Ultrastructural changes in the right ventricular myocardium during adaptation to cold stress: A transmission and scanning electron microscopy study

Cold stress is a complex factor that has a significant impact on the cardiovascular system. The myocardial response includes both functional and profound structural changes. Objective. The aim of the study is to comprehensively evaluate the ultrastructural changes in right ventricular cardiomyocytes and the extracellular matrix during cold stress. Materials and Methods. The study was conducted on male Wistar rats weighing 120–150 g. Tissue samples (right ventricular myocardium) were collected on days 3, 7, and 15 after the onset of cold stress. The specimens were prepared using standard protocols and analyzed using scanning (SEM) and transmission (TEM) electron microscopy. Results. During the early adaptation phase (day 3), SEM and TEM revealed signs of an acute stress response that was predominantly reversible. During the advanced pathological process (day 7), damage became more systemic and profound, affecting key cellular systems. With further exposure (day 15), the process transitioned to a phase of chronic myocardial remodeling. Conclusion. A comprehensive pattern of focal myocardial remodeling induced by cold stress is identified. The combination of ultrastructural signs of fibrosis, fatty degeneration, and calcification indicates significant changes in the cardiac muscle. It is likely that as early as day 3 of cold exposure, a cascade of events is triggered, leading to progressive diffuse-focal disruption of myocardial architecture across several interconnected structural and functional systems. These processes are not isolated; they are tightly intertwined and exacerbate one another.