Inadequate coronary adenosine response is a potential cause for false negative myocardial perfusion in cardiac stress magnetic resonance imaging (CMR). Recently, the splenic switch-off (SSO) sign has been identified as a promising tool to assure efficacy of adenosine.
We assessed the value of SSO to predict adenosine response, defined as an increase in myocardial blood flow (MBF) during quantitative myocardial perfusion 13N-ammonia positron emission tomography (PET).
Patients who underwent simultaneous CMR and 13N-ammonia PET myocardial perfusion imaging on a hybrid PET/MR device (Signa PET/MR, GE Healthcare) were included. Co-injection of Gadolinium-based contrast agent and 13N-ammonia was performed during rest and 3 minutes into standard adenosine stress. Patients with a myocardial flow reserve (MFR) of >1.5 or ischemia as assessed by PET were considered as true coronary adenosine responders. The presence or absence of SSO was visually assessed and relative CMR signal intensity increase between adenosine-induced stress and rest was calculated for spleen and myocardium. Consequently, a spleen-myocardium ratio (SMR) was derived.
All 33 included patients were true coronary adenosine responders (i.e. with an MFR >1.5 or presence of ischemia), whereas SSO was absent in 25 (76%) patients. MFR did not differ between patients with presence or absence of SSO (2.86 vs 3.28, p=0.32). SMR was significantly lower in patients with positive SSO (0.42 vs. 0.93; p<0.001). . No correlation was found between MFR and SMR (R = -0.178; p=0.32).
The absence of SSO does not exclude adenosine-induced MBF response.