Pulmonary Embolism Quiz

See Investigations. Option D is correct. The ECG in pulmonary embolism is often normal or non-specific, and the finding seen most often is sinus tachycardia. The heart speeds up because the obstructed pulmonary circulation, low oxygen levels, pain and anxiety all trigger the sympathetic nervous system, and because reduced forward flow of blood makes the heart beat faster to keep up. Other changes include non-specific ST-segment and T-wave changes, right axis deviation (the main electrical direction of the heart swings to the right) and right bundle branch block (delayed conduction down the right bundle of the heart), reflecting strain on the right ventricle. The famous S1Q3T3 pattern (a deep S wave in lead I, a Q wave and an inverted T wave in lead III) is moderately specific but occurs in only about 5% of patients. The ECG cannot diagnose PE. Its main use is to look for other causes of chest pain, such as a heart attack. A simple memory aid: the classic sign is rare and the common sign is boring, so expect a fast pulse rather than S1Q3T3.

• Commonest finding: sinus tachycardia, though the ECG is often normal or non-specific
• Other changes: non-specific ST-segment and T-wave changes, right axis deviation and right bundle branch block
• S1Q3T3: moderately specific but seen in only about 5% of patients
• Limit: the ECG cannot diagnose PE and mainly helps to look for other causes of chest pain