A recent study by Dr. Knott, published in Circulation, have shown the prognostic value of measuring myocardial blood flow (MBF) using artificial intelligence quantification of cardiovascular magnetic resonance (CMR) perfusion mapping in cardiovascular outcomes. According to this study, both MBF and myocardial perfusion reserve (MPR) were associated with death and major adverse cardiovascular events (MACE) independently of other clinical risk markers. Using this technique, quantitative analysis of myocardial perfusion for clinical use is now available.
Cardiovascular disorders, in particular, coronary artery disease are the leading causes of morbidity and mortality globally. Myocardial blood flow is a reflection of the coronary circulating system and its reduction is the culprit mechanism for acute and chronic coronary syndromes. Although current international guidelines recommend the quantitative measurement of coronary blood flow, the available assessment tools either are invasive or their prognostic value is still unclear. Using the perfusion mapping approach, the non-invasive, qualitative CMR system is now able to evaluate the MBF quantitatively. However, its prognostic significance in cardiovascular outcomes should be determined.
In a two-center, prospective study, patients with a suspected or known history of coronary artery disease referred for perfusion imaging studies. Patients with a diagnosis of infiltrative or inherited cardiomyopathy were excluded from the study. Using electronic patient records and other similar resources, patient comorbidities and outcomes were collected. All-cause mortality and MACE were considered the study outcomes. The study included 1049 patients who were followed for a median duration of 605 days. CMR scan was done in all the participants and perfusion maps were generated and MBF and myocardial perfusion reserve, known as the ratio of stress to rest MBF, were calculated.
In total, there were 42 (4%) deaths and 188 MACE in 174 (16.6%) patients. Myocardial perfusion markers were independently associated with MACE and death. For each unit decrease in MBF, the adjusted hazard ratio (HR) for death and MACE was 1.93 (95% CI 1.08-3.48, P=0.028) and 2.14 (95% CI 1.58-2.90, P<0.0001) respectively, findings that remained similar even after adjusting for age and other co-morbidities. Each unit decrease in MPR resulted in adjusted HR 2.45 (95% CI 1.42-4.24, P=0.001) for death and 1.74 (95% CI 1.36-2.22, P<0.0001) for MACE. MPR and MBF have been also demonstrated to be associated with death and MACE in patients without the evidence of regional perfusion defects on the clinical read.
Although the prognostic value of myocardial perfusion has been previously shown using Positron Emission Tomography (PET) scan, this study confirmed it through a different approach and by implicating a non-ionizing radiation technique which makes it favorable to previous studies. This study also demonstrated the superiority of MPR over stress MBF in predicting cardiovascular death. The possible explanation for the observed association between impaired myocardial perfusion and worse outcomes may be a mixture of coronary disease and microvascular dysfunction.
This study is limited by some points that are worthy of mentioning. Firstly, There may be confounding factors that were not adjusted for. Secondly, there is a possibility that some events were missed in the medical records of patients. Data from this study provide a new targetable risk factor in the management of patients with coronary artery disease.