Characterization of atrial remodeling studied remote from episodes of typical atrial flutter

Catheter ablation of typical atrial flutter improves cardiac chamber size and function

INTRODUCTION

Cavo-tricuspid isthmus (CTI) dependent atrial flutter (AFL) is one of the most common atrial arrhythmias involving the right atrium (RA) for which radiofrequency catheter ablation has been widely used as a therapy of choice. However, there is limited data on the effect of this intervention on cardiac size and function.

METHODS

A retrospective study was conducted on 468 patients who underwent ablation for CTI dependent typical AFL at a single institution between 2010 and 2019. After excluding patients with congenital or rheumatic heart disease, heart transplant recipients, or those without baseline echocardiogram, a total of 130 patients were included in the analysis. Echocardiographic data were analyzed at baseline before ablation, and at early follow-up within 1-year postablation. Follow-up echocardiographic data was available for 55 patients.

RESULTS

Of the 55 patients with CTI-AFL, the mean age was 64.2 ± 14.8 years old with 14.5% (n = 8) female. The average left ventricular ejection fraction (LVEF) significantly improved on follow-up echo (40.2 ± 16.9 to 50.4 ± 14.9%, p < .0001), of which 50% of patients had an improvement in LVEF of at least 10%. There was a significant reduction in left atrial volume index (82.74 ± 28.5 to 72.96 ± 28 mL/m2 , p = .008) and RA volume index (70.62 ± 25.6 to 64.15 ± 31 mL/m2 , p = .046), and a significant improvement in left atrial reservoir strain (13.04 ± 6.8 to 19.10 ± 7.7, p < .0001).

CONCLUSIONS

Patients who underwent CTI dependent AFL ablation showed an improvement in cardiac size and function at follow-up evaluation. While long-term results are still unknown, these findings indicate that restoration of sinus rhythm in patients with typical AFL is associated with improvement in atrial size and left ventricular function.

P-wave duration and interatrial conduction abnormalities in paroxysmal and persistent typical atrial flutter

Functional and structural changes, the enlargement of the right atrium is the background for the development of typical atrial flutter (AFL). These changes in ECG are manifested in the morphology of the initial part of the P-wave. The aim of the study was to assess the duration and morphology of the P-wave in patients with paroxysmal and persistent AFL. The study population consisted of 131 patients with AFL, 38 women and 93 men aged 66 years (60-72), divided in 62 patients with paroxysmal and 69 with persistent AFL. P-wave duration was measured with an electrophysiological system in all leads at a paper speed of 200 mm/s. The groups did differ in terms of gender (38/24 vs. 55/14, (M/F), p=0.033). Patients with persistent AF had a longer P-wave duration - 175±26.3 ms vs. 159±22.6 ms, p=0.01, and higher creatinine concentration - 1.2±0.60 mg/dl vs. 1.08±0.68 mg/dl, p=0.007. The presence and severity of interatrial conduction block (I-none, II-partial, III-total) was related to age of the patients (60.3±12.1 vs. 64.7±-8.3 vs. 68.9±9.5 years, respectively). Patients with persistent AFL show a longer P-wave compared to paroxysmal AFL, regardless of comorbidities and antiarrhythmic drugs. The arrhythmia-related longer P-wave duration should encourage the clinicians to restore sinus rhythm earlier in order to more effectively maintain it over the long term.

Comparison of Atrial Remodeling Caused by Sustained Atrial Flutter Versus Atrial Fibrillation

BACKGROUND

Atrial flutter (AFL) and atrial fibrillation (AF) are associated with AF-promoting atrial remodeling, but no experimental studies have addressed remodeling with sustained AFL.

OBJECTIVES

This study aimed to define the atrial remodeling caused by sustained atrial flutter (AFL) and/or atrial fibrillation (AF).

METHODS

Intercaval radiofrequency lesions created a substrate for sustained isthmus-dependent AFL, confirmed by endocavity mapping. Four groups (6 dogs per group) were followed for 3 weeks: sustained AFL; sustained AF (600 beats/min atrial tachypacing); AF superimposed on an AFL substrate (AF+AFLs); sinus rhythm (SR) with an AFL substrate (SR+AFLs; control group). All dogs had atrioventricular-node ablation and ventricular pacemakers at 80 beats/min to control ventricular rate.

