Aneurysmal Subarachnoid Hemorrhage Trial RandOmizing Heparin

Inclusion Criteria: 1. Age ≥ 18 and ≤ 70 years 2. Historical modified Rankin Scale Score 0-1 3. Aneurysmal subarachnoid hemorrhage caused by a ruptured saccular aneurysm confirmed by catheter angiography that is repaired by endovascular coil embolization. Initiation of the coil embolization procedure should occur within 48 hours from the time of the aneurysm rupture (ictus). In patients where the exact time of the ictus is uncertain, a reasonable estimate of the time of ictus may be assigned. This reasonable time estimate should be considered likely accurate to within hours of the true unknown time. 4. Quality of aneurysm embolization is interpreted to be Raymond-Roy Score of 1 (Complete) or 2 (Residual Neck) indicating that the aneurysm is adequately secured. A tiny amount of contrast in the body of the aneurysm is acceptable as long as the physician considers the aneurysm secured and to NOT represent a Raymond-Roy Score of 3 (Residual Aneurysm). 5. WFNS grade 1 or 2 as assessed after repair of the aneurysm during screening but prior to randomization. A patient who presents with a WFNS greater than 2 who then improves with resuscitation, ventriculostomy, or time is acceptable. 6. The pre-repair, admission head CT demonstrates an aSAH bleed pattern of "thick and diffuse" or "thick and focal" hemorrhage within the subarachnoid basal cisterns measuring ≥ 4 mm in the short axis and ≥ 20 mm in the long axis which is consistent with a modified Fisher grade 3 or 4. Intraventricular hemorrhage is acceptable. Enrollable patients must NOT have a parenchymal hemorrhage greater than 10 cc. Please refer to diagram below for examples. The hemorrhage location should be substantially within the supratentorial space and not isolated to the infratentorial space. 7. The location of the aneurysm should be the anterior circulation, posterior communicating, OR a basilar terminus (apex). Angiographic location of the aneurysm should be confirmed by catheter digital subtraction angiography (DSA) usually obtained during the coil embolization procedure. Patients with PICA or other posterior circulation aneurysms as the cause of the SAH should not be included because they typically cause primarily infratentorial bleed patterns. 8. Ability to screen the patient and obtain a head CT 2-12 hours after the completion of the coiling procedure and the ability to initiate the study drug 12 ± 8 hours after the completion of aneurysm coiling procedure. 9. After recovering from anesthesia following the aneurysm coiling procedure, the patient must remain a WFNS SAH grade ≤ 2 without evidence of a significant new focal neurological deficit including monoparesis / monoplegia, hemiparesis / hemiplegia, or receptive, expressive or global aphasia. New minor cranial nerve defect without any other new findings is permissible. If an NIHSS score was obtained prior to the aneurysm coiling procedure, a post-coiling (pre-enrollment) NIHSS score must not have increased by ≥ 4 points and GCS score must not be decreased by ≥ 2 points. The clinician at the local site should use their best clinical judgment as to whether a significant neurological decline has occurred due to the procedure. 10. Patient is willing and able to return for study follow-up visits. 11. Patient or their Legally Authorized Representative (LAR) has provided written informed consent. Exclusion Criteria: 1. Angio-negative SAH. 2. History or imaging suggesting that the current hemorrhage presentation is a recent re-rupture of the aneurysm. Prior sentinel headache with negative CT or prior sentinel headache where the patient did not seek medical attention does not exclude the patient. 3. Surgical Clipping (or plan for clipping) of the ruptured aneurysm or any non- ruptured aneurysm on the same admission. 4. Aneurysm is identified to be traumatic, mycotic, blister or fusiform type by catheter DSA. 5. Any intracranial stent placement or non-coil intra-aneurysmal device where dual- antiplatelet therapy is needed during admission. 6. Patient has additional aneurysm(s) that are untreated and could reasonably be considered a possible alternate cause of the aSAH based on the observed bleeding pattern. Adequate treatment of these aneurysms by coiling embolization would result in the aneurysms no longer causing an exclusion. MRI may be used in some situations to determine that the associated aneurysms did not rupture based on lack of blood seen adjacent to the additional aneurysms. 7. Patient received heparin in any form within the last 100 days prior to current presentation / admission. 8. Thrombocytopenia (platelet count less than 100,000 - assuming clumping has been ruled out as a cause). 9. New intraparenchymal hemorrhage or new infarction larger the 15cc in volume, or significant increased mass effect as seen on the post-coiling, pre-enrollment head CT when compared to baseline admission head CT. New hyperdensity on CT scan related to contrast staining is not an exclusion. 10. Patient has a documented history of heparin induced thrombocytopenia (HIT). 11. Patient developed SAH-induced cardiac stunning prior to enrollment, with an ejection fraction \<30%, or requiring IV medications for blood pressure maintenance. 12. Concurrent significant intracranial pathology identified prior to enrollment, including but not limited to, Moyamoya disease, high suspicion or documented CNS vasculitis, severe fibromuscular dysplasia, arteriovenous malformation, arteriovenous fistula, or malignant brain tumor. 13. Thrombolytic therapy within 24 hours prior to enrollment (rtPA, urokinase, etc.) 14. Plan for antiplatelet or oral anticoagulation therapy from the time of the coil embolization procedure until 14 full days after enrollment. Antiplatelet therapy may be resumed after the 14-day window. A single 325 mg Aspirin (or lower dose) given during the coil embolization peri-procedural period is acceptable if this is the local standard of care but should be documented. 15. Concomitant serious or uncontrolled disease such as severe infection, active (non- remission) cancer, severe organ dysfunction (severe heart failure, severe chronic kidney impairment requiring dialysis or severe chronic liver disease) or any coagulopathy (including DIC or bleeding diathesis). 16. Uncontrollable hypertension (\>180 systolic and/or \>110 diastolic) that is not correctable prior to enrollment. 17. Prior neurological disease/deficit or psychiatric disease that may continue to alter the results of neuropsychological evaluation, such as dementia, Multiple sclerosis, seizure disorder, severe traumatic brain injury, previous ruptured cerebral aneurysm or active major depression. Childhood seizures that have resolved and no longer require treatment are not part of this exclusion criteria. 18. Active Immunosuppression therapy including chronic corticosteroid usage. 19. History of gastrointestinal hemorrhage or major systemic hemorrhage within 30 days (including large flank or large retroperitoneal hematoma due to current admission coiling procedure requiring treatment), hemoglobin less than 6 g/dL, INR ≥1.5 after reversal of anticoagulants. 20. Major surgery (including open femoral, aortic, or carotid surgery) within previous 30 days. 21. Currently pregnant. 22. Enrollment in another research study that prescribes a therapeutic treatment that differs from the local standard of care, or that would conflict with this study in some other significant fashion. Registries or coil comparison studies are appropriate.