Diseases of the Aorta

, Eric M. Isselbacher2, Eric M. Isselbacher3 and Eric M. Isselbacher4



(1)
Harvard Medical School Cardiology Division, Department of Medicine, Massachusetts General Hospital, Boston, MA, USA

(2)
Harvard Medical School, Boston, USA

(3)
MGH Heart Center, Boston, USA

(4)
MGH Thoracic Aortic Center Cardiology Division, Department of Medicine, Massachusetts General Hospital, Boston, MA, USA

 



Introduction

Aortic Anatomy

General History and Physical Examination

Imaging Modalities

Chest Radiography (CXR)

Echocardiography and Ultrasonography

Computed Tomography (CT)

Magnetic Resonance (MR) Imaging

Aortography

Aortic Aneurysms

Definitions

Abdominal Aortic Aneurysms (AAA)

Thoracic Aortic Aneurysm (TAA)

Prevalence of Concurrent Aneurysms []

Thoracoabdominal Aortic Aneurysms

Acute Aortic Syndromes

Aortic Dissection

Intramural Hematoma []

Penetrating Atherosclerotic Ulcer of the Aorta (PAU)

Aortic Transsection

Vasculitides Involving the Aorta []

Giant Cell Arteritis (GCA)

Takayasu Arteritis

IgG4-Related Disease []

Quick Review (Table )

References


Abstract

The aorta is the largest artery in the body and diseases of the aorta, such as aneurysms, typically remain asymptomatic and undetected until either discovered incidentally on an imaging study or the development of an acute complication. When detected, both thoracic and abdominal aortic aneurysms should be followed carefully on serial imaging studies until large enough to merit intervention. In recent years, endovascular approaches have offered important alternatives to traditional open surgical techniques. Various classes of cardiac medications may have salutary effects on the aorta and can be used to reduce stress on the aorta and even improve vascular remodeling. The aorta is also affected by a number of congenital conditions as well as autoimmune vasculitides. For aortic coarctation, please refer to Chap. 21.


Abbreviations


AAA

Abdominal aortic aneurysm

ACC/AHA

American College of Cardiology/American Heart Association

ACEI

Angiotensin converting enzyme inhibitor

ACS

Acute coronary syndrome

AI

Aortic insufficiency

AS

Aortic stenosis

AV

Aortic valve

AVR

Aortic valve replacement

BAV

Bicuspid aortic valve

BP

Blood pressure

bpm

Beats per minutes

CABG

Coronary artery bypass graft

cm

Centimeter

CT(A)

Computed tomogram (angiography)

CXR

Chest x-ray

dP/dt

Change in pressure over change in time which is a measure of left ventricle ejection impulse, an index of shear stress on the aortic wall

DTAA

Descending thoracic aortic aneurysm

EVAR

Endovascular aortic aneurysm repair

GCA

Giant cell arteritis

HF

Heart failure

HR

Heart rate

IMA

Inferior mesenteric artery

IMH

Intramural hematoma of the aorta

IRAD

International Registry of Acute Aortic Dissection

LDL

Low density lipoprotein

LR

Likelihood ratio

M:F

Male to female ratio

mmHg

Millimeters of mercury

MMP

Matrix metalloproteinase

MR

Magnetic resonance

PAD

Peripheral artery disease

PAU

Penetrating atherosclerotic ulcer of the aorta

SBP

Systolic blood pressure

SD

Standard deviation

SMA

Superior mesenteric artery

STS

Society of Thoracic Surgeons

SVC

Superior vena cava

TAA

Thoracic aortic aneurysm

TAAA

Thoracoabdominal aortic aneurysm

TEE

Transesophageal echocardiography

TEVAR

Thoracic endovascular aortic repair

TGF

Transforming growth factor

TIA

Transient ischemic attack

TTE

Transthoracic echocardiography

USPSTF

United States Preventive Services Task Force



Introduction


The aorta is the largest artery in the body and diseases of the aorta, such as aneurysms, ­typically remain asymptomatic and undetected until either discovered incidentally on an imaging study or the development of an acute complication. When detected, both thoracic and abdominal aortic aneurysms should be followed carefully on serial imaging studies until large enough to merit intervention. In recent years, endovascular approaches have offered important alternatives to traditional open surgical techniques. Various classes of cardiac medications may have salutary effects on the aorta and can be used to reduce stress on the aorta and even improve vascular remodeling. The aorta is also affected by a number of ­congenital conditions as well as autoimmune vasculitides. For aortic coarctation, please refer to Chap.​ 21.


