6.4. Pulmonary embolism
Pulmonary embolism is a common and potentially lethal condition that can cause death in all age groups. A good clinician should consider the diagnosis if any suspicion of pulmonary embolism exists, because prompt diagnosis and treatment can dramatically reduce the morbidity and mortality of the disease. This pathological state is a blockage of the main artery of the lung or one of its branches by a substance that has traveled from elsewhere in the body through the bloodstream. Usually this is due to embolism of a thrombus (blood clot) from the deep veins in the legs, a process termed venous thromboembolism. A small proportion is due to the embolization of air, fat or amniotic fluid. The obstruction of the blood flow through the lungs and the resultant pressure on the right ventricle of the heart leads to the symptoms and signs of pulmonary embolism.
The commonest finding on electrocardiogram in pulmonary embolism is sinus tachycardia. Pulmonary embolism can occur without significant electrocardiographic abnormalities.
ECG may also show right ventricular ischemia, incomplete right bundle branch block pattern or S1Q3T3 pattern (S waves in lead I, Q waves and T wave inversion in lead III). These findings are due to the pressure and volume overload over the right ventricle which causes repolarization abnormalities. T wave inversion in leads V1 to V3 may indicate right ventricular dysfunction in pulmonary embolism. T inversion in inferior leads can also occur in pulmonary embolism. Right axis deviation is another important feature of pulmonary embolism, which is also indicated by the S waves in lead I in the S1Q3T3 pattern.