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The Right Ventricular Outflow Tract in Tetralogy of Fallot
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 One of the most common serious congenital heart conditions
is tetralogy
of Fallot, named for the French physician, Etienne
Fallot, who provided one of the earliest descriptions of
its features in 1888. There are four cardinal features of
the malformation (as indicated by the word tetralogy which
derives from the Greek word tetra – meaning four) including: It is the two latter features, the ventricular septal defect and the obstruction of right ventricular outflow, which together result in reduced blood flow to the lungs with resultant transfer of oxygen-poor (blue) blood to the body. The net result is the characteristic blue skin coloration seen in tetralogy patients (hence the descriptive name “blue babies” to describe children with tetralogy). The surgical treatment of tetralogy is therefore undertaken with two goals: to close the ventricular septal defect, which is fairly straightforward, and to relieve the right ventricular outflow tract obstruction, which is less straightforward and is the subject of this article. Components of the RVOT
In order to understand the treatment of right ventricular outflow tract (RVOT) obstruction, it is first necessary to be familiar with the components of the RVOT, of which there are three. As blood exits a normal right ventricle, it passes first through a relatively short muscular tube known as the infundibulum. Next, blood passes through the pulmonary valve that is itself a tubular structure with three leaflets or curtains that float together as the heart relaxes and serve to prevent blood from flowing backwards into the right ventricle. The third and last component of the RVOT is the main lung artery which conveniently is thought of as a tube, and which splits into a right and left lung artery a short distance above the pulmonary valve. Obstruction of the RVOT in patients with tetralogy may occur at one, two or all three of the component parts of the pathway of blood, and must be addressed wherever it occurs.
At the level of the infundibulum, a cross-section of the blood pathway would look much like a doughnut, with the substance of the doughnut being composed of ventricular muscle and the blood flowing through the center. If there is obstruction in the infundibulum, it may be relieved by the removal of some of the muscle in the wall of the doughnut (Figure 1), in effect enlarging the center of the doughnut. This approach is limited by the outer diameter of the doughnut: if the outer diameter is too small, removing all of the muscle will still leave obstruction. In such cases the treatment is to cut the doughnut and place an enlarging patch on the outer wall, resulting in an enlarged blood pathway and relief of the obstruction (Figure 2).
At the level of the pulmonary artery, the issue is even simpler than in the infundibulum. The wall of the artery has minimal thickness, so there is no doughnut wall to be removed. All enlargement of the pulmonary artery is therefore accomplished by means of the patch technique (Figure 3).
The most complex of the three levels of the RVOT is the pulmonary valve, because obstruction at the valve level may take several forms. In order to understand the function of the valve, it may be helpful to think of the pulmonary valve as being made up of three curtains (leaflets) suspended from a circular curtain rod. In some cases, the leaflets (curtains) of the valve may be fused together, causing obstruction by failing to separate as blood is transiting the valve. In this case, splitting the leaflets apart with a scalpel (or even bluntly with an instrument known as a dilator) may relieve the obstruction (Figure 4). In other cases, however, the valve obstruction may be a result of an abnormally small diameter of the valve and the valve diameter may have to be enlarged with a patch, as shown in Figure 5, in the same way that the pulmonary artery and some times the infundibulum is enlarged. In those circumstances in which a patch is necessary to enlarge the valve diameter, most of the time the artery and the infundibulum are small as well, so that a single patch may be used to enlarge all three levels of the RVOT. Such a patch is frequently termed a “trans-annular patch”, reflecting the fact that the approximately circular “curtain rod” in the pulmonary valve is known as an annulus. More on the trans-annular patch
The recognition of the early and late deleterious effects of trans-annular patches and leaking pulmonary valves is relatively recent. Nonetheless, a variety of innovations has resulted. As a fundamental principle, most surgeons have adopted a strategy of attempting to avoid enlarging the annulus of the pulmonary valve, even at the risk of leaving a mild degree of obstruction (this is in contrast to the historical approach of complete obstruction removal). Unfortunately, this approach is not applicable to children with extremely undersized pulmonary valves for whom a transannular patch is unavoidable. An approach that has been taken in these children is to attempt to cover the patch with an artificial curtain, which is often termed a monocusp, as illustrated in Figure 5. The initial experience with this technique was disappointing, in part because the techniques for construction of the monocusp were not well-worked out and in part because the materials used for the monocusp were not very durable. More recently, there has been much more encouraging experience as a result of better surgical design and construction, and as a result of more durable materials being employed. The RVOT continues to be the area of greatest interest and focus in children with tetralogy of Fallot, as our understanding of the early and late consequences of techniques to enlarge this area evolves. The simple concept of enlarging a narrowed area has, like most apparently simple problems in pediatric cardiovascular medicine, proved to be much more complex than initially thought. Nonetheless, the combination of better surgical techniques, better materials for reconstruction, better imaging techniques to study the problem with, and even the very real prospect of being able to “grow” a new pulmonary valve from a patient’s own tissue has led to the certainty that the results of today will be better than the results of yesterday, and that the results of tomorrow will be better still.
