Original Contribution
Circadian, weekly, and seasonal mortality variations in out-of-hospital cardiac arrest in Japan: analysis from AMI-Kyoto Multicenter Risk Study database

https://doi.org/10.1016/j.ajem.2010.06.018Get rights and content

Abstract

Background

Several studies have reported circadian, weekly, and seasonal variations in the rates of out-of-hospital cardiac arrest (OHCA). However, variations in the mortality of OHCA are not well known.

Methods and Results

We investigated the 1396 consecutive cases of OHCA with cardiac etiology between October 2004 and September 2008. There were 2 peaks in the occurrence of OHCA in early morning and late evening. There was a weekly pattern with an increased incidence on Mondays. We found a significant seasonal variation in the frequency of events, with a maximum during winter. There was a trend of reduced mortality in warmest 3 months, especially among a subgroup of ventricular fibrillation/pulseless ventricular tachycardia with arrest witnessed.

Conclusion

The present analyses demonstrated circadian, weekly and seasonal variations in the occurrence, and a seasonal variation in mortality in OHCA. Changes in temperature might influence the severity of OHCA and change the rate of success of cardiopulmonary resuscitation.

Introduction

Recently, the characteristics of out-of-hospital cardiac arrest (OHCA) have changed greatly owing to various efforts such as the provision of training for basic life support to the general public. The American Heart Association and the European Resuscitation Council published 2005 Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care to standardize worldwide cardiopulmonary resuscitation (CPR) and to increase the rate of survival of OHCA [1]. The use of automated external defibrillators (AEDs) by trained lay responders in community-based public-access defibrillation programs has been shown to increase survival after sudden cardiac arrest [2]. In Japan, AEDs were approved by the Ministry of Health, Labour, and Welfare in 2005. However, the conditions of OHCA in Japan exhibit some differences from those of Western countries. For example, although the morbidity of ischemic heart disease is lower than those of Western countries the rate of bystander CPR is also lower [3]. Furthermore, educational programs teaching CPR to the public are a long way behind those of Western countries. Despite considerable efforts to improve the various links in the chain of survival [4], OHCA remains associated with an exceptionally poor prognosis [5].

Many studies in the past decade have demonstrated circadian, weekly and seasonal variations in the onset of several acute cardiovascular disorders such as acute myocardial infarction [6], [7], cardiac arrhythmia [8], subarachnoid hemorrhage [9], ruptured aortic aneurysm [10], and pulmonary embolism [11], similar to those in OHCA [12], [13]. However, the majority of these studies examined the total number of occurrences of OHCA in Western countries, and Utstein-style-based reports are very rare [14]. Furthermore, to the best of our knowledge, there have been few studies that examined the circadian, weekly and seasonal variations of survival rate and long-term mortality of OHCA following the Utstein style. Knowledge about trends in the occurrence of OHCA might shed light on the problem of OHCA and facilitate the development of strategies aimed at improving the chances of survival from OHCA. The aim of our study is to explore the circadian, weekly, and seasonal variations in the incidence and survival rate of OHCA in Kyoto following the Utstein style.

Section snippets

Procedure

We conducted a prospective, multicenter observational study of all cases of OHCA taken to the 15 institutes that participated in the AMI-Kyoto multicenter risk study. The AMI-Kyoto Multi-Center Risk Study, a large multicenter observational study in which collaborating hospitals in Kyoto Prefecture have collected demographic, procedural, and outcome data on AMI patients, was established in 2000 in order to analyze these data and establish an emergency-hospital network for heart diseases in

Result

Among all the 2599 OHCA patients, 1396 patients had a cardiac etiology (53.9%), the median age was 75 years old (IQR, 62-84), and 57.5% of the patients were men. 51.9% of cases occurred at home. Of those with cardiac etiology, 463 were witnessed by a bystander (33.2%), and a bystander attempted CPR in 24.8% of these cases. In cases with a cardiac etiology and witnessed by a bystander, ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT) were found at the first cardiac rhythm

Discussion

In this study, we analyzed the circadian, weekly, and seasonal variations in the occurrence and mortality of OHCA in Kyoto according to the Utstein style. Recently, several pre- and in-hospital strategies to improve survival after OHCA have been introduced, such as basic life support training, public access and early defibrillation [2], increased use of CPR guidance by telephone from trained staff to bystanders [16], early revascularization [17], induction of mild hypothermia [18], and use of

Study limitations

This study has some potential limitations. Firstly, this study is an observational study and not a randomized control study. In addition, the institutes that participated in the AMI-Kyoto multicenter risk study were restricted to the core hospitals in Kyoto, so there is a possibility of selection bias. The assignment of patients to cardiac arrest was done clinically by physicians and observers. This may have led to under or over counting cardiac arrests. Confirming that the patients indeed had

Conclusions

We found that the occurrence of OHCA exhibited circadian, weekly, and seasonal variations. Although there were no circadian and weekly variations in survival rate, there was a tendency for a higher survival rate in summer, and especially among a subgroup of VF/pulseless VT patients with arrest witnessed by a bystander, there was a significant improvement in the prognosis of OHCA in summer compared with that in winter. Changes in mental and physical activity and changes in the environment and

Acknowledgment

The authors greatly appreciate the help of all members of the committee for this project and members of the institutes that participated in the AMI-Kyoto multicenter risk study: Kyoto Prefectural University of Medicine, Kyoto City Hospital, Kyoto First Red Cross Hospital, Kyoto Second Red Cross Hospital, Social Insurance Kyoto Hospital, Saiseikai Kyoto Hospital, Koseikai Takeda Hospital, Marutamachi Hospital, Kyoto Prefectural Yosanoumi Hospital, Maizuru Medical Center, Ayabe City Hospital,

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