Division of Cardiology Department of Internal Medicine Seoul National University Hospital Seoul South Korea.
Departments of Pathology Seoul National University Hospital Seoul South Korea.
Department of Radiation Oncology Seoul National University College of Medicine Seoul Korea.
Department of Radiation Oncology Seoul National University Hospital Seoul South Korea.
Cancer Research InstituteSeoul National University College of Medicine Seoul Korea.
Seoul National University College of Medicine Seoul Korea.
Abstract
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.
Figure 1 Ventricular myocardium irradiated with 30 Gy at 4 weeks. Irradiated left ventricular free wall subendocardium of rats was stained with hematoxylin and eosin (H&E), Masson trichrome (MT), and immunohistochemistry (Desmin, TUNEL [terminal deoxynucleotidal transferase–mediated biotin–deoxyuridine triphosphate nick‐end labeling] assay, and C4d immunostaining). Myocyte necrosis and apoptosis were not observed in rat hearts irradiated by 20 to 50 Gy. Intercellular space (interstitium) was widened but not fibrotic. Cellular rupture and destruction of myocytes were not observed. (×400 Magnification.)Figure 2 Electron microscope examination of the left ventricular myocardium of irradiated rat heart (30 Gy single fraction). Compared with normal intercalated discs (A), irradiated intercalated discs exhibited irregular widening focal protrusion (B) or segmental separation (C) peaking at 1 week. These abnormalities were observed in 30 Gy‐irradiated rats harvested at day 1 and were rarely observed after week 2. From week 2, intercalated discs exhibited irregularly widened longitudinal cell connections with adjacent gap junction vesicles (D). Damaged intercalated discs were narrowed after 3 weeks. Remodeling was uneven and twisted (E). (×50 000 Magnification.)Figure 3 Interstitial vacuolization. A, Temporal changes of the left ventricular subendocardial vacuolization. (×400 Magnification.) B, Boxplot of the percentage of vacuolization at 3 weeks according to radiation dose. The extent of vacuolization in 5 high‐power field was measured at left ventricular subendocardium using an Aperio Imagescope (Leica). All groups were statistically different from each group, except the 20 and 25 Gy groups and the 30, 40, 50 Gy groups. *** indicates P<0.001. C, The vacuolized area on hematoxylin and eosin (H&E) staining showed positive staining for CD68. (×400 Magnification.) Statistical difference was determined by 1‐way ANOVA with Tukey post hoc analysis.Figure 4 Interstitial and cytoplasmic edema after irradiation. A, Rat left ventricular midmyocardium on electron microscopy (×5000 magnification). B, Rat left ventricular midmyocardium on electron microscopy (×40 000 magnification), left ventricle irradiated with 30 Gy (3 weeks). Cellular membranes were dilated because of cytoplasmic swelling (red arrows). Interstitial edema widened intercellular spaces (red asterisks and white arrow). Subsarcolemmal and interfibrillar mitochondria (marked as “Mi”) were damaged and variable in size. Myofibrils (MFs) with Z and M lines were intact. No remarkable abnormalities in myocyte nuclei (marked as “Nu”) were noted.Figure 5 Main histopathologic findings. Irradiated rat heart myocardium (right) and normal rat heart myocardium (left) were compared. No cellular necrosis or apoptosis after irradiation was noted. Diffuse vacuolization was correlated with interstitial and subsarcolemmal edema. Intercalated discs between myocytes were widened with diverse patterns.Figure 6 ECG changes. Average values of 10 measurements of randomly selected beats during a 1‐minute recording were determined. The sample size was 15 per group at each time point. A, Resting heart rate was increased after irradiation compared with baseline measurements. B, The PR interval, representing the conduction velocity from atrium to ventricle, was slightly delayed and peaked at 3 weeks. C, The corrected QT interval, representing the intraventricular conduction property, was prolonged relative to baseline. D, The ST segment was depressed after irradiation but elevated after 2 weeks in most cases. The statistical difference between groups was calculated using 1‐way ANOVA with Dunnett post hoc analysis.
그림 출처: PubMed Central 공개 논문 (PMC8174197)
Conflict of interest statement
None.
그 밖의 정보
출판 형태
Journal Article, Research Support, Non-U.S. Gov't
저널
Journal of the American Heart Association · eISSN 2047-9980
