Objectives Part 1. Objectives Part 2. Fetal Circulation Transition to Postnatal Circulation Normal Cardiac Anatomy Ductal Dependence and use of PGE1

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1 Cardiac Physiology Gia Marzano, AC PNP Pediatric Cardiac Surgery Rush Center for Congenital Heart Disease Rush University Medical Center Objectives Part 1 Fetal Circulation Transition to Postnatal Circulation Normal Cardiac Anatomy Ductal Dependence and use of PGE1 Objectives Part 2 Basic principles of cardiac physiology Basic categories of congenital heart disease based on pathophysiology Application of physiology to your bedside management 1

2 Fetal Circulation Few Concepts Fetal heart starts developing during the 3 rd week of life By the 3 rd month of development, all major blood vessels are present and functioning. Pulmonary Blood Flow is Low Gas Exchange (Oxygen) occurs in placenta More Concepts Pulmonary Resistance is High Lungs are still underdeveloped Small pulmonary arteries have a thicker smooth muscle layer than similar arteries in adults. Fetal Circulation Overview Umbilical Circulation: Pair of umbilical arteries carry deoxygenated blood & wastes to placenta. Umbilical vein carries oxygenated blood and nutrients from the placenta. Placenta facilitates gas and nutrient exchange between maternal and fetal blood. 2

3 Fetal Circulation Overview Oxygenated blood from placenta is transported to the fetus through the Umbilical Vein Fetal Circulation Overview Most of the oxygenated blood bypasses the liver through the Ductus Venosus and mixes with De-Ox Blood from IVC Fetal Circulation Overview Blood travels from the IVC and enters the RA 3

4 Fetal Circulation Overview 40 % of oxygenated blood from the IVC bypasses the RV and is shunted to the LA via the Foramen Ovale The rest mixes with De-ox blood from the SVC and enters the RV Fetal Circulation Overview Blood then travels to the LV and is distributed through the aorta mainly to the coronaries and upper body (carotid and subclavian arteries) Only 1/3 of this volume goes to the lower body Fetal Circulation Overview Most blood from the IVC (60%) mixes with SVC blood and enters the RV from the RA Because the lungs are non-functional, most (90%) will be shunted away from the pulmonary arteries through the Ductus Arteriosus to the Descending Aorta and Placenta for oxygenation 4

5 Fetal Circulation Overview Blood circulates to the body and returns to the placenta via the umbilical arteries Fetal Circulation Overview Placenta reoxygenates blood returning from the umbilical arteries New fetal cardiac cycle Fetal Circulation Overview Parallel circulation with shunts (PFO and PDA) allows various lesions to provide adequate transport of blood to placenta for oxygenation and deliver it to the tissues RV performs ~ 2/3 cardiac work RV larger and thicker at birth 5

6 Transitional and Post-Natal Circulation What happens at birth?? The change from fetal to postnatal circulation happens very quickly. 2 major events: Changes initiated by baby s first breath. Elimination of the placenta Transitional Circulation Clamping of the umbilical cord: Eliminates the low resistance placental circulation peripheral vascular resistance increases decreases blood volume returning to the heart from IVC Transitional Circulation With initiation of pulmonary ventilation: Increased alveolar O2 pressure vasodilates the pulmonary arteries Pulmonary vascular resistance decreases significantly 6

7 Transitional Circulation Increase in systemic Vascular resistance + Drop in pulmonary Vascular resistance Pulm Blood flow increases 8-10 X Transitional Circulation Increased pulmonary blood flow increased pulmonary venous return into LA LAP >RAP the greater LAP (and lower IVC flow) closes the valve of the foramen ovale, preventing right-to-left shunting. Transitional Circulation PDA: changes from R2L conduit of blood to the descending aorta to a L2R conduit of blood to the lungs Ductus arteriosus constricts and closes functionally within several hours after birth, largely in response to the increase in oxygen tension. 7

8 Transitional Circulation PFO closure Ductus arteriosus closure These events result in the effective separation of the systemic and pulmonary circulations after birth. Ductal Dependence The Ductus Arteriosus In fetus: large channel that allows blood to bypass the lung circulation to the Dao and placenta for oxygenation as big as the Dao! (10mm) allows equalization of Ao and pulm arterial P The Ductus Arteriosus Role of O2 Thick muscular layer Towards late gestation, the muscle layer thickens and the lumen becomes smaller After birth, increased arterial O2 causes more constriction of the ductus Constriction decreases PO2 in the muscle severe hypoxia cell destruction and fibrosis Functional closure within hrs after birth Complete closure within 5-7 days, can be up to 21 days 8

