Catheter ablation in children has evolved to become a highly effective and safe therapy. Each iterative improvement in ablation technology provides another opportunity to investigate how much incremental benefit can be made without sacrificing safety. Contact force sensing catheters represent an example of such technology that has become commonplace in adult ablation. Its capability in predicting lesion size and collateral damage to critical structures has not been meticulously explored. Backhoff and colleagues describe an animal ablation model where they quantitate lesion characteristics at the atrium, atrioventricular groove, and ventricle using low and high contact force targets, with a specific focus on assessing for coronary arterial injury. In this controlled experiment, chronic lesion characteristics were widely variable (~0-8 mm diameter) yet there was a statistically significant (albeit small) increase in lesion diameter for high (vs low) contact force lesions delivered to the atrioventricular groove. The risk of chronic sub-clinical coronary artery injury was 1-2%.

Fetal atrioventricular block (AVB) is a failure of conduction from atria to ventricles. Immune- and non-immune-mediated forms occur, especially in association with congenital heart disease. Second-degree (2°) AVB may be reversible with dexamethasone and IVIG in immune-mediated disease. However, once third-degree AVB develops, it is deemed irreversible with need for a pacemaker and risk for cardiomyopathy. Rarely, 2° AVB is a transient, benign phenomenon in the immature conduction system. Few case series of transient AVB have been reported, but a management approach has not been defined. We report four patients with self-resolving, non-immune fetal AVB and outline a management strategy.

Pulsed-Field Ablation: What Are the Unknowns and When Will They Cease to Concern Us?Nathaniel A. Steiger* and Jorge Romero, MD*

Introduction: Novel ablation catheters equipped with mini-electrodes (ME) offer high resolution mapping for target tissue. This study aimed to evaluate the mapping performance and efficacy of ME catheters in radiofrequency ablation of paroxysmal supraventricular tachycardias (PSVTs). Methods: We prospectively enrolled 136 patients who were undergoing catheter ablation of PSVT including 76 patients with atrioventricular nodal reentrant tachycardia (AVNRT) and 60 patients with atrioventricular reentrant tachycardia (AVRT) or Wolff-Parkinson-White (WPW) syndrome. Patients were randomized to the ME group (ablation using a 4.5mm tip ME catheter) or the control group (ablation using a conventional 4mm tip catheter). The number of ablation attempt and cumulative ablation time to ablation endpoints, which was defined as an emergence of junctional rhythm in AVNRT or accessory pathway (AP) block in AVRT/WPW syndrome were compared. Results: During ablation procedures, discrete SP or AP electrograms were found in 27 (39.7%) patients in the ME group and 13 (19.1%) patients in the control group. The primary study outcomes were significantly lower in the ME group (ablation attempt number: 2.0 [1–4] vs. 3.0 [2–7] in the ME and control group, p=0.032; ablation time: 23.5 [5.0–111.5] vs. 64.5 [16.0–185.0] seconds, p=0.013). According to the PSVT diagnosis, ablation time to junctional rhythm was significantly shorter in the ME group in AVNRT. In AVRT/WPW syndrome, both ablation attempt number and ablation time to AP block showed trends favoring the ME group. Conclusion: The novel ME catheter was advantageous for identifying pathway potentials and reducing initial ablation attempt number and time in PSVT ablation. (ClinicalTrials.gov number, NCT04215640)

