A 43-year-old woman was admitted to the hospital for anticoagulation following a pulmonary embolism. She was found to have a deep venous thrombosis on further workup after a long plane ride coming back from visiting China. She denies any personal history of blood clots in her past, but she says that her mother has also had to be treated for pulmonary embolism in the recent past. Her past medical history is significant for preeclampsia, hypertension, polycystic ovarian syndrome, and hypercholesterolemia. She currently smokes 1 pack of cigarettes per day, drinks a glass of wine per day, and she currently denies any illicit drug use. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 111/min, and respiratory rate 23/min. On physical examination, her pulses are bounding and complexion is pale, but breath sounds remain clear. Oxygen saturation was initially 81% on room air, with a new oxygen requirement of 8 L by face mask. On day 6 of combined heparin and warfarin anticoagulation, her platelet count decreases from 182,000/mcL to 63,000/mcL. Her international normalized ratio (INR) is not yet therapeutic. What is the next best step in therapy?

Discontinue heparin and warfarin

Continue heparin and warfarin until INR is therapeutic for 24 hours

Continue heparin and warfarin, and administer vitamin K

Discontinue heparin; continue warfarin

Continue heparin; discontinue warfarin

A primary care physician who focuses on treating elderly patients is researching recommendations for secondary prevention. She is particularly interested in recommendations regarding aspirin, as she has several patients who ask her if they should take it. Of the following, which patient should be started on lifelong aspirin as monotherapy for secondary prevention of atherosclerotic cardiovascular disease?

A 63-year-old male with a history of a transient ischemic attack

An 83-year-old female with a history of a hemorrhagic stroke 1 year ago without residual deficits

A 75-year-old male who had a drug-eluting coronary stent placed 3 days ago

A 67-year-old female who has diabetes mellitus and atrial fibrillation

A 45-year-old female with no health problems

A 71-year-old man develops worsening chest pressure while shoveling snow in the morning. He tells his wife that he has a squeezing pain that is radiating to his jaw and left arm. His wife calls for an ambulance. On the way, he received chewable aspirin and 3 doses of sublingual nitroglycerin with little relief of pain. He has borderline diabetes and essential hypertension. He has smoked 15–20 cigarettes daily for the past 37 years. His blood pressure is 172/91 mm Hg, the heart rate is 111/min and the temperature is 36.7°C (98.0°F). On physical examination in the emergency department, he looks pale, very anxious and diaphoretic. His ECG is shown in the image. Troponin levels are elevated. Which of the following is the best next step in the management of this patient condition?

Clopidogrel, atenolol, anticoagulation and monitoring

CT scan of the chest with contrast

A 56-year-old man comes to the emergency department because of progressive swelling and pain in his left calf for 1 day. He does not have shortness of breath or chest pain. He has hypertension and chronic kidney disease. Current medications include enalapril, aspirin, simvastatin, and vitamin D. His temperature is 100.4°F (38°C), pulse is 84/min, and blood pressure is 135/92 mm Hg. Physical examination shows tenderness and swelling of the left lower extremity. A venous Doppler ultrasonography shows a thrombus in the left popliteal vein. Treatment with unfractionated heparin is begun. Two days later, physical examination shows improvement of symptoms. Laboratory studies at admission and 2 days after admission show: Admission Two days after admission Hemoglobin 11.2 g/dL 11.1 g/dL Leukocyte count 5,500/mm3 6,100/mm3 Platelet count 230,000/mm3 170,000/mm3 Serum Prothrombin time 12 seconds 13 seconds Partial thromboplastin time 30 seconds 55 seconds Estimated glomerular filtration rate 29 mL/min/1.73 m2 28 mL/min/1.73 m2 Which of the following is the most appropriate next step in management?

