A 60-year-old male hypeensive had a stroke 2 weeks prior to this sudden attack of dyspnea. The present ECG shows changes of S1 Q3 T3 and the V/Q pulmonary scan shows major areas of reduced perfusion. What is the probable diagnosis?

Dyspnoea is the most common symptom of pulmonary embolism,and tachypnoea is the most common sign.ECG in pulmonary embolism shows sinus tachycardia ,and S1Q3T3 sign-an S wave in lead I,a Q wave in lead III,and an inveed T wave in lead III.V/Q scan can be done if there is no previous cardiopulmonary disease,& it shows major areas of reduced perfusion due to increased pulmonary vascular resistance & impaired gas exchange. Reference:Harrison's medicine-18th edition,page no:2170-2172;Davidson's medicine-22nd edition,page no:722.