Diseases of the aorta Flashcards
What is the function of elastin in the media? What happens to it when we age?
Elastin in the media allows the aorta to expand during systole and recoil during diastole. With age, the elastic component of the aorta and its branches degenerates, and as collagen becomes more prominent, the arteries stiffen. Systolic blood pressure tends to rise with age because less energy is dissipated into the aorta during left ventricular contraction.
What is an aneurysms? What types are their available?
is an abnormal localized dilatation of an artery.
Diffuse ectasia, true aneurysm, and pseudoaneurysm
What is diffuse ectasia?
Diffuse ectasia develops in older patient as elastic fiber fragment, smooth muscle cells decrease in number, and acid mucopolysaccharide ground substance accumulates within the vessel wall.
What is true aneurysm? What types are there?
True aneurysm represents a dilation of all three layers of the aorta, creating a large bulge of the vessel wall. Fusiform aneurysm, is characterized by symmetrical dilation of the entire circumference of a segment of the aorta. Saccular aneurysm is a localized outpouching involving only a portion of the circumference.
What is pseudoaneurysm?
Pseudoaneurysm is contained rupture of the vessel wall that develops when blood leaks out of the vessel lumen through a hole in the intimal and medial layers and is contained by a layer of the adventitia or perivascular organized thrombus. They are very unstable and are prone to rupture completely.
what are the etiology and pathogenesis of a true aortic aneurysms? Both fo ascending and descending aortic aneurysm.
Ascending thoracic aortic aneurysms are characterized by cystic medial degeneration, a condition of degeneration and fragmentation of elastic fibers, with subsequent accumulation of collagenous and mucoid material within the medial layer. Cystic medial degeneration occurs with age and is associated with hypertension. It also develops in certain inherited disorders of connective tissue, such as:
- Marfan syndrome – is caused by missense mutation of the fibrillin-1 gene (FBN1), which impair formation of functional microfibrils in elastin. Abnormal fibrillin-1 also limits the binding and inactivation of TGF-β (which regulates proliferation and differentiation).
- Loeys-Dietz syndrome – is an autosomal dominant disorder caused by genetic mutations of TGF- β receptor.
- Ehlers-Danloas type IV syndrome - caused by mutations of the TGF-β receptor and genes encoding the smooth muscle-specific alpha-actin and beta-myosin heavy chain, which are important component of the contractile complex.
Aneurysms of the descending thoracic and abdominal aorta are associated with atherosclerosis (its risk factors) with other pathophysiologic mechanism, including a genetic predisposition, local vessel inflammation, and an imbalance between synthesis and degradation of extracellular matrix protein. Aneurysm formation is associated with markers of inflammation, including CRP and cytokines such as IL-6. Infrequent causes of aortic aneurysms include weakness of the media from infection of the vessel wall by bacteria and fungi.
What are the symptoms of aneurysm ?
Most aneurysms are asymptomatic, some may aware of a pulsatile mass. Thoracic aorta aneurysms may compress the trachea or mainstream bronchus, resulting in cough, dyspnea, or pneumonia. Compression of the esophagus can result in dysphagia, and involvement of the recurrent laryngeal nerve may lead to hoarseness. Abdominal aortic aneurysms may cause abdominal or back pain.
What does the risk of rupture depends on? Where does the blood goes?
The risk of rupture depends on the size on the aneurysm (due to the increase in wall tension). The mean rate of thoracic and abdominal aortic aneurysms expansion is 0.1 and 0.4 cm/year.
Aortic aneurysm can rupture or may leak slowly or burst suddenly, resulting in profound blood loss and hypotension. Thoracic aortic aneurysms may rupture into the pleural space, mediastinum, or bronchi. Abdominal aortic aneurysms may rupture into the retroperitoneal space or abdominal cavity into the intestine, resulting in massive gastrointestinal bleeding.
What are the treatment for aneurysm?
