A 60 year old frail male who had been hospitalised for 2 weeks develops onset of acute breathlessness and haemoptysis.His EKG shows Q wave and T inversion in lead III and prominent S wave in lead I.Atrial blood gasshowed PaO2 66 mm Hg, PaCO2 30 mm Hg and pH 7.42.The most useful investigation in his case would be -

A 60 year old frail male who had been hospitalised for 2 weeks develop

1.	A 60 year old frail male who had been hospitalised for 2 weeks develops onset of acute breathlessness and haemoptysis.His EKG shows Q wave and T inversion in lead III and prominent S wave in lead I.Atrial blood gasshowed PaO2 66 mm Hg, PaCO2 30 mm Hg and pH 7.42.The most useful investigation in his case would be -
A.	Chest X-ray
B.	Echocardiography
C.	Ventilation perfusion scan
D.	Serum LDH estimation
Answer» D. Serum LDH estimation