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The Superior Cavopulmonary Anastomosis - Relief for an Overworked Heart and Setting the Stage
Robert
D.B. "Jake" Jaquiss, M.D.; Chief,
Pediatric and Congenital Cardiothoracic Surgery,
Arkansas Children's Hospital; Professor, Department
of Surgery, University of Arkansas for Medical
Sciences College of Medicine
The SCPC is an operation that connects the superior vena cava, which carries all of the venous blood from the upper half of the body, directly to the right pulmonary artery (see Figure). The blood is then distributed to both lungs. The operation also includes (virtually always) removal of whatever source of lung blood flow had served the patient previously, typically either a surgically constructed shunt or a narrowed native pulmonary artery. Whether the former blood supply was a shunt or a narrowed pulmonary artery, the blood was “driven” to the lung by the action of the single ventricle. Thus, the construction of the SCPC and removal of the former source of blood to the lungs serves to “unload” the heart, which no longer has to power the blood to the lungs. This has several specific desirable effects for the heart including the removal of a volume load on the heart which no longer has to have the size or capacity to pump to body and lungs. This, in turn, may alter the geometry of the heart and heart valves in such a way as to reduce leakage from the valves within the heart. Even if there is no effect on the heart valves, there is a dramatic reduction in the energy requirements of the heart (and the patient), so that calories and nutrition can be diverted to growth instead of for fueling an overworked heart. In addition to benefits for the heart, the SCPC provides an important benefit to the lung arteries. Before the SCPC, blood is powered through the lung arteries under relatively high pressure. In some cases, the lung arteries may respond to this pressure by thickening or becoming more muscular. Unfortunately, muscular lung arteries are very unfavorable for Fontan physiology, and several of the early bad experiences with Dr. Fontan’s operation occurred in children whose lung arteries were simply too thick to permit the passive flow of enough blood to the lungs. When the SCPC is performed, the pressure driving blood through the lungs is very, very low and any prior tendency of lung artery muscularization and thickening is reversed. This process likely takes several weeks or even months, which is much better tolerated in SCPC patients where only half of the venous blood in the body must traverse the lung arteries, than in the original Fontan patients in whom all the venous blood was expected to traverse the lung arteries. If the SCPC is beneficial for the heart and the lungs in children with single ventricle hearts, it might be asked why the operation is not done immediately at birth rather than at several months of age. The reason is that the newborn baby has extremely muscular lung arteries, more muscular even than in a child whose lung blood supply is provided by a shunt. This is a reflection of the fact that before birth the body prevents blood from going to the lungs (where, after all, there is no air) by having very muscular lung arteries which constrict very tightly, preventing lung blood flow. With a baby’s first breath, the process of lung artery relaxation begins immediately, followed over the next several weeks and months by near complete regression of most of the muscle in the lung arteries, effectively preventing the constriction which was so helpful before birth. The pace of this relaxation and muscle regression is somewhat unpredictable in an individual child, but in virtually all children is complete by three months of age. Recognition of this time course has led to relatively early performance of SCPC in children, particularly if their hearts and lungs are perceived to be particularly distressed.
A few comments about the operation itself are of particular interest to patients and their families. Perhaps most important is that the operation is generally a very low-risk proposition, especially when compared with operations performed in the newborn time period. In part, this is because the operation is quite simple compared to most neonatal operations, and simplicity usually translates to safety in heart surgery. In part, SCPC is safe because it provides a tremendous net benefit to the heart and lungs. Another reason for the low risk associated with SCPC is that it is performed in children who are several months old, whose bodies are generally much more tolerant of the heart lung machine than are newborns. This age effect is exemplified by the observation that the lungs of especially young SCPC patients seem to work less well for the first few days after surgery than their older counterparts. Although this effect is transient, it may result in quite low oxygen levels for the first 48 hours after surgery in the youngest babies having the operation. A final comment about the SCPC is that it is an operation of many names. These include but are not limited to the SCPC, the bidirectional Glenn shunt, the hemi-Fontan, the caval, Stage II and a host of others. By whatever name, the SCPC is always among the favorite operations for any pediatric heart surgeon because it is safe and results in a happier heart (and patient). SCPC
Cardiac Transplantation at Arkansas Children's Hospital
Elizabeth A. Frazier, M.D.; Medical Director, Cardiac Transplantation Program, Arkansas Children's Hospital; Associate professor, Department of Pediatrics, University of Arkansas for Medical Sciences College of Medicine Abstract History of Pediatric Heart Transplant
in the United States Over the next 20 years surgeons at a small number of centers, most notably Stanford University, persevered with heart transplantations in adults. In 1976, Jean Borel discovered cyclosporine, a potent immunosuppressant drug derived from soil fungus (2). This was an important landmark in the history of cardiac transplant and has lead to significantly increased survival. In 1984, the world’s first successful pediatric transplant was performed on a 4-year-old boy at Columbia-Presbyterian Medical Center in New York City (3). “Baby Fae” was a name known around the world, as the 12-day-old child who received a baboon heart for treatment of hypoplastic left heart syndrome in an operation performed in 1984 by Dr. Leonard Bailey at Loma Linda University (1). Although the patient survived only 20 days, this xenotransplantation led the way for cardiac transplant in neonates with lethal congenital heart disease (1). History of Cardiac Program at Arkansas Children’s
Hospital Determining Who is a Heart Transplant Candidate In the early days of transplant strict criterion about anatomic variations, pulmonary vascular resistance or presence of other co-morbidities often prevented inclusion on the transplant list. Over time, there has been a broadening of acceptance criteria including patients with single lung (5), situs inversus and renal insufficiency among other complicating factors resulting in increased numbers of patients on the waiting list.
