Ventricular Septal Defect (VSD)

Overview

Definition

A ventricular septal defect (VSD) is a malformation of the interventricular septum (IVS) resulting in an abnormal communication between the left ventricle (LV) and the right ventricle (RV). This defect may present in isolation, or be a part of another anomaly, such as tetralogy of Fallot.

Classification

There are 4 main subtypes of VSD based on location along IVS:

1. Membranous (75% of cases):
   • Also called perimembranous or conoventricular
   • Most common subtype
   • Located at distal conal septum (just inferior to aortic valve)
   • In proximity to bundle of His
2. Muscular (20%):
   • Located along trabeculated muscular septum
   • Classified as anterior, mid-muscular, apical, or posterior
   • Common in premature infants
   • May be multiple
   • Most likely to undergo spontaneous closure
3. Inlet (5%):
   • Also called AV canal defect
   • Located around tricuspid annulus (inlet)
   • Always accompanies other endocardial cushion defects
   • Will not close spontaneously
4. Supracristal (5%):
   • Also called outlet defect
   • Located inferior to pulmonic valve at right ventricular outflow tract
   • More common in Asian population
   • Will not close spontaneously

Epidemiology

• The most common congenital heart defect (CHD): 25% of all CHDs
• Incidence: 5–50/1,000 live births
• Increased risk:
  • Family history: 3x increase
  • Maternal factors:
    • Obesity
    • Diabetes
    • Alcohol use → muscular VSD

Etiology

Exact mechanism is unknown. Genetic syndromes:

• Down syndrome (Trisomy 21)
• Patau’s syndrome (Trisomy 13)
• Edwards’ syndrome (Trisomy 18)

Pathophysiology and Clinical Presentation

Pathophysiology

Physiologic changes occur based on the size of the defect and the resistance across which the blood has to flow.

• Small VSD:
  • < 4 mm
  • Minimal left-to-right shunting due to high resistance within defect
  • Maintains RV pressure to normal
  • Rarely causes heart failure
• Moderate VSD:
  • 4–6 mm
  • Left-to-right shunt
  • Higher resistance (smaller defect) → pulmonary artery pressure < 50% of systemic pressure → least amount of change within ventricles and pulmonary circulation
  • Lower resistance (larger defect) → pulmonary artery pressure is > 50% of systemic pressure → pulmonary congestion and LV remodeling
• Large VSD:
  • > 6 mm
  • Very little resistance to flow across defect
  • Left-to-right shunt equalizes pressure between RV and LV
  • After birth, as fetal pulmonary vascular resistance (PVR) decreases → increased pulmonary blood flow → pulmonary hypertension → RV hypertrophy
  • Eisenmenger’s syndrome can occur once RV pressure is higher → right-to-left shunting and cyanosis

Clinical presentation

Age of presentation is usually around 2 months, unless a larger defect is present which becomes symptomatic within weeks of birth.

• Small VSD:
  • Usually asymptomatic
  • Incidental murmur
• Moderate/large VSD:
  • Poor feeding (sweating or fatigue)
  • Poor weight gain
  • Shortness of breath
  • Recurrent lung infections
  • Infective endocarditis

Diagnosis

Physical examination

• General appearance:
  • Pallor
  • Failure to thrive
• Precordial exam:
  • Displaced apex
  • Systolic thrill
  • Murmur:
    • Small VSD:
      • Harsh holosystolic
      • Grade 2 or 3
      • Left lower sternal border
    • Large VSD:
      • Systolic murmur with diastolic rumble (apex)
      • No murmur, if severe
• Signs of respiratory failure:
  • Tachypnea
  • Grunting
  • Nasal flaring
  • Retraction
  • Hypoxia
• Signs of heart failure:
  • Hepatomegaly
  • Tachycardia
  • S3 and S4 heart sounds

Imaging

• Echocardiography with color doppler: 
  • Confirmatory (can be done prenatally)
  • Evaluates:
    • Type and location
    • Size of defect
    • Extent of left-to-right shunt
    • Pulmonary arterial pressure
• Chest X-ray:
  • Increased pulmonary vascularization
  • Cardiomegaly
• ECG:
  • Normal in smaller defects
  • Moderate-to-large defects may show LV and RV hypertrophy

Management

Management

The management of a VSD is based on the size of the defect and the clinical symptoms of the patient.

• Small VSD/asymptomatic infant:
  • Re-evaluate every 2 years, if murmur present.
  • Follow up yearly to assess development of symptoms.
  • Majority will close spontaneously.
• Asymptomatic moderate-to-large VSD:
  • Regular follow-up with echocardiogram to assess hemodynamic stability.
  • Surgically repair once LV dilation occurs.
• Symptomatic patient:
  • Mild:
    • Adequate growth with mild tachypnea
    • Medical management
  • Moderate:
    • Signs of failure to thrive
    • Medical management with caloric intake
    • Bridge to surgical repair
  • Severe: 
    • Symptoms of heart and/or respiratory failure
    • Inpatient medical stabilization followed by immediate surgical repair
• Medical management:
  • Nutritional support
  • Heart failure → diuretics
  • Up-to-date vaccines
• Surgical management involves repairing defect with patch, usually before age of 1.

Prognosis

• Excellent long-term survival
• Majority of small and asymptomatic moderate VSD spontaneously close.
• Complications post-surgical repair are rare

Clinical Relevance

The following conditions are associated with VSD and can cause or modify the disease:

• Congestive heart failure: large VSD may result in severe left-to-right shunt causing reduced LV stroke volume, plus higher cardiac output from RV. This leads to pulmonary congestion and eventually right-sided heart failure.
• Failure to thrive: suboptimal weight gain and growth in children. As with majority of CHDs, 1st presentation of VSD may be infant or child failing to meet necessary caloric requirement for growth due to increased demand of overworking heart.
• Endocarditis: growth of infectious vegetations on endothelium of heart. Patients with VSDs are at increased risk of developing it.
• Aortic insufficiency: inability of AV to remain shut during diastole, causing reversed flow into LV. Due to low-pressure zone created in LV through VSD, AV prolapses and becomes insufficient.