Structural and electro-anatomical characterization of the equine pulmonary veins: implications for atrial fibrillation.

Abstract

INTRODUCTION/OBJECTIVES: Spontaneous pulmonary vein (PV) activity triggers atrial fibrillation (AF) in humans. Although AF frequently occurs in horses, the origin remains unknown. This study investigated the structural and electro-anatomical properties of equine PVs to determine the potential presence of an arrhythmogenic substrate. ANIMALS, MATERIALS AND METHODS: Endocardial three-dimensional electro-anatomical mapping (EnSite Precision) using high-density (HD) catheters was performed in 13 sedated horses in sinus rhythm. Left atrium (LA) access was obtained retrogradely through the carotid artery. Post-mortem, tissue was harvested from the LA, right atrium (RA), and PVs for histological characterization and quantification of ion channel expression using immunohistochemical analysis. RESULTS: Geometry, activation maps, and voltage maps of the PVs were created and a median of four ostia were identified. Areas of reduced conduction were found at the veno-atrial junction. The mean myocardial sleeve length varied from 28&#xa0;&#xb1;&#xa0;13 to 49&#xa0;&#xb1;&#xa0;22&#xa0;mm. The PV voltage was 1.2&#xa0;&#xb1;&#xa0;1.4&#xa0;mV and lower than the LA (3.4&#xa0;&#xb1;&#xa0;0.9&#xa0;mV, P&#xa0;<&#xa0;0.001). The fibrosis percentage was higher in PV myocardium (26.1&#xa0;&#xb1;&#xa0;6.6%) than LA (14.5&#xa0;&#xb1;&#xa0;5.0%, P&#xa0;=&#xa0;0.003). L-type calcium channel (Ca1.2) expression was higher in PVs than LA (P&#xa0;=&#xa0;0.001). T-type calcium channels (Ca3.3), connexin-43, ryanodine receptor-2, and small conductance calcium-activated potassium channel-3 was expressed in PVs. CONCLUSIONS: The veno-atrial junction had lower voltages, increased structural heterogeneity and areas of slower conduction. Myocardial sleeves had variable lengths, and a different ion channel expression compared to the atria. Heterogeneous properties of the PVs interacting with the adjacent LA likely provide the milieu for re-entry and AF initiation.