Role of right atrial endocardial structures as barriers to conduction during human type I atrial flutter. Activation and entrainment mapping guided by intracardiac echocardiography

Clinical and Electrophysiological Predictors of Isthmus Dependency in Atrial Flutter

Background: Atrial flutter (AFL) is a macro-reentrant tachycardia classified as cavotricuspid isthmus (CTI)-dependent or non-CTI-dependent based on its reliance on the CTI for conduction. CTI dependence can present as type I ECG (sawtooth flutter waves in inferior leads and positive P-waves in V1) or type II ECG (absence of these characteristics). This study aimed to identify clinical and electrophysiological parameters to improve CTI dependence prediction in AFL. Methods: Patients at the Ulm University Heart Center between 2010 and 2019 with AFL undergoing electrophysiological studies and ablation were enrolled. Clinical and electrophysiological parameters such as age, gender, prior comorbidities, interventions, and medication use were analyzed. Results: The study included 383 patients, with 70% presenting with type I ECG AFL. CTI dependence was observed in 242 (90.3%) type I ECG patients and 52 (45.2%) type II ECG patients. CTI-dependent AFL patients were younger and had fewer comorbidities. Predictors for CTI dependence in type I ECG included male gender (p = 0.006), absence of beta-blocker use (p = 0.031), no prior atrial fibrillation (p = 0.035), and no prior pulmonary vein isolation (p < 0.001). In type II ECG, predictors for CTI dependence included younger age (p = 0.016), male gender (p = 0.007), absence of arterial hypertension (p = 0.036), and longer atrial cycle length (p < 0.001). Conclusions: Identifying clinical and electrophysiological parameters enhances the ability to predict CTI dependence in AFL, offering valuable insights for tailored diagnostic and therapeutic approaches. Coupling these parameters with ECG findings holds promise for refining prediction accuracy and optimizing patient care.

A practical guide and review of the literature on zero-fluoroscopy electrophysiology catheter navigation by intracardiac echocardiography

Navigation of electrophysiology (EP) catheters using intracardiac echocardiography (ICE) is an emerging technique to avoid fluoroscopy and simplify EP procedures. It enables zero-fluoroscopy catheter ablation of most common arrhythmias such as atrial fibrillation, atrioventricular-nodal-reentry-tachycardia, or cavotricuspid isthmus-dependent atrial flutter. In this practical guide, we share our experience and illustrate the principles as well as common manoeuvres for endovascular and intracardiac EP catheter navigation relying solely on ICE visualisation. We also review the available data and highlight the topics which require further investigation in this field.

Antithrombotic therapy in atrial flutter: To anticoagulate or not, that is the question

Atrial fibrillation (AF) represents an arrhythmia fraught with significant morbidity, mortality, and financial burden for the health care system. Less attention is given to atrial flutter (AFL), which may occur as a stand-alone arrhythmia or coexist with AF in the same patient. Moreover, it is known that AF frequently develops after AFL ablation. Despite different pathophysiologies of AF and AFL, current guidelines provide identical indications for anticoagulation therapy in both arrhythmias, given the lack of trials in patients with AFL. This study attempts at providing an up-to-date literature review on the thromboembolic risk profile in AFL, focusing on differences between AFL and AF. Echocardiographic studies showed that the presence of spontaneous echocardiographic contrast (SEC) and thrombus are much less prevalent in patients with AFL than in those with AF. Patients with AFL had overall better left atrial appendage (LAA) function and lower coagulation marker levels than did patients with AF. Observational studies showed a significantly lower risk of stroke in patients with AFL than in those with AF. One study found a significantly higher ischemic stroke incidence in the AFL cohort only at CHA2DS2-VASc scores from 5 to 9 than in patients without AF or AFL. These findings imply that the thromboembolic risk inherent in AFL seems lower than that in AF. This should be considered in the context of a high chance of permanent AFL termination after successful cavotricuspid isthmus ablation, in contrast to the chronic clinical nature of AF. Although thromboembolic risk exists in AFL, prospective studies are warranted to establish the true prothrombotic properties of AFL, allowing the reassessment of anticoagulant treatment strategy.

Atrial Topology for a Unified Understanding of Typical and Atypical Flutter

BACKGROUND

Macroreentry stands as the predominant mechanism of typical and atypical flutter. Despite advances in mapping, many aspects of macroreentrant atrial tachycardia remain unsolved. In this translational study, we applied principles of topology to understand the activation patterns, entrainment characteristics, and ablation responses in a large clinical macroreentrant atrial tachycardia database.

METHODS

Because the atrium can be topologically seen as a closed sphere with holes, we used a computational fixed spherical mesh model with a finite number of holes to induce and analyze macroreentrant atrial tachycardia. The ensuing insights were used to interpret high-density activation maps, postpacing interval-tachycardia cycle length values (difference between postpacing interval and tachycardia cycle length), and ablation response in 131 cases of typical and atypical flutter (n=106 left atrium, n=25 right atrium).

RESULTS

Modeling of macroreentrant atrial tachycardia revealed that reentry on closed surfaces consistently manifests itself as paired rotation and that an odd number of critical boundaries is mathematically impossible. Together with mathematical confirmation by the index theorem, this led to a unifying construct that could explain the number of loops, difference between postpacing interval and tachycardia cycle length values, and ablation outcomes (termination, no change, or prolongation in tachycardia cycle length) in all 131 cases.

CONCLUSIONS

Combining topology with the index theorem offers a novel and cohesive framework for understanding and managing typical and atypical flutter.