RESULTS

Monitoring confirmed spontaneous AFL maintenance >99% of the time in dogs with AFL. At terminal open-chest study, left-atrial (LA) effective refractory period was reduced similarly with AFL, AF+AFLs and AF, while AF vulnerability to extrastimuli increased in parallel. Induced AF duration increased significantly in AF+AFLs and AF, but not AFL. Dogs with AF+AFLs had shorter cycle lengths and substantial irregularity versus dogs with AFL. LA volume increased in AF+AFLs and AF, but not dogs with AFL, versus SR+AFLs. Optical mapping showed significant conduction slowing in AF+AFLs and AF but not AFL, paralleling atrial fibrosis and collagen-gene upregulation. Left-ventricular function did not change in any group. Transcriptomic analysis revealed substantial dysregulation of inflammatory and extracellular matrix-signaling pathways with AF and AF+ALs but not AFL.

CONCLUSIONS

Sustained AFL causes atrial repolarization changes like those in AF but, unlike AF or AF+AFLs, does not induce structural remodeling. These results provide novel insights into AFL-induced remodeling and suggest that early intervention may be important to prevent irreversible fibrosis when AF intervenes in a patient with AFL.

[Atrial Flutter: up-to-date Problem Evaluation with Clinical Positions]

The review provides current ideas about the etiology and prevalence of atrial flutter (AF), mechanism and substrate of arrhythmogenesis, and principles of clinical and electrophysiological classification of this arrhythmia. Methods for conservative and surgical treatments of AF, including their comparative aspect, are described in detail. The review presented recent data on efficacy and potential risks of different approaches to reversing the arrhythmia. The authors indicated a need for early diagnosis and strict control of the sinus rhythm in AF, which would help a successful intervention not only to completely cure the existing arrhythmia but also to prevent other heart rhythm disorders, primarily atrial fibrillation.

Cardiac magnetic resonance-derived right atrial functional analysis in patients with atrial fibrillation and typical atrial flutter

BACKGROUND

Typical atrial flutter (AFL) often occurs in patients with atrial fibrillation (AF). Decision-making tools for application of prophylactic cavo-tricuspid isthmus (CTI) ablation at the time of AF ablation may improve outcomes. In this study, we sought to define the right atrial (RA) functional characteristics of AF patients with documented typical AFL.

METHODS

Consecutive patients that underwent cardiac magnetic resonance (CMR) prior to initial AF ablation in the Johns Hopkins Hospital were enrolled. The AF database was reviewed to identify prevalent and incident documented typical AFL. Feature tracking CMR analysis during sinus rhythm was utilized to quantify RA longitudinal strain and strain rate, as well as RA passive and active emptying fractions derived from phasic RA volumes.

RESULTS

A total of 115 patients were analyzed (mean age 59.1 ± 11.4 years, 78.3% male, 74.8% paroxysmal AF). Of all patients, 30 (26.1%) had typical AFL. Clinical characteristics and AF type did not differ among groups defined by the absence or presence of typical AFL. In contrast, RA longitudinal strain (41.6 ± 16.8% vs. 55.8 ± 17.1%, p ≤ 0.001), systolic strain rate (1.71 ± 0.85 s^-1 vs. 2.33 ± 0.93 s^-1, p = 0.002), and late diastolic strain rate (1.78 ± 1.02 s^-1 vs. 2.50 ± 0.91 s^-1 p ≤ 0.001) were significantly lower in patients with typical AFL. Although RA passive emptying fraction was similar among groups (18.9 ± 8.1 vs. 19.5 ± 8.0, p = 0.75), RA active emptying fraction was lower in patients with typical AFL (34.8 ± 12.3 vs. 40.8 ± 12.1, p = 0.02).

CONCLUSIONS

The reservoir and pump function of the RA is significantly reduced in patients with typical AFL. Prophylactic CTI ablation warrants further study as adjunctive therapy to AF catheter ablation in selected patients with RA dysfunction.

