Mechanism underlying mechanical dysfunction in the border zone of left ventricular aneurysm: A finite element model study

Background. The global left ventricular dysfunction characteristic of left ventricular aneurysm is associated with muscle fiber stretching in the adja cent noninfarcted (border zone) region during isovolumic systole. The mecha nism of this regional dysfunction is poorly understood. Methods. An anteroapical transmural myocardial infarct was created by coron ary arterial ligation in an adult Dorset sheep and was allowed to mature in to left ventricular aneurysm for 10 weeks. The animal was imaged subsequent ly using magnetic resonance imaging with simultaneous recording of intraven tricular pressures. A realistic mathematical model of the three-dimensional ovine left ventricle with an anteroapical aneurysm was constructed from mu ltiple short-axis and long-axis magnetic resonance imaging slices at the be ginning of diastolic filling. Results. Three model simulations are presented: (1) normal border zone cont ractility and normal aneurysmal material properties; (2) greatly reduced bo rder zone contractility (by 50%) and normal aneurysmal material properties; and (3) greatly reduced border zone contractility (by 50%) and stiffened a neurysmal material properties (by 1000%). Only the latter two simulations w ere able to reproduce experimentally observed stretching of border zone fib ers during isovolumic systole. Conclusions. The mechanism underlying mechanical dysfunction in the border zone region of left ventricular aneurysm is primarily the result of myocard ial contractile dysfunction rather than increased wall stress in this regio n. (C) 2001 by The Society of Thoracic Surgeons.