Ascending Aortic Aneurysms

Overview, Anatomy, and Pathophysiology

Definition and Epidemiology

• Normal ascending aortic dimensions are less than 3.6-3.7 cm on CT imaging.⁸
• Aortic dilation is defined as a diameter greater than 4.0 cm, while an aneurysm is defined as greater than 4.5 cm or 1.5 times the normal diameter.^1,7,8
• The incidence is estimated at 5-10 cases per 100,000 person-years.^1,3,7
• Risk factors include advancing age, male sex, hypertension, smoking history, genetic disorders (e.g., Marfan, Loeys-Dietz), bicuspid aortic valve (BAV), and family history.^1,3

Etiology

• Cystic medial necrosis is the most common mechanism, associated with age, hypertension, and elastic fiber fragmentation.^3,9,10
• Genetic and connective tissue disorders such as Marfan, Loeys-Dietz, Ehlers-Danlos, and familial thoracic aortic aneurysm and dissection account for a significant portion of cases with approximately 20% showing familial inheritance.¹
• BAV is present in 50-60% of cases, independently associated with increased risk of dilation and dissection.⁸
• Inflammatory aortitis and rare infectious causes contribute to a smaller subset (e.g., aortitis, syphilitic aortitis).¹

Classification by Anatomic Location

• The ascending aorta consists of 5 segments: aortic annulus, root (sinus of Valsalva), sinotubular junction, tubular ascending aorta, and aortic arch.⁸
• The Crawford classification (Figure 2) is commonly used to categorize thoracoabdominal aortic aneurysms based on the extent of aortic involvement, ranging from Type I to V.
• Aortic root aneurysms
  • Involves the aortic valve annulus, sinuses of Valsalva, and sinotubular junction
  • It can impair leaflet coaptation, leading to aortic insufficiency.^1,3
  • Common in Marfan syndrome, Loeys-Dietz, BAV, and connective tissue disorders^1,8
• Tubular ascending aortic aneurysms
  • Spares the root and aortic valve; involves the segment between the sinotubular junction and the origin of the brachiocephalic artery
  • Common in degenerative disease, hypertension, and aging^1,3

Pathophysiology

• Elastic fiber loss, proteoglycan accumulation, and smooth muscle loss compromise structural integrity, leading to necrosis of the aortic media.^3,9
• Systemic hypertension increases shear stress and promotes dilation.¹
• Aneurysm expansion increases wall tension exponentially (in accordance with Laplace’s law)
• The risk of dissection sharply rises above 5.0 cm, though 60% of dissections occur below 5.5 cm.⁶

Diagnosis, Evaluation, and Surgical Indications

Clinical Presentation

• Often asymptomatic; detected incidentally.³
• Common symptoms include chest/back pain, hoarseness (recurrent laryngeal nerve compression), dysphagia (esophageal compression), or superior vena cava syndrome (mediastinal compression).³
• Aortic insufficiency may present with dyspnea, orthopnea, or symptoms of heart failure.³
• Acute dissection or rupture causes sudden, severe chest or back pain, syncope, and shock.³

Imaging

• Transthoracic echocardiography is preferred for initial screening.^2,8
• TEE offers superior visualization of the aortic root, valve, and proximal/mid ascending aorta; however, it is unable to adequately assess the distal ascending aorta due to tracheal air artifact.²
• Computed tomographic angiography is considered the gold standard for preoperative planning because it can evaluate the entire thoracic aorta.^1,2
• MRI or magnetic resonance angiography is preferred for long-term surveillance in young patients (less than 50 years of age) due to superior soft-tissue contrast and lack of radiation.²

Risk Stratification and Surveillance

• Aneurysm size is the strongest predictor of adverse events.¹
• Indexed thresholds (e.g., aortic size index greater than 3.08 cm/m², area/height greater than 10 cm2/m) refine risk assessment.^1,8
• Rapid growth (greater than 0.5cm/year or greater than 0.3 cm/year for two years) indicates the need for surgical evaluation.^1,3
• Surveillance intervals:¹
  • Less than 4.0 cm, follow up every 2-3 years
  • Between 4.5 – 5.4cm, follow up every 6-12 months
  • High-risk patients (genetic syndromes, BAV) require more frequent follow-ups

Indications for Surgical Repair

• Standard repair is recommended at greater than 5.5 cm for sporadic aneurysms.^1,3
• Symptomatic aneurysms and/or rapid growth are a class I indication for surgical repair.^1,3

At experienced centers with multidisciplinary aortic teams, the surgical threshold for ascending aortic aneurysms has decreased from 5.5 cm to 5.0 cm for selected patients, with even lower thresholds for those with heritable conditions.¹

