Overview
Definition:
Subclavian artery transposition is a surgical procedure where the origin of the subclavian artery is detached from the brachiocephalic trunk or aortic arch and reimplanted onto the ascending aorta or a more distal arch vessel
It is primarily performed to facilitate the surgical repair of proximal aortic arch aneurysms or dissections, particularly those involving the origin of the great vessels.
Epidemiology:
Aortic arch aneurysms are less common than other forms of aortic aneurysms, representing a small percentage of all thoracic aortic aneurysms
They are more prevalent in older individuals with risk factors such as hypertension, atherosclerosis, connective tissue disorders (e.g., Marfan syndrome), and a history of smoking.
Clinical Significance:
The proximity of these aneurysms to the origin of the supra-aortic arteries (brachiocephalic trunk, left common carotid artery, left subclavian artery) poses significant challenges for surgical repair
Transposing the subclavian artery creates a more distal landing zone for aortic repair devices or sutures, reducing the risk of stroke, spinal cord ischemia, and other complications related to compromise of cerebral or limb perfusion
This procedure is critical for achieving durable and safe outcomes in complex aortic arch pathologies.
Indications
Primary Indications:
Proximal aortic arch aneurysms or dissections involving the origin of the left subclavian artery
Aneurysms or dissections that necessitate complete resection of the aortic arch origins
Situations where direct repair or other grafting techniques would compromise cerebral or subclavian flow
Historical indications also included subclavian steal syndrome, though less commonly addressed by transposition now.
Relative Indications:
Complex arch pathologies requiring extensive reconstruction
Need to optimize cerebral blood flow during arch repair
Patients with specific anatomical variations that make standard repair difficult.
Contraindications:
Severe comorbidities that preclude major open surgery
Absence of viable subclavian artery
Acute, extensive arch dissection that has already compromised the subclavian origin irreparably
Uncontrolled sepsis.
Diagnostic Approach
History Taking:
Detailed history of symptoms: chest pain (sudden, tearing for dissection, dull ache for aneurysm), neurological symptoms (stroke, transient ischemic attack, arm claudication, subclavian steal symptoms), dyspnea
Risk factor assessment: hypertension, hyperlipidemia, smoking, diabetes, family history of aortic disease, connective tissue disorders.
Physical Examination:
Blood pressure and pulse assessment in both arms to detect differential pressures (suggestive of subclavian stenosis or occlusion)
Auscultation for murmurs (aortic regurgitation, bruits)
Palpation of peripheral pulses
Neurological examination to assess for focal deficits
Examination for signs of connective tissue disorders.
Imaging Modality:
Computed Tomography Angiography (CTA) is the gold standard for visualizing the aortic arch, originating vessels, and the extent of the aneurysm or dissection
Magnetic Resonance Angiography (MRA) can also be used
Transesophageal Echocardiography (TEE) is crucial for intraoperative monitoring and assessment of aortic valve function
Conventional angiography may be used in select cases.
Differential Diagnosis:
Other causes of chest pain: myocardial infarction, pulmonary embolism, pericarditis
Other causes of aortic pathology: ascending aortic aneurysms, descending thoracic aortic aneurysms
Intrascapular pain syndromes
Other causes of neurological deficits: carotid artery disease, intracranial pathology.
Surgical Management
Preoperative Preparation:
Thorough cardiovascular assessment, including echocardiography and pulmonary function tests
Optimization of blood pressure
Anticoagulation and antiplatelet strategies need careful consideration
Consultation with anesthesia, cardiology, and neurology teams
Planning for cardiopulmonary bypass and hypothermic circulatory arrest is essential.
Procedure Steps:
Median sternotomy is typically performed
Cardiopulmonary bypass is initiated, often with antegrade cerebral perfusion via cannulation of the ascending aorta and left common carotid artery
The aortic arch is opened distal to the innominate artery
The left subclavian artery is carefully dissected proximally and distally
It is then transected and reimplanted end-to-side onto the ascending aorta or a proximal graft limb, creating a new origin distal to the aneurysm
A synthetic graft is then used to repair the excised aortic arch segment, ensuring adequate distal landing zones for both cerebral vessels and the transposed subclavian artery
Hypothermic circulatory arrest may be employed for complex arch reconstructions.
