Quantification of Myocardial Mass by Cardiac Computed Tomography: A Tool for Preprocedural Planning of Coronary Revascularization

In patients with stable angina, after initial triage and testing and an indication for further risk stratification and revascularization, invasive coronary angiography is performed. If intermediate coronary lesions are observed (defined as 40%–90% diameter stenosis), invasive coronary flow measurements are performed, fractional flow reserve (FFR) being a gold standard for the assessment of hemodynamic significance of coronary lesions.1,2 There is a wide variation in the extent and severity of coronary atherosclerosis in patients with stable coronary artery disease (CAD). Although the treatment of focal significant proximally located coronary lesions is straightforward, this may not be the case in patients with a more complex and extensive CAD or when lesions involve the side branches or more distal parts of the coronary arteries. This results in a wide variation of therapeutic decisions between the operators, often resulting in not performing revascularization of some lesions with a belief that the arteries perfuse a small myocardial mass.3 Moreover, the result of FFR that is used to determine the lesion severity is dependent not only on the severity of coronary stenosis but also on the amount of the viable myocardium perfused by a given artery. Indeed, vessels perfusing a larger myocardial mass have lower FFR values, whereas lesions of the same significance and smaller mass of viable myocardium result in higher FFR values.4 Calculation of myocardial mass also enhances our understanding of microvascular dysfunction, demonstrating lower myocardial mass in patients with structural coronary microvascular dysfunction.5 It is not possible to directly correlate myocardial perfusion defects on noninvasive ischemia testing to the coronary artery anatomy, and the information about the coronary anatomy and function is mentally linked by the interpreting physician. Also, due to technical reasons myocardial territories perfused by smaller coronary arteries or side branches of the main vessels might not show ischemia on the noninvasive ischemia testing and those lesions could be interpreted as insignificant. Nevertheless, even keeping this in mind, vessel-specific myocardial mass is not routinely assessed before coronary artery interventions, although this information could potentially contribute to more standardized and more accurate treatment decisions in patients with stable CAD. The assessment of myocardial mass with contrast enhanced computed tomography (CT) with a high special resolution and direct visualization of coronary arteries in the same scan could prove to be superior to traditional noninvasive ischemia detection by nuclear imaging or magnetic resonance imaging.