Skip to main navigation menu Skip to main content Skip to site footer

Original article

Vol. 151 No. 3738 (2021)

Heat-related cardiovascular morbidity and mortality in Switzerland: a clinical perspective

  • Florian Schulte
  • Martin Röösli
  • Martina S. Ragettli
Cite this as:
Swiss Med Wkly. 2021;151:w30013



AIMS: Previous studies found increased cardiovascular mortality during hot days, while emergency hospital admissions were decreasing. We explored potential underlying reasons by analysing clinically similar cardiovascular disease groups taking into account primary, underlying and immediate causes of death.

METHODS AND RESULTS: We assessed associations of daytime maximum temperature in relation to cardiovascular deaths and emergency hospital admissions between 1998 and 2016 in Switzerland. We applied conditional quasi-Poisson models with non-linear distributed lag functions to estimate relative risks (RRs) of daily cardiovascular mortality and morbidity for temperature increases from the median (22 °C) to the 98th percentile (32 °C) of the warm season temperature distribution with 10 days of lag. Cardiovascular mortality (n = 163,856) increased for total cardiovascular disease (RR 1.13, 95% confidence interval [CI] 1.08–1.19) and the disease groups hypertension (1.18, 1.02–1.38), arrhythmia (1.29, 1.08–1.55), heart failure (1.22, 1.05–1.43) and stroke of unknown origin (1.20, 1.02–1.4). In contrast, emergency hospital admissions (n = 447,577) decreased for total cardiovascular disease (0.91, 0.88–0.94), hypertension (0.72, 0.64–0.81), heart failure (0.83, 0.76–0.9) and myocardial infarction (0.88, 0.82–0.95). Opposing heat effects were most pronounced for disease groups associated with diuretic and antihypertensive drug use, with the age group ≥75 years at highest risk.

CONCLUSIONS: Volume depletion and vasodilation from heat stress plausibly explain the risk reduction of heat-related emergency hospital admissions for hypertension and heart failure. Since primary cause of death mostly refers to the underlying chronic disease, the seemingly paradoxical heat-related mortality increase can plausibly be explained by an exacerbation of heat effects by antihypertensive and diuretic drugs. Clinical guidelines should consider recommending strict therapy monitoring of such medication during heatwaves, particularly in the elderly.


