Definition:true aortic aneurysms (localized aortic enlargements contained by walls that,although attenuated,have all layers of normal aortic wall)and false aneurysms(localized enlargements in which the wall consists of advantitia and compressed periaortic fibrous tissue)as well as chronic aortic disections involving the ascending, arch, descending thoracic , or thoracoabdominal portion of the aorta.
History:Chronic Ascending,Arch,Descending and Thoracoabdominal Aortic Aneurysms has been chalanged by surgeon since 1902 when Rudolph Matas of New Orleans intoduced the repair of aortic Aneurysm from inside with no disection at out side wall of Aneurysm.this was not practice until D.Cooley,M.DeBakey popularized this in the abdominal aortic aneurysm repair.
Dubost and colleagues working in paris reported in 1952 the 1st successful case of aortic aneurysem resection and restoration of blood flow in the abdominal aorta by utilizing preserved aortic homograft(allograft).in 1953 DeBekey,Cooley reported successful resection with the same technic.
Aortic Homograft BANK were promptley established in some centers to provide Aortic replacement graft.
The resection of Descending Aortic Aneurysm was reported in 1951 by Lam and Aram ,by replacing Descending Aorta with homograft their patient developed paraparesis and died 6 weeks after operation with empyema of the lung.
Although diseases of the thoracic Aorta are among the most serious problems for cardiothoracic surgeon to deal progress has been made inthe past few years are enormous and overall surgical results are extremly gratifying .
Morphology
Arterio-sclerotic aneurysms involve almost equaly the ascending and descening aorta.More rarely involves the aortic arch and complete extent of thoracoabdominal aorta.
The arteriosclerotic aneurysms are usually fusiform shape which distinguishes these from Pear shape aortic aneurysm seen in patients with marfan syndrom.
In patients with nonmarfan syndrom aortic root aneurysm canbe sizeable and these are designated nonspecific ANULOAORTIC ECTASIA due to Myxomatous degeneration of aortic media .the aneurysm of these patients are in at the same risk of disection, rupture as in the marfan patients.
Marfan Aneurysm: In majority of patients with marfan syndrom sizeable aneurysm of the aortic root (anulo aortic ectasia) develops by age of 20 years and without surgical intervention almost 90% of them die as result of cardiovascular problems. In marfan syndrom in simplistic way the amount of elastin fibers are reduced and tensile stregth of aortic wall is markedlyreduced.
Aortic disection : is most common catastrophic illness of the aorta ,with frequency of 2000 new cases per year in the United States of America. From the first attempts at surgical intervention in 1935 by Curua,Balmer next 20 years was frusterating with high surgical mortality .In 1955 DeBakey ,Cooley opened era of modern surgery . In 1965 wheat Palmer, Bartley demonstrated the importance of blood pressure and aortic wall stress.
I will discuss:
1-Incidence,definition,classification of aortic disection .
2-Epidemilogy of recent series.
3-Pathogenesis and risk factrs.
4-Clinical features and noninvasive imaging approaches to diagnosis.
5-Surgical and medical management.
Incidenc, classifications of aortic disection .
Acute aortic disection occurs at rate of 5-10 person per million of population per year, which is 2-3 times the incidence of rupture abdominal aortic aneurysm. Male higher than female with ratio 3:1 from 50-70 years of age .Patients in 50-60 comprised 60% of all the patients,in female under 40 years of age occurs in pregnancy .
Aortic disection is relatively rare under age 40 except for familial predisposition ,marfan syndrom or congenital heart diseases such as aortic coarctation and bicuspid aortic valve. 95% of aortic disection arises in one of the two location:
1-Ascending aorta,few centimeters above aortic valve.
2-Descending aorta just beyond left subclavian artery.
3-Remaining 5% originate in the aortic arch or abdominal aorta.
Classification have evolved from those introduced by DeBakey.Stanford classification based upon the segment of aorta involved in disection rather than point of origin.
DeBakey classified 3 types of disection.
type one originate in ascending aorta and involves ascending ,arch and descending aorta.
type two 2 originate and limits to ascending aorta.
type three 3 originate distal to lt subclavian artery and extends to distal or proximal aorta.
Stanford classification recognizes two types .
type A (proximal or ascending)
Type B (distal or descending).
this classificaton is more than an anatomical distinction. Almost 75% of untreated patients with type A die within 2 weeks of disection. this is twice the incidence mortality of descending type in same interval.
Epidemiology.
In early series of medically managed cases the mortality was 50% in 1st 48 hours (1% /hour) risk then reduces in patients who survive beyond acute level (1st two weeks )but prognosis is poor for long term.
In type B conservative management is recomended unless spcific complications develops.
