The study was a follow-up of 2332 consecutive patients diagnosed with chronic heart failure at Castle Hill Hospital, Hull, UK. At their initial visit to the clinic all were asked if they would be willing to take part in clinical research projects. After a median follow-up of 55.7 months, analysis of the full cohort showed that 792 (34%) had died. However, survival was significantly associated with a willingness to take part in clinical trials, which more than halved the risk of death (hazard ratio 0.33).
The authors note that outcomes for patients with chronic heart failure are generally very poor; epidemiological studies show that around 40% of patients diagnosed with chronic heart failure die within a year of diagnosis. "However," says investigator Dr Andrew Clark from Castle Hill Hospital, "two-year mortality rate in recent trials of chronic heart failure trials has been in the order of 20%. And even in studies of very sick patients, mortality has only been 30%. So we wanted to see if taking part in a clinical trial was associated with a beneficial outcome."
Additionally, to explore the effect on survival of actually entering a clinical trial (rather than simply indicating a willingness to take part) survival after the first year was compared between "willing" patients who were recruited to a trial and willing patients who were not.
The single most powerful predictor of all-cause mortality in the whole cohort (p<0.0001) - from a multivariate model of 19 clinical and social variables - was willingness to take part in a trial, with a "protective" hazard ratio of 0.33 (95% CI, 0.26-0.40). This was a predictor of good outcome independent of age, severity of left ventricular dysfunction, renal function, sodium levels, drug use, and co-morbidities. Indeed, other likely protective variables, such as good mobility (HR 0.91) or appropriate medication were not significant predictors in the multivariate model.
However, results from the second analysis showed that actually being recruited into a clinical trial was not predictive of outcome. "We found no appreciable difference in survival between those who are actually recruited to an interventional trial within the first year and those who were not," says Dr Clark.
The investigators are unable to offer an obvious explanation for the findings, finding no systematic difference between their two study groups. They do, however, suggest that "being prepared to take part in a trial is a marker for better compliance with, and acceptance of, treatment". They add that "patients' attitudes to their illness and its treatment is an important aspect of their care".
The study also highlighted the difference between real-life heart failure patients and those recruited to clinical trials - and this, say the investigators, may explain the difference seen in survival rates between the populations in clinical trials and those in everyday life. "Our study contributes to the perception that heart failure trials can be unrepresentative of real life," says Dr Clark, "particularly as study designs often deliberately exclude patients with an inherently poor prognosis, such as those with anaemia or impaired renal function. Both these co-morbidities are common in real-life populations."