Clusters, Gaps, and Randomness: Vasovagal Syncope Recurrence Patterns.

ABSTRACT

OBJECTIVES: This study elucidated the temporal recurrence patterns of syncope in patients with frequent vasovagal syncope (VVS). BACKGROUND: Understanding the temporal distribution of fainting spells in syncope patients may illuminate biological processes and inform decision making. METHODS: Patients from the POST 2 (Prevention of Syncope Trial 2) were included; all had VVS and fainted ≥4 times in the study year, providing ≥3 interevent intervals (IEIs). Only fainting spells separated by ≥1 day were included. IEI distributions were analyzed using Poisson modeling and cumulative sum distributions. RESULTS: Twenty-four patients (5 males, 19 females; mean 33 years of age) had a total of 286 syncopal events and 262 IEIs, with a median 6 IEI. They resembled excluded subjects in age and sex but fainted more often in their lives (median 57 vs. 13 fainting spells, respectively; p < 0.0001) and in the previous year (median 23 vs. 3 fainting spells, respectively; p < 0.0001). Subjects had a median IEI duration of 8 (interquartile range 4 to 19) days. The IEI distributions were fit well by Poisson models with a median r2 of 0.94 (95% confidence interval 0.91 to 0.97). The patients' Poisson rate constant frequencies were 7 to 263 fainting spells/year with a median rate of 19 fainting spells/year. The modal syncope frequency was 10 to 15 fainting spells per year. Seven patients had biexponential distributions, and many patients fainted in clusters. CONCLUSIONS: Patients with frequent VVS have fainting spells that occur randomly in time. Clusters of syncope occur, and in this population, there is a central tendency to 10 to 15 fainting spells per year. This provides a quantitative measure of frequency and predictability that may afford individualized treatment goals.