Leora Yarboro, MD, and John A. Kern, MD
Concept
- Pathophysiology of aortic aneurysms
- Associated genetic syndromes
- Indications for operation
- Preoperative evaluation
- Imaging
- Operative strategy
- Conduit
- Distal anastomosis
- Bicuspid aortic valve disease
Chief complaint
“A 58-year-old man presents to clinic for evaluation of incidentally noted ascending aortic aneurysm (5.8 cm) and aortic stenosis.”
Differential
In this case there is little else in the differential. However, it is important to personally review the films to confirm the measurements of the aorta as well as the extent of involvement (i.e., root–transverse arch). Obtain any previous studies to determine rate of growth. Rule out chronic dissection.
History and physical
Many patients with ascending aortic aneurysms are asymptomatic. However, in your history be sure to ask about any chest pain, dyspnea, embolic events and ask about commonly associated conditions including: atherosclerosis, bicuspid aortic valve, family history, connective tissue disorders (Marfan’s syndrome, Loeys-Dietz, Ehlers-Danlos) and inflammatory conditions. Perform complete cardiovascular, pulmonary, and neurologic exams.
Pathophysiology
Aortic aneurysms can arise in the setting of connective tissue disorders, bicuspid valve disease or in an otherwise normal tri-leaflet valve (degenerative). The natural history of aortic aneurysms is to continue to dilate over time due to forces imposed in accordance with the Law of Laplace Tension = Pressure x Radius. Although some aneurysms stay remarkably stable over time. Risk of rupture and dissection are directly related to the diameter of the aneurysm with significant increase in mortality for ascending aneurysms > 6 cm.
Connective tissue disorders
Recommendations are covered under the chapter on Aortic Root Aneurysms but here are a few additional details:
Patients with connective tissue disorders typically present at a younger age and have higher risk of rupture at smaller diameters. Most centers recommend surgical intervention for ascending aortic aneurysm associated with connective tissue disorders at 4.5-5.0 cm.
- Marfan’s syndrome
- Autosomal dominant, prevalence 1/5000, mutation in gene on chromosome 15 encodes fibrillin-1. Phenotype is highly variable. Major diagnostic criteria include: positive family history of Marfan’s, pectus excavatum and/or arm span – height ratio > 1.05. Mitral insufficiency can also be associated with Marfan’s syndrome. Without surgery most patients with Marfan’s die in their third decade from complications of aortic root aneurysm. There is data to suggest that patients with Marfan’s syndrome should be on beta-blockers and angiotensin receptor blockers to reduce the rate of growth of aneurysms.
- Loeys-Dietz
- Mutation in TGF-B receptor. Patients may have hypertelorism, bifid uvula, and arterial tortuosity. Dissection can occur in children. May consider surgery for adults if aortic root > 4.4 cm (by CT) or descending thoracic aorta > 5 cm. For children, consider surgery when aortic root z-score is > 3 or expansion greater than 0.5 cm/yr.
- Ehlers-Danlos syndrome
- Autosomal inherited disorder of connective tissue COL3a1 gene encodes Type III collagen. Present with arterial or visceral rupture. Any surgery in this population carries increased risk—as such no formal guidelines exist for operative intervention.
Degenerative (sporadic) ascending aortic aneurysms
Occur in the setting of tri-leaflet aortic valve in patients without connective tissue disorders. May be associated with family history, hypertension, smoking and/or atherosclerosis. Aneurysms tend to grow at a rate of 0.1 cm/yr. Serial imaging is important in this population either with echo or CT scan. Growth rate > 1 cm/year or diameter > 5.5 cm in a patient with acceptable surgical risk is an indication for surgery.
Infectious/inflammatory aortic aneurysms
Syphilis destroys muscular and elastic fibers of media. Once commonly associated with ascending aneurysms, now less prevalent since improved antibiotic therapy.
Aneurysms associated with aortic dissection
Patients with previous dissection may have continued dilation of the ascending aorta. There is a faster growth rate and associated rate of rupture when compared to degenerative aneurysms.
Tests
- Contrasted CT scan or MRA: to evaluate the extent of the aneurysm including the carotids. You should know preoperatively whether a root or arch replacement is necessary. The CT scan should include abdomen and pelvis if femoral cannulation is considered. Carefully evaluate CT or MRA to see if aneurysm is abutting the sternum. This may increase risk of rupture during sternotomy.
- Echocardiogram: is also important in preoperative evaluation with special attention to valve disease and overall cardiac function. This study is limited and may be used to follow root aneurysms but should not be the sole study for operative planning for an ascending aneurysm.
- Cardiac catheterization: to evaluate coronary vessel disease.
- Pulmonary function tests (PFTs). Aneurysmal disease is more common in smokers with COPD. PFTs are not always essential but may help to determine perioperative risk.
- Labs: CBC, CHEM, Coagulations studies, Type and cross.
Index scenario (additional information)
“The patient has no family history of aneurysmal disease. He has no symptoms. His CT shows an isolated mid ascending aneurysm with no effacement of the sinotubular junction. The aneurysm tapers down to 4 cm proximal to the innominate artery. The AV mean gradient is 45 mmHg.”
Treatment/management
If the patient meets criteria for intervention, a thorough preoperative assessment is warranted. This patient needs an aortic valve replacement and ascending repair above the sinotubular junction. Imaging and preoperative assessment should proceed as discussed above. The patients systolic blood pressure should be kept between 90 and 110 mmHg.
