Voltage and propagation mapping: New tools to improve successful ablation of atrioventricular nodal reentry tachycardia.

INTRODUCTION: Mapping system is useful in ablation of atrioventricular nodal reentry tachycardia (AVNRT) and localization of anatomic variances. Voltage mapping identifies a low voltage area in the Koch triangle called low-voltage-bridge (LVB); propagation mapping identifies the collision point (CP) of atrial wavefront convergence. We conducted a prospective study to evaluate the relationship between LVB and CP with successful site of ablation and identify standard value for LVB. MATERIALS AND METHODS: Three-dimensional (3D) maps of the right atria were constructed from intracardiac recordings using the ablation catheter. Cut-off values on voltage map were adjusted until LVB was observed. On propagation map, atrial wavefronts during sinus rhythm collide in the site representing CP, indicating the area of slow pathway conduction. Ablation site was selected targeting LVB and CP site, confirmed by anatomic position on fluoroscopy and atrioventricular ratio. RESULTS: Twenty-seven consecutive patients were included. LVB and CP were present in all patients. Postprocedural evaluation identified standard cut-off of 0.3-1 mV useful for LVB identification. An overlap between LVB and CP was observed in 23 (85%) patients. Procedure success was achieved in all patient with effective site at first application in 22 (81%) patients. There was a significant correlation between LVB, CP, and the site of effective ablation (p = .001). CONCLUSION: We found correlation between LVB and CP with the site of effective ablation, identifying a voltage range useful for standardized LVB identification. These techniques could be useful to identify ablation site and minimize radiation exposure.

Validation of dual atrioventricular nodal physiology in dual atrioventricular nodal non-reentrant tachycardia via adenosine triphosphate injection during atrial pacing: A novel insight into the role of leftward inferior extension.

INTRODUCTION: Dual atrioventricular nodal non-reentrant tachycardia (DAVNNT) is a rare and challenging-to-diagnose arrhythmia, without previous reports associating it with a leftward inferior extension (LIE). METHODS: Diagnosis was made using adenosine triphosphate (ATP) injection during atrial pacing in a suspected DAVNNT patient. RESULTS: Ablation of the rightward inferior extension was unsuccessful in eliminating DAVNNT; however, subsequent ablation of the LIE successfully eradicated the arrhythmia. CONCLUSION: This unique case, marked by the first instance of DAVNNT caused by LIE, diagnosed through ATP injection, underscores the utility of this diagnostic approach and broadens the spectrum of our understanding and management of this condition.

High-density mapping of Koch's triangle during sinus rhythm and typical atrioventricular nodal re-entrant tachycardia, integrated with direct recording of atrio-ventricular node structure potential.

BACKGROUND: The mechanism of typical slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) and its anatomical and electrophysiological circuit inside the right atrium (RA) and Koch's Triangle (KT) are not well known. OBJECTIVE: To identify the potentials of the compact AV node and inferior extensions and to perform accurate mapping of the RA and KT in sinus rhythm (SR) and during AVNRT, to define the tachycardia circuit. METHODS: Consecutive patients with typical AVNRT were enrolled in 12 Italian centers and underwent mapping and ablation by means of a basket catheter with small electrode spacing for ultrahigh-density mapping and a modified signal-filtering toolset to record the potentials of the AV nodal structures. RESULTS: Forty-five consecutive cases of successful ablation of typical slow-fast AVNRT were included. The mean SR cycle length (CL) was 784.1 ± 6 ms and the mean tachycardia CL was 361.2 ± 54 ms. The AV node potential had a significantly shorter duration and higher amplitude in sinus rhythm than during tachycardia (60 ± 40 ms vs. 160 ± 40 ms, p < .001 and 0.3 ± 0.2 mV vs. 0.09 ± 0.12 mV, p < .001, respectively). The nodal potential duration extension was 169.4 ± 31 ms, resulting in a time-window coverage of 47.6 ± 9%. The recording of AV nodal structure potentials enabled us to obtain 100% coverage of the tachycardia CL during slow-fast AVNRT. CONCLUSION: Detailed recording of the potentials of nodal structures is possible by means of multipolar catheters for ultrahigh-density mapping, allowing 100% of the AVNRT CL to be covered. These results also have clinical implications for the ablation of right-septal and para-septal arrhythmias.

Demonstration of differential ventricular overdrive pacing during long RP' supraventricular tachycardia.

