Pediatric Cardiology: Congenital and Acquired Conditions
Introduction to Pediatric Cardiology
Pediatric cardiology is broadly categorized into two main groups for study:
Congenital/Structural/Anatomical defects.
Acquired conditions, which may manifest in infancy or later in life (often due to infectious causes).
Some overlap exists, such as congenital cardiomyopathy, which involves a genetic or familial disposition but may not manifest until later life.
The primary framework for evaluating cardiac defects involves three questions:
Where is the blood going?
What is the specific defect?
What are the resulting symptoms?
Fetal Circulation and Birthing Transition
Fetal Circulation Characteristics:
Circulation runs in parallel rather than in series.
The placenta, not the lungs, is the site of gas and nutrient exchange.
Circulation is designed to bypass the lungs, which are fluid-filled and non-functional for oxygenation in utero.
Pressures are reversed compared to postnatal life: Pulmonary Vascular Resistance (PVR) is high; Systemic Vascular Resistance (SVR) is low.
Only approximately of blood flow goes to the lungs in utero.
Parallel circulation allows the fetus to tolerate heart lesions that would be fatal after birth because oxygenated and deoxygenated blood mix freely.
The Four Fetal Shunts:
Placenta: Site of gas/nutrient exchange; receives of cardiac output.
Ductus Venosus: Shunts oxygenated blood from the umbilical vein past the liver directly to the Inferior Vena Cava (IVC) to preserve oxygen content for the brain and heart.
Foramen Ovale: An opening between the right and left atria allowing oxygen-rich blood to bypass the right ventricle and lungs.
Ductus Arteriosus: Connects the pulmonary artery to the aorta, diverting right ventricular output away from the high-resistance lungs.
Transition at Birth:
The first breath causes lung expansion and the introduction of oxygen, prostacyclin, and nitric oxide, which relax pulmonary arterioles (vasodilation).
PVR falls sharply, and pulmonary blood flow increases to times almost immediately.
Clamping the umbilical cord removes the low-resistance placenta, causing SVR to rise.
Increased SVR raises pressure on the left side of the heart, causing the foramen ovale to close.
Rising oxygen levels cause the ductus arteriosus to constrict and close, typically over a few days.
It takes to weeks for PVR to reach adult levels; consequently, mild defects may not be apparent until this time.
Inflammatory Diseases of the Heart
Three Layers and Corresponding Diseases:
Myocardium (Middle Muscle Layer): Myocarditis (usually viral).
Endocardium (Inner Lining and Valves): Endocarditis (usually bacterial or fungal).
Pericardium (Outer Sac): Pericarditis (viral, idiopathic, or post-operative).
Myocarditis:
Phases of Injury:
Acute Injury: Viral invasion of myocytes (first few days).
Subacute Phase: Systemic immune response, necrosis, and infection of healthy myocytes.
Chronic Phase: Diffuse injury and fibrosis (around day ) leading to ventricular dysfunction and dilation.
Clinical Presentation: Ranges from mild viral symptoms to cardiac arrest. Key sign is resting tachycardia out of proportion to fever or pain.
Diagnosis: Elevated ESR, CRP, Troponin, and BNP. Gold standard is biopsy (rarely done due to procedural risk).
Management: Heart failure treatment (diuretics, inotropes), activity restriction, and IVIG in the initial phase. Extracorporeal Membrane Oxygenation (ECMO) or Ventricular Assist Devices (VAD) may be used as a bridge to transplant.
Prognosis (Rule of Thirds): One-third recover with chronic dysfunction, one-third require transplant, and one-third pass away.
Endocarditis:
Requires damaged endocardium and an infectious agent (Turbulent flow \rightarrow Platelet-fibrin thrombosis \rightarrow Bacterial vegetation).
Risk Factors: Prosthetic valves, shunts, indwelling catheters, and injectable drug use.
Management: Prevention via AHA guidelines (Amoxicillin prophylaxis for dental procedures). Treatment involves IV antibiotics for to weeks.
Pericarditis:
The rate of fluid accumulation is more critical than the volume. Rapid accumulation leads to tamponade.
Clinical Presentation: Precordial chest pain (worsens with position), friction rub, and muffled heart sounds.
Beck's Triad/Tamponade Signs: Tachycardia, poor perfusion, narrowed pulse pressures, and pulsus paradoxus.
Management: NSAIDs (first line), pericardiocentesis, and potentially a pericardial window.
Pediatric Cardiomyopathies
Incidence: Highest in infants under year old. Most common cause of heart failure in children requiring transplant.
Four Types:
Dilated Cardiomyopathy (DCM): Chamber enlargement without wall thickening. Most common type. Systolic pump failure. Requires diuretics, ACE inhibitors, and anticoagulation (due to stagnant blood).
Hypertrophic Cardiomyopathy (HCM): Asymmetrical septal hypertrophy leading to stiff ventricles and impaired diastolic filling. Most common cause of sudden cardiac death in athletes under . Requires beta-blockers and avoidance of competitive athletics.
Restrictive Cardiomyopathy: Diastolic problem with stiff ventricles; very rare but has poor outcomes. Leads to atrial enlargement and pulmonary hypertension.