Pathology and risk factors
It appears that in the vast majority of disection 3 factors are involved :
1-Abnormal medial layer of the aortic wall.
2-Tear which initiates the process of the aortic disection.
3-Circulatory forces which propagate the progression of aortic disection ,Pulsatile flow ,mean arterial blood pressure.
Property of the arterial wall:The normal aortic wall contains ELASTIN ,COLLAGEN,SMOOTH MUSCLES. elastin maintains distensibility of the aortic wall ,collagen for structural integrity and resistance,smooth muscles for vascular tone.By the process of aging degenerative changes occur in most of the length of the aorta.Cystic medial necrosis defines damage to elastic tissue and smooth muscle cell loss and accumulation of basophilic ground substance. This process is normal physiology of aging but develops more rapidly in population with bicuspid aortic valve,pregnancy,and severly in marfan syndrom who comprise 11% of aortic disection population.The pausel is the mechanism by which the medial layer of the aorta is subject to accelerated rate of degeneration.The molecular genetic now demonstrated in the cases of marfan syndrom there is mutation of the gene on the chromosome 15 ,regulating synthesis of fibrillin which is the lipoprotein essential for structural integrity of aortic wall.89%-90% of aortic disection patient do not have marfan syndrom and the pathology of medial layers in this patients are poorly understood.
aortic tear:Aortic dilation due to disease medial layer increases wall tension of the aorta leading to tear in the most inner layer of the aorta (intima)which is starting point of aortic disection.Hemodynamic forces :The greatest impact of these forces are in the ascending aorta with each cardiac systol the 1st 2 cm of ascending aorta is subjected to the great pulsatile load (or dp/dt)determind by the contractility of the heart and most importantly the blood pressure.The most external motion and flexion also occur in the ascending aorta with each cardiac systol.The aortic dilation which mostly occur in ascending aorta greatly increases shear stress according to the LAPLACEs law, wall tension at constant arterial pressure increases with increasing luminal diameter.
In the case of type B disection the intimal tear is just distal to the lt subclavian artery.This is the site of the isthmus when mobile portion of the ascending aorta ,aortic arch joins the immobile portion of the descending aorta.This region of the aorta is subject to the significant amount of tortion ,flexion during each cadiaccycle .These forces can cause transverse tear in the intima ,conditions of sudden decelaration can occur in the car accident. Falls from heights can lead to direct traumatic disection.
Progress of disection:
Eperiments shows the disection propagates with high blood pressure and pulsatile flow.
diagnostic approach
:
1-Always consider diagnosis of acute aortic disection in patient with chest pain.
2-Chest pain (present in the 90% of the patients)
3-Hypertension 70%
4-Pulse deficit
5-Neuorological deficit
6-Cardiac and visceral ischemia
7-Aortic valve insuficiency (25-60% in type A )
8-Extravasation.High risk patient are those with pleural, mediastinal hematoma.Ominous if pericardial rub(abnormal heart sound),hemoptysis(coughing up blood),hematemesis present.Pericardial rub when presen is ominous sign indicating aortic root involvement with leakage of blood intothe pericardial sac.Indeed any signs of leakage of blood such as in the pericardial ,pleural,mediastinum,trchea,bronchus and gastrointestinal tract are ominous and patient is high risk surgical candidate.
Diagnostic procedures:
1-Beside of diagnostic suspicion ,chest xray(85% abnomal),angiogram(95% accuracy),cat scan of the aorta,mri(mag res image)and transesophageal echo cardiogram (TEE)together confirms the diagnosis.The TEE can be done at the bedside within 20 minutes with very high accuracy.
medical mangement of the acute disection:EKG monitor ,arterial and pulmonary pressure monitoring.Treatment:lower blood pressure with pharmocological agents(mean bp dp/dt).
In type A long term mortality still high ,post surgical repair .
Frech study reveals the aortic disection is an evolving process that may require one or several reoperation after initial repair and again close follow up is essential for timing of reoperation .Finaly in patient with aortic dilatation of aorta without disection it is reasonable to recomend operation in cases where aneurysm is six (6)cm in diameter or 5 cm in the case of marfan's syndrom,and certainly greater aggresiveness if patient symptomatic or aneurysm expanding.
In the Aneurysm of ascending aorta ,arch, and disecting aneurysms usually patient is cooled down to the tempreture of 27-18 centigrade (rectal temp)the distal portion of the ascending aorta is cross clamped and with usual cardiopulmonary technic the aneurysm or disection is resected and replaced with dacron graft or valve and graft if the aortic valve also is incompetent,or in some cases the aneurysm and disected portion can be replaced with human valve homograft and aortic conduit, the results at present are gratifying if the diagnosis is made early and proper intra operative precaution are utilized.
