Relationship between functional status and health-related quality-of-life after myocardial infarction

Despite increasing use in clinical and economic studies, no gold standard exists for the measurement of health-related quality of life (HRQL). One approach to assessing the validity of an HRQL instrument for a particular disease population is to examine the empirical relationship between HRQL patient scores and other accepted measures of health or functional status. In 185 patients (mean age 60 years, 79% male) at six months after myocardial infarction, we examined the relationship between patient responses to the Nottingham Health Profile (NHP), a generic HRQL instrument, and physician classification of patients by two widely used functional status indicators: the New York Heart Association (NYHA) classification and the Karnofsky Performance Status Scale. Analysis of NHP scores by NYHA strata confirms that lower HRQL is associated with poorer cardiac functional status (P < 0.0001) and this gradient is observed over all six NHP domains. Statistically significant (P < 0.001) associations were observed between patients' NYHA class and NHP domain scores for energy (Spearman r = 0.52), physical mobility (r = 0.45) and pain (r = 0.43). NHP scores for patients in NYHA Class I were similar to male population controls. A similarly consistent relationship was found between NHP and Karnofsky. We conclude that the NHP is able to discriminate between patients with differing levels of cardiac functioning as classified by NYHA and patient functioning as classified by Karnofsky. Demonstration of such discriminative properties is one important component in assessing the construct validity of HRQL measures.