Abstract
BackgroundInadequate coronary adenosine response is a potential cause for false negative ischemia testing. Recently, the splenic switch-off (SSO) sign has been identified as a promising tool to ascertain the efficacy of adenosine during vasodilator stress cardiovascular magnetic resonance imaging (CMR). We assessed the value of SSO to predict adenosine response, defined as an increase in myocardial blood flow (MBF) during quantitative stress myocardial perfusion 13 N-ammonia positron emission tomography (PET).MethodsWe prospectively enrolled 64 patients who underwent simultaneous CMR and PET myocardial perfusion imaging on a hybrid PET/CMR scanner with co-injection of gadolinium based contrast agent (GBCA) and 13N-ammonia during rest and adenosine-induced stress. A myocardial flow reserve (MFR) of > 1.5 or ischemia as assessed by PET were defined as markers for adequate coronary adenosine response. The presence or absence of SSO was visually assessed. The stress-to-rest intensity ratio (SIR) was calculated as the ratio of stress over rest peak signal intensity for splenic tissue. Additionally, the spleen-to-myocardium ratio, defined as the relative change of spleen to myocardial signal, was calculated for stress (SMRstress) and rest.ResultsSixty-one (95%) patients were coronary adenosine responders, but SSO was absent in 18 (28%) patients. SIR and SMRstress were significantly lower in patients with SSO (SIR: 0.56 ± 0.13 vs. 0.93 ± 0.23; p < 0.001 and SMRstress: 1.09 ± 0.47 vs. 1.68 ± 0.62; p < 0.001). Mean hyperemic and rest MBF were 2.12 ± 0.68 ml/min/g and 0.78 ± 0.26 ml/min/g, respectively. MFR was significantly higher in patients with vs. patients without presence of SSO (3.07 ± 1.03 vs. 2.48 ± 0.96; p = 0.038), but there was only a weak inverse correlation between SMRstress and MFR (R = -0.378; p = 0.02) as well as between SIR and MFR (R = -0.356; p = 0.004).ConclusionsThe presence of SSO implies adequate coronary adenosine-induced MBF response. Its absence, however, is not a reliable indicator for failed adenosine-induced coronary vasodilatation.
Highlights
Inadequate coronary adenosine response is a potential cause for false negative ischemia testing
Whether this condition is achieved remains difficult to assess in clinical routine because commonly used markers such as the hemodynamic response to adenosine are unreliable as they are prone to procedure-related confounders such as anxiety or adenosine-induced side effects [5, 6]
Contrary to modalities relying on the detection of relative regional differences in myocardial perfusion, such as cardiovascular magnetic resonance imaging (CMR) and single photon emission computed tomography (SPECT), positron emission tomography (PET) myocardial perfusion imaging (MPI) allows for absolute quantification of myocardial blood flow (MBF) and calculation of myocardial flow reserve (MFR) [9]
Summary
Inadequate coronary adenosine response is a potential cause for false negative ischemia testing. We assessed the value of SSO to predict adenosine response, defined as an increase in myocardial blood flow (MBF) during quantitative stress myocardial perfusion 13 N-ammonia positron emission tomography (PET). Induction of maximal coronary vasodilation is a crucial prerequisite for obtaining high diagnostic accuracy concerning the detection of obstructive coronary artery disease (CAD) [1,2,3,4] Whether this condition is achieved remains difficult to assess in clinical routine because commonly used markers such as the hemodynamic response to adenosine (i.e., a decrease in systolic blood pressure and/or increase in heart rate) are unreliable as they are prone to procedure-related confounders such as anxiety or adenosine-induced side effects [5, 6]. MFR served as the standard of truth and was assessed on a PET/CMR device with co-injection of 13N-ammonia and GBCA during adenosine stress
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