Significance of bundle branch block during atrioventricular nodal reentrant tachycardia

Implications of 2:1 atrioventricular block during typical atrioventricular nodal reentrant tachycardia

OBJECTIVE

The effects of 2:1 AV block (AVB) on AV nodal reentrant tachycardia (AVNRT) remain to be elucidated. This study was performed to localize the site of 2:1 AVB and elucidate the effects of 2:1 AVB on typical AVNRT.

METHODS

The His bundle (HB) electrograms during typical AVNRT with 2:1 AV block were reviewed in 24 patients. It was hypothesized that if 2:1 AVB at the HB or below changed tachycardia cycle length (TCL), the lower turnaround point of the reentrant circuit (RC) might be located within the HB and parts of the HB might be involved in the RC.

RESULTS

A HB potential was absent in blocked beats during 2:1 AVB in four patients (supra-Hisian block), and the maximal amplitude of the HB potential in blocked beats was the same as that in conducted beats in four patients (infra-Hisian block), and was significantly smaller than that in conducted beats (0.1 +/- 0.1 versus 0.5 +/- 0.2 mV, P < 0.05) in 16 patients (intra-Hisian block). Eight patients (33%) with intra-Hisian block had a nearly identical prolongation of the H-A and A-A intervals in blocked beats (12 +/- 3 and 13 +/- 2 ms, respectively) with unchanged A-H intervals, while the remaining 16 patients (67%) exhibited invariable A-A and/or H-A intervals.

CONCLUSION

The site of 2:1 AVB during typical AVNRT was estimated to be at the HB or below in 83% of the cases. Two-to-one intra-Hisian block transiently prolonged TCL, possibly indicating involvement of the proximal HB in the RC in one-third of typical the AVNRT cases with 2:1 AVB.

Participation of a concealed atriohisian tract in the reentrant circuit of the slow–fast type of atrioventricular nodal reentrant tachycardia

BACKGROUND

The retrograde fast pathway in typical atrioventricular nodal reentrant tachycardia (AVNRT) exhibits marked variation in its electrophysiologic properties.

OBJECTIVE

The purpose of this study was to characterize the retrograde fast pathway and localize the lower turnaround site of the reentrant circuit in typical AVNRT.

METHODS

Seventy-four patients with typical AVNRT were divided into two groups according to the response of the retrograde fast pathway to intravenous administration of adenosine triphosphate (ATP) during ventricular pacing: ATP-S [n = 47 (63.5%)] with and ATP-R without [n = 27 (36.5%)] His-atrial (H-A) block. H-A intervals were measured from the most proximal His-bundle electrogram to the earliest atrial activation during the tachycardia (HAt) and entrainment pacing from the parahisian right ventricular region (HAe). It was postulated that the HAt was the difference in conduction time between the lower common pathway (x) and retrograde fast pathway (y) (HAt = y - x), whereas HAe was the sum of the two (HAe = y + x). Hence, x = (HAe-HAt)/2. x >0 suggested the presence of a lower common pathway, whereas x <0 suggested the absence of a lower common pathway and lower turnaround site within the His bundle.

RESULTS

x was significantly smaller in ATP-R than ATP-S (-6 +/- 5 vs 4 +/- 4 ms, P <.05) and was <0 in 23 (85%) of 27 ATP-R patients. The maximal increment in H-A interval during ventricular pacing was significantly longer in ATP-S than ATP-R (35 +/- 33 vs 2 +/- 2 ms, P <.05).

CONCLUSION

A concealed atriohisian tract totally bypassing the atrioventricular node constituted the retrograde fast pathway in one third of all typical AVNRT cases.

Effects of right bundle branch block during atrioventricular nodal reentrant tachycardia

BACKGROUND

The significant role of bundle branch block during atrioventricular nodal reentrant tachycardia (AVNRT) is not clear. The purposes of this study were to study the effects of complete right bundle branch block (RBBB) on electrophysiological parameters during AVNRT and to define the significance of complete RBBB during AVNRT.

METHODS AND RESULTS

According to characteristics of electrocardiogram during sinus rhythm and AVNRT, 50 patients who underwent catheter ablation for slow-fast AVNRT were divided into three groups. Group I included 20 patients who had narrow QRS (< or = 110 ms) during sinus rhythm and AVNRT. Group II included 18 patients who had persistent RBBB (< or = 120 ms) during sinus rhythm and AVNRT. Group III included 12 patients who had narrow QRS during sinus rhythm, but they had narrow QRS and transient RBBB during AVNRT. The atrio-His (AH) interval (296+/-60 vs. 288+/-75 ms), His-ventricular (HV) interval (36+/-11 vs. 35+/-11 ms), His-atrial (HA) interval (72+/-24 vs. 71+/-28 ms), VA(HRA) interval (defined as the interval between the onset of ventricular depolarization and the onset of atrial activity of right high atrium; 34+/-24 vs. 37+/-25 ms), VA(CSO) interval (defined as the interval between the onset of ventricular depolarization and the onset of atrial activity of coronary sinus ostium; 13+/-28 vs. 26+/-23 ms) and tachycardia cycle length (TCL; 368+/-67 vs. 359+/-73 ms) during AVNRT were similar between group I and group II (all P > 0.05). In group III, the AH interval (255+/-81 vs. 246+/-83 ms), HV interval (44+/-5 vs. 42+/-11 ms), HA interval (66+/-19 vs. 70+/-15 ms), VA(HRA) interval (27+/-15 vs. 29+/-16 ms), VA(CSO) interval (23+/-25 vs. 21+/-25 ms) and TCL (322+/-76 vs. 316+/-77 ms) were not significantly different between AVNRT with narrow QRS and those with transient RBBB (all P > 0.05).

CONCLUSIONS

Persistent RBBB and transient RBBB have no significant effects on the electrophysiological parameters during AVNRT. These findings suggest that RBBB might not influence the conduction of lower common pathway or the circuit of AVNRT.