A comparison of the Norris and Killip coronary prognostic indices

Of the two most frequently used indices for classifying prognosis of patients with an acute myocardial infarction, the Killip index, because of its greater simplicity, is sometimes used instead of the more complicated and time consuming Norris index. The purpose of the current research was to correlate the classification of patients on the two indexes, and to determine reasons for disagreements in classification. Study patients for this comparison included 151 patients who died of a myocardial infarction and who were matched to each of 151 survivors for age, sex, race, and date hospitalization. Pertinent data were extracted from each patient's medical record by specially trained research technicians. The results indicate that many patients were "misclassified": 40% of the deaths were placed in the two lowest severity classes using the Killip scale, and 12% using the Norris index. Good agreement was found for comparisons between the 4-category Killip scale and the continuous scale Norris index ( Jaspen 's multiserial r = 0.67), but only fair agreement was noted when the Norris index was arranged into ordinal categories. Deficiencies in the Killip index included absence of crucial clinical features with prognostic power (e.g., age, systolic blood pressure, infarct location), while the Norris index was deficient in its requirement for a chest radiograph to estimate the presence of pulmonary edema and of cardiac enlargement. If future prospective studies confirm our analysis, research findings which have been based on one or the other of these indices should not be interpreted similarly.