56. Aortic Root Aneurysm- Clinical Scenarios

Muhammad Aftab, MD, Ismael de Armas, MD, and Faisal G. Bakaeen, MD, FACS

Concept

• Clinical Presentation of aortic root aneurysms
• Diagnostic modalities
• Indications for surgery and choice of conduit
• Technique of aortic root replacement
• Complications
• Follow up

Chief complaint

“A 44-year-old man is referred to you by his cardiologist for the evaluation of severe aortic regurgitation and enlarged aortic root after presenting with a 1-month history of increasing shortness of breath and cough. How would you proceed with work up and management?”

Differential

Usually patients with aortic root aneurysm are asymptomatic and the condition is diagnosed during the workup of other disease processes or it could cause symptoms such as pulmonary congestion that can masquerade as respiratory in origin. Symptoms such as shortness of breath and chest pain should also raise concern for pneumonia, dissection, aneurysmal disease, pulmonary embolism, or MI.

History and physical

A focused history should attempt to elicit any symptoms relevant to the aneurysm or aortic regurgitation such as chest pain, back pain or shortness of breath. Significant history of bleeding diathesis or significant dental pathology e.g., caries, infection is also important in preparation and planning for surgery. Ask for history/family history of Marfan disease, other connective tissue disorders or aneurysms. Evaluate for the risk factors of aneurysm formation and progression such as hypertension, atherosclerosis, and smoking. Physical examination of patient with un-ruptured aortic root aneurysms is often unremarkable. Nonetheless, check lungs for evidence of pulmonary edema, listen for murmurs and evaluate distal pulses. One may discover findings such as a water-hammer pulse with wide pulse pressure and low diastolic pressure and a decrescendo diastolic murmur. AAA is present in 10-20% of patients with atherosclerotic ascending aortic aneurysm. Patients with Marfan syndrome have characteristic features including thin, tall stature, lax joints, ectopia lentis and high arched palate. Also evaluate for the phenotypic features of Loeys-Dietz syndrome such as blue sclera, hypotelorism, bifid uvula, malar flattening, retrognathia, translucent skin with visible veins and arachnodactyly.

Tests

• CXR:prominent right mediastinal border. Aortic valve and aortic root calcifications (lateral projection).
• EKG. Usually there will be no EKG abnormality specific to aortic root aneurysm. However, left ventricular volume overload from aortic regurgitation is supported by increased QRS complex voltage (best seen in the chest leads) and prominent septal depolarization reflected by Q waves in leads V4 to V6.
• Echocardiogram. TEE is the imaging modality of choice. Accurate visualization of aortic root and ascending aorta is imperative. It is also important to determine if the aortic valve is bileaflet, since this may influence when to surgically intervene. Carefully evaluate valve anatomy to determine whether the valve repair is feasible. For aortic root measurements, the widest diameter, typically at the mid-sinus level should be used.
• Computed tomography angiography (CTA).Most common imaging to study the aorta. Ability to image the entire aorta including lumen, wall, branch vessels, arch, periaortic regions and distal aorta with 3-dimensional data. EKG gated imaging helps to eliminate motion artifact at the aortic root and helps assess coronary arteries, aortic valve morphology and function. While the widest diameter is typically at the mid sinus level, measurements should be taken at all four levels including annulus, sinotubular junction, mid sinus and ascending aorta. Limitation includes risk of contrast-induced nephropathy.
• Magnetic resonance imaging (MRI).A valuable imaging modality for diagnosis of thoracic aortic diseases in stable patients with sensitivities and specificities comparable to CT and TEE. A preferred imaging modality for patients requiring repeat imaging for the follow-up of aortic pathology without exposing them to radiation and iodinated contrast agents.
• Cardiac catheterization.Considerations should be given to perform cardiac catheterization to rule out presence of coronary artery disease in patients greater than 40. Make sure to define the ostial anatomy and look for anomalies such as a left from the right, right from left, or separate circumflex and LAD orifices.