Atrial flutter and sick sinus syndrome

BACKGROUND

Sick sinus syndrome (SSS) is a common condition resulting in reduced quality of life, syncope, and permanent pacemaker (PPM) implantation, but predictors have not been elucidated. Whereas atrial arrhythmias are frequently associated with SSS, we hypothesized that atrial flutter (AFL) would strongly predict SSS, given shared relationships with right atrial and particularly crista terminalis fibrosis.

OBJECTIVE

The study aimed to assess the impact of AFL on the occurrence of SSS and associated syncope and PPM implantation.

METHODS

Health care databases were used to identify adults aged ≥18 years receiving hospital-based care in California in 2005-2019. International Classification of Diseases codes were used to identify diagnoses and procedures. Patients were classified on the basis of the presence of AFL and atrial fibrillation (AF). Cox proportional hazards models adjusting for demographics and comorbidities were employed.

RESULTS

We included 29,357,609 individuals (54% female; mean age, 46 years), 101,243 with AFL alone, 1,674,680 with AF alone, and 284,547 with AF and AFL. After adjustment for age, sex, race and ethnicity, and comorbidities, AF, AFL, and both arrhythmias were each associated with increased risk of SSS and associated syncope and PPM implantation (all P < .001). In the population with AF, an additional AFL diagnosis conferred a higher risk for development of SSS (hazard ratio [HR],1.62; 95% confidence interval, 1.59-1.64), syncope (HR, 1.63; 1.54-1.72), and PPM implantation (HR, 1.74; 1.70-1.79).

CONCLUSION

AFL is associated with an increased risk of incident SSS and its adverse consequences, especially in patients with coexisting AF. AFL may be useful for risk stratification strategies to predict, to prevent, and to treat SSS.

Impact of Posterior Wall Isolation During AF Ablation on the Incidence of Left Atrial Flutter

BACKGROUND

Linear and complex electrogram ablation (LCEA) beyond pulmonary vein isolation (PVI) is associated with an increase in left atrial macro-re-entrant tachycardias (LAMTs). Posterior wall isolation (PWI) is increasingly performed to improve AF ablation outcomes. However, the impact of PWI on the incidence of LAMT is unknown.

OBJECTIVES

The purpose of this study was to establish the incidence of LAMT following PVI alone vs PVI + PWI vs PVI + PWI + LCEA.

METHODS

Consecutive patients undergoing catheter ablation for AF or LAMT post-AF ablation between 2008 and 2022 from 4 electrophysiology centers were reviewed with a minimum follow-up of 12 months.

RESULTS

In total, 5,619 (4,419 index, 1,100 redo) AF ablation procedures were performed in 4,783 patients (mean age 60.9 ± 10.6 years, 70.7% men). Over a mean follow-up of 6.4 ± 3.8 years, 246 procedures for LAMT were performed in 214 patients at a mean of 2.6 ± 0.6 years post-AF ablation. Perimitral (52.8% of patients), roof-dependent (27.1%), PV gap-related (17.3%), and anterior circuits (8.9%) were most common, with 16.4% demonstrating multiple circuits. The incidence of LAMT was significantly higher following PVI + PWI (6.2%) vs PVI alone (3.0%; P < 0.0001) and following PVI + PWI + LCEA vs PVI + PWI (12.5%; P = 0.019). Conduction gaps in previous ablation lines were responsible for LAMT in 28.4% post-PVI alone, 35.3% post-PVI + PWI (P = 0.386), and 81.8% post-PVI + PWI + LCEA (P < 0.005).

CONCLUSIONS

The incidence of LAMT following PVI + PWI is higher than with PVI alone but significantly lower than with more extensive atrial substrate modification. Given a low frequency of LAMT following PWI, empiric mitral isthmus ablation is not justified and may be proarrhythmic.

Identification of 2 Distinct Boundaries Distinguishes Critical From Noncritical Isthmuses in Ablating Atypical Atrial Flutter

BACKGROUND

Atypical atrial flutters often involve complex circuits. Classic methods of identifying ablation targets, including detailed electroanatomical mapping and entrainment within a well-defined isthmus, may not always be sufficient to allow the critical isthmus to be delineated and ablated, with flutter termination and prevention of reinduction.

OBJECTIVES

This study sought a systematic method to classify conduction barriers and isthmuses as critical or noncritical that would improve understanding and ablation success. We also sought a construct unifying single- and dual-loop re-entry. Re-entrant circuits are bounded on 2 sides, although these are not consistently identified. We hypothesized 2 distinct critical boundaries, and a critical isthmus could be consistently defined without requiring entrainment, and ablation connecting these 2 boundaries would terminate tachycardia.

METHODS

Activation maps were created electroanatomically. Conduction barriers were classified as noncritical barriers or critical boundaries. Critical boundaries showed sequential activation around the barrier, spanning ≥90% of the cycle length. Noncritical barriers showed nonsequential, parallel, or colliding activation or <90% of the cycle length. Only tissue separating the 2 critical boundaries defined a critical isthmus (CI); all others were considered noncritical. The effect of ablation across a CI was assessed.

RESULTS

Complete maps were obtained in 128 cases in 121 patients (28 atypical right atrial, 100 left atrial). In all cases, 2 distinct critical boundaries were identified. Ablation across a CI connecting these critical boundaries terminated tachycardia in 123 of 128 cases (96.1%). Failures were due to inability to achieve block across the isthmus.

CONCLUSIONS

Activation mapping of atypical atrial flutter allows consistent identification of 2 critical boundaries. Successful ablation connecting the 2 critical boundaries reliably results in termination of atypical atrial flutter.

Transition mechanisms from atrial flutter to atrial fibrillation during anti-tachycardia pacing therapy

BACKGROUND

Atrial anti-tachycardia pacing (aATP) has been shown to be effective for the termination of atrial tachyarrhythmias, but its success rate is still not high enough.

