Evaluation of fast pathway function: the importance of autonomic tone

Coronary sinus morphology in pediatric patients with supraventricular tachycardia

PURPOSE

The anatomic basis of atrioventricular node reentrant tachycardia (AVNRT) remains incompletely characterized in children. Differences in coronary sinus (CS) size and morphology have been observed in adults with AVNRT but have not been well characterized in children.

METHODS

Children (< 18 years) brought to the EP lab with supraventricular tachycardia for ablation underwent CS venography. A blinded pediatric interventional cardiologist performed CS measurements, which were indexed to body surface area. Patients were excluded if they were < 25 kg or had significant congenital heart disease.

RESULTS

Forty-six patients (age 14.2 ± 3.3 years) met inclusion criteria, 17 with AVNRT and 32 with an accessory pathway (AP). CS ostium (LAO projection, end-systole) was 7.8 ± 2.9 mm/m² for the AVNRT group versus 6.0 ± 2.5 mm/m² for the AP group (p = 0.04). CS "windsock" morphology was more prevalent in the AVNRT group (16/17, 94.1%) than the AP group (11/32, 34.3%) (p < 0.001). Within the AVNRT group, there was no correlation between CS ostium size and tachycardia cycle length (R = 0.01, p = 0.96), fast-pathway ERP (FPERP) (R = 0.42, p = 0.12), or A2-H2 at the FPERP (R = 0.25, p = 0.39).

CONCLUSIONS

Children with AVNRT have larger CS ostia and more prevalent windsock morphology. CS size/morphology did not correlate with EP properties of the AVNRT substrate. These features may explain the basis for the development of the electrophysiologic substrate for dual AV node physiology in children.

Prolongation of the fast pathway effective refractory period during cryoablation in children: a marker of slow pathway modification

BACKGROUND

The fast pathway effective refractory period (ERP) has been reported to decrease after slow pathway modification with radiofrequency (RF) energy. How the fast pathway ERP changes during the ablation application has not been reported with either RF or cryoenergy.

OBJECTIVES

Using the unique features of cryotherapy, this study assesses the short-term changes in fast pathway ERP during cryomodification of the slow pathway and examines whether these changes are a useful marker for successful slow pathway modification in children.

METHODS

Nineteen pediatric patients (median age 15.1 years, range 9.6-19.6 years; weight 60.7 kg, range 35.6-130.2 kg) with anterograde dual AV nodal physiology underwent slow pathway modification with catheter-based cryoablation. Programmed stimulation was performed during cryoapplications after reaching -25 degrees C to assess fast pathway and slow pathway conduction. Data were analyzed from 59 of 237 cryoapplications where the fast pathway ERP was measured more than once (n = 13 patients).

RESULTS

For 23 of 59 applications where the slow pathway was modified, the fast pathway ERP significantly increased during cryotherapy (Delta = 33.5 ms, P <.0001). The magnitude of fast pathway ERP prolongation during cryotherapy was larger when the slow pathway was modified than when there was no effect on slow pathway conduction (33.5 +/- 30.5 vs 5.8 +/- 18.9 ms, P =.0005). Prolongation of fast pathway ERP by >/=20 ms had 70% sensitivity and 72% specificity for predicting slow pathway modification. Following termination of cryoapplications, which resulted in slow pathway modification, the fast pathway ERP had significantly decreased from baseline (difference 44.5 ms, P <.0001). The effect on fast pathway ERP was not related to changes in cycle length during (R(2) = 0.04, P = .045) or after ablation (R(2) = 0.13, P = .012).

CONCLUSION

The fast pathway ERP prolongs during cryoapplications that result in slow pathway modification and shortens after termination of cryoapplications. The magnitude of fast pathway ERP prolongation during cryoapplication may be useful as a marker for successful slow pathway modification.

Delineation of AV Conduction Pathways by Selective Surgical Transection: Effects on Antegrade and Retrograde Transmission

INTRODUCTION

The role for transitional cells as determinants of AH and HA conduction was examined in the superfused rabbit AV junction.

METHODS

Bipolar electrodes and microelectrodes were used to record antegrade A-H and retrograde H-A activation, before and after transection of the transitional cell input to the compact AV node.

RESULTS

During pacing from the high right atrium, inferior to the coronary sinus os, beneath the fossa ovalis, or on the anterior limbus, AV Wenckebach block (WB) was mediated by identical transitional cells grouped in close apposition to the compact AV node. Paced WB cycle lengths were shorter from the high right atrium (196+/-12 msec) and inferior to the coronary sinus os (195+/-8 msec) versus the fossa ovalis (217+/-9 msec) or anterior limbus (206+/-11 msec). With His bundle pacing, retrograde HA WB (211+/-17 msec) was observed within the N cell region within the compact AV node. After transection of posterior and superior transitional cell input to the compact AV node, the antegrade AH WB cycle length was prolonged (245+/-18 msec), with an increased WB incidence within the NH region (compact AV node)(5% to 41%; p=0.014). The incidence of retrograde HA WB determined within the NH region was increased (30% to 88%), with a decrease in the stimulus-fast pathway conduction time (98+/-7 to 49+/-6 msec; p<0.01).

CONCLUSIONS

The data demonstrate (1) a common transitional cell population determining AH WB, independent of atrial stimulation site, and (2) a plasticity of transitional cell-compact AV node connections, with rapid AH and HA conduction favored by removal of posterior/superior AV nodal input.