The "a-dip" in M-mode of the pulmonary valve is caused by contraction of which structure?

The "a-dip" seen in M-mode of the pulmonary valve is specifically linked to the contraction of the right atrium. This dip represents the phase during which the right atrium contracts, pushing blood into the right ventricle and causing a brief moment of decreased jet flow through the pulmonary valve, which is effectively captured as the "a-dip" on the M-mode tracing.

It is important to understand the timing of cardiac events when interpreting M-mode echocardiograms; the "a-dip" occurs just after the P wave on an electrocardiogram (ECG), correlating with atrial contraction. This physiological understanding connects the observed M-mode pattern with the underlying cardiac anatomy and function, highlighting the role of the right atrium in this specific waveform.