Effects of left heart assist on geometry and function of the interventricular septum

Right ventricular (RV) dysfunction is a common but poorly understood problem associated with mechanical left heart assist (LHA). Left ventricular unloading may affect RV function even in normal hearts by altering geometry or function of the interventricular septum, although such changes have not been well defined. Accordingly, the purposes of this study were to quantify the effects of LHA on septal geometry and function in normal swine and to assess the resultant effects on RV function.

Domestic swine (50 kg, n = 10) were anesthetized and instrumented for collection of physiologic data and for open-chest LHA, which was accomplished by left atrial to subclavian artery bypass using a centrifugal pump. Both global and regional RV function data as well as two-dimensional echocardiographic data of septal geometry and function were collected at control levels and during both partial and full LHA. Short-axis echocardiographic images were obtained at the midventricular level and analyzed to quantify septal curvature (k; cm-1), systolic septal thickening (%), and systolic septal excursion (cm).

Partial LHA had no effect on either septal geometry or function. Full LHA resulted in decreased diastolic septal curvature (k = 0.10 +/- 0.07 versus 0.42 +/- 0.06 at control; p < 0.05), reduced systolic septal thickening (0.27 +/- 5.23 versus 29.32 +/- 8.61 at control; p < 0.05), and reversed leftward systolic septal excursion (-0.29 +/- 0.11 versus 0.11 +/- 0.03 at control; p < 0.05). End-diastolic septal position was shifted leftward during full LHA compared with control, but was associated with rightward systolic motion of the left ventricular mass and septum as a unit. There were no changes in global or free-wall RV function during either partial LHA or full LHA compared with control.

Left heart assist results in marked changes in both geometry and function of the interventricular septum in normal hearts. These changes, however, do not appear to be associated with changes in either global or regional RV function. Evaluation of the septum with echocardiography may be helpful in defining strategies for clinical application of this technology.