The dicrotic notch, often noted on a pressure waveform rather than directly on an ECG, is a small dip that occurs after the main upstroke in the arterial pressure tracing. It’s related to the closure of the aortic valve and the subsequent backflow of blood that creates this characteristic dip.
The dicrotic notch is primarily caused by the following events:
- Aortic Valve Closure: When the left ventricle contracts and blood is ejected into the aorta, the aortic valve opens. After the ventricle finishes contracting, the valve closes, and this closure results in a momentary increase in pressure in the aorta, followed by a decrease.
- Elastic Recoil: The aorta is highly elastic and can stretch during systole (when the heart beats). Once the blood flows into the aorta and the pressure from the left ventricle decreases, the elastic walls of the aorta spring back, which contributes to the dicrotic notch.
- Peripheral Resistance: The notch is also influenced by the resistance of smaller arteries. High peripheral resistance can enhance the dicrotic notch, making it more prominent on the pressure tracing.
While the dicrotic notch is not displayed on the ECG itself, understanding its relationship to the cardiac cycle, especially during the phases of ventricular contraction and relaxation, is vital in interpreting cardiovascular health.