58. Arch Aneurysms- Clinical Scenarios

John F. Lazar, MD, and Peter A. Knight, MD

Concept

• Indications
• Preoperative assessment
• Operative management (Hemiarch/total arch/elephant trunk)
• Circulatory arrest
• Brain protection options
• Chronic dissection

Chief complaint

“A 57-year-old man with known aortic diastolic murmur presents to your clinic after complaining to his PCP that he has increased shortness of breath. After a full work up, including chest CT and an echo he is found to have moderate aortic insufficiency and an ascending aortic aneurysm extending to the proximal arch of 5.5 cm in size.”

Differential

Aortic insufficiency with ascending/arch aneurysm, aortic dissection, coronary artery disease.

History and physical

Most patients with aortic aneurysms are asymptomatic and are discovered incidentally. Of those who present with symptoms, 25-75% present with chest pain (usually anterior chest). Acute pain generally implies impending rupture or dissection. Hoarseness of the voice implies stretching or damage to the recurrent laryngeal nerve. Risk factors include smoking, hypertension, atherosclerosis, personal history of chronic aneurysms or previous repair, bicuspid aortic valves, trauma, and genetic disorders such as Marfan and Ehlers-Danlos syndromes. The physical exam is often unremarkable. A diastolic murmur will be heard if dilation of aortic annulus results in AI.

If a thoracic aneurysm is diagnosed, a thorough vascular examination should follow looking for any peripheral vascular disease, carotid disease, and sequelae of distal embolization. It is also important to document a thorough neurologic exam to establish baseline clinical status in the event of changes postoperatively. Abdominal aortic aneurysms are present in 10 to 20% of patients with atherosclerotic involvement of an ascending aortic aneurysm.

Tests

• EKG: may be completely normal; if AI is present may have LV enlargement; assess for ischemic coronary changes.
• CXR: may be the first test to detect a silent aneurysm. An enlarged ascending aorta produces a convex contour of right superior mediastinum.
• CTA: is the test of choice for assessing the aortic aneurysm and provides rapid and precise evaluation of the root, ascending and arch. CT scanning detects areas of calcification, and accurately identifies dissections and mural thrombus. Axial measurements should be taken perpendicular to the line of flow. The entire thoracic and abdominal aorta should be scanned. The main disadvantage of CT scans is the need for contrast solution for optimal resolution, which may be contraindicated in those patients with renal insufficiency or a history of a dye allergy.
• MRI/MRA:effective means of assessing the aorta but is more suitable for those who cannot tolerate CTA dye and in a non-urgent setting.
• ECHO. TTE is good for evaluating the valves and ascending aorta but gives little information on the arch. Echo can also be used to corroborate aortic dimensions found by either CTA or MRI/MRA. TEE is done in the operating room and can help rule out Type A dissections.
• Cardiac catheterization. Rule out coronary artery disease in patients undergoing aneurysm repair prior to surgery. May be omitted safely in females of age < 35 and males < 40 with no cardiac risk factors.

Index scenario (additional information)

“Patient has no past medical or surgical history. He takes no medications. He used to smoke a pack a day for 20 years but quit 7 years ago. His father died suddenly in his 50’s from a ruptured aneurysm but the rest of his family is still alive and well. Other than being overweight and having a 3/6 diastolic murmur in the right parasternal position his physical exam is completely benign. The aneurysm extends into the proximal arch but tapers to normal size by mid-distal arch. The root is not dilated. The echo shows normal function, 3+ AI and a normal root. How would you like to proceed?”

Treatment/management

This patient has symptomatic AI which requires intervention as well as a 5.5 cm uncomplicated ascending/arch aneurysm that requires repair. In general, 5.5 cm is a safe cutoff for interventions on the arch. 5 cm is the threshold for Marfans, Ehlers-Danlos or bicuspid aortic valve, while even lower thresholds may be used for Loeys-Dietz (4.5 cm). Symptomatic aneurysms of any size require surgical intervention. Asymptomatic aneurysms should be addressed at the time of surgery for aortic valve procedures if the size is at least 4.5 cm and the patient is a reasonably good candidate. Finally, a growth rate of > 0.5 cm/yr justifies repair in asymptomatic patients with aneurysms less than 5.5 cm.

Additional preoperative testing

• Patients with poor pulmonary function should have spirometry and room air arterial blood gases.
• Smoking cessation, antibiotic treatment of chronic bronchitis, and chest physiotherapy may prove beneficial in elective situations.
• Severe carotid disease is a risk factor for stroke during aortic operations. Patients > 65 should have duplex imaging of their carotids pre-operatively or any patient with h/o TIA or bruits.
• Abdominal aortic aneurysms occur in 10 to 20% of patients with ascending aortic aneurysms and should be investigated.
• Head CT to ensure an intact Circle of Willis.

