COMPARISON OF IN-VIVO CARDIAC-FUNCTION WITH EX-VIVO CARDIAC-PERFORMANCE OF THE RAT-HEART AFTER THORACIC IRRADIATION

The aim of the study was to compare in vivo cardiac function with ex v ivo cardiac performance after local heart irradiation in the same rat. Left ventricular ejection fraction (LVEF) was measured in vivo by rad ionuclide ventriculography in Sprague-Dawley rats up to 16 months afte r a single dose of 20 Gy. Four days after in vivo measurements, cardia c performance was determined ex vivo, using the isolated working rat h eart preparation. After irradiation, cardiac performance measured ex v ivo deteriorated more rapidly than the in vivo measured LVEF. Within 4 months post-treatment, ex vivo cardiac output and stroke volume start ed to decrease and declined continuously throughout the observation pe riod of 16 months. The reduction in stroke volume was already signific ant (p < 0.04) at 4 months post-treatment, whereas the decline in card iac output was significant (p < 0.05) at 12 months post-treatment. In vivo, no change in LVEF was observed during the first 12 months post-t reatment. Thereafter, LVEF decreased rapidly from 65+/-2% to 46+/-8% ( p < 0.01), at 16 months post-treatment. Up to 12 months post-irradiati on, LVEF was not correlated to ex vivo cardiac output. At 16 months po st-treatment, when clinical symptoms of heart failure become evident, a positive relation between both parameters was found. The lack of cor relation between the in vivo and ex vivo measurements of cardiac funct ion during the first 12 months post-treatment might be explained by th e involvement of compensatory mechanisms being operative in vivo to ma intain sufficient cardiac output.