TOC | Cardiology   

Aneurysm of Aorta  

1. Abdominal Aortic Aneurysms
2. Thoraco Abdominal Aneurysms  
3. Dissecting Aortic Aneurysms    (* JAMA Feb.16, 2000;283 - New Insight )
   
4. Descending Thoracic Aortic Aneurysm
5. Ascending Aortic Aneurysms                                                                                                                 
6. Transverse Aortic Arch Aneurysms
7. Aortic Transection

Morphologically, aneurysms are classified into three types:

1. fusiform (spindle shaped), which involve the entire circumference of the aorta;
2. sacciform, which are characterized by a pouchlike protrusion from a narrow opening in the aortic wall; and
3. dissecting aortic, which are characterized by intramural separation, usually within the medial layer.

Etiology of Abdominal aortic aneurysms

• Atherosclerosis
• Syphilis
• Infection (mycotic)
• Trauma
• Relapsing polychondritis

Symptoms of Abdominal aneurysms
Most abdominal aortic aneurysms are asymptomatic before rupture.  Approximately 80% of aneurysms are identified incidentally on abdominal ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), or plain abdominal radiograph.

• Midabdominal, lumbar, or pelvic pain or vague discomfort.
• Shock (rupture of aneurysm into peritoneal cavity)
• Intestinal obstruction (duodenal compression)
• Peripheral edema (inferior vena caval compression)
• Gastrointestinal bleeding (rupture of aneurysm into duodenum)
• High-output heart failure (rupture of aneurysm into vena cava)
• Arterial insufficiency of legs (thrombosis of aneurysm or embolization of thrombus to legs)
• Acutely expanding aneurysms produce severe, deep back pain or abdominal pain radiating to the back. This may be accompanied by tenderness to palpation of the aneurysm. This presentation often precedes rupture and urgent treatment is required.  
• Less than 5% of patients with abdominal aortic aneurysm have evidence of embolization, usually small, to the distal arteries of the lower extremities. As many as 12% of aneurysms present for the first time with acute aneurysm rupture.
• About 5% of aneurysms present with nonspecific, idiopathic retroperitoneal inflammation and fibrosis. These aneurysms are referred to as inflammatory aneurysms. They are often associated with pain, fever, and fibrosis, which may involve the ureters and cause ureteral obstruction.

Aneurysms may cause pain in the abdomen or back, or pain may be referred to the thigh or scrotum. Complete thrombosis of an infrarenal abdominal aorta may produce symptoms of ischemia in the legs, and distal embolization of the atheromatous plaque, with or without intraluminal thrombus material, may produce signs of distal ischemia. An infrarenal abdominal aortic aneurysm may be detected on physical examination as a pulsatile abdominal aortic mass.  

Physical findings in patients with Abdominal aneurysms

• Palpable expansile mass in periumbilical area, often to left of midline
• Abdominal systolic bruit
• Decreased lower extremity pulses
• Continuous abdominal bruit and high-output heart failure (rupture of aneurysm into inferior vena cava)

DX:
Most abdominal aortic aneurysms are asymptomatic and are diagnosed incidentally during other diagnostic studies, such as plain radiography of the abdomen, abdominal ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI).

Approach to Abdominal aneurysm:
The risk of rupture of abdominal aortic aneurysms is directly related to the size of the aneurysm.
A 6-cm aneurysm is considered large and is an indication for operation unless extenuating medical risks exist.

Contraindications to elective surgical resection include severe cardiac, cerebral, pulmonary, or renal disease; uncontrolled malignant disease; and other severe or disabling diseases. The mortality rate for elective nonruptured aneurysm of the abdominal aorta is less than 2 to 3%.

