The assessment of myocardial viability: a review of current diagnostic imaging approaches

The management of patients with coronary artery disease, both in the post-infarction setting, and in patients with chronic advanced left ventricular (LV) dysfunction, is complicated by the presence of both reversibly damaged and infarcted myocardium. Although acute revascularization with thrombolytic therapy and percutaneous angioplasty have served to reduce the overall mortality from myocardial infarction, the ability to predict whether or not dysfunctional myocardium will recoverfollowing revascularization presents the clinician with a serious challenge. The success of revascularization, both on improvement of LV function, and short and long-term prognosis, depends on both the existence and extent of viable but dysfunctional myocardium present, as there is little to be gained from revascularizing a territory consisting exclusively of scar. There is a clear demand for procedures that can identify reversible asynergy prospectively and thus deliver the information that is needed for clinical decision-making. The objective of this review is to summarize the diagnostic tools that are currently availablefor the identification of reversible injury (ie., stunned or hibernating myocardium). The relative merits of echocardiography, nuclear medicine imaging, and magnetic resonance imaging are discussed in detail. Within the discussion of each modality, special attention is paid to the more recent innovations that have arisen to enhance the diagnostic and prognostic value of older approaches. Cost, availability, and local expertise will always affect the clinical popularity of a given diagnostic approach. However, the overriding conclusion that emerges from this review is that the future "techniques of choice" will be those that can reliably predict and quantify the extent of potential functional recovery.