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Home , Cardiac physiology, Ductus arteriosus, Fetal circulation, Foramen ovale (heart), Placenta, Truncus arteriosus

Cardiac

Gia Marzano, AC PNP Pediatric Cardiac Surgery Rush Center for Congenital Disease Rush University Medical Center

Objectives Part 1

• • Transition to Postnatal Circulation • Normal Cardiac • 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 Fetal Circulation Few Concepts • Fetal heart starts developing during the 3rd week of life • By the 3rd month of development, all major vessels are present and functioning. • Pulmonary Blood Flow is Low • () occurs in

More Concepts

• Pulmonary Resistance is High – are still underdeveloped – Small pulmonary 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 carries oxygenated blood and nutrients from the placenta. • Placenta facilitates gas and nutrient exchange between maternal and fetal blood.

2 Fetal Circulation Overview

• Oxygenated blood from placenta is transported to the through the

Fetal Circulation Overview

• Most of the oxygenated blood bypasses the through the and mixes with De-Ox Blood from IVC

Fetal Circulation Overview

• Blood travels from the IVC and enters the RA

3 Fetal Circulation Overview

• 40 % of oxygenated blood from the IVC bypasses the RV and is shunted to the LA via the • 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 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 to the and Placenta for oxygenation

4 Fetal Circulation Overview

• Blood circulates to the body and returns to the placenta via the umbilical arteries

Fetal Circulation Overview

• Placenta re- oxygenates blood returning from the umbilical arteries • New fetal …

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

5 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 : – 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 Transitional Circulation

Increase Drop in in systemic + pulmonary Vascular Vascular resistance 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 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 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 , 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 destruction and fibrosis • Functional closure within 10-15 hrs after birth • Complete closure within 5-7 days, can be up to 21 days

8 Ductus Arteriosus Role of • 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 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. , ) – 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 Therapy

• Indomethacin: inhibits PG production • PGE1: – relaxes the ductus arteriosus smooth muscle cells. – Effective within the first 7-10 days after birth – Dose: 0.05-0.1 mcg/kg/min – IV/PO

Prostaglandin Therapy Side Effects • Apnea • Fever • Flushing • Hypotension • Thrombocytopenia • Seizure • Pyloric gastric outlet obstruction

Questions?

11 Part 2

• Basic principles of cardiac physiology including Flow and pressure relationships Oxygen delivery Determinants of and

Let’s start with a case…

• You are admitting a 4 day old female who had no 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

12 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 . 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 Ohm’s Law

Pressure change (dP) Flow (Q) = ______Resistance (R)

Increased P  Increased Q Increased R  Decreased Q

Cardiac Physiology

• What is the purpose of the heart?

O2

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 Cardiac Physiology

Oxygen Delivery DO2 = CO x CaO2 Cardiac Output (CO) Arterial Oxygen Content (CaO2 art Rate (HR) x Volume (Hgb(SV) x 1.39 x SaO2) + (0.003 x PaO roke Volume is directly related to: Contractility

Cardiac Physiology

• What are we trying to achieve?

Maximize O2 delivery Provide adequate end perfusion Maintain BP

Determinants of blood pressure

15 Ohm’s Law

BP = Flow(Q) x Resistance(R)

What is Blood Pressure? BP

CO SVR (Afterload)

Heart rate

Intravascular Volume Contractility (Preload)

Maintaining Blood Pressure • Derrangement in: – Volume status – Cardiac function BP – Vascular tone – CO SVR

HR SV

Preload Contractility

16 Preload • Derrangement in: – Volume status – Cardiac function BP – Vascular tone – Heart rate CO SVR

HR SV

Preload 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 – Relationship between CVP and BP is important

17 Afterload (SVR) • Derrangement in: – Volume status – Cardiac function BP – Vascular tone – Heart rate CO 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 – , hypoxemia, pain, hypothermia – Aggressively treat/avoid these things • Afterload reducers – Milrinone, dobutamine, nitroprusside, NO

18 Contractility • Derrangement in: – Volume status – Cardiac function BP – Vascular tone – Heart rate CO SVR

HR SV

Preload Contractility

Contractility

• Often impaired • Requires treatment with – 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 Categories of CHD

Epidemiology of CHD

• Incidence estimated to be 8 to 10 cases per 1000 live (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 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 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 (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 Cyanotic CHD

• Mixing Lesions – TGA, TAPVR, , 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%, (ASD) 5-10%, (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 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 • Will present at 6 to 8 weeks of age • Exam: tachypnea, holosystolic murmur at LLSB, hepatomegaly • CXR: cardiomegaly, increased PVM

24 CXR - VSD

Management - VSD

• Diuresis • Inotropy with • Surgical repair when optimal

Acyanotic CHD

• Obstructive lesions (Pressure load) – Most common are (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 26 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 Management – Critical CoA

• Diuresis • Inotropy with dopamine or dobutamine • Prostaglandin (PGE1) infusion to re- open ductus arteriosus and restore systemic blood flow • Balloon angioplasty vs. surgical repair

Cyanotic CHD

• Decreased PBF – Most common lesions are (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 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 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 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, -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

31 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 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…

Contractility • Derrangement in: – Volume status – Cardiac function BP – Vascular tone – Heart rate CO SVR

HR SV

Preload Contractility

33 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