Selection of Patients for Open Surgical Repair
(Ref: Townsend: Sabiston Textbook of Surgery, 16th ed., 2001 )

1. Most patients with aneurysms larger than 5 cm are candidates for surgical repair if they are good surgical candidates and have a life expectancy greater than 2 years.
2. Patients with significant comorbidities and higher surgical risk may be considered if the aneurysm is large (greater than 6 to 7 cm).
3. Patients with aneurysms between 4 and 5 cm are candidates for repair if there is evidence of more than 0.5-cm enlargement over a 6-month period.
4. Patients with evidence of rapid expansion, tenderness in the region of the aneurysm, and back or abdominal pain, which may originate in the aneurysm, should undergo urgent aneurysm repair. Peripheral embolization originating from the aneurysm is an indication for repair, regardless of aneurysm size.

RX:
Treatment is essentially surgical and consists of resection of the aneurysm and graft replacement. A Dacron tube graft is used if the common iliac arteries are not affected; otherwise, a bifurcation graft is used.

Endovascular techniques were recently introduced to repair the aneurysm endoprosthetically. The prosthesis, which is introduced through the common femoral artery, is secured to the normal aortic wall above the aneurysm and distally beyond the aneurysmal disease. Both straight (tube) and bifurcation grafts have been employed. The completion of prospective randomized multicenter trial studies is required before the efficacy of these endovascular grafts can be recommended with confidence.

**  Rupture Rate of Large Abdominal Aortic Aneurysms         Lederle FA et al. JAMA 2002 Jun 12; 287:2968-72.

Recent data suggest that abdominal aortic aneurysms (AAAs) should be repaired when diameters reach 5.5 cm (Journal Watch May 14 2002). However, because some patients are at very high risk for operative complications, outcomes without surgery are of interest. Investigators at U.S. Veterans Affairs hospitals followed 198 patients (mean age, 74) who had AAAs that measured at least 5.5 cm and who did not undergo surgery because of either poor medical condition or patient refusal. AAAs were evaluated by ultrasound every 6 months.

During a mean follow-up of 1.5 years, all-cause mortality was 57%. For patients whose initial AAA diameters were 5.5 cm to 6.9 cm, risks for AAA rupture at 1 and 2 years were about 10% and 20%, respectively. For patients with initial diameters of 7 cm or larger, 1- and 2-year risks for rupture were 33% and 44%, respectively. Risk for rupture was related to AAA expansion: For example, when an observed AAA attained a diameter of 8 cm, 1- and 2-year risks were 36% and 55%, respectively. Eleven of 17 patients who underwent surgery for ruptures died.

Comment: In elderly populations like this one, with a high burden of underlying cardiopulmonary disease, the decision to perform elective AAA repair or not is difficult. These data will be useful when clinicians advise such patients about the pros and cons of surgery. In some cases, the balance may be tipped toward intervention if the AAA is amenable to endovascular repair instead of open surgery.— Allan S. Brett, MD        Journal Watch June 21, 2002

NEJM May 8, 2003 Small Abdominal Aortic Aneurysm  Vol. 349:1895  Janet T. Powell    

Thoraco-Abdominal Aneurysms        

Thoracoabdominal aneurysms, which are usually fusiform, involve different portions of the descending thoracic and abdominal aorta. Crawford's classification provides a better understanding of the surgical risks and the dreaded complications of paraplegia, parapesis, or both.

• Type I involves most of the descending thoracic and upper abdominal aorta above the renal arteries.
• Type II involves most of the descending thoracic aorta and most or all of the abdominal aorta; this type has the highest incidence of neurologic complications.
• Type III involves the distal descending aorta and most of the abdominal aorta.
• Type IV involves most or all of the abdominal aorta, including the visceral vessel segment.

The causes of these aneurysms are usually degeneration, atherosclerosis, and aortic dissection. Occasional causes are trauma, infection, and aortitis. Most of these aneurysms are fusiform. Without surgical resection, the 2-year survival rate is about 24%, with half of these deaths due to rupture of the aneurysm.

SX:
Thoracoabdominal aneurysms may be asymptomatic. Most, however, produce symptoms before rupture. The patient may complain of pain in the chest, abdomen, flank, or back, or symptoms may be related to compression of adjacent structures, such as the tracheobronchial tree, esophagus, or recurrent laryngeal nerve, the last causing hoarseness.

