Myocardial contraction patterns in non-ischaemic and ischaemic regions during acute coronary insufficiency

The effect of coronary insufficiency on the myocardial contraction pattern was studied in 11 thoractomized cats using apical long axis echocardiograms and cross-oriented segments in the anterior midwall. Myocardial tissue blood flow was studied using radiolabelled microspheres. After circumflex coronary artery occlusion, ejection shortening increased on average 17% for circumferential segments ( P <0⋅05) and 61% for longitudinal segments ( P <0⋅001). Hyperkinesis was also validated as augmented anterior endocardial wall motion and wall thickening. Circumflex occlusion increased end-systolic sphericity of the left ventricle ( P <0⋅05). Subsequent underperfusion of the left coronary artery, in two discrete steps, decreased subendocardial blood flow by, on average, 36% ( P <0⋅001) and 75% ( P <0⋅001) vs the post-occlusion value, while subepicardial flow did not change. While subendocardial blood flow decreased by 36%, systolic shortening of the global major axis decreased, by, on average, 77% ( P <0⋅001), shortening of the longitudinal segments by 36% ( P <0⋅001), and systolic shortening of the minor axis by 18% ( P <0⋅05), whereas shortening of midwall circumferential segments did not change. This study shows that changes in myocardial contraction in both non-ischaemic and ischaemic regions during coronary insufficiency are most pronounced in the direction of the cardiac major axis.