Seasonal variation in the incidence of inhospital cardiac arrest: analysis of three groups of cardiac arrest
© BioMed Central Ltd 2003
Published: 3 March 2003
Many studies have analysed circadian variation in the onset of cardiovascular disorders. Only a few studies have examined the occurrence of cardiac arrest by month of year. To our knowledge none has studied seasonal variation in the incidence of three kinds of inhospital cardiac arrest: nontraumatic with presumed noncardiac etiology cardiac arrest (NTNCA), traumatic cardiac arrest (TCA), and cardiac arrest (CA).
We performed a retrospective analysis of computerized records of all patients discharged from our hospital from September 1998 to September 2002. We examined 101,390 clinical computerized records. One thousand two hundred and ninety-three consecutive patients were included with the diagnosis of cardiac arrest using codes according to the International Classification of Diseases, Ninth Revision (ICD-9). We divided (using the ICD-9 codes) all cases found in the three groups: NTNCA, TCA, CA. Data were aggregated using the medical program Oracle and MS Access 2000 software. With the chi-square test we examined whether cardiac arrests uniformly occurred during seasons and months.
There were 1293 cardiac arrests with 956 NTNCA, 143 TCA, 194 CA. For our analysis we divided the year into four seasons: winter (December-February), autumn (September-November), spring (March-May), summer (June-August).
Our data shows a seasonal variation in all cases, with a greater number of cardiac arrests in winter (26.8%) and fewer in autumn (24.2%) and summer (24%). This variation is different among three groups: in the group of NTNCA there are more cases in spring (26%) and winter (25.8%) and fewer in autumn (23.7%), in the CA group the cases are more in winter (33.5%) and fewer in spring (20.6%) and summer (21.2%), and in the TCA there are more in autumn (25.8%) and fewer in spring (24.5%) and summer (24.5%). Unluckily the chi-square test did not reject uniformity over the whole year for all groups examined.
Our data show a seasonal variation in all cardiac arrests with a greater number of cases in the cold months. This trend is similar to that found in other studies. In particular we found a similar trend in the group of CA and of TCA: more cases in autumn and winter. The seasonal hormonal variation and stresses caused by shorter hours of daylight could explain this distribution. On the contrary the NTNCA group showed a different trend: more cardiac arrests in spring and winter. We suppose that the NTNCA cardiac arrests are not linked to the same seasonal hormonal variation of CA and TCA.
There are several limitations to our findings, one of the major is the use of a database using ICD-9 codes. Moreover our results were not confirmed by statistic test. Nevertheless we believe that our findings are reliable, because they were confirmed by several studies. In any case we suggest further research: large studies on the link between environmental factors and the NTNCA cardiac arrests.