Noncompaction Cardiomyopathy: Arrested compaction of fetal myocardium (weeks to ); heart becomes spongy with intratrabecular recesses.
Congenital Heart Defects (CHD)
Left-to-Right Shunts (Acyanotic):
Blood moves from the systemic (left) to the pulmonary (right) side due to lower PVR.
Leads to pulmonary over-circulation and heart failure (tachypnea, failure to thrive, diaphoresis with feeds).
Atrial Septal Defect (ASD): Wide fixed split . Secundum is the most common type.
Ventricular Septal Defect (VSD): Most common cardiac defect overall. Holosystolic harsh murmur.
Patent Ductus Arteriosus (PDA): Continuous machinery-like murmur.
Atrioventricular (AV) Canal: Strongly associated with Trisomy 21.
Truncus Arteriosus: Single vessel and large VSD; associated with DiGeorge syndrome.
Right-to-Left Shunts (Cyanotic):
Deoxygenated blood bypasses the lungs and enters systemic circulation.
Tetralogy of Fallot (TOF): 1. Pulmonary stenosis, 2. Right ventricular hypertrophy, 3. Overriding aorta, 4. VSD. Features a "boot-shaped heart" on X-ray.
Tet Spells: Hypercyanotic episodes. Managed by knee-to-chest positioning (increases SVR), oxygen, and morphine.
Transposition of the Great Arteries (TGA): Parallel circulations (Aorta from RV, Pulmonary Artery from LV). Requires an arterial switch procedure.
Left Ventricular Outflow Tract Obstruction:
Coarctation of the Aorta (Coarc): Narrowing near the ductus. Hallmark is discrepant pulses (strong upper, weak/absent femoral) and four-point blood pressure differences.
Hypoplastic Left Heart Syndrome (HLHS): Tiny left ventricle/aorta. Requires staged palliation: 1. Norwood, 2. Glenn, 3. Fontan.
Cardiac Surgery and Mechanical Support
Cardiopulmonary Bypass (CPB):
Uses a pump and oxygenator. Patients are heparinized (high bleeding risk).
Heart is arrested using cross-clamping and high potassium levels.
Risks include systemic inflammatory response, capillary leak, and ischemia-reperfusion injury.
ECMO and VAD:
VA ECMO: Supports heart and lungs.
VV ECMO: Supports gas exchange only (requires good cardiac output).
VAD: Bridge to transplant; takes over ventricular workload.
Acquired Functional Disorders: Syncope and POTS
Syncope: Transient loss of consciousness and muscle tone due to cerebral hypoperfusion.
Vasovagal (Neurocardiogenic): Most common and benign. Triggered by standing, heat, or dehydration. Prodrome: Nausea, lightheadedness, diaphoresis.
Cardiac Syncope Red Flags: Occurs while supine or during exertion; chest pain; palpitations; no prodrome; family history of sudden death.
Postural Orthostatic Tachycardia Syndrome (POTS):
Sustained tachycardia within minutes of standing without orthostatic hypotension.
Management: Increased fluid intake ( to ) and dietary salt.
Arrhythmias and Conduction Disorders
Supraventricular Tachycardia (SVT): Narrow QRS, rate >220\,\text{bpm} in infants, >180\,\text{bpm} in children. Treated with vagal maneuvers or rapid-push Adenosine.
Junctional Ectopic Tachycardia (JET): Common post-op complication ( to ). Communicate atria and ventricles are dissociated.
Long QT Syndrome: QT interval >460\,\text{ms}. High risk for Torsades de Pointes. Avoid Zofran (Ondansetron) and other prolonging drugs.
Ventricular Fibrillation (V-fib): Chaotic rhythm, no output. Requires immediate defibrillation.
Rheumatic Fever
Pathophysiology: Post-Group A Strep pharyngitis autoimmune response (molecular mimicry). Target: Heart valves (primarily mitral).
Jones Criteria (Revised): Required evidence of Strep (ASO titer or swab) plus 2 Major OR 1 Major and 2 Minor.
Major (JONES): Joints (Migratory polyarthritis), O (Heart/Carditis), Nodules (Subcutaneous), Erythema marginatum, Sydenham’s chorea.
Minor: Fever, arthralgia, elevated ESR/CRP, prolonged PR interval.
Management: Penicillin (primary prevention of the initial infection; secondary prevention of recurrence) and anti-inflammatories.
Questions & Discussion
Q: Does the anatomy scan show heart defects before the baby is born?
A: Yes, many are picked up on the 20-week anatomy scan, though not all. Some families lack access to prenatal care, or smaller defects may be missed until after the PVR drops postnatally.
Discussion on Zofran: A case was mentioned involving a 4-year-old who ingested eighteen Zofran tablets, leading to a QT interval of nearly . Poison control recommends Magnesium if QT exceeds .
Discussion on Clinical Hours: Simulation hours and lab hours count toward the semester total. Future clinical placements include Ochsner, Our Lady of the Lake, and Children’s Hospital, covering specialties like neuro, oncology, ortho, and neonatology.