Abstract:
Background: Myocardial infarction is associated with reduction in regional shortening, whereas regional rotation is preserved within the infarct. In the border zone opposite to the direction of rotation, however, rotation is reduced and in the contralateral border zone rotation is increased. To determine the mechanism of the dissociation between strain and rotation we studied a group of patients with myocardial infarction and utilized an LV simulation model. Methods and results: In 17 patients with anterior myocardial infarction, confirmed by MRI, circumferential strain (strainC) and rotation were measured in the anterior infarct zone, septal and lateral border zones and posterior remote zone by 2-D speckle tracking echocardiography. The Figure shows that strainC was markedly reduced in the infarct zone and moderately reduced and equal in both border zones. In contrast, regional rotation was highest in the septal and lowest in the lateral border zone. An LV finite element model was used to simulate the cardiac cycle. Reduction of active fiber contractility in the infarct region caused reduced systolic shortening and a reduced pull on the septal and lateral border zones. Decreased pull on the septum in the counter-rotation direction allowed the septum to rotate the most. Decreased pull on the lateral wall in the direction of rotation caused the lateral wall to rotate the least. Conclusion: The simulation results suggest that the observed variation in regional rotation is due to impaired shortening in the infarct region, causing abnormal tethering effects on its neighboring regions. The findings imply that regional rotation may not be well suited to localize myocardial ischemia.
