Acyanotic CHD: VSD, PDA, AVSD, Ducts

Overview

Lecture on pediatric cardiology focusing on acyanotic congenital heart disease: atrioventricular septal defect (AVSD), ventricular septal defect (VSD), patent ductus arteriosus (PDA), and duct-dependent circulation. Emphasis on concepts of left‑to‑right shunt, pulmonary blood flow, classification, clinical features, investigations, complications, and management.

Congenital Heart Disease: Basic Hemodynamic Concepts

• Acyanotic congenital heart diseases here are mainly left‑to‑right shunt lesions.

• Left‑to‑right shunt: blood from left heart (high pressure, oxygenated) moves to right heart (low pressure).

• Consequences:

  • Volume overload of right heart and pulmonary circulation.
  • Increased pulmonary blood flow → pulmonary congestion, recurrent infections, pulmonary hypertension.
  • Blood returns to left heart again → left atrial and ventricular volume overload → cardiomegaly and eventual heart failure.

• If obstruction is present (e.g., pulmonary stenosis, coarctation of aorta):

  • Pulmonary or systemic blood flow distal to obstruction is reduced.
  • Obstructive lesions can cause decreased pulmonary blood flow (oligemia) or decreased systemic flow.

Atrioventricular Septal Defect (AVSD) / AV Canal Defect

Definition & Anatomy

• Defect involving both atrial and ventricular septa at the level of atrioventricular valves.
• Caused by deficiency of atrioventricular (AV) septum / endocardial cushion tissue.
• Components may include:
  • Ostium primum atrial septal defect.
  • Inlet VSD.
  • Abnormal AV valves (mitral and tricuspid).

Associations

• Strongly associated with Down syndrome (Trisomy 21).
• 30% of AVSD cases associated with Down syndrome.
• Endocardial cushion defects are classical in Down syndrome.

Hemodynamics

• Left‑to‑right shunt occurs at both atrial and ventricular levels.
• Large volume of blood passes to right heart and pulmonary circulation, then returns to left heart.
• Leads to:
  • Overload of left atrium and ventricle → cardiomegaly.
  • Early development of pulmonary hypertension.

Clinical Features

• Present early in infancy with:
  • Congestive cardiac failure.
  • Recurrent pulmonary infections.
  • Failure to thrive.
• Cardiac enlargement: marked cardiomegaly due to left heart volume overload.
• On auscultation:
  • Loud S1 due to AV valve involvement.
  • Wide, often fixed, split S2 (massive pulmonary flow).
  • Mid‑diastolic rumbling murmur at lower left sternal border (increased flow across AV valves).
  • Systolic murmur due to AV valve regurgitation or VSD flow.
• ECG:
  • Left axis deviation.
  • Evidence of ventricular hypertrophy.

Chest X‑ray

• Cardiomegaly due to left atrial and left ventricular enlargement.
• Increased pulmonary vascularity.
• Enlarged main pulmonary artery.

Complications

• Early-onset congestive heart failure.
• Early, severe pulmonary hypertension.
• Failure to thrive and repeated infections.

Management

• Early surgical correction (closure of septal defects, AV valve repair) in infancy.
• Aim: prevent progression to irreversible pulmonary vascular disease and chronic heart failure.

Ventricular Septal Defect (VSD)

Definition & Epidemiology

• Defect in the interventricular septum causing communication between right and left ventricles.
• Most common congenital heart disease overall.
• Incidence around 2–3 per 1000 live births; about 1 in 1000 school‑age children.
• Affects males and females equally.

Associations

• May occur in isolation or as part of complex malformations:
  • Tetralogy of Fallot.
  • Truncus arteriosus.
  • Coarctation of aorta.
  • ASD.
  • Intracardiac obstructive lesions (pulmonary stenosis, aortic stenosis).
• Can be associated with abnormal moderator band or other ventricular wall anomalies.

Anatomical Classification (by location)

• Septum has:

  • Membranous part.
  • Muscular part (inlet, trabecular, outlet).

• Major anatomical types:

Size Classification (relative to aortic root)

• Compare defect diameter to aortic root diameter:

Hemodynamic Classification (by pressure)

• Based on pulmonary-to-systemic flow and pressure (Qp:Qs, CPQ ratio):
  • Small (restrictive) VSD: high pressure difference across defect, limited shunt.
  • Large (non‑restrictive) VSD: equalization of pressures in both ventricles; large shunt.
• With prolonged left‑to‑right shunt → increased pulmonary vascular resistance → pulmonary vascular obstructive disease → reversal of shunt (right‑to‑left) and Eisenmenger physiology.

