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

Ventricular Septal Defect, Muscular

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.

Trabecular (muscular) VSD is the second most common type of VSD, occurring in 5-20% of most series. Trabecular muscular VSDs are divided into separate distinct regional groups including midmuscular, apical, anterior, and posterior.¹ Midmuscular is the most common subtype of muscular VSD. Defects occurring centrally or along the margin of the interventricular septum and free wall are termed anterior VSDs. When multiple muscular VSDs occur with a very large communication between the ventricles, it is also known as "Swiss cheese" VSD. Frequently, spontaneous closure of small muscular VSDs occurs in the first 2 years of life (most by age 6 mo).

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

Without regard to type, VSD is the most common congenital heart defect in the first 3 decades of life, with an incidence between 1.5-4.2 cases for every 1000 live term infants. One study described an incidence of muscular VSD of 2.7 cases per 1000 live births.² VSD is more common in premature infants, with an incidence of 4.5-7 cases for every 1000 live births. 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% of congenital heart disease. Muscular VSD is the second most common type, accounting for as many as 40% of VSD cases identified in most surgical or autopsy series.

International

The prevalance of VSD worldwide is relatively constant. However, the type of VSD that predominates in a region widely varies. In the United States, perimembranous VSDs are most common. In Asia, subaortic VSDs (outlet type) are most common.³

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.

Muscular VSDs may spontaneously decrease in size and eventually close. Small muscular VSDs have the greatest likelihood of spontaneous closure, with closure rates approaching 80-90% by age 2 years. Muscular defects in these patients decrease in size due to growth of the ventricular myocardium, which fills in the defect. One study that used fetal echocardiography showed that 33% of all defects closed in utero, 44% of defects spontaneously closed within the first postnatal year, and 23% of defects did not close.⁴

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).

Multiple muscular VSDs, also known as "Swiss cheese" ventricular septum, are significantly more complex. Patients often show early signs of CHF. This lesion may require staged surgical palliation.

Race

Muscular VSD has no known significant racial predilection.

Sex

VSD is slightly more common in females than in males.

Age

Large muscular VSD may not present until age 6-8 weeks, when decreased PVR allows significant left-to-right shunting and clinical signs and symptoms of CHF. Most muscular VSDs present clinically in the neonatal period. Typically, these defects, especially the smaller defects, are not suspected at birth and may not be identified by auscultation until PVR begins to fall in the first few days to weeks of life. The VSD may manifest soon after birth if it is associated with significant additional congenital heart lesions or if it occurs with an associated chromosomal anomaly or syndrome.

Clinical

History

• Murmur
  • Most patients with small muscular ventricular septal defects (VSDs) are asymptomatic and come to medical attention due to the discovery of a systolic murmur.
  • Most murmurs have a delayed presentation in the newborn period, occurring in the first few days to weeks of age.
  • At birth, pulmonary vascular resistance (PVR) is high, which maintains an elevated right ventricular pressure equal to left ventricular pressure. As the PVR falls, the developing pressure gradient from left ventricle to the right ventricle allows high-velocity left-to-right shunting across the muscular VSD producing the typical holosystolic murmur.
• Progression of symptoms
  • Patients with an isolated large muscular VSD are typically asymptomatic in the immediate newborn period.
  • As PVR falls, the degree of left-to-right shunting is proportional to the size of the defect and the relative degree of PVR.
  • Congestive heart failure (CHF) signs include inadequate weight gain and growth along with recurrent lower respiratory tract infections in patients with large VSD without evidence of CHF but with elevated pulmonary artery pressure (greater than 50% systemic pressure) or greater than a ratio of 2:1.
  • The larger the VSD and the lower the PVR, the greater is the degree of left-to-right shunting.
  • Typically, infants with large VSDs present with signs and symptoms of CHF at age 6-8 weeks or later as 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 after feeding), and lethargy.
• Chromosomal anomalies
  • VSD is the most common congenital heart lesion (20-30%) in infants with chromosomal anomalies or syndromes.
  • Defects may be discovered in the first days of life due to additional diagnostic evaluation to exclude multiple congenital defects.

Physical

Typical physical examination findings are influenced to a significant degree by the size of the VSD and the degree of left-to-right shunting.

• Small VSD
  • Vital signs and weight gain are normal.
  • The precordium is quiet with a normal apical impulse.
  • The first heart sound is normal.
  • The second heart sound is typically narrowly split. The pulmonary component may be accentuated.
  • A third heart sound is generally not present.
  • A palpable thrill may be observed at the middle-to-lower left sternal border.
  • A grade III-VI/VI holosystolic murmur, which widely radiates throughout the precordium, is present along the left sternal border.
  • Intensity of the murmur is inversely proportional to the size of the defect, the left ventricle–to–right ventricle pressure gradient, and the degree of left-to-right shunting. In general, smaller defects produce the loudest murmur.
  • Systolic murmurs are usually holosystolic but may occasionally be crescendo or crescendo-decrescendo.
  • No diastolic murmur is typically present.
• Large VSD
  • Poor growth and poor weight gain are common.
  • Signs and symptoms of CHF may be present, including tachypnea, tachycardia, sweating, and pallor.
  • Hyperdynamic precordium with or without a precordial bulge secondary to underlying cardiomegaly.
  • Abnormal apical impulse with or without right ventricular tap is present; a thrill is uncommon with large VSDs.
  • A normal first heart sound and a narrowly split second heart sound with a loud pulmonary component are evident.
  • A prominent third heart sound is typically present at the apex, producing a gallop rhythm.
  • A II-III/VI holosystolic murmur is maximal at the left sternal border with wide precordial radiation.
  • A diastolic flow rumble may be present at the cardiac apex. This diastolic murmur is caused by a significant left-to-right shunt (at least a 2:1 left-to-right shunt) with excessive flow across a normal-sized mitral annulus.

Causes

• Inheritance
  • Muscular VSDs have a multifactorial etiology and are predominantly the result of spontaneous abnormalities in development.⁵
  • No correlation with maternal age or birth order is observed.
• Associated syndromes
  • VSD is the most common congenital heart lesion in most chromosomal anomalies and syndromes.
  • VSD is especially common in patients with trisomy 13, trisomy 18, and trisomy 21. In addition, there are numerous single gene deletion syndromes associated with VSDs.
  • The majority of VSDs (>95%) are not associated with chromosomal abnormalities.
• Associated noncardiac conditions
  • Prematurity
  • Syndromes and chromosomal anomalies
• Risk factors
  • Regular maternal cannabis slightly increases the incidence of VSD.⁶
  • The use of selective serotonin reuptake inhibitors (SSRIs) during early pregnancy slightly increases the incidence of VSD.⁷

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