Morphological investigation of myocardial sleeves with potential relevance to atrial fibrillation in Norwegian-Swedish Coldblooded trotters.

NSCTs possess arrhythmogenic anatomical substrates similar to AF-prone breeds, suggesting non-anatomical protective mechanisms.

This morphological study investigated myocardial sleeves (MSs) in the caval veins of Norwegian-Swedish Coldblooded Trotters (NSCTs), a breed with notably lower prevalence of atrial fibrillation (AF) compared to Standardbred racehorses (reported AF prevalence 1.3-2%), despite similar athletic demands. Researchers collected hearts from 33 NSCTs during postmortem examination and performed macro- and microscopic analyses of caval vein MSs, including quantification of fibrosis and myofibre orientation. Results demonstrated that MSs were present in both the cranial vena cava (CrVC) and caudal vena cava (CaVC) in all specimens. The CrVC exhibited a clearer anatomical border, while myocardial islands were exclusively identified in the CaVC. Interstitial fibrosis was significantly greater in the CaVC MS compared to the CrVC. Both veins displayed heterogeneous myofibre orientation, including transverse, longitudinal, and oblique arrangements, particularly pronounced in the CaVC. These structural features—fibrosis, myocardial islands, and disorganized myofibre orientation—are recognized substrates for arrhythmogenesis in other species and breeds. Crucially, the caval MS characteristics in NSCTs closely resembled those reported in breeds with higher AF prevalence, suggesting that anatomical substrate alone does not explain the breed's relative protection from AF. The authors conclude that other factors, potentially electrical, autonomic, or involving pulmonary vein MS properties, may confer protection against AF development in NSCTs, warranting further investigation.

This summary was distilled by AI and may occasionally misinterpret data. Confirm critical details with the primary literature before clinical application.