State of the Union: Pediatric Heart Surgery Today

An interview with David Kalfa, MD, PhD, Director of the Pediatric Heart Valve Center, Surgical Director of the Initiative for Pediatric Cardiac Innovation, and Director of the Kalfa Research Lab.

What’s new in the world of pediatric heart surgery?

There are probably three main things that are important and new. The first one is partial heart transplant or valve transplant. The second one is complex biventricular repair–using two ventricles in children for whom, only a few years ago, we would have offered a single ventricle repair. The third one is robotic pediatric cardiac surgery.

Partial Heart Transplants

Let’s dive into partial heart transplant. That’s when you use different parts of a donor's heart instead of transplanting the entire organ. By doing partial heart transplants, does that mean you’re able to save more lives with fewer hearts?

Yes, for two reasons. First, you could use different valves from the same heart for multiple recipients. So, Patient A would receive the aortic valve and the pulmonary valve and Patient B would get the mitral valve. Or you can even envision treating three patients with the same heart. One patient gets an aortic valve, the other one gets the pulmonary valve, and the third one gets a mitral valve.

The other way to think about it is with a domino concept, where the valves are coming from an explanted heart. You’re helping two children with one heart donor, right? There is Patient A, who passed away and gave the heart to Patient B, and then Patient B gives a valve to Patient C. And then actually from Patient B, you can envision that you can help Patient C with the aortic valve and Patient B with the pulmonary valve. It's a kind of cascade effect in terms of how many patients you can help. Also, in terms of resources, it avoids wasting good functioning valves.

We recently celebrated the first domino transplant in infants. What were the advances that allowed for this breakthrough?

In my lab, we went back to pushing toward the use of fresh organs in a transplant setting. This meant going to the operating room as soon as the valve became available to limit the cold ischemic time [the period of time the tissue is not in the body of someone] in either the donor or the recipient. Part of the new concept of the partial heart or valve transplant is to use immunosuppression.

When the cryopreservation process [which keeps organ tissue intact using low temperature] was developed, it helped tremendously with the preservation of the valve. It increased the availability of the valve and ease of implantation in the sense that you have an off-the-shelf, available-any-time cryopreserved homograft sitting in a bank–that’s instead of waiting for a donor to be available in the middle of the night. But cryopreserved is not good for the biological reason that it's not a living tissue anymore. The tissue calcifies and degenerates.

What does that mean for the storage of grafts in the future?

The main advantage of cryopreservation was to increase the pool and availability of the graft. My lab and I have developed a mid-term and long-term storage and rehabilitation strategy using a bioreactor to store and rehabilitate fresh, living valves.

Basically, instead of cryopreserving this valve, we put these valves into a bioreactor and expose this valve to physiologic or normal conditions from a biological standpoint and mechanical standpoint, of the valve.

Does the bioreactor basically keep the valve alive?

Yes! We keep the valve at 37 degrees, add a nutrient solution with different types of metabolic aids (which help with keeping the valve alive), and then we put them in the bioreactor, at pressure, where the valve opens and closes at a heart rate.

The whole idea is to keep this valve alive ex vivo [outside the body] so that we have off-the-shelf available living tissue of a patient that surgeons can get whenever they need. They do not have to wait for a donor. They don't have all the logistics and the huge costs of needing a plane to get a valve and then coming back in the middle of the night to do this type of operation.

How long can the bioreactor keep a valve alive?

For the time being, we showed that we were able to keep them alive for four weeks. And that’s very nice already, but I’m confident we can keep increasing this storage.

Complex Biventricular Repair Changes the Future

Let’s talk about biventricular repair. This is an alternative to traditional single-ventricle surgeries, which treat single-ventricle defects by helping one ventricle do the work of two. Walk us through it.

This is new in pediatric cardiac surgery—the will to push towards using two ventricles or one and a half ventricles instead of using only one ventricle where possible. A single ventricle pathway in children or adults with congenital heart defects is not good long-term.

Why is that?

First, with single ventricle surgery, you need to do three operations. The first operation is just to balance the amount of blood going to the body and the lungs. It can be a Norwood or a PA [pulmonary arterial] band–several different types of surgery can be used.

The second step is what we call the Glenn operation, which basically prepares the heart and lungs for passive circulation, and then the third step is the Fontan operation. And with that, you keep just one ventricle as a systemic ventricle, which means that it would be the ventricle pumping blood into the rest of the body. It doesn't go through a pump. Venous blood is connected directly to the pulmonary arteries, creating passive circulation on the right side to send venous blood into the lungs.

But having a passive circulation is eventually pretty bad physiologically because the venous blood is not pumped, is not sucked. At some point, you develop higher pressure in the venous system. In the long term, it creates venous hypertension in the kidneys, then dysfunction in the liver, and dysfunction in the lymphatic system.