We described the differential ventricular overdrive pacing during long RP' supraventricular tachycardia and discussed about its response leading to the dianosis.

The optimal slow pathway ablation site in atrioventricular nodal reentrant tachycardia cases with an inferiorly located His bundle.

INTRODUCTION: The optimal slow pathway (SP) ablation site in cases with an inferiorly located His bundle (HIS) remains unclear. METHODS AND RESULTS: In 45 patients with atrioventricular nodal reentrant tachycardia, the relationship between the HIS location and successful SP ablation site was assessed in electroanatomical maps. We assessed the location of the SP ablation site relative to the bottom of the coronary sinus ostium in the superior-to-inferior (SPSI), anterior-to-posterior (SPAP), and right-to-left (SPRL) directions. The HIS location was assessed in the same manner. The HIS location in the superior-to-inferior direction (HISSI), SPSI, SPAP, and SPRL were 17.7 ± 6.4, 1.7 ± 6.4, 13.6 ± 12.3, and -1.0 ± 13.0 mm, respectively. The HISSI was positively correlated with SPSI (R2 = 0.62; P < .01) and SPAP (R2 = 0.22; P < .01), whereas it was not correlated with SPRL (R2 = 0.01; P = .65). The distance between the HIS and SP ablation site was 17.7 ± 6.4 mm and was not affected by the location of HIS. The ratio of the amplitudes of atrial and ventricular potential recorded at the SP ablation site did not differ between the high HIS group (HISSI ≥ 13 mm) and low HIS group (HISSI < 13 mm) (0.10 ± 0.06 vs. 0.10 ± 0.06; P = .38). CONCLUSION: In cases with an inferiorly located HIS, SP ablation should be performed at a lower and more posterior site than in typical cases.

The impact of His bundle location and direction on the efficacy and safety of ablation.

BACKGROUND: The impact of the His bundle location and distance from the ablation site on ablation efficacy and complication risk remains unexplored. We determined the correlation between age, height, body mass index (BMI), and the His bundle location, and whether the distance between the His bundle and ablation target (DHIS-ABL) affects ablation safety and efficacy. METHODS: Overall, 346 patients with atrioventricular nodal re-entrant tachycardia (AVNRT) and 96 with atrioventricular re-entrant tachycardia (AVRT) were retrospectively analyzed. The distance between the His bundle and the coronary sinus ostium (DHis-CS), the height of the His bundle (HHIS), and DHIS-ABL were measured. Electrocardiograms were obtained 3 months post-ablation to assess recurrence and complications. RESULTS: Multiple linear regression showed that HHIS was negatively correlated with age in both groups. In AVNRT patients, DHIS-ABL was associated with age, height, and BMI; DHIS-CS was only negatively correlated with age. In AVRT patients, there was no significant correlation between the DHIS-ABL and age, height, or BMI. The recurrence rates in the AVNRT and AVRT groups were 0.9% and 8.7%, respectively. Subgroup analysis showed that patients with DHIS-ABL ≤ 10 mm had a higher recurrence rate than those with DHIS-ABL > 10 mm (p = .013). The incidence of third-degree atrioventricular block (AVB) complications was 0.2%. CONCLUSIONS: HHIS was negatively correlated with age but not with height and BMI. The DHIS-ABL correlated with age, height, and BMI in AVNRT patients. A short DHIS-ABL led to a higher rate of supraventricular tachycardia recurrence; whether this affects AVB risk warrants further studies with larger sample sizes.

Efficacy and safety between radiofrequency ablation and types of cryoablation catheters for atrioventricular nodal reentrant tachycardia: A Network Meta-analysis and Systematic Review.

