[A model analysis on the effects of left ventricular hypertrophy and dilatation on pump function and myocardial force...

The effects of hypertrophy and dilatation on myocardial force and shortening were analysed using Wong's formula for equatorial midwall stress in a thick-walled ellipsoid of revolution. Wall thickness, chamber volume and ejection fraction were treated as independent variables. An isolated increase in wall thickness reduces wall stress and, to a lesser extent, myocardial fiber shortening, i.e. myocardial function is overestimated from ventricular pressures and ejection fraction. Ventricular dilatation without a proportional increase in myocardial mass leads to an increase of myocardial force and shortening, i.e. myocardial performance is underestimated from ventricular function. A decrease of ejection fraction increases total systolic myocardial force considerably, leading to a shift to the right on the inverse relation of force and shortening. Therefore the efficiency of myocardial contraction is reduced and myocardial performance is better than ventricular pump function would indicate.