The Relationship between Regional Integrated Backscatter Levels and Regional Strain in Normal, Acutely Ischemic, and Reperfused Myocardium

摘要

Integrated backscatter (IB) and its cyclic variation (CV) are echocardiographic parameters often used for myocardial tissue characterization. Prior work has suggested that IB is directly related to regional scatterer density while its CV could be induced by local myocardial strain. The purpose of this study was to further test this hypothesis by simultaneously recording cyclic changes in IB and myocardial strain in normal, acutely ischemic and reperfused myocardium. In ten closed-chest pigs, acute myocardial ischemia was induced by inflating a PTCA balloon in the left circumflex coronary artery. Ra-diofrequency (RF) M-mode data of the ischemic region of the posterior wall were acquired before, during and immediately after the balloon occlusion. IB and regional radial strain were estimated from the same RF data sets. End-systole was defined on a simulataneously recorded left ventricular pressure trace. The negative radial strain (NRS) was plotted on top of the IB curve. At baseline, both the NRS and IB pattern paralleled and showed to be minimum at end-systole. During acute ischemia, marked post-systolic thickening was observed which resulted in a post-systolic peak in both the NRS and IB traces: the overall minimum in both curves was phase shifted, i.e. time-delayed. Moreover, the mean IB level increased acutely. Finally, at reperfusion, both the NRS and IB patterns returned to baseline with a minimum at end-systole. However, NRS showed some remaining characteristics of acute ischemic myocardium in contrast to the IB pattern that merely showed a hyperemic but normal response. IB and NRS thus paralleled over the whole cardiac cycle in normal and acutely ischemic myocardium. At reperfusion the IB curve normalized immediately while the NRS showed some remaining ischemic characteristics. These observations are in concordance with the hypothesis that changes in integrated backscatter are induced by regional three-dimensional strain.