<prompt> Diagnostic of acute pulmonary embolism isChest radiographESRECG changesD-dimer assay  <response>: Ans. d D-dimer assay. Ref. Harrison, Medicine, 18thChapter 103; fig. 58-2EVALUATION OF ACUTE PULMONARY EMBOLISM ECG may show RV hypertrophy with strain, RBBB, increased HR and T-wave inversion in V1 to V4. CXR is frequently normal. However Palla sign enlarged right descending pulmonary artery or Westermarks sign decreased pulmonary vascular markings peripherally or Hamptons hump. If clinical likelihood is low, then d-dimer, ELISA and USG lower extremities are done D-dimer is elevated in number of conditions other than pulmonary embolism, however, a negative D-dimer assay suggests that likelihood of PE is low. Patients with a low likelihood of DVT or a low-to-moderate likelihood of PE can undergo initial diagnostic evaluation with d-dimer testing alone without obligatory imaging tests. If the d-dimer is abnormally elevated, imaging tests are the next step VP lung scans are done in any stable patient with suspicion of PE and are investigation of choice. CT with contrast may be helpful, and may supplement VP Scan in coming days. Pulmonary arteriography is gold-standard and definitive 