MRI quantification of regional variations in left ventricular wall stress in normal subjects.

The object of this study was to analyse regional variations in end systolic left ventricular wall stress in normal subjects using three-dimensional ma gnetic resonance imaging (MRI) with excellent spatial resolution. Eight to 12 contiguous short axis sections of the left ventricle were acqui red from the apex to the base in apnoea with a rapid echo-gradient sequence in 15 healthy volunteers. The end systolic wall stress was calculated by t hree methods : Grossman's formula (CR) using the wall thickness and radius of curvature, Janz's formula (CS) using the surfaces, and a three-dimension al approach (C3D) providing a precise calculation of the radius of curvatur e. The values of wall stress obtained by CS and CR were lower (p< 0.001) at th e apex (3.2 and 3.3 10(3) newton/m(2) respectively) than at the base (6.9 a nd 7.1 10(3) newton/mt). There was no difference between the base and apex with the C3D method (8.0 and 9.0 10(3) newton/m(2) respectively, NS). The s ame results were observed at the inferior, lateral, anterior and septal seg ments with an increase at the base using the CS and CR formulae, the C3D re maining homogenous in the left ventricle except for the interventricular se ptum. The lateral wall stress was significantly lower with respect to the i nterventricular septum in all sections from the apex to the base, irrespect ive of the method of calculation used. The differences in regional wall stress from the base to the apex reported in healthy subjects seem to be related to an underestimation of left ventri cular wall thickness and an underestimation of the radius of curvature rath er than to a physiological phenomenon.