Operative steps

There are a few different ways to approach aortic arch aneurysm repairs. The main decision is whether to perform a hemiarch, total arch or elephant trunk. This decision depends almost exclusively on the distal extent of the aneurysm. Usually you can be well prepared for either intervention ahead of time based on the CT scan, but things may get altered in the OR. All of these cases require circulatory arrest. Right axillary cannulation is safe for all of these. Retrograde brain perfusion through the SVC is reasonable for an uncomplicated hemiarch but the more advanced the procedure becomes the more likely that antegrade brain protection will be needed. The operative details that follow all assume axillary artery cannulation with antegrade brain perfusion (see below for details of circulatory arrest).

• LBIV, arterial line in left arm and leg, general endotracheal anesthesia, pulmonary artery catheter, foley.
• temp probe in the bladder, nasopharynx and venous perfusate.
• Brain monitoring: EEG, Bispectral index (BIS).
• Check the intraoperative TEE for AI and aortic dimensions.
• Dissect right axillary artery (or right femoral artery for arterial cannulation).
• Median sternotomy, pericardial stay sutures, inspect aorta.
• Heparin 400 mg/kg, arterial cannulation, 2 stage venous cannula or bicaval if retrograde brain perfusion, retrograde coronary cannula; once ACT is 480 initiate CPB, +/-LV vent through right superior pulmonary vein.
• Commence cooling while you mobilize the distal ascending aorta and proximal arch and dissect out the great vessels.
• Clamp and arrest with antegrade/retro/direct coronary.
• Once the patient is at 18-20° C and the EEG is silent, give a dose of cardioplegia, position the patient in Trendelenburg and pack the head in ice. +/- pentobarbital and mannitol given.
• CPB is turned off.

Hemiarch

• The aorta is transected longitudinally along the ascending aneurysm and inspected proximally and distally.
• Ascending aorta is transected along the lesser curve to create a cuff extending from the base of the innominate artery on the right to approximately mid arch or 1 cm proximal to the ligamentum arteriosum and the recurrent laryngeal nerve. The further you transect the more difficult the anastomosis becomes.
• Clamp the right innominate and initiate antegrade brain perfusion at 500 mL/min (or 10-15 cc/kg) with a mean pressure of 40-60 mmHg. Check for backflow through the left CCA. If not then place a coronary perfusion catheter up the LCCA and Y it into the antegrade perfusion circuit at a similar flow rate.
• Size the aorta with freestyle sizers to determine the aortic graft diameter required.
• The distal graft is beveled and anastomosed to the aorta with a continuous 3-0 or 4-0 polypropylene suture (a cuff of Teflon felt or strip of pericardium can be used outside the aorta for friable tissue).
• Once the anastomosis is complete, remove the clamp on the right innominate, gradually resume systemic flow while deairing the graft, clamp the graft and check the back wall carefully for hemostasis.
• Begin rewarming at approximately 1° C/5 min until 36° C.
• This completes the hemiarch – the remainder of the procedure is dictated by the proximal pathology.

Total arch

• Indicated when the aneurysm extends into the mid arch. Need to decide if head vessels are aneurysmal and need reconstruction. If not, the head vessels can be fashioned to the graft as an island.
• While cooling dissect out the arch and head vessels (may need an expanding incision into the neck). Prepare the appropriate graft. The limbs to the innominate and head vessels/LSCA are typically 12 and 8 mm respectively. Trifurcated grafts are available, or any combination of bifurcated or single limb grafts can be sewn individually to the respective vessels.
• Once the circulation is arrested, transect the proximal arch vessels and the aorta along the lesser curve up to the level of the distal arch which is often beyond the LSCA. Clamp the LCCA if too much blood return obscures your view. Note that if the LSCA is too deep in the chest for a feasible anastomosis it can be ligated. The distal anastomosis can then be done proximal to the LSCA which can be bypassed at a future date or off pump at the end of the case, prior to protamine.
• Usually a bifurcated graft to the R innominate and the left CCA is sewn first and then clamped to allow antegrade brain flow through both head vessels. If reimplanting the LSCA it is sewn next. Then the distal anastomosis and finally the appropriate graft to graft anastomoses. Trifurcated grafts may decrease the number of anastomoses. Whatever the method, stick to what you know best.
• Note that if the proximal arch vessels can be preserved then you may be able to sew them into the graft collectively as an island.
• Deair, clamp the graft, resume systemic flow and complete your proximal work or proximal anastomosis. A graft extension may be required to avoid kinking if an ascending is being performed as well.

Elephant trunk

• Indicated for distal arch or isthmus involvement.
• Follow the same steps as in the total arch except instead of an end-to-end anastomosis between the distal aorta and distal graft the distal 5-10 cm of the graft needs to be invaginated within the aorta and then sutured into place.
• On completion of the suture line, the graft is everted, and the head vessels are sewn into the graft with a running prolene as an island.
• The graft is de-aired, clamped and hemostasis is assessed. The proximal work is completed.
• The trunk can later be incorporated into the reconstruction of the descending aorta either by open or endovascular techniques.

Circulatory arrest

• At 18° C cerebral metabolism and oxygen consumption are 17 to 40% of normothermia. Measure temperatures at the bladder, nasopharyngeal and venous perfusate. Monitor brain with EEG or BIS. Most investigators report increased mortality and adverse neurologic outcomes after 40 to 65 minutes of circulatory arrest. Most surgeons try to keep the period of arrest at less than 40 minutes if the operation allows. Consider antegrade brain perfusion for procedures lasting > 30 minute.

