Analysis of intracardiac electrocardiogram during ill-sustained tachycardia - Door to a successful troubleshooting of 'unnecessary' defibrillator discharge.

A 50-year-old gentleman with old anterior wall myocardial infarction with implantable cardioverter defibrillator (ICD, Abbott Medical, Fortify ST VR 1235-40) presented with recurrent appropriate ICD shock. The ICD stored EGM indicated a possibility of supraventricular tachycardia (SVT) rather than ventricular tachycardia (VT) when the morphology match was found high. Bundle brunch re-entry (BBR) VT was another differential. An EP study conducted on antiarrhythmic drugs (AAD) induced reproducible but only ill-sustained tachycardia too short to perform any SVT maneuvers during tachycardia. However, critical analysis of the tachycardia electrograms suggested atypical AVNRT as the most likely mechanism. The other differentials were atrial tachycardia (AT) and BBR VT. Manoeuvres during sinus rhythm and ventricular pacing excluded other diagnosis. A single point radiofrequency ablation (RFA) near the SP region cured the arrhythmia. The reason for misclassification of SVT as VT was also sought for. It was found that the shocks were received due to fulfilment of 2/3 criteria (sudden onset and regular tachycardia). Hence, he received therapy despite an appropriate morphology match favouring SVT. This is one of the known limitations of ICDs where regular SVTs (AVNRT/AVRT or AT) may receive inappropriate ICD therapies. After slow pathway modification there was no further recurrence of either SVT or VT; hence, a substrate modification was deferred.

Effect of Ablation Energy Source on Outcomes of Slow Pathway Modification for AVNRT in Children.

BACKGROUND: Selection of radiofrequency ablation (RF) or cryoablation (Cryo) for atrioventricular nodal re-entrant tachycardia (AVNRT) in children remains controversial due to a lack of contemporary comparison studies in this population. OBJECTIVES: This study sought to compare outcomes of RF and Cryo for AVNRT in the pediatric population. METHODS: AVNRT ablation outcomes were retrospectively analyzed utilizing the National Cardiovascular Data Registry IMPACT (Improving Pediatric and Adult Congenital Treatment) Registry from April 2016 to March 2019. Data from subjects 1 to 21 years of age undergoing elective first-time slow pathway (SP) modification for AVNRT were included. Exclusion criteria included <1 year of age, congenital heart disease, and >1 ablation target. Cases were analyzed by ablation energy: 1) RF only; 2) Cryo only; 3) radiofrequency ablation switching to cryoablation (RF→Cryo); and 4) cryoablation switching to radiofrequency ablation (Cryo→RF). The primary outcome was acute ablation failure. Secondary outcomes included in-hospital adverse events. RESULTS: Among 2,448 patients (mean age 13.6 ± 3.4 years, 60% female), RF only was employed in 43% (n = 1,046), Cryo only in 49% (n = 1,201), RF→Cryo in 6% (n = 135), and Cryo→RF in 66 (3%). Acute ablation failure occurred in 1.3% (n = 33), with no difference by energy source (1% in RF only, 1.5% in Cryo only, 1.5% in RF→Cryo, 3% in Cryo→RF; P = 0.5). Atrioventricular (AV) block requiring permanent pacemaker did not occur in any group; transient AV block occurred in 0.4% of the cohort, with no difference by group. CONCLUSIONS: In this largest pediatric study of AVNRT ablation, RF and Cryo demonstrated comparable high acute success and rare documentation of AV block that did not result in temporary or permanent pacing. Longitudinal data are important for further comparison of these modalities with regard to recurrence risk and late complications.

Analysis of ST segment depression in supraventricular tachycardia and its relationship with underlying mechanism.