Operative steps
The procedural steps will vary depending on the extent of the aneurysm and whether the aortic valve needs to be replaced.
Normal aortic valve, no root or arch involvement
- Perioperative monitors. PA catheter, cerebral oximetry, Foley catheter with temperature probe, transesophageal echo, and arterial line.
- Cannulation. Central cannulation can be used for an isolated ascending aortic aneurysm if there is enough room to cannulate and clamp beyond the dilated portion. This is usually accomplished with a high cannulation in the arch. These purse strings need to be very secure. Consider pledgeted purse strings. An alternative is to axillary cannulate.
- Cardioprotection. Antegrade and retrograde cardioplegia lines are placed as well as a left ventricular vent. A left ventricular vent can be omitted if there is no significant aortic insufficiency (be able to describe alternate methods of decompressing the left ventricle in the case of fibrillation). Cool to 34° C.
- Dissection. Transect ascending aortic aneurysm at midpoint. Extend proximally leaving enough room to safely do the anastomosis above the coronary ostia. Distally leave a rim of aorta to sew to before the clamp.
- Graft. Impregnated Dacron graft and 4-0 prolene suture to perform anastomosis. Felt may be used to reinforce aorta if tissue is felt to be of poor quality or connective tissue disorder. Remember not to leave the graft too long as it may kink when the heart fills. Perform the distal anastomosis first with running 4-O prolene suture. Then you may clamp the graft and check the back side for hemostasis. Then pack and perform the proximal anastomosis in a running fashion. Place root vent in the graft prior to cross clamp removal and turn off vents while performing the distal anastomosis to aid in deairing.
- Postoperatively maintain tight blood pressure control. Discharge on beta-blocker, ARB and statin.
Expected outcomes
- Known complications from aortic surgery include bleeding (2.4-11% requiring reoperation) neurologic injury (1.9-5%). Reports of perioperative mortality range from 1.7%-17.1%.
Potential questions/alternative scenarios
“Not enough room to cannulate and cross clamp distally.”
Plan for axillary or femoral cannulation. If still not able to clamp with adequate sewing cuff, then may need circulatory arrest (see arch aneurysm chapter).
“Graft is kinked when heart fills.”
It can be easy to overestimate the amount of graft necessary. You can try to plicate the graft along the lesser curve. You may need to cross clamp and arrest the heart in order to remove a portion of the graft and sew graft to graft.
“Aortic dissection occurs with cannulation.”
Potential complication of untreated aneurysms and can occur during cannulation of the aneurysm. Be prepared to discuss alternate cannulation strategies, cooling protocols and repair (see dissection chapter).
“Patient has left ventricular distension once commencing bypass.”
Significant aortic insufficiency may be present. You should have a sense that this may happen preoperatively. Be prepared to clamp and arrest the heart with retrograde. In the acute setting if you do not yet have an antegrade vent in place, you can decompress the heart by transecting the aorta. You can then deliver direct coronary cardioplegia. You can also decompress the heart via an LV vent if you have one in place. If the valve is not competent it should be replaced.
“Patient has a bicuspid aortic valve with mean gradient of 48 mmHg, shortness of breath and a 4.7 cm ascending aneurysm.”
Bicuspid aortic valve disease occurs in 1-2% of the population. Males 4:1. Most have 3 sinuses and 2 cusps (fusion of the right and left cusps). Dominant circumflex circulation with small right coronary. At risk for premature degenerative changes in the media of aortic root and ascending aorta. Consider ascending aorta replacement if performing aortic valve replacement in bicuspid aortic valve and ascending aorta > 4.5 cm.
“The aorta ruptures during the median sternotomy.”
For a presumed rupture you need to ensure you have sufficient help available in the room. Place towel clamps to close the sternum. Ask anesthesia to get PRBC in the room. Let perfusion know of impending need for cannulation. Do not try and fix or dissect out the rupture at this time since this will only make the tear worse. For the most part, towel clamps on the sternum can provide reasonable tamponade. Dissect out the femoral artery, give heparin, place your retractor attempt to tamponade the ruptured area if possible, with manual compression while you gain venous access by direct puncture and cannulation of the right atrium. Place a basket sucker in the field for drainage into the CPB reservoir. Start cooling in the event you need circulatory arrest. Once you are stable on bypass try to clamp the aorta above the rupture and arrest the heart. Now continue with your resection and repair. Place your retrograde coronary sinus cannula and LV vent if needed. Note that for aneurysms that are at risk of rupture or closely abutting the sternum it may be best to perform your sternotomy with the heart on bypass through the axillary and groin. If there is a very high chance of entering the vessel you might even cool to 18° C for circulatory arrest if needed prior to sternotomy.
Pearls/pitfalls
- Surgical intervention for ascending aneurysm > 5.5 cm diameter.
- Consider surgery for ascending aneurysm > 5 cm in patients with bicuspid aortic valve or 4.5 cm for connective tissue disorder.
- Aneurysms tend to grow at a rate of 0.1 cm/yr. Growth rate > 0.5 cm/year or diameter > 5.5 cm in a patient with acceptable surgical risk is an indication for surgery.
- Make sure to look for root or arch involvement prior to surgery.
Suggested readings
- Elefteriades JA. Natural history of thoracic aortic aneurysms: indications for surgery, and surgical versus nonsurgical risks. Ann Thorac Surg. 2002 Nov;74(5):S1877-80.
