A 54-year-old woman presents to the outpatient clinic reporting a three-week history of pr… — USMLE Step 2 CK

A 54-year-old woman presents to the outpatient clinic reporting a three-week history of progressively worsening exertional dyspnea, fatigue, and bilateral lower extremity swelling. She states that she now requires three pillows to sleep comfortably at night without waking up short of breath. Her medical history is significant for estrogen-receptor-negative, HER2-positive breast cancer, for which she underwent surgical resection and completed a chemotherapy regimen containing doxorubicin and cyclophosphamide six months ago. She is currently receiving maintenance therapy with trastuzumab. Vital signs show a temperature of $37.1^\circ C$ ( $98.8^\circ F$ ), heart rate of $105\text{ /min}$ , respiratory rate of $22\text{ /min}$ , and blood pressure of $114/74\text{ mmHg}$ . Pulse oximetry is $94\%$ on room air. Physical examination reveals an elevated jugular venous pressure of $9\text{ cm H}_2\text{O}$ , fine bibasilar crackles, and a distinct third heart sound ( $S_3$ ). Pitting edema is present to the mid-calves bilaterally.

Recent laboratory studies are as follows:

Laboratory Test	Patient Result	Reference Range
Thyroid-stimulating hormone (TSH)	$2.2\text{ }\mu\text{U/mL}$	$0.5-5.0\text{ }\mu\text{U/mL}$
Arterial $pH$	$7.46$	$7.35-7.45$
Arterial $pCO_2$	$31\text{ mmHg}$	$35-45\text{ mmHg}$
Arterial $pO_2$	$70\text{ mmHg}$	$75-105\text{ mmHg}$

Which of the following is the most appropriate next step in management?

Transthoracic echocardiographyAnswer
B
Pulmonary function testing
C
Intravenous piperacillin-tazobactam
D
Initiation of levothyroxine
E
Intravenous sodium bicarbonate

Answer

The most appropriate next step in management is to perform a transthoracic echocardiography.

The correct answer is transthoracic echocardiography because this patient exhibits classic signs and symptoms of acute decompensated heart failure (orthopnea, elevated JVP, S3 gallop, pulmonary crackles, and peripheral edema). Her recent treatment with doxorubicin (an anthracycline) and ongoing treatment with trastuzumab place her at an exceptionally high risk for chemotherapy-induced cardiotoxicity. Doxorubicin causes dose-dependent, irreversible myocyte necrosis leading to dilated cardiomyopathy, while trastuzumab causes a usually reversible decline in contractility. Echocardiography is the essential next step to evaluate the left ventricular ejection fraction (LVEF) and guide subsequent heart failure management.

Step-by-Step Solution

Identify the patient's primary clinical syndrome.

The patient presents with progressive dyspnea, orthopnea, elevated jugular venous pressure, an S3 gallop, and bilateral lower extremity edema, which are hallmark signs of acute decompensated heart failure.

Recognizing the pattern of volume overload and pump failure is required to differentiate this from primary pulmonary or endocrine pathologies.

Assess the patient's risk factors based on her oncologic history.

The patient received doxorubicin (an anthracycline) and is currently taking trastuzumab (a HER2 monoclonal antibody). Both are known to be highly cardiotoxic.

Anthracyclines cause dose-dependent, irreversible myocyte necrosis, while trastuzumab causes a typically reversible decline in myocardial contractility. The combination significantly amplifies the risk of dilated cardiomyopathy.

Determine the best diagnostic test to confirm the suspected etiology.

Transthoracic echocardiography should be ordered.

Echocardiography is the gold standard, non-invasive initial test to evaluate left ventricular ejection fraction (LVEF), structural abnormalities, and confirm the diagnosis of chemotherapy-induced cardiomyopathy.

Key Concept

Patients treated with cardiotoxic chemotherapeutic agents (e.g., anthracyclines, trastuzumab) who present with signs of volume overload must be promptly evaluated for chemotherapy-induced cardiomyopathy using transthoracic echocardiography.

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