Stacey Chen and Deane E. Smith
This chapter is a revision and update of that included in the previous editions of the TSRA Review written by Sandeep Sainathan (2nd edition), J. Chad Johnson (1st edition), and Jason A. Williams (1st edition).
Background
Aortic dissections are classified based on either the DeBakey or Stanford classification systems. The DeBakey classification is an anatomical description of the dissection based on location of the original intimal tear and extent of the dissection. The Stanford classification is based on involvement of the ascending aorta. A type B aortic dissection according to the Stanford classification involves the descending thoracic or thoracoabdominal aorta distal to the left subclavian artery (LSA) without involvement of the ascending aorta.
Pathophysiology
An aortic dissection occurs when there is a tear in the intima, resulting in the entry of blood, creating a false lumen. Due to high pressures in the aorta, the blood entering through this tear can cause the tear to extend in either a retrograde or antegrade fashion along the length of the aorta. This process is characterized as acute (≤14 days), subacute (15 to 90 days), or chronic (>90 days). The risk of aortic dissection is increased in patients with disease processes that weaken the integrity of the aortic wall, such as long-standing hypertension, atherosclerosis, tobacco use, pre-existing aneurysm, and connective tissue disorders (i.e., Marfan syndrome, Ehlers-Danlos syndrome, Loeys-Dietz syndrome, familial thoracic aortic aneurysm and dissection).
Clinical presentation
Acute Type B Dissection
The first step in the clinical evaluation of a patient with an acute type B aortic dissection is to determine if the patient has an uncomplicated or complicated type B aortic dissection. Patients with acute uncomplicated type B aortic dissection typically present with sudden onset back pain, which is initially experienced at the dissection site, but may migrate as the dissection progresses. Patients with acute complicated type B aortic dissection present with malperfusion syndrome in addition to sudden onset back pain. The clinical presentation of malperfusion in a patient with an acute complicated type B aortic dissection varies depending on the affected vasculature. Patients may present with abdominal pain (i.e., mesenteric ischemia), renal failure (i.e., renal ischemia), and/or lower extremity pain and pulse deficits from femoral artery compromise. In addition, in the setting of aortic rupture, patients will present with hemodynamic instability. Painless dissection can also occur, although rare.
Subacute and Chronic Type B Dissection
Patients with subacute or chronic type B aortic dissections are often asymptomatic. These patients are followed with surveillance imaging to evaluate for aneurysmal formation and growth. Infrequently, chronic type B aortic dissection patients may present with compressive symptoms related to an enlarging dissected aorta.
Diagnosis
Diagnosis is based on both physical examination findings and radiologic imaging. In addition to symptoms, physical examination including a complete pulse examination is important to determine any signs of malperfusion. Computed tomography angiogram (CTA) is the preferred diagnostic imaging modality. CTA can demonstrate the true and false lumen with an intimal flap, extent of the dissection, diameter of the aorta, presence of thrombus in the false lumen, presence of aortic rupture, and malperfusion or organ ischemia.
Treatment
Acute Type B Dissection
First-line treatment for uncomplicated acute type B aortic dissection is anti-impulse therapy, typically with a β-blocker designed to decrease blood pressure and heart rate, and pain control. Once patients are medically optimized in the hospital, surveillance imaging should be performed. Patients should undergo CTA or magnetic resonance angiography (MRA) prior to hospital discharge with follow-up imaging at 3, 6, and 12 months then annually thereafter to evaluate for aneurysmal formation, size of the false lumen, or dissection recurrence, which may indicate the need for surgical repair of a subacute or chronic type B aortic dissection.
Complicated acute type B aortic dissection is defined as persistent pain despite adequate medical management, evidence of end-organ malperfusion, or signs of impending rupture. Surgical management is indicated in these cases with either thoracic endovascular aortic repair (TEVAR) or open surgical repair. The principle of open surgical treatment is resection of the intimal tear and closure of the false lumen with re-approximation of the dissected aortic wall. While studies have not demonstrated a difference in late survival in patients who undergo TEVAR compared to open surgery, TEVAR is the treatment of choice in patients with complicated acute type B aortic dissection due to lower incidences of postoperative complications and short-term morbidity and mortality.
