ULTRASTRUCTURAL ALTERATIONS IN THE RIGHT AND LEFT-VENTRICULAR MYOCARDIUM FOLLOWING MULTIPLE LOW-ENERGY ENDOCARDIAL COUNTERSHOCKS IN ANESTHETIZED DOGS

SCHIRMER, U., ET AL.: Ultrastructural Alterations in the Right and Lef t Ventricular Myocardium Following Multiple Low Energy Endocardial Cou ntershocks in Anesthetized Dogs Both high energy transthoracic and dir ect epicardial defibrillation can result in RV and LV myocardial damag e, but little is known about the damage due to defibrillation using an endocardial RV electrode. Furthermore, disturbances in postdefibrilla tion oxidative metabolism have been reported and may be caused by prim ary injury of mitochondrial integrity and function, but information ab out ultrastructural mitochondrial alterations is rare. We therefore st udied, in 13 fox hounds, RV and LV ultrastructural alterations followi ng multiple low energy endocardial countershocks. Using an ICD and an endocardial defibrillation system a median of 54 (43-74) countershocks with a cumulative energy of 1,558 J (844-2, 141 J) was delivered. Aft er termination of countershocks, RV and LV myocardium was examined by electron microscopy. In both ventricles, severe myocardial alterations were found, including swollen mitochondria, disruption of mitochondri al crests, and loss of integrity of the mitochondrial inner and outer membranes. At the first time a semiquantitative score, originally deve loped for postischemic injury, was successfully used to grade the post countershock mitochondrial alteration, which showed a more pronounced damage in the RV (2.69 +/- 0.22 points) compared to the LV (2.18 +/- 0 .22; P = 0.021). We conclude that even the use of endocardial lead sys tems with low energy countershocks may lead to severe mitochondrial da mage, especially in the RV.