How did the acute ischemic heart disease predictive instrument reduce unnecessary coronary care unit admissions?

The use of the acute ischemic heart disease predictive instrument reduced coronary care unit (CCU) admissions for patients without acute ischemic heart disease by 30%. One hypothesis holds that it reinforced physicians' correctly low estimates of the probability of acute ischemia, supporting a decision against CCU admission, another that it lowered physicians' over-high probability estimates for acute ischemia so that CCU admission was felt to be unnecessary. The authors asked 86 physicians to estimate the probability of acute ischemia for each of three study cases and to decide on CCU admission. For the low-probability case, the mean of physicians' probability estimates for acute ischemia was 46%, vs. the predictive instrument's calculated probability of 19% (p less than 0.00001), a 142% over-estimation by the physicians. For the medium-probability case, the mean of physicians' estimates was 54%, vs. the calculated probability of 58% (not significant). For the high-probability case, the mean of physicians' estimates was 82%, vs. the calculated probability of 78% (not significant). All cases for which physicians considered not admitting to the CCU corresponded to their probability estimates of acute ischemia's being in a threshold range of approximately 10 to 30%. These results support the hypothesis that the mechanism by which the predictive instrument reduces unnecessary CCU admissions is by downward correction of physicians' overly-high suspicions of acute cardiac ischemia into a threshold range for which CCU admission is considered unnecessary.