Exploring the periodicity of cardiovascular events in Switzerland: Variation in deaths and hospitalizations across seasons, day of the week and hour of the day,☆☆

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Abstract

Purpose

The purpose of this study is to explore the periodical patterns of events and deaths related to cardiovascular disease (CVD), acute myocardial infarction (AMI) and stroke in Swiss adults (≥ 18 years).

Methods

Mortality data for period 1969–2007 (N = 869,863 CVD events) and hospitalization data for period 1997–2008 (N = 959,990 CVD events) were used. The annual, weekly and circadian distribution of CVD-related deaths and events were assessed. Multivariate analysis was conducted using multinomial logistic regression adjusting for age, gender and calendar year and considering deaths from respiratory diseases, accidents or other causes as competitive events.

Results

CVD deaths and hospitalizations occurred less frequently in the summer months. Similar patterns were found for AMI and stroke. No significant weekly variation for CVD deaths was found. Stratification by age and gender showed subjects aged < 65 years to present a higher probability of dying on Mondays and Saturday, only for men. This finding was confirmed after multivariate adjustment. Finally, a circadian variation in CVD mortality was observed, with a first peak in the morning (8–12 am) and a smaller second peak in the late afternoon (2–6 pm). This pattern persisted after multivariate adjustment and was more pronounced for AMI than for stroke.

Conclusion

There is a periodicity of hospitalizations and deaths related to CVD, AMI and stroke in Switzerland. This pattern changes slightly according to the age and sex of the subjects. Although the underlying mechanisms are not fully identified, preventive measures should take into account these aspects to develop better strategies of prevention and management of CVD.

Introduction

Seasonality of mortality from cardiovascular diseases (CVD) has been observed and analyzed worldwide. Several hypotheses have been put forward to explain seasonal, monthly, weekly and hourly variations in CVD deaths such as temperature-driven alterations in blood pressure [1], stress [2], thrombotic activity [3], fibrinogen concentration [4] or cholesterol changes in diet [5], [6] but no consistent causality has been proven.

In regards to seasonal or monthly variation, it has been shown that winter months lead to more deaths by AMI and stroke [3], [7], [8] particularly in areas subject to heterogeneous weather throughout the year. In areas with minimal seasonal climatic changes such as Taiwan, there appears to be no such seasonal variation in the incidence of stroke [9]. Many studies have also observed that older patients (≥ 65 years of age) are more influenced by seasonal changes than the younger patients (< 65 years of age) [10], possibly because the temperature extremes affect their thrombotic activity more seriously [3]. Conversely, the summer months usually present the lowest mortality rates from CVD [11], [12].

In regards to the variation according to the day of the week, interesting observations have been found. For instance young men present a stronger weekly variation than their older counterparts, both regarding stroke [13] and AMI [14] mortality. In the younger subgroup, the peak incidence occurred on Mondays for strokes [13] and on Mondays and Saturdays for AMI [14]. This pattern may be explained by work-related stress inducing a release of catecholamines (Blue Monday) or the “weekend warrior phenomenon” by which normally sedative office workers participate in more strenuous physical activities resulting in an increase incidence of sudden death on Saturdays.

Finally, a circadian rhythm has also been noted for all CVD. According to several studies, strokes and AMI are more likely to occur in the morning (6 am–noon) with a second and smaller peak in the afternoon (~ 3 pm) [8], [15], [16], while a nadir has been observed during night hours. This pattern has pushed some authors to put forward prevention strategies [17].

Switzerland is characterized by a low mortality from CVD and also by a consistent season pattern, with large temperature amplitude. Still, to our knowledge, no study has ever focused on the periodicity of CVD mortality, including AMI and stroke in Switzerland. Hence, we used the data from the Swiss mortality database to assess the seasonal, daily and hourly death rates due to CVD, including AMI and stroke. The results were further confirmed by the analysis of hospital discharge data.

Section snippets

Mortality database

Mortality data was provided by the federal office of statistics (www.bfs.ch). The database records all deaths occurring in Switzerland since 1969. The data collected include gender, age at death, main and surrogate causes of death, and date and hour of death. Regarding the hour of death, the information was only available for 1979 onwards. Two international classifications of diseases (ICD) of the World Health Organization were employed: ICD-8 (before 1995) and ICD-10 (after 1994).

For this

Database description

Data from 2,362,430 deaths was analyzed, of which 869,863 (36.8%) from CVD, 361,322 (15.3%) from AMI and 221,972 (9.4%) from stroke. Among CVD deaths, 89.2% occurred in subjects aged over 65 years and 52.3% in women. The corresponding values for AMI were 85.1% and 44.2%, and for stroke 92.8% and 59.0%.

Data from 11,353,651 hospitalizations was analyzed, of which 959,990 (8.5%) from CVD managed on-site. Among patients managed on-site for CVD, almost seven out of ten (69.1%) were aged 65 years and

Discussion

To our knowledge, this is the first study to assess the periodicity of death from CVD in Switzerland. Our results confirm the findings of previous studies conducted in other countries and provide interesting data for a better seasonal and daily planning of the emergency management of CVD.

Conclusion

In Switzerland CVD events and deaths present specific seasonal, weekly and circadian patterns. These patterns appear to be influenced by different factors and their importance varies according to gender and age. This information could be applied to optimize preventive and emergency health resources.

The following are the supplementary data related to this article.

. Multivariate analysis of the distribution of cardiovascular disease (CVD) events per month, Switzerland. Results are expressed as odds

Author contributions

PMV and MR researched the data and wrote the manuscript. FP and HS reviewed/edited the manuscript and contributed to the discussion.

Pedro Marques-Vidal is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

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    All authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.

    ☆☆

    This study was not funded.

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