Background: Epicardial pacemakers are known as an alternative for endocardial pacemakers in some cases such as heart block, and complex congenital heart diseases. Considering recent advances and improvement of epicardial lead subtypes, it is essential to investigate the long-term function of them. In this study, we aimed to assess the sensing and pacing characteristics, and survival of bipolar steroid-eluting and unipolar non-steroid-eluting epicardial pacemakers. Methods: We conducted an entirely concentrated search on the documents of all patients who had undergone epicardial lead implantation in the Shaheed Rajaie Cardiovascular, Medical & Research Center during 2015-2018. Implant, and follow up data were extracted. Kaplan Meier analysis and Weibull regression hazards model were applied for the survival analysis. Results: eighty-nine leads were implanted for 77 patients. Of the total leads, 52.81%, 53.93%, and 47.19% were implanted in children (under-18-year-old), females, and patients with congenital heart diseases, respectively. Bipolar steroid-eluting leads comprised 33.71% of 89 leads. Pacing threshold of unipolar non-steroid-eluting leads that were implanted on the left ventricle and right atrium increased significantly during the follow up to greater records than bipolar steroid-eluting leads. Survival analysis also revealed that bipolar steroid-eluting leads are significantly better in 48-month survival (Weibull HR: 0.13 (95%CI, 0.02-0.99), p-value, 0.049). Age, ventricular location of the lead, and acute pacing characteristics were not associated with survival. Conclusions: Bipolar steroid-eluting epicardial leads have an acceptable survival compared with unipolar non-steroid-eluting, without a significant difference regarding patients age. Therefore, they could be an excellent alternative for endocardial ones.

Title: Reply to “Pro-arrhythmia with Anti-arrhythmic Drugs in Patients with Idiopathic Ventricular Arrhythmia: A Common Problem with Vague Definitions and Complex Interactions”Jacky K. K. Tang MD1 and Marc W. Deyell MD MSC1,2Heart Rhythm Services, Division of Cardiology, University of British ColumbiaCentre for Cardiovascular Innovation, University of British ColumbiaWord Count: 538 (including references)Address for correspondence:Dr. Marc William DeyellHeart Rhythm Services, St. Paul’s Hospital200 – 1033 Davie St.Vancouver, B.C., Canada, V6E 1M7Phone: 604-806-8256; Fax: 604-806-8723Email: [email protected]@MarcDeyellCompeting Interests: Dr. Deyell reports research grants from Biosense Webster and honoraria from Biosense Webster, Medtronic and Abbott.Funding: This work was supported by the UBC Division of Cardiology Academic Practice Plan.Drs. Hasdemir and Payzin have cogently brought up one of the primary challenges in studying patients with frequent premature ventricular complexes (PVCs) and evaluating the impact of therapy. They highlight, based on their prior study,(1) that a group of patients may actually experience a significant increase in PVC burden (>50%) with medical therapy, which obviously raises concerns that this may enhance deleterious effects of PVCs, particularly in the long term.With the advent of ambulatory monitoring, it was recognized early that PVC burden could be highly variable, leading to measurement error when using a 24-hour monitor. This error is highest when performing before-and-after studies of the effect of intervention on PVC burden, using single monitoring periods of 24 hours prior to and after intervention. In particular, spontaneous reductions in PVC burden can overestimate treatment effects. This error can be minimized in two ways, through serial monitoring (repeated measures) or longer-term monitoring (>48h). Indeed, an elegant study by Dr. Mullis and colleagues, using 14 day patch monitors, showed a median absolute day-to-day fluctuation in PVC burden of almost 10% among patients with a high burden of PVC.(2) Thus, an apparent “pro-arrhythmic” effect of a medication may simply reflect inefficacy and expected variation in PVC burden.In our prior work,(3) published in this journal and referenced by Drs. Hasdemir and Payzin, we were also limited by using only 24-hour ambulatory monitors to assess PVC burden. However, we did include a control group on no medical therapy, to mitigate the effect of measurement error, by obtaining an estimate of variation in PVC burden in the absence of therapy. In our study, we observed a “pro-arrhythmic effect” (>50% increase in PVC burden), in 2.5% (1/40) of patients on no medical therapy, 7.5% (4/53) on beta blockers/calcium channel blockers and 11.1%% (3/27) on class I/III antiarrhythmic therapy. Despite the trend, these were not significantly different (p=0.28 and p=0.14 for beta blocker/calcium channel blocker and class I/III antiarrhythmics versus no therapy).This does not negate a potential pro-arrhythmic effect of medical therapy in a minority of patients. However, more definitive proof of a pro-arrhythmic effect, distinguishing this from spontaneous variation in PVC burden, would require demonstration of a decrease in PVC burden with cessation of therapy. This would best be accomplished with a blinded, cross-over trial design.Drs. Hasdemir and Payzin remind us to always critically assess, and reassess, our therapies for patients with frequent PVCs. We must always evaluate whether treatment is warranted (in the majority of cases it is not), and whether patients are at risk for adverse events, particularly from class I and III antiarrhythmics. Frequent PVCs make physicians uncomfortable but we should not rush to treatment and expose patients to unnecessary harm.References:1. Turan OE, Aydin M, Odabasi AY, Inc M, Payzin S, Hasdemir C. Therapeutic Inefficacy and Proarrhythmic Nature of Metoprolol Succinate and Carvedilol Therapy in Patients With Idiopathic, Frequent, Monomorphic Premature Ventricular Contractions. Am J Ther 2021;29:e34-e42.2. Mullis AH, Ayoub K, Shah J et al. Fluctuations in premature ventricular contraction burden can affect medical assessment and management. Heart Rhythm 2019;16:1570-1574.3. Tang JKK, Andrade JG, Hawkins NM et al. Effectiveness of medical therapy for treatment of idiopathic frequent premature ventricular complexes. Journal of Cardiovascular Electrophysiology 2021;32:2246-2253.