9 Ductus Arteriosus Role of Prostaglandins Produced by the wall of the ductus and placenta 2 types: PGI2 and PGE2 Relax the ductus arteriosus smooth muscle Metabolized in the lungs After birth, PG ductal closure Ductus Arteriosus in Congenital Heart Disease In many CHD cases (mainly cyanotic), ductus does not close normally after birth: TA/PA/TGA: arterial O2 remains low after birth lower stimulus for constriction Left-sided lesisons (Ao atreasia, coarctation): arterial O2 increases after birth but the high PAP/flow keeps ductus patent Ductus Arteriosus in Congenital Heart Disease Ductal Dependency Normally, ductus carries ~ 60 % of combined C.O from the PA to the DAo If LV outflow tract is obstructed (e.g. aortic valve atresia, coarctation, interruption): larger portion of combined C.O crosses the ductus (~90%) larger Ductus 9

10 Ductus Arteriosus in Lt sided lesions Ductal Dependency After birth: need the ductus to provide most of systemic blood flow (from PA to Ao) Ductus Arteriosus in Congenital Heart Disease If RV outflow is narrow (e.g. pulmonary atresia, tricuspid atresia) minimal blood from RV to ductus small ductus Ductus Arteriosus in Rt sided lesions Ductal Dependency After Birth: Need the ductus to maintain pulmonary blood flow 10

11 Prostaglandin Therapy Indomethacin: inhibits PG production PGE1: relaxes the ductus arteriosus smooth muscle cells. Effective within the first 7-10 days after birth Dose: mcg/kg/min IV/PO Prostaglandin Therapy Side Effects Apnea Fever Flushing Hypotension Thrombocytopenia Seizure Pyloric gastric outlet obstruction Questions? 11

12 Part 2 Basic principles of cardiac physiology including Flow and pressure relationships Oxygen delivery Determinants of blood pressure and cardiac output Let s start with a case You are admitting a 4 day old female who had no prenatal care and presented to the ED with poor feeding, respiratory distress, lethargy and poor urine output. PGE infusion was started in the ED. On exam, she is floppy with grunting respirations and her skin appears gray. Let s start with a case VS:T 97 P 190 R 70 BP 40/P SpO2 92% PE: Chest: coarse BS with retractions Heart: tachycardic, no murmur Abd: soft, liver 4cm below RCM Ext: gray, cool, cap refill 5 sec, poor distal pulses 12

13 Let s start with a case Labs: WBC 8.2 Hg 11 Hct 33 Plt 189 Lytes:Na132/K5/Cl103/CO8/BUN13/Cr0.9 ABG: 6.99/32/54/8/-16/85% CXR: cardiomegaly, increased PVM ECHO: critical CoA Questions A nursing student asks why is that baby gray? How will you answer? Then she asks why the baby is so hypotensive. You explain The MD decides to transfuse prbc and asks you to get consent from the parents. What will you tell them is the reason for the transfusion? Flow and Pressure Relationship (all you really need to know to understand any concept in cardiac critical care.seriously!) 13

14 Ohm s Law Flow (Q) = Pressure change (dp) Resistance (R) Increased P Increased Q Increased R Decreased Q Cardiac Physiology What is the purpose of the heart? O 2 Cardiac Physiology Delivery of oxygen (DO2) is a direct function of the cardiac output (CO) and the arterial oxygen content (CaO2) DO2 = CO x CaO2 14

15 Cardiac Physiology Oxygen Delivery DO2 = CO x CaO2 Cardiac Output (CO) Arterial Oxygen Content (CaO2 art Rate (HR) x Stroke Volume (Hgb (SV) x 1.39 x SaO2) + (0.003 x PaO roke Volume is directly related to: Preload Afterload Contractility Cardiac Physiology What are we trying to achieve? Maximize O 2 delivery Provide adequate end organ perfusion Maintain BP Determinants of blood pressure 15