Embryology & Natural History

• Interventricular septum forms from muscular ridge growing upwards and fusing with endocardial cushions.
• Small residual defects may remain.
• Spontaneous closure:
  • ~25% by 18 months.
  • Up to ~50% by 4–5 years.
  • Most small VSDs that will close do so by 9–10 years.
• Small VSDs: usually minimal symptoms, often detected as incidental murmur.
• Large VSDs: present early (4–6 weeks of age) with CCF and failure to thrive.

Clinical Features

• Depend on size:

Small VSD:

• Often asymptomatic.
• Normal growth and development.
• No heart failure.
• Prominent, loud pansystolic (holosystolic) murmur at lower left sternal border; often with palpable thrill.
• No or minimal cardiomegaly and minimal pulmonary overcirculation.

Moderate VSD:

• May have mild to moderate failure to thrive.
• Decreased exercise tolerance.
• More frequent respiratory infections.
• Signs of left ventricular volume overload.

Large VSD:

• Early, frequent congestive heart failure from 4–6 weeks of life.
• Marked failure to thrive.
• Recurrent chest infections and respiratory distress.
• With long‑standing large VSD: development of pulmonary hypertension and Eisenmenger syndrome.

Auscultation

• Pansystolic (holosystolic) murmur:
  • Best heard at lower left sternal border.
  • Due to continuous flow from left ventricle to right ventricle during systole.
• Precordial hyperactivity due to volume overload.
• Heart sounds:
  • S1: often normal or accentuated depending on AV valve flow.
  • P2:
    • Normal or mildly accentuated in small/moderate VSD.
    • Loud and single in severe pulmonary hypertension / Eisenmenger.
• Additional murmurs:
  • Mid‑diastolic flow murmur at apex or lower left sternal border if large shunt.
  • Possible murmurs of associated valve insufficiency.

ECG Features

• Small VSD: often normal or mild changes.
• Moderate VSD: left ventricular hypertrophy (LVH); sometimes left atrial enlargement.
• Large VSD:
  • Biventricular hypertrophy (LVH + RVH) as pulmonary vascular resistance increases.
  • With advanced pulmonary vascular disease: predominantly RVH.
• Postoperative:
  • Right bundle branch block (RBBB) is very common after surgical VSD closure.

Chest X‑ray

• Relation of findings to shunt magnitude:

• Degree of cardiomegaly and pulmonary vascular markings is directly related to magnitude of left‑to‑right shunt.

Complications

• Congestive cardiac failure (especially in moderate to large defects).
• Recurrent pulmonary infections.
• Pulmonary arterial hypertension → pulmonary vascular obstructive disease.
• Eisenmenger syndrome:
  • Chronic large VSD left untreated → increased pulmonary resistance → reversal of shunt (right‑to‑left).
  • Deoxygenated blood enters systemic circulation → cyanosis and clubbing.
• Infective endocarditis:
  • Turbulent high‑velocity jet predisposes to endocarditis.
  • Most frequently involves septal leaflet of tricuspid valve or adjacent structures.

Investigations

• Echocardiography (2D + Doppler):
  • Defines number, size, and exact location of defects.
  • Estimates pressures, Qp:Qs ratio (magnitude of shunt).
  • Detects associated lesions (ASD, outflow obstruction, AV valve abnormalities).
• Cardiac catheterization:
  • Not routine for all; used for hemodynamic assessment when needed.
  • Shows step‑up in oxygen saturation at right ventricle and pulmonary artery levels indicating left‑to‑right shunt.

Management

Medical Management

• For heart failure:
  • Diuretics, ACE inhibitors, digoxin as required (especially in large VSD).
  • Nutritional support, treat infections.
• Activity:
  • No exercise restriction if no pulmonary hypertension and no significant symptoms.
• Infective endocarditis prophylaxis:
  • Indicated in VSD (due to high‑velocity jet).
  • Not routinely indicated in isolated ASD.

Device Closure / Surgery

• Device closure:

  • Used for suitable perimembranous or muscular VSDs.
  • Technically more challenging for perimembranous defects (risk of conduction system injury, device embolization).
  • Potential complications: device embolization, hemolysis, heart block.

