Safety of slow pathway ablation in patients with long PR interval: further evidence of fast and slow pathway interaction

Incidence, clinical characteristics, electrophysiological characteristics and outcomes of patients with baseline PR prolongation undergoing radiofrequency ablation for Atrioventricular nodal reentrant tachycardia

AIMS AND OBJECTIVES

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common supraventricular tachycardia (SVT). Prolonged PR interval(>200 ms) on baseline electrocardiogram (ECG) is uncommon in such patients. The aim of the current study was to evaluate the incidence, clinical, electrophysiological characteristics, and outcomes of patients with baseline prolongation of PR interval undergoing radio-frequency ablation (RFA) for AVNRT.

METHODS

Over 10 years, out of the total number of 1435 patients with diagnosed AVNRT, 16 patients had prolonged PR intervals at baseline. All underwent elective RFA. A retrospective analysis of clinical, and electrophysiological characteristics and outcomes was done. The PR interval and atria-ventricular block cycle length values were compared with those patients with a normal interval at baseline and had undergone a successful slow pathway modification for AVNRT.

RESULTS

Out of 1435 patients with AVNRT, 16 (0.9 %) patients had baseline PR prolongation on ECG. The mean(+SD) age of the study population was 62.9 + 15.9 years. 10 (62.5 %) were males. The average PR interval was 264.2 + 24.1 ms. Slow fast AVNRT was seen in all. The anatomical site of success for ablation was the lower part of Koch's triangle in all patients. During ablation, a good sustained junctional rhythm was noted in all, with no AV (Atrioventricular) block or PR prolongation noted during ablation in any of the patients. PR interval decreased by more than 20 ms in 10 (62.5 %) patients. AVBCL (AV node block cycle length) increased on an average of 58.7 ms post-ablation. Only one patient developed AV block on follow-up.

CONCLUSION

A prolonged PR interval on baseline ECG is uncommon in patients with AVNRT. In these patients, slow pathway modification can be done safely and effectively. AVBCL (AV node block cycle length) increases immediately post-ablation. The risk of AV block though low persists on follow-up.

New insights into atrioventricular nodal anatomy, physiology, and immunochemistry: A comprehensive review and a proposed model of the slow-fast atrioventricular nodal reentrant tachycardia circuit in agreement with direct potential recordings in the Koch's triangle area

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most frequent regular tachycardia in humans. In this review, we describe the most recent discoveries regarding the anatomical, physiological, and molecular biological features of the atrioventricular junction that could underlie the typical slow-fast AVNRT mechanisms, as these insights could lead to the proposal of a new theory concerning the circuit of this arrhythmia. Despite several models have been proposed over the years, the precise anatomical site of the reentrant circuit and the pathway involved in the slow-fast AVNRT have not been conclusively defined. One possible way to evaluate all the hypotheses regarding the nodal tachycardia circuit in humans is to map this circuit. Thus, we tried to identify the slow potential of nodal and inferior extension structures by using automated mapping of atrial activation during both sinus rhythm and typical slow-fast AVNRT. This constitutes a first step toward the definition of nodal area activation in sinus rhythm and during slow-fast AVNRT. Further studies and technical improvements in recording the potentials of the atrioventricular node structures are necessary to confirm our initial results.

Impairment of the antegrade fast pathway in patients with atrioventricular nodal reentrant tachycardia can be functional and treated by slow pathway ablation: a case report study

Background

Slow pathway (SP) ablation is considered to be the standard treatment for symptomatic atrioventricular nodal reentrant tachycardia (AVNRT). This may be challenging in patients with documented PR interval prolongation due to the potential increased risk of atrioventricular (AV) block in some patients.

Case Summary

We report two cases of symptomatic recurrent AVNRT refractory to medical treatment with significant baseline PR interval prolongation (304 ms and 336 ms). In both of these cases, the baseline electrophysiological study demonstrated dual AV nodal physiology with a functional antegrade fast pathway and evidence for transient normalization of the PR interval. Slow/fast AVNRT was confirmed in both cases. Slow pathway ablation was successfully performed resulting in normalization of the PR interval to 144 ms and 168 ms with no evidence of AV block. After a mean follow-up of 30 months, the patients remained asymptomatic with normal PR interval, no recurrence of AVNRT, and no documentation of high degree AV block.

Discussion

Our cases illustrate a common dilemma when dealing with patients with AVNRT and prolonged baseline interval. We show that SP ablation is feasible and safe as long as a preserved antegrade FP is present.

Shortening of the atrial-His bundle interval during atrial pacing as a predictor of successful ablation for typical atrioventricular nodal re-entrant tachycardia

Aims

Shortening of the atrial-His bundle (AH) interval during the sinus rhythm is occasionally observed after slow pathway ablation for atrioventricular nodal re-entrant tachycardia (AVNRT). In addition, high-rate atrial pacing is useful for avoiding atrioventricular block. We hypothesized that shortening of the AH interval during slow pathway ablation under high-rate atrial pacing would lead to successful ablation of typical AVNRT.

