Stent Thrombosis Secondary to Ticagrelor Resistance as Demonstrated by Thromboelastography

Introduction: We describe cases of stent thrombosis while on ticagrelor, with demonstrated ticagrelor resistance on Thromboelastography Platelet Mapping (TEG). Case description: The patient is a 61 year old male with a ST elevation myocardial infarction (STEMI) requiring stents 4 days before admission. The patient returned with a stent thrombosis, due to ticagrelor noncompliance. During his stay, the patient was restarted on ticagrelor, with all doses documented to have been given as scheduled. He had a new STEMI 2 days later in the hospital and was sent again for PCI, which showed another stent thrombosis. Thrombelastography® Platelet Mapping™(TEG) showed resistance to ticagrelor with 7.0% inhibition and a maximum amplitude (MA) of 71.2 mm with ADP and was replaced by prasugrel. TEG on prasugrel showed inadequate inhibition, with an inhibition of 0.0% with a MA of 77.8 with ADP, but retesting the sample with whole blood luminescence aggregometry showed adequate inhibition with ADP. The patient was discharged on prasugrel and had no further episodes of stent thrombosis to date. Discussion: Stent thrombosis is a dreaded complication of on-treatment platelet reactivity. With ticagrelor, stent thrombosis is rare due to its nature as a direct P2Y12 inhibitor that does not require metabolization. There is only one other reported case, to our knowledge, of stent thrombosis with laboratory confirmed ticagrelor resistance. An analysis of the Platelet inhibition and patient Outcomes trial showed that stent thrombosis is less frequent with ticagrelor compared to clopidogrel. There is little research to explain ticagrelor resistance and known drug interactions are not clinically significant. Testing for P2Y12 inhibitor resistance is an area in need of elucidation, with few consensus guidelines regarding the definition of resistance and how the multiple platelet function tests compare to one another.