1、Aortic Dissection,Anatomy,Physiology and Principles of Therapy,History,1555 Vesalius diagnosed a pulsating tumor near the vertebrae in a patients back and called it “a dilatation of the aorta”1826 1826 Laennec introduced the term dissecting aneurysm 1800s surgery was performed on the entity by John
2、Hunter, Astley Cooper and others even before the era of general anesthesia Early operations were designed to produce distal internal fenestration to cause downstream decompression of the aorta.,History,1951 Lam and Aram introduced homografts for repair of descending thoracic aneurysms 1953 Cooley an
3、d DeBakey used artificial grafts for repair 1953 Bahnson introduced aneurysmorrhaphy 1957 cardiopulmonary bypass became available,Definition,True aneurysm localized enlargement of the aorta contained by all the layers of the aortic wall False aneurysm enlargement contained by the aortic adventitia a
4、nd periaortic fibrous tissue.,Definition,Aortic dissection Sudden catastrophic event in which a tear in the intima allows blood to escape from the true lumen of the aorta rapidly separating the inner from the outer layer of the media Column of blood is driven by the force of the left ventricular sys
5、tolic pressure which strips the intima from the adventitia,Definition,Acute less than 14 days old Chicken or the egg ? Hemorrhage in the media causes rupture of the intima or dissecting hematoma in an intimal tear.,Causes of Aneurysm,Medial degeneration and local dilatation Atherosclerosis Syphilis
6、(ascending only) Bacterial infections (mycotic) Congenital abnormalities Trauma Annuloaortic ectasia,Causes of Dissection,Inherent weakness of the aortic wall Hypertension 70-90% Pregnancy Iatrogenic Bicuspid aortic valve and coarctation Closed chest trauma,Pathophysiology,Law of Laplace: As a spher
7、e increases in size, the wall tension of the sphere increases Weakened wall Dilatation Expansion with pressure-related symptoms Rupture,Natural History,Not well documented Signs, symptoms and prognosis related to the size of the aneurysm Thoracic aneurysms larger than 6 cm are more prone to rupture
8、than the smaller ones 5 year survival for symptomatic aneurysms is 27% whereas 58% with asymptomatic ones survived the same period of time. Rupture is the most common cause of death,Natural History,Many patients with dissection die acutely due to cardiac tamponade or dissection of the LAD 8% of asce
9、nding ruptures survive without treatment 75% survive descending dissection,Classification,Type I - Begins at the aortic valve and may proceed to and include the abdominal aorta Type II Begins distal to the left subclavian artery and can encompass the entire aorta to the iliac arteries,Anatomical Con
10、siderations,Pathoanatomy,Dissection of the ascending aorta arises within several centimeters of the aortic valve 66% Dissection of the descending aorta occur just beyond the left subclavian artery at the ligamentum arteriosum Small percentage occur at the transverse arch or descending aorta,Pathophy
11、siology,After dissection into the media, blood rushes into the dissected area Necrosis of the aortic wall then develops several days after the event observed in 62% of cases Complications include aortic rupture, obstruction and occlusion of aortic branches,Clinical Signs and Symptoms,Demographics,Ma
12、les females 3:1 Sixth or seventh decade of life Patients with ascending dissection are about ten years younger at presentation than those with descending dissection,Symptoms,Sudden, severe chest pain tearing sensation in the anterior chest radiating to the arms or to between the scapulae May have sy
13、ncope, neurologic signs, weakness, hypotension.,Physical Findings,Paralysis Muffled heart tones New onset aortic insufficiency murmur Unequal blood pressure and pulses in the extremities Jugular venous distention tamponade Abdominal pain acute Acute hypertension and anuria,Diagnosis,Plain chest radi
14、ograph widened mediastinum, pleural effusion Electrocardiogram may resemble acute myocardial infarction particularly if the LAD is affected CT scan identifies the problem but does not provide a road map Angiography gold standard Transesophageal echocardiography,Therapy,Ascending Dissection,Surgical
15、emergency Can only be treated by operation May or may not require aortic valve replacement and/or coronary bypass surgery depending on the progression of the dissection Mortality about 20% depending on other medical problems and the presence of neurological symptoms,Descending Dissection,Therapy con
16、troversial If rupture present operation is the only alternative In the absence of rupture, medically treated patients do better than those undergoing operation due to comorbidities,Goal of Operative Therapy,Obliteration of the site of the intimal tear and the false lumen Reapproximation of the disse
17、cted aorta Repair of aortic valve or replacement with valve conduit Perform bypass grafting as needed,Conduct of the Operation,Appropriate preoperative assessment General anesthesia Cardiopulmonary bypass Ascending dissection profound hypothermia with circulatory arrest Descending dissection bypass
18、with/without arrest,Goal of Medical Therapy in Descending Dissection,Reduce the force of the blood traversing the weakened aortic wall Decrease cardiac contractile force beta blockade Increase runoff - vasodilators,Repair of Descending Dissection,Distal dissection with leakage of blood from the aorta Compromise of arterial supply to a specific organ or limb Continuous thoracic pain Extension of the dissection during medical therapy,Complications,False aneurysms Redissection Paralysis 12% Stroke Renal failure Infection,