• Indications for surgical closure:

  • Significant left‑to‑right shunt:
    • Qp:Qs > 2:1 generally accepted as indication.
    • Qp:Qs > 1.5:1 with symptoms / LV volume overload.
  • Symptomatic infants with large VSD and heart failure not controlled with medical therapy.
  • Evidence of increasing pulmonary vascular resistance.
  • Prevention of Eisenmenger physiology.

• Timing:

  • Symptomatic infants with large VSD: surgery as early as possible in infancy (often by 6–12 months; sometimes earlier).
  • Infants responding to medical therapy: surgery by 12–18 months.
  • Asymptomatic children with significant shunt: usually before 4 years of age.
  • Small VSD with Qp:Qs < 1.5: generally no surgery; observe for spontaneous closure.

• Contraindication to closure:

  • Very high pulmonary vascular resistance approaching or exceeding systemic levels:
    • PVR/SVR ratio ≥ 0.5–0.6 (here transcript notes ≥0.4–0.5 as concerning).
    • Established, irreversible Eisenmenger syndrome.

Postoperative Complications

• Right bundle branch block (most common).
• Complete heart block (may require permanent pacemaker).
• Residual shunt in a minority.
• Neurologic complications related to circulatory arrest (rare).

Patent Ductus Arteriosus (PDA)

Definition & Anatomy

• Persistent patency of normal fetal connection between pulmonary artery and aorta after birth.
• Communication between descending aorta (near origin of left subclavian) and pulmonary artery.
• Normally closes functionally within 48–96 hours after birth, then anatomically later.
• Persistent patency beyond this period results in PDA (left‑to‑right shunt lesion).

Epidemiology & Associations

• More common in females.
• Classical in congenital rubella syndrome.
• In preterm babies:
  • Ductal wall (muscular media) is immature; PDA is very common.
  • In term babies, wall is better developed; closure more likely but some remain patent.

Hemodynamics

• After birth, systemic pressure > pulmonary pressure.
• Blood flows from aorta (left side, high pressure) to pulmonary artery (right side, lower pressure).
• Consequences:
  • Volume overload of pulmonary circulation and left heart.
  • Increased pulmonary blood flow → pulmonary congestion and infections.
  • Blood returns to left atrium and left ventricle → LV volume overload and cardiomegaly.
  • Large PDA: wide pulse pressure and bounding pulses due to runoff into pulmonary circulation.

Time Course of Closure

• Functional (physiological) closure:
  • Usually within 48–96 hours after birth in normal term newborns.
• If remains open beyond 96 hours:
  • Acts as persistent left‑to‑right shunt.
  • Leads progressively to pulmonary overcirculation and left heart overload.

Clinical Features

• Depend on size:

Small PDA:

• Often asymptomatic.
• Normal growth.
• Murmur may be the only finding.

Moderate to Large PDA:

• Congestive heart failure.
• Failure to thrive.
• Recurrent pneumonia, recurrent respiratory infections.
• Tachypnea, feeding difficulties in infants.
• Wide pulse pressure and bounding peripheral pulses:
  • Due to large difference between systolic and diastolic pressures (runoff into pulmonary artery).

Other Clinical Clues (very important for exams)

• Metabolic acidosis (due to poor systemic perfusion from runoff).
• Unexplained hypercapnia (CO₂ retention) on ABG.
• These are key clues for PDA in exam questions (especially in preterm).

Auscultation

• Continuous "machinery" murmur:

  • Best heard in second left intercostal space, just below left clavicle.
  • Continuous because flow persists in both systole and diastole (pressure gradient between aorta and pulmonary artery persists throughout cardiac cycle).

• With pulmonary hypertension and decreased gradient:

  • Murmur may shorten or become only systolic.
  • In very severe pulmonary vascular disease, murmur may disappear.

Chest X‑ray

• Findings:

ECG

• Left ventricular hypertrophy in large PDAs.
• In very large PDA with pulmonary vascular disease, biventricular hypertrophy can be seen.

Complications

• Congestive cardiac failure.
• Recurrent respiratory infections and chronic lung disease.
• Pulmonary hypertension; pulmonary vascular obstructive disease.
• Eisenmenger PDA (late):
  • Shunt reversal → cyanosis (often affecting lower body more if shunt is distal).
• Infective endarteritis / endocarditis involving ductus region or adjacent vessels.
• Neurologic complications (e.g., intraventricular hemorrhage in preterm as part of overall instability).
• Renal failure due to chronic low diastolic pressure and poor perfusion.