OBJECTIVE

The main objective of this study was to investigate the mechanisms of atrial flutter (AFL) termination by aATP and the transition from AFL to atrial fibrillation (AF) during aATP.

METHODS

We developed a multi-scale model of the human atrium based on magnetic resonance images and examined the atrial electrophysiology of AFL during aATP with a ramp protocol.

RESULTS

In successful cases of aATP, paced excitation entered the excitable gap and collided with the leading edge of the reentrant wave front. Furthermore, the excitation propagating in the opposite direction collided with the trailing edge of the reentrant wave to terminate AFL. The second collision was made possible by the distribution of the wave propagation velocity in the atria. The detailed analysis revealed that the slowing of propagation velocity occurred at the exit of the sub-Eustachian isthmus, probably due to source-sink mismatch. During the transition from AFL to AF, the excitation collided with the refractory zone of the preceding wave and broke into multiple wave fronts to induce AF. A similar observation was made for the transition from AF to sinus rhythm. In both cases, the complex anatomy of the atria played an essential role.

CONCLUSION

The complex anatomy of atria plays an essential role in the maintenance of stable AFL and its termination by aATP, which were revealed by the realistic three-dimensional simulation model.

Impact of cavotricuspid isthmus ablation for typical atrial flutter and heart failure in the elderly-results of a retrospective multi-center study

Introduction

While in the CASTLE-AF trial, in patients with atrial fibrillation and heart failure with reduced ejection fraction, interventional therapy using pulmonary vein isolation was associated with outcome improvement, data on cavotricuspid isthmus ablation (CTIA) in atrial flutter (AFL) in the elderly is rare.

Methods

We included 96 patients between 60 and 85 years with typical AFL and heart failure with reduced or mildly reduced ejection fraction (HFrEF/HFmrEF) treated in two medical centers. 48 patients underwent an electrophysiological study with CTIA, whereas 48 patients received rate or rhythm control and guideline-compliant heart failure therapy. Patients were followed up for 2 years, with emphasis on left ventricular ejection fraction (LVEF) over time. Primary endpoints were cardiovascular mortality and hospitalization for cardiac causes.

Results

Patients with CTIA showed a significant increase in LVEF after 1 (p < 0.001) and 2 years (p < 0.001) in contrast to baseline LVEF. Improvement of LVEF in the CTIA group was associated with significantly lower 2-year mortality (p = 0.003). In the multivariate regression analysis, CTIA remained the relevant factor associated with LVEF improvement (HR: 2.845 CI:95% 1.044-7.755; p = 0.041). Elderly patients (≥ 70 years) further benefited from CTIA, since they showed a significantly reduced rehospitalization (p = 0.042) and mortality rate after 2 years (p = 0.013).

Conclusions

CTIA in patients with typical AFL and HFrEF/HFmrEF was associated with significant improvement of LVEF and reduced mortality rates after 2 years. Patient age should not be a primary exclusion criterion for CTIA, since patients ≥70 years also seem to benefit from intervention in terms of mortality and hospitalization.

Interpretation of Typical and Atypical Atrial Flutters by Precision Electrocardiology Based on Intracardiac Recording

Atrial flutter is a term encompassing multiple clinical entities. Clinical manifestations of these arrhythmias range from typical isthmus-dependent flutter to post-ablation microreentries. Twelve-lead electrocardiogram (ECG) is a diagnostic tool in typical flutter, but it is often unable to clearly localize atrial flutters maintained by more complex reentrant circuits. Electrophysiology study and mapping are able to characterize in fine details all the components of the circuit and determine their electrophysiological properties. Combining these 2 techniques can greatly help in understanding the vectors determining the ECG morphology of the flutter waveforms, increasing the diagnostic usefulness of this tool.

Pathophysiology of Typical Atrial Flutter

Nowadays, the pathophysiology mechanism of initiation and maintenance of reentrant arrhythmias, including atrial flutter, is well characterized. However, the anatomic and functional elements of the macro reentrant arrhythmias are not always well defined. In this article, we illustrate the anatomic structures that delineate the typical atrial flutter circuit, both clockwise and counterclockwise, paying attention to the inferior vena cava-tricuspid isthmus (CTI) and crista terminalis crucial role. Finally, we describe the left atrial role during typical atrial flutter, electrophysiologically a by-stander but essential in the phenotypic electrocardiogram (ECG).

Catheter ablation of atrial arrhythmias in patients post-Fontan

Atrial arrhythmias are highly prevalent in the aging Fontan population and contribute importantly to morbidity and mortality. Although the most common arrhythmia is scar-based intra-atrial re-entrant tachycardia, various other arrhythmias may occur including focal atrial tachycardia, atrioventricular node-dependent tachycardias, and atrial fibrillation. The type and prevalence of atrial arrhythmia is determined, in part, by the underlying congenital defect and variant of Fontan surgery. While the cumulative incidence of atrial tachyarrhythmias has decreased substantially from the atriopulmonary anastomosis to the more recent total cavopulmonary connection Fontan, the burden of atrial arrhythmias remains substantial. Management is often multi-faceted and can include anticoagulation, anti-arrhythmic drug therapy, pacing, and cardioversion. Catheter ablation plays a key role in arrhythmia control. Risks and benefits must be carefully weighed. Among the important considerations are the clinical burden of arrhythmia, ventricular function, hemodynamic stability in tachycardia, suspected arrhythmia mechanisms, risks associated with anaesthesia, venous access, approaches to reaching the pulmonary venous atrium, and accompanying co-morbidities. Careful review of surgical notes, electrocardiographic tracings, and advanced imaging is paramount, with particular attention to anatomic abnormalities such as venous obstructions and displaced conduction systems. Despite numerous challenges, ablation of atrial arrhythmias is effective in improving clinical status. Nevertheless, onset of new arrhythmias is common during long-term follow-up. Advanced technologies such as high-density mapping catheters and remote magnetic guided ablation carry the potential to further improve outcomes. Fontan patients with atrial arrhythmias should be referred to centers with dedicated expertise in congenital heart disease including catheter ablation, anaesthesia support, and advanced imaging.

