Heart Defects

Fetal vs. Neonatal Circulation

  • Understanding the transition from fetal to neonatal circulation is crucial for understanding implications when the transition doesn't happen normally.
  • Heart develops at 4-7 weeks gestation.
  • In utero, gas exchange occurs in the placenta, not the lungs.

Fetal Circulation

  • Oxygenated placental blood enters via umbilical veins.
  • Blood shunts through the ductus venosus in the liver.
  • Enters the right side of the heart.
  • Mixed venous blood shunts through the foramen ovale in the atria.
  • Then through the ductus arteriosus.
  • Returns to the aorta and placenta via the umbilical artery.

Neonatal Circulation

  • At birth, transitional circulation occurs, shifting gas exchange from placenta to lungs.
  • Pulmonary vascular resistance (PVR) is high in the fetus but decreases rapidly over the first 12-24 hours of life, increasing pulmonary blood flow.
  • Takes 2-3 weeks to reach normal infant PVR; may be delayed in premature infants.
  • Foramen ovale and ductus arteriosus start to close at birth.
  • Neonate normally does not have intracardiac shunting as those close.

Comparison Chart

  • Fetus:
    • High pulmonary vascular resistance.
    • Low systemic vascular resistance.
    • Low cardiac output.
    • Gas exchange in the placenta
  • Neonate:
    • Pulmonary vascular resistance drops.
    • High systemic vascular resistance.
    • High cardiac output.
    • Gas exchange in the lungs.

Ductus Arteriosus

  • In utero, it connects the pulmonary artery to the descending aorta.
  • Allows most of the blood from the right ventricle to bypass the fetus's non-functioning lungs.
  • Constricts at birth in response to increased PaO2PaO_2 and loss of placental prostaglandins.
  • In term infants, there should be no shunting of blood across the ductus arteriosus.

Patent Ductus Arteriosus (PDA)

  • The ductus arteriosus doesn't close.
  • Results in left-to-right shunting of blood due to higher systemic pressure.
  • A small amount of blood flow returns back into the pulmonary circulation.
  • Increases blood flow to the right side of the heart.

Foramen Ovale

  • Opening in the septum between the right and left atria of the fetus, allowing right-to-left shunting of blood.
  • After birth, changes to left-to-right shunting because systemic vascular pressures are higher than pulmonary vascular pressures.
  • Functional closure at birth from increased left atrial pressure due to increased pulmonary blood return.
  • Anatomic closure occurs when the septum closes completely.

Shunting

Left-to-Right Shunting
  • Oxygenated blood from systemic circulation enters the pulmonic circulation.
  • Body still receives oxygenated blood.
  • Patient is acyanotic.
Right-to-Left Shunting
  • Deoxygenated blood from the pulmonic circulation enters the systemic circulation.
  • Body receives deoxygenated blood.
  • Patient may have cyanosis.

Vascular Resistance

Increased Pulmonary Vascular Resistance
  • Vasoconstriction in the pulmonary bed.
Decreased Pulmonary Vascular Resistance
  • Vasodilation in the pulmonary bed.
Increased Systemic Vascular Resistance
  • Vasoconstriction.
Decreased Systemic Vascular Resistance

  • Vasodilation.

  • Vasoconstriction = decreased flow.

  • Vasodilation = increased flow.

  • Blood flow follows the path of least resistance.

Congenital Heart Defects - When to Worry

  • Murmur and cyanosis together are concerning.
  • Worsening cyanosis with crying.
  • Failed hyperoxia test: cyanosis worsens with supplemental oxygen.
  • Abnormal weight loss or poor feeding.
  • Difference between upper and lower extremity pulses.
  • Rule out congenital heart defect in any very sick baby.

Syndromes Associated with Heart Defects

  • Trisomy 21 (Down Syndrome): Atrioventricular septal defects.
  • Trisomy 18: VSDs, hypoplastic left heart syndrome.
  • Turner Syndrome: VSD, coarctation of the aorta.
  • Williams, DeGeorge, and Noonan's are also associated with congenital heart defects.

Classifying Congenital Heart Defects

  • Acyanotic
    • Increased pulmonary blood flow (left-to-right shunt).
    • Ventricular outflow obstruction.
  • Cyanotic
    • Decreased pulmonary blood flow (increased pulmonary vascular resistance).
    • Increased pulmonary blood flow.

Terminology

  • Atresia: Missing or not developed.
  • Stenosis: Narrowed, stiff, or not flexible.
  • Hypoplastic: Small, not developed well.
  • Septal: Refers to atrial or ventricular wall.
  • Anomalous: Wrong connection, moving in the wrong direction.
  • Tetralogy: Four.