DX:
Rarely, the diagnosis is made by palpation of the abdominal aortic component. A plain radiograph of the chest showing widening of the descending thoracic aorta is most common. MRI or CT provides a more exact diagnosis, including the location and extent of the aneurysm. Total contrast aortography in multiple views is necessary for complete evaluation of associated disease of the renal, visceral, or iliac arteries.

RX:
Treatment is surgical, consisting primarily of graft replacement. A combined thoracoabdominal incision is usually used. A Carlens (double-lumen endotracheal) tube provides deflation of the left lung and selective ventilation of the right lung.

Paraplegia, paresis, or both are the most dreaded complications of operation for thoracoabdominal aneurysms. A number of factors are involved, including the aortic clamp time and the extent of the aorta replaced. Among the methods that have been advocated to minimize neurologic complications are atrial-femoral bypass, femoral-to-femoral bypass, cerebrospinal fluid drainage, and somatosensory evoked potential monitoring. Distal aortic perfusion, reimplantation of critical spinal arteries, and drainage of cerebrospinal fluid are particularly valuable. The incidence of paraplegia or paresis is 31% in type II aneurysms but significantly less in other types of thoracoabdominal aneurysms when the simple cross-clamp technique is used. Woven Dacron grafts are employed. An island of aortic tissue containing the renal and visceral vessels, as well as spinal arteries, can often be incorporated onto the main graft. This difficult major surgical procedure can now be performed with an expected survival rate of more than 90%.

Dissecting Aortic Aneurysms                   Classsification |  RX

Dissecting aneurysms of the aorta are characterized by an intimal tear with hemorrhagic intramural separation of the medial layer of the aortic wall. The intimal tear originates, with decreasing frequency, in the ascending aorta, the descending aorta, and the aortic arch. The dissection usually extends distally but may extend proximally and creates a false lumen. Initial dissection may result in rupture and fatal hemorrhage. The dissection may also rupture into the pericardium to involve the aortic valve or coronary arteries and produce cardiac tamponade, acute aortic valvular insufficiency, heart failure, or occlusion of the coronary arteries. Distal dissection may cause obstruction of the major brachiocephalic arteries and cause a stroke or occlusion of the renal or mesenteric arteries followed by renal failure, mesenteric infarction, or occlusion of the iliac arteries with resulting ischemia in the limbs. The predominant underlying pathologic condition is medial degeneration in Marfan's syndrome.  Most patients have associated uncontrolled hypertension. Additional risk factors include pregnancy, coarctation, and idiopathic kyphoscoliosis. The initial course of the disease has an extremely grave prognosis, with death in 50% of patients within the first 2 days of onset. A small percentage of patients survive a few years without treatment. Aortic dissection occurs twice as often in men as in women, and most patients are in the fourth to seventh decades of life.

JAMA Feb.16,200;283:897  -  While sudden onset of severe sharp pain was the single most common presenting complaint, the clinical presentation was diverse. Classic physical findings such as aortic regurgitation and pulse deficit were noted in only 31.6% and 15.1% of patients, respectively, and initial chest radiograph and electrocardiogram were frequently not helpful (no abnormalities were noted in 12.4% and 31.3% of patients, respectively). Computed tomography was the initial imaging modality used in 61.1%. Overall in-hospital mortality was 27.4%. Mortality of patients with type A dissection managed surgically was 26%; among those not receiving surgery (typically because of advanced age and comorbidity), mortality was 58%.   Mortality of patients with type B dissection treated medically was 10.7%. Surgery was performed in 20% of patients with type B dissection; mortality in this group was 31.4%.

The DeBakey classification of aortic dissection is as follows:

• type I, the dissecting process involves the entire aorta, usually originating in the ascending aorta, but it may begin anywhere in the aorta and extend both proximally and distally;
• type II, the dissecting process is limited to the ascending aorta (aortic valvular insufficiency can occur with both types);
• type III, the intimal tear usually arises in the descending thoracic aorta at or just distal to the left subclavian artery and may extend distally to the diaphragm or the aortic bifurcation.