Index scenario (additional information)

“He is a 6-foot-tall, thin gentleman with a significant smoking history and worsening dyspnea on exertion. He is noted to have a holo diastolic murmur radiating towards the apex. His CXR revealed a prominent right mediastinal border. On echocardiogram he is noticed to have gross aortic root dilatation, a trileaflet non-stenotic aortic valve with severe aortic valve regurgitation, mild mitral regurgitation and moderately dilated LV. His aortic root diameter is 7.2 cm (mid sinus) on CT scan and tapers down to normal size at the mid ascending.”

Treatment/management

Criteria for surgical intervention of an ascending aortic aneurysm includes:

• Sporadic (5.5 to 6.0 cm)
• Connective tissue disorder (4.5 to 5.0 cm)
• Bicuspid aortic valve (5.0 to 5.5 cm)

The surgical procedure to be performed on an aortic root aneurysm will be dictated by the status of the aortic valve and the condition of the patient. If the aortic valve is structurally normal a valve sparing procedure is becoming a popular treatment choice at experienced centers. When choosing the valved conduit consideration should be given to the patients’ age, life expectancy, underlying disease condition, comorbidities, lifestyle, preference, risk of bleeding from anticoagulation, risk of possible reoperation and finally surgeons experience. Aortic root replacement using a graft and mechanical valve (composite or separate) is recommended for younger patients (age < 60 years) with no contraindication to anticoagulation or patients of any age requiring anticoagulation for other indication such as pulmonary thromboembolism, atrial fibrillation or mechanical valve in other valvular position. Advantages include long term durability and relatively ease of implantation compared to other root replacement options. Complications are related to thromboembolic events and anticoagulation.

When tissue valve is desired during aortic root replacement, a stented bovine or porcine bioprosthetic valve is hand sewn to a tube graft to make a composite biological valve graft conduit. Bioprosthetic grafts are recommended in patients older than 65 years of age with the benefit of freedom from anticoagulation as well as better durability in elderly patients. Bioprosthetic valved graft conduit may also be used in patients of any age with medical or personal contraindication to anticoagulation.

For the David procedure (valve sparing root replacement) theaortic valve is preserved by reimplanting it inside the Dacron tube graft. This is possible in almost 30% of patients requiring aortic root replacement. This is ideal in patients with root dilatation, AI and structurally normal valves.

The stentless composite porcine aortic root grafts such as Freestyle (Medtronic, Inc., Minneapolis, MN), Prima plus (Edwards Life Sciences, Irvine, CA) and Toronto Root (St. Jude, Minneapolis, MN) are alternate options for biological root replacement. The most commonly used graft is Freestyle porcine root. This option is recommended in patients older than 65 years with no risk factor for thromboembolic conditions, thus offering them freedom from anticoagulation. Benefits over the tissue valve may include enhanced durability, superior hemodynamics, and less patient prosthesis mismatch. Homografts may be considered for endocarditis and a Ross is an option for very young patients < 40-year-old who do not want anticoagulation.

Operative steps

Aortic root replacement

• Wide prep and drape in case the femoral vessels and or right axillary artery are necessary for cannulation. Median sternotomy and pericardial dissection carefully palpate the aorta for calcifications. The distal ascending aorta at the location free of disease is the preferred access for arterial cannulation. Other option is the axillary or femoral artery. In general, a dual stage atriocaval cannula through the right atrial appendage is the preferred method for venous drainage, unless the aortic aneurysm is large enough to preclude the access of the right atrium for cannula placement. In this case the right femoral vein becomes an option for venous cannulation.
• A large aortic aneurysm abutting the sternum, redo aneurysm or evidence of contained rupture are situations where one may consider being on pump through the axillary and femoral vein prior to the sternotomy. A surgeon should be prepared to go on emergent cardiopulmonary bypass by femoral arterial and venous cannulation in a patient who becomes hemodynamically unstable (due to rupture or tamponade).
• Prior to initiating CPB, have the necessary exposure and access for retrograde cardioplegia and cross clamping since a patient with severe AI may very well fibrillate with CPB. Initiate CPB with moderate hypothermia, +/- LV vent through right superior pulmonary vein (RSPV). Cardioplegia is delivered in an antegrade fashion into aortic root if there is no aortic regurgitation or directly into each coronary ostium as well as retrograde cardioplegia into the coronary sinus.
• Ascending aorta is transected 3 to 4 cm above the sinotubular junction. Aortic valve is inspected for possible preservation otherwise leaflets are excised, and annulus is debrided if necessary.
• Orientation of right and left coronary arteries and their height above the annulus is noted for coronary reimplantation. The coronary arteries are dissected free from the root with few millimeters of aortic wall as coronaries buttons and are adequately but carefully mobilized to allow for tension free implantation into the root graft.