An 80-year-old man underwent catheter ablation for atrial tachycardia (AT), which developed after catheter ablation for atrial fibrillation. The AT was diagnosed as dual-loop tachycardia, which included peri-mitral and roof-dependent ATs. An ethanol infusion into the vein of Marshall resulted in left phrenic nerve paralysis. During the procedure, the phrenic nerve paralysis was completely relieved.

There is still uncertainity about the use of CT-scan for LAAO device sizing. The main reason for this disappointing position is likely to relate to the scarcity of robust data, since there is still difference among institutions with regards how to perform measurement of the devices. Dallan et al. (1) report their own experience on the use of a novel computed tomography angiography-based (CTA) for sizing the Watchman Flex device for left atrial appendage occlusion (LAAO) . The authors through the TruPlan software package that a pre-procedural CTA sizing protocol can be applied successfully with ICE guidance and provide excellent procedural outcomes.The applied CTA protocol is safe and can provide high success rates with the WatchmanTM FLX device reducing the number of deployment attempts and reducing the risk of complications.

Dr. Rahul George Muthalaly MBBS, MPH1,2, Dr. Roy M John MBBS, PhD, FRCP3Monash Heart, Monash Health, Melbourne VICVictorian Heart Institute, Monash University, Melbourne VICStanford University, Palo Alto, CA 94304 USACorresponding Author:Dr. Rahul G MuthalalyPh: [email protected] information for all other authors:[email protected] Count: 1238 wordsFunding: NoneConflict of Interest: NoneAblation for atrial fibrillation (AF) is an established therapy that continues to grow in scope and indication(1). The benefits of AF ablation are well recognized in heart failure and symptomatic paroxysmal AF. Additionally, the recent EAST-AFNET4 trial demonstrated benefit for an early AF rhythm control strategy even in asymptomatic patients (2). This change in paradigm from rate and rhythm control equivalence may be partially related to the increasing use of AF ablation for rhythm control. As ablation therapy continues to proliferate, questions of how to optimise procedural outcomes at a health service level arise. A key component of this optimisation is defining predictors of outcomes related to ablation procedures.One such predictor is procedural case volume. Studies outside of AF ablation have demonstrated complex relationships between institutional size, procedural volume, case difficulty and outcomes. Published data on transcatheter aortic valve replacement (TAVR) for example, suggest a durable link between hospital case volume and mortality even after adjusting for institutional learning curves and known risk factors for poor outcomes (3). These insights have relevance for AF ablation for which there is wide-ranging procedural variation across factors such as lesion sets and type of ablation energy. The relationship between AF ablation volume and outcomes have been explored in previous studies(4, 5). Tonchev and colleagues, in a meta-analysis, demonstrated a significantly lower risk of complications in centres performing >100 procedures per year (OR 0.62, 95%CI 0.53 to 0.73) (4). This carried over to mortality, which was significantly lower in high volume centres (OR 0.33, 95% CI 0.26-0.43). Ablation efficacy was also greater in higher volume centres. Importantly, the majority of procedures included in this meta-analysis of real-world data were undertaken in low volume centres (70.9% in centres with <100 procedures/year) alerting to the reality that high-volume centers are not readily available to most patients.The influence of energy types (cryoballoon ablation versus catheter based radiofrequency ablation) on the relationship between procedural volume and outcomes is less well defined. This is of relevance as cryoablation appears to have a gentler learning curve than radiofrequency ablation for centres that are newly introducing AF ablation(6). In this issue of the journal , Kanaoka and