Surgical radiofrequency ablation of atrial flutter: which operation should we choose?

The treatment of atrial flutter (AFL) in patients without structural heart disease (SHD) by transcatheter radiofrequency ablation of the cavotricuspid isthmus (CTI) and bilateral pulmonary veins has achieved good results. We report three cases of typical AFL treated by surgical radiofrequency ablation. One patient, without SHD, successfully underwent CTI ablation and cardioversion. The other two patients, with SHD, underwent CTI ablation, partial right atrial ablation and pulmonary vein isolation, but a normal sinus rhythm was not achieved. Therefore, standard maze IV surgery may be the best choice in patients with AFL and SHD.

Pacing site- and rate-dependent shortening of retrograde conduction time over the slow pathway after atrial entrainment of fast-slow atrioventricular nodal reentrant tachycardia

Introduction

We tested our hypothesis that atrial entrainment pacing (EP) of a) the common‐type (com‐) fast‐slow (F/S‐) atypical atrioventricular nodal reentrant tachycardia (AVNRT) using a typical slow pathway (SP), or b) the superior‐type (sup‐) F/S‐AVNRT using a superior SP, both modify the retrograde conduction time across the SP immediately after termination of EP (retro‐SP‐time).

Methods

We measured the difference in the His‐atrial interval (HA difference) immediately after cessation of EP, performed at 2 ± 2 rates from the high right atrium (HA[1]‐HRA) versus from the proximal coronary sinus (HA[1]‐CS) in 17 patients with com‐F/S‐AVNRT and 11 patients with sup‐F/S‐AVNRT. We also measured the atrial‐His and HA intervals of the first and second cycles immediately after cessation of EP and during stable tachycardia.

Results

Unequal responses, defined as a ≥ 20‐ms HA difference at ≥1 EP rates, were observed in 16 patients (57%), including 7 with com‐ and 9 with sup‐F/S‐AVNRT. Irrespective of the EP rate, all unequal responses of com‐F/S‐AVNRT were due to a shorter HA[1]‐CS than HA[1]‐HRA, with a mean 34 ± 11 ms HA difference, whereas all unequal responses of sup‐F/S‐AVNRT were due to a longer HA[1]‐CS than HA[1]‐HRA, with a mean 49 ± 25 ms HA difference. The unequal responses resolved within two cycles after the cessation of EP.

Conclusions

We have identified a little‐known pacing site‐ and pacing rate‐dependent shortening of the retro‐SP‐time.

Identification of Low-Voltage Areas: A Unipolar, Bipolar, and Omnipolar Perspective

Low-voltage areas (LVAs) are commonly considered surrogate markers for an arrhythmogenic substrate underlying tachyarrhythmias. It remains challenging to define a proper threshold to classify LVA, and it is unknown whether unipolar, bipolar, and the recently introduced omnipolar voltage mapping techniques are complementary or contradictory in classifying LVAs. Therefore, this study examined similarities and dissimilarities in unipolar, bipolar, and omnipolar voltage mapping and explored the relation between various types of voltages and conduction velocity (CV).

Novel insights in pathophysiology of postoperative atrial fibrillation

Objectives

Atrial extrasystoles are usually benign; however, they can also trigger atrial fibrillation. It is most likely that if atrial extrasystoles provoke a larger amount of conduction disorders and a greater degree of endo-epicardial asynchrony, the risk of postoperative atrial fibrillation increases. To test this hypothesis, we investigated the effect of programmed atrial extrasystoles on endo-epicardial conduction and postoperative atrial fibrillation.

Methods

Twelve patients (58% male, age 68 ± 7 years) underwent simultaneous endo-epicardial mapping (256 electrodes) of the right atrium during sinus rhythm and programmed atrial extrasystoles provoked from the right atrial free wall. Areas of conduction block were defined as conduction delays of ≥12 milliseconds and endo-epicardial asynchrony as activation time differences of exact opposite electrodes of ≥15 milliseconds.

Results

Endo-epicardial mapping data of all programmed atrial extrasystoles were analyzed and compared with sinus rhythm (median preceding cycle length = 531 milliseconds [345-787] and median sinus rhythm cycle length = 843 milliseconds [701-992]). All programmed atrial extrasystoles were aberrant (severe, moderate, and mildly aberrant, respectively, n = 6, 3, and 3) and had a mean prematurity index of 50.1 ± 11.9%. The amount of endo-epicardial asynchrony (1% [1-2] vs 6.7 [2.7-16.9], P = .006) and conduction block (1.4% [0.6-2.6] vs 8.5% [4.2-10.4], P = .005) both increased during programmed atrial extrasystoles. Interestingly, conduction block during programmed atrial extrasystoles was more severe in patients (n = 4, 33.3%) who developed postoperative atrial fibrillation (5.1% [2.9-8.8] vs 11.3% [10.1-12.1], P = .004).

Conclusions

Atrial conduction disorders and endo-epicardial asynchrony, which play an important role in arrhythmogenesis, are enhanced during programmed atrial extrasystoles compared with sinus rhythm. The findings of this pilot study provide a possible explanation for enhanced vulnerability for postoperative atrial extrasystoles to induce postoperative atrial fibrillation in patients after cardiac surgery.