Surgical Techniques:
Variations include direct reimplantation to the ascending aorta, interposition grafting, or use of a multi-branched graft
The specific technique depends on the extent of disease and the surgeon's preference
Cerebral protection strategies are paramount, often involving mild hypothermia, retrograde or antegrade cerebral perfusion.
Anesthesia Considerations:
Careful hemodynamic management is critical due to the extensive nature of the surgery
Neuromonitoring (e.g., somatosensory evoked potentials, motor evoked potentials) is vital
Maintaining adequate cerebral perfusion pressure during circulatory arrest is a priority.
Postoperative Care
Icu Management:
Close monitoring of hemodynamics, respiratory status, and neurological function
Aggressive pain management
Early mobilization as tolerated
Strict blood pressure control to prevent stress on the repair site.
Monitoring Parameters:
Continuous ECG, arterial blood pressure (often with arterial line), central venous pressure
Neurological checks at regular intervals
Urine output monitoring
Laboratory monitoring: CBC, electrolytes, renal function, coagulation profile.
Medications:
Intravenous antihypertensives (e.g., nicardipine, labetalol) for blood pressure control
Analgesics
Prophylactic antibiotics
Anticoagulation or antiplatelet therapy as per protocol, balancing the risk of thrombosis against bleeding.
Rehabilitation:
Early ambulation
Pulmonary physiotherapy
Gradual return to normal activity
Long-term follow-up with regular imaging studies to monitor the integrity of the repair.
Complications
Early Complications:
Stroke or transient ischemic attack due to manipulation of the arch vessels
Spinal cord ischemia leading to paraplegia
Bleeding from the suture lines or graft
Myocardial infarction
Graft infection
Acute kidney injury
Pneumonia
Arrhythmias.
Late Complications:
Graft dehiscence or pseudoaneurysm formation
Stenosis at the anastomosis
Late graft infection
Progressive aneurysmal disease in other segments of the aorta
Neurological deficits that may manifest later
Subclavian steal phenomenon developing if the transposed artery is compromised.
Prevention Strategies:
Meticulous surgical technique, including adequate distal landing zones and secure anastomoses
Aggressive perioperative blood pressure control
Judicious use of cardiopulmonary bypass and hypothermic circulatory arrest
Neuromonitoring and prompt intervention for any signs of ischemia
Careful perioperative fluid management
Postoperative anticoagulation/antiplatelet therapy as indicated.
Prognosis
Factors Affecting Prognosis:
Extent and nature of the aortic pathology (dissection vs
aneurysm)
Patient's overall health status and comorbidities
Successful exclusion of the aneurysm and adequate perfusion of head and upper extremities
Intraoperative complications
Quality of the surgical repair.
Outcomes:
When performed in experienced centers, subclavian artery transposition can significantly improve outcomes for patients with proximal aortic arch aneurysms, allowing for successful aortic repair and reducing the risk of catastrophic complications
Long-term survival is largely dependent on the management of underlying risk factors and the potential for future aortic events.
Follow Up:
Lifelong surveillance with regular imaging (CTA or MRA) is recommended to monitor the integrity of the graft and the remaining aorta for any signs of disease progression or complications
Regular clinical assessment for neurological symptoms or symptoms of limb ischemia is also important.
Key Points
Exam Focus:
Understanding the indications for transposition, the surgical steps, crucial intraoperative management (cerebral protection, bypass), and common early/late complications
Differentiate from other arch repair strategies
Know the key imaging modalities and their roles.
Clinical Pearls:
Always assess bilateral arm pulses and blood pressures preoperatively
Meticulous dissection of the subclavian artery is crucial to avoid injury
Adequate proximal and distal graft anastomoses are key to long-term success
Judicious use of hypothermic circulatory arrest is essential for brain protection during complex arch reconstructions.
Common Mistakes:
Inadequate distal landing zone for aortic graft
Compromising the left vertebral artery origin if it arises from the aortic arch
Insufficient cerebral protection during circulatory arrest
Failing to recognize and manage postoperative bleeding or stroke.