Impact of Unfractionated Heparin on Cardiac Sarcoidosis Evaluation with Cardiac PET: Not Worth the Added Effort and Risk?

Objectives FDG PET is increasingly used for the diagnosis of cardiac sarcoidosis. Physiologic accumulation of FDG in the myocardium can interfere with interpretation of results. In addition to dietary modifications, unfractionated heparin (UFH) administration has been suggested prior to FDG administration to improve myocardial shift to fatty acid metabolism, potentially increasing the sensitivity for detection of myocardial inflammation. Although case reports have illustrated improved myocardial suppression of physiologic FDG uptake with UFH administration, this has not been systematically evaluated. We aimed to evaluate the impact of UFH on suppression of physiologic FDG myocardial uptake in patients undergoing evaluation for cardiac sarcoidosis.

Methods Results from 256 FDG PETs for evaluation of cardiac sarcoidosis were included in retrospective analyses. All patients fasted 12 hours prior to FDG injection and were restricted to a low carb, high protein diet 24 hours prior to the exam. Patients were questioned for contraindications to UFH administration. Those without a contraindication received 50 IU/kg UFH IV 15min prior to FDG administration (N = 150). Those with a heparin contraindication received no UFH (N = 106). Rate of incomplete myocardial suppression on PET was calculated for each group. To evaluate the applicability of this study’s findings in patients without a heparin contraindication, UFH administration was prospectively stopped prior to all FDG PET studies for cardiac sarcoidosis beginning 10/1/15. Interim analysis was performed in 26 patients to determine the rate of non-diagnostic studies secondary to incomplete myocardial suppression without UFH administration.

Results There was no significant difference in rate of incomplete myocardial suppression with UFH administration (12.7%; 19/150) or without UFH (13.2%; 14/106; χ2 = 0.016, p-value = 0.899). Interim analysis since stopping UFH administration in all patients regardless of contraindication reveals a similar rate of incomplete myocardial suppression of 15.4% (χ2 = 0.084, p-value = 0.772). Of the 4 patients that demonstrated incomplete myocardial suppression, one patient demonstrated focal on diffuse myocardial FDG uptake corresponding to perfusion defect on rest cardiac PET and delayed gadolium enhancement on cardiac MRI, and therefore the study was felt to be diagnostic.

Conclusions Although UFH administration has been suggested to improve suppression of physiologic myocardial FDG uptake in PET evaluation of cardiac sarcoidosis, the results of this study do not support its use. Incomplete myocardial suppression continues to be a limitation of FDG PET in the evaluation of cardiac sarcoidosis, but other methods are needed to improve the detection of myocardial inflammation with FDG PET.