16 Ohm s Law BP = Flow(Q) x Resistance(R) What is Blood Pressure? BP CO SVR (Afterload) Heart rate Stroke Volume Intravascular Volume (Preload) Contractility Maintaining Blood Pressure Derrangement in: Volume status Cardiac function Vascular tone Heart rate CO BP SVR HR SV Preload Contractility 16

17 Derrangement in: Volume status Cardiac function Vascular tone Heart rate Preload HR CO Preload BP SVR SV Contractility Determinants of Cardiac Output Preload - Resting fiber length before contraction -End diastolic ventricular volume -If preload is increased, SV and capability for pressure generation are increased. Frank-Starling Mechanism -Compliance dependent CVP CVP: Central venous pressure Transduced via RA lines or CVL Reflects the intravascular volume status of the patient and the filling pressure of the ventricle Relationship between CVP and BP is important 17

18 Derrangement in: Volume status Cardiac function Vascular tone Heart rate Afterload (SVR) CO BP SVR HR SV Preload Contractility Afterload Any factor that resists the ejection of blood from the heart (SVR or obstruction) With increasing afterload, shortening is decreased and slowed. Afterload reduction increases fiber shortening. Decreasing afterload helps the heart contract Afterload Afterload (SVR) increased by Acidosis, hypoxemia, pain, hypothermia Aggressively treat/avoid these things Afterload reducers Milrinone, dobutamine, nitroprusside, NO 18

19 Derrangement in: Volume status Cardiac function Vascular tone Heart rate Contractility HR CO Preload BP SVR SV Contractility Contractility Often impaired Requires treatment with inotropes Milrinone, epinephrine, dobutamine, dopamine Calcium is an important component Putting it all together Decreased Cardiac Output can be caused by: Decreased preload Increased (or decreased) afterload Impaired contractility All therapies aimed at maximizing these parameters 19

20 Categories of CHD Epidemiology of CHD Incidence estimated to be 8 to 10 cases per 1000 live births (0.8% - 1%) Increased to 5% - 15% in parents with CHD Prevalence increases as better treatments are available Age at presentation varies greatly and depends on type of lesion and severity Age at Presentation 20

21 Epidemiology of CHD Categories of CHD Patients with too much PBF CHF Patients with too little PBF Blue Patients with too little systemic blood flow Gray Categories of CHD Acyanotic Congenital Heart Disease L R Shunt (Volume load) Obstructive (Pressure load) Cyanotic Congenital Heart Disease Decreased PBF Mixing lesions 21

22 Acyanotic CHD L R Shunt lesions (Volume load) VSD, ASD, PDA, AV Canal Common denominator is communication between systemic and pulmonary circulations Magnitude of shunt depends on size of defect and relative SVR and PVR which will change over time Acyanotic CHD Obstructive lesions (Pressure load) CoA, AS, IAA Common denominator is obstruction of blood flow/ventricular outflow Lead to left heart failure (pulmonary edema) circulatory collapse Cyanotic CHD Decreased PBF TOF, PS with PFO, tricuspid atresia, pulmonary atresia Common denominator is obstruction to pulmonary blood flow and a means of shunting R L 22

23 Cyanotic CHD Mixing Lesions TGA, TAPVR, truncus arteriosus, HLHS Common denominator is that there is complete mixing of systemic and pulmonary venous return without obstruction to PBF Acyanotic CHD L R Shunt lesions (Volume load) Most common lesions are ventricular septal defect (VSD) 20-25%, atrial septal defect (ASD) 5-10%, patent ductus arteriosus (PDA) 5-10, AV Canal 2% Common denominator is communication between systemic and pulmonary circulations Magnitude of shunt depends on size of defect and relative SVR and PVR which will change over time 23

24 Pathophysiology of VSD Qp:Qs is increased Increased PBF leads to decreased lung compliance, increased WOB, pulmonary edema Chronic increased PBF leads to increased PVR (Eisenmenger s physiology) PHTN Clinical Presentation - VSD History: poor feeding, diaphoresis with feeds, delayed growth and development, repeated pulmonary infections Will present at 6 to 8 weeks of age Exam: tachypnea, holosystolic murmur at LLSB, hepatomegaly CXR: cardiomegaly, increased PVM 24

