Infarction-associated pericarditis. Rarity of diagnostic electrocardiogram.

To examine how often pericarditis is associated with myocardial infarction and how often it is diagnosable by electrocardiographic changes, we determined the frequency of diagnostic (Stage I) ST-segment changes in 423 consecutive patients admitted to the coronary-care unit. Careful auscultation and electrocardiography were performed at least once daily in all patients and at least twice daily in those presenting with new chest pain of any description or a pericardial rub. Thirty-one patients had pericardial rubs, usually detected within the first four days after admission. Only 1 of the 31 had diagnostic electrocardiographic changes. The 31 patients with pericarditis differed significantly from the 392 patients without pericarditis in several respects: male predominance; Killip Classes II, III, and IV; and Q-wave infarcts. However, differences in the location of the infarct and in mortality were not statistically significant. We conclude that during acute infarction-associated pericarditis the pericardial rub is the most frequent clinical sign, and ST-segment changes diagnostic of pericarditis are rare. Our findings are consistent with the confinement of pericardial involvement to the infarct zone.