Today, we’re examining a clinical case of a 67-year-old woman with intermittent palpitations and progressive fatigue over three months. Can you identify potential arrhythmias or cardiac abnormalities based on her ECG and laboratory findings? Enhance your clinical reasoning by synthesizing this information to understand her condition and the necessary diagnostic steps ahead.
A 67-year-old woman comes to the office because of intermittent palpitations and progressive fatigue for the past three months. The patient does not have a cough, shortness of breath, or chest pain. Past medical history is significant for type II diabetes mellitus and hyperlipidemia. Current medications include metformin and atorvastatin. Family history is noncontributory. She has a 20-pack-year smoking history and does not use alcohol or illicit drugs. Her temperature is 37.33°C (99.2°F), pulse is 120/minute and irregularly irregular, respirations are 17/min, and blood pressure is 130/75 mm Hg. ECG and laboratory findings are shown below.

Laboratory value | Result |
Hemoglobin | 13.5 g/dL |
Leukocyte count | 8000/mm3 |
Platelet count | 230,000/mm3 |
Creatinine | 1.9 g/dL |
BUN | 35 mg/dL |
Which of the following is the best treatment option to prevent long-term complications in this patient?
A. Salmeterol
B. Low-molecular-weight heparin
C. Warfarin Correct: See Main Explanation
D. Hydrochlorothiazide
E. Tiotropium
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 2 CK Question is…
C. Warfarin
Before we get to the Main Explanation, let’s see why the answer wasn’t A, B, D, or E. Skip to the bottom if you want to see the correct answer right away!
A. Salmeterol
Incorrect: Salmeterol is a β2 adrenergic agonist that can worsen the heart rate in patients with atrial fibrillation.
B. Low-molecular-weight heparin
Incorrect: Low-molecular-weight heparin is not recommended for long-term prophylactic management in patients with atrial fibrillation. Moreover, this patient should avoid it due to her renal insufficiency (creatinine >1 g/dL). Oral anticoagulants (direct thrombin inhibitors and factor Xa inhibitors) can be used when warfarin is contraindicated or not available.
D. Hydrochlorothiazide
Incorrect: Hydrochlorothiazide is an antihypertensive agent that has no role in the management of atrial fibrillation.
E. Tiotropium
Incorrect: Tiotropium is an anticholinergic agent indicated in chronic obstructive pulmonary disease management.

This patient presents with progressive fatigue and palpitations, with an irregular heart rate documented on ECG consistent with atrial fibrillation (AF). In addition to rate and rhythm control, long-term anticoagulation with warfarin or another oral anticoagulant (e.g. dabigatran) is indicated due to the high risk of future thromboembolism given her CHA2DS2-VASc is ≥2.
Systemic thromboembolism and stroke are major long-term complications in patients with atrial fibrillation. Treatment with anticoagulation has been shown to reduce the annual risk of stroke by 64% compared to placebo and by 37% compared to antiplatelet therapy alone.
Warfarin inhibits vitamin K- dependent ɣ-carboxylation of glutamic acid residues of clotting factors II, VII, IX, and X by inhibiting the VKOR complex, thus depleting functional vitamin K reserves and reducing the synthesis of active clotting factors. In addition to AF, warfarin has been used as an adjunct to reduce the risk of systemic embolism (e.g., recurrent myocardial infarction, stroke) after myocardial infarction and prophylaxis and treatment of thromboembolic disorders (e.g., venous, pulmonary) and embolic complications arising from cardiac valve replacement.
Warfarin therapy should be monitored to determine dose adjustments required to optimize the time in the therapeutic range (TTR). Warfarin affects the extrinsic coagulation pathway, measured by the prothrombin time (PT) due to early depletion of factor VII. PT readings from different institutions cannot be accurately compared (due to testing kits from other companies). Therefore, the PT gets converted into a standardized value, the international normalized ratio (INR). A regular INR is ≤1.1, and while on warfarin, the general goal INR lies between 2 and 3.

Major Takeaway
Warfarin is a vitamin K antagonist used for chronic anticoagulation (e.g., venous thromboembolism prophylaxis, and prevention of stroke in patients with atrial fibrillation). In laboratory assays, it affects the extrinsic coagulation pathway and therefore is monitored by serum PT and INR levels. The target INR in patients on warfarin lies between two and three.
References
- Steinberg, B. A., & Piccini, J. P. (2014). Anticoagulation in atrial fibrillation. Bmj, 348, g2116.
- Michaud G.F., & Stevenson W.G. (2018). Atrial fibrillation. Jameson J, & Fauci A.S., & Kasper D.L., & Hauser S.L., & Longo D.L., & Loscalzo J(Eds.), Harrison’s Principles of Internal Medicine, 20e. McGraw-Hill.

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