Typically at end-systole, the interventricular septum (IVS) bows rightward as the left ventricle’s pressure (LV) exceeds that of the right ventricle (RV). However, when the RV is strained (e.g., massive pulmonary embolism), the pressure overload can lead to flattening or even paradoxical bowing of the IVS. In a short-axis view of both ventricles, this can lead to the characteristic “D-sign” indicative of RV strain.
Here’s a chest CT (PE protocol) showing this finding. Note that this imaging is timed for contrast in the pulmonary artery (not shown), so the RV remains enhanced, whereas contrast has not quite reached the LV. Nevertheless, one can appreciate the large RV:LV size ratio and the “D-sign” in red.
Furthermore, the parasternal short-axis view on transthoracic echocardiography shows the same finding of RV strain.
Here’s another parasternal short-axis view demonstrating RV pressure and volume overload.