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Correspondence
Sex as a determinant of prehospital ECG in ST- and non-ST elevation myocardial infarction patients
  1. Kristina Klerdal1,
  2. Christoph Varenhorst2,
  3. Stefan James2,
  4. Lars Alfredsson1,
  5. Hans Blomberg3,
  6. Tahereh Moradi1,4
  1. 1Unit of Cardiovascular Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
  2. 2Department of Medical Sciences, Cardiology and Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden
  3. 3Department of Surgical Sciences, Anesthesiology and Intensive Care, Uppsala University Hospital, Uppsala, Sweden
  4. 4Centre for Epidemiology and Social Medicine, Health Care Services, Stockholm County Council, Stockholm, Sweden
  1. Correspondence to Kristina Klerdal, Unit of Cardiovascular Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Box 210, Stockholm SE-171 77, Sweden; Kristina.Klerdal{at}ki.se

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We read the article by Quinn et al1 on the effects of prehospital 12-lead ECG (PHECG) on processes of care and mortality with great interest. The authors conclude that when a PHECG was used, patients with ST-elevation myocardial infarction and non-ST elevation myocardial infarction had better survival compared with those without. Interestingly, among the determinants associated with PHECG use, the authors identify female patients to be less likely to have a PHECG than male patients.

When the authors discuss possible explanations to the sex differences in PHECG use, they suggest that the predominately male emergency medical services workers might be reluctant to perform a PHECG on female patients because of the need for intimate exposure. Furthermore, female patients might also be less willing to agree to a PHECG compared with men. We argue that a more plausible explanation is uncontrolled confounding of presenting symptoms and type of myocardial infarction.

When we analysed a similar ST-elevation myocardial infarction and non-ST elevation myocardial infarction population in the Swedish comprehensive SWEDEHEART2 register, we found an OR for women versus men to receive a PHECG comparable to that in the article by Quinn et al (SWEDEHEART: OR=0.89; 95% CI 0.87 to 0.92) versus Quinn et al (OR=0.87; 95% CI 0.86 to 0.89). In Sweden, 64% of the ambulance specialist nurses were male (The National Board of Health and Welfare).

In accordance with previous findings,3 we found women to report chest pain as their presenting symptom in a lesser degree than men, 77.5% vs 84.8%. Patients with atypical myocardial infarction symptoms (eg, no chest pain) are less likely to receive a PHECG compared with patients with chest pain, in SWEDEHEART 12.6% vs 35.1%. When stratifying according to presenting symptoms, the sex differences almost disappeared (table 1). In addition, non-ST elevation myocardial infarction patients are less likely to receive a PHECG compared with ST-elevation myocardial infarction patients, in SWEDEHEART 23.4% vs 46.4%. Non-ST elevation myocardial infarction occurs more frequently than ST-elevation myocardial infarction in female patients, in SWEDEHEART 38.0% vs 33.6%. This is also true in the Myocardial Ischaemia National Audit Project (MINARP) cohort,4 which Quinn et al analysed. After stratification of presenting symptom and myocardial infarction type, the sex differences completely disappeared.

Table 1

Prehospital 12-lead electrocardiogram (PHECG) use and sex in patients who came via emergency medical services

We believe that if Quinn et al controls for presenting symptom and myocardial infarction type, the difference in PHECG use among men and women will disappear.

References

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Footnotes

  • Contributors TM contributed to acquisition of data. KK conceived the letter, analysed the data and wrote the first draft. CV, SJ, LA, HB and TM contributed with editing of the content and specifics of the letter. All authors reviewed and approved the final product.

  • Competing interests None.

  • Ethics approval Regionala etikprövningsnämnden i Stockholm (Dnr:2009/587-32).

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

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