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Congenital Heart Defects, Fetal Circulation, and Extrauterine Transition Developed by Lisa Fikac, MSN, RNC-NIC Original Author Stacey Cashwell, MSN, RN Expiration Date - 2/27/17 This continuing education activity is provided by Cape Fear Valley Health System, Training and Development Department, which is an approved provider of Continuing Nursing Education by the North Carolina Nurses Association, an accredited approver by the American Nurses Credentialing Center’s Commission on Accreditation. 0.8 Contact hours will be awarded upon completion of the following criteria: • • • Completion of the entire activity Submission of a completed evaluation form Completion a post-test with a grade of at least 85%. The planning committee members and content experts have declared no financial relationships which would influence the planning of this activity. Microsoft Office Clip Art is the source for all graphics unless otherwise noted. These graphics used with permission. • • • • Discuss risk factors associated with congenital heart defects (CHD). Identify milestones in cardiac development. Describe fetal circulation. Discuss changes that occur during extrauterine transition. Many times when parents are told that their baby has a heart defect, they immediately assume the worst whether the defect is simple or complex. • • They do not always hear or completely comprehend all the information that the medical team has given to them. It is the nurse's role to reinforce the information communicated by the medical team. o In order to do that, the nurse needs to have a basic understanding of Cardiac development Fetal circulation Transition to extrauterine circulation after birth Most of the time, the exact cause of congenital heart disease (CHD) is unknown. • • Many people assume that CHD is associated with a genetic defect. However, about 8% of CHDs can be attributed to chromosomal abnormalities. About 85-90% of CHD cases are found to be due to many factors. CHD tends to occur most frequently in males. • • The ratio of male occurrence to female occurrence is 3-4:1. However, atrial septal defects (ASDs) and patent ductus arteriosus (PDAs) tend to occur more frequently in females. CHD occurs in • 1-3% of all live births • 20-25% of preterm infants • 85% of preterm infants with a birthweight of < 800 grams are due to the high incidence of patent ductus arteriosus (PDA) in this group The risk of CHD increases by 1-3% if the mother has a • • History of CHD Previous child or children with CHD CHD is associated with several genetic syndromes, which include • • • • • Trisomy 13 (Patau Syndrome) o Infants with this syndrome frequently have Ventricular septal defects (VSDs) PDA Trisomy 18 (Edward's Syndrome) o Infants with this syndrome frequently have VSDs PDA Trisomy 21 (Down Syndrome) o Infants with this syndrome frequently have ASDs Atrioventricular (AV) canal VSDs PDA Turner's Syndrome (gonadal dysgenesis) o Infants with this syndrome frequently have Coarctation of the aorta Aortic stenosis Chromosomal deletions o Deletions usually involve chromosomes numbers 4, 5, 13, or 18. o There are a wide variety of defects which may range in severity from simple to complex. CHD is also often seen in infants with VACTERL association. • VACTERL is an acronym for a constellation of congenital, multi-system defects. The acronym stands for • • • • • • Vertebral defects, such as neural tube defects. Anorectal defects, such as anal atresia with or without a fistula. Cardiac defects, such as o VSD o Dextrocardia o Valve defects. Tracheo-Esophageal fistula which often has an associated esophageal atresia. Renal defects, such as o Polycystic kidney disease o Hydronephrosis o Agenesis of one kidney o The presence of only one umbilical artery instead of two may indicate renal defects. Limb defects, such as o Thumb deformities o Hypoplasia of the digits o Syndactyly o Polydactyly About 2% of CHDs can be attributed to environmental factors. Maternal alcohol use is associated with • • • • • VSDs, with or without subpulmonic and subaortic stenosis Coarctation of the aorta Aortic regurgitation Atrial septal defects (ASDs) Tetralogy of Fallot CHD is associated with exposure to several different medications - • • • • Thalidomide - various defects Anticonvulsants o VSD o PDA o Coarctation of the aorta o Ventricular hypertrophy Antineoplastics - dextrocardia Lithium o Ebstein's anomaly o ASD o Tricuspid atresia Exposure to toxins can cause a variety of defects with the severity ranging from simple to complex. Some of toxins include • • • Asbestos Paint Chemicals in textiles Several maternal health problems are linked to CHD. Maternal illnesses that are related to CHD include • • • • Diabetes mellitus o Infants of diabetic mothers frequently have VSDs PDA Coarctation of the aorta Transposition