CHICAGO – Surgeons can expect to see more abdominal organ transplant recipients presenting with aortic aneurysms, as transplant survival rates increase along with the age of organ donors and recipients.
“The consensus is that abdominal aortic aneurysms (AAAs) have a more aggressive course post-transplant and within that context, probably need to be managed more aggressively,” Dr. Michael J. Englesbe of the University of Michigan, Ann Arbor said at the annual Northwestern Vascular Symposium.
Dr. Michael J. Englesbe
Some 270,000 Americans are living with a functioning liver or kidney graft, and their average age has risen from 47 years to 57 years over the last decade.
Though the data isn’t great, it’s hypothesized that the immunosuppression prerequisite for successful organ transplantation promotes the progression of atherosclerosis and aneurysm growth in transplant patients, he said.
New-onset diabetes, hyperlipidemia, and hypertension are all common post-transplant due to immunosuppression therapy. Aortic aneurysms are also reported to rupture at smaller sizes in transplant recipients.
Intriguingly, the opposite effect has been observed in experimental animal models, where immunosuppression with calcineurin inhibitors and mammalian target of rapamycin (mTOR) inhibitors has been shown to stabilize atherosclerotic lesions and inhibit aneurysm expansion.
The reason for this disparity is unclear, but immunosuppressants likely augment other cardiovascular comorbidities such as hypertension and atherosclerosis and this may trump their anti-inflammatory effects and lead to worse aneurysm disease and faster expansion in humans, Dr. Englesbe speculated in an interview.
As for when aneurysms should be fixed, kidney transplant candidates should undergo AAA repair prior to transplantation since the risk of renal complications after aneurysm repair puts the allograft at risk, Dr. Englesbe advised. Either an open or endovascular approach can be used.
In liver transplant candidates, elective AAA repair should be avoided if possible and is contraindicated if any signs of hepatic decompensation are present such as muscle wasting, ascites, platelet count less than 50 x 109/L, or encephalopathy. For well-compensated cirrhotic patients, endovascular repair is best.
One of the most important considerations for any solid-organ transplant patient undergoing aneurysm repair is perioperative management of immunosuppression, Dr. Englesbe stressed.
Transplant patients are maintained on oral calcineurin inhibitors such as cyclosporine and tacrolimus (Prograf) throughout the perioperative period to prevent organ rejection, but these drugs have nephrotoxic effects. About 10% of recipients, typically the sicker patients, will be switched to mTOR inhibitors such as everolimus (Afinitor) and sirolumus (Rapamune) as a kidney-sparing alternative.
“Part of the mechanism of these [mTOR] drugs is that they really affect fibroblast functioning, so patients that are on these medications, their wound will fall apart and they will invariably get a hernia,” Dr. Englesbe said. “You have to stop them upwards of about 6 weeks before surgical intervention, and I think this is also true for many endografts.”
He highlighted a case in which an mTOR inhibitor was started three months after liver transplant due to renal dysfunction in a patient who was fully healed, but within three weeks, “her wound fell apart, completely fell apart.” She developed several seromas underneath her incision, one of which became infected and took months to close.
“The transplant professionals – your nephrologists, your cardiologists – aren’t going to know this fact, but as a transplant surgeon it’s usually the first question we’re going to ask with respect to any post-transplant patient we’re going to operate on, so it’s something to keep in mind,” Dr. Englesbe said.
Another take-home message was the importance of maintaining kidney function in kidney recipients presenting with aortic aneurysm, as mortality in these patients is about 10-fold higher once the kidney fails, he said. A recent study reported that AAAs are significantly more common in kidney than liver transplant recipients (29.6% vs. 11.4%; P = .02), despite a similar prevalence for any aneurysm (4%) in both groups (J Vasc Surg. 2014 Mar;59;594-8).
When kidney recipients present, preoperative imaging of the aorta from the aneurysm to the kidney allograft is mandatory, he said. Endovascular repair is preferred, whenever possible.
The renal graft is typically sewn to the external iliac artery 3 cm to 10 cm from the bifurcation of the external and internal iliac arteries. Because of this, repair is challenging when aneurysmal disease involves the iliac artery, Dr. Englesbe observed. Aneurysmal dilation is less common in the external iliac, but stenting an iliac aneurysm can still compromise inflow to the transplanted kidney.
Several surgical techniques including axillofemoral bypass, aortofemoral shunt, or extracorporeal circuit have been reported to preserve renal function during open AAA repair in renal transplant recipients. These techniques are not without their own risk of complications and should be avoided in patients with low creatinine, but are appropriate in patients with marginal or impaired renal function, according to Dr. Englesbe, who reported having no relevant disclosures.