High-dose cardiac irradiation in rats caused early conduction delay, ST-segment changes, and structural alterations like intercalated disc widening and edema without myocardial necrosis.
Does high-dose cardiac irradiation cause early histologic, ultrastructural, and functional changes in rat hearts?
Early antiarrhythmic effects of cardiac radioablation may result from conduction disturbances and membrane potential alterations due to edema and intercalated disc widening, rather than myocardial necrosis.
Background Noninvasive cardiac radioablation is employed to treat ventricular arrhythmia. However, myocardial changes leading to early-period antiarrhythmic effects induced by high-dose irradiation are unknown. This study investigated dose-responsive histologic, ultrastructural, and functional changes within 1 month after irradiation in rat heart. Methods and Results Whole hearts of wild-type Lewis rats (N=95) were irradiated with single fraction 20, 25, 30, 40, or 50 Gy and explanted at 1 day or 1, 2, 3, or 4 weeks' postirradiation. Microscopic pathologic changes of cardiac structures by light microscope with immunohistopathologic staining, ultrastructure by electron microscopy, and functional evaluation by ECG and echocardiography were studied. Despite high-dose irradiation, no myocardial necrosis and apoptosis were observed. Intercalated discs were widened and disrupted, forming uneven and twisted junctions between adjacent myocytes. Diffuse vacuolization peaked at 3 weeks, suggesting irradiation dose-responsiveness, which was correlated with interstitial and intracellular edema. CD68 immunostaining accompanying vacuolization suggested mononuclear cell infiltration. These changes were prominent in working myocardium but not cardiac conduction tissue. Intracardiac conduction represented by PR and QTc intervals on ECG was delayed compared with baseline measurements. ST segment was initially depressed and gradually elevated. Ventricular chamber dimensions and function remained intact without pericardial effusion. Conclusions Mononuclear cell-related intracellular and extracellular edema with diffuse vacuolization and intercalated disc widening were observed within 1 month after high-dose irradiation. ECG indicated intracardiac conduction delay with prominent ST-segment changes. These observations suggest that early antiarrhythmic effects after cardiac radioablation result from conduction disturbances and membrane potential alterations without necrosis.
Cha et al. (Thu,) conducted a other in Ventricular arrhythmia (animal model) (n=95). High-dose irradiation vs. Baseline measurements was evaluated on Histologic, ultrastructural, and functional changes within 1 month. High-dose cardiac irradiation in rats caused early conduction delay, ST-segment changes, and structural alterations like intercalated disc widening and edema without myocardial necrosis.
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