Aortic Anatomy






  • The largest artery in the body; muscular


  • Histologically contains three layers:



    • Intima (endothelium supported by internal elastic lamina)


    • Media (smooth muscle cells and numerous elastic fibers that give the aorta remarkable tensile strength)


    • Adventitia (collagenous support matrix with external elastic lamina, and site of entry of the vasa vasorum externae)


  • The segments of the aorta are differentiated by their anatomic location, size, and branch vessels (Table 11-1). Dimensions in males are slightly larger than in females, and the aortic diameters generally increase with age.


    Table 11-1
    Aorta anatomy










































    Aortic segments
    Divisions
    Approximate diameters (cm)
    Major branch arteries

    Ascending
    Root (sinuses of Valsalva)
    ≤4.0
    Right and left main coronary arteries

    Ascending aorta
    ≤3.5
    None

    Arch
    		  
    ≤3.0
    Brachiocephalic (innominate), left subclavian, and left common carotid arteries

    Descending
    		  
    ≤2.5
    Intercostal, spinal, bronchial arteries

    Abdominal
    Suprarenal
    ≤2.0
    Celiac axis, SMA, and renal arteries

    Infrarenal
    ≤2.0
    IMA, common iliac arteries


General History and Physical Examination






  • Relevant history:



    • Due to aorta: Chest, back, abdominal, flank pain or discomfort.


    • Due to complications of aortic disease



      • Depends on the segment of the aorta affected and branch vessels and distal organ territories that are impacted.


      • Look for neurological symptoms, syncope, heart failure, myocardial infarction, renal failure, thromboembolic disease, compression of adjacent structures such as nerves, esophagus or tracheobronchial tree.


  • Past medical history aortic disease, vascular disease, hypertension (HTN), thromboembolic events, trauma


  • Family history: aortic disease


  • Physical examination:



    • Bilateral blood pressure (BP) and pulses (radial, carotid, femoral), pulsus paradoxus


    • Look for evidence of aortic insufficiency (AI), tamponade, heart failure and neurological deficit, pulsatile abdominal mass


Imaging Modalities



Chest Radiography (CXR)






  • CXR has overall limited sensitivity (∼30–60 %) for thoracic aortic aneurysm, and alone cannot be used to exclude acute or chronic aortopathy.


  • Calcification or tortuosity of the ascending, arch, and descending thoracic aorta may be visualized, but this is a non-specific finding in the elderly.


  • Opacification of the aorticopulmonary window, enlargement of the thoracic aorta, increased mediastinal width, displacement of trachea from midline, or obscured/irregular aortic margin may indicate thoracic aortic aneurysm, dissection, or rupture. Displaced intimal calcium and pleural effusion may indicate dissection.


Echocardiography and Ultrasonography






  • Portable, avoids radiation and contrast media, and can be deployed intra-operatively.


  • Transthoracic Echocardiography (TTE)



    • TTE cannot provide a comprehensive exam of the aorta, but certain regions can be visualized: aortic valve and root, ascending aorta, arch, descending, and abdominal aorta


    • TTE is reasonable for assessing aortic valve disorders and monitoring aortic root and ascending aortic dilatation (e.g. especially in Marfan syndrome). It is not sensitive enough to rule out thoracic aortic dissection (sensitivity 70 %).


  • Transesophageal Echocardiography (TEE)



    • TEE can visualize the ascending aorta, transverse arch, and entire descending thoracic aorta. The distal ascending aorta and proximal aortic arch may be obscured by the trachea.


    • TEE, in contrast to other modalities, can provide functional information such as flow dynamics in true and false lumens, detection of AI, detection of cardiac tamponade, and assessment of left ventricular function.


  • Abdominal ultrasonography is the technique of choice for screening for infrarenal abdominal aortic aneurysm (AAA), but is less accurate as applied to the suprarenal aorta or branch vessels.


Computed Tomography (CT)






  • CT is a highly accurate, rapid, reproducible, and readily available technique for detecting and sizing aortic aneurysms and for the diagnostic evaluation of suspected aortic dissection.