Ultra-high resolution mapping of reverse typical atrial flutter: electrophysiological properties of a right atrial posterior wall and interatrial septum activation pattern

PURPOSE

We aimed to elucidate the right atrial posterior wall (RAPW) and interatrial septum (IAS) conduction pattern during reverse typical atrial flutter (clockwise AFL: CW-AFL).

METHODS

This study included 30 patients who underwent catheter ablation of CW-AFL (n = 11) and counter-clockwise AFL (CCW-AFL; n = 19) using an ultra-high resolution mapping system. RAPW transverse conduction block was evaluated by the conduction pattern on propagation maps and double potentials separated by an isoelectric line. The degree of blockade was evaluated by the %blockade, which was calculated by the length of the blocked area divided by the RAPW length. IAS activation patterns were also investigated dependent on the propagation map.

RESULTS

The average %blockade of the RAPW was significantly smaller in patients with CW-AFL than those with CCW-AFL (25 [3-74]% vs. 67 [57-75]%, p < 0.05). CW-AFL patients exhibited 3 different RAPW conduction patterns: (1) a complete blockade pattern (3 patients), (2) moderate (> 25% blockade) blockade pattern (2 patients), and (3) little (< 25% blockade) blockade pattern (6 patients). In contrast, the little blockade pattern was not observed in CCW-AFL patients. Of 11 CW-AFL patients, 4, including all patients with an RAPW complete blockade pattern, had an IAS activation from the wavefront from the anterior tricuspid annulus (TA), and 6 had an IAS activation from the wavefronts from both the anterior TA and RAPW. One patient had IAS activation dominantly from the wavefront from the RAPW.

CONCLUSIONS

RAPW transverse conduction blockade during CW-AFL was less frequent than during CCW-AFL, which possibly caused various IAS activation patterns.

Ultrahigh resolution electroanatomical mapping of the transverse conduction of the right atrial posterior wall in cases with and without typical atrial flutter

INTRODUCTION

The right atrial posterior wall (RAPW) is known to form a conduction barrier during typical atrial flutter (AFL). We evaluated the transverse conduction properties of RAPW in patients with and without typical AFL using an ultrahigh resolution electroanatomical mapping system.

METHODS AND RESULTS

This study included 41 patients who underwent catheter ablation of AF, typical or atypical AFL, in whom we performed RAPW mapping with an ultrahigh resolution mapping system during typical AFL and coronary sinus ostial pacing with three different pacing cycle lengths (PCLs) (1) PCL1: PCL within 40 ms of the AFL cycle length in patients with typical AFL or 250-300 ms for those without, (2) PCL2: 400 ms, (3) PCL3: PCL just faster than the sinus rate. Local RAPW conduction block was evaluated by propagation mapping and local double potentials separated by an isoelectric line. The functional block was defined as areas blocked during shorter PCLs but conductive during longer PCLs. The degree of blockade was calculated by dividing the blocked length by RAPW length (%blockade). Only two patients demonstrated a fixed complete RAPW block (100%, %blockade). Thirty-one patients demonstrated a partial block of RAPW, and the %blockade during PCL1-3 was 49.4 ± 19.8%, 39.5 ± 19.2%, and 35.0 ± 22.9% in this group, respectively. Functional block areas were frequently observed above the fixed block area adjacent to the RA-inferior vena cava junction. Transverse conduction block was more frequently observed in patients with typical AFL at any longitudinal level of RAPW.

CONCLUSION

RAPW transverse conduction block is lower-side dominant and greater in patients with typical AFL than those without.

The intra-extracardiac Fontan: preliminary results

OBJECTIVE

Since the intra-extracardiac Fontan (IECF) was popularized by Jonas in 2008, its claimed advantages over the traditional extracardiac or lateral tunnel Fontan are simplicity, suitability for nearly all subsets, flow characteristics, low risk of sinus node artery injury, and possibly, a lower incidence of arrhythmias. In this paper, we present our early experience with this modification of the Fontan operation.

METHODS

Between 2009 and 2018, 10 patients underwent IECF on cardiopulmonary bypass (CPB) and cardioplegic arrest at our institute. Analysis of preoperative, intraoperative, and early follow-up results was performed. A polytetrafluoroethylene (PTFE) graft was sutured proximally to the orifice of the inferior vena cava (IVC) and distally to the ipsilateral bidirectional superior cavopulmonary (BSCP) junction.

RESULTS

Nine patients had undergone a previous BSCP connection, and one patient had a primary IECF. Diagnoses were double outlet right ventricle (n = 2), unbalanced atrioventricular septal defect with associated atrioventricular valve regurgitation (n = 3), single ventricle with anomalies of cardiac situs (n = 2), and tricuspid atresia with borderline pulmonary arteries (n = 1) or tricuspid atresia with borderline pulmonary artery pressures (n = 2). Median aortic cross-clamp and CPB times were 42 min and 82 min respectively. There were no early or late deaths. Median intensive care stay was 3 days (1 to 23 days). There were no arrhythmias. Mean duration of pleural effusions was 9.5 (median 5.5) days. There were no arrhythmias at a median follow-up of 5 years (range 1 month to 9.3 years).

CONCLUSION

The IECF is simple, particularly at reoperations, in borderline patients and those needing concomitant intracardiac procedures. Early results are promising. These patients need constant surveillance.

Distribution of Conduction Disorders in Patients With Congenital Heart Disease and Right Atrial Volume Overload

OBJECTIVES

This study sought to quantify characteristics of atrial conduction disorders in patients with right atrial (RA) volume overload.

