ALTERATIONS IN MYOCYTE SHAPE AND BASEMENT-MEMBRANE ATTACHMENT WITH TACHYCARDIA-INDUCED HEART-FAILURE

Chronic supraventricular tachycardia (SVT) results in left ventricular (LV) dilatation and dysfunction. However, the underlying mechanisms responsible for LV failure in this setting are not known. LV force production is dependent on the coupling of myocytes to the extracellular matrix, which is mediated through the basement membrane. This study was designed to determine whether alterations in myocyte geometry and basement membrane attachment are associated with LV failure in a pacing-induced model of cardiomyopathy. Echocardiographic measurement of LV function was performed in six pigs after 3 weeks of pacing-induced SVT (240 beats/min) and in eight sham-operated controls. Myocytes from these hearts were isolated, and attachment studies to specific components of the basement membrane were performed using laminin, fibronectin, and collagen IV. The SVT group when compared with the control group showed a significant reduction of LV fractional shortening (14 +/- 2% versus 31 +/- 2%, respectively; p < 0.05), increased end-diastolic dimension (50 +/- 1 versus 35 +/- 1 mm, respectively; p < 0.05), and lengthening of isolated myocytes (196 +/- 18 versus 142 +/- 9-mu-m, respectively; p < 0.05). Myocyte attachment to laminin (50-mu-g/ml) was significantly decreased at 60 minutes in the SVT group compared with the control group (18.2 +/- 4.5 versus 60.9 +/- 4.5 cellS/mm2, respectively; p < 0.05). Similar reductions in myocyte attachment to fibronectin and collagen IV were observed. Ultrastructural examination of LV sections revealed focal disruptions of the basement membrane-sarcolemmal interface and a reduced number of sarcolemmal festoons in SVT hearts compared with control hearts (0.8 +/- 0.6 versus 2.8 +/- 0.8/4-mu-m, respectively; p < 0.05). These alterations in myocyte morphology and basement membrane attachment may contribute to the LV failure associated with chronic SVT. Further, these structural changes may play a significant role in the progression of ventricular dysfunction as well as recovery from chronic SVT.