BACKGROUND: Electrocardiographic diagnosis of causes of supraventricular tachycardia (SVT) is sometimes difficult and application of routine algorithms can lead to misdiagnosis in as many as 37 % of patients. ST segment depression may be useful in diagnosing the nature of SVT. METHODS: We reviewed surface electrocardiogram (ECG) characteristics of 300 patients having SVT with 1:1 AV relationship and correlated findings with electrophysiology study (EPS) findings. Final diagnosis of AVNRT (Atrioventricular nodal reentrant tachycardia), Orthodromic AVRT (atrioventricular reentrant tachycardia) and atrial tachycardia (AT) was correlated with ECG parameters like heart rate, ST segment depressions and QRS morphology. RESULTS: Out of 300 patients, majority patients included in study, were having AVNRT or AVRT. ST depression predicted AVRT if the ST depression was ≥ 2 mm (overall sensitivity of 38.3 % and specificity of 93.8 % to predict AVRT) and was downsloping in morphology (sensitivity of 36.9 % and specificity of 94.7 % to predict AVRT). At heart rates ≥214 beats per minute (bpm) as measured by 7 small squares of ECG at 25 mm/s, downsloping ST depression ≥2 mm had a sensitivity 37.9 % of and specificity of 89.2 % to predict AVRT. At heart rate <214 bpm, downsloping ST depression ≥2 mm had sensitivity of 37.2 % and specificity of 96.5 % to predict AVRT. Downsloping ST depression of ≥2 mm helps to differentiate AVNRT from AVRT. CONCLUSION: A downsloping ST segment depression ≥2 mm predicted SVT being an AVRT and can be used as a useful criteria in diagnosing the tachycardia.

RF catheter ablation of AVNRT in a patient with interrupted inferior vena cava anomaly with hemiazygos continuity with persistent left superior vena cava.

Intrahepatic interruption of the inferior vena cava (IVC) with continued hemizygous is a very rare abnormality and sometimes it may be accompanied by other cardiovascular abnormalities. Continuation of the hemizygous vein draining into the right atrium through the left superior vena cava (LSVC) is much rarer. In this paper, we have presented a patient who had simultaneous IVC interrupted with persistent LSVC and suffered from Atrioventricular nodal reentrant tachycardia (AVNRT). Finally, radiofrequencies (RF) catheter ablation for AVNRT was successfully performed through a left subclavian vein access.

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.

A short RP tachycardia in congenitally corrected transposition. What is the mechanism?

A 51-year-old female with congenitally corrected transposition of great arteries (CCTGA), situs solitus, dextrocardia, atrial septal defect and persistent left superior vena cava underwent electrophysiology study for recurrent palpitations with documented narrow complex, short RP tachycardia. With a catheter in the region of the anterior mitral annulus, a His signal was recorded and HV interval was 35 msec. Tachycardia was induced with a ventricular extrastimulus. During the tachycardia there was 1:1 ventriculo-atrial conduction and central atrial activation with a VA interval of 20 msec. The recorded His signal could be seen after the QRS. What is the mechanism of the tachycardia?

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.

Activation pattern within Koch's triangle during sinus rhythm in patients with and without atrioventricular nodal reentrant tachycardia.

BACKGROUND: Several studies have visualized the slow pathway during sinus rhythm using high-density mapping of Koch's triangle (KT) in patients with atrioventricular nodal reentrant tachycardia (AVNRT). However, it is unclear whether the slow pathway can be visualized in all people. Therefore, we evaluated the activation pattern within KT during sinus rhythm in patients with and without AVNRT. METHODS: High-density mapping using the Advisor HD Grid mapping catheter (Abbott) within KT during sinus rhythm was created in 10 patients with slow-fast AVNRT and 30 patients without AVNRT. RESULTS: In 8 (80%) patients with AVNRT, the activation pattern pivoting around a block line (BL) within KT was observed. In 12 (40%) patients without AVNRT, similar activation pattern pivoting around BL was observed, but jump was observed in 11 (92%) of these patients. In all patients, the activation pattern pivoting around BL was observed in 17 (85%) of 20 patients with jump, but only 3 (15%) of 20 patients without jump (p < 0.0001). During jump, there was a long period of no potential from the last atrial potential within KT to the His bundle potential, suggesting the slow pathway conduction through the rightward inferior extension that cannot be visualized. A linear ablation between the pivot point and the septal tricuspid annulus was successful for slow-fast AVNRT. CONCLUSION: Although the slow pathway could not be visualized using high-density mapping during sinus rhythm, the activation pattern pivoting around BL within KT was observed in most patients with the dual pathway physiology, with or without AVNRT.

