Sudden death in competitive athletes: does a circadian variation in occurrence exist?

Sudden death (SD) is an unexpected death, occurring within one hour from onset of symptoms, in ordinary conditions of life, and in presence of witnesses. The majority of SD are sudden cardiac deaths (SCD), since coronary heart disease is the most frequent cause, but pulmonary embolism, rupture of aortic aneurysms, and stroke are also included. Many studies has shown that the occurrence of acute cardiovascular events, including SCD, is not evenly distributed in time, but respects circadian patterns. In the lack of available data, we aimed to investigate whether a circadian pattern of SD in athletes exists, searching across multiple public, non-specialized web databases, cases of SD occurred in competitive athletes during their competition, from the year 2000. Different databases were independently cross-searched from two authors with specific different competence, a medical doctor and a journalist with sport competence. The collected cases were included in two groups for analysis: (A) cases with precise (30 minutes) time of SD, and (B) cases with probable (within a 6-hour interval: night: 00:00–05:59 AM; morning: 06:00–11:59 AM; afternoon 12:00–05:59 PM; and evening: 06:00–11:59 PM). The group (A) was analyzed applying partial Fourier series, by means of a chronobiologic software that selects the harmonic(s) best explaining the variance of the data. Thirty-seven athletes with SD were included in the group (A), and a total of 63 were included in the group (B) (age 18-37 years, mean 26.64.8). As for group (A), chronobiologic analysis yielded a significant circadian variation, characterized by a bimodal frequency peak. The main circadian peak was registered at 04:58 PM, and a smaller accessory peak was found at 08:29 AM/PM. Overall, the circadian rhythm (peak at 07:00 PM, trough at 2:56 AM) was highly significant (p<0.001). For group (B), chi-square test showed a statistically significant difference (p=0.024), with highest frequency of cases in the evening (n= 25, 39.7%) and lowest during nighttime (n= 7, 11.1%). This preliminary study shows that also in athletes SD exhibits a circadian pattern of onset, characterized by two frequency peaks. Although with the limitations of small size sample and the possible conditioning effect of competition time schedule, it is interesting that the circadian pattern of SD onset in athletes resembles that of common people, with evening and morning peaks. It is possible that, in addition to vigorous exercise during competition, temporally related physiologic changes determining electrical myocardial vulnerability, may also play a triggering role.