Management of PDA

General Measures

• Fluid restriction:
  • Very important in preterm infants with PDA and heart failure.
  • Reduces pulmonary congestion and workload on heart.
• Oxygen should be used judiciously; extreme hyperoxia may favor ductal closure, but in specific cyanotic lesions ductal patency may be desired.

Role of Diuretics / Inotropes / ACE inhibitors

• In contrast to VSD:
  • Diuretics/inotropes may be used for heart failure.
  • The transcript stresses that "inotropes" (referred to as "injection") have no specific role as primary PDA‑closing drug; main pharmacologic closure is with prostaglandin synthesis inhibitors.

Pharmacologic Closure (especially in preterm PDA)

• Goal: inhibit prostaglandin synthesis to induce ductal constriction.

• Drugs:

• In term babies:
  • Pharmacologic closure may be attempted, but if fails, device or surgical closure is considered.

Surgical / Device Closure

• Indications:
  • Hemodynamically significant PDA with symptoms.
  • Failure of medical therapy.
  • Risk of endarteritis.
• Techniques:
  • Surgical ligation or division (traditional).
  • Transcatheter coil or device closure (older infant/child).
• After closure, hemodynamics and symptoms improve; prognosis generally excellent.

Duct‑Dependent Circulation

Concept

• Some congenital heart diseases require a patent ductus arteriosus to maintain adequate systemic or pulmonary blood flow (hemodynamic stability).
• If duct closes in these conditions, severe hypoperfusion or hypoxemia and shock can occur.
• For such lesions, maintenance (not closure) of PDA is life‑saving.

Maintenance of Ductal Patency

• Prostaglandin E1 (PGE1) infusion:
  • Keeps ductus arteriosus open.
  • Used as emergency therapy in duct‑dependent lesions.
• Important: opposite pharmacologic strategy compared to closing a PDA.

Duct‑Dependent Systemic Circulation

• Conditions where systemic blood flow is blocked or severely reduced from left heart; duct is needed to supply systemic circulation:

• In these, closure of ductus causes acute systemic hypoperfusion and shock.

Duct‑Dependent Pulmonary Circulation

• Conditions where pulmonary blood flow is severely decreased; duct allows systemic blood to reach pulmonary artery:

• In these, closure of ductus → profound cyanosis and hypoxemia.

Parallel Circulation

• In some complex lesions (e.g., TAPVR and truncus arteriosus), parallel rather than series circulation occurs.
• The transcript notes:
  • TAPVR (total anomalous pulmonary venous return).
  • Truncus arteriosus.
• In such cases, mixing lesions and shunt pathways (including ASD, VSD, PDA) are critical to systemic and pulmonary flow balance.

Key Terms & Definitions

• Left‑to‑right shunt: movement of oxygenated blood from systemic side (left heart, aorta) to pulmonary side (right heart, pulmonary artery), resulting in volume overload of lungs and left heart.
• Pulmonary hypertension: increased pressure in pulmonary artery; may progress to irreversible pulmonary vascular disease.
• Eisenmenger syndrome: reversal of shunt (right‑to‑left) due to long‑standing pulmonary hypertension, causing cyanosis and clubbing.
• Perimembranous VSD: VSD involving membranous septum ± small adjacent muscular portion; most common anatomical type.
• Swiss cheese septum: multiple muscular VSDs giving perforated appearance; surgical closure is difficult.
• Duct‑dependent circulation: circulation in which PDA must remain open to maintain either systemic or pulmonary blood flow; requires PGE1 infusion.
• Continuous machinery murmur: classical continuous murmur of PDA, heard in second left intercostal space.
• Bounding pulse & wide pulse pressure: characteristic of large PDA due to high systolic and low diastolic pressure.

Action Items / Next Steps for Study

• Review four‑chamber cardiac anatomy and normal flow to apply concepts to any lesion.
• Memorize:
  • VSD classifications (anatomical, size, hemodynamic).
  • Age‑related spontaneous closure probabilities of small VSDs.
  • Key clinical differences between ASD, VSD, PDA on auscultation and X‑ray.
• Practice MCQs on:
  • Associations (Down syndrome with AVSD; rubella with PDA).
  • Clues like metabolic acidosis and CO₂ retention in PDA.
  • Duct‑dependent lesions and when to use PGE1 vs NSAIDs.
• Re‑draw schematics for:
  • Left‑to‑right shunt pathways in VSD, AVSD, PDA.
  • Eisenmenger transition (pressure changes and shunt reversal).
• Revise indications, timing, and contraindications for surgical/device closure of VSD and PDA.