Metabolic and structural abnormalities in dogs with early left ventriculardysfunction induced by incessant tachycardia

Objective-To assess morphologic and metabolic abnormalities in dogs with ea rly left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP). Animals-7 Beagles. Procedure-Plasma carnitine concentrations were measured before and after de velopment of ELVD induced by RRVP. At the same times, transvenous endomyoca rdial biopsy was performed, and specimens were submitted for determination of myocardial carnitine concentrations and histologic, morphometric, and ul trastructural examination. Results-In 4 dogs in which baseline plasma total carnitine concentration wa s normal, RRVP induced a decrease in myocardial total and free carnitine co ncentrations and an increase in myocardial esterified carnitine concentrati on. In 3 dogs in which baseline plasma total carnitine concentration was lo w, plasma and myocardial carnitine concentrations were unchanged after paci ng. Structural changes associated with pacing included perinuclear vacuoliz ation in 3 dogs. Morphometric analyses indicated there was a decrease in my ofiber cross-sectional diameter and area following pacing. Electron microsc opy revealed changes in myofibrils and mitochondria following pacing. Conclusions and Clinical Relevance Results indicated that moderate to sever e alterations in myocyte cytoarchitecture are present in dogs with ELVD ind uced by RRVP and that in dogs with normal plasma carnitine concentrations, myocardial carnitine deficiency may be a biochemical marker of ELVD. Result s also indicated that transvenous endomyocardial biopsy can be used to eval uate biochemical and structural myocardial changes in dogs with cardiac dis ease.