Mechanical composite valve graft (CVG) conduit

• After excising the aortic leaflets and debridement of aortic annulus, mechanical valve sizers are used to choose appropriate CVG. The valve and conduit can also be sewn as separate entities if desired. Pledgeted horizontal mattress non-absorbable sutures are used to implant the valved conduit with the rigid sewing cuff in an intra-annular position. These sutures are placed across the annulus from the aorta to LVOT and then across the sewing ring of CVG. CVG is seated and sutures are tied. Coronary arteries are then reimplanted. A round opening is made in the tube graft using an ophthalmic cautery device. Coronary artery buttons are sutured to the opening with continuous 5-0 prolene sutures starting with the left and finishing with the right coronary implantation without tension or kinking. If the aortic tissue is friable a ring of felt may be used to reinforce the anastomosis.

Bioprosthetic composite stented valved graft (CVG) conduit

• Bioprosthetic valve sizers are used to select the valve required. Usually a tube graft of size 3 to 5 mm larger than the valve is chosen. The hand sewn composite valve graft conduit is then sewn to the annulus using the same technique as described for mechanical CVG conduit implantation.

Valve sparing aortic root replacement

• Aorta is transected just beyond the aneurysmal dilatation. Aortic root is first dissected circumferentially down to the lowest point of aortic annulus. All three aortic sinuses of valsalva are excised, leaving a 5 mm aortic wall rim around the valve leaflets. Multiple interrupted horizontal mattress 2-0 Ticron sutures are placed from inside to outside the LVOT just below the aortic valve. Sutures are placed in a single horizontal plane along the fibrous portion of LVOT and below the nadir of the valve leaflets and commissural structures. Care should be taken to avoid injury to the conduction system in the membranous septum and the number of sutures in this area could be minimized because this is not the haemostatic suture line. A Dacron tube graft with diameter equal to double the average leaflet height is selected. This is typically 26-28 mm for women and 28-30 mm for men. Previously placed sutures through LVOT are passed through the graft and tied on outside of the graft. Sutures are spaced symmetrically along the muscular interventricular septum and correspondingly closer on the Dacron graft in the fibrous portion of LVOT thus correcting the annular dilatation. Fibrous portion of LOVT is the location where dilatation occurs in patients with connective tissue syndromes. The Dacron graft is trimmed 2-3 cm above the commissures, which are then pulled vertically and suspended to the graft using 4-0 pledgeted mattress prolene sutures. Now the valve, which sits entirely inside the graft, is re-implanted to the graft using 4-0 prolene sutures in running fashion along the residual sinus tissue. Coronary buttons are then reimplanted to their respective sinuses. Aortic cusps are inspected for coaptation and any leaflet prolapse is corrected if necessary. Neoaortic sinuses are created by plicating 2-3 mm of graft material in each sinus at the level of commissure by placing figure of eight 5-0 prolene suture. Alternatively, a commercially available graft with the sinuses of valsalva can also be used. Intraoperative aortic valve competence can be evaluated by clamping the distal end of graft and injecting cardioplegia under pressure. Absence of ventricular distension suggests no more than trace aortic insufficiency. Distal anastomosis is then performed to distal ascending aorta.