Basically, at some point, this single ventricle physiology fails, and all of these patients require heart transplants. Very frequently, a heart and liver transplant.

How does the biventricular approach differ?

To make it simple, there are ways to make a smallish ventricle grow little by little. By increasing the flow through the ventricle, especially in neonates and infants, you can make the ventricle grow.

For example, in borderline LV (left ventricle) patients, those who have a smallish left ventricle, it’s a strategy to make the smallish left side structures grow. The main thing we do is open up the inflow of the left ventricle, which is the mitral valve, by doing a mitral valve repair to promote more blood into it. We then fix and open up the outflow of the left ventricle, which is the aortic valve, by doing an aortic valve repair.

By also restricting the communication between the left atrium and the right atrium by making it smaller, there is less blood going from the left atrium to the right atrium. You force the blood to go from the left atrium to the left ventricle by restricting this communication, preventing the blood from going to the right side of the heart and pushing it towards the left side of the heart. And then, finally, by increasing the amount of blood coming from the lungs.

If more blood is coming from the left atrium and goes into the left ventricle, it makes the left ventricle grow. This is called a staged LV recruitment strategy. Depending on the patient’s abnormality, there is potential to do this in different ways.

How long do you let this growth occur? Is there a certain amount of growth that's a benchmark?

Not necessarily. We adapt to how the patient responds to the strategy. So, we would do the Norwood, and then three to six months later, we do a cardiac MRI and a cath, and we see the hemodynamics and what the patient needs. Then we do this staged LV recruitment surgery that I just described, and based on that, six to 12 months later, you repeat an MRI and you repeat a cath. And then you make a decision about whether or not you need to go back again to make the ASD [atrial septal defect] a little bit smaller or work on the mitral valve.

Or, if you are happy with how it looks in terms of hemodynamics and anatomy, you can actually go to ventricle repair and close the ASD completely. Each patient is different, and there are so many ways to do it.

At what age do you generally start the biventricular repair process?

The first stage is neonatal surgery, the Norwood procedure, usually. The second stage is around six to nine months of age. And then the next step varies a lot from patient to patient, but about six to 12 months later. So, let's say that you can consider doing a final two ventricle repair around one and a half or two years of age, roughly.

Does that mean that once the ventricle is growing on its own, there is no need for further intervention?

Yes, theoretically, right? Theoretically, you end up with the two ventricles repaired. In real life, things are a little bit more complicated because, to begin with, the mitral valve is not normal. The aortic valve is not normal. The LV is not normal, and we don’t have a huge amount of follow-up on these patients. We cannot say that 10 or 20 years later, this patient will not need a mitral valve replaced or another type of repair. But at least theoretically, you have two working ventricles.

The whole point of doing all of this is to avoid the physiology of the single ventricle and the physiology of the Fontan operation, which is, as we all know, very bad. I was talking about heart transplant and liver transplant at the same time. These are huge operations. These patients are very sick. Even when we counsel parents in the prenatal period about a single ventricle pathway, we have to mention heart transplant and liver transplant at 30 years of age because it is so likely.

Is biventricular repair becoming the standard of treatment at Columbia?

In the scope of the history of pediatric heart surgery, it's still new. I would say that the majority of centers would still offer a single ventricle pathway just because of that and because it's safer to go the single ventricle pathway for the first years of life. In terms of immediate outcomes, it is safer to do what we have been doing for 40 years instead of pushing the boundaries toward rehabilitating a ventricle.

That being said, at Columbia, we consider an LV recruitment strategy for every single patient. So here, for us, it's becoming the first line of treatment. If we think that it's reasonable to do it, we would–absolutely.

In complex biventricular repair, we can even do something called a reverse double switch or a ventricular switch. This we call systemic RV strategy. So, for example, if we think we cannot recruit the left ventricle and make it grow because the patient is too old or the mitral valve is too small for any reason. We can switch the use of the ventricle, which means that we know that this small left ventricle cannot be used to assume a full cardiac output, systemic cardiac output, which makes enough blood into the whole body. But this right ventricle is good enough and big and large enough. We will use the right ventricle as a systemic ventricle and the smallish left ventricle as a sub-pulmonary ventricle. Physiology can determine a lot of these things.

Are these decisions all based on the child’s individual anatomy and physiology?

Oh yes, absolutely. We use echocardiography, MRI, catheterization, CT, and even a 3D cat scan. Then, we do a 3D virtual reconstruction of the heart to understand the actual geometry of what can be done inside the heart to create these new baffles. Using this 3D virtual reconstruction, you can actually perform virtual surgery.

