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.

Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia in Patients With Congenital Heart Disease.

Atrioventricular (AV) nodal reentrant tachycardia represents the most common regular supraventricular arrhythmia in humans, and catheter ablation of the so called slow AV nodal pathway has been effectively performed for decades. In patients with congenital heart disease, a combination of different factors makes catheter ablation of AV nodal reentrant tachycardia substrate particularly challenging, including abnormal venous access to intracardiac structures, abnormal intracardiac anatomy, potentially deviant and often unpredictable sites of the specific conduction system, loss of traditional anatomic landmarks, and congenital cardiac surgery that may complicate the access to the AV nodal area. Published experiences have confirmed the efficacy and the relative safety of such procedures when performed by experts, but the risk of complications, in particular AV block, remains non-negligible. A thorough knowledge and understanding of anatomic and electrical specificities according to underlying phenotype are essential in addressing these complex cases. Considering the major consequences associated with AV block in patients with complex congenital heart disease, particularly those without low risk access for transvenous ventricular pacing (eg, single ventricle physiology or Eisenmenger syndrome), the individual risk-benefit ratio should be carefully evaluated. The decision to defer ablation may be the wisest approach in selected patients with either infrequent or hemodynamically tolerated arrhythmias, or when the location of the AV conduction pathways remains uncertain. This narrative review aims to synthetize existing literature on catheter ablation of AV nodal reentrant tachycardia in congenital heart disease, to present main features of common associated pathologies, and to discuss approaches to mapping and safely ablating the slow AV nodal pathway in challenging cases.

Arrhythmic manifestation in ß-thalassemia cardiomyopathy: a complex management.

A young male with ß-thalassemia major was implanted with a single-chamber Implantable cardioverter-defibrillator (ICD) for a cardiac arrest due to ventricular fibrillation. He received multiple inappropriate shocks due to atrioventricular nodal re-entrant tachycardia (AVNRT) treated with radiofrequency catheter ablation and then to high-rate atrial tachycardia refractory to amiodarone and not inducible during electrophysiological study. He refused empirical pulmonary vein isolation. Upgrading to biventricular ICD and performing atrioventricular node ablation avoided further inappropriate shocks.

Intrinsic Electrical Remodeling Underlies Atrioventricular Block in Athletes.

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Effectiveness and safety of AV node ablation after His bundle pacing in patients with uncontrolled atrial arrhythmias.

INTRODUCTION: In patients with uncontrolled atrial fibrillation, atrioventricular (AV) node ablation after permanent His bundle pacing (p-HBP) could be a therapeutic option for heart rate (HR) control. We aimed to demonstrate the advantages of AV node ablation with p-HBP, and to describe its effectiveness and safety. METHODS: This descriptive observational study included patients with uncontrolled permanent atrial arrhythmias who were candidates for HR control (January 2019 to July 2020) and underwent p-HBP and AV node ablation. RESULTS: A total of 39 patients were included. The median left ventricular ejection fraction (LVEF) was 55% (45-60); 46.1% in NYHA class II and 43.6% in NYHA class III. p-HBP was achieved in 92.3% (n = 36), and AV node ablation was successfully performed in all patients. The LVEF improved in patients with reduced LVEF (baseline, 35% [23.8-45.3%]; follow-up, 40% [35-56.5%], p < 0.05); the NYHA class also showed improvement (baseline, 71.4% patients in class III and 7.1% in class II, and at follow-up, 78.6% patients in class II and 14.3% in class I). In patients with previously normal LVEF, LVEF remained stable; nevertheless, a significant NYHA class improvement was observed (baseline, 63.6% class II and 31.8% class III patients; follow-up, 54.5% class I and 45.5% class II patients). The His thresholds and lead parameter values did not significantly change during the follow-up and remained stable. CONCLUSIONS: In patients with uncontrolled atrial arrhythmias who underwent AV node ablation after p-HBP, the NYHA class improved and the LVEF increased in those with reduced baseline LVEF. The values of pacing parameters were acceptable and remained stable during the follow-up.

Clinical symptoms of limited exercise capacity linked to AAI-DDD functionality: An in silico and in vivo approach.