Surgical treatment is considered for ascending aortic aneuryms greater than 5.5 to 6.0 cm. Surgical repair for descending thoracic aortic aneurysms measuring 6.5 to 7.0 cm, for abdominal aortic aneurysms measuring 5.5 cm or more, and for smaller aneurysms that enlarge at a rate greater than 1 cm/year.
Surgical repair of abdominal aortic aneurysm involves placement of a prosthetic graft. The operative mortality for such procedures at high-volume institutions is 1% to 2%.
Medical management, including risk factor reduction (smoking cessation). β-blockers may reduce the expansion rate of thoracic aortic aneurysms in patients with marfan syndrome.
What is aortic dissection?
Aortic dissection – blood from the vessel lumen passes through a tear in the intima into the medial layer and spreads along the artery.
- Acute intramural hematoma is a variant of aortic dissection characterized by a hemorrhage in the wall of the aorta without intimal tear.
- Penetrating atherosclerotic ulcer result from erosion of a plaque into the aortic wall.
- Aortic rupture may be a complication of aortic dissection, intramural hematoma, penetrating atherosclerotic ulcer, or result from trauma.
What are the etiology and pathogenesis of aortic dissections?
The diving force of the systemic pressure helps blood to enter into the media and propagate along the plane of the muscle layer. Another potential origin of aortic dissection is rupture of vasa vasorum with hemorrhage into the media, forming a hematoma in the arterial wall that subsequently tears through the intima and into the vessel’s lumen.
Conditions that interferes with the normal integrity of the elastic or muscular component of the medial layer predispose to aortic dissection. Such degeneration may arise from chronic hypertension, aging, and/or cystic medial degeneration. Traumatic insult to the aorta can initiate dissection.
How are dissections classified?
Dissections are classified into standard type A and B, depending on their location and extent.
- Typical A dissection – the ascending aorta and/or aortic arch is involved, regardless of the site of the primary tear.
- Typical B dissection doesn’t involve the ascending aorta and arch, confined to the descending thoracic and abdominal aorta.
What are the symptoms of aortic dissection?
Severe pain with a “tearing” or “ripping” quality in the anterior chest (type A dissections) or between the scapulae (type B dissections). The pain then radiates along the aorta anywhere in the thorax or abdomen.
Other symptoms include (1) rupture through the adventitia anywhere along the aorta; (2) occlusion of the major branches of the aorta by the propagating hematoma within the vessel wall, which compresses the lumen and can result in myocardial infarction (coronary artery involvement), stroke (carotid artery involved), visceral ischemia, renal failure, or loss of pulse in an extremity; and (3) extension into the aortic root, with disruption of the aortic valve.
Hypertension is detected either as a cause of dissection, a result of the sympathetic nervous system response to the severe pain, or because of diminished renal vascular flow, with activation of renin-angiotensin system. If the dissection has occluded one of the subclavian arteries, difference in systolic blood pressure between the arms are noted. In a type A dissection, an early diastolic murmur can be detected on auscultation. Leakage from a type A dissection into the pericardial sac may produce signs of cardiac tamponade.
With what can we diagnos a patient which dissection?
Technique to detect dissection include contrast-enhanced CT, transesophageal echocardiography (TEE), MR angiography, and contrast angiography.
What are the treatment available for aortic dissection?
Suspicion of acute aortic dissection warrants immediate medical therapy to reduce SBP (aiming for 120) and to decrease the force of the left ventricular contraction and to minimize aortic wall shear stress.
Pharmacologic agents include: β-blocker and vasodilators (such as sodium nitroprusside) to reduce blood pressure.
In proximal (type A) dissection, surgical therapy involves repairing the intimal tear, suturing the edges of the falsa channel, and if necessary, inserting a synthetic aortic graft.
Uncomplicated type B dissections are managed with aggressive medical therapy alone; early surgical intervention doesn’t improve the outcome in these patients. However, if there is clinical evidence of propagation of dissection, compromise of major branches of the aorta, impending rupture, or continued pain. Percutaneous catheter-based repair with endovascular stent grafts can be used to stable patients with type B dissections.
