Abstract
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Background: Adenosine induces splenic vasoconstriction, which has been used to assess the adequacy of pharmacological stress in Cardiac MRI, where almost 10% of patients are shown to be understressed, leading to false negative results. We aimed to document the prevalence of inadequate stress in Rubidium PET perfusion, by assessing splenic response ratio (SRR) which is (Spleen stress/Liver stress)/(Spleen rest/Liver rest).
Methods: 59 consecutive patients referred for Rubidium PET perfusion were analyzed retrospectively. 36 Men 23 women, mean age 67. Patients received 6 minutes' adenosine infusion (140 mcg/min/kg) for 6 minutes and Pulse and Blood Pressure (BP) were recorded. Spleen and liver Rb-82 activity was measured at stress and rest and the SRR calculated and related to change in haemodynamics during adenosine vasodilatation, and Global Myocardial Flow Reserve (MFR).
Results: The spleen was visualized in all patients. SRR inversely correlated with change in pulse (r=0.62) but not with change in BP (r=0.04), nor correlated with Global MFR(r=0.1).
Conclusions: SRR potentially identifies non-responders to adenosine vasodilatation, identified by a lack of heart rate response. Non-responders are at risk for false negative results on Rubidium PET perfusion. Repeat scans with increased adenosine, an alternative stress agent, or fully compliant preparation could improve test performance.
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