Methods and results

This retrospective study included 37 patients in whom successful ablation of typical AVNRT was performed under atrial pacing. The AH interval was measured immediately before the first radiofrequency (RF) application and immediately after the last RF application, prior to the first induction. Twenty-five of 37 patients achieved procedural success at the first induction (i.e. successful group). No patients developed a prolonged AH interval or atrioventricular block. The AH interval was shortened by an average of 14.6 ± 7.7 and 1.8 ± 1.2 ms in the successful and other patient groups, respectively (P < 0.01). An AH interval decrease of > 10 ms was observed in 23 of 27 (85%) patients in the successful group, whereas all other patients had an AH interval decrease of < 5 ms.

Conclusion

Shortening of the AH interval during high-rate atrial pacing is a predictor of the successful ablation for typical AVNRT.

How to Approach Difficult Cases of AVNRT

OPINION STATEMENT

Our approach to the ablation of atrioventricular nodal reciprocating tachycardia (AVNRT), the most common supraventricular tachycardia, is as follows: We first attempt ablation in the right atrial posteroseptum anterior to the coronary sinus ostium with a 4-mm non-irrigated tip catheter. If ablation within the triangle of Koch is unsuccessful with radiofrequency (RF), we switch to cryoablation and target a more superior (mid septal) region. We also utilize cryoablation if RF ablation produces transient VA block (absence of retrograde conduction during junctional rhythm) or a fast junctional rhythm (<350 msec). If cryoablation were to fail, or is not available, we would then suggest ablation within the coronary sinus targeting the roof (2-4 cm from the os) using a 3.5-mm irrigated tip catheter. If tachycardia were still inducible despite these measures, we would then proceed with transseptal puncture (given our greater experience with this over a retrograde aortic approach) and perform RF ablation along the posteroseptal left atrium and inferoseptal mitral annulus utilizing an irrigated tip catheter. In our experience, cryoablation reliably results in elimination of the slow pathway. The only left atrial ablation for AVNRT at our institution in the past year was performed because a patent foramen ovale allowed for rapid left atrial access, facilitating left atrial ablation of the slow pathway.

Improvement of atrioventricular conduction following catheter ablation of atrioventricular nodal reentry tachycardia in a patient with a prolonged PR interval

We herein present the case of a 60-year-old male with narrow QRS tachycardia who had a remarkable PR prolongation during sinus rhythm. The tachycardia was diagnosed as a slow-fast atrioventricular nodal reentry tachycardia. Slow pathway ablation was performed after the confirmation of the presence of an antegrade fast pathway. Following the elimination of the slow pathway, the PR and atrio-His intervals became shortened from 470 and 420 to 170 and 120 ms, respectively. Moreover, the improvement of atrioventricular conduction after the slow pathway ablation lasted for at least 34 months.

Catheter ablation of atrioventricular nodal reentrant tachycardia in patients with a prolonged PR interval at sinus rhythm

Radiofrequency transcatheter ablation is an effective and safe treatment for atrioventricular node reentry tachycardia. Slow pathway ablation is considered the ablative technique of choice, but when atrioventricular nodal reentrant tachycardia is associated with a prolonged PR interval at sinus rhythm, a higher risk of delayed atrioventricular (AV) block has been reported. Studies on the subject are few, enrolling low numbers of patients with variable selection criteria and producing different results. Hence, optimal ablation strategy remains controversial. The aim of this study is to review the available knowledge on the topic. Experience from our centers is also briefly reported.

Fast pathway ablation using cryotherapy for a patient with a long PR interval in sinus rhythm and AVNRT

A 53-year-old man with previous aortic valve surgery presented with paroxysmal narrow complex tachycardia, induced by exercise. His PR interval was greater than 400 ms when in sinus rhythm and atrioventricular nodal reentry tachycardia (AVNRT) was diagnosed with invasive electrophysiological studies. Single echoes were repeatedly inducible with single-paced extrastimuli. Cryotherapy was then used to ablate the fast pathway using single echoes to monitor anterograde slow pathway and retrograde fast pathway function during ablation.

[Invasive electrophysiology: complications, nightmares and their management]

Most minor side effects of ablation in the right atrium and right ventricle relate to femoral venous catheterization but there is a small risk of severe complications including atrioventricular (AV) block, damage of surrounding structures and thromboembolic events. Impairment of AV conduction can occur during ablation of atrioventricular re-entrant tachycardia, ablation of anteroseptal, mid-septal and parahisian accessory pathways, ablation of ectopic atrial tachycardia originating from the vicinity of the atrioventricular node and when ablating the septal isthmus for typical atrial flutter. Damage of the right coronary artery is a very rare complication after inferior isthmus ablation with high energy. The thromboembolic risk during and after cardioversion and ablation of atrial flutter is higher than previously recognized and anticoagulation therapy decreases this risk. The risk of perforation and tamponade during ablation in the right atrium and right ventricle is very low but particular caution is necessary in thin-walled structures such as the coronary sinus and the upper right ventricular outflow tract. Phrenic nerve injury can be avoided by pacing from the mapping electrode before application of radiofrequency energy at the right atrial free wall. Limitation of power output depending on the site of ablation and titration of energy application with continuous control of temperature and impedance should be considered to minimize the risk of complications.