INTRODUCTION: Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common supraventricular tachycardia referred for ablation. Periprocedural conduction system damage was a primary concern during AVNRT ablation. This study aimed to assess the incidence of permanent atrioventricular (AV) block and the success rate associated with different types of catheters in slow pathway ablation. METHOD: A literature search was performed to identify studies that compared various techniques, including types of radiofrequency ablation (irrigated and nonirrigated) and different sizes of catheter tip cryoablation (4, 6, and 8-mm), in terms of their outcomes related to permanent atrioventricular block and success rate. To assess and rank the treatments for the different outcomes, a random-effects model of network meta-analysis, along with p-scores, was employed. RESULTS: A total of 27 studies with 5110 patients were included in the analysis. Overall success rates ranged from 89.78% to 100%. Point estimation showed 4-mm cryoablation exhibited an odds ratio of 0.649 (95%CI: 0.202-2.087) when compared to nonirrigated RFA. Similarly, 6-mm cryoablation had an odds ratio of 0.944 (95%CI: 0.307-2.905), 8-mm cryoablation had an odds ratio of 0.848 (95%CI: 0.089-8.107), and irrigated RFA had an odds ratio of 0.424 (95%CI: 0.058-3.121) compared to nonirrigated RFA. CONCLUSION: Our study found no significant difference in the incidence of permanent AV block between the types of catheters. The success rates were consistently high across all groups. These findings emphasize the potential of both RF ablation (irrigated and nonirrigated catheter) and cryoablation as viable options for the treatment of AVNRT, with similar safety and efficacy profile.

Cannon A wave validation as a diagnostic tool in paroxysmal supraventricular tachycardias.

OBJECTIVE: The presence of cannon A waves, the so called "frog sign", has traditionally been considered diagnostic of atrioventricular nodal re-entrant tachycardia (AVNRT). Nevertheless, it has never been systematically evaluated. The aim of this study is to assess the independent diagnostic utility of cannon A waves in the differential diagnosis of supraventricular tachycardias (SVTs). METHODS: We prospectively included 100 patients who underwent an electrophysiology (EP) study for SVT. The right jugular venous pulse was recorded during the study. In 61 patients, invasive central venous pressure (CVP) was registered as well. CVP increase is thought to be related with the timing between atria and ventricle depolarization; two groups were prespecified, the short VA interval tachycardias (including typical AVNRT and atrioventricular reciprocating tachycardia (AVRT) mediated by a septal accessory pathway) and the long VA interval tachycardias (including atypical AVNRT and AVRT mediated by a left free wall accessory pathway). RESULTS: The relationship between cannon A waves and AVNRT did not reach the statistical significance (OR: 3.01; p = .058); On the other hand, it was clearly associated with the final diagnosis of a short VA interval tachycardia (OR: 10.21; p < .001). CVP increase showed an inversely proportional relationship with the VA interval during tachycardia (b = -.020; p < .001). CVP increase was larger in cases of AVNRT (4.0 mmHg vs. 1.2 mmHg; p < .001) and short VA interval tachycardias (3.9 mmHg vs. 1.2 mmHg; p < .001). CONCLUSION: The presence of cannon A waves is associated with the final diagnosis of short VA interval tachycardias.

Catheter ablation of atrioventricular nodal reentrant tachycardia with an irrigated contact-force sensing radiofrequency ablation catheter.

INTRODUCTION: Radiofrequency ablation (RFA) slow pathway modification for catheter ablation of atrioventricular nodal reentrant tachycardia (AVNRT) is traditionally performed using a 4-mm nonirrigated (NI) RF ablation catheter. Slow pathway modification using irrigated, contact-force sensing (ICFS) RFA catheters has been described in case reports, but the outcomes have not been systematically evaluated. METHODS: Acute procedural outcomes of 200 consecutive patients undergoing slow pathway modification for AVNRT were analyzed. A 3.5-mm ICFS RFA catheter (ThermoCool SmartTouch STSF, Biosense Webster, Inc.) was utilized in 134 patients, and a 4-mm NI RFA catheter (EZ Steer, Biosense Webster, Inc.) was utilized in 66 patients. Electroanatomic maps were retrospectively analyzed in a blinded fashion to determine the proximity of ablation lesions to the His region. RESULTS: The baseline characteristics of patients in both groups were similar. Total RF time was significantly lower in the ICFS group compared to the NI group (5.53 ± 4.6 vs. 6.24 ± 4.9 min, p = 0.03). Median procedure time was similar in both groups (ICFS, 108.0 (87.5-131.5) min vs. NI, 100.0 (85.0-125.0) min; p = 0.2). Ablation was required in closer proximity to the His region in the NI group compared to the ICFS group (14.4 ± 5.9 vs. 16.7 ± 6.4 mm, respectively, p = 0.01). AVNRT was rendered noninducible in all patients, and there was no arrhythmia recurrence during follow-up in both groups. Catheter ablation was complicated by AV block in one patient in the NI group. CONCLUSION: Slow pathway modification for catheter ablation of AVNRT using an ICFS RFA catheter is feasible, safe, and may facilitate shorter duration ablation while avoiding ablation in close proximity to the His region.