  • CT is also helpful at mapping branch vessels, and for detecting mimics of aortic disease (e.g. pericardial disease, gastrointestinal disease).


Magnetic Resonance (MR) Imaging






  • MR is also a highly accurate technique for aortic imaging. However, the study time is lengthy and the patient is relatively inaccessible, making this modality unsuitable for acute or unstable patients.


  • MR is most often performed with intravenous gadolinium as a contrast agent, but the “black-blood” technique with spin-echo sequences can provide satisfactory images without the need for gadolinium.


Aortography






  • Catheter-based aortography is an invasive technique that can demonstrate the full extent of aneurysmal disease and dissection, map branch vessel involvement, and demonstrate the presence of AI.


  • However, aortography is not readily available in most settings, requires an expert ­physician operator, and requires that potentially unstable patients undergo a prolonged procedure.


Aortic Aneurysms



Definitions






  • Aneurysm  =  dilatation of the aorta involving all three vessel wall layers. Pseudoaneurysm  =  contained leak of blood in communication with vessel.


  • Fusiform  =  symmetric circumferential bulging of the aorta. Saccular  =  asymmetric ­localized bulging of the aortic wall.


Abdominal Aortic Aneurysms (AAA)






  • Epidemiology: up to 3 % prevalence >50 years, and 5 %  >65 years, with M:F ratio up to 10:1 [1].



    • Infrarenal AAA represents the most common location.


  • Etiology [2]:



    • Chief pathophysiologic factors are atherosclerosis and smoking. Male gender, advanced age, dyslipidemia, and family history also contribute.


    • Inflammation, both primary or secondary to atherosclerosis, is increasingly recognized as a key factor that results in oxidative stress in the aortic media, deterioration of aortic tensile properties, and apoptosis of smooth muscle cells.


    • There is an increased prevalence of AAA among first-degree relatives of affected individuals. Genetic basis still unclear (may include structural proteins, proteases such as matrix metalloproteinases (MMP), or immunomodulatory genes).


    • Bacteria and mycobacteria can generate infectious (also known as mycotic) aneurysms.


  • History and Examination [3, 4]



    • Most AAA are asymptomatic, and diagnosed on physical examination or incidentally on imaging.


    • Patients may have persistent pain in the lower abdomen or lower back, with a “­gnawing” character.


    • New or worsening pain may herald AAA expansion or rupture.


    • Classic triad of AAA rupture  =  pain, hypotension, and pulsatile abdominal mass.


    • Space-occupying effects of AAA include extremity ischemia, gastrointestinal or ­ureteral obstruction.


    • Palpation of a pulsatile mass may help detect AAAs large enough to merit repair ­(sensitivity 68 %, positive predictive value 43 %), but alone is not sufficient to exclude AAA.



      • Sensitivity correlates with AAA diameter (61 % for 3.0–3.9 cm, 82 % for >5.0 cm), but sensitivity decreases with obesity.


      • Palpation maneuvers for AAA are not believed to cause rupture.


    • Auscultation of bruits does not help diagnose AAA.


  • Screening and Diagnosis



    • Screening by exam and ultrasound is recommended by American College of Cardiology (ACC)/American Heart Association (AHA) (class I in 2006 guidelines) for males above age 60 who are siblings or offspring of parents with AAA.


    • The United States Preventive Services Task Force (USPSTF) recommends abdominal ultrasonography screening for infrarenal AAA in all males age 65–74 who have ever smoked (ACC/AHA 2006 guidelines IIa recommendation)


    • There are no recommendations for screening females or older males.


  • Prognosis: Risk of rupture varies with size. Annual risks are 0.3 % for AAA diameter <4.0 cm, 1.5 % for 4.0–4.9 cm, and 6.5 % for 5.0–5.9 cm [5].



    • Females with AAA have a greater risk of rupture than males, and experience rupture at smaller AAA diameters.


    • Overall mortality from AAA rupture >50–80 %.


    • Mural thrombus within an AAA is associated with increased rates of growth and ­cardiovascular events.


  • Medical Treatment



    • Smoking cessation and lipid control (LDL goal <70 mg/dL) is essential.



      • Studies of statins in AAA suggest possible reduction in AAA growth.


    • Aspirin, reduction in BP, and reduction of dP/dt are reasonable.


    • Beta-blockers carry a IIa recommendation for reducing the rate of AAA growth. For repair of atherosclerotic AAA, perioperative beta-blockade has a class I indication.


