Atrial Septal Defect: Understanding the Characteristic Heart Murmur

What Is the Typical Heart Murmur in Atrial Septal Defect?

In cases of atrial septal defect (ASD), the characteristic heart murmur is typically a 2-3/6 systolic ejection murmur heard best at the left sternal border, specifically in the second intercostal space. This sound results from the abnormal flow of blood between the heart's chambers. Since the left side of the heart operates under higher pressure than the right, blood flows from the left atrium to the right atrium through the defect in the septum.

This left-to-right shunting increases the volume of blood flowing into the right ventricle, causing it to enlarge. Despite the increased blood flow, the pulmonary valve remains normal. However, when the enlarged right ventricle meets the normal-sized pulmonary valve, it can create a functional obstruction, leading to a murmur that can be detected during a physical examination.

Key Auscultatory Findings in Atrial Septal Defect

One of the most diagnostic signs of ASD is a fixed splitting of the second heart sound (S2), particularly at the pulmonic area. This fixed splitting remains constant regardless of the patient's breathing pattern, making it a hallmark of atrial septal defects.

In addition to the systolic ejection murmur, a murmur related to relative tricuspid valve stenosis may be heard in the pulmonic area. These combined findings help clinicians identify the condition and differentiate it from other congenital heart defects.

How Murmurs Evolve as the Disease Progresses

As the condition progresses, especially in cases with significant left-to-right shunting, additional auscultatory changes may occur. When pulmonary blood flow dramatically increases, exceeding systemic circulation, a mid-diastolic murmur due to relative tricuspid stenosis may be detected at the lower left sternal border (fourth to fifth intercostal spaces).

With further progression, if pulmonary hypertension develops, the dynamics of blood flow change. The right ventricle pumps less blood into the pulmonary artery, leading to a decrease in the intensity of the systolic murmur. At this stage, the fixed splitting of S2 may disappear, and signs of pulmonary hypertension become more prominent.

Advanced Signs of Atrial Septal Defect

In later stages of the disease, regurgitant murmurs may appear. A systolic murmur of tricuspid regurgitation can often be heard at the tricuspid area, while a diastolic murmur of pulmonary regurgitation may be detected at the pulmonic area. These findings suggest complications related to long-standing volume overload and pulmonary hypertension.