A basic recipe for treating complicated aortic dissection
A basic recipe for treating complicated aortic dissection
It was only last month when I came across a post of an aortic aneurysm in a difficult spot (link) and I couldn’t help chiming in some comments. Reading it now, I sound insufferable, because I wrote,
“Depends on etiology and patient risk stratification. Also assuming aneurysm goes to level of SMA and right renal artery origins and involves side opposite celiac. Options depending on resources of your institute: 1.Open repair with cannulation for left heart bypass and/or circulatory arrest 2.Open debranching of common hepatic, SMA, R. Renal from infrarenal inflow and then TEVAR 3.FEVAR from custom graft from manufacturer on protocol 4.Parallel grafting to CA, SMA, R. RA with TEVAR 5.Surgeon modified FEVAR 6.Open Repair We would have a multidisciplinary huddle around this patient -Vascular, Cardiac Surgery, Cardiology, Anesthesia, and ID (if needed) to help choose. Be ready to refer to a center with more resources -including prepping patient for transfer and imaging -including uploading images to the cloud for transfer with patient’s permission. More info please”
More Info Please, Indeed
The post I commented on was of a saccular aneurysm in the transdiagphragmatic segment of aorta. Ironically, only a few weeks later, I got called from hospital transfer center about a patient with a leaking aortic aneurysm, a type V thoracoabdominal aortic aneurysm as it turned out, from an outside hospital, needing urgent attention, and we accepted in transfer based on the conversation I had with the tranferring physician. And that was the problem -usually in taking these inter-hospital transfers, you have to pray that the precious CT scans come along with the patient burned correctly onto a CD-ROM. You can buy and watch a movie in 4K resolution over the internet -about 4 gigabytes, but a patient’s CT scan which is about 200 megabytes -because of various self imposed limits, overly restrictive interpretations of laws, and lack of computer skills, these life saving images get transferred on CD in 2019. That last time I purchased a CD for anything was over 15 years ago.
An Interested Party
The technical solution –to use the internet to transfer critical life saving information between hospitals – came about when our IT folks took an interest in my quarterly complaint email about using the newfangled internet for sharing files. After mulling various solutions ranging from setting up a server to using commercial cloud solutoins, we came upon the compromise of using our internal cloud with an invitation sent to the outside hospital. I would send this invitation to upload the DICOM folder of the CD-ROM to an outisde email address. It was simple and as yet untried until this night. “Would the patient agree to have his CT scan information transmitted to us electronically?” I asked the other physician. He assured me that the patient was in agreement.
It Takes Two to Tango
Of course, being able to transfer these pictures requires a willing partner on the other side, and the referring physician made it clear he did not have the technical expertise to do so. It took a bit of social engineering to think about who would have that ability. Basically, aside from myself, who spend all their time in dark rooms in the hospital in front of giant computer monitors? The radiologists! I got through to the radiologist who had interpreted the report and explained the simple thing I needed. Gratefully, he agreed, and I sent him a link to our cloud server. I explained to him, “When you receive this, clicking the link opens a browser window and then you open the CD-ROM and find the DICOM folder and drag and drop it on the browser window.” The 200-500 megabytes of data then get sent in electronic form, as it was meant to in 2019.
The Internet Saves a Life
The brutal truth is that in locking down a computer system, many hospitals make it impossible to even load an outside CD-ROM, creating many self imposed barriers to care. Thankfully, at CCAD, we were able to work together to find a secure solution. With the CTA on our servers, I was able to review the study within 15 minutes of accepting the patient, and arrange for the right team to be assembled, and confirm that we had the right material (stent grafts) for treating the patient. When the patient arrived, OR was ready to go, saving hours of time that normally would have been required if the CT scan had to be reviewed from the CD-ROM that came with the patient. Sometimes, the CD-ROM does not come, and in a critical situation, the CTA has to be repeated with some risk to the patient for complications of the contrast and radiation.
What to Do
The patient had a 8cm sphere shaped aneurysm arising in the transdiagphragmatic aorta, leaking into the right pleural cavity.
