Overestimation of infarct size by quantitative two-dimensional echocardiography: the role of tethering and of analytic procedures.

Analyses of regional left ventricular systolic wall motion or thickening overestimate infarct size. We used quantitative two-dimensional echocardiographic analysis of systolic thickening and contrast two-dimensional echocardiography to evaluate causes for that overestimation. The following possibilities were considered: "tethering," defined as dysfunction of contrast-enhancing myocardium adjacent to ischemic or contrast-negative regions, and the role of standard center of mass analysis algorithms, which may overestimate wall motion abnormalities because of the axis shift produced by simultaneous systolic expansion of the ischemic segment and systolic contraction of the nonischemic segment. In the short-axis view in 12 animals, the echo contrast defect (ECD) occupied 32 +/- 7% of the left ventricular circumference. Extent of dysfunction by the center of mass analysis was 39 +/- 5% of the left ventricular circumference and correlation with ECD size was .68 (SEE = 5.2%). Thus 8 +/- 6% of the circumference of the left ventricle was assessed to be dysfunctional yet enhanced with contrast. Tethering accounted for only half of this (4 +/- 4% of left ventricular circumference) and involved less than 1 cm on either side of the ECD. The remaining overestimation by the center of mass analysis correlated significantly (r = .89, p less than .01) with the amount of systolic expansion of the ECD. This expansion of the ECD (increase in angle subtended by the ECD of 11 +/- 8%) was produced by the systolic shift in the center of mass toward the dysfunctional segment from contraction of the opposite, nonischemic segment.(ABSTRACT TRUNCATED AT 250 WORDS)