Absolute stress myocardial blood flow is reduced in patients with prior cardiac disease despite normal perfusion and ejection fraction on rubidium-82 PET: an Arabian Gulf cohort

Purpose Rubidium-82 (⁸ 2 Rb) PET is typically interpreted using perfusion category and left ventricular ejection fraction (LVEF), but absolute myocardial blood flow (MBF) and flow reserve (MFR) may add information. We investigated whether absolute stress MBF differs between patients with and without prior cardiac disease when studies appear normal, in an Arabian Gulf population with high rates of diabetes and obesity. A secondary exploratory aim compared quantitative parameters between predefined PET categories. Patients and methods This retrospective single-centre study included 292 source-verified patients (mean age 63.1 ± 12.1 years; 56.8% male) who underwent adenosine-stress ⁸ 2 Rb PET/CT, classified by the PET C-category system. The primary analysis compared, within normal-appearing studies (C1 perfusion with resting LVEF ≥ 50%; n = 84), those with prior cardiac disease ( n = 38) and those without ( n = 46). A secondary exploratory analysis compared these same 46 patients (Normal) with the remaining 246 (Abnormal). Analyses used Mann–Whitney U tests with Cohen's d and 95% confidence intervals, with Bonferroni correction. Results Among normal-appearing studies, patients with prior cardiac disease had lower global stress MBF (2.25 vs. 2.99 mL/min/g; d = −0.78, 95% CI −1.22 to −0.33) and lower RCA stress MBF (2.25 vs. 3.29; d = −1.02, −1.47 to −0.56); rest MBF was also lower (d = −0.47, −0.91 to −0.04), whereas MFR (d = −0.37, −0.80 to 0.07), LVEF and LV volumes did not differ. In the secondary comparison, stress MBF and MFR separated the predefined categories comparably (DeLong Z = 0.89, p = 0.372) and both more strongly than LVEF (Z = 3.54, p < 0.001); because the categories are defined in part by these parameters, this represents relative separation within the classification scheme and not diagnostic accuracy. Conclusions In this Arabian Gulf cohort, patients with prior cardiac disease had lower absolute stress MBF despite normal perfusion category and ejection fraction. These exploratory findings support further prospective evaluation of absolute stress MBF as an adjunct to conventional PET interpretation. Because rest and stress flow fell together with a preserved ratio, and because haemodynamic, medication and infarct-related explanations could not be excluded, no mechanism is inferred.