Electroanatomical Mapping System-Guided vs. Intracardiac Echocardiography-Guided Slow Pathway Ablation: A Randomized, Single-Center Trial.

Radiofrequency (RF) catheter ablation is an effective treatment option for targeting the slow pathway (SP) in atrioventricular nodal reentry tachycardia (AVNRT). Previous data suggested that using intracardiac echocardiography (ICE) guidance could improve procedural outcomes when compared to using fluoroscopy alone. In this prospective study, we aimed to compare the effectiveness of an electroanatomical mapping system (EAMS)-guided approach with an ICE-guided approach for SP ablation. Eighty patients undergoing SP ablation for AVNRT were randomly assigned to either the ICE-guided or EAMS-guided group. If the procedural endpoint was not achieved after 8 RF applications; patients were allowed to crossover to the ICE-guided group. The ICE-guided approach reduced the total procedure time (61.0 (56.0; 66.8) min vs. 71.5 (61.0; 80.8) min, p < 0.01). However, the total fluoroscopy time was shorter (0 (0-0) s vs. 83.5 (58.5-133.25) s, p < 0.001) and the radiation dose was lower (0 (0-0) mGy vs. 3.3 (2.0-4.7) mGy, p < 0.001) with EAMS-guidance. The ICE-guided group had a lower number of RF applications (4 (3-5) vs. 5 (3.0-7.8), p = 0.03) and total ablation time (98.5 (66.8-186) s vs. 136.5 (100.5-215.8) s, p = 0.02). Nine out of 40 patients (22.5%) in the EAMS-guided group crossed over to the ICE-guided group, and they were successfully treated with similar RF applications in terms of number, time, and energy compared to the ICE-guided group. There were no recurrences during the follow-up period. In conclusion, the utilization of ICE guidance during SP ablation has demonstrated notable reductions in procedural time and RF delivery when compared to procedures guided by EAMS. In challenging cases, an early switch to ICE-guided ablation may be the optimal choice for achieving successful treatment.

Automatic algorithmic driven monitoring of atrioventricular nodal re-entrant tachycardia ablation to improve procedural safety.

Background: During slow pathway modification for atrioventricular nodal reentrant tachycardia, heart block may occur if ablation cannot be stopped in time in response to high risk electrogram features (HREF). Objectives: To develop an automatic algorithm to monitor HREF and terminate ablation earlier than human reaction. Methods: Digital electrogram data from 332 ablation runs from February 2020 to June 2022 were included. They were divided into training and validation sets which contained 126 and 206 ablation runs respectively. HREF in training set was measured. Then a program was developed with cutoff values decided from training set to capture all these HREF. Simulation ablation videos were rendered using validation set electrogram data. The videos were played to three independent electrophysiologists who each determined when to stop ablation. Timing of ablation termination, sensitivity, and specificity were compared between human and program. Results: Reasons for ablation termination in the training set include short AA time, short VV time, AV block and VA block. Cutoffs for the program were set to maximize program sensitivity. Sensitivity and specificity for the program in the validation set were 95.2% and 91.1% respectively, which were comparable to that of human performance at 93.5% and 95.4%. If HREF were recognized by both human and program, ablations were terminated earlier by the program 90.2% of times, by a median of 574 ms (interquartile range 412-807 ms, p < 0.001). Conclusion: Algorithmic-driven monitoring of slow pathway modification can supplement human judgement to improve ablation safety.

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.

Ventriculoatrial Block and His-His Changes During Supraventricular Tachycardia: Diagnostic and Mechanistic Implications.

Supraventricular tachycardia (SVT) with ventriculoatrial (VA) block can represent a diagnostic challenge. We present a case of SVT where His-His interval shortening was repeatedly observed during episodes of VA block. This novel observation is more diagnostically suggestive of atrioventricular nodal re-entrant tachycardia, as opposed to orthodromic re-entry using a nodofascicular or nodoventricular pathway where a constant His-His is recorded during episodes of VA block. (Level of Difficulty: Intermediate.).