Predictors and Incidence of Atrial Flutter After Catheter Ablation of Atrial Fibrillation

Atrial flutter (AFL) is a common form of arrhythmia recurrence after atrial fibrillation (AF) ablation. We aimed to define (1) the incidence of AFL and (2) the clinical factors associated with cavo-tricuspid isthmus dependent (typical) and atypical AFL, after AF ablation. The retrospective cohort consisted of 1,029 patients that underwent initial radiofrequency AF ablation from May 2005 to December 2013 at a single academic center. Patients with missing follow-up data, history of AFL ablation, and those with undocumented AFL were excluded. Atrial volumes were measured using three-dimensional cardiac computed tomography or magnetic resonance imaging. A total of 607 patients were included in the final cohort (age 59.2 ± 10.6 years, 76.0% men, 58.7% paroxysmal AF). During a median follow-up of 845 days (interquartile range 389 to 1,597 days), 122 (20.1%) patients developed AFL. Of these, 17 had typical AFL, 98 had atypical AFL, and 7 patients had both circuits. In the multivariable Cox regression analysis, only right atrial volume index (hazard ratio [HR] 1.25 per 10 ml/m2, confidence interval [CI] 95% 1.10 to 1.42) was associated with incident typical AFL; whereas persistent AF (HR 1.59, CI 95% 1.06 to 2.40), linear lesions (HR 1.58, CI 95% 1.02 to 2.46) and left atrial volume index (HR 1.17 per 10 ml/m2, CI 95% 1.07 to 1.27) were associated with incident atypical AFL. In conclusion, noninvasive measures of right and left atrial remodeling are strongly associated with incident AFL after AF ablation. Strategies to prevent incident AFL using these measures after index ablation warrant further investigation.

Arrhythmias in dilated cardiomyopathy

Patients with dilated cardiomyopathies (DCM) face a significant burden of arrhythmias, including conduction defects such as atrioventricular block and interventricular delay in the form of left bundle branch block, resulting in altered electromechanical coupling that can exacerbate heart failure. Atrial fibrillation is common and carries an adverse prognosis. Ventricular arrhythmias and sudden cardiac death generally occur late in the disease course. Sustained monomorphic ventricular tachycardia accounts for most of the sustained ventricular arrhythmias in DCM. This article summarizes common forms of arrhythmias encountered in patients with DCM, and reviews the relevant electrophysiologic basis of these arrhythmias and their management.

Predictors of sick sinus syndrome in patients after successful radiofrequency catheter ablation of atrial flutter

PURPOSE

The identification of sick sinus syndrome (SSS) in patients with atrial flutter (AFL) is difficult before the termination of AFL. This study investigated the patient characteristics used in predicting a high risk of SSS after AFL ablation.

MATERIALS AND METHODS

Out of 339 consecutive patients who had undergone radiofrequency ablation for AFL from 1991 to 2012, 27 (8%) had SSS (SSS group). We compared the clinical characteristics of patients with and without SSS (n=312, no-SSS group).

RESULTS

The SSS group was more likely to have a lower body mass index (SSS: 22.5±3.2; no-SSS: 24.0±3.0 kg/m²; p=0.02), a history of atrial septal defects (ASD; SSS: 19%; no-SSS: 6%; p=0.01), a history of coronary artery bypass graft surgery (CABG; SSS: 11%; no-SSS: 2%; p=0.002), and a longer flutter cycle length (CL; SSS: 262.3±39.2; no-SSS: 243.0±40; p=0.02) than the no-SSS group. In multivariate analysis, a history of ASD [odds ratio (OR) 3.7, 95% confidence interval (CI) 1.2-11.4, p=0.02] and CABG (7.1, 95% CI 1.5-32.8, p=0.01) as well as longer flutter CL (1.1, 95% CI 1.0-1.2, p=0.04) were independent risk factors for SSS.

CONCLUSION

A history of ASD and CABG as well as longer flutter CL increased the risk of SSS after AFL ablation. While half of the patients with SSS after AFL ablation experienced transient SSS, heart failure was associated with irreversible SSS.