Acyanotic Defects with Increased Pulmonary Blood Flow

Patent Ductus Arteriosus (PDA)
  • Normal fetal channel between pulmonary artery and aorta remains open.
  • Higher chance in premature infants.
  • Left-to-right shunting, increased blood flow to the right side of the heart.
  • Closure: pharmacologically with indomethacin, interventional catheterization, or surgical ligation.
Atrial Septal Defect (ASD)
  • Opening between the two atria.
  • More common in females.
  • Shunting between atria, magnitude determined by ventricular compliance and defect size.
  • Small defects may close on their own.
  • Large defects: increased left-to-right shunting with age, risk for heart failure and pulmonary hypertension.
  • Surgical repair: patched in cardiac cath lab or surgically through thoracotomy/sternotomy.
Ventricular Septal Defect (VSD)
  • Opening in the ventricular septal wall between left and right ventricles.
  • Left-to-right shunting with increased pulmonary blood flow.
  • Systemic pressure > pulmonary pressure, some blood passes through the hole back into the right ventricle and recirculates to the pulmonary circulation.
  • Amount and direction of shunting determined by systemic and pulmonary pressures, VSD size, and other lesions.
  • Large VSD: congestive heart failure, pulmonary hypertension.
  • Small VSD: may close on their own.
  • Surgery: patch or percutaneous device closure for small VSD.
  • Post-op: watch for arrhythmias.
Atrioventricular Septal Defects (AV Canal Defects)
  • Often associated with Trisomy 21 (Down Syndrome).
  • Components:
    • Deformity of tricuspid and mitral valves resulting in a common AV valve.
    • Atrial septal defect.
    • Ventricular septal defect.
  • Surgical repair in infancy: ASD and VSD closed with a patch, mitral valve repaired.
  • Post-op: complicated, pulmonary hypertension and heart block can develop.
  • May need additional repair later in life if defects reopen.

Acyanotic Defects with Ventricular Outflow Tract Obstruction

Aortic Stenosis
  • Malformation of the aortic valve causing obstruction to blood flow leaving the left ventricle.
  • Aortic valve commissures are fused.
  • Stenosis = narrowed opening.
  • Severity is related to the degree of narrowing.
  • Most severe form: critical aortic stenosis, presents at birth with circulatory shock.
  • Dependent on a patent ductus arteriosus for adequate systemic circulation.
  • Surgical intervention: interventional cardiac catheterization with balloon valvuloplasty or surgical approach with sternotomy and incising fissures.
  • Post-op: related to degree of left ventricular dysfunction.
Coarctation of the Aorta
  • Narrowing of the descending aorta impeding blood flow.
  • Elevated pressure proximally and decreased pressure distally to the narrowing.
  • Symptoms depend on aortic arch hypoplasia and amount of stricture.
  • Open patent ductus arteriosus in the newborn allows perfusion to the lower extremities.
  • Discordant pulses: different pulses between upper and lower extremities; be suspicious for coarctation of the aorta.
  • Neonates with severe obstruction (critical coarctation of the aorta) present with heart failure and shock.
  • Require prostaglandin infusion to keep PDA open until surgical correction.
  • Monitor for apnea in patients receiving prostaglandin.
  • Monitor postoperatively for hypertension.
Pulmonary Stenosis
  • Narrowing of the pulmonary valve, obstructing blood flow as it leaves the right ventricle.
  • Right ventricular outflow tract obstruction.
  • Repair: balloon valvuloplasty or surgical intervention.

Cyanotic Malformations with Decreased Pulmonary Blood Flow

Tetralogy of Fallot
  • Underdevelopment of the right ventricular infundibulum.
  • Four Malformations:
    1. Pulmonary stenosis with right ventricular outflow obstruction.
    2. Right ventricular hypertrophy.
    3. Overriding aorta.
    4. Large VSD.
  • Severity of right ventricular tract obstruction determines the patient's symptoms.
  • Variable degrees of cyanosis.
  • Operatively complicated.
  • Post-op: monitor right ventricular failure, improve contractility, optimize oxygen demands, maintain AV synchrony, adequate preload, low pulmonary vascular pressures, watch for bleeding.
Tet Spells
  • Hypoxic episode before surgical repair.
  • Begins with irritability and hyperpnia, increasing cyanosis progressing to syncope or cardiac arrest.
  • Secondary to spasm of the infundibulum or sudden drop in systemic vascular resistance.
  • Treatment:
    • Keep patient calm and comfortable.
    • Morphine for agitation.
    • Knee-to-chest position.
    • Supplemental oxygen.
    • Intubation if needed.
    • Saline bolus (10-20 mL/kg).
    • Sodium bicarbonate or propranolol IV.
    • Phenylephrine to increase systolic blood pressure.
  • Patients with significant tet spells may need earlier surgical repair.
Tricuspid Atresia
  • Rare cardiac malformation.
  • Tricuspid valve is not patent.
  • Patient must have a patent foramen ovale or an atrial septal defect for blood flow.
  • Typically have a hypoplastic right ventricle and right ventricular outflow tract obstruction.
  • Blood flows through atrial communication from the right atrium to the left atrium and then down into the left ventricle.
  • Some blood enters the aorta, and some enters the pulmonary artery.
  • Treatment: prostaglandin infusion to keep foramen ovale open, surgery within the first week of life.

