Wednesday, January 19, 2011

TMC Volume 2, Issue 3
section III: Much Better Than the Owner of a Lonely Heart

The heart is an amazing organ. It’s one of the essential pieces of the human body; without it, blood would sit limply in our veins and arteries (indeed, veins and arteries would have no real purpose!) and our cells would quickly use up all the oxygen in it, asphyxiating themselves faster than you can say “and this little piggy went to Kathmandu.”

Important as it may be, the heart is essentially an enormous muscle (or rather group of muscles) that functions as a pump. It draws blood in through the veins and out through the arteries, from the body, to the lungs, and back to the body again. This group of muscles, only about the size of your fist, moves about 2,000 gallons of blood a day. That means it takes your heart only about 5 minutes to circulate all of the blood in your entire body one time. Pretty impressive for such a small piece of equipment!

Obviously today’s focal point is the heart. Namely, Hypoplastic Left Heart Syndrome (HLHS). HLHS is a congenital heart disease (present at birth) which presents several complications, and usually requires an organ transplant by the end of the first year. Until the 1980s, HLHS patients who didn’t get a transplant didn’t have much left for them but prayers. During that time however, a surgeon and a cardiologist teamed up to develop a surgical intervention that could give all those individuals who failed to find donors a chance at life. Dr. Alfred Blalock and Helen B. Taussig developed the Blalock-Taussig Shunt (the current one is known as the MBTS or Modified Blalock-Taussig Shunt), an intervention that couples the pumping power of the heart with a small redirection of one of the subclavian arteries (or the addition of a body-friendly artificial tube) to provide blood to the lungs.  Another, more recent intervention is called the Right Ventricle-to-Pulmonary Artery Shunt (RVPAS) or Sano Shunt, where an artificial tube connects the right ventricle directly to the pulmonary artery. If that makes sense, then you probably already know a thing or two about cardiology. For the rest of us, here’s a layman’s description of this disease:

-       A normal heart contains 2 sides and 4 compartments. The sides are closed off from each other but work independently together. The right side receives deoxygenated blood (blue) from the body and sends it to the lungs and the left side receives oxygenated blood (red) from the lungs and sends it to the body.
original image: http://en.wikipedia.org/wiki/File:Hypoplastic_left_heart_syndrome.svg

-       A patient with HLHS has a left ventricle (the bottom compartment on the left side) that is hypoplastic – smaller than normal. This is due to various factors, mostly complications or errors during the fetal organ development.
original image: http://en.wikipedia.org/wiki/File:Hypoplastic_left_heart_syndrome.svg

-       Since the heart relies upon both positive and negative pressure forces to circulate, the incorrect sizes of any chambers (and even the arteries and veins) can result in inadequate pumping of blood through the heart to the lungs and etc. depending on which chamber has been affected.
-       More specifically in HLHS patients, the smaller size of the left ventricle ends up preventing their blood from reaching the rest of the body. HLHS patients also have a patent ductus arteriosus – the wall between the pulmonary artery (away from heart, going to lung) and the aorta (from left side to the body) has a hole in it.
-       As a result, a patient with untreated HLHS eventually succumbs to a slow, systemic suffocation, where cells and systems begin to die due to the lack of circulating oxygenated blood. By then end of the first year of life, untreated HLHS patients will die.

As you can see, this condition is deadly serious. Untreated HLHS has a 100% morbidity rate within 1 year. As a congenital disease, imagine how devastating to a parent it must be to hear this diagnosis. “What can I do to save my child?” “What can be done to give these children a chance at life?” These are the questions that immediately spring to mind. and from these questions came the answer we have so far: the Norwood Procedure.

The Norwood is the first of a 3-step surgical intervention that has increased the survival rate of non-transplant HLHS patients by almost 70%. It involves bypassing the defective ventricle (in this case, left) and placing all the pumping duties onto the effective one (right). The first steps of this procedure therefore involve bypassing the left ventricle by opening the atrial wall between the two sides of the heart. This allows both oxygenated and deoxygenated blood to mix, and lets the right ventricle’s pumping action to move all of the blood that is in the heart. Also, because of the patent ductus arteriosus (that hole in the wall), blood pumped from the right ventricle to the pulmonary artery escapes into the aorta. For those HLHS patients without a patent ductus arteriosus, one is made. The result is this mixture of oxygenated and deoxygenated blood that flows almost entirely into the aorta and out to the body. Unfortunately, the problem here is that since the system is no longer divided into two separate, closed systems with different flow directions connected at the lungs, it’s turned into one enormous open system with only ONE directional flow. The deoxygenated blood travels from the body, to the heart, back out to the body. To fix this, two interventions mentioned before were developed.


