Key to ECG abnormalities (must be in two loads, excluding aVR); ST—, ST-segment "straightening;" STT^, ST segment elevated at least 1 mm or depressed at least 1 mm; TT4-, T wave "hyperacute" (>50% of R wave) or inverted at least 1 mm; ST0/T0, above-specified changes absent.

Directions: To determine a given patient's probability of acute ischemia, start by answering the questions at the top of the chart about the presence of chest pain and whether or not it is the chief complaint. This will lead to one of the three large boxes or probability values. Under the History heading are questions regarding history of heart attack or nitroglycerine (NTG) use. Choose the row that corresponds to the patient's report of none, one, or both of these historical features. Then to find the specific probability value, move across the appropriate row to the column corresponding to the ECG ST-segment and T-wave changes for the given patient. For example, for a patient with a chief complaint of chest pain, no history of heart attack or nitroglycerine use, and 1 mm of ST-segment depression and T-wave inversion, the probability of true ACI would be 78%. (Reproduced from McCarthy BD, Wong JB, Selker HP: Detecting acute cardiac ischemia in the emergency department: A review of the literature. J Gen Intern Med 5:365-373. Reprinted with permission of Blackwell Science, Incorporated.

Note: Specific definitions of clinical features (questions) for original ACI predictive intrument are modified for use in this chart.

should be periodic, not just static. The pitfalls of not ordering ECGs in younger, atypical patients and of misinterpretation should be anticipated. Finally, clinicians should not be reluctant to obtain a second opinion, by fax transmission if necessary, for difficult tracings (Table 9).

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