The patient was otherwise a healthy middle aged man with risk factors of smoking and hypertension. The centerline reconstructions showed the thoracic aorta above the aneurysm to be around 20mm in diameter and same below, with the celiac axis and superior mesenteric artery in the potential seal zone of a stent graft. The only plaque seen was around the level of the renal arteries and was focal and calcified. Looking at the list I had made as a comment to the Linked-In post, I realized that I really only had one viable option.
Open repair, usually the most expeditious option, was made challenging by the right hemothorax, making a left thoracotomy hazardous if the lung had to be deflated. Cardiopulmonary bypass would have to be arranged for, and that adds a metabolic hit that greatly raises the stakes. Of the endovascular solutions, the only viable option was TEVAR to exclude the rupture and debranching of the celiac axis and superior mesenteric artery. To those who would advocate for parallel grafts, there was no room in the normal 20mm diameter aorta. And branch systems for rupture are some time in the future. Also, the patient was becoming hypotensive. So the planned operation was first TEVAR to stop the bleeding, and then open surgical debranching. A hybrid repair.
The smallest stent graft we have is a 21mm graft, but it would not be suitable for this aorta. In practice, the normal aorta is quite elastic and will dilate much more than what is captured on a CTA. The next size we have is 28mm graft and I chose this to exclude the rupture, which was done percutaneously.
As seen below, the graft excluded the celiac and SMA. Late in the phase of the final aortogram (second panel) there was an endoleak that persisteed despite multiple ballooning. The timing suggested the intercostals and phrenic vessels contributed to a type II endoleak, but it was concerning.
The bypasses were sent from the infrarenal aorta to the common hepatic artery and the SMA close to its origin, and the origins of the celiac axis and SMA were clipped. The bypasses were then done with a 10x8mm bifurcate Dacron graft originally for axillofemoral bypassing. It had spiral rings which I removed at the anastomosis and this resulted in a kink at the closer bypass. Usually, I loop this for iliomesenteric bypass but there was not enough distance from the infrarenal aorta. I have to add a little trick I modified from my pediatric surgery experience as a resident -a Heinecke-Mikulwicz graftoplasty:
This worked to relieve the kink as evidenced on the aortogram above. After closing the laparotomy, I placed a chest tube in the right chest. The patient had a course prolonged by a classic systemic inflammatory response syndrome, with fevers, chills, and leukocytosis. He bled for a while but stopped with correction of his coagulopathy. All blood cultures were negative, but a CT scan was performed out of concern for the endoleak, and the possibility of continued bleeding.
No endoleak was detected as the sac was fully thrombosed. There was a consolidation of the blood in the right chest, but it resolved with fibrinolytic therapy.
This case illustrates several points I have been making on this blog.
I was invited by Dr. Martin Maresch to speak on complicated type B aortic dissections. Should be an exciting day.
The patient is middle aged and had a type B thoracic aortic dissection (TBAD) as a consequence of recreational substances that acutely raised his blood pressure. At the outside hospital, he had a CTA showing the dissection extending from his left subclavian artery and causing occlusion of his superior mesenteric artery (SMA). He developed abdominal pain and was swiftly transported to our acute aortic syndrome unit. He was taken to the operating room and underwent a TEVAR of the dissection and stenting of his SMA -this is similar to other cases I have discussed in prior posts so I am omitting the technical details. The stent covered the left subclavian artery origin to exclude the origin of the dissection. The stent was extended to the distal thoracic aorta but did not go to the celiac origin.
Post procedure, his lactate never rose and he was maintained on the usual post procedure protocol of keeping MAP’s (mean arterial pressure) above 80mmHg. His left subclavian artery was covered but I do not routinely bypass, especially when the left vertebral artery is at least equal in size to the contralateral one. I don’t often place spinal drains for urgent/emergent cases particularly in patients who have never had infrarenal aortic surgery and patent hypogastric arteries. He was kept sedated overnight and awoke in the morning unable to move his legs to command. He had no pain sensation up to his umbilicus.
A spinal drain was emergently placed and his blood pressure was raised to MAPs of 90+, but these failed to reverse his paralysis. After discussion among my world class partners, I chose to take the patient back for a carotid subclavian bypass which was done through a single incision with a dacron bypass graft.
