Assessment of myocardial viability in patients with postischemic left ventricular dysfunction: role of myocardial contrast echocardiography.
The distinction between viable and nonviable dysfunctional left ventricular (LV) segments after acute myocardial infarction is very important, because revascularization increases survival only in patients with viable myocardial tissue. Recent studies have highlighted a mismatch between two highly specific investigations for viability assessment: dobutamine echocardiography, which measures inotropic reserve, and myocardial contrast echocardiography (MCE), which measures microvascular perfusion. Viability and functional reserve are not synonymous. Maintenance of microvascular perfusion, independently of functional reserve, attenuates left ventricular remodelling, reduces the risk of major cardiac events, and increases survival. MCE provides similar perfusion information as myocardial blush, but image quality is much higher. Quantitative analysis of digital data provides more accurate diagnostic MCE information than qualitative analysis of video signal intensity. In a recent study relating MCE findings to histologic data, MCE-derived quantitative data were closely correlated with microvascular density and capillary area, and inversely correlated with collagen content. One of the contrast agents routinely used for MCE is SonoVue, a second generation microbubble contrast agent, which is characterized by high response to ultrasound energy, ease of destruction at high energy, and strong harmonic signal at low energy. Recommendations for the assessment of postischemic LV dysfunction: routine use of MCE, followed by dobutamine echocardiography if perfusion is documented. If MCE is negative, revascularization is not indicated; if both tests are positive, revascularization is strongly recommended; if they are discordant, useful information can be obtained by assessing the extent of 201T1 viability.