ARORA and Life in the Heart Center
William Fiser, M.D.; Research Director, Pediatric and Congenital Cardiothoracic Surgery, Arkansas Children’s Hospital; Assistant Professor of Surgery, University of Arkansas for Medical Sciences College of Medicine. ARORA, the Arkansas Regional Organ Recovery Agency,
serves all three transplant centers in Little Rock
and hospitals throughout the majority of the state
for organ and tissue donor services. I serve as the
medical director of ARORA, a faculty member for the
University of Arkansas for Medical Sciences College
of Medicine, as well as a medical staff member at ACH.
ARORA is an independent non-profit agency which is
certified by CMS, UNOS and the FDA. ARORA’s mission
is to make every effort to provide organs and tissues
for life-saving and life-enhancing transplantation.
This is accomplished through continuous hospital involvement,
which includes hospital training, and through community
involvement by providing public education. The staff
will strive to be ethical and professional, thus providing
care, dignity, honor and respect to all families, donors
and recipients.
In-house coordinator’s
role The most important message you can take away from this brief article is the importance of organ and tissue donation. Think about it. Talk about it with your family. Express your feelings about it. Save a life!
Feeding Difficulties and the Infant with Single Ventricle Physiology
Ashley Harry, A.P.N.; Heart
Center, Arkansas Children’s Hospital. Feeding intolerance can be a significant source of morbidity after a Norwood procedure. Feeding difficulties can prolong hospital stay and have been implicated in interstage death between hospital discharge and second-stage palliation. Establishing adequate oral intake is generally the last clinical hurdle to overcome prior to hospital discharge and is a major determinant of hospital length of stay. Systematic evaluation of swallowing function allows appropriate tailoring of feeding regimens or leads to possible placement of gastrostomy tubes.
After surgery … An occupational therapist is instrumental in the assessment
of evaluating a patient’s motor skills and readiness
to attempt oral feeding. Oral stimulation is initially
performed, and when appropriate, the therapist attempts
to feed by mouth. Assessments are made of the patient’s
ability to coordinate sucking and swallowing, stamina,
signs and symptoms of gastroesophegeal reflux and signs
and symptoms of aspiration. If a patient is unable
to demonstrate feeding tolerance, an upper GI as well
as a swallow study may be conducted. Finding a feeding strategy
If a patient has abnormal gastrointestinal anatomy, vocal cord dysfunction, aspiration on swallow study, gastroesophogeal reflux or is at greater risk for developing aspiration related to marginal cardiopulmonary status, a nissen fundiplication with gastrostomy tube is advised. A nissen fundiplication is a procedure that wraps the stomach around the esophagus. This tightens the valve between the stomach and esophagus and prevents reflux of gastric contents into the esophagus. Gastrostomy tubes are placed directly into the stomach and provide a safe route to administer nutrition. Gastrostomy tubes may be temporary or permanent. Feeding patients with hypoplastic left heart syndrome or other single ventricle physiology can be challenging. The best outcome for managing feeding difficulties requires a multidisciplinary approach. The goal of feeding patients with single ventricles is to provide the safest route to administer nutrition. When the goal is obtained, appropriate weight gain is achieved, thus better preparing these tenuous patients for their second-stage palliation.
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 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?
Spotlight on Tracey Marek, Radiologic Technician
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 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?
New Nursing Director Named for CVICU
The Cardiovascular Intensive Care Unit (CVICU) at
ACH is under new nursing leadership with the recent
appointment of Trenda Ray, M.N.Sc., A.P.N., as
its nursing director. Ray has been a member of the
ACH Team since 1997. Her career path has progressed
from providing direct patient care as a nurse in
NICU to an Advanced Practice Nurse (APN) role in
the CVICU, where she provided clinical management
and treatment for critically ill post-operative heart
patients.
New Staff for the Heart Center
Nischal K. Gautam, M.D. Himesh Vyas, M.D.
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