Role of interatrial conduction in atrial fibrillation: Mechanistic insights from renewal theory-based fibrillatory dynamic analysis.

Background: Interatrial conduction has been postulated to play an important role in atrial fibrillation (AF). The pathways involved in interatrial conduction during AF remain incompletely defined. Objective: We recently showed physiological assessment of fibrillatory dynamics could be performed using renewal theory, which determines rates of phase singularity formation (λf) and destruction (λd). Using the renewal approach, we aimed to understand the role of the interatrial septum and other electrically coupled regions during AF. Method: RENEWAL-AF is a prospective multicenter observational study recruiting AF ablation patients (ACTRN 12619001172190). We studied unipolar electrograms obtained from 16 biatrial locations prior to ablation using a 16-electrode Advisor HD Grid catheter. Renewal rate constants λf and λd were calculated, and the relationships between these rate constants in regions of interatrial connectivity were examined. Results: Forty-one AF patients (28.5% female) were recruited. A positive linear correlation was observed between λf and λd (1) across the interatrial septum (λf r2 = 0.5, P < .001, λd r2 = 0.45, P < .001), (2) in regions connected by the Bachmann bundle (right atrial appendage-left atrial appendage λf r2 = 0.29, P = .001; λd r2 = 0.2, P = .008), and (3) across the inferior interatrial routes (cavotricuspid isthmus-left atrial septum λf r2 = 0.67, P < .001; λd r2 = 0.55, P < .001). Persistent AF status and left atrial volume were found to be important effect modifiers of the degree of interatrial renewal rate statistical correlation. Conclusion: Our findings support the role of interseptal statistically determined electrical disrelation in sustaining AF. Additionally, renewal theory identified preferential conduction through specific interatrial pathways during fibrillation. These findings may be of importance in identifying clinically significant targets for ablation in AF patients.

Prospective cross-sectional study using Poisson renewal theory to study phase singularity formation and destruction rates in atrial fibrillation (RENEWAL-AF): Study design.

BACKGROUND: Unstable functional reentrant circuits known as rotors have been consistently observed in atrial fibrillation and are mechanistically believed critical to the maintenance of the arrhythmia. Recently, using a Poisson renewal theory-based quantitative framework, we have demonstrated that rotor formation (λf) and destruction rates (λd) can be measured using in vivo electrophysiologic data. However, the association of λf and λd with clinical, electrical, and structural markers of atrial fibrillation phenotype is unknown. METHODS: RENEWAL-AF is a multicenter prospective cross-sectional study recruiting adult patients with paroxysmal or persistent atrial fibrillation undergoing clinically indicated catheter ablation. Patients will undergo intraprocedural electrophysiologic atrial fibrillation mapping, with λf and λd to be determined from 2-minute unipolar electrogram recordings acquired before ablation. The primary objective will be to determine the association of λf and λd as markers of fibrillatory dynamics with clinical, electrical, and structural markers of atrial fibrillation clinical phenotype, measured by preablation transthoracic echocardiogram and cardiac magnetic resonance imaging. An exploratory objective is the noninvasive assessment of λf and λd using surface ECG characteristics via a machine learning approach. RESULTS: Not applicable. CONCLUSION: This pilot study will provide insight into the correlation between λf/λd with clinical, electrophysiological, and structural markers of atrial fibrillation phenotype and provide a foundation for the development of noninvasive assessment of λf/λd using surface ECG characteristics will help expand the use of λf/λd in clinical practice.

A Randomised Controlled Trial on the Effect of Nurse-Led Educational Intervention at the Time of Catheter Ablation for Atrial Fibrillation on Quality of Life, Symptom Severity and Rehospitalisation.

BACKGROUND: Atrial Fibrillation (AF) is a common condition associated with impaired quality of life (QOL) and recurrent hospitalisation. Catheter ablation for AF is a well-established treatment for symptomatic patients despite medical therapy. We sought to examine the effect of point specific nurse-led education on QOL, AF symptomatology and readmission rate post AF ablation. METHODS: Forty-one patients undergoing AF ablation were randomised to Nurse Intervention (NI) versus Control (C), n=22 vs. 19. Both groups were well matched with respect to age, sex and AF subtype. All patients completed SF36 and AF Symptom Checklist, Frequency and Severity Scale questionnaires at baseline and six months post ablation. The NI group underwent nurse education on admission, prior to discharge, and with telephone contact. RESULTS: Baseline SF-36 and AF Symptom Checklist, Frequency and Severity scores were similar. The NI group showed significant differences compared to Control with respect to higher QOL on the SF-36 score of Physical Functioning and Vitality at six months. There were significant improvements in seven components of the AF Symptom Checklist, Frequency and Severity at six months in the NI group with a trend in a further seven. There was no difference in AF related hospital readmissions at six months between C and NI groups (10.5% vs. 13.6%, p=ns). CONCLUSION: Nurse-led education at time of AF ablation is associated with improved QOL and reduced symptom frequency and severity compared to usual care.

Cardiac resynchronisation therapy in patients with atrioventricular nodal disease and reduced ejection fraction - can we afford it?

BACKGROUND: Recent pacing guidelines from the European Society of Cardiology recommend cardiac resynchronisation therapy (CRT) in patients with an atrioventricular (AV) nodal pacing indication and reduced ejection fraction (EF). However, concerns over added expenditure may limit its widespread implementation. We investigate the potential incremental cost of biventricular over right ventricular pacing if such a practice was adopted. METHODS: Retrospective analysis was performed of devices implanted over eight years. The database was analysed for device type, pacing indication and EF. Cost analysis was performed. RESULTS: 1751 devices were implanted over eight years at an averaged cost of AUD$1,369,125 per year. 172 with CRT were excluded. 25.4 (11.6%) patients per year had an EF≤50% and AV nodal disease. 18.4 were in sinus rhythm (SR) and 7.0 in atrial fibrillation (AF). Of these, 13.5 (6.2%) had EF≤45% (9.9 SR, 3.6 AF) and 8.2 (3.8%) had EF≤35% (5.6 SR, 2.6 AF). Based on an incremental cost of $4,000 per device, if all patients with EF≤50% received CRT, the total cost increment per year equates to $73,500 for SR patients or $101,500 if AF patients were included. In patients with EF≤35% and EF≤45%, this amounts to $22,500 and $39,500 per year for SR patients respectively or $33,000 and $54,000 per year if AF patients were included. Depending on the EF and rhythm, this represents a 1.6% to 7.4% increase per year in the pacing budget for an increased patient population of between 2.6% (EF≤35% in SR) to 11.6% (EF≤50%). CONCLUSION: A small proportion of additional patients will qualify for CRT based on the chosen cut-off and rhythm. Although the individual incremental cost for biventricular over right ventricular pacing is high in patients with AV nodal disease and reduced EF, overall this represents at most, a modest increase in the total pacing budget.