Ratio of infarct subtended volume to surface area by 3-D echocardiography: in vivo measurement of infarct dilation and aneurysm formation

Measurement of myocardial infarct size, aneurysm formation and LV remodeling may provide valuable data for assessing therapy and prognosis. 2D echo methods estimating these are based on geometric assumptions of LV size and shape and assumptions of image position and orientation. To eliminate these the authors have developed a nongeometric method using an unconstrained 3D echocardiograph composed of a real-time scanner, an acoustic spatial locater and a personal computer. Its novel feature is use of a line of intersection display-the display of the common line of intersection of a reference image and the real-time image. This line is rapidly re-computed and re-displayed in each image during scanning. It is used to eliminate image plane positioning errors by guiding acquisition of 8-10 short axis images of the LV to completely define the ventricle and infarct margins. Chamber boundaries are traced and infarct margins are marked on the appropriate boundaries. 3D reconstruction is then carried out by a polyhedral surfacing algorithm and volumes and surface areas are computed The in vitro accuracies for computation of ventricular volume, total endocardial surface area and `infarct´ surface area are 1-4%. In vivo standard error for ventricular volume is 4-7 ml. and for total endocardial surface area is 5-8 cm<sup>2</sup> when compared to MRI. Changes of ventricular volume provide a global estimate of infarct size and remodeling. The ratio of `infarct´ surface area to total endocardial surface area also provides a useful estimate of infarct size. The authors have recently extended their algorithm to compute the volume subtended by the infarct to estimate infarct dilation. The chords joining the margins of the infarct in each image are defined. The tetrahedron volume computation algorithm is then applied to these new boundaries and the infarct subtended volume computed. The ratio of infarct subtended volume to infarct surface area will increase as the infarct dilates providing an index of aneurysm formation independent of the degree of ventricular enlargement and remodeling. In conclusion: 3D echo provides a new, quantitative clinical index of infarct dilation for assessment of therapy