A CT pulmonary angiogram shows a saddle embolus straddling the main pulmonary artery bifurcation with right heart strain (RV:LV ratio >1.0, interventricular septum D-sign). What does the D-sign indicate?
- A Left ventricular pressure overload with septal flattening towards the right
- B Right ventricular pressure overload causing septal flattening towards the left ventricle ✓
- C Pericardial effusion with cardiac tamponade
- D Pulmonary hypertension from mitral stenosis
Correct answer: B. Right ventricular pressure overload causing septal flattening towards the left ventricle
Explanation
The D-sign on CT describes flattening or bowing of the interventricular septum towards the left ventricle, caused by right ventricular pressure overload (as in massive pulmonary embolism). Elevated RV pressure exceeds LV diastolic pressure, pushing the septum leftward, giving the LV a D-shaped appearance on axial CT. An RV:LV diameter ratio >1.0 combined with the D-sign indicates right heart strain and predicts a high-risk, potentially fatal PE course, guiding thrombolytic therapy decisions.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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