Patient Characteristics
At the time of their transplants, 73 percent of the patients were listed as Status 1. Status 1,including status 1A and 1B, indicated that the patient was hospitalized in the cardiovascular intensive care unit and required intravenous inotropes, mechanical ventilation and, in some cases, mechanical support such as extracorporeal membrane oxygenation (ECMO). Twenty-seven percent of the patients were Status 2; that is, they were waiting for a donor heart but did not require additional hospital supportive measures prior to surgery (Figure 3).
Bridge to Transplant Because of the size constraints of small children, the engineering to create adequate support pumps has lagged behind that for adults. Thus, ECMO has been the best, and until recently, the only way to support a child with cardiorespiratory failure. When a patient becomes unstable despite maximal medical support, ECMO can be utilized to allow additional waiting time until the donor organ becomes available. ECMO has been used to “bridge” 60 patients at ACH. Twenty-nine of these patients received a transplant after being supported for 35 hours to 1,078 hours. Five additional patients recovered, either from acute myocarditis(3) or postcardiotomy myocardial dysfunction (2). The majority of patients who died on ECMO suffered multisystem organ failure despite the mechanical support or neurologic injury secondary to bleeding or embolism related to anti-coagulation or clot. Eight patients from hospitals in Texas, Louisiana, Kansas, Tennessee, Mississippi and Connecticut were transported to ACH via mobile ECMO for the specific indication of bridging to transplant. In 2004, ACH began participating in a multi-institutional protocol for the Debakey Micromed VAD® Child. This is a ventricular assist with an implantable pump designed for children aged 5 years to 16 years with body surface area between 0.7-1.2 m2. It provides nonpulsatile flow and operates from a battery pack. This device was first used at ACH in October 2004 to bridge a 14-year-old boy for 56 days to a successful transplant. This was an historic occasion for the ACH Cardiac Transplant Program, making it the first center in the United States to use this device successfully in a pediatric patient. Post-transplant Care
Once a donor heart is available, the operation in a patient with cardiomyopathy is usually straightforward with use of a biatrial or bicaval anastomosis. Patients transplanted with complex congenital heart disease often require a prolonged, difficult operation to restructure various anomalies that may be present. Pediatric patients, in general, have higher 30-day mortality that increases inversely with age and pre-transplant diagnosis. Primary graft failure and acute nonspecific graft failure is responsible for approximately 50 percent of the early deaths and may reflect donor quality or preservation, an area of important research. A triple drug, immunosuppressive protocol comprised of cyclosporine or tacrolimus, corticosteroids and mycophenolate mofetil, is typically used. In high-risk patients with renal insufficiency or on ECMO, a “renal-sparing” protocol may be used with induction therapy utilizing a polyclonal antibody preparation. This allows a delay in the administration of the calcineurin drugs for the first five days or so post-transplant to allow better recovery of renal function after cardiopulmonary bypass. Antithymocyte globulin is commonly used as an induction agent. There is a delicate balance between providing adequate immunosuppression to prevent rejection and avoiding predisposition to opportunistic infections. Acute rejection and primary graft failure are the most common causes of death in the first three years after transplant. By five years post-transplant, coronary artery vasculopathy is followed by graft failure, acute rejection and lymphoma as the leading causes of death (4). Patient Outcomes
The oldest surviving transplant patient at ACH is now 16 years old and was transplanted on the day of her second birthday. Arkansas Children’s Hospital participates in a multi-institutional study group, the Pediatric Transplant Study Group (PHTS) that studies patients under 18 years old who undergo transplantation. Because patient numbers are so limited at each center, having enough statistical power to analyze data from a single-center experience is difficult. The PHTS began in 1993 and is comprised of 22 institutions, all of which submit their patient data and combine efforts to study a larger patient
population. In the most recent PHTS analysis of 90 ACH pediatric
patients from 1993 to 2003, the one-year survival rate
is 83 percent, the 3-year survival rate is 75 percent,
the 5-year survival rate is 72 percent, and 10-year survival
rate is 51 percent (Figure 4). This is comparable
to survival in the International Society for Heart and
