Seasonal variation in patient characteristics and in-hospital outcomes of Takotsubo syndrome: a nationwide retrospective cohort study in Japan

Although there is reportedly seasonal variation in the occurrence of Takotsubo syndrome (TTS), it is unknown whether there is a relationship between season and patient characteristics, or whether season influences outcomes. Using the Diagnosis Procedure Combination database in Japan, we retrospectively identified 4306 patients (mean age 73.6 years) hospitalized with TTS between January 2011 and December 2013. We divided patients into four groups according to season of admission [n = 914, Spring (March-May); n = 1243, Summer (June-August); n = 1245, Autumn (September-November); n = 904, Winter (December-February)]. The outcomes were in-hospital mortality and cardiovascular complications. We compared patient backgrounds and outcomes across seasons and estimated the adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for outcomes in logistic regression analyses adjusted for multiple propensity scores. Although there was no significant difference in age across seasons, the proportion of males differed significantly (from 18.5% in autumn to 23.9% in winter; p = 0.016). The incidence of psychiatric disease (from 4.9% in spring to 7.9% in summer; p = 0.025) and sepsis (from 0.8% in winter to 2.6% in summer; p = 0.019) also differed significantly with season. In-hospital mortality was not significantly influenced by season (p = 0.377): spring, 5.1%; summer, 6.0%; autumn, 4.6%; winter, 6.0%. However, in-hospital mortality ranged widely across months from 3.0% in September to 7.5% in April. The incidence of ventricular tachycardia/fibrillation was significantly different (p = 0.038): spring, 2.2% (reference); summer, 3.3% (aOR 1.46, 95% CI 0.84-2.51); autumn, 2.7% (aOR 1.27, 95% CI 0.72-2.22); winter, 4.4% (aOR 1.92, 95% CI 1.11-3.33). Although season did not appear to influence the in-hospital mortality of TTS, monthly variation may exist in the risk of death in patients with TTS. There were significant seasonal variations in the proportions of males, patients with psychiatric disease or sepsis, and the incidence of ventricular arrhythmias among patients with TTS.