A 68-year-old left-handed man presents to the cardiology clinic complaining of recurrent c… — USMLE Step 2 CK

A $68$ -year-old left-handed man presents to the cardiology clinic complaining of recurrent chest pain. He describes the pain as a severe, pressure-like sensation that reliably occurs when he plays tennis or performs strenuous overhead activities with his left arm. The pain completely resolves within $5$ minutes of rest. Interestingly, he reports that he can walk on a treadmill for $45$ minutes without experiencing any chest discomfort. His past medical history is significant for peripheral artery disease, tobacco use disorder, and severe coronary artery disease. He underwent coronary artery bypass grafting (CABG) $14$ months ago, receiving a left internal mammary artery (LIMA) graft to the left anterior descending (LAD) artery and a saphenous vein graft to the right coronary artery.

Vital signs include a heart rate of $72$ /min. Blood pressure is $152/88$ mmHg in the right arm and $108/68$ mmHg in the left arm. Physical examination reveals a distinct bruit auscultated over the left supraclavicular fossa. An electrocardiogram obtained during an episode of pain shows new ST-segment depressions in the anterior leads, which resolve completely after rest.

Which of the following is the most appropriate definitive management for this patient's underlying condition?

Endovascular stenting of the left subclavian arteryAnswer
B
Reoperative coronary artery bypass grafting to the left anterior descending artery
C
Escalation of antianginal therapy with a long-acting nitrate
D
Endarterectomy of the left internal carotid artery
E
Surgical ligation of the left vertebral artery

Answer

The correct intervention is revascularization of the left subclavian artery, most commonly via endovascular stenting.

This patient's presentation is the classic description of coronary-subclavian steal syndrome, a rare but highly significant complication that can occur in patients with a prior LIMA-to-LAD bypass graft. The patient has a severe stenosis of the left subclavian artery proximal to the origin of the LIMA, which is indicated by the prominent left supraclavicular bruit and the significant blood pressure drop (

>15

mmHg difference) in the left arm. At rest, blood flow to the arm and heart may be sufficient. However, during strenuous left arm exertion (like playing tennis), local vasodilation dramatically decreases vascular resistance in the arm. Because the proximal subclavian artery is occluded, blood flows along the path of least resistance: retrogradely from the LAD, up the LIMA, and into the distal subclavian artery to supply the exercising arm. This 'steals' blood away from the anterior myocardium, causing angina and ST-segment depressions. The hallmark clinical clue is angina provoked by upper extremity exercise but NOT by lower extremity exercise (e.g., walking on a treadmill). The definitive management is to correct the underlying inflow obstruction by revascularizing the left subclavian artery, most commonly via percutaneous transluminal angioplasty and stenting, which restores antegrade flow to both the arm and the heart.

Step-by-Step Solution

Analyze the symptom triggers in the context of the patient's surgical history.

The patient experiences angina exclusively during left upper extremity exertion, despite excellent tolerance for lower extremity exertion (treadmill). He has a LIMA-to-LAD graft.

This specific trigger pattern strongly suggests a localized hemodynamic issue involving the left arm circulation, rather than generalized progression of coronary artery disease.

Evaluate the physical examination findings.

There is a blood pressure discrepancy of

>40

mmHg (lower in the left arm) and a left supraclavicular bruit.

These findings are diagnostic of a hemodynamically significant stenosis in the left subclavian artery proximal to the origin of the left vertebral and LIMA branches.

Synthesize findings to determine the underlying pathophysiology.

The patient has Coronary-Subclavian Steal Syndrome.

During left arm exercise, local vascular resistance drops. Due to the proximal subclavian stenosis, blood flows retrogradely from the LAD, up the LIMA, and into the left arm, stealing oxygenated blood from the myocardium and inducing anterior ischemia.

Select the definitive management strategy.

Endovascular stenting (or surgical bypass) of the left subclavian artery.

Relieving the proximal stenosis normalizes the pressure gradient, restoring normal antegrade flow down both the LIMA and the left arm, which permanently resolves the angina.

Key Concept

Coronary-Subclavian Steal Syndrome

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