His paralysis resolved. He was discharged home, ambulating without assistance. Spinal cord complications are reported to occur between 1-5 percent of patients undergoing TEVAR for complicated TBAD. They were seen in 2 of 72 patients in the TEVAR arm of the INSTEAD trial (Circulation, 2009 vol. 120(25) pp. 2519-28), and was permanent in 1. While there are some who routinely place prophylactic drains, it is unclear to me that they have a significant effect if placed unselectively. I will place a Preop drain in the instance of infra renal graft, hypogastric arterial occlusive disease. In the instance of a dominant left vertebral, I will perform concomitant bypass, but just as often not. This is a gratifying and rare outcome of paralysis reversed with a carotid subclavian bypass when spinal drain and permissive hypertension did not.
Type B aortic dissections (TBAD) are frequently seen here at the Clinic as we serve as a regional referral center. As a trainee, I read the chapters discussing all the classifications and discussions of the biomechanics and felt quite intimidated by the all the moving parts involved in an aortic dissection, and I missed the main point about TBAD. Aside from the rupture risk due to the attenuation of the adventitia and hypertension, the acute TBAD is a rapidly developing stenosis of the aorta due to the inflation of a wind sock balloon created by the dissection flap. You can assume any flow that occurs in the false lumen is limited by the area of the proximal tear which is always smaller than the area of the aortic lumen. The true lumen is still perfusing the lower half of the body, and because of the volume filling effect of the flap, flow is restricted. The equivalent physiology is seen in aortic coarctation. Long term, the false lumen behaves like a pseudoaneurysm and may thrombose, continue to grow, or both.
Our group looked at CT’scans on 80 consecutive patients and found that the true lumen to false lumen ratio of less than 0.37 is predictive of the need for intervention.
This makes hemodynamic sense as it approximates the 70% critical stenosis borderline for other arteries. It explains why closing the opening of the dissection, the opening of the wind sock, and expanding the true lumen effectively treats malperfusion.
This patient whose CTA is shown above was transferred with increasing abdominal pain, inability to control blood pressure, and worsening lactic acidosis.
There was nearly complete obliteration of the true lumen throughout the aorta and occlusion of the left renal artery and dissection into the celiac and superior mesenteric arteries.
Aortography showed the dissection, and absence of visceral vessels from the injection which was from the aortic root. True lumen position was confirmed with IVUS.
A thoracic stent graft was delivered across the left subclavian artery origin up to the innominate artery origin -the patient had a bovine arch. Immediately, there was filling of the visceral vessels with re-establishment of true lumen flow.
The renal occlusion appeared improved but there was still a stenosis due to deflated dissection flap and this was stented (panel right above).
His abdominal pain remitted and his lactate normalized. His creatinine stabilized and has since normalized.
Again, if the true-lumen is compressed, the aorta is stenotic because there is a wind sock inflated in it. TEVAR offers a minimally invasive option, frequently percutaneous, for treating this.
The figure above shows the summarizes the problem that brought the patient to his local hospital and triggered his transfer to our acute aortic syndrome unit. The concept is that all chest pain of cardiovascular origin gets intake through a vast intensive care unit staffed by cardiovascular intensivists. Stabilization, workup, transfer to operating room or interventional suite all happens in an ICU that encompasses almost a city block.
The patient is an older middle aged man with sudden onset of back and abdominal pain. He was on coumadin for a prior SMV thrombosis and treatment for a ruptured appendicitis -antibiotics with plan for staged appendectomy. CT at his local hospital revealed a type B aortic dissection (TBAD) that extended into his superior mesenteric artery.
The aortic dissection terminated in the infrarenal aorta. The celiac and SMA had true and false lumen perfusion, the right kidney was perfused through the false lumen, the left through the true. Both legs received true lumen flow.
The dissection started at the left subclavian artery origin. The false lumen compressed the true lumen up at the proximal descending thoracic aorta. This is an important finding because in this configuration with much of the filling of the dissection from the distal reentry sites, the false lumen acts like a pressurized, compressive lesion. With time, the adventitia around the false lumen may become aneurysmal if the false lumen fails to thrombose or obliterate. When the dissection is acute, the flap may cause a direct obstruction to flow or a dynamic one that depends on the pressure difference between true and false lumen.
In this patient, thrombosis occured in the SMA beyond the origin due to dissection and decreased flow. This was consistent with the patient’s complaint of generalized abdominal pain and examination findings of pain out of proportion to the exam, indicating acute mesenteric ischemia.
