Dr. Frank Rademakers,
Prof. Schwitter stressed the fact that severe stenotic lesions have a higher risk for obstruction, causing an acute coronary syndrome (ACS), and therefore require treatment. CMR perfusion is a good technique to identify these patients with regional ischemia and decide on treatment with revascularisation. In ACS patients, there are usually several ruptures occurring at the same time without all of them causing myocardial infarcts. These silent ruptures can contribute to sudden increases in lesion stenosis grade. Ruptures in higher grade lesions will lead more often to complete occlusion and thus ACS. Targeting these lesions makes more sense from a prognostic perspective and improves outcome of the patient. Perfusion imaging is thus a strong prognostic factor for infarction, but overall presence and severity of coronary lesions is as well. What perfusion imaging has to offer in addition is the quantification of ischemia, which is the area subtended by the lesion, but also the possible extent of myocardial infarction in case of an occlusion of that lesion. CMR can thus guide by itself the management of patients with stable angina, without the risk of radiation and without the need for anatomic information (until an intervention is required). Since there is a very strong correlation between the presence and extent of ischemia and the occurrence of ACS (natural history of the lesion), one can relate that to the known risks of interventions by CABG, bare or drug eluting stents and thus decide on treatment options.
Anatomy remains important since a test in stable patients requires accuracy, prognostic power and documented impact on treatment. Over the years we moved from anatomy and the need for surgical revascularization to more focus on perfusion with choice for revascularization only in patients with moderate to severe ischemia (but this is not tested in RCTs) to, more recently, a strategy which requires complete revascularization, as this carries the best prognosis. He argues that the extent of coronary disease has a major impact on outcome by determining the choice of revascularization. Moreover, he strongly made the point that perfusion imaging requires absolute but not relative perfusion assessment (as in SPECT) in the setting of multivessel disease, thus limiting the use of this non-invasive test in the setting of severe, extensive ischemia. On the other hand, coronary CT has a very high negative prognostic power in the absence of significant lesions. Moreover there is a strong relation between number of diseased vessels and outcome as well, making CT a technique with an excellent negative predictive value but also a strong positive predictive power. Confronted with patients with an intermediate pre-test risk, one could go for a functional or a CT: he tested this in a group of patients and found that CT can make a more clear-cut distinction between patients requiring further diagnostic workup and/or referral to the cathlab and those patients who can be sent home. Non-invasive testing, and certainly exercise stress testing, is not able in this group of intermediate pre-test risk to make this distinction and often requires further functional or anatomic testing to come to a final treatment and therapeutic decision. Therefore, he argues that CT is a good choice for the workup of patients with intermediate pre-test risk. Furthermore, anatomic knowledge is always needed to discern between left main and 3VD, diffuse versus local disease, to identify multiple lesions per vessel, to unmask collateral circulation, etc. FFR guided therapy is known to be better than angiographic information alone to guide invasive therapy, but FFR is in some way anatomy guided itself and certainly invasive. In the following discussion, several more points were made to stress the importance of quantification of perfusion rather than relative testing as done with SPECT, since that carries problems for proper diagnosis in 3 vessel disease and left main disease. PET can achieve this, but CMR as well is showing a good track record so far. A remark from the audience focused on the CASS results which cannot be extended to the present day since the medical treatment has changed tremendously and this impacts on the interpretation of the results. Also the interference by the presence or not of decreased LV function (EF) should be taken into account. There remains some difference in opinion about the absolute number of occlusions in tight versus intermediate lesions, but the data certainly support the higher rate of plaque rupture and occlusion in significant lesions; it depends on the difference in these rates and the relative occurrence of these type of lesions, and these have not been fully elucidated. Anyhow, since we do not have a focal treatment available for treating intermediate lesions (only a more aggressive general preventive attitude), to make a decision on intervention or not, the knowledge on the presence and severity of ischemia is crucial.
Imaging in stable angina
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