Cyanotic Defects with Increased Pulmonary Blood Flow

Transposition of the Great Arteries
  • Great arteries (aorta and pulmonary artery) are switched: aorta arises from the right ventricle, and pulmonary artery comes from the left ventricle.
  • Creates parallel pulmonary and systemic circulations.
  • Patient is dependent on some type of shunt for survival (PDA, PFO, ASD).
  • Cyanotic blood recirculation.
  • Treatment:
    • Stabilize neonate at birth.
    • Prostaglandin infusion.
    • Balloon septostomy to create ASD.
    • Arterial switch operation (cardiopulmonary bypass).
    • Post-op: myocardial dysfunction.
Truncus Arteriosus
  • Conal truncal septation fails to separate during fetal development; pulmonary artery and the aorta don't split.
  • Single valve vessel above the right and left ventricles (truncus).
  • Large ventricular septal defect.
  • Associated with DiGeorge syndrome.
  • Surgical repair: extensive neonatal cardiovascular surgical procedure.
  • Complex postoperative course, subsequent surgical procedures necessary.
Total Anomalous Pulmonary Venous Return (TAPVR)
  • Anomalous = abnormal.
  • Drainage of the pulmonary veins into the systemic veins or into the right atrium, rather than the left atrium.
  • Total (all four veins) or partial (one to three veins).
  • Severity of cyanosis increases with increased obstruction to pulmonary venous return.
  • Treatment: immediate neonatal surgical repair.
Hypoplastic Left Heart Syndrome
  • Hypoplastic = small or nonexistent.
  • Underdevelopment of structures on the left side of the heart.
  • Left-sided valves, mitral (connects the left atrium to the left ventricle), and aortic valves have stenosis or atresia.
  • The left ventricle is hypoplastic or nonexistent, narrowed aortic valve.
  • Ascending aorta can vary from minuscule in size to well-formed.
  • Treatment:
    • Diagnosed in utero.
    • Birth: Prostaglandin infusion to keep PDA open.
  • Path of Blood Flow:
    • High pressures cause left-to-right shunt at the atrial level.
    • Deoxygenated blood goes out to the body through the patent ductus arteriosus.
  • Several Surgeries:
    • 1st palliation stage one is the Norwood repair: to create a common atrium (essentially large ASD), create a neoaorta (new aorta) and systemic perfusion is improved. Still has ductal dependent flow to allow the Right ventricle to do systemic perfusion.
    • 2nd surgery around 6 months of age: the superior vena cava is connected to the pulmonary artery to reduce the volume load on the right ventricle.
    • Around 2-4 years of age: baffle created so blood returning to the heart from the lower body comes from the inferior vena cava and goes directly into the pulmonary artery.
  • Ultimately- the right ventricular gets wear and tear on chamber pumping blood into systemic circulation and may need heart transplantations.

Cardiac Catheterization

  • Common procedure for patients with cardiac defects.
  • Can be diagnostic and interventional.
  • Measures pressure and saturations in cardiac chambers and great vessels.
  • Cardiac output can be directly measured.
  • Cardiac biopsy can be done.
  • Interventional: balloon dilation, closure device placement, balloon atrial septostomy.
  • Monitor for arrhythmias, air embolization, myocardial infarction, perforation, bleeding, and infection.
  • Watch extremities' distal perfusion and catheter site.

Family Support

  • Having a child with a congenital heart defect is stressful for the family.
  • Excellent care requires a multidisciplinary team effort.
  • Parents may face tough decisions and reality shock.
  • Bonding with a fragile baby can be challenging.
  • Complex defects may need multiple surgeries and long-term follow-up.
  • Families may need to learn to give complicated medications.
  • Many patients have feeding issues and may need enteral tubes.
  • Can result in growth issues and neurodevelopmental delays.
  • Support groups can be helpful for parents.
  • Genetic testing and counseling may be needed.
  • Social workers, spiritual counselors, and bereavement counseling may be needed.
  • Consider family dynamics and the needs of siblings.
  • Education is important for both the cardiac defect and normal newborn care.

Postoperative Techniques

  • Improved intraoperative techniques have improved outcomes.
  • Repair vs. Palliation (repair fixes but palliation does not)
  • Cardiopulmonary bypass provides tissue perfusion and oxygenation.
  • Myocardial protection: hypothermia and circulatory arrest, cardioplegic solution.

