Prognostic significance of the Karnofsky Performance Status score in patients with acute myocardial infarction: Comparison with the left ventricular ejection fraction and the exercise treadmill test performance

The prognostic significance of functional status has not been previously studied in the setting of acute myocardial infarction. We assessed the Karnofsky Performance Status (KPS) score, a simple functional status scale that is commonly used to categorize physical ability, in 849 patients with acute myocardial infarction who were enrolled in the Multicenter investigation of the Limitation of infarct Size (MILIS) study. We then compared the KPS score with other predictors of prognosis in these patients. In patients who presented with acute myocardial infarction, a lower KPS score (<8 on a scale of 1 to 10) 3 weeks before the index infarction was associated with a higher incidence of congestive heart failure, in-hospital cardiac arrest, and mortality during hospitalization, as compared with patients with KPS scores ≥8 (each p < 0.001). Cumulative 1-year and 4-year mortality rates were significantly higher in patients with KPS scores <8, as compared with patients with KPS scores ≥8 (42.5% vs 12.6% at 1 year and 61.6% vs 25.1% at 4 years, respectively; both p < 0.001). The left ventricular ejection fraction on admission was significantly lower in patients with KPS scores <8, as compared with those with KPS scores ≥8 (p < 0.019). The cumulative mortality rate was equally well predicted by low KPS score and by left ventricular ejection fraction (both p < 0.0001). The KPS score, as assessed 6 months after the index infarction, was compared with the outcome on an exercise treadmill test that was performed at the same time in 719 patients. The cumulative mortality rate was better predicted by lower KPS score (p < 0.0001) than by inability to perform the exercise test for cardiac reasons (p < 0.02). Of those patients who were able to complete a modified Bruce protocol, those with low KPS scores had a significantly higher frequency of inability to exercise beyond stage I of a modified Bruce protocol, as compared with patients with higher KPS scores. (Odds ratio = 2.29, confidence interval = 1.35 to 3.90). The cumulative mortality rate was significantly higher in patients with 6-month scores <8, as compared with patients with 6-months KPS scores ≥8 (26.1% vs 9.1%, respectively at 4 years; p < 0.001). These findings suggest that the KPS score, a simple performance status scale that is easily used in the setting of acute myocardial infarction, may be auseful method of assessing prognosis after myocardial infarction and may be as effective as left ventricular ejection fraction and exercise treadmill test performance in the prediction of subsequent mortality rates.