Brain protection options

• Antegrade brain perfusion: Line pressure is monitored. The head vessels are collectively perfused with cold blood between 10-18° C and at approximate flows of 10-15 mL/kg/min. Perfusion pressures are restricted to 40 to 60 mmHg which can be difficult to monitor unless you have a left radial arterial line. Most go off of either weight-based flows or a flat rate of 500 mL/min.
  • Retrograde cerebral perfusion (RCP): During RCP the SVC is snared and perfused at blood pressures not exceeding 25-30 mmHg that is monitored via CVP, temperatures between 8 and 18°C, and flows between 250 and 400 mL/min. In theory RCP has the added benefit of flushing atherosclerotic material and air from the brachiocephalic vessels while keeping the brain cool.

Potential questions/alternative scenarios

“A stable patient with occasional chest pain is referred to you for evaluation of a chronic Type I dissection with a 5.7 cm aneurysm involving the ascending and proximal arch.”

This patient has a symptomatic dissection and aneurysmal disease both of which require treatment. The operation proceeds very much like that of a Type A dissection with circulatory arrest and an open distal anastomosis. In this case the aneurysm involves the proximal arch and thus requires a hemiarch configuration as described above. If the aneurysm proceeded more distally, a total arch or even elephant trunk may be necessary. The only technical difference in the setting of dissected head vessels is that these vessels must be anastomosed directly in an end-end fashion to the tube graft limbs rather than an island for a total arch or elephant trunk. Also, the chronic dissection flaps should be fenestrated or resected as far as possible.

“On the preoperative imaging you notice an aberrant left vertebral artery on a patient who was being worked up for a total arch replacement due to an isolated arch aneurysm.”

On occasion the left vertebral artery (LVA) will exit the arch directly. This requires duplex US evaluation of the right vertebral artery (RVA) to ensure patency and antegrade flow. With a patent normal RVA, the LVA can be temporarily occluded during selective cerebral perfusion and reimplanted during patient rewarming. Three options have been used: 1.) direct reimplantation of the LVA into the left common carotid artery 2.) attachment of a portion of reverse saphenous vein to the vertebral artery 3.) anastomosis to the arch graft or the left subclavian limb of the trifurcated graft. A very small LVA (< 2 mm) with a patent RVA may be ligated.  

“You are called to evaluate a patient with a known arch and descending aneurysm who is complaining of excruciating chest pain. Workup for MI is negative and there is no evidence of dissection. However, there is some periaortic density concerning for a contained early rupture.”      
The issue here is that an elephant trunk would normally be the ideal procedure for this patient, but it does not allow for a distal seal until the completion elephant trunk is performed. This patient needs a complete procedure involving the arch and descending thoracic aorta. A hemi-clamshell incision or “thoracosternotomy” extended into left 4th ICS allows adequate exposure for both the standard cannulation techniques and the distal repair. An elephant trunk-like strategy can still be used with the graft invaginated through the isthmus and anastomosed distally to the descending aorta. The head vessels would be sewn as an island unless they were aneurysmal.

“You are presented with an 86-year-old relatively healthy female with a 6.5 cm ascending aneurysm which tapers to 4.5 cm at the proximal arch. She has no familial genetic syndromes.”

Elderly patients do not tolerate circulatory arrest as well as their younger counterparts. They have a higher risk of stroke and heart failure. The 4.5 cm proximal arch does not necessarily have to be addressed in this setting. The arterial cannula can be placed high on the arch with carefully placed pledgeted cannulation sutures and the clamp can be beveled proximal to the cannula and along the lesser curve. Alternatively, the axillary can be cannulated if it proves too hazardous to cannulate high on the arch. An isolated ascending replacement can then be performed without circulatory arrest.

Pearls/pitfalls

• Clarify whether the patient does or does not have an indication for repair of the aneurysm.
• Clarify the location and extent and decide whether it needs a hemiarch, total arch, or elephant trunk.
• Consider whether a hemiclamshell is needed to definitively address the arch and descending in a single setting (usually only in the case of rupture).
• Decide on your cannulation strategy and brain protection strategy.
• Know the sequence of arch anastomosis depending the type of graft you are using. Also know the sequence of de-airing and removal of clamps.

Suggested readings

• Brinster DR, Rizzo RJ, and Bolman RM. Ascending aortic aneurysms. Cohn LH (ed). Cardiac Surgery in the Adult. New York: McGraw-Hill Medical. 2008:1223-1250.
• Spielvogel D, Mathur MN, and Griepp RB. Aneurysms of the aortic arch. Cohn LH (ed). Cardiac Surgery in the Adult. New York: McGraw-Hill Medical. 2008:1251-1276.
• Caffarelli AD, Van der Starre PJ, and Mitchell RS. Ascending and arch aneurysms of the aorta. Yu DD et al. (eds). The Johns Hopkins Manual of Cardiothoracic Surgery. New York: McGraw-Hill Medical Pub. 2007:663-700.