BACKGROUND

Patients with an interatrial shunt are prone to developing atrial fibrillation (AF), which may be related to conduction disorders occurring due to atrial stretch.

METHODS

Thirty-one patients undergoing surgery for an interatrial shunt (49 ± 14 years of age) underwent epicardial sinus rhythm mapping of the RA, Bachmann's bundle (BB), and left atrium (LA). Conduction delay (CD) was defined as interelectrode conduction time (CT) of 7 to 11 ms and conduction block (CB) as CT ≥12 ms. Prevalence of CD or CB (percentage of mapped region), length of lines, and severity of CB (75th percentile of CTs ≥12 ms) were analyzed.

RESULTS

All patients had some degree of CD and CB. Prevalence of CD and CB was higher in the RA and BB than in the LA (p < 0.0083 after Bonferroni correction). The longest CB line within each patient was found in the RA in most patients (52%). Interindividual variation in prevalence and lengths of lines was considerable. CB was more severe in the RA than in the LA (p < 0.0083). Within the RA, conduction disorders were more prevalent and more severe in the intercaval region than in the RA free wall (p < 0.05).

CONCLUSIONS

In patients with an interatrial shunt, conduction disorders during sinus rhythm are most pronounced in the RA-particularly the intercaval region-and BB. Knowledge of the conduction during sinus rhythm is essential to determine the relevance of conduction disorders for initiation and perpetuation of AF.

Revisiting an Underrecognized Strategy for Rhythm Management: Hybrid Therapy for Patients who Convert from Atrial Fibrillation to Flutter on Antiarrhythmic Drugs

Atrial fibrillation (AF) is often treated with antiarrhythmic drugs (AADs) or catheter ablation. In a unique subset of patients, AF can convert to atrial flutter (AFL) after the initiation of an AAD. It has previously been shown that, in this subset of patients, cavotricuspid isthmus (CTI) ablation followed by the continuation of the AAD regimen has an unusually high rate of successfully maintaining sinus rhythm. This is an underrecognized approach toward rhythm management in such patients. However, the reason(s) for such a high degree of efficacy with this hybrid therapeutic approach are unclear. We suggest that conversion from AF to AFL selects for a group of patients in whom AF is particularly responsive to the effects of the AAD. Since CTI ablation is essentially curative of AFL, the combination of both techniques results in a high efficacy of sinus rhythm maintenance. Further investigation is required to confirm these hypotheses.

An unusual propagation pattern along the tricuspid annulus after cavo-tricuspid isthmus ablation: Insights into posterior transverse conduction revealed by an ultra-high-resolution 3-dimensional mapping system

Cavo-tricuspid isthmus (CTI) ablation is a cornerstone of atrial flutter ablation. The goal of CTI-dependent flutter ablation is achievement of bidirectional CTI block. Usually bidirectional CTI block is confirmed by atrial activation during septal and lateral atrial pacing or the use of differential pacing maneuvers. According to the pathological findings, the transmural muscle fibers connect the endo- and epicardium. An epicardial-endocardial breakthrough (EEB) sometimes interferes with the confirmation of bidirectional block. Recently, a new ultra-high-resolution 3-dimentional mapping systems (Rhythmia^®, Boston Scientific, Marlborough [Cambridge] MA, USA) that allows rapid ultra-high-resolution electroanatomical mapping was introduced. A 64-year-old man with a sustained atrial flutter (AFL) was referred to us. Catheter ablation was performed using an ultra-high-resolution 3-dimensional mapping system. Here, we report the case of a patient with an EEB visualized by ultra-high-resolution 3-dimensional mapping. <Learning objective: The crista terminalis are recognized as the anatomic structure responsible for line of conduction block at the posterior right atrial wall. This block line is mainly functional, and transverse conduction across the posterior wall can be observed. This is the first report to visualize the EEB and examine its influence on the conventional electrophysiological findings.>.

Predictors of acute inefficacy and the radiofrequency energy time required for cavotricuspid isthmus-dependent atrial flutter ablation

PURPOSE

Although cavotricuspid isthmus-dependent atrial flutter (CTI-AFL) ablation is a highly efficacious treatment, a bidirectional CTI block cannot be achieved in some patients. In this study, we sought to determine the predictors of acute inefficacy of CTI-AFL ablation and the predictors of the radiofrequency (RF) energy time required to achieve a complete bidirectional CTI block.

METHODS

All consecutive patients who underwent stand-alone CTI-AFL ablation in our institution, except patients with congenital heart disease, were included in this retrospective study. Clinical, echocardiographic, and ablation data were collected from the Arrhythmia Unit and Imaging Unit databases and medical charts.

RESULTS

Three hundred and fifty-five patients, with a mean age 63 ± 12 years, were included. The ablation was acutely inefficacious in 30 patients (9%). Tricuspid regurgitation was the only independent predictor of acute inefficacy of CTI-AFL ablation (OR 3.161, 95% CI 1.084-9.220, p = 0.035) and was associated with a longer RF time required to achieve CTI bidirectional block (p = 0.031). Age was inversely correlated with the RF time required to achieve a bidirectional CTI block (r = -0.133, p = 0.025). A previous CTI RF ablation, chronic obstructive pulmonary disease (COPD), the use of an irrigated catheter, and advanced age were the independent predictors for requiring less RF energy time to achieve a bidirectional CTI block.

CONCLUSIONS

Tricuspid regurgitation is associated with less acute efficacy in CTI-AFL ablation. Prior CTI ablation, COPD, use of an irrigated catheter, and advanced age are independent predictors for needing less RF energy time to achieve a complete bidirectional CTI block.