25 CXR - VSD Management - VSD Diuresis Inotropy with digoxin Surgical repair when optimal Acyanotic CHD Obstructive lesions (Pressure load) Most common are coarctation of the aorta (CoA) 8-10%, aortic stenosis (AS) 5%, interrupted aortic arch (IAA) 1% Common denominator is obstruction of blood flow/ventricular outflow Lead to left heart failure (pulmonary edema) circulatory collapse 25

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27 Ductal Dependence To provide pulmonary blood flow (PBF) Critical PS To provide systemic blood flow (SBF) Critical CoA To allow mixing - TGV Pathophysiology of Critical CoA In fetal life, the descending aorta is supplied by the PDA With closure of the duct, systemic circulation is impaired which leads to poor perfusion, acidosis and circulatory collapse Clinical Manifestations Critical CoA History: CHF symptoms (poor feeding, diaphoresis), poor urine output Will present in first few days to weeks of life Exam: tachypnea, poor perfusion, decreased femoral pulses, shock, often NO MURMUR, usually gallop present CXR: cardiomegaly, pulmonary edema 27

28 Management Critical CoA Diuresis Inotropy with dopamine or dobutamine Prostaglandin (PGE1) infusion to reopen ductus arteriosus and restore systemic blood flow Balloon angioplasty vs. surgical repair Cyanotic CHD Decreased PBF Most common lesions are Tetralogy of Fallot (TOF) 10%, pulmonic stenosis with PFO (PS) 5-8%, tricuspid atresia 1-2%, pulmonary atresia (PA) <1% Common denominator is obstruction to pulmonary blood flow and a means of shunting R L 28

29 Tetralogy of Fallot Consists of four components Large VSD Right ventricular outflow tract obstruction Right ventricular hypertrophy Overriding Aorta Only two components are important VSD large enough to equalize pressure (R=L) RVOT obstruction how severe determines if patient shunts R L ( Blue Tet ) or L R ( Pink Tet ) Clinical Presentation of TOF History: cyanosis or hypoxic spells, dyspnea on exertion, squatting Exam: cyanotic ( Blue Tet ), murmur variable usually loud (grade III-IV) systolic ejection murmur with thrill CXR: boot shaped heart, decreased PVM 29

30 CXR - TOF Cyanotic CHD Mixing Lesions Most common lesions are transposition of the great arteries (TGA) 5%, total anomolous pulmonary venous return (TAPVR) 1%, truncus arteriosus <1%, hypoplastic left heart syndrome (HLHS) <1% Common denominator is that there is complete mixing of systemic and pulmonary venous return without obstruction to PBF 30

31 Pathophysiology of TGA Pulmonary and systemic circulations are parallel Defects permitting mixing are essential for survival ASD, VSD, PDA Poor mixing results in hypoxia, acidosis and death Clinical Presentation of TGA History: cyanosis, poor feeding, dyspnea Presents in the first few days of life Exam: systolic murmur of VSD may be present, may have no murmur CXR: cardiomegaly, egg-shaped cardiac silhouette Management of TGA Treat acidosis Administer O2 to decrease PVR and increase PBF (increase mixing) PGE1 to reopen ductus and increase mixing Balloon atrial septostomy 31

32 Summary All congenital heart lesions can be categorized based on flow and pressure relationships Caring for these patients entails maximizing oxygen delivery and maintaining adequate blood pressure Back to our case You are admitting a 4 day old female who had no prenatal care and presented to the ED with poor feeding, respiratory distress, lethargy and poor urine output. PGE infusion was started in the ED. On exam, she is floppy with grunting respirations and her skin appears gray. Questions A nursing student asks why is that baby gray? How will you answer? 32

33 Categories of CHD Patients with too much PBF CHF Patients with too little PBF Blue Patients with too little systemic blood flow Gray Questions Then she asks why the baby is so hypotensive. You explain Derrangement in: Volume status Cardiac function Vascular tone Heart rate Contractility HR CO Preload BP SVR SV Contractility 33

34 Questions The MD decides to transfuse prbc and asks you to get consent from the parents. What will you tell them is the reason for the transfusion? Cardiac Physiology Oxygen Delivery DO2 = CO x CaO2 Cardiac Output (CO) Arterial Oxygen Content (CaO2) art Rate (HR) x Stroke Volume (Hgb (SV) x 1.39 x SaO2) + (0.003 x PaO 34