eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology

Ventricular Septal Defect, Perimembranous

Author: Michael D Taylor, MD, PhD, Assistant Professor, Departments of Pediatrics (Division of Cardiology) and Radiology, Baylor College of Medicine, Texas Children's Hospital
Coauthor(s): Benjamin W Eidem, MD, FACC, FASE, FAAP, Associate Professor, Divisions of Pediatric Cardiology and Cardiovascular Diseases, Department of Pediatrics, Mayo Clinic College of Medicine
Contributor Information and Disclosures

Updated: Nov 25, 2008

Introduction

Background

Normal closure of the ventricular septum occurs through multiple concurrent embryologic mechanisms that help to close the membranous portion of the septum: (1) downward growth of the conotruncal ridges forming the outlet septum, (2) growth of the endocardial cushions forming the inlet septum, and (3) growth of the muscular septum forming the apical and mid-muscular portions of the septum.

Ventricular septal defects (VSDs) occur when any portion of the ventricular septum does not correctly form or if any of components do not appropriately grow together. The ventricular septum is complete by 6 weeks' gestation. VSDs are typically classified according to the location of the defect in one of the 4 ventricular components: the inlet septum, trabecular septum, outlet/infundibular septum, or membranous septum. This article specifically addresses defects in the trabecular muscular septum.

The precise etiology of muscular septal defect formation is unknown. However, the proposed mechanisms are many. Muscular defects may occur because of a lack of merging in the walls of the trabecular septum or because of excessive resorption of muscular tissue during ventricular growth and remodeling.

The precise etiology of any delay in closure is unknown. Perimembranous VSD is caused by failure of the endocardial cushions, the conotruncal ridges, and the muscular septum to fuse at a single point in space.

Perimembranous VSDs are located in the left ventricle outflow tract beneath the aortic valve. It is the most common VSD subtype in the United States, occurring in 75-80% of cases. Defects may extend into adjacent portions of the ventricular septum. When tissue forms on the right ventricular septal surface (often thought to be atrioventricular valvular in origin), it is termed an aneurysm of the membranous septum. Such tissue serves as a mechanism of spontaneous closure. The defect may be partially or completely occluded by the septal leaflet of the tricuspid valve.

Pathophysiology

Independent of the type of VSD, the hemodynamic significance is determined by 2 factors: the size of the defect and the resistance to flow out of the right ventricle, including the pulmonary vascular resistance (PVR) and anatomic right ventricular outflow obstruction.

In small-to-moderate VSDs, left-to-right shunting is primarily limited by the size of the defect. Conversely, in large VSDs without right ventricular outflow obstruction, the left-to-right shunting is determined by the relative degree of PVR and systemic vascular resistance.

Because PVR is high at birth and does not reach its nadir until age 6-8 weeks, the development of significant left-to-right shunting and pulmonary overcirculation, often termed congestive heart failure (CHF), can be delayed until the second or third month of life. Additional cardiac lesions that increase left-to-right shunting (eg, atrial septal defect, patent ductus arteriosus) may predispose patients to earlier development of CHF. Noncardiac abnormalities, including prematurity, infection, anemia, or other congenital anomalies also may predispose infants to significant symptoms of heart failure.

Additional congenital heart lesions (eg, muscular right ventricular outflow tract obstruction, pulmonary valve stenosis, pulmonary venous obstruction, persistent elevation of PVR, mitral stenosis) can restrict shunting, possibly leading to right-to-left trans-VSD flow, depending on the ultimate resistance balance between the systemic and the total right-sided resistances.

Frequency

United States

VSD is the most common congenital heart defect in the first 3 decades of life, with an incidence of 1.5-3.5 cases for every 1000 liveborn term infants. VSD is more common in premature infants with an incidence of 4.5-7 cases for every 1000 liveborn infants. Clinically significant VSD that requires medical or surgical management accounts for only 15% of such defects (0.35-0.50 cases for every 1000 live births). When viewing congenital heart disease in total, solitary VSD cases account for 20-40% of congenital heart disease. Perimembranous VSD is the most common type, accounting for as many as 50% of VSD cases identified in most surgical or autopsy series.

Mortality/Morbidity

Morbidity and mortality are influenced by the number and size of VSDs, the degree of left-to-right shunting, presence of associated congenital heart defects, presence of associated noncardiac defects and syndromes, and age at repair of VSD.

Perimembranous VSDs may spontaneously decrease in size and eventually close. Closure rates as high as 50% have been reported in some series. Patients with a small VSD have an excellent prognosis. Many small defects decrease in size or spontaneously close. Continued follow-up care is warranted until documented VSD closure occurs. Small perimembranous VSDs may lead to development of aortic insufficiency.

For patients with moderate-sized VSD, defects may allow the development of voluminous left-to-right shunting in the first few months of life as PVR falls. Failure of medical management with persistent evidence of CHF is the primary indication for surgical closure of moderate-sized defects. Fewer than 25% of moderate-sized defects require surgical closure.

