OPTIMIZATION OF LV GEOMETRIC MODIFICATIONS

Abstract

Devices that modify left ventricular geometry by creating a bi-lobed ventricle to reduce wall stress are being developed as a treatment for dilated cardiomyopathy. Similar to these devices, left ventricular reduction surgery (LVRS) modifies ventricular geometry and consequently wall stress, but has had mixed clinical results. To evaluate the maximum functional benefit of geometrical modification devices (GMD) a simple analytical model of ventricular geometry modification was developed and coupled to numerical optimization techniques. The wall tension-length relations were determined from the pressure-volume characteristics of the dilated ventricle and these myocardial properties were then used to predict cardiac function following application of a GMD or LVRS. The model predicts both types of modifications cause increased end-systolic elastance and decreased diastolic compliance, consistent with reported animal experiments. Analysis of a dilated ventricle with an initial ejection fraction (EF) of 10% predicted a maximum stroke volume increase of 47% and 14% for a GMD and LVRS respectively. A ventricle with a 17% EF, under identical loading conditions, with the corresponding optimized GMD showed a 6% increase in stroke volume, however any extent of LVRS decreased the stroke volume. The results show optimum GMD application and LVRS are dependent on the systolic and diastolic properties of the dilated ventricle. Matching the extent of modification to the specific LV is needed if acute function is not to be degraded.