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The heemodynamic changes in the pulmonary circulation following acute myocardial infarction are complex and incompletely understood. In order to obtain a clearer picture of these and so help to develop a more rational form of therapy, serial measurements of pulmonary arterial and right ventricular pressures have been made in patients with a recent cardiac infarct. The float right heart catheter has proved so useful in monitoring progress, especially in relation to therapy with diuretics, etc., that we now use it more or less routinely in all acutely ill patients with cardiac infarction. Changes in right heart pressures have been examined in relation to the general clinical picture, chest x-ray appearances, arterial oxygen tension, systemic blood pressure, and cardiac output.SUBJECTS AND METHODS Twenty-six consecutive patients admitted to the Intensive Coronary Care Unit at Hammersmith Hospital within 48 hours of the onset of an acute myocardial infarction were examined in three ways. The diagnosis was based on a typical history of prolonged cardiac pain, together with pathognomonic serial electrocardiographic changes (Q wave, S-T segment, and T wave changes) or changes suggestive of infarction (T wave changes or bundle-branch block) associated with a transient rise in lactic dehydrogenase enzyme (over 250 units, with over 50% heat stable).The average age of the patients was 59 years, with a range of 40 to 87. There were 22 men and 4 women. Nineteen of the patients were admitted with their first infarct, but 8 of these had previously suffered from angina. The remaining 7 patients had had one or more infarcts previously. One patient was studied during two successive infarcts. Six patients were known to have had hypertension before the infarct. Two had Received January 21, 1967. associated chronic bronchitis and one had trivial rheumatic mitral incompetence. None had diabetes mellitus. Five patients died and in each case necropsy confirmed the presence of a recent cardiac infarct.Studies were made on 27 episodes of infarction, including 2 infarcts in 1 patient. Of the infarcts, 20 were anterior, 6 were posterior, and in 1 the site was uncertain, being obscured by the presence of left bundle-branch block.Pressure Measurements. Right heart pressures were measured through fine polyethylene (PE60) tubing cut to a length of 100 cm. The PE60 catheter was introduced percutaneously into an antecubital vein by the Seldinger technique (1953) and the tip floated into the right ventricle or pulmonary artery under pressure control. Occasional extrasystoles were noted as the tip of the catheter passed through the right ventricle, but no other arrhythmia occurred. The catheter tip was left either in the right atrium or in the pulmonary artery for up to 9 days, and a litre of 5 per cent dextrose containing 10,000 units of heparin was slowly dripped through the tubing over each 24 hours. Leaving this catheter in place for up to 9 days did not give rise to complications.A Statham P23Gb transducer was used. The system as a whole had ...

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