Anesthetic and Surgical Management

Preoperative Considerations

• Optimize the patient’s BP with beta-blockers to reduce shear stress with a target HR less than 60-70 bpm.³
• Review imaging to assess aneurysm extent, root involvement, valve disease, and cannulation strategy.¹
• Manage aortic insufficiency by maintaining preload and avoiding bradycardia and hypertension.⁴
• Prepare large-bore intravenous access, blood products, and vasopressors.⁴
• Preoperative functional status is the strongest independent predictor of perioperative death, with completely dependent functional status yielding threefold higher mortality risk.⁶ Common comorbidities include smoking-related coronary and pulmonary disease, hypertension, and diabetes in approximately 10% of patients.⁶
• Antihypertensive medication is recommended for patients with sporadic thoracic aortic aneurysm and BP ≥130/80 mm Hg, with beta-blockers and/or angiotensin II receptor blocker therapy being reasonable choices absent contraindications.²

Medical Optimization

• Moderate- or high-intensity statin therapy is reasonable in patients with thoracic aortic aneurysm and clinical or imaging evidence of atherosclerosis.²
• Smoking cessation interventions are strongly recommended, as even passive smoke exposure may increase rupture risk.³

Intraoperative Monitoring

• Invasive arterial monitoring should be placed before induction for tight BP control.⁴
• Consider central venous access for vasoactive infusions.⁴
• TEE should be utilized for continuous assessment of the valve, aneurysm, and cannulation guidance.^1,4
• Cerebral near-infrared spectroscopy can monitor cerebral perfusion.⁵

Anesthetic Management

• Slow, controlled induction to avoid hypertension, tachycardia, and aortic wall stress.

Overview of Surgical Options

• Surgery for ascending aortic aneurysms depends on the extent of disease, valve involvement, and patient-specific factors. The main surgical approaches include:

Valve-Sparing Aortic Root Replacement – “David Procedure”

• Valve-sparing surgery is indicated for patients less than 65 years old with healthy valve leaflets.
• Techniques
  • Reimplantation Technique (David I): The aneurysmal aortic sinuses are excised along with the coronary arteries, and the aortic valve is reimplanted inside a cylindrical Dacron graft.
  • Remodeling Technique (Yacoub): The aortic sinuses are excised and replaced with a tailored tubular Dacron graft with three neo-aortic sinuses.
• Advantages
  • By preserving native valve leaflets, the valve has the potential to last a lifetime, avoiding the inevitable structural degeneration of bioprosthetic valves or the need for lifelong anticoagulation with mechanical valves.

Modified Bentall Procedure (Composite Valve Graft)

• Technique
  • The modified “Button Bentall” procedure involves excision of the aortic valve, aortic root, and ascending aorta, suture of a composite graft into the aortic root and ascending aorta, mobilization of coronary arteries with a small rim of aortic tissue, and anastomosis of the arteries to openings in the aortic graft.
  • The coronary ostia are detached from the surrounding aortic tissue, widely mobilized, and individually sutured to the aortic graft.

Supracoronary Ascending Aortic Replacement (Wheat Procedure)

• When the disease involves the ascending aorta with normal sinuses of Valsalva, supracoronary aortic replacement is performed and can be combined with aortic valve replacement

Hemiarch Replacement

• Hemiarch replacement involves replacing the ascending aorta and performing an open distal anastomosis to resect the entire concavity of the arch down to the proximal descending thoracic aorta.
• Used when the proximal arch is involved but does not require complete arch replacement.

Total Arch Replacement with Frozen Elephant Trunk (FET)

• Indications
  • Acute type A dissection as an adjunct to total arch replacement when there is distal aortic malperfusion
  • Complex tears affecting distal arch and proximal descending aorta
  • Aneurysms of distal arch or proximal descending aorta
  • Severe arch disruption
• Technique
  • Hybrid stent-graft prostheses (FET) encompass a covered stent sutured to the distal end of a conventional tube graft to provide expansive radial force on the distal portion, combining conventional surgery with endovascular techniques.

Cardiopulmonary Bypass Considerations

• Cannulation strategies include the aortic, axillary, or femoral artery depending on anatomy.⁴
• If the aortic arch is involved, then hypothermic circulatory arrest with cerebral perfusion strategies is recommended.^3-5
• TEE guidance confirms cannula placement and assesses for dissection.⁴

Noncardiac Surgery in Patients with Ascending Aortic Aneurysms

• Repair should not be delayed when surgical indications are met.^2,3
• Aneurysms greater than 5.5cm (greater than 5.0cm in experienced centers) or those with rapid growth should be repaired prior to elective, non-cardiac surgery.²
• Elective non-cardiac surgery is generally acceptable below repair thresholds, but requires strict hemodynamic control, avoidance of acute hypertension, and adherence to American College of Cardiology Foundation/American Heart Association cardiovascular risk guidelines.^2,3

Postoperative Management

• Control systolic BP within 100 to 120 mmHg to protect anastomotic sites.^2,3
• Monitor for bleeding via chest tube output, labs, and serial point of care tests.⁴
• Conduct frequent neurologic exams to identify new focal neurologic deficits that might suggest a stroke or spinal cord ischemia.^3,5
• Early extubation (6-12 hours) reduces the risk of respiratory complications.⁴
• Long-term surveillance and strict BP control is crucial.^2,3