Patient Selection for EndoAVF

[Chris Beck]
Can you provide our listeners the broad view of dialysis and need for fistula creation?

[Neghae Mawla]
The thing about vascular access or dialysis access in particular is these patients are hooked at the machine, and the machine is running at about, on average, 400 ml per minute. You've got to have a large caliber access, and something that will support pulling the blood at 400, running it through, and returning it all back. That's where just a plain, old access doesn't work. I explain to my patients, "Put an IV in, it's not going to run fast enough." So that's really where the concept of vascular access came in, and if I remember correctly in the early days, they were doing femoral artery puncture. They were using the arterial blood pressure to actually pump through the entire circuit. We're 50-60 years out now from the original Cimino fistula. The arteriovenous fistula allowed us to use venous access for both needles instead of an arterial access and a venous access. The first innovation has been this EndoAVF in terms of how to create the anastomosis in a simpler way.

[Chris Beck]
For some people who don't know anything about this procedure, can you talk about the difference between what a standard surgically created fistula looks like versus an EndoAVF?

[Neghae Mawla]
So if you look at an upper arm fistula, the surgical fistula is usually anastomosed to the brachial artery above the cubital fossa. So, you've got a cephalic alpha, and it's an end-to-side anastomosis, and so either you will have a cephalic outflow or you will have a basilic outflow. The basilic vein gets transposed and elevated as well because as it travels up the arm, it tends to dive in underneath the bicep's muscle. Just the way it courses, it's hard for the patient to sit there on dialysis with the needles on the inside of the arm. So, the surgeon will elevate it, and transpose it, bringing it more to the front, so the dialysis nurses can access it. Because the endo-anastomosis is actually in the proximal forearm, you get a little bit more real estate in terms of cannulations on… For dialysis I actually utilize the median cubital vein for my cannulation site. So if I've got an endo basilic, meaning that there's no cephalic outflow, I will plan on cannulating across the median cubital vein, and I have been able to get almost most of my patients cannulated without a basilic elevation or transposition. One of the really nice advantages of an endo option is if the patient only has a basilic vein, then it doesn't absolutely require an elevation and transposition because that's actually a pretty big surgery sometimes, especially on these elderly patients.

[Chris Beck]
We have a lot of trainees who are listeners, can you talk about what people mean when they say Fistula First, and why fistula creation is so important for the dialysis population? Why not just put catheters in everybody?

[Neghae Mawla]
It's all about outcomes in terms of infection rates and quality. The quality of dialysis with a catheter is always lower, and the only reason catheters are still around is because of immediate use. Even then immediate use graft still takes two or three days to let the soft tissue swelling to calm down before you can access it. The graft is immediate use, but the tissue may not allow immediate use, and a lot of times that's okay, but the infection rates for catheters are higher. The outcomes with catheters at the dialysis level are clearly lower, so that's why we made a big push to avoid catheters. The outcomes for fistulas are better than graft in terms of lifespan, and infection, so that's why this initiative came out with Fistula First, to really try to get a fistula in someone who's a candidate because that's where the better outcomes were. Now, the newest guidelines have gone away from a Fistula First on everybody to more of a right access for the right patient at the right time. We recognize that a 90-year old patient who starts on dialysis, whose lifespan is a year and a half or two years, may not need to go through the hassle of getting a fistula in and struggling to get mature. Maybe a graft is better for a patient, or maybe the catheter is better for a patient. Now the algorithm is starting to change, and the question of where does EndoAVF come into this algorithm is also unclear at this time. The idea behind the Fistula First initiative was really based on the fact that a mature fistula is better than a mature graft, which is better than a catheter.

[Chris Beck]
Regarding EndoAVF fistula, can you talk about, first, who is a candidate, and what does the pre-procedure or evaluation look like to tease apart who and who is not a candidate for the EndoAVF?

[Neghae Mawla]
Everything is done with ultrasound screening for me in my center, so the first question is to figure out, "Are they an upper arm fistula candidate or not?" So your EndoAVFs are an upper arm fistula either utilizing the cephalic vein or the basilic vein. There's no forearm EndoAVF options. If they are an upper arm fistula candidate, then it's a matter of additional screening of the perforating vein to figure out, "Are they an endo candidate?" A lot of patients are not an endo candidate, but can be a surgical brachiocephalic or a brachiobasilic fistula for example. It really boils down to the anatomy of the perforating vein, which is typically antecubital fossa. It’s really identifying where does that perforating vein go? The perforating vein really just communicates the deep veins and the surface veins. If you look at your surface veins, meaning the cephalic and the basilic as your fistula outflow for cannulation for dialysis, if that perforating vein will communicate between one of those or both of those down to the radial veins and/or ulnar veins, then that gives you an EndoAVF option.

