Type A Aortic Dissection

Unlike elective surgery for TAAs, TAAD repair is generally an emergency procedure, and the real-time operative approach can deviate from the original plan. As the extent of surgical repair is dictated primarily by the location(s) of the intimal entry tear(s), intraoperative decision-making is critical.

A median sternotomy is performed for exposure, preceded or followed by arterial and venous cannulation, initiation of CPB, and cooling to the desired temperature for hypothermic cardiac arrest (HCA). The choice of cannulation site is dictated by the extent of dissection, hemodynamic stability, and patient-specific factors. Femoral artery cannulation can be performed when prompt initiation of CPB is desired, although right axillary artery cannulation might be preferable because it facilitates ACP during HCA and can be associated with superior outcomes relative to femoral artery cannulation. Central cannulation of the true lumen of the ascending aorta can also be performed under the guidance of TEE or epiaortic ultrasound. Placement of a left ventricular vent and a retrograde cardioplegia cannula is usually necessary in the setting of AR. Surgical goals include excision of the primary intimal tear, obliteration of the false lumen, resumption of forward blood flow through the true lumen, and correction of associated pathologic conditions, such as AR and malperfusion.

The standard TAAD repair entails a supracoronary hemiarch replacement with the distal anastomosis performed under HCA, which facilitates direct inspection of the aortic arch to ensure the absence of distal tears. When an intimal tear extends into the aortic root, a composite graft or a valve-sparing Bentall procedure may be necessary when the left and right coronary sinuses are involved. If involvement is limited to the noncoronary sinus, limited repair of the aortic root may be performed without the need for coronary artery reimplantation. Dissections involving a coronary ostium may require ligation of the affected ostium in combination bypass grafts. Surgical approaches to repair the distal extent of the TAAD vary from an ascending aorta replacement to a hemi- or total-aortic arch replacement with or without an elephant trunk procedure that can be classic or frozen (FET) (Figures 9.10 and 9.11). The choice of technique requires weighing the risk of late reintervention against the operative risk of a more complex distal repair.

Approximately 20% to 30% of patients who survive the initial surgery for aortic dissections extending into the abdominal aorta (DeBakey type I) require future reinterventions on the distal aorta. The FET procedure has shown promise as an adjunct to standard surgical repair. It not only facilitates false-lumen thrombosis and aortic remodeling but also expedites the second-stage surgery for the downstream aorta; the hybrid stent-graft prosthesis can also serve as the extended landing zone for future endovascular repair. Concerns about potential increases in spinal cord ischemia associated with the procedure have prompted the use of short endografts (10-15 cm in length). Other modified approaches to hybrid aortic arch repair have been discussed in a previous section (Figures 9.12 and 9.13).

Type B Aortic Dissection

TBAD is managed medically unless complications have developed or are impending. TEVAR has become a popular intervention in the current era due to the high mortality and considerable morbidity associated with open repair. The goal of TEVAR for TBAD is to obliterate the blood flow into the false lumen by covering the intimal entry tear, thereby promoting expansion of the true lumen. Although the benefits of TEVAR for complicated TBAD are well known, there remains great interest in exploring whether earlier TEVAR might improve outcomes in uncomplicated TBAD, especially in patients with high-risk imaging and clinical features. Prophylactic TEVAR in conjunction with medical therapy was associated with less incomplete or no false-lumen thrombosis, aortic dilation, and rupture in the ADSORB (Acute Dissection: Stent graft OR Best medical therapy) trial, as well as improved 5-year aorta-specific survival and delayed disease progression in the INSTEAD-XL (Investigation of Stent Grafts in Patients with Type B Aortic Dissection) trial. Larger trials with longer-term data are still needed to determine precisely when TEVAR should be performed in uncomplicated TBAD and how it influences patient outcomes. The technical considerations and limitations of TEVAR are discussed in previous sections.

References

• El-Hamamsy I, Ouzounian M, Demers P, et al. State-of-the-art surgical management of acute type A aortic dissection. Can J Cardiol. 2016;32:100-109.
• Hanif H, Dubois L, Ouzounian M, et al; Canadian Thoracic Aortic Collaborative (CTAC) Investigators. Aortic arch reconstructive surgery with conventional techniques vs frozen elephant trunk: a systematic review and meta-analysis. Can J Cardiol. 2018;34:262-273.
• Isselbacher EM, Preventza O, Hamilton Black J 3rd, et al; Peer Review Committee Members. 2022 ACC/AHA guideline for the diagnosis and management of aortic disease: a report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines. Circulation. 2022;146:e334-e482.
• Waterford SD, Gardner RL, Moon MR. Extent of aortic replacement in type A dissection: current answers for an endless debate. Ann Thorac Surg. 2018;106:1246-1250.