Discontinue heparin and initiate argatroban

Continue unfractionated heparin

Anticoagulation in ACS for USMLE Step 2 CK: High-Yield Internal Medicine Lessons

Anticoagulation in ACS - The Clotting Crisis

Goal: Prevent thrombus extension & re-occlusion.
Agents: Choice depends on strategy (PCI vs. medical) & bleeding risk.
- Unfractionated Heparin (UFH): Preferred for planned PCI/CABG due to short half-life. Monitor aPTT. ⚠️ Risk of HIT.
- LMWH (Enoxaparin): Good for medical management. Requires renal dose adjustment.
- Bivalirudin: For PCI, especially with high bleeding risk or HIT.

Coagulation cascade & anticoagulant targets

⭐ Fondaparinux, used in medically managed NSTEMI, has the lowest bleeding risk but is contraindicated as the sole anticoagulant during PCI due to a higher risk of catheter thrombosis.

The Anticoagulant Arsenal - Meet the Players

A rapid-comparison of parenteral anticoagulants used in Acute Coronary Syndrome.

Anticoagulant and antiplatelet mechanisms of action

Class	Mechanism of Action	Administration	Key Monitoring	Reversal Agent
Unfractionated Heparin (UFH)	Binds Antithrombin III, inactivating Thrombin (IIa) & Factor Xa equally.	IV infusion	aPTT (activated partial thromboplastin time)	100% Protamine Sulfate
LMWH (e.g., Enoxaparin)	Binds Antithrombin III, preferentially inactivating Factor Xa > IIa.	Subcutaneous (SC)	Anti-Xa levels (esp. in renal failure)	Partial w/ Protamine Sulfate
Bivalirudin	Direct Thrombin Inhibitor (DTI) - binds directly to thrombin's active site.	IV infusion	ACT (activated clotting time)	None (short half-life)
Fondaparinux	Selective Factor Xa inhibitor via Antithrombin III.	Subcutaneous (SC)	Not required	None

Strategic Selection - The ACS Playbook

Your choice of anticoagulant is guided by the specific ACS type and the intended management strategy-balancing ischemic prevention with bleeding risk.

Invasive (PCI): Unfractionated Heparin (UFH) or Bivalirudin are the agents of choice.
Medical (Conservative): Fondaparinux is preferred due to a superior safety profile (↓ bleeding).
⚠️ Fondaparinux & PCI: If a patient on fondaparinux requires PCI, administer a bolus of UFH to prevent catheter thrombosis.

⭐ In NSTEMI, Fondaparinux is the only anticoagulant that has demonstrated a mortality benefit (OASIS-5 trial) and carries the lowest risk of major bleeding, making it a prime choice for medically managed patients.

Risks & Regimens - The Fine Print

Major Risks
- ⚠️ Bleeding: Most common complication. Monitor hemoglobin/hematocrit.
- Heparin-Induced Thrombocytopenia (HIT): Suspect if platelets drop >50%. A prothrombotic state.
Key Contraindications
- Active internal bleeding
- Recent major surgery or trauma (especially CNS)
- Severe thrombocytopenia (<100,000/μL)
Dosing & Adjustments
- UFH: 60 U/kg bolus, then 12 U/kg/hr infusion.
- Enoxaparin: 1 mg/kg SC q12h. If CrCl <30 mL/min, dose q24h.

⭐ In HIT, immediately stop all heparin products and start a direct thrombin inhibitor (e.g., Argatroban, Bivalirudin). Do not use LMWH due to high cross-reactivity.

Heparin-Induced Thrombocytopenia Pathophysiology

Dual Antiplatelet Therapy (DAPT), combining aspirin and a P2Y12 inhibitor, is the cornerstone of treatment for all ACS patients.

The choice of P2Y12 inhibitor-clopidogrel, prasugrel, or ticagrelor-depends on the clinical scenario and bleeding risk.

Prasugrel is contraindicated in patients with a history of stroke or TIA due to increased bleeding risk.

A parenteral anticoagulant (e.g., heparin, enoxaparin, bivalirudin) is added to DAPT during the initial phase.

Glycoprotein IIb/IIIa inhibitors are reserved for high-risk patients undergoing PCI.

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