The relationship between cardiac functional capacity and patients’ symptom-specific utilities for angina: some findings and methodologic lessons

Forty-one angina patients with coronary disease were interviewed to examine the correlation between prespecified and individualized weights for disease-specific measures of the effects of angina on the patients' well-being. Modifications of the Canadian Cardiovascular Society (CCS) scale for angina and the Duke Activity Specific Index (DASI) were used to rate functional capacity with prespecified items. Disease-specific utilities based on descriptions of functional status were obtained directly, and again indirectly with different anchoring conditions to control for noncardiac comorbidity. Correlations between the functional-capacity measures and the derived utilities were not strong, ranging from -0.25 (p > 0.1) to -0.35 (p = 0.02). Correlation between the two prespecified measures was higher (r = -0.51 or -0.69, both p < 0.01, for DASI versus CCS graded from walking and stair-climbing, respectively). The direct and indirect disease-specific utility scores were similar (r = 0.92, p < 0.01). The method described provides an approach to measuring disease-specific utilities by adapting existing scales for use in a standard gamble. It confirms that prespecified functional status scores inconsistently reflect patients' valuations of functional states. Further investigation should address whether the observed null effect of comorbidity on disease-specific utilities arose from inadequate coverage of the comorbidity issues in patient interviews or from lack of power given the small size of the feasibility study.