Temporal and comparative outcomes of cardiac electrophysiology abstracts

Although conferences are important vehicles for discussing scientific findings, the translation of presented research into peer-reviewed manuscripts is a crucial subsequent step in the research process. Given the evolving subspecialization of cardiology, we sought to characterize the temporal and comparative outcomes of abstracts presented at a subspecialty cardiac electrophysiology conference. Abstracts presented at the Heart Rhythm Society conference (1994 through 2006; HRS abstracts) and abstracts presented at the American Heart Association conference (2003; AHA abstracts) were studied. Subsequent publications, impact factors, and citation rates were determined. A total of 3,850 HRS and 1,000 AHA abstracts were studied. More human abstracts were presented at HRS than AHA (p <0.05). Compared with HRS abstracts, more AHA abstracts were published (p <0.001) and had higher impact factors and citation rates (p <0.001 for both). These differences were attributable in part to the greater proportion of human HRS abstracts. Compared with HRS abstracts, electrophysiology-related AHA abstracts were published less (p <0.001), and these publications had similar impact factors (p = 0.38) although greater citation rates (p = 0.001). The number and publication rate of HRS abstracts increased over the 15-year period, as did their publication impact factors and citation rates (p <0.001 for all). In conclusion, there are significant differences between AHA and HRS abstracts. Although AHA abstracts were more likely to be published overall, the publication rate and impact of electrophysiology abstracts presented at both a subspecialty (HRS) and a major cardiovascular conference (AHA) were comparable. There has also been a growth in the number and impact of cardiac electrophysiology abstracts presented at HRS in recent years.

The Role of Pericardial and Epicardial Fat in Atrial Fibrillation Pathophysiology and Ablation Outcomes

Emerging evidence suggests that epicardial and pericardial fat are related to the presence, severity and outcome of AF. These associations, independent of generalized obesity, suggest that they may become increasingly useful as markers for risk stratification or monitoring in the clinical setting. Mechanistically, studies have suggested the effects of epicardial and pericardial fat may be mediated by local adipokines, inflammation, fatty infiltration, modulation of AF drivers and left atrial dilatation. Given the dual epidemics of AF and obesity, in the present paper we review the role that the ectopic adipose tissue surrounding the heart has in the pathogenesis of AF. Further inquiries in this active area of investigation may ultimately lead to new insights in how to best combat these interrelated epidemics and reduce the societal burden of AF.

Cardiac electrophysiology in mice: a matter of size

Over the last decade, mouse models have become a popular instrument for studying cardiac arrhythmias. This review assesses in which respects a mouse heart is a miniature human heart, a suitable model for studying mechanisms of cardiac arrhythmias in humans and in which respects human and murine hearts differ. Section I considers the issue of scaling of mammalian cardiac (electro) physiology to body mass. Then, we summarize differences between mice and humans in cardiac activation (section II) and the currents underlying the action potential in the murine working myocardium (section III). Changes in cardiac electrophysiology in mouse models of heart disease are briefly outlined in section IV, while section V discusses technical considerations pertaining to recording cardiac electrical activity in mice. Finally, section VI offers general considerations on the influence of cardiac size on the mechanisms of tachy-arrhythmias.

Conduction velocity restitution of the human atrium--an efficient measurement protocol for clinical electrophysiological studies

Conduction velocity (CV) and CV restitution are important substrate parameters for understanding atrial arrhythmias. The aim of this work is to (i) present a simple but feasible method to measure CV restitution in-vivo using standard circular catheters, and (ii) validate its feasibility with data measured during incremental pacing. From five patients undergoing catheter ablation, we analyzed eight datasets from sinus rhythm and incremental pacing sequences. Every wavefront was measured with a circular catheter and the electrograms were analyzed with a cosine-fit method that calculated the local CV. For each pacing cycle length, the mean local CV was determined. Furthermore, changes in global CV were estimated from the time delay between pacing stimulus and wavefront arrival. Comparing local and global CV between pacing at 500 and 300 ms, we found significant changes in seven of eight pacing sequences. On average, local CV decreased by 20 ± 15% and global CV by 17 ± 13%. The method allows for in-vivo measurements of absolute CV and CV restitution during standard clinical procedures. Such data may provide valuable insights into mechanisms of atrial arrhythmias. This is important both for improving cardiac models and also for clinical applications, such as characterizing arrhythmogenic substrates during sinus rhythm.