USMLE Step 2 Clinical Knowledge

A 66-year-old man with atrial fibrillation, hypertension, diabetes and prior transient ischemic attack asks about stroke prevention. He has no bleeding history and normal renal function. CHA₂DS₂-VASc score is 5. What is the most appropriate recommendation?

1. Aspirin 81 mg daily Antiplatelet monotherapy is substantially inferior to anticoagulation for stroke prevention in atrial fibrillation and is no longer recommended for this indication.
2. Warfarin with target INR 2.0–3.0 Effective and acceptable, but not preferred in non-valvular disease with normal renal function. Warfarin remains indicated for mechanical valves and moderate-to-severe mitral stenosis, where DOACs are contraindicated.
3. A direct oral anticoagulant correct Correct. At a score of 5 the annual stroke risk clearly justifies anticoagulation, and DOACs are preferred over warfarin in non-valvular atrial fibrillation for comparable efficacy, lower intracranial hemorrhage rate, and no INR monitoring.
4. Aspirin plus clopidogrel Less effective than anticoagulation with a bleeding risk approaching it. Reserved for patients who genuinely cannot take an anticoagulant.
5. No antithrombotic therapy A score of 5 with a prior TIA places him at high annual stroke risk; withholding treatment would be indefensible.

The point: CHA₂DS₂-VASc drives the decision; HAS-BLED identifies modifiable bleeding risk rather than a reason to withhold. DOACs first in non-valvular AF; warfarin for mechanical valves and rheumatic mitral stenosis.

Source: ACC/AHA/HRS guideline for the management of atrial fibrillation American College of Cardiology / AHA · tier 2, specialty society or college

A 27-year-old woman at 32 weeks' gestation presents with painless bright red vaginal bleeding. The uterus is soft and non-tender, fetal heart tracing is reassuring, and she is hemodynamically stable. What is the most appropriate next step?

1. Transabdominal ultrasound to locate the placenta correct Correct. Painless bright red bleeding in the third trimester is placenta previa until imaging says otherwise, and ultrasound must precede any vaginal examination.
2. Administer misoprostol to induce labor Wrong and dangerous. Inducing labor in possible previa risks massive hemorrhage, and there is no indication to deliver a stable 32-week pregnancy.
3. Kleihauer–Betke test and observation alone Has a role in assessing fetomaternal hemorrhage and Rh immune globulin dosing, but it does not tell you where the placenta is.
4. Immediate cesarean delivery Premature. She is stable at 32 weeks with a reassuring tracing; expectant management with steroids is preferable to delivering a preterm infant without indication.
5. Digital vaginal examination to assess cervical dilation The classic harmful answer. Digital examination in undiagnosed placenta previa can provoke catastrophic hemorrhage.

The point: Third-trimester bleeding: painless and bright red suggests previa (ultrasound first, no digital exam); painful with a rigid tender uterus suggests abruption (clinical diagnosis, ultrasound may be normal). Give Rh immune globulin if the mother is Rh negative.

Source: ACOG practice guidance — placenta previa and third-trimester bleeding ACOG · tier 2, specialty society or college