Fast-slow atrioventricular nodal re-entrant tachycardia incorporating superior and inferolateral left atrial slow pathways.

BACKGROUND: A 70-year-old man revealed a rare type of atrioventricular nodal re-entrant tachycardia (AVNRT) involving distinct retrograde pathways, superior slow pathway, and inferolateral left atrial slow pathway. RESULT: Radiofrequency ablation was successfully performed on the noncoronary cusp and in the left atrium, respectively, to eliminate the tachycardias. DISCUSSION AND CONCLUSION: Due to the anomalous electrical conduction patterns, careful diagnosis and ablation strategies were necessary to avoid the risk of atrioventricular block. These findings underscore the diversity and complexity of AVNRT and highlight the importance of tailored therapeutic approaches.

Junctional rhythm during cryoablation for typical atrioventricular nodal reentrant tachycardia.

INTRODUCTION: Cryoablation is being used as an alternative to radiofrequency (RF) ablation for atrioventricular nodal reentrant tachycardia (AVNRT) owing to the lower risk of atrioventricular block (AVB) compared to RF ablation. Junctional rhythm often occurs during successful application of RF ablation for AVNRT. In contrast, junctional rhythm has rarely been reported to occur during cryoablation. This retrospective study evaluated the characteristics of junctional rhythm during cryoablation for typical AVNRT. METHODS AND RESULTS: This retrospective study included 127 patients in whom successful cryoablation of typical AVNRT was performed. Patients diagnosed with atypical AVNRT were excluded. Junctional rhythm appeared during cryofreezing in 22 patients (17.3%). These junctional rhythms appeared due to cryofreezing at the successful site in the early phase within 15 s of commencement of cooling. Transient complete AVB was observed in 10 of 127 patients (7.9%), and it was noted that atrioventricular conduction improved immediately after cooling was stopped in these 10 patients. No junctional rhythm was observed before the appearance of AVB. No recurrence of tachycardia was confirmed in patients in whom junctional rhythm occurred by cryofreezing at the successful site. CONCLUSION: Occurrence of junctional rhythms during cryoablation is not so rare and can be considered a criterion for successful cryofreezing. Furthermore, junctional rhythm may be associated with low risk of recurrent tachycardia.

Retrograde fast pathway cryoablation inside the coronary sinus for slow-fast atrioventricular nodal reentrant tachycardia in a patient with persistent left superior vena cava.

INTRODUCTION: Persistent left superior vena cava (PLSVC) is accompanied by enlarged coronary sinus (CS) and deformation of the triangle of Koch. This makes anatomical evaluation of the atrioventricular (AV) nodal pathways difficult. METHODS: We attempted cryoablation of retrograde fast pathway located in the enlarged CS roof of PLSVC for slow-fast AV nodal reentrant tachycardia (AVNRT) induced by inadvertent antegrade fast pathway elimination during ablation of left atrial tachycardia. RESULTS: Slow-fast AVNRT was successfully eliminated without AV block progression. CONCLUSIONS: This is the first case of successful retrograde fast pathway ablation of the CS ostial roof for slow-fast AVNRT with PLSVC.

Selective and non-selective right bundle pacing for the diagnosis of bundle branch reentry ventricular tachycardia.

AIMS AND BACKGROUND: Bundle branch reentry ventricular tachycardia (BBRVT) can be seen in patients with conduction disease. In this report, we describe the use of conduction system pacing for its diagnosis. METHODS AND RESULTS: BBRVT was induced in two patients with infra-nodal conduction disease. Bundle branch reentry ventricular tachycardia with a left bundle branch block morphology was observed in the first patient (type A), whereas the second patient had a right bundle branch block morphology (type C).The diagnosis of BBRVT was confirmed in both patients by ventriculo-atrial dissociation, and the interdependence of the conduction system and the ventricular tachycardia cycle length variations.Selective and non-selective RB pacing was observed in the two patients during apical right ventricular pacing for entrainment of BBRVT with evidence of manifest entrainment with non-selective RB capture in the first patient, and concealed entrainment by selective RB capture in the second patient. Other criteria for entrainment including a short post-pacing interval at the right bundle pacing site were noted. CONCLUSION: Right bundle pacing is feasible in patients with BBRVT and may be a helpful manoeuver for the diagnosis of BBRVT.

