Human persistent atrial fibrillation is maintained by rotors: the jury is still out

Personalized Evaluation of Atrial Complexity of Patients Undergoing Atrial Fibrillation Ablation: A Clinical Computational Study

Simple Summary

Atrial fibrillation is a type of arrhythmia that occurs when the electrical activity of the heart in the atrium is not coordinated, and its consequences can be lethal. The driving source that initiates this chaotic activity can be located anywhere in the atrium, but most frequently appears in certain areas such as the pulmonary veins. In this study, we developed a new estimation method to evaluate possible source location and complexity of the arrhythmia using computer simulations. This method represents mathematical descriptions of natural processes that can be used to mimic a real scenario, including specific information such as the atrial anatomy. Here, we identified a specific biomarker the enabled obtaining a foci distribution map and found that elimination of pulmonary vein drivers was associated with a successful long-term ablation outcome. This study could, therefore, help to identify and characterize patients in order to better plan the ablation procedure.

Abstract

Current clinical guidelines establish Pulmonary Vein (PV) isolation as the indicated treatment for Atrial Fibrillation (AF). However, AF can also be triggered or sustained due to atrial drivers located elsewhere in the atria. We designed a new simulation workflow based on personalized computer simulations to characterize AF complexity of patients undergoing PV ablation, validated with non-invasive electrocardiographic imaging and evaluated at one year after ablation. We included 30 patients using atrial anatomies segmented from MRI and simulated an automata model for the electrical modelling, consisting of three states (resting, excited and refractory). In total, 100 different scenarios were simulated per anatomy varying rotor number and location. The 3 states were calibrated with Koivumaki action potential, entropy maps were obtained from the electrograms and compared with ECGi for each patient to analyze PV isolation outcome. The completion of the workflow indicated that successful AF ablation occurred in patients with rotors mainly located at the PV antrum, while unsuccessful procedures presented greater number of driving sites outside the PV area. The number of rotors attached to the PV was significantly higher in patients with favorable long-term ablation outcome (1-year freedom from AF: 1.61 ± 0.21 vs. AF recurrence: 1.40 ± 0.20; p-value = 0.018). The presented workflow could improve patient stratification for PV ablation by screening the complexity of the atria.

STRUCTURAL AND FUNCTIONAL BASES OF CARDIAC FIBRILLATION. DIFFERENCES AND SIMILARITIES BETWEEN ATRIA AND VENTRICLES

Evidence accumulated over the last 25 years suggests that, whether in the atria or ventricles, fibrillation may be explained by the self-organization of the cardiac electrical activity into rapidly spinning rotors giving way to spiral waves that break intermittently and result in fibrillatory conduction. The dynamics and frequency of such rotors depend on the ion channel composition, excitability and refractory properties of the tissues involved, as well as on the thickness and respective three-dimensional fiber structure of the atrial and ventricular chambers. Therefore, improving the understanding of fibrillation has required the use of multidisciplinary research approaches, including optical mapping, patch clamping and molecular biology, and the application of concepts derived from the theory of wave propagation in excitable media. Moreover, translation of such concepts to the clinic has recently opened new opportunities to apply novel mechanistic approaches to therapy, particularly during atrial fibrillation ablation. Here we review the current understanding of the manner in which the underlying myocardial structure and function influence rotor initiation and maintenance during cardiac fibrillation. We also examine relevant underlying differences and similarities between atrial fibrillation and ventricular fibrillation and evaluate the latest clinical mapping technologies used to identify rotors in either arrhythmia. Altogether, the data being discussed have significantly improved our understanding of the cellular and structural bases of cardiac fibrillation and pointed toward potentially exciting new avenues for more efficient and effective identification and therapy of the most complex cardiac arrhythmias.