[Chris Beck]
It seems like whether or not you have a perforating vein and maybe the position or connection of that perforating vein is very important, but is there anything else regarding vessel diameter or arterial inflow that you look for on the preprocedural ultrasound?

[Neghae Mawla]
The general rule of thumb is a cephalic or basilic outflow of two and half millimeters, which is your general criteria for a surgical fistula. That's where I start with. In addition to just the basilic, I also look at the median cubital vein because that comes into play for the EndoAVF. I look at a 2.0 mm for a median cubital vein or the cubital cephalic, perforating veins are 2.0 mm, and then the artery dimensions are all at the minimum of 2.0 mm. So really, it's two and half at the outflow, and 2.0 everywhere else is really the threshold in terms of your vessel criteria. If you're looking at Ellipsys, it's really looking at radial, proximal radial artery perforating vein, and your outflow. If you're looking at a WavelinQ, you're looking at ulnar artery, in addition to ulnar veins in that proximal territory, and your radial veins in that proximal territory as well for your anastomosis.

[Chris Beck]
For those who don't know, or may not have any experience with this, when you say proximal territory, will just clarify?

[Neghae Mawla]
Sure. Everything is at the proximal forearm, so we're looking right at the bifurcation of the brachial artery into the radial and the ulnar. Typically right around the range of the recurrent radial artery is where that perforator comes down and communicates just adjacent to the radial artery. On the ulnar side, we look to keep it in the common ulnar artery before the interosseous take off.

[Chris Beck]
In your experience, what are the most common things that you're evaluating for in EndoAVF? What are the most common veins you see that exclude them from being a candidate for the procedure?

[Neghae Mawla]
It all boils down to vessel anatomy. I've tended to notice patients that have a high bifurcation of the brachial artery in the upper arm sometimes don't have a perforator, and sometimes it doesn't communicate very well because it just seems like their superficial outflows are not that good, and they stay small. Some people have large cephalic, basilic drainage. It's a matter of which highway am I going to take home. For dialysis I need that large cephalic and basilic drainage, and I've noticed that high bifurcations tend to have very big radial veins, and very big ulnar veins, but their superficial veins are not that big, or they just don't communicate well into the deep level. It's not that I haven't done any [like that], but they are less common of a catch. Then, it's just those variants where everything drains into the brachial veins, and they have no cephalic or basilic outflow. A lot of people don't have perforators. My capture rate is right around 50% I think, in terms of my screenings to those that are a candidate for EndoAVF.

[Chris Beck]
In your mind, who is the patient that comes in that is an ideal candidate for the procedures completely based on the anatomy that you find on the ultrasound?

[Neghae Mawla]
It is all based off anatomy really. Then, it's just a matter of talking to the patient and saying, "Okay, which way do you want to go?" In general, the dilemma is not so much when it's an endo versus an open option. You can tell them, "Look, we can do this endo or we can do it open." Most of them choose the endo option. The dilemma in terms of discussions is if they have a forearm radial cephalic option, and they also have an endo upper arm option, then what's the right access for them? I don't know that there is an answer, a good answer or a standard answer yet because our standard algorithm always says just to really start in the forearm, and then work your way up for surgical fistula. But now, this endo anastomosis is at the deep level, and if an endo fistula doesn't take or goes down, it usually goes down at the deep level near at the anastomosis or at the perforating vein. I've had a couple of patients that failed my EndoAVF that went back later and got a radial cephalic fistula surgically, and they're doing fine. Those are the ones that I have discussions with the patients to say, "Hey, which way do you want to go? Do you want to start with the forearm, or do you want to start with the upper arm?" The question is, if an EndoAVF takes, and lasts them five years, then can you go back and do a radial cephalic fistula when that goes down? It depends on, again, where it fails.

[Chris Beck]
If the patient goes just on radial cephalic fistula, and that fails, can you do Endo AV fistula subsequently?

[Neghae Mawla]
Yes, you can. I've noticed there's almost a bimodal curve towards EndoAVF. The elderly patients, even if they have a radial cephalic option, will choose an EndoAVF just to avoid the surgical open, just to avoid anesthesia. Someone who's 75, we'll look at lifespan. If you get them one good access, that may be the only one they need to get their access for the remainder of their time on dialysis. So, the elderly patients will preferentially choose an upper arm EndoAVF over a radial cephalic fistula. The young patients who are in their 20s and 30s will do the same, choosing upper arm for the cosmetic reasons more than lifespan reasons. But, the patients who are in their middle age, that are more in their 40s, 50s, and even early 60s, it's a 50-50 split. A lot of them say, "I want to preserve all the access choices I can." I say, "Okay, then start with the Cimino." Some of them say, "No, let's go ahead and start up here."