Are changes in myocardial integrated backscatter restricted to the ischemic zone in acute induced ischemia? An in vivo animal study

Integrated backscatter (IB) from a myocardial region, calculated from radio frequency echocardiographic data, has been proposed as a useful parameter f or investigating changes in myocardial tissue induced by ischemia. In 10 cl osed-chest dogs, 5 minutes of myocardial ischemia was induced by either a p roximal occlusion of the circumflex coronary artery (CX) (5 dogs), resultin g in extensive ischemia in the posterior wall, or by occluding the distal C X vessel (5 dogs) to produce a small localized ischemic zone in the posteri or wall. High-resolution digital radiofrequency data from the whole left ve ntricular myocardium, in the imaging plane during one complete heart cycle, were acquired with a whole-image realtime acquisition approach. Regions in the septum and posterior wall (both ischemic tissue and, in the case of di stal occlusions, tissue surrounding the ischemic zone) were chosen for anal ysis, and IB and cyclic variation (CV) of IB were calculated. Post occlusio n, an increase in mean IB values was found in the ischemic segment. However an increase in CV was also observed in the peri-ischemic zone for the dist al CX occlusion and in the septum after proximal CX occlusion. These findin gs show that changes in CV are not restricted to the ischemic zone but may also occur in distal myocardium. This may be explained by changes in the re gional contractile state and loading conditions of the "normal" myocardium, which are altered in response to the distal ischemia.