Fundamental concepts in myocqrdial viability assessment revisited: when knowing how much is 'alive' is not enough

摘要

In recent years, it has become evident that myocardial dysfunction in ischaemic heart disease is not always a result of infarction and that contractile function can improve significantly after revascularisation. A number of non-invasive techniques have been developed in an attempt to identify these patients with dysfunctional but viable myocardium, since it is generally agreed that it is this group, as compared to the group with irreversible myocardial damage, that has a favourable clinical risk-to-benefit profile for undergoing coronary revascularisation. The primary aim of these non-invasive techniques is to provide a regional map of the heart in which the amount of viable myocardium is quantified. Unfortunately, currently available techniques, such as single photon emission computed tomography (SPECT), dobutamine stress echocardiography (DSE), and positron emission tomography (PET), have various limitations. For example, what is measured may not be the direct presence and exact quantity of viable myocytes, but a physiologic parameter, such as contractile reserve or perfu-sion, that has only an indirect relation to viability. Other limitations related to the specific technique include partial volume effects due to poor spatial resolution (SPECT, PET), attenuation and scatter artefacts (SPECT), errors in registration between comparison images (DSE), and the occasional inability to visualise all parts of the left ventricular myocardium (DSE).