Optimal method for ablation of atypical AVNRT.

BACKGROUND: Considering that ablation of atypical AVNRT may be unsuccessful after ablation at the right posterior septum, in this study, we aimed to present an optimal method for ablation of atypical AVNRT. Also, we evaluated the efficacy of this technique for preventing recurrences. METHODS: This is a prospective, double-center study. It was conducted on 62 patients with atypical AVNRT referred for radiofrequency ablation. The patients were randomly divided into two groups before ablation: 1-Group A (n = 30): treated with conventional ablation at the anatomic area of the slow pathway; 2-Group B (n = 32): ablation was done 2 mm higher in the septum during fluoroscopy. RESULTS: The mean age of patients in groups A and B were 54 ± 11.7 and 55 ± 12.2, respectively (P = 0.43). In group A, ablation was successful in 24 (80%) patients following right-sided slow pathway ablation, and the remaining patients required further treatment with either a left-side approach (N = 4, 13.3%) or ablation of additional regions (N = 2, 6.7%). In group B, ablation was successful in all patients. After a 48-month follow-up, recurrence of symptomatic atypical AVNRT was detected in 4 (13.3%) patients of group A and none of group B patients (p < 0.001). CONCLUSION: In patients with atypical AVNRT, ablation 2 mm above the conventional area is more promising regarding success rate and recurrence of the arrhythmia.

Atrial echo beats as a novel mechanism of periodic fluctuation in cycle length of atrial tachycardia.

Atrial echo beats due to a dual-atrioventricular nodal pathway are a possible cause of fluctuating tachycardia in cycle length (CL) but have not been reported so far. Here, we present a case of an 82-year-old man with symptomatic atrial tachycardia (AT), which was accompanied by periodic fluctuations in atrial sequence at the coronary sinus. Electrophysiological study (EPS) for atrioventricular conduction and three-dimensional (3D) electro-anatomical mapping system explained that the mechanism of periodic fluctuations was due to atrial echo beats through a dual-atrioventricular nodal pathway.

AVNRT cryoablation in children <26 kg: efficacy and safety of electrophysiologically guided low-voltage bridge strategy.

The recently published "electrophysiologically guided low-voltage bridge (LVB) strategy" is effective in the ablation of atrioventricular nodal re-entry tachycardia (AVNRT) in children. This study aimed to evaluate its efficacy and safety in children <26 kgs. Fourteen children [64% males, median age 6.5 years (IQR 6-8 years), median weight 25.5 kg (IQR 24-26 kg)] with AVNRT were treated. In all patients, we detected a LVB associated to a typical slow pathway potential. The acute success rate was 100% with a mean of 5.5 cryoablation deliveries. All procedures were performed with near-zero fluoroscopic exposure (median time 0.15 min, IQR 0-0.7 min), in six patients fluoroscopy was 0 min. There were no complications or recurrences during the follow-up (median 20.91 months, IQR 11.7-26.7 months).

Catheter ablation of atrioventricular nodal reentrant tachycardia, when AVNRT presented as a fetus or infant.

BACKGROUND: Atrioventricular nodal reentrant tachycardia (AVNRT) does not commonly present during infancy. Although relative safety of catheter ablation of AVNRT has been demonstrated in pediatrics, this procedure is rarely indicated in children <15 kg. METHODS: Retrospective review of seven cases of AVNRT that presented in children younger than 1 year of age and required catheter ablation for definitive management. Electrophysiology (EP) study was planned with two or three catheters. Area of ablation determined by voltage mapping, propagation sinus wave collision and slow pathway potential location. Ablation performed with cryothermal energy. No fluoroscopy was used. RESULTS: Presentation ranged from 36 weeks of gestation to 11 months of age. Two presented in fetal life and two in the neonatal period. The median age of ablation was 20 months (range 17-31 months). The median weight at ablation was 11.4 kg (range 8.9-14.9 kg). Median follow-up time was 16 months. All had typical AVNRT. The median tachycardia cycle length was 216 ms. 100% successful rate using cryoablation. No complications. No recurrence of tachycardia during the follow-up period. CONCLUSION: Slow AV nodal pathway cryoablation may be safely performed, with good short and medium-term outcomes in patients under 15 kg.

Pseudo-pacemaker syndrome with prolonged PR interval: A narrative review.