BACKGROUND: Exercise capacity is an important aspect of quality of life in patients undergoing pacemaker implantation. Device algorithms for ventricular pacing avoidance have been developed to avoid unnecessary and potentially harmful effects of right ventricular pacing. However, little data exists on the immediate response of these algorithms to sudden AV block during exercise. METHODS: The ventricular pacing avoidance algorithms of four pacemaker manufacturers were tested in an ex-vivo model. The RSIM-1500-USB Device-Interactive Heart Simulator (Rivertek Medical Systems, Inc.) was used to simulate three different scenarios: the first one starting with an initially conducted atrial pacing rate of 60 min-1 , the second one starting with an atrial rate of 120 min-1 and finally a scenario starting with an atrial rate of 150 min-1 . In all three scenarios, the initially conducted atrial rate was followed by a sudden, long lasting episode of third-degree AV-block. The response to those scenarios was recorded for each of the (brand-specific) ventricular pacing avoidance algorithms. RESULTS: In the first scenario, the simulation resulted in a ventricular pause of 1333 ms (Boston Scientific), 2000 ms (Medtronic and Microport), and 2340 ms (Biotronik). In the second and third scenario, different results were observed across devices. All simulations of the second and third scenario resulted in repetitive 2:1 block response (during eight cycles) in Boston Scientific and Biotronik devices. These scenarios were confirmed in patient cases. CONCLUSION: Simulator based observations of unanticipated pacemaker-induced 2:1 block response during exercise may explain clinical symptoms experienced by some patients having a two-chamber pacemaker.

Predictors of AVNRT Recurrence After Slow Pathway Modification.

Atrioventricular nodal reentry tachycardia (AVNRT) is the most common regular supraventricular tachycardia (SVT). Slow pathway modification (SPM) is the accepted first line treatment with reported success rates around 95%. Information regarding possible predictors of AVNRT recurrence is scarce.Out of 4170 consecutive patients with SPM in our department from 1993-2018, we identified 78 patients (1.9%) receiving > 1 SPM (69% female, median age 50 years) with a recurrence of AVNRT after a successful SPM. We matched these patients for age, gender and number of radiofrequency applications during first SPM with 78 patients who received one successful SPM in our center without AVNRT recurrence. Both groups were analyzed for possible predictors of a recurrence of AVNRT during long-term follow-up. The recurrence group contained a significantly lower proportion of patients with an occurrence of junctional beats during SPM (69% versus 89%, P = 0.006). Moreover, significantly more cases of previously diagnosed atrial fibrillation/tachycardia (AF/AT; 21% versus 5%, P = 0.007) and inducible AF/AT during electrophysiology study (23% versus 6%, P = 0.006) were present in the recurrence group. While more than half of patients had a recurrence within the first year, in 20% symptoms reappeared ≥ 4 years after ablation.In a small percentage of patients, AVNRT recurs after an initially successful ablation. Interestingly, these patients had significantly fewer junctional beats during ablation and a higher rate of other (inducible) arrhythmias. AVNRT recurrence spanned a considerable timeframe and should remain a differential diagnosis, even years after ablation.

High-degree atrioventricular block in COVID-19 hospitalized patients.

AIMS: The novel coronavirus SARS-CoV-2 has shown the potential to significantly affect the cardiovascular system. Cardiac arrhythmias are commonly reported complications in COVID-19 hospitalized patients. METHODS AND RESULTS: While tachyarrhythmias seem most common, we describe four cases of COVID-19 patients who developed a transient high-degree atrioventricular (AV) block during the course of their hospitalization. All four patients who developed a high-degree AV block during their hospitalization with COVID-19 did not require permanent pacing. CONCLUSION: Similarly to most AV blocks associated with infectious organisms and given its transient nature, this case series suggests that conservative management strategies should be preferred in COVID-19 patients who develop complete heart block.

Automated rhythm-based control of radiofrequency ablation close to the atrioventricular node: Preclinical, animal, and first-in-human testing.

BACKGROUND: The risk of heart block during radiofrequency ablation of atrioventricular (AV) nodal reentrant tachycardia and septal accessory pathways is minimized by rapidly ceasing ablation in response to markers of risk, such as atrioventricular dissociation, fast junctional rhythm, PR interval prolongation, or 2 consecutive atrial or ventricular depolarizations. Currently this is done manually. OBJECTIVES: The objectives of this study were to build and test a control system able to monitor cardiac rhythm and automatically terminate ablation energy when required. METHODS: The device was built from off-shelf componentry. Preclinical testing involved real-time input of electrogram/electrocardiogram data from 209 ablation procedures (20 patients) over slow (n = 19) and fast (n = 1) AV nodal pathways. The device response speed was compared with the human response speed. The device's ability to prevent heart block was tested in 5 sheep. First-in-human testing was then performed in 12 patients undergoing AV nodal reentrant tachycardia ablation. RESULTS: Risk conditions necessitating shutoff of ablation (200 total; 111 preclinical and 89 first-in-human) were detected by the device with 100% sensitivity and 94% specificity, automatically terminating ablation while still allowing successful ablation in all patients. Device shutoff of ablation was always faster than human response (median difference 1.24 seconds). In each of 5 sheep, 40 consecutive attempts to cause heart block by ablating over the His bundle were unsuccessful because of automatic shutoff in response to rhythm change. CONCLUSION: Automated shutoff of ablation close to the AV node in response to markers of the risk of heart block is feasible with high accuracy as well as faster response than human response. The system may improve the safety of ablation near the AV node by preventing heart block.

The bradycardic agent ivabradine decreases conduction velocity in the AV node and in the ventricles in-vivo.

Ivabradine blocks hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels, thereby lowering the heart rate, an action that is used clinically for the treatment of heart failure and angina pectoris. We and others have shown previously that ivabradine, in addition to its HCN channel blocking activity, also inhibits voltage-gated Na channels in vitro at concentrations that may be clinically relevant. Such action may reduce conduction velocity in cardiac atria and ventricles. Here, we explore the effect of administration of ivabradine on parameters of ventricular conduction and repolarization in the surface ECG of anesthetized mice. We found that 5 min after i.p. administration of 10 mg/kg ivabradine spontaneous heart rate had declined by ~13%, which is within the range observed in human clinical studies. At the same time a significant increase in QRS duration by ~18% was observed, suggesting a reduction in ventricular conduction velocity. During transesophageal pacing at heart rates between 100 and 220 beats/min there was no obvious rate-dependence of ivabradine-induced QRS prolongation. On the other hand, ivabradine produced substantial rate-dependent slowing of AV nodal conduction. We conclude that ivabradine prolongs conduction in the AV-node and in the ventricles in vivo.

Twin atrioventricular nodes, arrhythmias, and survival in pediatric and adult patients with heterotaxy syndrome.

BACKGROUND: Heterotaxy syndrome is likely to involve arrhythmias from associated conduction system abnormalities, which are distinct in different subtypes of isomerism and may change further after interventions and remodeling. OBJECTIVE: The purpose of this study was to understand the risk of arrhythmias and its relation to isomerism subtypes. METHODS: Patients diagnosed between 1980 and 2019 as having heterotaxy syndrome were enrolled and grouped as right atrial isomerism (RAI), left atrial isomerism (LAI), or indeterminate isomerism. RESULTS: Of the 366 patients enrolled, 326 (89.1%) had RAI, 35 (9.6%) LAI, and 5 (1.4%) indeterminate isomerism; 71 (19.4%) patients were adults. Arrhythmias occurred in 37.2% of patients (109 supraventricular tachycardia [SVT], 8 atrial fibrillation/flutter, 12 ventricular tachycardia, and 14 paced bradycardia). Freedom from arrhythmias by the age of 1, 5, 10, 20, and 40 years was 0.849, 0.680, 0.550, 0.413, and 0.053, respectively. Twin atrioventricular nodes were identified in 51.5% of patients with RAI, 8.7% of patients with LAI, and 40.0% of patients with indeterminate isomerism and were the key predictors of SVT. Indeterminate isomerism was also a risk factor for SVT. Other forms of tachycardia appeared relatively late. Sinus bradycardia with junctional rhythm was common in LAI (48.7%) and less in indeterminate isomerism (20.0%), with none occurring in RAI. Only in patients with RAI who showed the poorest survival, ventricular tachycardia worsened the long-term survival. CONCLUSION: RAI was the predominant subtype of heterotaxy in this cohort. Collectively, the median RAI/LAI ratio was 0.731 and 5.450 in Western and East Asian studies, respectively. Arrhythmias, tachycardia, or paced bradycardia were common, but the spectrum was distinct among subtypes.

Coexistence of sinus bradycardia and junctional tachycardia in a patient with fibrotic atrial cardiomyopathy.

A 65-year-old woman was referred for catheter ablation in the treatment of persistent tachycardia after surgery for atrial fibrillation and mitral regurgitation. Bipolar voltage mapping of both atria revealed that severe and extensive atrial fibrosis isolated the sinoatrial node from the atrioventricular junction and led to the coexistence of sinus bradycardia and persistent junctional tachycardia.

BRASH Syndrome with Hyperkalemia: An Under-Recognized Clinical Condition.

BRASH syndrome is characterized by bradycardia, renal failure, use of an atrioventricular nodal blocker (AVNB), shock, and hyperkalemia. These symptoms represent an ongoing vicious cycle in a patient with a low glomerular filtration rate taking an AVNB. Decreased clearance of the medication and hyperkalemia associated with renal failure synergize to cause bradycardia and hypoperfusion. This reaction causes renal function to worsen, thereby perpetuating the cycle of BRASH syndrome.

Concomitant genetic ablation of L-type Cav1.3 (α1D) and T-type Cav3.1 (α1G) Ca2+ channels disrupts heart automaticity.

Cardiac automaticity is set by pacemaker activity of the sinus node (SAN). In addition to the ubiquitously expressed cardiac voltage-gated L-type Cav1.2 Ca2+ channel isoform, pacemaker cells within the SAN and the atrioventricular node co-express voltage-gated L-type Cav1.3 and T-type Cav3.1 Ca2+ channels (SAN-VGCCs). The role of SAN-VGCCs in automaticity is incompletely understood. We used knockout mice carrying individual genetic ablation of Cav1.3 (Cav1.3-/-) or Cav3.1 (Cav3.1-/-) channels and double mutant Cav1.3-/-/Cav3.1-/- mice expressing only Cav1.2 channels. We show that concomitant loss of SAN-VGCCs prevents physiological SAN automaticity, blocks impulse conduction and compromises ventricular rhythmicity. Coexpression of SAN-VGCCs is necessary for impulse formation in the central SAN. In mice lacking SAN-VGCCs, residual pacemaker activity is predominantly generated in peripheral nodal and extranodal sites by f-channels and TTX-sensitive Na+ channels. In beating SAN cells, ablation of SAN-VGCCs disrupted late diastolic local intracellular Ca2+ release, which demonstrates an important role for these channels in supporting the sarcoplasmic reticulum based "Ca2+ clock" mechanism during normal pacemaking. These data implicate an underappreciated role for co-expression of SAN-VGCCs in heart automaticity and define an integral role for these channels in mechanisms that control the heartbeat.

An Experimental Study on Rapid Localization of the Atrioventricular Node During Open-Heart Surgery.

BACKGROUND: To verify the validity and feasibility of using a mechanical compression method to locate the atrioventricular node in open-heart surgery. METHODS: Ten healthy miniature pigs were used to establish an animal model of the beating heart under cardiopulmonary bypass. During the operation, the atrioventricular node and its surrounding areas were stimulated by mechanical compression (mechanical compression method), and the occurrence of complete atrioventricular block was judged by real-time electrocardiograph monitoring and direct observation of the heart rhythm to identify the position of the atrioventricular node. The final localization of the atrioventricular node was determined using the iodine staining method, and the results were used as the "gold standard" to test the effectiveness and feasibility of the mechanical compression method for locating the atrioventricular node. RESULTS: With the beating heart model, complete atrioventricular block occurred after mechanical compression of the "atrioventricular node" area in 10 pigs. Nine pigs regained normal conduction immediately after the compression was released, and one pig failed to recover. No atrioventricular block or other arrhythmias occurred after mechanical compression of the "non-atrioventricular node" area. The sensitivity of the method was 86.6%, specificity was 100.0%, misdiagnosis rate was 0.0%, missed diagnosis rate was 13.4%, positive predictive value was 100.0%, negative predictive value was 97.9%, positive likelihood ratios were +∞, negative likelihood ratios were 13.4%, accuracy was 98.1%, and diagnostic odds ratio was +∞. CONCLUSION: This study innovatively proposes the application of the mechanical compression method to locate the atrioventricular node during operation and preliminarily proves that this method is effective and feasible through animal experiments.

Revisiting right anterior oblique projections for the triangle of Koch: implications from computed tomography.

BACKGROUND: Variability in the anatomy and orientation of the triangle of Koch (TK) complicates ablation procedures involving the atrioventricular (AV) node. We used CT angiography (CTA) to assess the anatomical TK orientation, the CS ostium direction, and the relationship between the two, and we validated an individualized CS-guided projection during ablation procedures. METHODS: In 104 patients without structural heart disease undergoing computed tomography (CT) angiography, TK orientations were determined in relation to the coronary sinus ostium (CSo) as well as two standard right anterior oblique (RAO) projection angles (30o and 45o) commonly used in ablation procedures. RESULTS: A CS-guided RAO projection (RAOCS) was shown to best track the orientation of the TK compared to RAO30° and 45°, with TK orientation strongly correlating with the CSo direction (r = 0.86, P < 0.001). In addition, the mean relative difference between the angle of the CSo and TK orientation was 5.54 ± 0.48°, consistent with a reduction in the degree of image shortening compared to traditional RAOs. Moreover, in vivo validation following ablation revealed that using a CS-guided projection limited the degree of on-screen image shortening compared to both the RAO30° and 45° in 25 patients with catheter ablation procedures. CONCLUSION: In hearts with a normal structure, the CSo direction offers a reliable predictor of the TK orientation which can be used to guide the projection of the TK during ablation procedures.