Clinical significance of splenic switch-off in adenosine triphosphate N-ammonia positron emission tomography in patients without coronary artery disease.

PURPOSE

Splenic switch-off (SSO) is defined as a decrease in splenic radiotracer uptake following pharmacological stress. This study aimed to assess the clinical utility of SSO on adenosine triphosphate (ATP) N-ammonia positron emission tomography (PET) in patients without coronary artery disease (CAD).

MATERIALS AND METHODS

We analyzed 63 patients (mean age, 67 ± 11 years; 34 males) who underwent ATP N-ammonia PET without significant CAD on invasive coronary angiography or cardiac computed tomography within 6 months. Visual assessment of the SSO was conducted by two independent observers, with disagreements resolved by a third observer. We divided the patients into two groups according to the presence (positive) or absence (negative) of SSO and compared global myocardial flow reserve (MFR) and myocardial blood flow (MBF) between the two groups. In addition, the relationship between the reduced MFR and SSO was investigated.

RESULTS

Negative SSO was observed in 15 of 63 patients. Global MFR and global stress MBF were significantly higher in the positive SSO group than in the negative SSO group (2.4 ± 0.6 vs. 1.6 ± 0.6, P < 0.001, and 2.3 ± 0.5 vs. 1.5 ± 0.5 ml min g, P < 0.001, respectively). Global rest MBF showed no significant difference between the two groups (1.0 ± 0.2 vs. 1.0 ± 0.3 ml min g, P = 0.80). In the negative SSO group, 12 of the 15 (80%) patients had a reduced MFR (<2.0). In contrast, in the positive SSO group, 15 of the 48 (31.3%) patients had a reduced MFR, which was suggestive of coronary microvascular dysfunction (CMD).

CONCLUSIONS

The presence of a splenic response based on the visual assessment of SSO may be used to identify an adequate pharmacological response. This can affect the diagnosis of CMD in patients with reduced MFR without CAD. This study showed the clinical utility of splenic switch-off in adenosine triphosphate N-ammonia positron emission tomography in patients without coronary artery disease.