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Ventricular Septal Defect

Authors: Merry Faye Graff, Ryan Wilkie Reviewers: Julena Foglia, Dave Nicholl, Taylor Krawec, Emily J. Doucette, Andrew Grant* Danielle Nelson* * MD at time of publication Legend: Ventricular Septal Defect (VSD): Pathogenesis and clinical findings Variants in genes involved in cardiac development (e.g., GATA4) DiGeorge syndrome** (deletion on chromosome 22q11) Holt-Oram syndrome (TBX5 mutations) Down syndrome** (Trisomy 21) (more commonly AVSD) CHARGE syndrome Infection Medication (e.g., isoretinoin) Uncontrolled metabolic conditions (e.g., diabetes**) Environmental exposures (e.g., alcohol) Genetic factors that ↑ susceptibility Complex interplay between genetic susceptibility & environmental factors Maternal factors during pregnancy that ↑ risk Disruption in formation of interventricular septum during fetal heart development Ventricular Septal Defect (VSD) Defect in interventricular septum that allows blood to shunt from the left ventricle (LV) to the right ventricle (RV) LV pumps against high systemic vascular resistance (SVR) & RV pumps against lower pulmonary vascular resistance (↓ after birth) Blood flows through VSD from LV to RV during systole (left-to-right shunt) Small defect (<4 mm) between ventricles Moderate (4-6 mm) to large defect (>6 mm) between ventricles Narrow (restrictive) defect between ventricles provides intrinsic resistance to flow Wide (unrestrictive) defect between ventricles offers little resistance to blood flow ↑ Volume of blood in pulmonary circulation ↑ Turbulent blood flow through small defect ↓ Turbulent blood through large defect Pulmonary arterial hypertension (PAH)** ↑ Pulmonary venous return to left heart Grade 3 to 5/6 harsh holosystolic murmur Grade 1 to 2/6, mid-frequency, holosystolic murmur Loud pulmonic S2 on auscultation ↑ Pulmonary vascular markings on x-ray LV undergoes eccentric hypertrophy to accommodate chronic ↑ volume ↑ Left atrial pressure Dilation of tricuspid annulus LV dilation & myocardial stretch impairs contractile function Lateral displacement of cardiac apex on x-ray Mitral regurgitation Impaired ejection (systolic dysfunction) results in ↓ stroke volume & ejection fraction ↑ LV end-diastolic pressure ↑ Pulmonary venous pressure Mid-diastolic murmur ↓ Cardiac output (CO) Left heart failure** Pulmonary edema (fluid accumulation in pulmonary interstitium & alveoli) Sympathetic nervous system is activated Systemic venous congestion Renin-angiotensin aldosterone system** is activated ↑ Work of breathing Diaphoresis Pallor ↑ Heart (excessive rate sweating) Peripheral edema Hepatomegaly Na+ & fluid retention Shortness of breath ↑ Respiratory rate **See corresponding Calgary Guide slide Complications Published Oct 17, 2015; updated Dec 7, 2025 on www.thecalgaryguide.com Prolonged PAH drives reactive constriction & permanent remodeling of pulmonary vessels Chronic ↑ RV afterload Irreversible PAH RV hypertrophy & dilation to overcome ↑ afterload Dilation ↑ RV wall stress ↑ RV stretch impairs ability to eject blood ↑ RV end-diastolic pressure RV pressure > LV pressure Right heart failure** Eisenmenger syndrome** (shunt reversal, right-to-left shunt) Pathophysiology Mechanism Sign/Symptom/Lab Finding