Abstract
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Introduction: Myocardial perfusion imaging (MPI) by means of positron emission tomography (PET) allows for accurate quantitative assessment of myocardial blood flow (MBF) and myocardial flow reserve (MFR). Multiple non-pathological factors such as sex and age are known to alter flow values; however, universal hyperemic MBF and MFR thresholds are often used across all age groups in clinical practice. The purpose of this study is to characterize normal values of hyperemic MBF and MFR evaluated by PET MPI with Rubidium-82 and dipyridamole in subjects with low risk of coronary artery disease (CAD), accounting for sex and age.
Methods: This is a single-center database retrospective study of patients who underwent a Rubidium PET MPI at the Montreal Heart Institute (MHI) between 2017 and 2020. Patients with low CAD risk, defined as normal Rubidium MPI (Summed Stress Score, SSS <3) with calcium score of 0 and without prior history of infarction, revascularization, or insulin dependent diabetes, were identified in the MHI PET clinical database. A total of 1463 patients met inclusion criteria and were included in the analyses. Patients were divided into 10 groups based on sex and age (≤50, 51-60, 61-70, 71-80, and ≥81 y). Lower thresholds for normal values of each group were defined by computing the 5th percentile of the hyperemic MBF and MFR distributions using the Hoffmann method. MBF and MFR values are presented as median (interquartile range). Corrected MFR values were corrected for resting rate-pressure product (RPP) using a reference resting RPP of 8400.
Results: Median resting MBF, hyperemic MBF, MFR, and corrected MFR for both sexes and age groups are presented in Table 1. Hyperemic MBF were negatively correlated (Fig. A) with age for females (r=0.352, p<0.001) and males (r=0.421, p <0.001). Global hyperemic MBF thresholds for normal values were 2.70, 2.37, 2.23, 1,91, 1.58 mL/min/g in females and 2.24, 2.05, 1.75, 1.33, 1.18 mL/min/g in males for the age group ≤50, 51-60, 61-70, 71-80, and ≥81 y, respectively (Fig. B). Global MFR thresholds for normal values were 2.33, 2.11, 1.75, 1.55, 1.38 in females and 2.28, 2.23, 2.31, 1.48, 1.21 in males for the age group ≤50, 51-60, 61-70, 71-80, and ≥81 y, respectively. Global corrected MFR thresholds for normal values were 2.11, 1.94, 1.87, 1.59, 1.67 in females and 1.88, 1.51, 1.71, 1.27, 1.35 in males for the age group ≤50, 51-60, 61-70, 71-80, and ≥81 y, respectively (Fig. C). Overall, hyperemic MBF (p <0.001) and MFR (p=0.021) were higher in females vs males.
Conclusions: We characterized normal hyperemic MBF and MFR threshold values based on sex and age group in low CAD risk patients. Overall, females had higher hyperemic MBF and MFR compared to male, for all age groups. Hyperemic MBF and MFR decreased with increasing age for both males and females. Sex and age should be taken into consideration when analyzing hyperemic MBF and MFR values.
