Increased fatality and difficult diagnosis of in-hospital acute myocardial infarction: comparison to lower mortality and more easily recognized pre-hospital infarction. 
We studied 510 patients in the Columbia, South Carolina metropolitan area with documented acute myocardial infarction (AMI) in 1978 to investigate differences in clinical characteristics and outcome between patients who experienced AMI while inside the hospital (IN-AMI) and those who experienced AMI outside the hospital environment (EX-AMI).  Mortality for IN-AMI patients (66%) was significantly higher (p less than 0.0001) than for EX-AMI patients (22%), and remained higher (p less than 0.05) even after exclusion of high-risk IN-AMI patients (surgical patients, those with serious underlying noncardiac illness, and those with underlying cardiac illness as the reason for hospital admission).  Medical IN-AMI patients experienced fewer typical forms of AMI symptoms (p less than 0.05) and did not reach an intensive care unit significantly sooner than did EX-AMI patients.  Time from onset of AMI symptoms to death was not significantly different between IN-AMI and EX-AMI groups (p = 0.22).  Therefore AMI occurring during hospitalization was associated with poor early prognosis even after exclusion of high-risk patients.  These results emphasize the need for improved approaches to prevention, identification, and management of AMI patients.