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Research Christmas 2018: Heart Of The Matter

Christmas, national holidays, sport events, and time factors as triggers of acute myocardial infarction: SWEDEHEART observational study 1998-2013

BMJ 2018; 363 doi: (Published 12 December 2018) Cite this as: BMJ 2018;363:k4811
  1. Moman A Mohammad, physician intern1,
  2. Sofia Karlsson, physician intern1,
  3. Jonathan Haddad, medical student1,
  4. Björn Cederberg, medical student1,
  5. Tomas Jernberg, senior consultant cardiologist and professor in cardiology,2,
  6. Bertil Lindahl, senior consultant cardiologist and professor in cardiology3,
  7. Ole Fröbert, senior consultant cardiologist and professor in cardiology, interventional cardiologist4,
  8. Sasha Koul, consultant cardiologist and interventional cardiologist1,
  9. David Erlinge, senior consultant cardiologist and professor in cardiology, interventional cardiologist1
  1. 1Department of Cardiology, Clinical Sciences, Lund University, Skane University Hospital, Lund, Sweden
  2. 2Department of clinical sciences, Danderyd’s University Hospital, Karolinska Institutet, Stockholm, Sweden
  3. 3Department of Medical Sciences and Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden
  4. 4Örebro University, Faculty of Health, Department of Cardiology, Örebro, Sweden
  1. Correspondence to D Erlinge: david.erlinge{at} (or @DavidErlinge on Twitter)
  • Accepted 5 November 2018


Objectives To study circadian rhythm aspects, national holidays, and major sports events as triggers of myocardial infarction.

Design Retrospective observational study using the nationwide coronary care unit registry, SWEDEHEART.

Setting Sweden.

Participants 283 014 cases of myocardial infarction reported to SWEDEHEART between 1998 and 2013. Symptom onset date was documented for all cases, and time to the nearest minute for 88%.

Interventions Myocardial infarctions with symptom onset on Christmas/New Year, Easter, and Midsummer holiday were identified. Similarly, myocardial infarctions that occurred during a FIFA World Cup, UEFA European Championship, and winter and summer Olympic Games were identified. The two weeks before and after a holiday were set as a control period, and for sports events the control period was set to the same time one year before and after the tournament. Circadian and circaseptan analyses were performed with Sunday and 24:00 as the reference day and hour with which all other days and hours were compared. Incidence rate ratios were calculated using a count regression model.

Main outcome measures Daily count of myocardial infarction.

Results Christmas and Midsummer holidays were associated with a higher risk of myocardial infarction (incidence rate ratio 1.15, 95% confidence interval 1.12 to 1.19, P<0.001, and 1.12, 1.07 to 1.18, P<0.001, respectively). The highest associated risk was observed for Christmas Eve (1.37, 1.29 to 1.46, P<0.001). No increased risk was observed during Easter holiday or sports events. A circaseptan and circadian variation in the risk of myocardial infarction was observed, with higher risk during early mornings and on Mondays. Results were more pronounced in patients aged over 75 and those with diabetes and a history of coronary artery disease.

Conclusions In this nationwide real world study covering 16 years of hospital admissions for myocardial infarction with symptom onset documented to the nearest minute, Christmas, and Midsummer holidays were associated with higher risk of myocardial infarction, particularly in older and sicker patients, suggesting a role of external triggers in vulnerable individuals.


  • Contributors: All authors were involved in the study design, data analysis, and revision of the manuscript and read and approved the final manuscript. DE is the guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

  • Funding: This work was supported by The Swedish Heart and Lung Foundation, Swedish Scientific Research Council, SSF (TOTAL-AMI), Knut and Alice Wallenberg Foundation, and ALF and Skane University Hospital funds. The sponsors had no involvement in the study design, collection, analysis, or interpretation of data or writing of the manuscript or in the decision to submit manuscript for publication.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: This study was approved by Lund University’s ethical committee (2015/297).

  • Data sharing: No additional data available.

  • Transparency: The lead authors (MAM, DE) affirm that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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