Traditional approaches for risk assessment of ischemic heart disease are based on the physiological consequences of an epicardial coronary stenosis. Of note, normal coronary arteries or non-obstructive coronary artery disease is a common finding in women with signs and symptoms of ischemia [4], in our study we found out a fair number of males being affected by non-obstructive coronary artery disease about 86% of the affected, even though most of the study population were male, we wanted also to get a different perspective as more studies were done to female like a WISE study (Women Ischemia Syndrome Evaluation) [5,6,7,8,9], we also found out a fair number of patients had hypertension about 50%, few had diabetes mellitus 16 and 17% had both hypertension and diabetes mellitus, and those without hypertension and diabetes mellitus were 17%. What we have learned is that sometimes we need to think beyond our capacity in order to achieve the goal which is an accurate diagnosis, we have seen patients who presented with classical angina symptoms with ECG findings supporting ischemic changes but coronary angiography revealing TIMI III flow which means normal coronary flow, this means most of us clinicians when we get such results we believe the patient doesn’t have ischemic cardiac disease meaning no obstructive coronary artery disease but on further assessment and investigation with PET/CT scan we find out there is reduced coronary flow reserve reflecting the presence of non-obstructive coronary artery disease. There is one patient who had both risk factors hypertension and diabetes mellitus, but his CFR was normal but those who were smoking and had hypertension were mostly affected with an average CFR of 1.2, and there those who had no history of smoking, no hypertension and not diabetic but were symptomatic had a reduced CFR about 25%.
Coronary flow reserve is a non-invasive measure of coronary vasomotor function that integrates the hemodynamic effects of epicardial coronary stenosis, diffuse atherosclerosis and microvascular dysfunction on myocardial tissue perfusion [10] CFR can be measured non-invasively by PET, transthoracic Doppler echocardiography and cardiac MRI, in our study we chose PET because dynamic PET imaging affords robust and reproducible measurements of absolute myocardial blood flow (MBF) in ml/min/g at rest and during pharmacological stress which allows the calculation of CFR (defined as a ratio between MBF at stress and MBF at rest [10, 11]). For N-13 ammonia and Rb-82 tracers, CFR less than 2 is considered abnormal [12]. In our study we found out that 58% of our study population had reduced CFR of less than 2 of which they had normal CAG thus confirming the diagnosis of microvascular coronary artery disease and showing the high sensitivity of PET in diagnosing such condition supporting the literature.
Our study reveals the role of PET/CT in diagnosing microvascular coronary artery disease, irrespective of the natural history of the disease and other investigation findings, we should have high suspicion index on how to go further especially when we suspect the diagnosis of microvascular coronary artery disease, in so doing we will appropriately give the perfect management of such patients otherwise we might lose them, as they may have poor prognosis when they are not appropriately treated, as evidently in WISE study which showed that after 10 years follow up, cardiovascular death or myocardial infarction occurred in 6.7% of women with no evident coronary artery disease, and in 12.8% of those with non-obstructive coronary artery disease [13].
Hypertension and dyslipidemia are predictors of low coronary flow reserve irrespective of the concomitant effect of potential confounders. The CFR is often altered in arterial hypertension because of increased afterload or abnormalities of the LV structure (such as LVH) and function. The CFR is also reduced in patients with hyperlipidemia [14], this is in relation to our study were almost all patients with hypertension (n = 4 out of 5) 33.3% had low CFR and all patients who had dyslipidemia 16.6% had also low CFR thus concurring with the literature. We also found out all 41.6% of patients who had abnormal LV wall motion had low CFR, CFR is more sensitive than abnormal regional wall motion. However, the data for flow and function can be complimentary in terms of predicting underlying angiographic anatomy, because abnormal wall motion can include coronary artery disease and a normal CFR can exclude it [15].