colleagues present data on the relationship between procedural volume, energy type and acute procedural outcomes based on analysis of the Japanese National Database of Insurance Claims and Specific Health Check-ups. The authors identified 270,116 patients from this database undergoing first-time AF ablation with cryoablation or radiofrequency energy. A small subset of patients who underwent hot balloon and laser ablation were excluded as the numbers were too low. Complications were identified using administrative coding for the most common diagnoses associated with ablation risks. Ablation success could only be defined using coding for repeat AF ablation or initiation of anti-arrhythmic drug within 1 year.The authors split hospitals into quartiles using case volume resulting in groups with medians of 69 (very low), 157 (low), 252 (high) and 469 (very high) procedures per year. They found that the relative risk of peri-procedural complications was approximately 10-20% lower in all other groups when compared with the very low procedural volume hospitals. Cubic spline plots demonstrated a plateau effect, with no further reduction in complications when hospitals approach 150-200 cases per year. Similarly, when considering AF recurrence assessed by repeat ablation or initiation of anti-arrhythmic drugs up to 1 year, there was approximately a 10% relative risk reduction in the low, high and very high-volume hospitals when compared to very low-volume centres. Of note, there appeared to be a similar plateau volume of approximately 150-200 cases per year above which the benefit attenuated. The relationship between procedural volume and outcomes was however, only seen with RF ablation. Among the more than 56,000 cryoablation cases, there were no significant differences in complications or recurrence in the low, high or very high procedural volume hospitals when compared with the very low volume hospitals. Of note, there was a similar burden of AF related comorbidities in the radiofrequency and cryoablation populations.These results of Kanoaka and colleagues add further evidence to the notion that, when it comes to AF ablation, there appears to be a threshold of hospital procedural volume above which the risk of complications and recurrence decreases. The finding of a threshold in the range of 150-200 procedures per year, is in keeping with previous work suggesting benefits in excess of 100 procedures per year(5). Additionally, the present study sheds new light on the effect of ablation type on this relationship. In keeping with the recognition that cryoablation appears to offer an easier learning curve, the effect of procedural volume on both safety and efficacy outcomes was eliminated when considering only cryoablation cases.Limitations of the study have to be recognized. The study is observational, retrospective and derived from a national database. These factors admit the potential for unmeasured confounders and imperfect assessment of outcomes. The definition of ablation success was based on coding for repeat ablation or use of antiarrhythmic drugs within the first year. This definition, although pragmatic, does not account for recurrence occurring outside of 1 year or recurrence that did not result in repeat ablation or anti-arrhythmic drug therapy. Furthermore, complications were defined using administrative coding. Notably, this coding was not able to identify phrenic nerve injury, which occurs in approximately 5-6% of patients undergoing cryoablation(7). In addition, significant differences existed between the RF and cryoablation groups. There was a greater proportion of paroxysmal AF in the cryoablation compared to RF group (74% versus 46%). Because RF ablation allows for more flexibility in ablation lesion set, this energy form tends to be used in those with more advanced atrial remodelling. Hence, it is very likely that the RF group comprised a more complex patient group with a greater dependence on operator experience and case volume. The observed differences in learning curve between the two