Pulsus paradoxus in acute myocardial infarction.

Sixteen patients, admitted no later than eight hours after the onset of the first stage of acute myocardial infarction, underwent systemic, pulmonary, and pulmonary wedge pressure measurements on admission and 24 and 48 hours after the first symptoms. A decrease in systolic blood pressure during inspiration equal to or greater than 15 mm Hg was found in 56 percent of the cases at admission, 53 percent at 24 hours, and 41 percent at 48 hours. No correlation could be found between this and: (1) pulmonary wedge pressure, (2) arteriovenous oxygen difference (volume percent), (3) location, and (4) extension of the necrosis. The last was indirectly assessed by the maximum levels of creatine phosphokinase attained. We discuss the previously postulated mechanisms causing pulsus paradoxus and formulate a theory to explain in acute uncomplicated myocardial infarction.