Ascending Aortic Aneurysm

An ascending aortic aneurysm is dilatation of the tubular aorta between the sinotubular junction and the brachiocephalic artery. The normal diameter is up to about 37 mm in men and 34 mm in women. An aneurysm is 1.5 times the expected size, usually 45 mm or more.

About 60% of thoracic aortic aneurysms involve the ascending aorta. Incidence is about 5 to 10 in every 100,000 each year, and rises with age.

Causes are hypertension and degeneration, bicuspid aortic valve (20 to 40% have ascending dilatation), heritable disease (Marfan, Loeys-Dietz, familial thoracic aortic disease), Turner syndrome, aortitis, infection (syphilis, tuberculosis), poststenotic dilatation in aortic stenosis, trauma and cocaine use.

The aneurysm is silent until it dissects, ruptures or causes aortic regurgitation.

Pathophysiology. Medial degeneration with fragmented elastin and loss of smooth muscle weakens the wall, and wall stress rises with diameter and pressure. In bicuspid disease, abnormal flow and developmental defects contribute.

Growth is usually 1 to 2 mm each year. Risk of dissection or rupture rises sharply at over 55 to 60 mm, and is about 2% each year at 5.0 to 5.9 cm and 7% or more at 6.0 cm or over in older series.

• Asymptomatic in most. Chest pain, dyspnoea, palpitations or heart failure from aortic regurgitation.
• Compression of the superior vena cava or airway when large. Hoarseness is uncommon in ascending disease.
• Early diastolic murmur of aortic regurgitation, wide pulse pressure, and a systolic ejection murmur with a bicuspid valve.
• Features of a syndrome (Marfan, Loeys-Dietz, Turner) or of aortitis (fever, absent pulses, arm pressure difference of over 10 mm Hg).

Red flags.

• Sudden severe tearing chest or back pain, syncope or neurological deficit
• Growth of 3 mm or more each year
• Diameter of 55 mm or more, or 50 mm in bicuspid valve disease or connective tissue disease
• New severe aortic regurgitation
• Fever with raised inflammatory markers (infected or inflammatory aneurysm)

• Chest X-ray. Widened mediastinum, calcified aortic outline. A normal film does not exclude an aneurysm.
• Echocardiography. Diameter of the sinuses, sinotubular junction and ascending aorta, valve morphology, regurgitation grade, ventricular size and function.
• ECG-gated CT or MR angiography. Maximum diameter perpendicular to the flow axis, extent into the arch, wall thickening and calcification. Use the same modality for follow up.
• Risk indices. Aortic size index (diameter in cm divided by body surface area in m2) over 2.75 cm/m2 is high risk, as is a cross-sectional area to height ratio over 10 cm2/m.
• Cause. Syphilis serology, tuberculosis tests, ESR, CRP, ANCA and IgG4 when aortitis or infection is suspected. Genetic testing for young patients, those with features of a syndrome or a family history. Screening echocardiography of first degree relatives.

Differential diagnosis.

• Aortic root aneurysm and aortic arch aneurysm
• Aortic dissection and intramural haematoma
• Aortic pseudoaneurysm and mycotic aneurysm
• Aortitis
• Mediastinal mass and tortuous aorta
• Poststenotic dilatation without a true aneurysm

Medical.

• Blood pressure under 130/80 mm Hg, with resting heart rate 60 to 70/min where tolerated.
• Bisoprolol 2.5 mg orally once daily, increased to 5 to 10 mg once daily, maximum 20 mg daily (do not exceed 10 mg daily at creatinine clearance under 20 mL/min or in severe liver impairment). Contraindicated in severe asthma, sinus node disease and high grade atrioventricular block without a pacemaker.
• Ramipril 2.5 mg orally once daily, increased every 2 to 4 weeks to 10 mg once daily (maximum 10 mg daily, and 5 mg daily at creatinine clearance under 30 mL/min), or losartan 25 to 50 mg once daily increased to 100 mg once daily (maximum 100 mg daily). Check potassium and creatinine 1 to 2 weeks after each change. Contraindicated in pregnancy and bilateral renal artery stenosis. No drug has been shown to slow growth in degenerative aneurysm.
• Atorvastatin 20 to 40 mg orally once daily for atherosclerotic risk, with liver enzymes at baseline and 3 months. Aspirin 75 to 100 mg once daily only with established vascular disease.
• Stop smoking, avoid fluoroquinolones, stimulants and heavy isometric exertion.

Indications for surgery.

• Degenerative or sporadic aneurysm: 55 mm or more. Smaller thresholds apply to small patients (aortic size index over 2.75 cm/m2), growth of 5 mm or more in 1 year, or 45 mm or more when cardiac surgery is needed for another reason.
• Bicuspid aortic valve: 55 mm or more, 50 mm or more with a risk factor (family history of dissection, growth of 3 mm or more each year, coarctation, uncontrolled hypertension), or 45 mm or more when valve surgery is needed.
• Marfan syndrome: 50 mm or more (45 mm with a risk factor). Loeys-Dietz syndrome: 40 to 45 mm. Turner syndrome: aortic size index over 2.5 cm/m2.
• Symptoms, severe aortic regurgitation or acute dissection at any size.
• Operation: supracoronary replacement with a tube graft, with aortic valve replacement or repair, or root replacement when the root is involved, and hemiarch replacement when the arch is involved. Elective operative mortality is about 1 to 3% in experienced centres, with stroke in about 1 to 3%.
• After a mechanical valve: warfarin 5 mg orally once daily at the start (2 to 3 mg in older adults, liver impairment or interacting drugs), adjusted to an INR of 2.5 (2.0 to 3.0) for a bileaflet valve without risk factors or 3.0 (2.5 to 3.5) with risk factors, no fixed maximum, with INR every 2 to 3 days at the start, weekly until stable, then every 4 to 12 weeks. After a biological valve or a graft alone: aspirin 75 to 100 mg once daily.

Acute aortic syndrome (emergency). Morphine 2.5 to 5 mg intravenously, titrated.

Esmolol 500 microgram/kg intravenously over 1 minute, then infusion 50 microgram/kg/min, repeating the bolus and increasing the infusion by 50 microgram/kg/min every 4 to 5 minutes, maximum 200 microgram/kg/min, to a heart rate near 60/min and systolic pressure of 100 to 120 mm Hg.

Sodium nitroprusside 0.3 microgram/kg/min is added only after beta blockade if the pressure stays high (usual 0.5 to 3 microgram/kg/min, maximum 10 microgram/kg/min, no more than 10 minutes at the maximum rate).

Immediate CT angiography and emergency surgery for ascending involvement.

Aortitis or infection. Treat the cause with the specialist team, and operate when the disease is controlled unless the aorta is leaking.

Special groups.

• Pregnancy: with an ascending aorta of 45 mm or more in Marfan syndrome (or 40 mm in Turner syndrome with a high index) pregnancy is not advised. Continue metoprolol tartrate 25 to 100 mg orally twice daily, maximum 200 mg daily in this setting. Stop ramipril, losartan and statins before conception.
• Region: test for syphilis and tuberculosis in sub-Saharan Africa and Asia, where they remain causes.

Monitoring. Imaging at 6 months after diagnosis, then yearly if stable, every 6 months at 45 mm or more or with rapid growth. Blood pressure at every visit. After surgery, imaging at 1 year, then every 2 to 3 years.

Referral and escalation. Refer to a thoracic aortic programme. Emergency for suspected dissection or rupture.