Atrial Septal Defect: Key Concepts Explained

Shunt Assessment with Echocardiography

Background

The human heart is the engine that circulates blood throughout the body, supplying oxygen and nutrients to tissues and organs while removing waste products like carbon dioxide. When an intracardiac shunt is present, blood can travel from areas of higher pressure to lower pressure and ultimately disrupt the circulation of blood throughout the human body.

There are four types of atrial septal defects (ASD), with the secundum ASD being the most common. This type of defect can be effectively assessed using echocardiography. Key parameters to evaluate include right heart remodeling, pulmonary hypertension, flow patterns, and the Qp:Qs ratio. In today’s session, we will explore a case involving a left-to-right shunt and share useful scanning tips and techniques.

Key Concepts

When additional blood flow enters the right heart through an ASD, the primary concern should be: “How does this extra volume affect the right side of the heart?” Volume overload can lead to enlargement of the right atrium and right ventricle. According to the Frank-Starling law, the heart’s stroke volume increases as the amount of blood it receives (end-diastolic volume or preload) rises, but only up to a certain limit.

The right ventricle will dilate to accommodate the increased preload, causing the myocardial fibers to stretch. This results in a more forceful contraction and an increased stroke volume. However, as this added volume persists over time, the heart’s pumping efficiency declines, which can eventually lead to heart failure. A significant atrial septal defect can reduce contractility, further decreasing stroke volume and cardiac output.

Now, let’s explore even deeper insights into how the art of echocardiography can reveal the full impact of an ASD on the heart—available exclusively to our premium subscribers.