Lung Transplantation registry. Unfortunately, in both
adult and pediatric patients, survival continues to decline
at a linear rate even well beyond 15 years post-transplant
(4, 6). The Future of the Cardiac Program at Arkansas Children’s Hospital
For many patients with congenital and acquired heart disease, cardiac transplant is the only hope for long-term survival. These patients remain challenging with their complex anatomy and previous surgical palliations. The delicate balance of immunosuppressive medications to prevent rejection but not leave a patient susceptible for infection and malignancy continues to be problematic. As patients survive longer, chronic renal failure and coronary vasculopathy occur over time and have serious implications on quality of life. The ACH Cardiac Transplant Program looks to the future to develop strategies to improve survival in this group of patients. As the art and science of medicine continues to evolve, the ACH Cardiac Transplant Program hopes to develop newer and better strategies to improve survival and quality of life in this patient population.
Sadia Malik, M.B.B.S., M.P.H.; Arkansas Children's Hospital; Assistant Professor of Pediatrics, Section of Pediatric Cardiology, University of Arkansas for Medical Sciences What is Marfan syndrome? How is it diagnosed? How common is this condition? What treatments do you prescribe for someone
diagnosed with Marfan? What do you tell Marfan patients about modifying
their lifestyles?
Ritu
Sachdeva, M.D.; Cardiology, Arkansas Children's Hospital; Assistant
Professor, Department of Pediatrics, Division of Pediatric Cardiology, University
of Arkansas for Medical Sciences The segmental variation in tissue velocities derived by TDI has been attributed to changes in cardiac translation that accompany myocardial contraction and relaxation. TDI can be performed in two forms: pulsed-wave or color modes. Pulsed-wave TDI allows for recording of a high-quality Doppler profile of the motion of cardiac structures. It measures peak myocardial velocities and is particularly useful for measuring long-axis ventricular motion. Because the apex of the heart remains relatively stationary throughout the cardiac cycle, mitral annular motion is considered a good marker for overall longitudinal left ventricular contraction (systole) and relaxation (diastole). Color TDI uses a color-coded representation of myocardial velocities superimposed on routine 2-dimensional or M-mode images to indicate the direction and velocity of myocardial motion. Color TDI mode is superior to pulsed-wave TDI due to its ability to evaluate multiple structures and segments in a single view and increased spatial resolution. However, its application in the pediatric population has not been as widespread.
Earlier studies evaluating the clinical applications of TDI involved the adult population. However, now there are references available for normal healthy infants and children (1, 2). It has been shown that cardiac growth affects the TDI velocities primarily in the first year of life. Clinical Applications of TDI: Click here for references
Janet Bryant; Heart Transplant Coordinator, Arkansas Children's Hospital Heart Center What is your role at ACH and how long have you worked here? How is your job rewarding?
How did you become interested in pediatric cardiology or cardiovascular
surgery? What do you want people to know about the Heart Center at Arkansas
Children's Hospital?
What do you enjoy most about working with children? What has been your most memorable moment working in the Heart Center
at Arkansas Children’s Hospital? What is your greatest professional achievement?
Kathy Ainley, R.N.; Heart Transplant Coordinator, Pediatric Cardiology, Arkansas Children's Hospital What is your role at ACH, and how long have you worked here? Why is your job rewarding? How did you become interested in pediatric cardiology or cardiovascular
surgery? What do you want people to know about the Heart Center at Arkansas
Children’s Hospital?
What has been your most memorable moment working in the Heart Center
at Arkansas Children’s Hospital?
I have so many since I have been here so long. My 6-year-old patient seeing Jesus and telling her parents she wanted to go with him. My other patient, at his first Thanksgiving meal after transplant, was eating so much his grandfather asked him if he had enough. He said, “I’m still breathing aren’t I?” Although this isn’t about the work, most of the cardiologists and nurses came to Paragould for my mother’s funeral and the others covered for them. Several nurses and doctors arrived at my mother’s house within an hour or two to stay with me until my brothers could get to me. That is the kind of people I work with. What is your greatest professional achievement?
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