Ablation for Atrioventricular Nodal Reentrant Tachycardia with a Prolonged PR Interval During Sinus Rhythm: The Risk of Delayed Higher-Degree Atrioventricular Block

INTRODUCTION

Delayed higher-degree atrioventricular (AV) block can develop after slow pathway ablation for AV nodal reentrant tachycardia with a preexisting first-degree AV block. Retrograde fast pathway ablation is considered as an alternative approach for patients with a markedly prolonged PR interval and no demonstrable anterograde fast pathway function at baseline. This study aimed to determine the long-term reliability of AV conduction after retrograde fast pathway ablation in comparison to slow pathway ablation in patients with AV nodal reentrant tachycardia and a first-degree AV block at baseline.

METHODS AND RESULTS

Among 43 patients with AV nodal reentrant tachycardia and a prolonged PR interval (defined as >or=200 msec), 10 patients without demonstrable dual pathway physiology underwent ablation of the retrograde fast pathway, and 33 patients with dual pathway physiology underwent slow pathway ablation. Persisting intraprocedural second- or third-degree AV block requiring pacemaker implantation occurred in one patient (10%) after retrograde fast pathway ablation and in one patient (3%) after slow pathway ablation. During the long-term follow-up of 61 +/- 39 months after retrograde fast pathway ablation, no delayed second- or third-degree AV block occurred, and the PR interval remained unchanged (308 +/- 60 msec vs 304 +/- 52 msec). During the follow-up of 37 +/- 25 months after slow pathway ablation, a delayed complete heart block developed in two patients, and a second-degree AV block developed in two patients. Three patients aged 66, 75, and 76 years died suddenly of unknown cause 4, 16, and 48 months following slow pathway ablation, respectively.

CONCLUSIONS

Slow pathway ablation was associated with a significant risk of a delayed higher-degree AV block in patients with AV nodal reentrant tachycardia and a prolonged PR interval at baseline. Retrograde fast pathway ablation for patients with a first-degree AV block and no demonstrable dual pathway physiology was associated with a higher intraprocedural risk of complete AV block but did not result in the development of higher-degree AV block during the long-term follow-up of up to 9 years.

Long-term safety and efficacy of slow pathway ablation in patients with atrioventricular nodal re-entrant tachycardia and pre-existing prolonged PR interval

The association of atrioventricular nodal re-entrant tachycardia (AVNRT) and pre-existing prolonged PR interval is unusual. Radiofrequency (RF) ablation in such patients may be associated with an increased risk of immediate and delayed AV block. The aim of our study is to assess the long-term efficacy and safety of slow pathway ablation in this population. We studied 10 patients (4 males and 6 females) with pre-existing prolonged PR interval of 68 consecutive patients with AVNRT. All had slow-fast subtype of AVNRT. The mean PR interval was 222 +/- 15 ms before RF. The patients with pre-existing prolonged PR were older (69 +/- 15 vs. 54 +/- 17, P = 0.008) and their tachycardias were slower (387 +/- 102 vs. 323 +/- 73 ms; P < 0.05). Transient complete AV block (<5 s) occurred in two patients. None had permanent complete AV block. One patient had a significant increase in PR interval (from 220 to 320 ms). The mean post-RF PR interval was 232+/-37 ms (P = n.s.). Over a mean follow-up of 39 +/- 21 months, none had a recurrence of tachycardia nor developed higher degree AV block. In conclusion, in patients with AVNRT and pre-existing prolonged PR interval, a slow pathway ablation appeared efficient and safe. From our data, no delayed AV block developed on a long follow-up. Most of the patients with periprocedural transient AV block had no evidence of dual AV node physiology, suggesting that, in this population, absence of dual AV node physiology may be associated with a higher risk of AV block during slow pathway ablation.

Radiofrequency Catheter Ablation of Fast Pathway via Unconventional Right Subclavian Venous Access for Atrioventricular Nodal Reentrant Tachycardia

We report the case of a patient with atrioventricular nodal reentry tachycardia (AVNRT), who was found to have obstruction of the inferior vena cava (IVC) by a calcified mass during an electrophysiologic study (EPS). Subsequently, complete EPS was performed via a combined right internal jugular and subclavian venous access. Successful radiofrequency catheter ablation of the fast pathway was performed via the unconventional right subclavian venous route.

Retrograde fast pathway ablation for atrioventricular nodal reentry associated with markedly prolonged PR intervals

Three patients with typical atrioventricular nodal reentrant tachycardia (AVNRT) and markedly prolonged PR intervals (>300 ms) without dual pathway physiology at baseline or during isoproterenol infusion underwent successful fast pathway ablation and remained asymptomatic without recurrent AVNRT, atrioventricular block, or symptomatic bradycardia for a mean of 19 months. In patients with recurrent AVNRT and markedly prolonged PR intervals, selective ablation of the retrograde fast pathway can eliminate AVNRT without further impairment of anterograde atrioventricular nodal function.