Stanford Classification of  Aortic Dissections

• Type A - All dissections involving the ascending aorta, regardless of the site of origin
• Type B - All dissections not involving the ascending aorta

Descriptive Classification of Aortic Dissections

• Proximal Includes - DeBakey types I and II or Stanford type A
• Distal Includes - DeBakey type III or Stanford type B

RX:
Medical treatment is indicated initially in patients with uncomplicated aortic dissection, particularly in those with aneurysms of the descending thoracic aorta, evidence of imminent rupture, or occlusion of a major aortic branch. Medical treatment includes controlling the blood pressure and reducing cardiac contractility with nitroprusside and Beta-blockers as labetalol, propranolol. The goal is to stabilize the patient's condition so that elective surgical resection can be performed if surgical intervention is necessary. If there is evidence of imminent rupture with pain indicating continued dissection or occlusion of a major branch of the aorta, emergency surgery is imperative.

[Normodyne (Labetalol)  IV bolus 20 mg slowly over 2 min, additional 40 or 80 mg can be given at 10 min interval until desired BP achieved.  Max. effect usually occurs within 5 min of each injection.  Max. dose 300 mg total IV.  Half life is 5-8 hours.  Then, 100, 200, 300 mg tab.  Start 100 mg bid, usual dose 200-400 mg bid PO.   Ref: Chest 1991;99:724 Asfoura JY, Vidt DG]

[Esmolol (Brevibloc) initial loading dose of 0.5 mg/kg IV over 1 min, followed by infusion of 0.05 mg/kg/min, the rate can be increased at 4 min intervals by 0.05 mg/kg/min.  Rates beyond 0.3 mg/kg/min have not been shown to provide added therapeutic benefit. The half-life is about 9 min. The concentration of the med should be < 10 mg/ml due to vein irritation.]

If the diagnosis of aortic dissection is suspected, contrast aortography usually gives the surgeon the necessary information to treat the patient. In addition, CT, MRI, or transesophageal ultrasonography is useful for defining the location and extent of the aortic dissection.

Treatment of types I and II aortic dissection is surgical after initial stabilization. There is a high incidence of rupture into the mediastinum or pericardium with tamponade or involvement of the aortic valve and heart failure. Operation consists of resection of the proximal segment of the ascending aorta and replacement with a woven Dacron graft, including obliteration of the false lumen by approximation of the inner and outer walls with the use of cardiopulmonary bypass and cardioplegia. Some patients require concomitant aortic valve replacement and reattachment of the coronary arteries.

In type III dissection, patients are initially treated medically to control hypertension and cardiac contractility.
Surgical treatment is required in patients who have complications with continued pain, suggesting further dissection; evidence of compromise of perfusion to the mesenteric/renal arteries or legs; or continued enlargement of the false lumen. For pts with type III dissections who do not have life-threatening complications, operative therapy may be delayed. [Ref: Circulation 1990;82 (Suppl IV):39 Glower DD, Fann JL; Circulation 1992;86 (Suppl II):1 Neya K, Omoto R]

Resection of the descending thoracic aorta, with obliteration of the distal false lumen and replacement with a woven or albumin-coated Dacron graft, is the procedure of choice.

All patients with a history of dissection of the aorta should be examined annually with serial CT scans to evaluate the aorta and false lumen for evidence of further aortic disease. Most of these patients require control of hypertension. Surgical results of treatment of aortic dissection have been extremely gratifying with minimal perioperative morbidity and good long-term results. 

Ref:
Rakel: Conn's Current Therapy 1998, 50th ed., Copyright © 1998 W. B. Saunders Company
Joseph Alpert: Manual of Cardiovascular Diagnosis & Therapy
Braunwald : : Heart Disease 1997,  5th Ed

06202002