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Coronary Subclavian Steal Syndrome — FRCA Final MCQ

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HardCardiothoracic AnaesthesiaCoronary Subclavian Steal SyndromeFRCA Final

A 60-year-old man (ASA III) has a coronary artery bypass graft using a left internal mammary artery (LIMA) to the LAD. Post-operatively in ICU, his arterial blood gas shows a metabolic acidosis with lactate 8.5 mmol/L despite adequate cardiac output (CI 3.0). His left radial arterial line is showing an unusually low blood pressure compared to the right. What is the explanation for the left radial pressure discrepancy?

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Correct answer: E — Vasospasm from hypothermia

Coronary-subclavian steal syndrome occurs when proximal left subclavian artery stenosis (upstream of the LIMA graft origin) causes reversal of blood flow in the LIMA – blood flows AWAY from the heart through the LIMA to supply the left arm, 'stealing' from the coronary circulation. This causes: (1) myocardial ischaemia via the LIMA territory (elevated lactate), (2) lower left arm blood pressure compared to right (left subclavian stenosis reduces distal pressure). The left radial arterial line reads lower because it is measuring pressure distal to the stenosis. Diagnosis: duplex ultrasound of subclavian arteries. Treatment: subclavian artery stenting or bypass.

Reference: RCOA – 2023 – Cardiothoracic ICU; NICE – 2020 – Peripheral arterial disease