Acute massive pulmonary embolism is an emergency requiring immediate treatment. The right heart functional reserve is the major determinant of acute survival. Because most of the deaths resulting from the initial haemodynamic insult occur either immediately or within a few hours, the relief of pulmonary vascular obstruction must be as fast as possible. This can be achieved by thrombolytic treatment, perhaps combined with mechanical fragmentation of the clot through catheter techniques, or by embolectomy. All these measures have inherent risks and must therefore be applied only in patients with unequivocal evidence that the acute haemodynamic failure is caused by massive pulmonary embolism. Morbidity and mortality of patients receiving thrombolysis or embolectomy with an incorrect diagnosis will be very high. In order to initiate aggressive treatment without delay, the challenge is to diagnose this disorder promptly. The problems are magnified by the fact that patients with massive pulmonary embolism are often too ill to transport to locations where diagnostic tests can be carried out.

Acute massive pulmonary embolism should be suspected in hypotensive, cyanotic, and dyspnoeic patients when there is evidence of (or predisposing factors for) venous thrombosis, clinical evidence of acute right heart failure (high jugular venous pressure, an S3 gallop at lower sternum, tachycardia, and tachypnoea), and ECG signs of right heart strain. The differential diagnosis includes all conditions that can lead to acute circulatory collapse, particularly if they are also likely to cause acute dyspnoea. The most important are left heart failure, cardiac tamponade, ventricular septal rupture, myocardial infarction, aortic dissection, tension pneumothorax, and severe asthma. The absence of pulmonary rales is the warning that the haemodynamic problems do not result from left ventricular impairment, but a pattern similar to acute massive pulmonary embolism can result from right ventricular infarction.