Association between high and low ambient temperature and out-of-hospital cardiac arrest with cardiac etiology in Japan: a case-crossover study
Yamazaki and Michikawa Environmental Health
and Preventive Medicine
Association between high and low ambient temperature and out-of-hospital cardiac arrest with cardiac etiology in Japan: a case-crossover study
Shin Yamazaki 0
Takehiro Michikawa 0
0 Environmental Epidemiology Section, Centre for Health and Environmental Risk Research, National Institute for Environmental Studies , Onogawa 16-2, Tsukuba 305-8506 , Japan
Objective: The objective of the study was to examine the association between high and low temperature and outof-hospital cardiac arrest (OHCA) with cardiac etiology. Methods: The study was conducted under a case-crossover design. Subjects were 97,500 patients aged 40 years or older with OHCA having a cardiac etiology in Tokyo, Osaka, and Fukuoka Prefecture from 2005 to 2012. We used national data with an Utstein-style resuscitation registration. Temperature was categorized into five categories with cut points of 5, 10, 24, and 30 °C. The reference category was 10-23.9 °C. Conditional logistic regression was used with adjustment for daily means of relative humidity, atmospheric pressure, and wind speed and daily amount of precipitation and hours of daylight. Results: Exposure to high temperature (≥30 °C) increased the risk of OHCA (OR = 1.11, 95% confidence interval (CI) 1.04-1.18). Further, low temperature (<5 °C) and relatively low temperature (5-9.9 °C) were also associated with OHCA (OR = 1.20, 95% CI 1.16-1.25; OR = 1.10, 95% CI 1.07-1.13, respectively). The temperature-OHCA association curves were U-shaped or J-shaped, and the association was more prominent among those aged 80 years or older. Conclusion: This study shows that the occurrence of OHCA with cardiac etiology is associated with low temperature. In addition, the occurrence is also associated with high temperature in those aged 80 years or older.
Introduction
Many studies have provided estimates of death
attributable to either heat or cold [
1, 2
]. For example, a
multicountry study showed that mortality risk increased
slowly for cold temperatures below the minimum
mortality temperature and quickly at high temperature [3].
With regard to death caused by cardiovascular disease, a
large American study found that 2-day mean extreme
high and low temperatures were associated with
increased risk of death [
4
]. In addition, a Chinese study
showed that out-of-hospital coronary death (OHCD)
from the Chinese death register was associated with
14day mean temperature. The temperature-OHCD
association curves in that study were U- or J-shaped and
showed that extreme temperature significantly increased
the risk of OHCD [
5
]. In contrast, a systematic review
pointed out that the effects of temperature on
cardiorespiratory morbidity appeared to be smaller and more
variable than previous findings related to
cardiorespiratory mortality [
6
]. In Japan, the occurrence of adult cases
of out-of-hospital cardiac arrest (OHCA) with cardiac
etiology increases with decreasing temperature during
the day, in elderly people in particular [
7
].
Japan is presently aging more rapidly than any other
country in the world. In 2014, the percentage of the
population aged 65 and over (percentage of elderly) was
26.0% (previous year: 25.1%) and 12.5% for that aged
75 years old and over (the old elderly; 15.92 million
people) [
8
]. With the progress of aging, it is expected that
the number of people experiencing OHCA will increase.
A previous Japanese study suggested that the
frequency of OHCA with cardiac etiology increases with
decreasing temperature during the day [
7
]. However,
analysis on the effect of extremely hot temperature on
OHCA in that study was insufficient.
Here, we examined the association between extreme hot
and cold temperatures and OHCA with cardiac etiology
in Japan.
Methods
Study design
The study was conducted under a time-stratified
casecrossover design, which is typically used to assess brief
changes in risk associated with transient exposures [
9, 10
].
Case-crossover studies can be regarded as a special type of
case-control study in which each case serves as its own
control, thereby providing inherent control of potential
confounding by fixed individual characteristics such as
sex, race, diet, and age. “Time-stratified” indicates the
method by which the control periods were chosen.
Specifically, we stratified time into months to select days
for control periods that fell on the same day of the week
within the same month as the date of the occurrence of
OHCA (day of the index period).
Data collection
We used national data with an Utstein-style
resuscitation registration. Subjects were patients with OHCA of
presumed cardiac origin who were treated by emergency
medical service personnel in Tokyo, Osaka, and Fukuoka
Prefecture from January 1, 2005, to December 31, 2012.
We restricted subject age to 40 years or older. The data
were obtained from the Japanese Fire and Disaster
Management Agency. Outcome was the occurr (...truncated)