Which measurement is indicated by the arrow on this image?

The Doppler tissue imaging waveform shown indicates the systolic annular velocity of the tricuspid valve annulus, labeled as S’. This measurement reflects right ventricular systolic function by quantifying the velocity of longitudinal myocardial motion during systole.

The a’ wave corresponds to atrial contraction, not systole. S’ assesses systolic function, whereas e’ and a’ relate to diastolic phases.

This assessment method is detailed in the "Textbook of Clinical Echocardiography, 6e", Chapter on Right Ventricular Function and Tissue Doppler Imaging【20:320-325†Textbook of Clinical Echocardiography】.