Congenital Heart And Pediatric Electrophysiology

Kahle AK, Gallotti RG, Alken FA, Meyer C, Moore JP. J Am Heart Assoc. 2021 Jul 6;10(13): e020835. doi: 10.1161/JAHA.121.020835. Epub 2021 Jun 14.PMID: 34121415    Take Home Points: The central obstacles varied with the type of IART (single vs double loop) and most commonly involved an atriotomy, tricuspid annulus, and/or inferior vena cava. Anatomic central obstacles were associated with a longer pathway length, faster central isthmus conduction velocity (CV), faster non-isthmus CV, and smaller coefficient of variability. Prior right heart surgery were associated with a shorter pathway length, slower central isthmus CV, and slower non-isthmus CV. For small circuits (pathway length <9 cm), central isthmus CV was always <0.15 m/s whereas non-isthmus CV was always <0.5 m/sec Acute success was 95% but recurrence at ~ 1 year was 26%. Arrhythmia-free survival was better in patients with “homogeneous” versus ‘heterogeneous” circuit CV during tachycardia (90% vs. 57%) Commentary by Dr. Akash Patel (San Francisco, CA, USA) Congenital and Pediatric Cardiac EP section editor: Atrial arrhythmias after congenital heart disease are commonly seen in adulthood as a result of adverse atrial remodeling. This is a result of atrial dilation from hemodynamic burden and areas of scar secondary to surgical repair. As a result of these changes, critical isthmuses and areas of slow conduction develop allowing for intra-atrial reentrant tachycardia (IART). Our current understanding of the specific conduction velocities and pathway lengths that allow for IART to occur in ACHD patients is limited. The recent advent of ultra-high density electroanatomic mapping (UDHM) has allowed for a more detailed understanding of arrhythmia mechanisms. This study aimed to characterize conduction velocity patterns and pathway lengths of IARTs in relation to the underlying anatomical substrate in a cohort of adults with congenital heart disease using UDHM.   This was a retrospective study of all consecutive ACHD patients undergoing UHDM guided catheter ablation using the Rhythmia System for supraventricular tachycardia between February 2017 and September 2020 at two centers (University Heart and Vascular Center Hamburg-Eppendorf and the University of California, Los Angeles). There was a total of 81 patients undergoing 85 procedures with a median age of 38.5 years (IQR: 31– 55). The demographics of the total cohort included a large spectrum of congenital heart defects including single ventricle palliation (19%), septal defects (15%), tetralogy of Fallot (10%), transposition of the great vessels (10%), atrial switch procedure (10%), and Ebstein anomaly (10%). Of note, prior ablations were done in 51% of patients. Please see Table below for details of baseline characteristics.   All underwent standardized procedure protocols, mapping, and ablation. Procedures were conducted under general anesthesia or deep sedation. An intracardiac reference catheter was used in all cases. If the coronary sinus was present, then a steerable 6-F decapolar diagnostic catheter was used (72%). If there was no access to the coronary sinus, then a catheter was placed in the pulmonary artery or systemic venous atrium (28%). Transeptal and/or transbaffle access was obtained when appropriate (42%). The Rhythmia system’s open-irrigated 64-electrode minibasket catheter (Orion; Boston Scientific) and an open-irrigated 3.5-mm tip mapping and ablation catheter (IntellaNav MiFi OI; Boston Scientific) were used for mapping and ablation.   UHDM was performed of the entire chamber anatomy for all inducible tachycardias using the basket catheter. Activation and voltage maps were created using standard settings (a bipolar voltage <0.05 mV was considered scar and a bipolar voltage of 0.05 to 0.5 mV was considered border zone, with additional adjustments based on operator). Patterns of wavefront propagation and activation were used to identify the critical isthmus in addition to global atrial histogram analysis (Lumipoint). Minimal entrainment mapping was performed. Further delineation of multiple-loop, dual-loop, and single loop tachycardias were done.   Irrigated catheter ablation was performed with max power of 40 W and peak temp of 42°C. Linear ablation was done at the practical isthmus which was defined as the narrowest pathway between scars, anatomical or functional obstacles, with the least concern for collateral damage. Bidirectional block was confirmed with mapping when possible. Procedural success was defined as termination of all stable, inducible supraventricular tachycardias without catheter-induced ectopy and lack of re-inducibility.   