energy sources may have been less striking or even absent, had the groups been matched. The study however, has the advantage of the use of a database that covers of 98% of the Japanese population and magnitude of case volume included, allow for valuable insights.Abundant work has now demonstrated that hospital procedural volume is a key component of optimising outcomes from any complex interventional procedure(3, 5). The improved outcomes observed as a result of hospital procedural volume are likely due to a wide-range of additional factors that include appropriate patient selection, an experienced electrophysiology laboratory team and standardized, guideline-directed pre- and post-procedural management(8). The Heart Rhythm Society’s 2020 AF Centres of Excellence whitepaper outlines the rationale and guidance for key components of an AF Centre of Excellence(8). However, as the increasing benefit of AF ablation creates an increasing demand for the procedure, a balance must be struck between having very few centres of excellence and abundant centres with limited experience. In this context, the results of the current study by Kanoaka and colleagues are valuable and raises the possibility of a two-tiered approach. That of lower volume centres providing less complex procedures such as cryoablation for simpler cases of AF and higher volume ‘Centres of Excellence’ providing advanced ablation procedures for more complex AF cases. Such a division of labor may strike the balance between ablation availability and optimal outcomes. This differentiation, based on the characteristics of procedure offered and type of patients treated, will likely achieve greater importance as future technologies such as pulsed field ablation emerge and promise faster, safer and easier ablation strategies for AF(9).References1. Hindricks G, Potpara T, Dagres N, Arbelo E, Bax JJ, Blomström-Lundqvist C, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS): The Task Force for the diagnosis and management of atrial fibrillation of the European Society of Cardiology (ESC) Developed with the special contribution of the European Heart Rhythm Association (EHRA) of the ESC. European Heart Journal. 2020;42(5):373-498.2. Kirchhof P, Camm AJ, Goette A, Brandes A, Eckardt L, Elvan A, et al. Early Rhythm-Control Therapy in Patients with Atrial Fibrillation. New England Journal of Medicine. 2020;383(14):1305-16.3. Vemulapalli S, Carroll JD, Mack MJ, Li Z, Dai D, Kosinski AS, et al. Procedural Volume and Outcomes for Transcatheter Aortic-Valve Replacement. New England Journal of Medicine. 2019;380(26):2541-50.4. Cheung JW, Yeo I, Cheng EP, Ip JE, Thomas G, Liu CF, et al. Inpatient hospital procedural volume and outcomes following catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol. 2020;31(8):1908-19.5. Tonchev IR, Nam MCY, Gorelik A, Kumar S, Haqqani H, Sanders P, et al. Relationship between procedural volume and complication rates for catheter ablation of atrial fibrillation: a systematic review and meta-analysis. Europace. 2021;23(7):1024-32.6. Velagic V, Prepolec I, Pasara V, Puljevic M, Puljevic D, Planinc I, et al. Learning curves in atrial fibrillation ablation – A comparison between second generation cryoballoon and contact force sensing radiofrequency catheters. Indian Pacing and Electrophysiology Journal. 2020;20(6):273-80.7. Heeger C-H, Sohns C, Pott A, Metzner A, Inaba O, Straube F, et al. Phrenic Nerve Injury During Cryoballoon-Based Pulmonary Vein Isolation: Results of the Worldwide YETI Registry. Circulation: Arrhythmia and Electrophysiology. 2022;15(1):e010516.8. Piccini JP, Sr., Allred J, Bunch TJ, Deering TF, Di Biase L, Hussein AA, et al. Rationale, considerations, and goals for atrial fibrillation centers of excellence: A Heart Rhythm Society perspective. Heart Rhythm. 2020;17(10):1804-32.9. Reddy VY, Dukkipati SR, Neuzil P, Anic A, Petru J, Funasako M, et al. Pulsed Field Ablation of Paroxysmal Atrial Fibrillation: 1-Year Outcomes of IMPULSE, PEFCAT, and PEFCAT II. JACC: Clinical Electrophysiology. 2021;7(5):614-27.