Atrial Flutter, Typical and Atypical: A Review

Clinical electrophysiology has made the traditional classification of rapid atrial rhythms into flutter and tachycardia of little clinical use. Electrophysiological studies have defined multiple mechanisms of tachycardia, both re-entrant and focal, with varying ECG morphologies and rates, authenticated by the results of catheter ablation of the focal triggers or critical isthmuses of re-entry circuits. In patients without a history of heart disease, cardiac surgery or catheter ablation, typical flutter ECG remains predictive of a right atrial re-entry circuit dependent on the inferior vena cava-tricuspid isthmus that can be very effectively treated by ablation, although late incidence of atrial fibrillation remains a problem. Secondary prevention, based on the treatment of associated atrial fibrillation risk factors, is emerging as a therapeutic option. In patients subjected to cardiac surgery or catheter ablation for the treatment of atrial fibrillation or showing atypical ECG patterns, macro-re-entrant and focal tachycardia mechanisms can be very complex and electrophysiological studies are necessary to guide ablation treatment in poorly tolerated cases.

Ablatogenomics: can genotype guide catheter ablation for cardiac arrhythmias?

Previously confined to the management of rare inherited arrhythmia syndromes, a role for genetics within cardiac electrophysiology has begun to emerge for more common arrhythmias, including atrial fibrillation (AF). Catheter ablation for AF is an invasive procedure effective for restoring normal rhythm, however, fails in up to 40% of those undergoing their first procedure and carries a risk for serious adverse events. Recent studies have suggested that a common genetic variant within chromosome 4q25 may be a powerful predictor of procedural success, highlighting the potential of an 'ablatogenomic' strategy. Although still in its infancy, an ablatogenomic approach for AF may facilitate delivery of ablation to those most likely to benefit, while sparing those prone to fail from its risks.

P wave morphology in guiding the ablation strategy of focal atrial tachycardias and atrial flutter

Focal atrial tachycardias arise preferentially from specific locations within the atria. Careful analysis of the P wave can provide useful information about the chamber and likely site of origin within that chamber. Macro-reentrant atrial flutter also tends to occur over a limited number of potential circuits. In this case, the ECG usually gives a guide to the chamber of origin, but unless it shows a specific morphology it is less useful in delineating the circuit involved. Nonetheless, prior knowledge of the likely chamber of origin helps to plan the ablation strategy.

Novel strategies in the ablation of typical atrial flutter: role of intracardiac echocardiography

Radiofrequency ablation (RFA) of the cavo-tricuspid isthmus (CTI) is one of the most frequently performed procedures in electrophysiology. Despite a high success rate, ablation of the CTI can be unusually difficult in some cases. Multiple tools like angiography, 3D mapping, remote navigation and intracardiac echocardiography (ICE) have been introduced to facilitate typical flutter ablation. This review article summarizes the clinical value of different strategies and tools used for CTI ablation focusing on the importance of approaches utilizing ICE.

Crista Terminalis as the Anterior Pathway of Typical Atrial Flutter: Insights from Entrainment Map with 3D Intracardiac Ultrasound

BACKGROUND

The precise location of truly active reentry circuits of typical atrial flutter (AFL) has not been well identified. The purpose of this study was to verify our hypothesis that the posterior block line is located along the posteromedial right atrium (PMRA) and the crista terminalis (CT) is the anterior pathway of AFL, with real-time intracardiac echo (ICE).

METHODS

The entire right atrium (RA) three-dimensional activation and entrainment mapping were evaluated during AFL in 18 patients using CARTO sound.

RESULTS

The CT was clearly visualized by ICE and the local electrograms along the CT were single potentials in all the patients. The CT was recognized as the truly active anterior pathway based on entrainment mapping in all patients. Double potentials were recorded along the PMRA. Entire RA entrainment mapping could be performed in 16 patients. The reentry circuits were separated into three passages. The first was around the tricuspid annulus (TA), the second the anterior superior vena cava (SVC; AFL waves passed between the anterior SVC and RA appendage), and the last the posterior SVC (between the posterior SVC and upper limit of the PMRA). All three of these passages were active in four, around the TA and anterior SVC in eight, around the TA and posterior SVC in three, and around only the anterior SVC in one patient.

CONCLUSIONS

The CT functions as the anterior pathway of typical AFL, and the posterior block line was located along the PMRA. Dual or triple circuits were recognized in the majority of AFL patients.

Data analysis in cardiac arrhythmias

Cardiac arrhythmias are an increasingly present in developed countries and represent a major health and economic burden. The occurrence of cardiac arrhythmias is closely linked to the electrical function of the heart. Consequently, the analysis of the electrical signal generated by the heart tissue, either recorded invasively or noninvasively, provides valuable information for the study of cardiac arrhythmias. In this chapter, novel cardiac signal analysis techniques that allow the study and diagnosis of cardiac arrhythmias are described, with emphasis on cardiac mapping which allows for spatiotemporal analysis of cardiac signals.Cardiac mapping can serve as a diagnostic tool by recording cardiac signals either in close contact to the heart tissue or noninvasively from the body surface, and allows the identification of cardiac sites responsible of the development or maintenance of arrhythmias. Cardiac mapping can also be used for research in cardiac arrhythmias in order to understand their mechanisms. For this purpose, both synthetic signals generated by computer simulations and animal experimental models allow for more controlled physiological conditions and complete access to the organ.

Assessment of long-term quality of life after cavotricuspid isthmus ablation for typical atrial flutter

BACKGROUND

Cavotricuspid isthmus (CTI) ablation is the treatment of choice in preventing recurrences of typical atrial flutter (AFl). However, little is known about long-term quality of life (QoL) after CTI ablation.