Stentless aortic root xenograft

• The implantation technique of aortic root xenograft is similar to that described for CVG replacement with few technical considerations. After excising the aortic valve leaflets the size of aortic annulus is measured. The bioprosthesis selected may be of the same size or 2 mm larger than aortic annulus. The coronary anatomy of porcine aortic root differs from the human root as the coronary ostia of porcine root are relatively closer to each other (90-110° apart) compared to humans (120-140° apart). To place the prosthesis in an anatomical position relative to the coronaries it is usually rotated 120° such that the porcine non-coronary sinus will be used for reimplantation of either right or left coronary artery. It is also very critical to attach the left coronary artery perfectly to its corresponding sinus, avoiding any kinking which may result into postoperative coronary insufficiency. The inflow suture cuff of the bioprosthesis is attached to the aortic valve annulus using either continuous or interrupted horizontal mattress sutures. The suture line can be further reinforced with either Teflon felt or strip of autologous pericardium.
• After completion of aortic root replacement using your procedure of choice systemic rewarming is started. The heart is deaired with TEE guidance and a warm shot of cardioplegia is typically given before removing the cross clamp. That final shot of cardioplegia can help detect significant bleeding along suture lines and test for valve competence. The cross clamp is removed, an aortic vent is placed. Temporary pacing wires are placed, and the LV vent could be removed if there is no ventricular distension and the cardiac contractility is resumed. Lung ventilation is started.

Potential questions/alternative scenarios

“You just finished replacing the aortic root and while deairing, you notice > 1 mm ST elevation in the inferior leads (II, III, and AVF). How would you manage that?”

Postoperative coronary insufficiency is the most dreaded complication. Although it is not a common complication after aortic root replacement, it is often caused by the kinking and changes in the orientation of the proximal RCA. This can be prevented by careful sizing with the heart engorged, meticulous technique of coronary implantation and ensuring that coronary ostia are properly aligned. It is suspected in the situation of difficulty in coming off cardiopulmonary bypass, new regional wall motion abnormality, arrhythmias, new EKG changes and unexplained right ventricular failure in the presence of non-obstructed coronaries. This can also be caused by inadequate myocardial protection, coronary air embolism, and protamine or transfusion related reaction. An early decision to bypass the involved artery with the saphenous vein graft is crucial.

“You complete a valve sparing root replacement and discover 3+ AI.”

If this occurs you must be prepared to go back on CPB, arrest the heart, resect the valve and replace with a mechanical or bioprosthetic valve.

“When coming off CPB you notice persistent blood coming from behind the proximal anastomosis.”

This can be a serious condition that is difficult to fix. One should anticipate that the etiology is bleeding from the root. The other possibility is bleeding from the LCA suture line. Manipulating the graft and placing sutures posteriorly in a blinded fashion is not advisable. The most prudent course of action is to pack the root with sponges or mild topical agents and wait. Do not give protamine until you have reasonable hemostasis. Eventually remove the packing and check. If it is persistent and the source is not clear, then go back on CPB and address. One may even have to re-arrest to adequately achieve hemostasis and potentially replace the root. An alternative in a patient who will not withstand a second cross clamp at that point in time is to pack, give heparin and, if needed, leave the chest open with a planned second look after reversing all coagulation factors. If you need to replace the root, you might consider a homograft or xenograft which may offer better hemostasis for friable tissues.

“How do you follow these patients?”

Blood pressure control and anticoagulation management requires a close postoperative follow up. Scheduling of post-operative CT or MRI is required to assess the growth of non-resected aorta and to evaluate for possible aneurysm formation. CT scan or MRI of the aorta is reasonable at 1, 3, 6, and 12 months and, if stable, annually thereafter so that any threatening enlargement can be detected in a timely fashion.

“How would you manage this patient if he is asymptomatic and aortic root diameter is 3.5 cm?”