His laboratory findings were within normal ranges, indicating this was early in the process. It is important to remember that no lab value correlates with acute mesenteric ischemia except very late in the process, and acute mesenteric ischemia remains a clinical diagnosis (reference 1) that is associated with a high mortality rate.
He was taken to the hybrid operating room. Right groin access was achieved and wire access to the arch was achieved. IVUS (Intravascular ultrasound, Volcano) was used to confirm the location of the wire -I believe this is an important adjunct as simply passing the wire doesn’t guarantee travel up the true lumen.
A conformable TAG endograft (CTAG, Gore) was delivered through a 24F sheath into position. Two devices were used to cover the thoracic aorta from the left subclavian artery to a position immediately above the celiac axis. The left subclavian was partially covered -the bare stents covering the rest.
This excluded the proximal entry tear of the TBAD. IVUS (image below) showed improved lumenal diameter of the true lumen into the SMA.
Once this was done, wire access into the SMA was achieved. This was technically challenging from the groin, and the backup plan was access from the left brachial artery which had been prepped. With patience, 6French access into the SMA was achieved. The origin was stented with a balloon expandable 8mm x3cm stent -sizing was based on IVUS and CT. This creates an alarming arteriogram as the stent appears oversized on subsequent runs -it is important to remember that the false lumen still takes up space beyond. Arteriography located the thrombosed segment and the reconstituted SMA beyond.
Wire access was achieved across the thrombus. At this point, I had a range of options for thrombectomy including simply aspirating which retracting a catheter. This was not optimal as I could lose subsequent wire access or reenter the false lumen. The other option was an open thrombectomy and patch angioplasty -the thighs were prepped in case we had to harvest vein. Again, in the setting of dissection and going into the mesentery, an open revascularization while feasible, is challenging.
Thrombectomy catheters like Angiojet were available, but I chose to try the Export aspiration catheter (Medtronic). It is simple to set up and goes over a 0.14 wire. It is designed for the coronaries which have a similar lumenal diameter as the SMA. It worked well in this setting in retrieving thrombus which had a pale element that may have indicated some chronicity.
The completion arteriogram was satisfying.
The SMA completely filled as did the celiac axis and both renal arteries. I opted not to treat the right renal artery as we had given 250mL of contrast, and it was filling well without intervention. The patient was making excellent urine and his blood pressure had been maintained with mean arterial pressures above 70mmHg. At this point, IVUS confirmed good deployment of the stent.
The sheath was removed and the access site repaired. The general surgeons explored the patient and found all the bowel to be well perfused with pulsatile flows seen in the mesenteric arcade. The appendix was removed.
On waking, the patient was noted to not move his legs. A spinal drain was expertly placed by our cardiac anesthesia staff and his blood pressure was raised to MAP’s above 80. He recovered motor function in his legs soon after. I usually don’t place preop CSF drains in this scenario in the presence of good pelvic circulation, no history of infrarenal aortic interventions, and patency of the left subclavian artery. That said, with TEVAR of TBAD, there is a small incidence of paraplegia (1-5%) which I emphasize in my preoperative discussion.
He was started on heparin anticoagulation postop because of his history of SMV and now SMA thrombosis, interrupting it briefly to remove the CSF drain. A CTA was obtained to confirm absence of bleeding showing obliteration of the dissection in the aorta and good patency through the true lumen of the SMA.
Most importantly, he had complete relief of his abdominal pain.
The treatment of acute mesenteric ischemia has greatly evolved since I presented my paper in 2002. While open revascularization remains a gold standard, it is becoming increasingly apparent that good to better results may be obtained with an endovascular approach. Dan Clair, our chair, has made the comment that early revascularization with endovascular technique is analogous to emergent PTCA in occlusions of the coronary system and that re-establishing flow is a critical first step.
Open exploration still is the mainstay of managing acute mesenteric ischemia, but laparoscopic exploration remains feasible. This patient underwent open conversion after an initial laparoscopic exploration to remove a ruptured retrocecal appendix that had been treated for over a month on antibiotics. Without bowel necrosis, a second look is usually unnecessary, but is critical when threatened bowel is left behind.