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Epidemiology
Research
Risk of sudden cardiac death in relation to season-specific cold spells: a case–crossover study in Finland
  1. Niilo R I Ryti1,
  2. Elina M S Mäkikyrö1,
  3. Harri Antikainen2,
  4. Eeva Hookana3,
  5. M Juhani Junttila3,
  6. Tiina M Ikäheimo1,
  7. Marja-Leena Kortelainen4,
  8. Heikki V Huikuri3,
  9. Jouni J K Jaakkola1
  1. 1Center for Environmental and Respiratory Health Research (CERH), Faculty of Medicine, University of Oulu, Oulu, Finland
  2. 2Department of Geography, University of Oulu, Oulu, Finland
  3. 3Department of Research Unit of Internal Medicine, Medical Research Center Oulu, Oulu University Hospital, Oulu, Finland
  4. 4Department of Forensic Medicine, University of Oulu, Oulu, Finland
  1. Correspondence to Professor Jouni J K Jaakkola; jouni.jaakkola{at}oulu.fi

Abstract

Objective To test a priori hypothesis of an association between season-specific cold spells and sudden cardiac death (SCD).

Methods We conducted a case–crossover study of 3614 autopsy-verified cases of SCD in the Province of Oulu, Finland (1998–2011). Cold spell was statistically defined by applying an individual frequency distribution of daily temperatures at the home address during the hazard period (7 days preceding death) and 50 reference periods (same calendar days of other years) for each case using the home coordinates. Conditional logistic regression was applied to estimate ORs for the association between the occurrence of cold spells and the risk of SCD after controlling for temporal trends.

Results The risk of SCD was associated with a preceding cold spell (OR 1.33; 95% CI 1.00, 1.78). A greater number of cold days preceding death increased the risk of SCD approximately 19% per day (OR 1.19; 95% CI 1.07 to 1.32). The association was strongest during autumn (OR 2.51; 95% CI 1.27 to 4.96) and winter (OR 1.70; 95% CI 1.13 to 2.55) and lowest during summer (OR 0.42; 95% CI 0.15 to 1.18) and spring (OR 0.89; 95% CI 0.45 to 1.79). The association was stronger for ischaemic (OR 1.55; 95% CI 1.12 to 2.13) than for non-ischaemic SCD (OR 0.68; 95% CI 0.32 to 1.45) verified by medicolegal autopsy.

Conclusions Our results indicate that there is an association between cold spells and SCD, that this association is strongest during autumn, when the weather event is prolonged, and with cases suffering ischaemic SCD. These findings are subsumed with potential prevention via weather forecasting, medical advice and protective behaviour.

  • sudden cardiac death
  • sudden death
  • cold spell
  • temperature
  • weather
  • cardiac epidemiology

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/

https://doi.org/10.1136/bmjopen-2017-017398

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    Footnotes

    • Contributors NRIR and JJKJ designed the study. MLK contributed significantly to the performing of the medicolegal autopsies over 1998–2011. EH complemented the autopsy data to constitute the FinGesture database under the supervision of MJJ and HVH. HA collected the weather data from Finnish Meteorological Institution, designed and applied the GIS model to produce the case-specific exposure data. EMSM designed the SAS program for the main analyses and executed the analyses together with NRIR. TMI contributed expertise in cold-related physiology and substantial scientific input in interpretation of the results. HVH contributed expertise in cardiology and substantial scientific input in the interpretation of the results. JJKJ contributed expertise in epidemiology and public health and substantial scientific input in interpretation of results. NRIR and JJKJ drafted the manuscript and all authors have accepted the final version. JJKJ and HVH have equal senior authorship, had full access to all of the data in the study, and take responsibility for the integrity of the data and the accuracy of the data analysis.

    • Funding This work was funded by the Research Council for Health, Academy of Finland (grant no. 266314 and 267435), University of Oulu Strategic Funding for CERH, Emil Aaltonen Foundation, Sigrid Juselius Foundation, and Foundation for Cardiovascular Disease. The funders of the study had no role in study design, data collection, data analysis, data interpretation, writing of the report, or the decision to submit the article for publication. The authors are independent of the funders.

    • Competing interests None declared.

    • Ethics approval This study complies with the Declaration of Helsinki and has been approved by the Ethics Committee of the Oulu University Hospital (ID of the approval EETTMK: 18/2014). National Supervisory Authority for Welfare and Health (Valvira) has approved the review of postmortem data by the investigators.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement There are no additional data available.