There is no medical therapy which will treat the underlying condition resulting into aortic root dilatation or aneurysm. Guidelines for the medical treatment of patients with aortic aneurysms include strict control of hypertension, optimization of lipid profile, smoking cessation, and risk factor modifications for the atherosclerosis.

“What are the Genetic syndromes and familial conditions associated with aortic root aneurysms and how do they affect treatment and management?”

The genetic syndromes associated with aortic root aneurysms are Marfan syndrome, Loeys-Dietz Syndrome, Ehlers-Danlos Syndrome and familial thoracic aortic aneurysm and dissection syndrome (FTAAD). Bicuspid aortic valve patients are also known to have associated aneurysmal disease. Patients with these conditions should undergo elective operation at smaller diameters (4.0 to 5.0 cm depending on the condition) to avoid acute dissection or rupture.

• Marfan syndrome – Symptomatic aneurysm, asymptomatic with of diameter > 5.0 cm, Asymptomatic with diameter < 5.0 cm with family history of aortic dissection at < 5.0 cm, rapidly expanding > 0.5 cm/year, Aortic diameter > 4.0 cm in Marfan women desiring pregnancy (Class IIA, Level of evidence C).
• Loeys-Dietz syndrome – Aortic diameter ≥ 4.2 cm by transesophageal echocardiogram (internal diameter) or 4.4 to 4.6 cm or greater by computed tomographic imaging and/or magnetic resonance imaging (external diameter), Class IIA, Level of Evidence: C.
• Bicuspid Aortic Valve – Symptomatic aneurysm, Asymptomatic aneurysm with diameter > 5.0 cm or diameter > 4.5 cm in patients undergoing aortic valve repair or replacement (Class I, level of evidence C).

“You are doing a redo aortic root replacement and you find it very difficult to dissect the tissue around the aortic root especially posteriorly. What are its implications and your options?”

This implies that mobilization of coronary arteries will be difficult or even dangerous. One option is the Cabrol technique which involves coronary reimplantation by placement of 8-10 mm interposition tube graft to each coronary ostium and then side to side anastomosis to the main aortic graft.

Alternate option includes the direct implantation of right coronary button, which is usually easier to mobilize, and reimplantation of left coronary artery using an interposition graft between left coronary ostium and aortic graft (Hemi-Cabrol).

Pearls/pitfalls

• Criteria for surgical intervention includes: sporadic (5.5 to 6.0 cm), connective tissue disorder (4.5 to 5.0 cm), bicuspid aortic valve (5.0 to 5.5 cm).
• When presented with an aortic root aneurysm decide whether it needs to be resected or not.
• Decide what type of root replacement technique is ideal and which one you are the most comfortable describing.
• Make sure the preoperative workup is complete including risk assessment distal aortic imaging and cardiac catheterization.
• Recognize potential complications and solutions of root replacement.

Suggested readings

• Yuh DD, Vricella LA, Baumgartner VA (eds). The Johns Hopkins Manual of Cardiothoracic Surgery. 1st ed. New York, NY: McGraw Hill; 2007:585-606.
• Khonsari S, Sintek CF. Cardiac Surgery: Safeguards and Pitfalls in Operative Technique. 4th ed.Philadelphia, PA: Lippincott Williams & Wilkins; 2008.
• Franco KL and Thorani VH (eds). Cardiothoracic Surgery Review. 1st ed. Philadelphia, PA: Lippincott Williams & Wilkins;2012:315-327.
• Hiratzka LF, Bakris GL, Beckman JA, et al. 2010. ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM Guidelines for the Diagnosis and Management of Patients with Thoracic Aortic Disease. J Am Coll Cardiol. 2010;55:e27-e129.
• Bonow RO, Carabello BA, Chatterjee K, et al. ACC/AHA 2006 Guidelines for the Management of Patients with Valvular Heart Disease: a Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (writing committee to revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease). Circulation. 2006;114:e84-231.