Experience with hybrid procedures (as an alternative to branched grafts) - results from a single centre

Aortic dissections (AD) occur when blood is redirected from the aorta (true lumen) through an intimal tear into the media of the aortic wall (false lumen). A dissection plane is created within the media that separates the intima from the overlying adventitia over a variable length of aorta. Acutely, AD can be lethal whilst those surviving the initial event go onto have variable manifestations of the disease.

AD are classified by their location and the extent of the dissection. The particular type is then further sub-classified by the timing of the dissection. Traditionally, dissections presenting within the first two weeks have been termed acute while the term chronic is reserved for those patients who present at greater than two months following the initial event. More recently, the term sub-acute has been used to describe the period between two weeks and two months.

The two classification systems most widely used in clinical practice are the Debakey and Stanford classification systems (Figure 1). The simpler Stanford classification divides AD into types A (any involvement of the ascending aorta) and B (limited to the descending aorta distal to the left subclavian artery).

Acutely, regardless of whether the true and false lumens communicate, perfusion of aortic side branches may be compromised by the AD causing end-organ ischaemia (Figure 2). This is an indication for urgent operative intervention.

Chronically, the weakened outer aortic wall of AD, composed of partial media and the adventitia, may dilate, resulting in aneurysm formation. If the extent of aortic involvement is large enough, dissecting thoraco-abdominal aortic aneurysms (TAAA) can occur. This long-term complication is the reason for operative intervention in the majority of chronic AD regardless of type. These TAAA are defined by the involvement of the origins of the coeliac, superior mesenteric and renal arteries. Crawford's classification is universally accepted (Figure 3), although Safi subsequently added a fifth class of TAAA in his version of the classification system.

The open repair of AD, dissecting TAAA and TAAA have a high mortality and morbidity when treated by open techniques. These risks have persisted despite advances in operative technique (including left heart bypass, spinal cord protection, hypothermic cardiopulmonary arrest and selective visceral perfusion) and higher standards of perioperative care.

In 1991, Parodi used the first endovascular stent-graft (EVSG) in an infra-renal abdominal aortic aneurysm7. As a direct evolutionary step, by 1994, endovascular techniques had developed such that Dake was able to use an EVSG for descending thoracic aortic aneurysms. This use of EVSG for TAAA limited to the thoracic segment showed significant early promise. However their use for more extensive AD, dissecting TAAA and TAAA and was necessarily limited by the presence of the visceral and renal arteries in the chest and abdomen.

Hybrid repairs of AD, dissecting TAAA and TAAA refer to procedures combining both open surgical and endovascular techniques (either staged or within the context of one operative procedure). By re-vascularising vital aortic side branches first, it is then possible to achieve total endovascular aneurysm exclusion. When the visceral and renal vessels are involved and require retrograde re-vascularisation, we refer to this operation as the visceral hybrid repair.

Experiences of Hybrid Repairs
Hybrid repairs of TAAA begin with an open abdominal procedure to first re-vascularise the visceral and or renal vessels depending on their relationship to the TAAA. This is followed by aortic endovascular stent-grafting (either as part of the same procedure or intentionally delayed). These repairs are particularly attractive as they avoid the need for a thoracotomy, supra-coeliac aortic cross clamp, left or full heart bypass and extensive tissue dissection.

In 1999, Quinones-Baldrich et al were the first to report such a combined endovascular and open surgical approach for a type IV TAAA. Previous abdominal aortic surgery and concomitant visceral artery aneurysms precluded an open repair. Retrograde visceral bypasses from a limb of a pre-existing bifurcated aortic tube graft were performed followed by TAAA stent-grafting.

Following this report, several centres around the world have published individual cases/small series (<5) of hybrid approaches to TAAA. The results of these cases are encouraging considering the complicated nature of the TAAA disease process as well as the patients' co-morbidities. Of the 30 patients in this combined series, spinal cord ischaemia appeared to be rare or went unreported. Other post-operative complications were greatly reduced and intensive care stay was less than that of open TAAA surgery. Of note, no standard operative technique was employed and there was much variation in the EVSG used.

More recently, Resch et al have reported their series of 13 staged hybrid repair of TAAA27. They all underwent retrograde visceral bypasses (11 ilio-visceral and two infrarenal aortic - visceral) as a first procedure prior to completion with EVSG. They report a 30-day mortality of 23% (3/13) for all patients. Their mean follow-up in the 10 surviving patients was 23 months (1-45) during which time a further two deaths were related to the hybrid repair. Two Patients unfortunately suffered paraplegia and two further patients had transient paraplegic events.

St Mary's Visceral Hybrid Repair Technique
The patient is placed in a supine position under general and epidural anaesthesia, with routine cerebrospinal fluid drainage. We routinely use cell salvage techniques (with rapid infusers available) and invasive monitoring with arterial and central venous lines, urethral catheterisation, and transoesophageal echocardiography (Photograph A, over page).

A mid-line laparotomy allows for adequate exposure of the abdominal aorta, the origin of each renal artery, the coeliac axis, and the superior mesenteric artery (SMA). The inflow site for visceral bypass grafting is determined by previous abdominal aortic surgery and distal extent of aneurysmal disease. Where a previous infra-renal repair has been undertaken the bypass grafts are anastomosed in an end-to-side fashion to the existing graft. Where an infra-renal repair is possible, this is completed first and bypass grafts are subsequently sutured as before. If the infra renal aorta is normal an arteriotomy is performed and the bypass grafts anastomosed in an end-to-side fashion to the native aorta. If the aneurysmal disease extends to the bifurcation, one external iliac artery provides the inflow sites (Photograph B).

Most often two inverted (14 by 7mm or 16 by 8mm) Dacron grafts function as the conduits. The renal arteries are sequentially anastomosed in an end-to-side fashion. The two remaining graft limbs are routed along the base of the small bowel mesentery to the coeliac axis and SMA in an end-to-side fashion. If Doppler signals are satisfactory in the bypass grafts (with the origins of the native vessel clamped) they are subsequently suture-ligated to prevent retrograde flow into the aneurysm sac (termed Type II endoleak) (Photograph C).

Following successful visceral and renal bypass a suitable access site is chosen for endovascular stent deployment: usually a dedicated conduit attached to the common iliac artery or the abdominal aorta. An angiogram catheter is introduced on the contra-lateral side and the stents are deployed in a sequential fashion from the left subclavian artery through the thoracic aorta to the landing zone. Completion angiography after adjunctive procedures (extension cuff, giant Palmaz stent, balloon moulding) then confirms exclusion of the aneurysm (Photograph D).