Witnessing ischemia or proofing coronary atherosclerosis: two different windows on the same or on different pathways precipitating cardiovascular events?

Risk stratification and prevention of future cardiac events is an extremely relevant part of the daily medical practice in the large population of asymptomatic or scarcely symptomatic patients. The strategies available to this purpose encompass programs intended either to reduce progression and complications of atherosclerosis, and revascularization procedures aimed to reduce total ischemic burden. The former represents a primary prevention approach and fights the substrate of ischemic heart disease. The latter, instead, is used to reduce the total ischemic burden and thus implies to identify those patients in whom ischemia can be life threatening because of its severity and extension. Today, at least two imaging methods are available for this task: coronary calcium scoring by x-ray CT and ischemia assessment by myocardial perfusion imaging. Although both approaches can accurately estimate cardiovascular risk, from a theoretical point of view, the assessment of ischemia evaluates the functional consequences of coronary obstructions and thus the target of revascularization procedure, while estimating the total atherosclerotic burden represents an indirect index of it. This difference might appear academic in its nature, given the current model of ischemic heart disease pathophysiology that assumes and predicts a very tight correlation between the severity of a coronary stenosis and its capability to cause ischemia. However, the majority of studies focused on the combined risk assessment with both approaches confirm the relevance of this issue. In fact, among 7785 patients reported in the literature, coronary calcium scoring most often resulted in positive findings (78%). However, this sign of atherosclerosis was associated with inducible ischemia in only one-fifth of patients. In the near future, coronary calcium scoring will be easily and immediately completed by the noninvasive definition of coronary stenoses. At that time we will face a still largely unknown risk: the presence of a stenosis in the absence of symptoms and of ischemia. Evaluating the effectiveness of different protocols will thus be needed to improve our capability to help these patients.