of the great vessels Maternal infections, either bacterial or viral. o Infants who have been exposed to maternal infection frequently have PDA Pulmonary stenosis Previous family history of CHD, particularly in the mother or a sibling. Loss of perfusion and/or oxygenation to the mother or placenta can result in a cardiac defect. o The type of cardiac defect directly depends on the point during development at which the insult occurs. o Illnesses that can impair perfusion or oxygenation include lupus and chronic respiratory problems. Heart development is identifiable at 18-19 days post-conception. • • • At this point, the heart is a single tube with an ebb and flow type of circulation. The heart beat is uncoordinated. Abnormal development during this time in gestation includes transposition of the great vessels and dextrocardia. At 3-4 weeks post-conceptional age, the single cardiac tube expands and begins to coil to the right with the bottom portion moving to the top and the top portion moving to the bottom. • • • Primitive atria and ventricles are first identified. A single great arterial vessel (truncus arteriosus) extends from the ventricle until the fourth week of life. Although there is a coordinated heart beat with a rate of 60-70 bpm, it is not sufficient to sustain life. At 5-6 weeks post-conceptional age, cardiac septation begins and is completed during this time. • • • All 4 chambers are clearly identifiable. The primitive atrioventricular (AV) valves appear. These are o Tricuspid valve - located between the right atrium and right ventricle o Mitral valve - located between the left atrium and left ventricle There is still only one great vessel, the truncus arteriosus. At 9-11 weeks post-conceptional age, the great vessel starts its rotation and septation into two vessels, known as • Pulmonary artery • Aorta All of the valves are developed and in place • • • Tricuspid - right side Mitral - left side Semi-lunar - valves to the pulmonary artery and aorta At 10-12 weeks post-conceptional age, rotation and septation of the great vessel is complete. • The heart, which was initially located in the midline of the chest, completes its migration to the LEFT side of the chest. Click here to view 3-D view of fetal cardiac development All organ development values are + 1-2 weeks • Teratogenic events can occur at any time during organ development. o The particular defect is directly related to the specific developmental sequence occurring at the time of the insult. e.g.: maternal hypoxia at the time of AV development might result in tricuspid atresia. From Fetal circulation. (2014). In UpToDate 21.12-C22.20. Retrieved January 31, 2014. In utero, the majority of the fetal blood volume bypasses pulmonary circulation. • It does this by leaving the right side of the heart and using 2 of 3 fetal shunts. Although the fetus does make respiratory-like movements, the placenta is the organ that • • • Delivers nutrients for growth and development Facilitates effective oxygen and carbon dioxide exchange Meets all organ and tissue needs There are three fetal shunts that allow fetal circulation to bypass the lungs and use the placenta as the fetal organ of oxygenation and nutrition. • • • Foramen ovale Ductus arteriosus Ductus venosus The foramen ovale is the opening in the septum between the right and left atria. • • This allows the blood to bypass the lungs. Approximately 50% of the blood volume passes through this shunt. The ductus arteriosus is the passage located between the pulmonary artery (PA) and aorta. • • • • In utero, blood leaves the PA and enters the aorta. o This is what is referred to as a RIGHT-to-LEFT shunt. Like the foramen ovale, the ductus arteriosus allows blood to by-pass the lungs. Approximately 30% of blood volume passes through this shunt. If the ductus arteriosus remains open, it becomes known as the patent ductus arteriosus (PDA). The ductus venosus is the opening located on the underside of the liver in the portal system. • This allows the umbilical vessels access to and from the placenta. For some people, a picture is worth a thousand words, and everything is clear for them. For others, those thousand words are needed.....another way of viewing fetal circulation. Blood enters the inferior vena cava, joining with the blood returning from the upper body and head via the superior vena cava, and then enters the right atrium Part of the blood in the right atrium passes through the foramen ovale to the left atrium The remainder of the blood in the right atrium crosses over the tricuspid valve and enters the right ventricle The right ventricle ejects the blood into the main pulmonary artery, across the semi-lunar pulmonic valve The main pulmonary artery carries blood to the lungs, BUT • • • The lungs are fluid filled and there is significantly lowered pulmonary oxygen levels. This