METHODS AND RESULTS

From 01/2003 to 05/2005, 94 patients who consecutively underwent typical AFl ablation were included in the study. An SF-36 health questionnaire was self-administered before ablation and at follow-up. Transformed scores were calculated, adjusted for age and sex and then normalized and standardized for the Spanish population. Additionally, the minimal important differences (MID) were calculated to assess the smallest change in QoL that patients perceived as positive. A linear regression model was constructed to assess long-term QoL predictors. All SF-36 scales were lower than Spanish population scores. After a mean (SD) follow-up of 6.25 (0.5) years, all scales, except Bodily Pain, were higher than baseline. There was a significant difference for Physical Role (46.4 vs. 38.6, p < 0.001), Vitality (44.4 vs. 41.9, p = 0.038) and Mental Health (46.1 vs. 42.0, p = 0.001). However, only Physical Role achieved the criteria for MID. Recurrence of AFl, basal QoL, history of diabetes mellitus, atrial fibrillation and oral anticoagulation were predictors of long-term QoL.

CONCLUSION

CTI ablation provides a significant improvement in long-term QoL for the dimensions of Physical Role, Vitality and Mental Health, although the smallest positive change that patients perceive as positive was only observed for Physical Role. Previous diabetes mellitus, atrial fibrillation, oral anticoagulation, basal QoL and AFl recurrence were determinants of a worse long-term QoL.

Impact of a 4q25 genetic variant in atrial flutter and on the risk of atrial fibrillation after cavotricuspid isthmus ablation

BACKGROUND

The prediction of atrial fibrillation (AF) following catheter ablation of atrial flutter (Afl) would be helpful to facilitate targeted arrhythmia monitoring and anti-coagulation strategies. A single nucleotide polymorphism, rs2200733, is strongly associated with AF. We sought to characterize the association between rs2200733 and prevalent Afl and to determine if the variant could predict AF after cavotricuspid isthmus ablation.

METHODS AND RESULTS

We performed a genetic association study of 295 patients with Afl and/or AF and 469 controls using multivariable logistic regression. The variant was then assessed as a predictor of incident AF after cavotricuspid isthmus ablation in 87 consecutive typical Afl patients with Cox proportional hazards models. The rs2200733 rare allele was associated with an adjusted 2.06-fold increased odds of isolated Afl (95% CI: 1.13-3.76, P = 0.019) and an adjusted 2.79-fold increased odds of a combined phenotype of AF and Afl (95% CI: 1.81-4.28, P < 0.001). Following catheter ablation for Afl, carrier status of rs2200733 failed to predict an increased risk of AF either among all subjects (adjusted HR: 0.94; 95% CI: 0.58-1.53, P = 0.806) or among those with isolated Afl (adjusted HR: 1.29; 95% CI: 0.51-3.26, P = 0.585).

CONCLUSIONS

Our study demonstrates that Afl, whether occurring in isolation or along with AF, is associated with the rs2200733 AF risk allele. Genetic carrier status of rs2200733 failed to predict an increased risk of incident or recurrent AF following catheter ablation for Afl. These findings suggest that the causal mechanism associated with rs2200733 is germane to both AF and Afl.

P-wave abnormality predicts recurrence of atrial fibrillation after electrical cardioversion: a prospective study

BACKGROUND

Maintenance of atrial fibrillation (AF) is related to atrial electrical inhomogeneity and resultant chaotic reentry. Our aim was to test the hypothesis that abnormalities of P morphology on the surface electrocardiogram (ECG) predict recurrent AF following electrical cardioversion (ECV).

METHODS

A 12-lead ECG was recorded after ECV for persistent AF in 77 patients (51 men, 65 ± 10 years) and repeated 1 month later. P-wave duration was obtained in each lead using blinded on-screen measurement. Maximum P-wave duration (P-max) was defined as the longest measurable P-wave duration in any lead. P-wave dispersion (PWd) was calculated as the maximum-minimum P-wave duration.

RESULTS

One month after ECV, 29 (38%) patients maintained sinus rhythm. Compared with the sinus rhythm group, those with recurrent AF had significantly greater PWd (66 ± 19 vs 57 ± 16 ms, P = 0.024) and included more patients with P-max ≥142 ms (65% vs 38%, P = 0.023). Using a cutoff of ≥62 ms for PWd and ≥142 ms for P-max, both indices had similar predictive value (sensitivity 66.7 and 64.6%, specificity 58.6 and 62.1%, respectively). In multiple regression analysis, including established clinical predictors, P-max ≥142 ms was the only independent predictor of AF recurrence (P = 0.025).

CONCLUSION

A prolonged P-wave duration measured by 12-lead ECG predicts recurrent AF within 1 month after ECV.

Triggers and anatomical substrates in the genesis and perpetuation of atrial fibrillation

The definition of atrial fibrillation (AF) as a functional electrical disorder does not reflect the significant underlying structural abnormalities. Atrial and Pulmonary Vein (PV) muscle sleeve microstructural remodeling is present, and establishes a vulnerable substrate for AF maintenance. In spite of an incomplete understanding of the anatomo-functional basis for AF, current evidence demonstrates that this arrhythmia usually requires a trigger for initiation and a vulnerable electrophysiological and/or anatomical substrate for maintenance. It is still unclear whether the trigger mechanisms include focal enhanced automaticity, triggered activity and/or micro re-entry from myocardial tissue. Initiation of AF can be favored by both parasympathetic and sympathetic stimulation, which also seem to play a role in maintaining AF. Finally, evolving clinical evidence demonstrates that inflammation is associated with new-onset and recurrent AF through a mechanism that possibly involves cellular degeneration, apoptosis, and subsequent atrial fibrosis.