Transmural heterogeneity of myocardial contraction and ischemia. Diagnosis and clinical implications.

ABSTRACT

Myocardial contraction behaves heterogeneously, being greater in subendocardial than in subepicardial layers. Similarly, during acute myocardial ischemia or infarction, the subendocardium is the first myocardial layer to suffer. Conventional two-dimensional echocardiography cannot distinguish the transmural extension of myocardial ischemia or infarction, showing akinesia also when only the subendocardium is affected. Novel ultrasonographic techniques (like tissue characterization with integrated backscatter or Doppler tissue imaging) and nuclear magnetic resonance tagging can investigate myocardial contraction in different transmural layers and distinguish subendocardial from transmural ischemia or infarction. With the advent of thrombolysis and primary angioplasty in the acute phase of myocardial infarction a correct diagnosis of the extension of myocardial necrosis cannot ignore its transmural wavefront development. The salvage of the subepicardial layer does not give direct information on overall myocardial thickening but is one of the major determinants of overall left ventricular dysfunction and size. Although it is still necessary to investigate this phenomenon, new ultrasonographic techniques give us important information and more opportunities to appropriate diagnosis and future treatment of cardiac patients.