results in vasoconstriction of the pulmonary arterial bed and increased pulmonary vascular resistance (PVR)l Blood looks for the path of least resistance instead of pumping against such a high PVR It finds the ductus arteriosus (DA) A large volume of blood passes through the DA into the aorta The remainder of the blood continues along the PA to the pulmonary circulation Blood nourishes the pulmonary arterial bed to foster its health and growth Blood returns to the heart via the four pulmonary veins..... Blood enters the left atrium where it mixes with the blood that previously passed through the foramen ovale Blood crosses over the mitral valve and enters the left ventricle For the second time, blood exits the heart The left ventricle ejects the blood into the aorta, across the semi-lunar aortic valve At the aortic arch, the blood mixes with blood coming across the DA The total blood volume of the fetus is together again The blood proceeds down the descending aorta, ultimately entering the systemic circulation Following circulation systemically, the blood makes its way to the placenta via the umbilical vessels and the ductus venosus • Systemic vascular resistance (SVR) is decreased, allowing ready access to and from the placenta, a large lobular organ with very little vascular resistance After giving up waste products and picking up nutrients and oxygen from the placenta, the blood starts the trip again This process works well for the fetus while in utero, even when pulmonary and/or cardiac defects are present. In utero, the placenta is the organ of oxygenation, not the lungs. When birth occurs, three major events must take place in order for the neonate to make the transition from placenta-based oxygenation to pulmonary-based oxygenation......to survive. 1. Pulmonary vascular resistance (PVR) must decrease. 2. Systemic vascular resistance (SVR) must increase. 3. The fetal shunts must close. AT BIRTH... When the neonate is delivered, the chest mechanically expands, and the infant takes his first breath. • • Oxygen rushes in, and the alveoli expand. EFFECTIVE respirations are established. When gas exchange begins, the pulmonary arterial bed dilates, and PVR decreases. • This process increases pulmonary blood flow. Once the umbilical cord is clamped, SVR increases, and cardiac return from the body increases. • Cardiac output to the lungs and body also increases. When all of these events take place - Normal, adult, pulmonary-based circulation is established, and fetal shunts close. The heart begins the transition from a fetal right-sided heart dominance to an adult leftsided heart dominance. After extrauterine transition, blood flows in the customary adult, pulmonary-based circulatory pattern. The inferior vena cava (IVC) and superior vena cava (SVC) return blood to the Right atrium and then, ejects over the Tricuspid valve to the Right ventricle and then, ejects over the Pulmonary semi-lunar valve to the Main pulmonary artery to the Right and left pulmonary arteries that carry blood to the Lungs where gas exchange occurs, then Blood returns via the four pulmonary veins to the Left atrium and ejects over the Mitral valve to the Left ventricle and ejects over the Aortic semi-lunar valve to the Aorta where blood is carried to the System circulation The transition from placenta-based oxygenation to pulmonarybased oxygenation is complete! American Psychological Association. (2010). Publication Manual of the American Psychological Association, Sixth Edition. Washington, DC: Author. Askin, D.F. (2009). Fetal-to-neonatal transition – what is normal and what is not? Part I: the physiology of transition. Neonatal Network, 28(3), e33-e36. Askin, D.F. (2009). Fetal-to-neonatal transition – what is normal and what is not? Part I: redflags. Neonatal Network, 28(3), e37-e40. Federspiel, M.C. (2010). Cardiac assessment in the neonatal population. Neonatal Network, 29(3), 135-142. Fernandes, C.J., Weisman, L.E., & Kim, M.S. (2014). Physiologic transition from intrauterine to extrauterine life. In UpToDate Online 21.12-C22.20. http://www.uptodate.com/contents/physiologic-transition-from-intrauterine-toextrauterinelife?source=search_result&search=fetal+circulation&selectedTitle=1%7E79 (Retrieved January 31, 2014). Gardner, S.L., Carter, B.S., Enzman-Hines, M., & Hernandez, J.A. (2011). Merenstein & Gardner's Handbook of Neonatal Intensive Care, 7th Edition. St. Louis: Mosby-Elsevier. Verklan, M.T. & Walden, M. (Eds.) (2010). Core Curriculum for Neonatal Intensive Care Nursing, 4th Edition. St. Louis: Saunders-Elsevier. Yeung, F. (2007). Heart embryology. In Cardiac Embryology. Retrieved January 31, 2014, from http://pie.med.utoronto.ca/HTBG/index.htm The authors would like to thank Creative Memories™ for their kind permission for our use of their graphics in Mother-Baby University learning activities.