Offline processing of all maps with the Rhythmia software was done with original, unprocessed data at a single center. The maps were analyzed for central obstacles, central isthmus, pathway length, conduction velocity (CV), and coefficient of variability.   The central obstacles were defined as anatomic if circumnavigating normal cardiac structures and surgical if a prior operative substrate was involved (i.e., surgical incisions, anastomoses, plications, scarring, patch or baffle material). The central isthmus was defined as the midpoint of an area of slow conduction that encompassed 30% of the tachycardia cycle length. The width of this isthmus was measured between 2 fixed or functional barriers of electroanatomic scar. The pathway length was the shortest distance around the central obstacle. Large circuits were considered > the 50th percentile and small circuits were < the 50th percentile for length. The conduction velocity was calculated using isochronal maps split into 10 segments. The first segment was set to the central isthmus exit site. The bar distance around the central obstacle was measured for each isochrone. The CV was calculated as each bar distance divided by 10% of the tachycardia cycle length. The CV was calculated for both the central isthmus and non‐isthmus regions of the pathway. Slow conduction was defined as <0.3 m/s. The coefficient of variability was the standard deviation divided by the mean of all 10 CV values calculated in a given tachycardia circuit. The greater values corresponded to more heterogeneous CV patterns. The median value was used to classify circuits as “heterogeneous” versus “homogeneous.” See Figure Below.     There was a total of 85 catheter ablation procedures with a total of 156 supraventricular tachycardias seen. Of these, 136 (87%) were completely mapped. The median tachycardia cycle length (TCL) was 290 ms (IQR: 250–341). Tachycardia mechanisms were single-loop IART (60%), dual-loop (13%), and multiple-loop (14%). Of note, there was focal atrial tachycardia (19%), AVNRT (4%), AVRT (2%), and Twin AVN (1%) seen in the remainder of the cohort. The tachycardia was located in the right atrium (79%), the pulmonary venous chamber/left atrium (15%), both atrium (4%), and coronary sinus (2%).   The central obstacles varied with the type of IART. For single-loop IART, the most common obstacles were atriotomy (29%) and the tricuspid valve annulus (28%). For dual-loop IART, the most common combinations were the tricuspid valve annulus with an atriotomy (33%) or the inferior vena cava (17%).   The type of central obstacle, anatomic vs surgical, impacted circuit characteristics. Anatomic central obstacles were associated with a longer pathway length, faster central isthmus CV, faster non-isthmus CV, and smaller coefficient of variability. There was no difference in TCL based on type of central obstacle.Central ObstacleAnatomicSurgicalp-valueTotal Pathway Length (mm)119.3IQR: 80.4–150.377.7 mmIQR: 63.1–94.7p=0.001Central Isthmus CV (m/sec)0.11 m/sIQR: 0.06–0.240.07 m/sIQR: 0.05–0.10p=0.016Non-isthmus CV (m/sec)0.52 m/sIQR: 0.33–0.710.38 m/sIQR: 0.27–0.46p=0.009Slow isochrones (n)4IQR: 2.3–6.86IQR: 5–7p=0.008Smaller coefficient of variability0.65IQR: 0.56–0.820.82IQR: 0.69–0.92p=0.004Tachycardia Cycle (msec)282.5IQR: 247–320270IQR: 232.5–310p=0.33 The location of prior surgery also impacted circuit characteristics. A prior history of right heart surgery was associated with a shorter pathway length, slower central isthmus CV, and slower non-isthmus CV. There was no difference in TCL based on side of surgery.Central ObstacleRight Heart SurgeryLeft Heart Surgeryp-valueTotal Pathway Length (mm)76.3 mmIQR: 52.8–95.2113.0IQR: 66.6–130.9p=0.026Central Isthmus CV (m/sec)0.07IQR: 0.05–0.100.10IQR: 0.06–0.21p=0.047Non-isthmus CV (m/sec)0.36IQR: 0.25–0.470.52 m/sIQR: 0.28–0.60p=0.036Slow isochrones (n)6IQR: 5–85 IQR: 3.5–7p=0.027Smaller coefficient of variabilityNANANATachycardia Cycle (msec)285 msIQR: 260–322280 msIQR: 230–317p=0.63     The total pathway length was directly related to the central isthmus CV (R2=0.45; P<0.001) and non-isthmus CV (R2=0.71; P<0.001). For small circuits (pathway length <9 cm), central isthmus CV was always <0.15 m/s whereas non-isthmus CV was always <0.5 m/s. See Figure below.     The TCL was directly related to the non-isthmus CV (R2=0.07; P<0.031). A faster non-isthmus CV was associated with shorter TCL.   Post-ablation assessment of conduction block showed that both the non-isthmus CV and conduction time were similar to that during tachycardia (0.42 m/s [IQR: 0.31 – 0.62] vs 0.41 m/s [IQR: 0.28 – 0.64], β coefficient=0.9, R2=0.94; P<0.001) and 172.5 ms [IQR: 158.8–192.5] vs 185.5 ms [IQR: 161– 205.6], β coefficient=0.9, R2=0.85; P<0.001). A validation map to tachycardia non-isthmus conduction time ratio >85% (range 85%–120%) was encountered in all cases of UHDM-validated isthmus block. See Figure Below.     