Wow.

This is all an extremely important part of surgical planning. Technology is really how we advance in these ways.

Does virtual surgery planning shorten the surgical time in the OR?

Definitely. It significantly decreases the time spent in the operating room. It makes the bypass time and the cross-clamp time shorter. You decrease the risk of having to redo something. It helps with counseling the parents, which is very important too. It helps with education for both the surgical team and the cardiology team.

The pediatric cardiology team can finally understand exactly what it takes to perform this type of operation. In the operating room, they didn't see it, and now they do. So, the cardiology fellow understands what we are talking about in terms of repair, what to do, the impact of the repair, and the risk related to the repair. So, multiple advantages!

Do you use virtual surgery for most procedures or just the most complex?

I would say only complex because it takes time, and virtual planning doesn't help with easy or straightforward surgery.

But sometimes, despite all of this, we still don’t know what we need to do for a complex repair or the feasibility of an approach. There are times when we're not able to make a good decision. When we have a borderline left ventricle, and we don't know if we should go to a Norwood operation, a single ventricle pathway, see what happens, and then potentially make the left ventricle grow, or go directly to a two ventricle approach.

Even with all of these tools, we are not able to answer this question, but with more research, we will. We’re working on it, and it will be reaching the clinical world very soon.

So many factors must go into that too, even down to the strength of the child for recovery.

Yes, absolutely. Our specialty is so individual, and it needs to be because every single patient is different. There’s a continuum of lesions, right? You can talk about a tiny non-existent ventricle to a normal size, and then in between, you have everything. And then, at each part of the spectrum, you have variation.

Robotic Surgery Offers New Options for Cosmetic Results

Robotic surgery has reached the pediatric heart world. Will you explain how that may change things?

The whole concept is to be less invasive, but the main advantage in children is really the cosmetic aspect of things—to avoid a scar. This is a noninvasive approach that avoids the wound related to sternotomy [surgical opening of the chest]. It’s a gradual progression: We first started with what’s called the mini-invasive vertical axillary approach, which is less invasive. And now, this is the next natural step.

In adults, the rationale for robotic surgery is also to improve outcomes in terms of shorter hospital stays, quicker recovery, etc. That's not necessarily the case here because children recover very quickly from heart surgery. But the cosmetic reason is very important because there are some studies that show the psychological impact. The fact that the child doesn't have to see the scar on their chest in the mirror every morning or when they go to the beach with their friends. They’re always aware of it.

Does the pediatric heart surgery team collaborate with the adult heart surgery for robotic operations?

It’s all teamwork and collaboration between the pediatric and adult robotic teams. I’m training now, working with Dr. Arnar Geirsson [Director of the Surgical Heart Valve Program and robotic heart surgery specialist]. We’ll start with very simple cases, an ASD [atrial septal defect] where we just have to close the hole between the right atrium and the left atrium.

Do you expect to apply robotics to more procedures as well?

Absolutely. Then we can expand the indication on ASD, potentially VSD [ventricular septal defect], partial AV [atrioventricular] canal defects, septal defect, and PAPVR [partial anomalous pulmonary venous return– which means that the veins from the right lung are going to the right side instead of the left side]. This can easily be done with robotic surgery. Potentially some mitral valve repair too. So that would be the spectrum we’re looking at.

How do you present robotic surgery to parents? Is this viewed as an option for families to consider rather than a recommendation?

Yes, exactly. You can go either way, right? I would never consider or offer this type of approach if it decreases the safety of the surgery or the excellence of the outcome. This always comes first.

But yes, at the end of the day, it’s the decision of the parents or the kids themselves. We’re talking about patients up to 18 and 19, sometimes 21. Cosmetic results are important to them.

There is a lot of advancement happening, what are you most excited about?

Really, all three things: partial heart transplant, biventricular repair, and robotics. But I’m excited to now create a formalized complex biventricular repair program at Columbia. And then develop the robotic program too.

Have you had any special moments in the last year that have stuck with you or inspired you?

The Domino heart transplant was special. There are also one or two complex cases of biventricular repair in which the patient is referred for a Fontan, knowing what it means 20 years later, and then they leave the hospital with two ventricles functioning well. That is extremely gratifying! You know that treatment really helped the patient, even if the patient and parents don't really realize it. It reminds me why I'm doing this kind of job and why we are pushing hard on these advancements.

One last thing, what do you do for fun?

Do you consider taking care of three babies fun? That is really what I do when I’m not here; it’s my fun. But I also like to do something new and different every year. I love electronic music so one year I did some mixing. I play a little piano so another year I was playing with a jazz band. One year was Krav Maga, martial arts. I always like to try something different and grow.