SPA: An index for measuring changes in the shape of the left ventricle in two-dimensional echocardiography

Abstract

An index for measuring the changes in the shape of the left ventricle is proposed: the square of the perimeter divided by the area of the figure (SPA). The expected values for regular geometric figures are derived from first principles (SPA values for a circle and a prolate ellipse are 4π or 12.6 and 5π or 15.7, respectively). The SPA is unaffected by the size of the figure. The SPA of the left ventricle in normal children (10) and children with hypertrophic obstructive cardiomyopathy (HOCM) (7), congestive cardiomyopathy (3), and congenital heart disease (12) were determined using a planimeter and an opisometer on prints of two-dimensional echocardiograms (parasternal long-axis views). It was found that the shape of the normal ventricle during systole conforms to that of a prolate ellipse. This was also true in the children with congenital heart disease provided there was no marked right ventricular volume overload. The greatest distortions in shape were found in children with HOCM (highest SPA of 57.6). In children with congestive cardiomyopathy, the shape of the left ventricle approximates that of a circle, as shown by the SPA value of 12.6. Further research may unveil more clinical applications of this mathematical index. The SPA may become a simple and useful tool in quantitative two-dimensional echocardiography.