General Postoperative Principles

  • Patients are at risk for both bleeding and clotting.
  • Monitor chest tube drainage closely.
  • Be concerned for bleeding when chest tube drainage is >3 mL/kg/hour for >3 hours, or 5-10 mL/kg/hour in any 1 hour.
  • Patients may require volume replacement.
  • Monitor for signs of tamponade (blood in the pericardial sac).
    *acute increase in filling pressures. such as the right atrial pressure, left atrial pressure, and the central venous pressure, or you can see equalization of the right and left atrial pressures. So normally, the left atrial pressure is higher than the right. acute decrease or a sudden stopping of that chest tube drainage. You can see neck vein distension and systemic hypotension and narrowed pulse pressure. In tamponade, there's compression of the atria and restricted venous return. so there's decreased ventricular preload. Hypotension may not respond to volume administration because the heart can't squeeze, that's really the problem.
  • Hemodynamic Monitoring:
    • Continuous ECG monitoring.
    • Expect higher heart rates (cardiac stressor).
    • Rhythm disturbances are common (Junctional Ectopic Tachycardia, Atrial Ectopic Tachycardia).
    • Ventricular arrhythmias and atrial fibrillation are common in adolescents or adults with congenital heart defects.
    • Heart block or conduction delays can be associated with septal defect repairs, septal myectomy, and AV valve abnormalities.
    • Anesthesia effects and bypass can cause issues.
    • Increased catecholamines, electrolyte/metabolic changes, intravascular volume changes, hypoxemia, and temperature instability can also affect heart rate and rhythm.
    • Indwelling arterial catheter is needed to assess beat-to-beat variability in blood pressure.
  • High potential for low cardiac output and poor perfusion.
    • Timely recognition is essential.
    • Right atrial pressure/central venous pressure: systemic venous return, right heart preload, right heart function, right ventricular end-diastolic pressure.
      • Decreased RAP/CVP = hypovolemia.
      • Increased RAP/CVP = RV failure, pulmonary hypertension.
    • Left atrial pressure: pulmonary venous pressure, left heart preload, left heart function, left ventricular end-diastolic pressure.
      • Decreased LAP = hypovolemia.
      • Increased LAP = LV failure, increased LV afterload.
    • Maintain adequate preload and reduce afterload.
  • Oxygenation and Ventilation:
    • Airway protection and gas exchange are key.
    • Be careful with suctioning (stress response).
    • Be careful with supplemental oxygen, especially in patients with single ventricle physiology, because the pulmonary dilation effects of oxygen can be detrimental to the patient and a lot of fluid might come because of dilation which might flood the patients lungs.
  • Fluid and Electrolytes:
    • IV fluid choice varies with the institution and surgeon's preference.
    • Some patients need restricted sodium.
    • Monitor fluid balance continually.
    • Watch for electrolyte imbalances (potassium, hyponatremia, hypocalcemia).
    • Monitor glucose levels; infants at high risk for hypoglycemia.
  • Monitor renal function and urine output.
  • Acidosis adversely affects myocardial function.
  • Pharmacologic support with catecholamines or vasodilators: maintain adequate preload, reduce afterload, and maintain cardiac output.
  • Temporary Pacing Wires:
    • Watch for signs of infection and bleeding after removal.
    • Report over/undersensing and non-capture.
  • Thermal Regulation:
    • Hypothermia is reversed postoperatively, but post-op, pt might need careful but slow rewarming.
    • Hypothermia prolongs bleeding, delays hemodynamic stabilization, and leads to acidosis.
  • Feeding and Nutrition:
    • Monitor for necrotizing enterocolitis.
    • Patients have increased caloric requirements.
  • Follow hospital policy for dressing and wound care.
  • Most patients receive antibiotics for infection prophylaxis.
  • Seizures:
    • Seizures are the most common neurologic complication after operation.
    • Assess for potential causes, e.g., electrolyte/acid-base imbalances, hypoglycemia, cerebral ischemia.
  • Pain Management is essential after operation to prevent uncontrolled pain, increasing myocardial oxygen demands, therefore increasing the patient risk.

Cardiac Assist Devices

  • Indicated after cardiac surgery for low cardiac output syndrome
  • Also used for other patients with persistent low cardiac output such as those with cardiomypathies, inflammatory diseases, intractable arrhythmias, or a systemic illness such as septic shock
  • General Goals include maintaining adequate cardiac output to prevent multi organ failure, and to prevent infection and bleeding.
  • We use hemodynamic monitoring and will assess the cardiac output to help care for child with assist device. Along with monitoring the devices flow rates to see if the numbers all match up with the volumes of blood. Volume status will be monitored along with tamponade.