  1. Costello A, Abbas M, Allen A, Ball S, Bell S, Bellamy R, et al. Managing the health effects of climate change: Lancet and University College London Institute for Global Health Commission. Lancet. 2009 May;373(9676):1693–733.
  2. Bunker A, Wildenhain J, Vandenbergh A, Henschke N, Rocklöv J, Hajat S, et al. Effects of Air Temperature on Climate-Sensitive Mortality and Morbidity Outcomes in the Elderly; a Systematic Review and Meta-analysis of Epidemiological Evidence. EBioMedicine. 2016 Apr;6:258–68.
  3. Confalonieri U, Menne B, Akhtar R, Ebi KL, Hauengue M, Kovats RS, et al. Human health. In: Climate Change 2007: Impacts, Adaptation and Vulnerability Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press; 2007. p. 391–431.
  4. Gasparrini A, Guo Y, Hashizume M, Lavigne E, Zanobetti A, Schwartz J, et al. Mortality risk attributable to high and low ambient temperature: a multicountry observational study. Lancet. 2015 Jul;386(9991):369–75.
  5. Ragettli MS, Vicedo-Cabrera AM, Schindler C, Röösli M. Exploring the association between heat and mortality in Switzerland between 1995 and 2013. Environ Res. 2017 Oct;158(May):703–9.
  6. Vicedo-Cabrera AM, Sera F, Guo Y, Chung Y, Arbuthnott K, Tong S, et al. A multi-country analysis on potential adaptive mechanisms to cold and heat in a changing climate. Environ Int. 2018 Feb;111(111):239–46.
  7. Rodrigues M, Santana P, Rocha A. Modelling of Temperature-Attributable Mortality among the Elderly in Lisbon Metropolitan Area, Portugal: A Contribution to Local Strategy for Effective Prevention Plans. J Urban Health. 2021 Apr;1–16: [cited 2021 Aug 5]
  8. Saucy A, Ragettli MS, Vienneau D, de Hoogh K, Tangermann L, Schäffer B, et al. The role of extreme temperature in cause-specific acute cardiovascular mortality in Switzerland: A case-crossover study. Sci Total Environ. 2021 Oct;790:147958.
  9. Lee JY, Röösli M, Ragettli MS. Estimation of Heat-Attributable Mortality Using the Cross-Validated Best Temperature Metric in Switzerland and South Korea. Int J Environ Res Public Health. 2021 Jun;18(12):6413.
  10. Institute for Health Metrics and Evaluation (IHME). GBD Compare [Internet]. 2018 [cited 2018 Oct 4]. Available from:
  11. Moghadamnia MT, Ardalan A, Mesdaghinia A, Keshtkar A, Naddafi K, Yekaninejad MS. Ambient temperature and cardiovascular mortality: a systematic review and meta-analysis. PeerJ. 2017 Aug;5:e3574.
  12. Campbell S, Remenyi TA, White CJ, Johnston FH. Heatwave and health impact research: A global review. Health Place. 2018 Sep;53:210–8.
  13. Ponjoan A, Blanch J, Alves-Cabratosa L, Martí-Lluch R, Comas-Cufí M, Parramon D, et al. Effects of extreme temperatures on cardiovascular emergency hospitalizations in a Mediterranean region: a self-controlled case series study. Environmental health : a global access science source. 2017;16(1):32.
  14. Turner LR, Barnett AG, Connell D, Tong S. Ambient temperature and cardiorespiratory morbidity: a systematic review and meta-analysis. Epidemiology. 2012 Jul;23(4):594–606.
  15. Ragettli MS, Vicedo-Cabrera AM, Flückiger B, Röösli M. Impact of the warm summer 2015 on emergency hospital admissions in Switzerland. Environ Health. 2019 Aug;18(1):66.
  16. Basu R, Pearson D, Malig B, Broadwin R, Green R. The effect of high ambient temperature on emergency room visits. Epidemiology. 2012 Nov;23(6):813–20.
  17. Bundesamt für Statistik. Schweizerische Todesursachenstatistik - Richtlinien für die ärztliche Bescheinigung der Todesursachen. 1996 [cited 2020 Jun 22]. Available from:
  18. Nose H, Kamijo YI, Masuki S. Interactions between body fluid homeostasis and thermoregulation in humans. Handb Clin Neurol. 2018;156:417–29.
  19. Rowell LB, Brengelmann GL, Murray JA. Cardiovascular responses to sustained high skin temperature in resting man. J Appl Physiol. 1969 Nov;27(5):673–80.
  20. Schlader ZJ, Wilson TE, Crandall CG. Mechanisms of orthostatic intolerance during heat stress. Auton Neurosci. 2016 Apr;196:37–46.
  21. Heidari L, Winquist A, Klein M, O’Lenick C, Grundstein A, Ebelt Sarnat S. Susceptibility to Heat-Related Fluid and Electrolyte Imbalance Emergency Department Visits in Atlanta, Georgia, USA. Int J Environ Res Public Health. 2016 Oct;13(10):E982. [cited 2020 Apr 17] Available from:
  22. Petitti DB, Hondula DM, Yang S, Harlan SL, Chowell G. Multiple Trigger Points for Quantifying Heat-Health Impacts: New Evidence from a Hot Climate. Environ Health Perspect. 2016 Feb;124(2):176–83.
  23. Borgman MA, Zaar M, Aden JK, Schlader ZJ, Gagnon D, Rivas E, et al. Hemostatic responses to exercise, dehydration, and simulated bleeding in heat-stressed humans. Am J Physiol Regul Integr Comp Physiol. 2019 Feb;316(2):R145–56.
  24. Meyer MA, Ostrowski SR, Overgaard A, Ganio MS, Secher NH, Crandall CG, et al. Hypercoagulability in response to elevated body temperature and central hypovolemia. J Surg Res. 2013 Dec;185(2):e93–100.
