The local repolarization heterogeneity in the murine pulmonary veins myocardium contributes to the spatial distribution of the adrenergically induced ectopic foci

An atrial tachyarrhythmias is predominantly triggered by a proarrhythmic activity originate from the pulmonary veins (PV) myocardial sleeves; sympathetic or adrenergic stimulation facilitates PV proarrhythmia. In the present study the electrophysiological inhomogeneity, spatiotemporal characteristics of the adrenergically induced ectopic firing and sympathetic nerves distribution have been investigated in a murine PV myocardium to clarify mechanisms of adrenergic PV ectopy. Electrically paced murine PV demonstrate atrial-like pattern of conduction and atrial-like action potentials (AP) with longest duration in the mouth of PV. The application of norepinephrine (NE), agonists of α- and β-adrenergic receptors (ARs) or intracardiac nerves stimulation induced spontaneous AP in a form of periodical bursts or continuous firing. NE- or ARs agonists-induced SAP originated from unifocal ectopic foci with predominant localization in the region surrounding PV mouth, but not in the distal portions of a murine PV myocardium. A higher level of catecholamine content and catecholamine fiber network density was revealed in the PV myocardial sleeves relative to LA appendage. However, no significant local variation of catecholamine content and fiber density was observed in the murine PV. In conclusion, PV mouth region appear to be a most susceptible to adrenergic proarrhythmia in mice. Intrinsic spatial heterogeneity of AP duration can be considered as a factor influencing localization of the ectopic foci in PV.

Pathophysiology of Paroxysmal and Persistent Atrial Fibrillation: Rotors, Foci and Fibrosis

Recent advances in our understanding of the mechanisms underlying atrial fibrillation (AF) have further underscored the complex pathophysiological basis of the arrhythmia. It has become apparent that the current clinical classification of AF does not reflect the severity of the underlying atrial disease. Atrial fibrosis has been identified as the key structural change in different substrates that are responsible for the perpetuation of AF. Three-dimensional electroanatomical mapping and late gadolinium-enhanced magnetic resonance imaging are novel modalities that can be used to facilitate identification and quantitation of atrial fibrosis for improved delineation of the AF substrate. Advances in AF mapping technology using endocardial 'panaromic' basket-type catheter and non-invasive body surface electrodes have facilitated the identification of two major arrhythmic mechanisms of interest, namely rotational ('rotors') and ectopic focal activations ('foci'). Ongoing research on these potential drivers of AF may provide guidance to more mechanistic based therapies to improve outcomes for this complex arrhythmia in the future. Here, we aim to review the differences in AF substrate in those with paroxysmal and more persistent forms of the arrhythmia by evaluating fibrosis, rotors and foci, towards improved AF substrate classification and individualised substrate based therapies.