We would like to thank the authors for their letter and interest in our manuscript. We appreciate their valuable comments. The authors have raised the following important points: 1. The heterogenicity of our cohort with mitral valve surgery (MVS) 2. Elucidating the characteristics and causes of ventricular arrhythmias (VA) in patients with primary versus secondary mitral disease as well as in those with ischemic versus non-ischemic heart disease 3. The paucity of cardiac magnetic resonance imaging (MRI) as a limitation of the study 4. The need for careful evaluation of patients prior to ablation since most arrhythmias did not originate from the perimitral area.

The aortic sinuses of Valsalva are an important ablation site in non-ischemic substrates and in patients with idiopathic ventricular arrhythmias. Siontis and colleagues have demonstrated that these sites should also be considered for ablation in patients with infarct-related inferior axis VT. Low voltage in the aortic sinuses of Valsalva or in the sub-aortic region should prompt further evaluation of these regions for ablation.

A 77-year-old woman with palpitations was referred for a second radiofrequency ablation for persistent atrial tachycardia (AT). She previously underwent pulmonary vein (PV) isolation for paroxysmal atrial fibrillation, linear ablation between the 3’o clock position of the mitral annulus (MA) and left PV from the endocardium, and ablation inside the coronary sinus (CS) for perimitral atrial tachycardia (PMAT) in the first procedure. A baseline 12-lead electrocardiogram in the second procedure showed stable AT with a cycle length (CL) of 250 ms. No PV reconnection was observed. The CS catheter was placed from 3:30 to 5:00 on the MA, and a proximal-to-distal pattern of CS activation during AT was observed. Activation mapping in the left atrial (LA) endocardium using a three-dimensional mapping system (CARTO3, Biosense Webster, Diamond Bar, CA, USA) revealed a sequence of counterclockwise rotations of the MA. Figures 1A and 1B show the intracardiac electrograms during high-output (20 V) and low-output (5 V) atrial entrainment pacing at a pacing CL of 240ms from CS 3,4, which corresponds to the 4’o clock position of the MA. Dose residual conduction occur across the mitral isthmus (MI) endocardium, epicardium, or both? What is the electrophysiological mechanism during high- and low-output entrainment pacing?

Background: The changes in ventricular repolarization after cardiac resynchronization therapy (CRT) are poorly understood. Objective: Address this knowledge gap using a multimodality approach including electrocardiographic and echocardiographic measurements in patients and using patient-specific computational modeling. Methods: In 33 patients electrocardiographic and echocardiographic measurements were performed before and at various intervals after CRT, both during CRT-ON and temporary CRT-OFF. T-wave area was calculated from vectorcardiograms, reconstructed from the 12-lead ECG. Computer simulations were performed using a patient-specific eikonal model of cardiac activation with spatially varying action potential duration (APD) and repolarization rate, fit to a patient’s ECG. Results: During CRT-ON T-wave area diminished within a day and remained stable thereafter, whereas QT-interval did not change significantly. During CRT-OFF T-wave area doubled within 5 days of CRT, while QT-interval and peak-to-end T-wave interval hardly changed. Left ventricular (LV) ejection fraction did not significantly increase before 1 month of CRT. Computer simulations indicated that the increase in T-wave area during CRT-OFF can be explained by changes in APD following chronic CRT that are opposite to the change in CRT-induced activation time. These APD changes were associated with a reduction in LV dispersion in repolarization during chronic CRT. Conclusions: T-wave area during CRT-OFF is a sensitive marker for adaptations in ventricular repolarization during chronic CRT that may include a reduction in LV dispersion of repolarization.

A document by Mohamad El Moheb. Click on the document to view its contents.

Radiofrequency (RF) ablation has been the most widely employed energy source for catheter ablation to date. However, most of conventional RF ablation energy dissipates into the bloodstream before reaching the target tissue. Technology that conveys RF energy exclusively toward target tissue may potentially improve the quality, safety, and outcome of the RF ablation procedures. RF ablation using a novel insulated-tip catheter (SMT, Sirona Medical Technologies, Windsor, CT) may refine RF ablation in the future to minimize the risk of iatrogenic complications. Although it is still unclear whether the results of the SMT catheter can be translated to a human beating heart, the data for SMT catheter of this study are very promising.

The Esophagus Going SteadyTina Baykaner, MD, MPH and Duy T. Nguyen, MDStanford University, Stanford, CA , USA

Other editorials do not seem to include editorials. If you are sure you want one, let me know.

vHPvSD ablation represents a quantum leap from the RF settings that have traditionally been used in electrophysiology. If used to its full potential, it may improve procedural efficiency by reducing ablation and procedure times. However, with great power comes great responsibility; we need to ensure that we use it judiciously and safely.