  25. Gasparrini A, Armstrong B, Kenward MG. Distributed lag non-linear models. Stat Med. 2010 Sep;29(21):2224–34.
  26. Scovronick N, Sera F, Acquaotta F, Garzena D, Fratianni S, Wright CY, et al. The association between ambient temperature and mortality in South Africa: A time-series analysis. Environ Res. 2018 Feb;161:229–35.
  27. Whelton PK, Carey RM, Aronow WS, Casey DE Jr, Collins KJ, Dennison Himmelfarb C, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol. 2018 May;71(19):e127–248.
  28. Ponikowski P, Voors AA, Anker SD, Bueno H, Cleland JG, Coats AJ, et al. 2016 ESC Guidelines for the Diagnosis and Treatment of Acute and Chronic Heart Failure. Rev Esp Cardiol (Engl Ed). 2016 Dec;69(12):1167.
  29. Gasparrini A, Armstrong B, Kovats S, Wilkinson P. The effect of high temperatures on cause-specific mortality in England and Wales. Occup Environ Med. 2012 Jan;69(1):56–61.
  30. Lian H, Ruan Y, Liang R, Liu X, Fan Z. Short-Term Effect of Ambient Temperature and the Risk of Stroke: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health. 2015 Jul;12(8):9068–88.
  31. Fischer U, Arnold M, Nedeltchev K, Schoenenberger RA, Kappeler L, Höllinger P, et al. Impact of comorbidity on ischemic stroke outcome. Acta Neurol Scand. 2006 Feb;113(2):108–13.
  32. Ostwald SK, Wasserman J, Davis S. Medications, comorbidities, and medical complications in stroke survivors: the CAReS study. Rehabil Nurs. 2006 Jan-Feb;31(1):10–4.
  33. Sun Z, Chen C, Xu D, Li T. Effects of ambient temperature on myocardial infarction: A systematic review and meta-analysis. Environ Pollut. 2018 Oct;241:1106–14.
  34. Ruperti Repilado FJ, Doerig L, Blum S, Aeschbacher S, Krisai P, Ammann P, et al. Prevalence and predictors of atrial fibrillation type among individuals with recent onset of atrial fibrillation. Swiss Med Wkly. 2018 Sep;148(3738):w14652. [cited 2019 Dec 11] Available from:
  35. van den Hurk K, de Kort WL, Deinum J, Atsma F. Higher outdoor temperatures are progressively associated with lower blood pressure: a longitudinal study in 100,000 healthy individuals. J Am Soc Hypertens. 2015 Jul;9(7):536–43.
  36. Ernest H. Starling. The Linacre lecture on the Law of the Heart. London: Longmans, Green and Co.; 1918 [cited 2020 May 1]. 30 p. Available from:
  37. Yancy CW, Jessup M, Bozkurt B, Butler J, Casey DE Jr, Drazner MH, et al.; American College of Cardiology Foundation; American Heart Association Task Force on Practice Guidelines. 2013 ACCF/AHA guideline for the management of heart failure: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2013 Oct;62(16):e147–239.
  38. Williams B, Mancia G, Spiering W, Agabiti Rosei E, Azizi M, Burnier M, et al.; ESC Scientific Document Group. 2018 ESC/ESH Guidelines for the management of arterial hypertension. Eur Heart J. 2018 Sep;39(33):3021–104.
  39. Fitzsimons JT. Angiotensin, thirst, and sodium appetite. Physiol Rev. 1998 Jul;78(3):583–686.
  40. Oldenburg B, MacDonald GJ, Shelley S. Controlled trial of enalapril in patients with chronic fluid overload undergoing dialysis. Br Med J (Clin Res Ed). 1988 Apr;296(6629):1089–91.
  41. Hausfater P, Megarbane B, Dautheville S, Patzak A, Andronikof M, Santin A, et al. Prognostic factors in non-exertional heatstroke. Intensive Care Med. 2010 Feb;36(2):272–80.
  42. Balmain BN, Sabapathy S, Jay O, Adsett J, Stewart GM, Jayasinghe R, et al. Heart Failure and Thermoregulatory Control: Can Patients With Heart Failure Handle the Heat? J Card Fail. 2017 Aug;23(8):621–7.
  43. Smirnova MD, Svirida ON, Ageev FT. Protective measures of patients with cardiovascular diseases from exposure to heat waves: medicated and non-medicated. Ter Arkh. 2019 Mar;91(1):101–7.
  44. Tait PW, Allan S, Katelaris AL. Preventing heat-related disease in general practice. Aust J Gen Pract. 2018 Dec;47(12):835–40.
  45. Sweeney KG. Heat-related deaths. J Insur Med. 2002;34(2):114–9.
  46. Yellon DM, Pasini E, Cargnoni A, Marber MS, Latchman DS, Ferrari R. The protective role of heat stress in the ischaemic and reperfused rabbit myocardium. J Mol Cell Cardiol. 1992 Aug;24(8):895–907.
  47. Balmain BN, Sabapathy S, Louis M, Morris NR. Aging and Thermoregulatory Control: The Clinical Implications of Exercising under Heat Stress in Older Individuals. BioMed Res Int. 2018 Aug;2018:8306154.
  48. Armstrong B, Sera F, Vicedo-Cabrera AM, Abrutzky R, Åström DO, Bell ML, et al. The Role of Humidity in Associations of High Temperature with Mortality: A Multicountry, Multicity Study. Environ Health Perspect. 2019 Sep;127(9):97007.
  49. Buckley JP, Samet JM, Richardson DB. Commentary: does air pollution confound studies of temperature? Epidemiology. 2014 Mar;25(2):242–5.
  50. Biondi-Zoccai G, Frati G, Gaspardone A, Mariano E, Di Giosa AD, Bolignano A, et al. Impact of environmental pollution and weather changes on the incidence of ST-elevation myocardial infarction. Eur J Prev Cardiol. 2020 Jun; :2047487320928450.

Most read articles by the same author(s)