Pseudo-pacemaker syndrome (PPMS) is a rare complication of first-degree atrio-ventricular (AV) block in which a very prolonged PR interval causes AV dyssynchrony and subsequent symptoms of hemodynamic instability in the absence of an implanted pacemaker. The aim of this manuscript was to describe a unique case of PPMS and to provide a comprehensive review of the topic to help clinicians in the diagnosis and management of this condition. Through systematic research on PubMed, Google Scholar, EBSCO, and Ovid MEDLINE and using the search strings "pseudo-pacemaker syndrome" and "symptomatic first-degree AV block," we identified 14 articles accounting for 17 cases of PPMS, including our case report. The most common age group for PPMS was middle-aged and young adults, with an average age of 47 years. Palpitations were the most common presenting symptom and four main etiologies of PPMS were identified, as follows: (1) Idiopathic PPMS with evidence of impaired conduction over the AV node (20% of cases), (2) PPMS associated with reversable inflammatory causes (13%) or (3) associated with iatrogenic surgical or interventional procedures leading to the permanent damage of the normal AV conduction system (20%), and, finally, (4) PPM related to dual AV nodal physiology (DAVNP) as a primary finding (27%) or occurring after fast or slow pathway ablation for treatment of AV nodal re-entrant tachycardia (AVNRT) (20%). Treatment should be patient-tailored and based on the specific etiology once identified. However, the treatment of PPMS due to DAVNP without AVNRT presentation is yet to be clarified.

Fetal Supraventricular Tachycardia: Histologic Evidence of Accessory Pathways Due to Incomplete Annulus Fibrosus Formation.

BACKGROUND: Atrioventricular (AV) reentrant tachycardia is a common type of supraventricular tachycardia (SVT) that occurs in the fetus and neonate. Although many tachycardias resolve within several weeks of birth or respond to medical management, disruptions in the cardiac annulus fibrosus and development of additional accessory pathways may lead to refractory dysrhythmia resulting in fetal hydrops and ultimately, fetal death. OBJECTIVES: While accessory pathways have been well documented anatomically in adult and childhood tachyarrhythmias, there are no reports of the histology of these pathways in human fetuses with SVT. RESEARCH DESIGN, SUBJECTS, MEASURES: This is a small case series of 2 fetuses with a history of SVT that resulted in fetal hydrops. RESULTS: In both cases, examination of the cardiac conduction system was unremarkable and examination of the atrioventricular junction revealed a focally thinned and/or discontinuous annulus fibrosus with documented direct continuity between the atrial and ventricular myocardium in 1 case. CONCLUSIONS: This case series demonstrates that thinning or absence of the annulus fibrosus is a feature seen in fetal SVT, and the development of subsequent aberrant AV connections due to defective formation of the annulus fibrosus suggests a possible cause for these arrhythmias.

Multicenter cohort study on duration of antiarrhythmic medication for supraventricular tachycardia in infants.

Antiarrhythmic medication (AM) is commonly used to prevent supraventricular tachycardia (SVT) recurrence in infants. Our aim was to determine whether a shorter duration of AM is sufficient to prevent atrioventricular reentrant tachycardia (AVRT) recurrence and evaluate risk factors for recurrence of SVT after discontinued AM.This multicenter cohort study included all infants diagnosed with SVT in the five university hospitals in Finland between 2005 and 2017. Those diagnosed between 2005 and 2012 received AM for 12 months (group 1), and those diagnosed between 2013 and 2017 received AM for 6 months (group 2). A total of 278 infants presented with AVRT (group 1, n = 181; group 2, n = 97), and the median AM duration was 12.0 months (interquartile range [IQR] 11.4-13.4) and 7.0 months (IQR 6.0-10.2), respectively. Propranolol was the most frequently used first-line AM (92% and 95%). Recurrence-free survival rates were over 88% until 12 months after AM prophylaxis in both groups, without any statistically significant difference between them. Independent risk factors for recurrence of SVT after discontinuation of AM were need of combination AM (HR 2.2, 95% CI 1.14-4.20), Wolff-Parkinson-White (WPW) syndrome (HR 2.4, 95% CI 1.25-4.59), and age over 1 month at admission (HR 2.2, 95% CI 1.12-4.48).    Conclusion: Shortening AM duration in infants from 12 to 6 months does not seem to lead to more frequent SVT recurrence. The risk factors for recurrence of SVT were WPW syndrome, need of combination AM, and age over 1 month.