Methods for assessing quality of life in the Cardiac Arrhythmia Suppression Trial (CAST)

The CAST was a randomized, double-blind placebo-controlled multicentre trial of antiarrhythmic medications designed to suppress ventricular arrhythmias in patients after an acute myocardial infarction (MI). A collection of 21 items derived from established scales was used to assess aspects of quality of life in CAST. The questions focused on symptoms, mental health, physical functioning, social functioning, life satisfaction, and life expectancy. Additional aspects included exposure to major stressful life events, and perceived social support and social integration. Work status was also recorded. Using the baseline values of 1465 (98%) out of 1498 patients enrolled in the CAST main study between 15 June 1987 and 19 April 1989, the reliability and validity of the scales used in CAST were computed. High internal consistency reliability (≥0.70) was found for Symptoms, Mental Health, and Physical Functioning. The discriminative validity, in particular for Symptoms, Mental Health, Physical and Social Functioning, showed that patients with heart failure and previous MI, as well as those suffering from angina and dyspnea, had a worse quality of life than those patients who were not experiencing these symptoms. It was concluded that the scales selected to form the CAST quality of life questionnaire were both reliable and clinically valid for this patient population and therefore could be used to detect disease progression and treatment effects.