Stability of Time-tradeoff Utilities in Survivors of Myocardial Infarction

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Abstract
To investigate whether time-tradeoff utilities of survivors of myocardial infarction change over time and whether changes in utilities correlate with changes in functional status, the authors conducted serial interviews using a time tradeoff and three measures of functional status in a cohort of 67 patients who had recently had myocardial infarction. The patients were also asked to rate their overall health on a rating scale and were asked about chest pain, exercise status, and employment status. Each patient was interviewed two to five times over one and a half years. The mean (95% Cl) time-tradeoff score for all patients was 0.88 (0.84, 0.93). Over a mean interval of 8.4 months, 28 (42%) patients changed Karnofsky scores, 28 (42%) changed Specific Activity Scale classes, and 11 (16%) changed New York Heart Association classes, with most changes representing improvements in functional status. Scores on the rating scale improved by a mean (95% Cl) of 0.06 [(0.03, 0.10); p < 0.002], but scores on the time tradeoff remained stable, with a mean (95% Cl) change of 0.03 [(-0.02, 0.08); p = NS]. Changes in time-tradeoff scores did not correlate with changes in Specific Activity Scale classes (Kendall's τ = 0.21), New York Heart Association classes (τ = -0.02), or Karnofsky scores (τ = 0.14); with changes on the verbal rating scale (R = 0.20); with changes in chest pain status (τ = -0.05), exercise status (τ = 0.11), or employment status (τ = 0.11); or with interim hospitalizations (τ = 0.05). The authors conclude that, in this relatively stable group of survivors of myocardial infarction, time-tradeoff utilities remained stable, and that changes in time-tradeoff utilities did not correlate with changes in function. Key words: functional status; quality of life; utility; patient preferences; myocardial infarction. (Med Decis Making 1993;13:161-165)