In a Modified Blalock-Taussig Shunt:
a better, non copyright-infringing image can be found at: http://www.pted.org/?id=doubleoutlet3#
 -       Blood flows from the right ventricle into the pulmonary artery, through the patent ductus arteriosus and into the aortic arch.
-       A small piece of Gore-Tex tubing is sutured (stitched) into incisions made on one of the subclavian arteries (branching from the aorta), allowing the blood that is pumped to the aorta to be diverted back to the lungs to be oxygenated.

In a RVPA or Sano Shunt:
original image can be found at: http://www.babypennington.com/?m=200708&paged=3

-       Blood flows from the right ventricle into the pulmonary artery, through the patent ductus arteriosus and into the aortic arch.
-       A small piece of Gore-Tex Tubing is connected directly to a small incision made on the right ventricle to an incision made on the pulmonary artery. This allows some of the blood that enters the right ventricle to be pumped directly to the lung for oxygenation.

Two simple, elegant solutions coming from years of practical knowledge and expert understanding. It’s amazing to me how practical and practiceable these two surgeries are sometimes. But I digress. The point here is that there is an ongoing debate about the effectiveness of one procedure over the other. Some hospitals and surgeons cling to the MBTS religiously, while other hospitals and surgeons defend the RVPAS with righteous fanaticism. How does one go about settling this dispute once and for all, for the children?

SCIENCE.

You may be thinking, “of course. It’s simple. Run a trial where half of the HLHS patients receive one procedure, while the other half receives the other. Compare results.” And it is so easy. Except when you realize that the survival rates for these surgeries differ, and differ for a number of different reasons. How simple is it to ask a parent to have their child be randomly assigned to two procedures, where one has a 35% mortality rate, while the other 25%? “Of course, for the sake of science, I will submit my child to a 10% higher chance of death.”

No one will do that.

But that’s what makes this part so amazing. It did happen. Starting in 2005, a group of scientists and doctors began asking hospitals to ask patients if they were willing to participate in a clinical research trial concerning HLHS surgery. Resistance was strong at first, and eventually 5 hospitals agreed to be primary sites. 5 hospitals. In the entire country. Later, 10 more auxiliary sites joined in for a total of 15. As they began to ask patient families for consent, it was clear that there was an arduous road ahead.  Patients don’t come to the hospital to hear the words “we’re going to try this out” or “your child’s procedure will be randomized”. They don’t take kindly to statistics like “your child may receive a procedure that is up to 10% less effective than an alternate procedure.”  Even “Our hospital is participating in clinical research concerning pediatric heart surgery. Your child’s surgery will be one of two procedures, and the results of their will be used to determine the effectiveness of one over the other.” But they had to settle on something. And I’m sure they settled on something close to the last one.

They ended up with a pool of 549 eligible patients. These were randomized to one of the two procedures, and there progress was tracked for 5 years. Following the initial procedure, there is a 6-month follow up surgery, and a 1-year evaluation for transplantation. After the first 12 months, they found that 64% if the MBTS patients and 74% of the RVPAS patients had survived. Other variables continued to be tracked, and these children were watched for the next 5 years for complications, surgical interventions, and other cardiac-related issues. A wealth of information was obtained and real data was found that helped science and medicine build its understanding of the disease and the intervention.

But things were sacrificed. Scientific presuppositions. Surgeon preferences. Surgical intuitions. Pride. Fear. Hope. Life.

I am by no means trying to discount the evidence found in this study. Nor am I trying to write a piece on ethics or morality in science and scientific discovery. I am simply trying to paint a picture. As accurately as I can, of a situation that is, at first glance, seemingly simple. There are so many things that can be said when looking at something like this…it’s intriguing, engaging for me to think about. Finally being able to know that one intervention has more survivability than another? That’s great. Knowing that perhaps 10% of the participants could have survived if they had been given the correct treatment? Terrifying… Knowing that this is the primary means, the only real means, by which science, medicine, and knowledge can be furthered? Harrowing. Awesome. Maddening. Sombering. Disgusting. Saddening. Amazing.

This study is continuing, and there are still so many variables left to be processed, measured, and analyzed in order to reach more definitive conclusions. But the data has been obtained. The work has already been done. That. Just. Happened.

And to be honest, I would have loved to be a part of it.