    • Angiotensin converting enzyme inhibitors (ACEI) may, in addition to BP reduction, reduce rate of AAA rupture.


    • Several studies have hinted a role for macrolide and tetracycline antibiotics based on a possible effect on Chlamydophila (previously thought to be important in AAA ­pathogenesis), and for anti-inflammatory and anti-metalloproteinase properties. However, such therapies are not yet recommended for clinical use.


  • AAA Repair [3]:



    • Indications: given high mortality from ruptured AAA, prophylactic repair should be undertaken when infrarenal AAA ≥5.5 cm in males and 5.0 cm in females. Infrarenal AAA of 4.0–5.4 cm should be re–imaged every 6–12 months.



      • Size threshold smaller in females, in those with small body habitus, or those with family history of AAA or rupture.


      • Growth velocity >0.5 cm/year may be an indication for repair.


      • Symptoms always constitute an indication for repair.


      • Suprarenal AAA (or thoracoabdominal aneurysms, see below) may be repaired at sizes of 5.5–6.0 cm.


    • Surgical repair of AAA



      • Resection of aneurysm and replacement with a synthetic graft.


    • Endovascular aortic aneurysm repair (EVAR) [6–9]



      • Percutaneous fluoroscopically-guided deployment of an expanding endovascular stent inside the aneurysm and attached to the aorta at the proximal and distal aneurysm margins, thereby excluding the aneurysm from aortic blood flow.


      • Only about half of AAA patients have anatomy suitable for EVAR: anatomic considerations include aneurysm length, proximal and distal landing zones, tortuosity, aneurysm thrombus or calcium, iliac artery diameter.


      • EVAR reduces peri- and immediate post-procedure morbidity and mortality and post-operative hospitalization, but whether the long-term outcomes are improved or are as durable as open surgical repair remains under investigation. Randomized trials suggest no difference in long-term mortality (EVAR-1, DREAM and OVER trials), although a single retrospective Medicare analysis from 2012 suggests higher all-cause mortality at 2.5 years from open repair vs. EVAR [9].


      • Endoleak: EVAR is associated with endoleak, or persistent blood flow into the aneurysm sac due to inability to completely exclude it from circulation.


      • Post-EVAR patients require imaging surveillance at 1, 6, and 12-months, in order to monitor for endoleaks, assess graft position, check aneurysm sac size, and gauge need for reintervention (class I).


      • Repair endoleaks that leak into aneurysm sac around an imperfect seal at proximal and/or distal anastomosis of stent graft OR structural defect, e.g. tear, stent fracture, etc.


      • EVAR patients have an approximately 10 % higher reintervention rate at 6 years compared to open repair.


    • The 2011 ACC/AHA guidelines on peripheral artery disease (PAD) give a class I recommendation for “open or endovascular repair of infrarenal AAAs” in “good surgical candidates.”



      • There is a class IIa recommendation for open AAA repair in good surgical candidates who could not comply with surveillance imaging post-EVAR.


    • Due to short-term advantages, EVAR has been considered for higher risk patients (e.g. older, high perioperative risks). However, the EVAR-2 trial studied patients deemed “physically ineligible” to undergo open repair and found no improvement in all-cause mortality versus medical therapy alone.



      • The 2011 ACC/AHA PAD guidelines give EVAR a class IIb recommendation in high risk surgical patients (uncertain benefit in this group).


Thoracic Aortic Aneurysm (TAA)






  • Epidemiology: TAA is believed to be about one-third as common as AAA. Because TAA is a clinically silent disease, the incidence is estimated from autopsy series at 3–4%.



    • TAA is most commonly seen  >age 50; the age of onset is earlier than for AAA.


    • Male:Female ratio is ∼2:1, as compared to AAA which has a much higher ratio.


  • Anatomic location:



    • Ascending aorta: 60 %



      • Root aneurysms are associated with Marfan syndrome, and ascending aortic aneurysms with bicuspid aortic valve or sporadic aneurysms.


    • Arch: 10 %


    • Descending thoracic aorta: 40 %


    • Thoracoabdominal (see below): <10 %


    • Multiple aneurysms: <10 %


  • Etiology [10–12]:

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Jul 13, 2016 | Posted by in CARDIOLOGY | Comments Off on Diseases of the Aorta

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