USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What structural change is seen in the heart morphology of Atrial Septal Defect (ASD)?

1. Right ventricular hypertrophy (RVH)

2. Concentric left ventricular hypertrophy (LVH)

3. Left atrial enlargement (LA)

4. Right atrial dilatation (RA)

The correct answer is: Right atrial dilatation (RA)

In the case of Atrial Septal Defect (ASD), the primary structural change observed in heart morphology is right atrial dilation. This occurs due to the left-to-right shunting of blood caused by the defect in the atrial septum, which allows oxygenated blood from the left atrium to flow into the right atrium. The increased volume of blood entering the right atrium results in its dilation as it accommodates the excess blood volume. Furthermore, the right ventricle often experiences increased blood flow as well, which can lead to contributions to right ventricular changes over time, but the most specific and direct consequence of an ASD is the dilation of the right atrium. This process can also eventually affect the right ventricle and overall heart function, emphasizing the importance of recognizing the initial changes that occur in the atria due to the defect itself. Left ventricular hypertrophy or concentric hypertrophy, as well as left atrial enlargement, are not standard morphological changes associated with ASD. Instead, those changes are typically seen in conditions that involve increased pressure or volume loading on the left side of the heart, such as aortic stenosis or mitral valve disease. Therefore, understanding that right atrial dilation is the hallmark change