Clinical improvement of vasovagal syncope in the absence of specific therapies: The Seinfeld effect.

Vasovagal syncope can persist for decades and recur sporadically but many patients appear to improve after being seen in specialty clinics. The absence of specific and proven effective therapy raises the possibility that this might be due to regression to the mean or to a placebo effect. However, analysis using the Poisson distribution indicates the extreme unlikeliness that regression to the mean is the explanation. A main cause of the placebo effect is expectancy. Subject expectancy is the influence of the subject's anticipation of benefit on outcomes, and observer expectancy is the influence of investigator or physician attitudes and behavior on subject response. Ample data support the role of expectancy in outcomes of syncope patients. Moreover, expectancy can vary depending on the type of ineffective intervention. Interestingly, studies in which patients are blinded but the investigator is not show similar patient benefits compared with completely open label studies consistent with a strong observer expectancy effect due to physician-subject interaction. These results suggest the paramount importance of properly conducted randomized clinical trials in assessing biomedical interventions, and also illuminate the powerful potential of studies aimed at enhancing the expectancy effect on patient outcome.