What does the dicrotic notch on an arterial pressure tracing signify?

• A. The dicrotic notch marks aortic valve closure; end of systole and start of diastole.
• B. The dicrotic notch marks mitral valve closure; onset of atrial contraction.
• C. The notch indicates the systolic peak pressure of the aorta.
• D. The notch marks the opening of the aortic valve.

Answer: (A)

The dicrotic notch signals a switch from systole to diastole. It appears on the arterial pressure trace right after the systolic peak and is produced when the aortic valve closes. That closure causes a brief brief backflow against a closed valve, which creates a small secondary deflection—the notch—and marks the start of diastolic pressure.

So this notch isn’t about mitral valve closure (which happens at the start of systole) or about the opening of the aortic valve (that occurs at the beginning of systole). It also isn’t the systolic peak itself—the peak is the highest point during ejection, whereas the notch comes right after it.