Cor Pulmonale from Repeated Pulmonary Embolism

Introduction Though Virchow (1856) recognized that antemortem clots in the pulmonary arteries were usually due to emboli, for many years thrombosis in situ was regarded as more frequent. Belt (I939a) showed conclusively that pulmonary infarction was due to embolism in the majority of cases, and usually originated in phlebothrombosis in the lower limbs or pelvis. Thrombosis frequently complicates embolism, and may also occur on local lesions of the pulmonary arteries. In longstanding cases when the clot is partly organized an underlying embolus is difficult to identify. Both thrombosis and embolism in the pulmonary arteries are frequent complications of pulmonary hypertension. Atheromatous plaques in the pulmonary arteries may be the site of thrombosis, and the low cardiac output favours thrombosis in the leg veins which gives rise to emboli. Immobilization is an important factor reducing venous flow and producing phlebothrombosis in the legs or pelvis after surgical operations and in the puerperium. Pulmonary emboli frequently arise from these thrombi, and may complicate thrombophlebitis in varicose veins or following injury or infection. The effects of a pulmonary embolus depend on the size of the vessel which is blocked. In the smaller arteries no change in the lung can be detected, but in a larger vessel occlusion is followed by infarction of the lung distal to the obstruction. Emboli in the main pulmonary arteries do not produce striking effects unless more than twothirds of the pulmonary circulation is blocked. There may be transient faintness, dyspnoea, dry cough, or a sense of tightness in the chest. Some patients show a temporary rise in systemic venous pressure (Wood, 1956). When obstruction to the pulmonary blood flow exceeds the critical level there is a sudden fall of cardiac output producing the clinical picture of acute cor pulmonale. These patients often die within a few days, but survivors show right ventricular failure which gradually resolves, though recurrence is frequent. The clinical evidence of repeated pulmonary embolism thus varies greatly. There may be dramatic major attacks or transient symptoms of doubtful significance. Some episodes are completely silent. Attacks of pulmonary infarction with pleuritic pain and haemoptyses are frequent and may be mistakenly diagnosed as pneumonia (Evans, I956). Each pulmonary embolus is quickly impacted in the pulmonary arterial tree and becomes reduced in size, so decreasing the obstruction to blood flow. In some patients after repeated pulmonary embolism the pulmonary artery pressure becomes permanently raised. Unless some other mechanism is operating, this implies that recurrent embolism or secondary thrombosis is continuing throughout the course of the disease. Wood (I956) suggests that in a proportion of subjects a rise in pulmonary artery pressure, whatever the cause, initiates vasoconstriction in the pulmonary vascular bed. The raised pulmonary artery pressure itself produces intimal proliferation in the smaller vessels which also tends to increase the obstruction. These changes are probably responsible for the sustained pulmonary hypertension that may follow repeated pulmonary embolism. These patients present with evidence of pulmonary hypertension in the absence of other cardiac or parenchymal lung disease, and if untreated progressively deteriorate and die with intractable right ventricular failure.