulse.