Reentry Circuit Research Articles

State of the Art: Mapping Strategies to Guide Ablation in Ischemic Heart Disease.

Catheter ablation to prevent ventricular tachycardia (VT) that emerges late after a myocardial infarction aims to interrupt the re-entry substrate. Interruption of potential channels and regions of slow conduction that can be identified during stable sinus or paced rhythm is often effective and a number of substrate markers for guiding this approach have been described. While there is substantial agreement with different markers in some patients, the different markers select different regions for ablation in others. Mapping during VT to identify critical re-entry circuit isthmuses is likely more specific, and most useful when VT is incessant or frequent during the procedure or when sinus rhythm substrate ablation fails. Both approaches are often combined. These methods for identifying and characterizing post-infarct-related arrhythmia substrate and the re-entry circuits are reviewed.

Arrhythmias in thyroid dysfunction

Thyroid dysfunction is associated with characteristic changes in heart rate and arrhythmias. Thyroid hormones act through genomic and non-genomic effects on myocytes and influence contractility, relaxation and action potential duration through avariety of mechanisms. Atrial fibrillation is the most common arrhythmia associated with thyroid dysfunction, it occurs in both euthyroidism and hyperthyroidism in clear association with T4 levels. Mechanistically, in the hyperthyroid state, increased automaticity and triggered activity, together with ashortened refractory period and slowing of the conduction speed, lead to the initiation and maintenance of multiple intraatrial reentry circuits. Influences from the autonomic nervous system and hemodynamics controlled by thyroid hormones act as modulators for arrhythmias, which are promoted by acorresponding substrate (significant impact of comorbidities). Concerning therapy, in addition to treating hyperthyroidism, the initial therapeutic focus is on adequate rate control and anticoagulation in patients with ahigh risk of thromboembolism. Ablation of atrial fibrillation can be considered later on, although there is an increased likelihood of recurrence compared to patients without hyperthyroidism.Prolongation of the QT interval and increase in QT dispersion are involved in the formation of ventricular arrhythmias. Epidemiological data suggest an association of elevated T4 levels with ventricular arrhythmias and sudden cardiac death. However, this seems to be mainly relevant for patients with underlying cardiac disease (e.g. ICD users).

SVT in the EP lab: electrograms don't always show the reentry circuit

SVT in the EP lab: electrograms don't always show the reentry circuit

A case of biatrial tachycardia involving the intercaval bundle with assumed dual loop reentry.

Epicardial connections provided the anatomical substrate for the biatrial reentry circuit. The connections between the right atrium and right pulmonary vein were called "intercaval bundle," and there are few reports of atrial flutter related to this bundle. We present a case of a biatrial tachycardia, involving the intercaval bundle.

The Role of KACh Channels in Atrial Fibrillation.

This manuscript explores the intricate role of acetylcholine-activated inward rectifier potassium (KACh) channels in the pathogenesis of atrial fibrillation (AF), a common cardiac arrhythmia. It delves into the molecular and cellular mechanisms that underpin AF, emphasizing the vital function of KACh channels in modulating the atrial action potential and facilitating arrhythmogenic conditions. This study underscores the dual nature of KACh activation and its genetic regulation, revealing that specific variations in potassium channel genes, such as Kir3.4 and K2P3.1, significantly influence the electrophysiological remodeling associated with AF. Furthermore, this manuscript identifies the crucial role of the KACh-mediated current, IKACh, in sustaining arrhythmia through facilitating shorter re-entry circuits and stabilizing the re-entrant circuits, particularly in response to vagal nerve stimulation. Experimental findings from animal models, which could not induce AF in the absence of muscarinic activation, highlight the dependency of AF induction on KACh channel activity. This is complemented by discussions on therapeutic interventions, where KACh channel blockers have shown promise in AF management. Additionally, this study discusses the broader implications of KACh channel behavior, including its ubiquitous presence across different cardiac regions and species, contributing to a comprehensive understanding of AF dynamics. The implications of these findings are profound, suggesting that targeting KACh channels might offer new therapeutic avenues for AF treatment, particularly in cases resistant to conventional approaches. By integrating genetic, cellular, and pharmacological perspectives, this manuscript offers a holistic view of the potential mechanisms and therapeutic targets in AF, making a significant contribution to the field of cardiac arrhythmia research.

Non-invasive assessment of the ventricular tachycardia isthmus during sinus rhythm

Abstract Background The ablation of ventricular tachycardias (VT) presents significant challenges due to the complex and time-consuming approaches involved in identifying arrhythmogenic regions. Combining non-invasive electrocardiographic imaging (ECGI) with endocardial mapping could potentially enhance the efficacy of interventions. Objective To evaluate the capability of ECGI in guiding operators towards areas of VT isthmuses during sinus rhythm. Methods Patients with scar-related VT, confirmed by late gadolinium enhancement cardiac magnetic resonance, were prospectively enrolled. We compared the areas of slowed conduction identified by ECGI with the VT sustaining regions identified endocardially. Simultaneous Electroanatomical Mapping (EAM) and ECGI mapping were performed during VT ablation procedures. In patients in whom a hemodynamically stable VT was maintained, the reentry circuit was mapped endocardially, and the ablation target was identified. The left ventricle was segmented into 9 regions, categorized as either VT-isthmus or non-VT isthmus based on EAM findings. Prior to ablation, local activation times (LAT) and conduction velocity (CV) ECGI sinus maps were computed. Slow conduction was quantified non-invasively by computing different ECGI metrics per region, including the mean and the standard deviation (SD) of LAT and CV, the regional Total Activation Time (rTAT) – time span between the earliest and latest activated nodes–, and the Slow Conduction Velocity (SCV) – the percentage of nodes where velocity falls below 60 cm/s -. Results The study included 20 consecutive patients with ischemic cardiomyopathy who were referred for VT ablation. A total of 21 regions linked to the VT isthmus were identified endocardially in 17 patients (age: 66.1±8.8 years, 94.1% male, left ventricular ejection fraction: 26.4±7.3%). Figure 1 illustrates the correlation between the VT circuit and the ECGI sinus map in two patients with extensive left ventricular fibrosis. ECGI metrics related to VT isthmuses exhibited a higher standard deviation in both LAT (18.1±2.0 vs 9.8±1.2 ms; p=0.001), and CV (50.4±4.7 vs 37.1±2.8 cm/s; p=0.011), and a greater percentage of nodes with slowed conduction (13.7±2.7 vs 7.4±1.6 %; p=0.029), compared to non-VT isthmus regions, Figure 2. Multivariate logistic regression analysis revealed that SD-LAT was the strongest predictor of VT isthmus localization. Conclusion ECGI has demonstrated the capability to pinpoint slowed conduction areas responsible for VT in sinus rhythm, showing promise in planning and guiding VT ablation strategies. This advancement paves the way for further research into using this non-invasive tool to improve risk stratification methods for ventricular arrhythmias.

The importance of scar border zone size in VT presentation and recurrence in post MI patients

Abstract Introduction Available mapping data in post-myocardial infarction patients describe ventricular tachycardia (VT) re-entry circuit characteristics of slow VT, that are typically related to transmural scars. Fast VTs with cycle lengths close to the refractory period may be related to functional re-entry in the scar border zone. Functional re-entry related border zone VTs may be difficult to control by ablation. Purpose The aims of this study are (1) to describe electroanatomical voltage map (EAVM) characteristics in post myocardial infarction (MI) patients with spontaneous and inducible fast VTs and (2) to assess the relation between scar border zone size and ablation outcomes. Methods Consecutive post-MI patients undergoing VT ablation at a tertiary referral center from January 2012 to November 2018 were included. Fast VT was defined as a VT cycle length (VTCL) = ventricular refractory period + max. 30ms. Areas of scar border zone (using 0.5 – 2.1mV/3.0mV cut-offs (according to LV remodeling stage; LVEF<47% and LV end-systolic volume index of >50 ml/m2)) were measured on the EAVM and correlated with clinical outcomes. Results In total, 138 patients were included (86% male; left ventricular ejection fraction 35±10%; 86% remodeled LV). Twenty-three patients (17%) had ≥1 fast VT (mean VTCL 275±52ms) at presentation, mean VTCL of the remaining patients 397±88ms). The median scar border zone size was 27% [IQR 20-38] of the left ventricular endocardial surface. Patients who presented with a spontaneous fast VT had a larger border zone than patients with slower VT (32% [IQR 28 – 41] vs. 25% [IQR 16 – 36], p=0.01). After ablation, 79 (57%) patients remained inducible for any VT, including 59/79 (75%) for a fast VT (median VTCL fast VT 260ms [IQR 236 -280]). Patients who remained inducible for fast VTs had a larger border zone than patients who remained inducible for slower VTs (35% [IQR 27 – 44] vs. 26% [IQR 20 – 36], p<0.001). During a median follow-up of 26 months [IQR 8 – 47], 45 patients (33%) had a VT recurrence (mean VTCL 357±98ms). Patients with a below median (27%) scar border zone area had a lower VT recurrence rate compared to patients with an above median scar border zone area (recurrence rate: 16/66 (24%) vs. 29/72 (40%), p=0.03). Kaplan-Meier survival analysis showed better free VT survival in the below median border zone patients (Log-rank: p<0.05) (Figure 1). Conclusion Patients who present with spontaneous fast VTs or who remain inducible for fast VTs after ablation have larger scar border zones during EAVM compared to patients with presenting or remaining slower VTs. A larger border zone appeared to be associated with higher VT-recurrence rates. The scar border zone may play an important role as VT substrate for (fast) VTs and may not be easily targeted by current ablation techniques.VT-free survival stratified by median BZ

Vericiguat suppresses ventricular tachyarrhythmias inducibility in a rabbit myocardial infarction model.

The VICTORIA trial demonstrated a significant decrease in cardiovascular events through vericiguat therapy. This study aimed to assess the potential mechanisms responsible for the reduction of cardiovascular events with vericiguat therapy in a rabbit model of myocardial infarction (MI). A chronic MI rabbit model was created through coronary artery ligation. Following 4 weeks, the hearts were harvested and Langendorff perfused. Subsequently, electrophysiological examinations and dual voltage-calcium optical mapping studies were conducted at baseline and after administration of vericiguat at a dose of 5 μmol/L. Acute vericiguat therapy demonstrated a significant reduction in premature ventricular beat burden and effectively suppressed ventricular arrhythmic inducibility. The electrophysiological influences of vericiguat therapy included an increased ventricular effective refractory period, prolonged action potential duration, and accelerated intracellular calcium (Cai) homeostasis, leading to the suppression of action potential and Cai alternans. The pacing-induced ventricular arrhythmias exhibited a reentrant pattern, attributed to fixed or functional conduction block in the peri-infarct zone. Vericiguat therapy effectively mitigated the formation of cardiac alternans as well as the development of reentrant impulses, providing additional anti-arrhythmic benefits. In the MI rabbit model, vericiguat therapy demonstrates anti-ventricular arrhythmia effects. The vericiguat therapy reduces ventricular ectopic beats, inhibiting the initiation of ventricular arrhythmias. Furthermore, the therapy successfully suppresses cardiac alternans, preventing conduction block and, consequently, the formation of reentry circuits.

Upper common pathway analysis using late atrial premature depolarization in atrioventricular nodal reentry tachycardia

BackgroundAnatomic and electrophysiologic findings suggest that the actual circuit of atrioventricular nodal reentrant tachycardia (AVNRT) involves the perinodal atrium. However, occasional instances in which the atrium is dissociated from the AVNRT have led to the concept of an upper common pathway (UCP). ObjectiveWe aimed to assess the prevalence of UCP in AVNRT using a late atrial premature depolarization (LAPD) maneuver. MethodsPatients who were diagnosed with typical AVNRT by electrophysiologic studies were enrolled. For evaluation of the presence of UCP, an LAPD was given at the coronary sinus ostium (osCS) during AVNRT, and then pacing was repeated incrementally every 10 ms. Electrograms in the earliest retrograde atrial activation site (ERAS) near the proximal His were mapped and recorded during the pacing. Results were interpreted as follows: absence of UCP—an LAPD from the osCS can reset the tachycardia without depolarizing the ERAS; presence of UCP—an LAPD from the osCS can depolarize the ERAS without resetting the tachycardia; and indeterminate—an LAPD from the osCS either resets the ERAS and tachycardia simultaneously or does not reset both. ResultsThe LAPD maneuver was performed in 126 patients with AVNRT. It demonstrated an absence of UCP in 121 (96.0%) patients and the presence of UCP in 3 (2.4%) patients; the result was indeterminate in 2 (1.6%) patients. ConclusionThe LAPD maneuver revealed that the presence of UCP is indicated in only rare cases of AVNRT. In most AVNRT cases, the atrium is involved in the reentry circuit.

The Upper Common Pathway in Atrioventricular Nodal Reentrant Tachycardia: A Comprehensive Review of Evidence and Current Perspectives.

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of paroxysmal supraventricular tachycardia, and its diagnostic and therapeutic approaches have been well-established. Traditionally, AVNRT is understood to be an intranodal reentry having two bystander pathways; the upper common pathway (UCP) which connects to the atrium and the lower common pathway which connects to the ventricle. However, the existence of the UCP remains a subject of ongoing debate. The assertion of the UCP's presence is supported by electrophysiological evidence suggesting that the atrium is not essential for the perpetuation of AVNRT. Nonetheless, numerous anatomical studies have failed to identify any structure that could be conclusively designated as the UCP. The histological and electrophysiological characteristics of the slow and fast pathways, which are the core components of AVNRT, suggest the inclusion of atrial myocardium in the reentry circuit. While clear interpretation of these discrepancies remains elusive, potential explanations may be derived from existing evidence and recent research findings concerning the actual AVNRT circuit.

Scar architecture affects the electrophysiological characteristics of induced ventricular arrhythmias in hypertrophic cardiomyopathy.

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) detects myocardial scarring, a risk factor for ventricular arrhythmias (VAs) in hypertrophic cardiomyopathy (HCM). The LGE-CMR distinguishes core, borderzone (BZ) fibrosis, and BZ channels, crucial components of re-entry circuits. We studied how scar architecture affects inducibility and electrophysiological traits of VA in HCM. We correlated scar composition with programmed ventricular stimulation-inducible VA features using LGE intensity maps. Thirty consecutive patients were enrolled. Thirteen (43%) were non-inducible, 6 (20%) had inducible non-sustained, and 11 (37%) had inducible sustained mono (MMVT)- or polymorphic VT/VF (PVT/VF). Of 17 induced VA, 13 (76%) were MMVT that either ended spontaneously, persisted as sustained monomorphic, or degenerated into PVT/VF. Twenty-seven patients (90%) had LGE. Of these, 17 (57%) had non-sustained or sustained inducible VA. Scar mass significantly increased (P = 0.002) from non-inducible to inducible non-sustained and sustained VA patients in both the BZ and core components. Borderzone channels were found in 23%, 67%, and 91% of non-inducible, inducible non-sustained, and inducible sustained VA patients (P = 0.003). All 13 patients induced with MMVT or monomorphic-initiated PVT/VF had LGE. The origin of 10/13 of these VTs matched scar location, with 8/10 of these LGE regions showing BZ channels. During follow-up (20 months, interquartile range: 7-37), one patient with BZ channels and inducible PVT had an ICD shock for VF. Scar architecture determines inducibility and electrophysiological traits of VA in HCM. Larger studies should explore the role of complex LGE patterns in refining risk assessment in HCM patients.

Ventricular Tachycardia Catheter Ablation: Retrospective Analysis and Prospective Outlooks-A Comprehensive Review.

Ventricular tachycardia is a potentially life-threatening arrhythmia associated with an overall high morbi-mortality, particularly in patients with structural heart disease. Despite their pivotal role in preventing sudden cardiac death, implantable cardioverter-defibrillators, although a guideline-based class I recommendation, are unable to prevent arrhythmic episodes and significantly alter the quality of life by delivering recurrent therapies. From open-heart surgical ablation to the currently widely used percutaneous approach, catheter ablation is a safe and effective procedure able to target the responsible re-entry myocardial circuit from both the endocardium and the epicardium. There are four main mapping strategies, activation, entrainment, pace, and substrate mapping, each of them with their own advantages and limitations. The contemporary guideline-based recommendations for VT ablation primarily apply to patients experiencing antiarrhythmic drug ineffectiveness or those intolerant to the pharmacological treatment. Although highly effective in most cases of scar-related VTs, the traditional approach may sometimes be insufficient, especially in patients with nonischemic cardiomyopathies, where circuits may be unmappable using the classic techniques. Alternative methods have been proposed, such as stereotactic arrhythmia radioablation or radiotherapy ablation, surgical ablation, needle ablation, transarterial coronary ethanol ablation, and retrograde coronary venous ethanol ablation, with promising results. Further studies are needed in order to prove the overall efficacy of these methods in comparison to standard radiofrequency delivery. Nevertheless, as the field of cardiac electrophysiology continues to evolve, it is important to acknowledge the role of artificial intelligence in both the pre-procedural planning and the intervention itself.

Heat and cold stress increases the risk of paroxysmal supraventricular tachycardia.

Paroxysmal supraventricular tachycardia (PSVT) is a common arrhythmia in adults. Its occurrence depends on the presence of the reentry circuit and the trigger of the paroxysm. Stress, emotional factors, and comorbidities favour the occurrence of such an episode. We hypothesized that the occurrence of PSVT follows extreme thermal episodes. The retrospective analysis was based on the data collected from three hospital emergency departments in Poland (Olsztyn, Radom, and Wroclaw) involving 816 admissions for PSVT in the period of 2016-2021. To test the hypothesis, we applied the Universal Climate Thermal Index (UTCI) to objectively determine exposure to cold or heat stress. The risk (RR) for PSVT increased to 1.37 (p = 0.006) in cold stress and 1.24 (p = 0.05) in heat stress when compared to thermoneutral conditions. The likelihood of PSVT during cold/heat stress is higher in women (RR = 1.59, p< 0.001 and RR = 1.36, p = 0.024, respectively) than in men (RR = 0.64 at p = 0.088 and RR = 0.78, p = 0.083, respectively). The susceptibility for PSVT was even higher in all groups of women after exclusion of perimenopausal group of women, in thermal stress (RR = 1.74, p< 0.001, RR = 1.56, p = 0.029, respectively). Females, particularly at the perimenopausal stage and men irrespective of age were less likely to develop PSVT under thermal stress as compared to thermoneutral conditions. Progress in climate change requires searching for universal methods and tools to monitor relationships between humans and climate. Our paper confirms that the UTCI is the universal tool describing the impact of thermal stress on the human body and its high usefulness in medical researches.

Upper turnaround point in a reentry circuit of the idiopathic left posterior fascicular ventricular tachycardia.

The anatomic extent of the reentry circuit in idiopathic left posterior fascicular ventricular tachycardia (LPF-VT) is yet to be fully elucidated. We hypothesized that entrainment mapping could be used to delineate the reentry circuit of an LPF-VT, especially including the upper turnaround point. Twenty-three consecutive LPF-VT patients (mean age, 29±9 years, 18 males) were included. We performed overdrive pacing with entrainment attempts at the left bundle branch (LBB) and the left His bundle (HB) region. Overdrive pacing from the LBB region showed concealed fusion in all 23 patients (post-pacing interval [PPI], 322.1±64.3ms; tachycardia cycle length [TCL], 319.0±61.6ms; PPI-TCL, 3.1±4.6ms) with a long stimulus-to-QRS interval (287.9±58.0ms, approximately 90% of the TCL). Pacing from the same LBB region at a slightly faster pacing rate showed manifest fusion with antidromic conduction to the LBB and minimal in-and-out time to the LBB potential (PPI-TCL, 21.3±13.7ms). Overdrive pacing from the left HB region showed manifest fusion with a long PPI-TCL (53.9±22.5ms). Our pacing study results suggest that the upper turnaround point in a reentry circuit of the LPF-VT may extend to the proximal His-Purkinje conduction system near the LBB region but below the left HB region. The LPF may constitute the retrograde limb of the reentry circuit.

Features of Catheter Treatment of Non-Isthmus-Dependent Atrial Flutter

Atrial flutter (AF) is caused by the re-circulation of the wave of electrical excitation of the myocardium (reentry) around the anatomical substrate which circulates within the atrial tissues. This is always a macro re-entry. Such an anatomical barrier, around which circulation can occur, can be the superior or inferior vena cava, rings of the tricuspid or mitral valves, the mouth of the coronary sinus, pulmonary veins, postoperative scar.&#x0D; The aim. To determine the specifics of elimination, success rate, and long-term outcome with various preablation and postablation diagnostic techniques for non-isthmus-dependent atrial flutter (NIDAFL).&#x0D; Materials and methods. The study included 26 patients who underwent radiofrequency ablation of atypical NIDAFL.&#x0D; Results. As a result of radiofrequency ablation, a sinus rhythm was restored in 17 patients during the procedure. In 7 cases, when the typical, isthmus-dependent AF was removed, the tachycardia cycle and the morphology of the R wave changed. Mapping showed that in 7 cases the direction of the re-entry front changed, and instead of the circulation of excitation through the cavatricuspid isthmus, it then passed around the atriotomy scar. In 2 cases, a change in the cardiac cycle was observed after radiofrequency ablation, but the excitation circulation was the same around the atriotomy scar, only the tachycardia cycle increased. As a result of the use of our techniques, arrhythmia was eliminated in all 21 patients with an atriotomy AF during one procedure. Five patients with AF of a different localization of the re-entry circuit also had their arrhythmia eliminated, although 8 procedures (for five patients) were performed (on average 1.6). There were no complications. During the follow-up period of 1.8±0.7 years, 2 patients had a recurrence of arrhythmia, and they underwent a repeat procedure to eliminate the arrhythmia. One patient developed typical AF that had not been observed before, which was successfully eliminated.&#x0D; Conclusion. Catheter treatment of atypical NIDAFL is quite a non-trivial task, because, as our experience shows, several types of tachycardia occur in a significant number of patients. In cases of restoration of sinus rhythm as a result of the application, it is necessary to check the inducibility of another arrhythmia. But despite everything, catheter removal of NIDAFL is quite effective, especially for atriotomy AF, although it requires more X-ray exposure and a relatively large number of applications. The use of navigation systems has helped to improve the results of such interventions in more complex cases.

Abnormal Atrial Potentials Recorded During Sinus Rhythm or Pacing Represent Substrates for Reentrant Atrial Tachycardia.

Abnormal atrial potentials (AAPs) recorded during sinus rhythm/atrial pacing may indicate areas of slow conduction capable of supporting reentrant atrial tachycardia (AT). Therefore, we sought to examine the relationship between AAPs and AT circuits. One hundred twenty-three reentrant ATs in 104 patients were analyzed. AAPs, consisting of fragmented potentials and split potentials, were assessed using the Rhythmia LUMIPOINT algorithm. There was 93±13% overlap between areas with AAPs during sinus rhythm/atrial pacing and areas of slow conduction along the reentry circuit during AT. The cumulative area of AAPs was smaller in patients with localized-reentrant ATs compared with anatomic macro-reentrant ATs (20.0 [14.6-30.5] versus 28.9 [21.8-35.6] cm2; P=0.021). Patients with perimitral ATs had larger areas of AAPs on the lateral wall whereas patients with roof-dependent ATs had larger areas of AAPs on the roof and posterior wall (P≤0.018 for all comparisons). The patchy scar that was associated with localized-reentrant AT exhibited a larger area of AAPs at its periphery than the scar that did not participate in localized-reentrant AT (3.1 [2.4-4.5] versus 1.0 [0.7-1.6] cm2; P<0.001). AAPs recorded during sinus rhythm/atrial pacing are associated with areas of slow conduction during reentrant AT. The burden and distribution of AAPs may provide actionable insights into AT circuit features, including in cases in which ATs are difficult to map.

Scar-related atrial macroreentries: Different arrhymogenic basis generates different reentry type.

Catheter ablation is an established therapeutic strategy to treat scar-related macroreentry atrial tachycardia (MAT). However, the scar properties and arrhythmogenicity and the reentry type have not been clearly defined. A total of 122 patients with scar-related MAT were enrolled in this study. The atrial scars were classified into two categories: spontaneous scars (Group A: n=28) and iatrogenic scars (Group B: n=94). According to the relationship between scar location and the reentry circuit, MAT was described as scar pro-flutter MAT, scar-dependent MAT, and scar-mediated MAT. The reentry type of MAT was significantly different between Groups A and B: pro-flutter (40.5%vs. 62.0%, p=0.02), scar-dependent AT (40.5%vs. 13.0%, p<0.001), and scar-mediated AT (19.0%vs. 25.0%, p=0.42). After a median follow-up of 25 months, 21 patients with AT recurrence were observed. Compared with the spontaneous group, there was a lower recurrence rate of MAT in the iatrogenic group (28.6%vs. 10.6%, p=0.03). Scar-related MAT has three reentry types, and the proportion of each type varies with the scar properties and its arrhythmogenic basis. Optimization of the ablation strategy based on the scar properties to improve the long-term outcome of catheter ablation of MAT is necessary.

Sex differences in catheter ablation for ventricular tachycardia in structural heart disease: a single center 10-years experience

Abstract Funding Acknowledgements Type of funding sources: None. Background Women are underrepresented in studies concerning ventricular tachycardia (VT) catheter ablation (CA). Different etiologies and type of structural heart diseases (SHD) are well established in women; nonetheless conflicting results about efficacy and safety of CA in women have been reported. Purpose To evaluate acute and long-term outcome of VT CA in SHD in women compared to men in a high-volume tertiary Center. Methods All consecutive procedures were included from January 2010 to December 2021. Clinical characteristics, VT etiologies and procedure data of female patients were compared to male population. Catheter ablation was performed according to standard protocol in our center. In mappable VTs, the reentry circuit was characterized, and ablation aimed at VT interruption during radiofrequency (RF); otherwise, a substrate modification approach aiming at late potentials abolition or ablation at sites of slow conduction during sinus rhythm was performed. Following ablation, prevention of any VT inducibility and substrate modification was considered ablation endpoint. Acute results, complications, and VT recurrences during follow up were analyzed comparing the two groups. Results Among 1608 overall VT CA procedures, 141 procedures were performed in 117 women. Female were younger, with less comorbidities, less ischemic VT etiology and higher left ventricular ejection fraction (LVEF) as compared to men (Table 1). They were also less likely ICD carriers. No significant differences were found with regards to: epicardial approach (39.7% vs 35.3%, p=0.68); VT inducibility at baseline (57.4% vs 67.6%, p=0.14), VT termination during RF (87.6% vs 77.6%, p=0.51), and prevention of any VT inducibility at the programmed electrical stimulation (PES) after ablation (79.5% vs 78.1%, p=0.7). Major complications occurred in 4.9% of females as compared to 4.3% of male patients. At median follow-up of 25 months, VT recurrences occurred in 24.7% of female population and 27.5% of male group (p=0.42). Cumulative VT-free survival was comparable in both groups (Figure 2). Conclusions Women with SHD have favorable acute and long-term outcome of VT ablation, despite a high prevalence of non-ischemic etiologies. VT recurrence rate and procedure safety is comparable to male patients, suggesting that catheter ablation can be offered as an effective treatment to women with refractory ventricular arrhythmias.

Prevalence of sustained atrial arrythmias and treatment with zero fluoroscopy or near zero fluoroscopy catheter ablation in Slovenian orthotopic heart transplant recipients

Abstract Funding Acknowledgements Type of funding sources: None. Background Due to advances in surgical techniques and immunosuppression survival of heart transplant (HT) recipients has improved significantly, with that the prevalence of sustained atrial arrhythmias (SAA) in these patients is increasing. In HT recipients antiarrhythmic therapy options are limited. Radiofrequency ablation (RFA) represents a viable but underutilized option after other etiologies of SAA such as acute allograft rejection and vasculopathy are excluded. Limiting radiation exposure in HT recipients, who are exposed to 3,5 times (1) greater radiation dose compared to general population and are significantly more susceptible to develop malignancies, is essential. Purpose Our aim was to analyse prevalence and type of SAA in Slovenian orthotopic HT recipients and analyse feasibility and procedural outcomes of zero (ZF) or near zero fluoroscopy (NZF) RFA treatment approaches. Methods We performed a retrospective analysis of HT recipients between 2002 and 2022. We re-evaluated all available ECGs of suspected arrhythmias of included patients for presence and type of SAA. We further analysed HT patients that underwent RFA for SAA at our centre. All procedures were performed primarily with 3D electroanatomical mapping system and intracardiac echocardiography guidance. Either ZF or NZF approaches were used. The primary endpoint of all procedures was SAA termination and acute success was deemed when subsequent attempts to reinduce SAA failed. Long-term success was defined as the absence of any spontaneous SAA during 12-month follow-up. Results Among 364 consecutive HT recipients 19 patients (5,2%) were evaluated for SAA. Of those 7 (37%) presented as typical atrial flutters (AFL), 9 (47%) as atypical AFL, 2 (11%) as focal atrial tachycardia (FAT) and 1 (5%) as slow-fast atrioventricular nodal reentry tachycardia. In 2 (11%) patients with AFL, SAA was a result of acute allograft rejection. In 10 (53%) patients SAA occurred in first 3 months after HT. In the remaining 9 patients SAA occurred late, median 6,6 years after HT (25th-75th IQR: 7,7 years). RFA was performed in 7 (37%) patients. In all patients procedures were acutely successful however in 2 patients additional RFA procedures were needed for long-term success. All in all, 10 RFA procedures were performed (Table 1). All cases had macro or micro reentrant AFL with a median of 2,0 re-entry circuits mapped (25th-75th IQR: 3,3 re-entry circuits) during the procedure – that included typical cavotricuspid isthmus AFL, perimitral AFL, and several right atrium (RA) scar-related or incision related AFL. In 2 cases additional RA FAT were ablated. Five (50%) procedures were performed with ZF. No major procedure related complications were observed. Conclusion In HT recipients ZF or NZF RFA of SAA appears to be feasible and safe, but still underutilised, treatment option. Our case series demonstrates favourable acute and long-term outcomes however larger data is needed to support these results.

Robustness of electrocardiographic imaging in the presence of electrical noise

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): Ministerio de Ciencia, Innovación y Universidades; Generalitat Valenciana Background Electrocardiographic Imaging (ECGI) allows evaluating the cardiac substrate non-invasively. However, the inverse solution is strongly dependent on the noise of the body surface signals. Zero-order Tikhonov regularization together with L-curve optimization, widely used in ECGI studies, allows minimizing the sources of noise to find an optimal solution. Objective Evaluate the effect of electrical and noise on the L-curve optimization in computer simulations of atrial activity and in the physiological interpretation of the inverse solution. Methods Five atrial simulations of regular rhythms (3 atrial flutter and 2 sinus rhythm) were used for computing the ECGI with five signal-to-noise ratios (SNR) (from 3dB to 40dB). ECGI was computed by zero-order Tikhonov regularization and L-curve optimization. The regularization parameter (λ) and the shape of the curve were analysed. Electrical noise was added to signals from an atrial flutter patient to study the effect on real ECGI signals. Local activation time (LAT) maps were obtained to evaluate the quality of the ECGI in front of noise. Correlation coefficient (CC) of LAT maps was computed between simulated electrograms and ECGIs. Results The level of noise was found to be correlated with the optimal regularization parameter (λ), (SNR 3dB, λ&amp;gt;10-6, SNR 40dB, λ&amp;lt;10-9). LAT maps for the optimal λ and higher were able to find relevant information about the simulation and patient independently on the SNR (CC3dB-EGM = 0.66±0.1, CC40dB-EGM = 0.76±0.1). Similar behaviour was observed in real atrial flutter signals (CC3dB-Ref = 0.83, CC10dB-Ref = 0.93). LAT maps from the atrial flutter were able to accurately locate the reentry circuit, as found in the electroanatomical map independently on the SNR. Conclusion LAT maps derived from ECGI are robust against the presence of noise. Although the reconstructed potentials are smoother with increasing levels of noise, LAT maps with and without noise show a good correlation thanks to an increased regularization. Figure 1. A. Local activation times (LAT) map of a reference electrogram (EGM) from a computer simulation of sinus rhythm in the atria. B. Electrocardiographic imaging maps (ECGI) obtained from the simulation A for different levels of electrical noise and regularization parameters. C. Example of LAT map obtained with ECGI and the endocardial map of a typical atrial flutter together with LAT maps with increased electrical noise but comparable results (CC &amp;gt; 0.83).