Ablations were acutely successful in 95% of cases. The median follow-up was 369 days (IQR: 224–534). During this time, recurrence was seen in 21 of 81 patients (25.9%). Arrhythmia-free survival was better in patients presenting with tachycardias with “homogeneous” versus ‘heterogeneous” circuit CV (90% versus 57%; p=0.038). See Figure Below   This well-designed retrospective study provides a detailed assessment of arrhythmia circuit properties in a large cohort of heterogeneous ACHD patients using the Rhythmia mapping system. The findings of this study are consistent with our conventional understanding of IART requiring a critical isthmus and varying conduction times to support tachycardia maintenance. The study provides some additional novel insights into IART circuits in ACHD patients.   IARTs types and properties varied based on location of surgery and type of central obstacle (anatomic vs post-surgical). IARTs that involved anatomic substrate or left sided surgery demonstrated longer pathway circuits with faster CV. IARTs with post-surgical substrate or right sided heart surgery had smaller pathway circuits and slower CV. See Figure Below.   These overall differences in circuit length are expected as central obstacles (i.e., atrioventricular valves) are larger obstacles than post-surgical incisional lines that can be short or have small electroanatomic conduction gaps. However, it is important to note that some anatomic IARTs course around smaller distances such as peri-caval IART. This was not analyzed separately but could provide a reason for overlap in circuit findings between the anatomic and post-surgical central obstacles. The study also noted a difference in circuit measures between left and right sided surgery. This reason for this is unknown but could be explained by a variety of factors including more complex left sided surgery (i.e., more incisional scars), presence or absence of left atrial MAZE, or dilated left atrium compared to right atrium. Overall, these findings clearly suggest a correlation between anatomic factors and arrhythmias findings which warrant further investigation.   This study showed a slower conduction velocity at the central isthmus compared to the non-isthmus in keeping with our fundamental understanding for reentrant mechanisms. In particular, all small circuits demonstrated a central isthmus CV of <0.15m/sec. However, this study showed that the TCL correlated with the non-isthmus CV rather than the central isthmus CV. The author suggests that this may play an important role in IART maintenance.   The use of CV seems to be an important measurement that could aid in substrate-based ablation, especially in the setting of non-inducibility or non-sustained IARTs. CV analysis could also be used to reduce the risk of recurrence by 1) determining if CV heterogeneity exists which is associated with higher recurrence rate and 2) providing an alternative method to assess conduction block.   Overall, this study demonstrated an acute procedural rate of 95% and a recurrence rate of 25.9% at ~ 1 year of follow-up. These numbers are on par with other single center studies and reflect the ongoing issue with atrial arrhythmias ablation in ACHD patients that show good acute success but high recurrence rates. Other studies have shown that recurrences are due to development of new arrhythmias or previous ablated arrhythmias. This study did not identify the type of arrhythmias that recurred, but does provide potential mapping strategies to increase acute procedural success and reduce risk of recurrence.   This study does have some limitations outside of its retrospective design. First, entrainment mapping was not performed to delineate bystander circuits from the critical isthmus which may result in additional substrate ablation. Second, heterogeneity in anatomic factors (atrial chamber size), surgical techniques, and anatomy may contribute to additional differences in pathway length and CV. Third, the benefit of using CV analysis for a substrate ablation approach is unknown and would benefit from comparative analysis of redo cases. Fourth, only the Rhythmia system was used, and these findings have not been validated with other mapping systems. Finally, electroanatomic mapping was not compared to 3D anatomic imaging to ensure full chamber mapping was performed.   Overall, this study aids in our understanding of the complexity of IARTs in ACHD patients and provides novel measurements which could aid in improved procedural success.