For patients with large muscular VSDs, surgical repair is indicated at any time during the first year of life if the infant fails to grow appropriately despite optimal medical management. Surgical risk and mortality for patients with large VSDs is higher in the first 2 months of life (10-20%) than after age 6 months (1-2%), although these figures are currently decreasing. Elective surgical closure of large VSDs should be planned within the first year of life to prevent development of irreversible pulmonary vascular obstructive disease (ie, Eisenmenger syndrome).

Race

Inheritance patterns of different VSDs widely vary by race. Perimembranous VSD has no known racial predilection. Defects located in a subpulmonary position, such as supracristal defect, are more common in the Asian population.

Sex

VSDs are slightly more common in females than in males.

Age

Most perimembranous VSDs present clinically in the neonatal period secondary to a murmur. These defects, especially the smaller defects, are not typically suspected at birth and may not be identified by auscultation until PVR begins to fall in the first few days to weeks of life. Large perimembranous VSDs may not present until patients are aged 6-8 weeks, when decreased PVR allows significant left-to-right shunting and clinical signs and symptoms of CHF. VSDs may present soon after birth if associated with significant additional congenital heart lesions or if they occur with an associated chromosomal anomaly or syndrome.

Clinical

History

• Murmur
  • Most patients with small perimembranous ventricular septal defects (VSDs) are asymptomatic but come to medical attention because a systolic murmur is discovered.
  • Patients with isolated large perimembranous VSDs are typically asymptomatic in the newborn period.
• Progression of symptoms
  • Typically, infants with large VSDs present with signs and symptoms of pulmonary overcirculation or congestive heart failure (CHF) at age 6-8 weeks or older, as pulmonary vascular resistance (PVR) continues to fall and the degree of left-to-right shunting increases.
  • Signs and symptoms include poor feeding, decreased weight gain, tachypnea, tachycardia, sweating (especially with feeding), and lethargy.
• Chromosomal anomalies
  • VSDs are the most common congenital heart lesion (20-30%) in infants with chromosomal anomalies or syndromes.
  • These defects may be discovered in the first days of life when additional diagnostic evaluations are performed to exclude multiple congenital defects.

Physical

Size of the VSD and degree of left-to-right shunting significantly influence findings in a typical physical examination.

• Small VSDs
  • Normal vital signs with normal weight gain
  • Quiet precordium with normal apical impulse
  • Normal first heart sound
  • Narrowly split second heart sound; occasional accentuated pulmonary component
  • Absent third heart sound
  • Palpable thrill at the mid-to-lower left sternal border (very small VSDs)
  • A Grade II-VI/VI holosystolic murmur: A Grade II-VI/VI that widely radiates throughout the precordium is present along the left sternal border. The intensity of the murmur is usually inversely proportional to the size of the defect, the LV-to-RV pressure gradient, and the degree of left-to-right shunting. In general, smaller defects produce louder murmurs. Systolic murmurs from VSDs are usually holosystolic; they may occasionally sound crescendo or crescendo-decrescendo.
  • Absent diastolic murmur with small VSDs
• Large VSDs
  • Poor growth and weight gain occur.
  • Symptoms of CHF, including tachypnea, tachycardia, sweating, and pallor present.
  • Hyperdynamic precordium with or without precordial bulge is due to underlying cardiomegaly.
  • Abnormal apical impulse can present with or without right ventricular tap; a thrill is uncommon with large VSDs.
  • Normal first heart sound and a narrowly split second heart sound with occasional loud pulmonary component are evident
  • A loud holosystolic murmur with wide precordial radiation maximal at the left mid-sternal border.
  • A prominent third heart sound that produces a gallop rhythm typically is present at the apex.
  • A mid-diastolic flow rumble may be present at the cardiac apex. This diastolic murmur is caused by a significant (at least 2:1 ratio) left-to-right shunt with excessive flow across a normal mitral annulus.

Causes

• Inheritance
  • Perimembranous VSDs have a multifactorial etiology and are predominantly the result of spontaneous abnormalities in development.
  • No significant correlation between the cause of VSDs and the age of the mother or the birth order of the child is observed
• Associated syndromes
  • VSDs are the most common congenital heart lesion associated with chromosomal anomalies and syndromes.
  • VSDs are especially common in patients with trisomy 13, trisomy 18, and trisomy 21.
  • Nearly 95% of VSDs are not associated with chromosomal abnormalities.
• Associated noncardiac conditions
  • Prematurity
  • Syndromes and chromosomal anomalies
• Risk factors
  • Regular maternal cannabis use slightly increases the incidence of VSD.¹
  • The use of selective serotonin reuptake inhibitors (SSRIs) during early pregnancy slightly increases the incidence of VSD.²

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