In acute type B dissections, the goal of TEVAR is to cover the intimal tear with a stent graft thereby reducing pressure in the false lumen. In patients with acute type B dissections and malperfusion syndrome, malperfusion of the side branches can result in either dynamic or static obstruction. Dynamic obstruction is the most common form of malperfusion and it results from compression of the true lumen by the false lumen resulting in compromised flow into the branch vessel. Coverage of the primary entry tear, which relieves the false lumen pressure, typically restores perfusion to the compromised branch vessels. Static obstruction is a form of malperfusion that occurs due to intimal flap extension into the branch vessel and will require stenting into the vessel. Not infrequently, the primary tear is in proximity to the LSA, which may require coverage of the LSA to obtain an adequate proximal seal. When this is necessary, consideration should be made for prophylactic LSA revascularization. The 2010 Society for Vascular Surgery (SVS) Committee on Aortic Disease recommendations for consideration of LSA revascularization are as follows:
1. In patients undergoing elective TEVAR where coverage of the LSA is necessary, routine preoperative revascularization is recommended (Grade 2, Level C evidence).
2. In patients where the anatomy to be treated involves perfusion to vital organs routine preoperative revascularization is recommended (Grade 1, Level C evidence). Examples are: patent left internal mammary to coronary artery bypass graft, termination of the left vertebral artery into the posterior inferior cerebellar artery, absent/atretic/occluded right vertebral artery, patent left arm arteriovenous shunt for dialysis, prior infrarenal aortic surgery with previously ligated lumbar and sacral arteries, extensive coverage (i.e. >20 cm) of the descending thoracic aorta, hypogastric artery occlusion, and presence of early aneurysmal disease where future intervention may involve the distal thoracic aorta.
3. In patients who present with an acute thoracic emergency requiring urgent TEVAR where coverage of the left subclavian artery is necessary, consideration for LSA revascularization should be individualized based on patient anatomy, urgency of the procedure, and surgical expertise for LSA revascularization (Grade 2, Level C evidence).
In patients with unfavorable anatomy or genetically mediated type B aortic dissection (i.e., connective tissue disorder), open surgical repair rather than TEVAR is recommended.
Chronic Type B Dissection
Treatment of patients with chronic, uncomplicated type B aortic dissection should be focused on blood pressure control, clinical follow-up, and surveillance imaging with lifestyle modification (i.e., avoid contact sports and isometric heavy weightlifting). Aneurysmal formation (>1cm expansion over 1 year) of a chronic type B aortic dissection is the most common indication for surgical intervention. Additional indications for surgical repair are: malperfusion, dissection recurrence, and expanding false lumen (i.e., >5mm expansion of the total aortic diameter in 6 months or >60mm of the total aortic diameter). Thus, survivors of acute type B aortic dissection require life-long surveillance imaging.
While TEVAR is the treatment of choice for patients with complicated acute type B aortic dissection, the optimal treatment for chronic type B aortic dissection is unclear. Surgical options are open repair, TEVAR, or hybrid repair, however there are no randomized control trials comparing the three techniques. Traditionally, open surgical repair is preferred in patients with favorable anatomy and patients with connective tissue disorders. The principle of open surgical treatment is replacement of the diseased descending thoracic and/or thoracoabdominal aorta with a graft to restore visceral perfusion. The goal of TEVAR in chronic type B aortic dissection is the same as in an acute type B aortic dissection. However, the main concerns with TEVAR for chronic type B aortic dissection is the persistence of the false lumen due to the minimal remodeling capacity of the chronically diseased aortic tissue and the thickened intimal dissection flap that may not readily re-approximate to the native aortic wall. Surgical options for chronic type B aortic dissection remain an area of ongoing debate and research.
Suggested Readings
- Brunkwall J, Lammer J, Verhoeven E, et al. ADSORB: a study on the efficacy of endovascular grafting in uncomplicated acute dissection of the descending aorta. Eur J Vasc Endovasc Surg. 2012;44(1):31-36.
- Erbel R, Aboyans V, Boileau C, et al. 2014 European Society of Cardiology guidelines on the diagnosis and treatment of aortic diseases: document covering acute and chronic aortic diseases of the thoracic and abdominal aorta of the adult. Eur Heart J. 2014;35(41):2873-2926.
- Fattori R, Cao P, De Rango P, et al. Interdisciplinary expert consensus document on management of type B aortic dissection. J Am Coll Cardiol. 213;61(16):1661-1678.
- Lombardi JV, Hughes GC, Appoo JJ, Bavaria JE, Beck AW, Cambria RP, et al. Society for Vascular Surgery (SVS) and Society for Thoracic Surgeons (STS) reporting standards for type B aortic dissections. J Vasc Surg. 2020;71(3):723-747.
- Matsumura JS, Rizvi AZ; Society for Vascular Surgery. Left subclavian artery revascularization: Society for Vascular Surgery Practice Guidelines. J Vasc Surg. 2010;52(4 Suppl):65S-70S.
