Seasonal variations in chronic heart failure (CHF), which include increased hospitalizations in the winter months, are extensively documented in the northern<!–[if supportFields]> XE “northern” <![endif]–><!–[if supportFields]><![endif]–> hemisphere, but there are few data regarding the phenomenon of seasonal variation of CHF in the southern hemisphere. By analyzing the prevalence of CHF within the state of South Australia<!–[if supportFields]> XE “Australia” <![endif]–><!–[if supportFields]><![endif]–> from 1994–2005, Inglis et al. (2008) observed increases in CHF-related morbidity and mortality in the winter months (June-August).—Dylan Farrell
Inglis, S.C<!–[if supportFields]> XE “carbon, C” <![endif]–><!–[if supportFields]><![endif]–>., Clark, R., Shakib, S., Wong, D., Molaee, P., Wilkinson, D., Stewar, S. 2008. Hot summers and heart faiure: seasonal variations in morbidity and mortality in Australian heart failure patients (1994–2005). European Journal of Heart Failure 10, 540–549.
Chronic heart failure, a condition in which the structure or function of the heart is impaired in its capability to supply blood flow to meet the body’s needs, is a common condition among men and women around the world. Individuals greater than 75-years old are most vulnerable to mortality and morbidity related to CHF. The prevalence of CHF within South Australia greatly affects the population and national healthcare system.
Inglis et al. analyzed clinical data in a cohort of 2961 patients with diagnosed CHF conditions that were admitted to South Australia<!–[if supportFields]> XE “Australia” <![endif]–><!–[if supportFields]><![endif]–>’s largest tertiary referral hospital. CHF-related hospital admissions were confirmed by clinical symptoms and documented evidence, such as echocardiograph data and other cardiac investigations. The researchers also examined respiratory-related morbidity for investigation of comparable seasonal variation. All causes of hospitalizations, including all unplanned hospital visits and death from any cause, were also examined for evidence of seasonal variation.
Significantly higher rates of CHF hospitalizations were observed in July (winter) than in February (summer). Trends also seen in respiratory-related morbidity, all causes of hospitalizations, and all causes of mortality, something the authors note also occurs in the northern<!–[if supportFields]> XE “northern” <![endif]–><!–[if supportFields]><![endif]–> hemisphere. The mortality rates for males and females were very similar, 8 vs. 7 deaths per 100 at risk.
The observed seasonal variance in morbidity and mortality may be explained by a number of physiological mechanisms. Studies by Cui et al. (2005) and Green et al. (2006) found that cutaneous vasodilator response to heat was reduced in patients with CHF, whereas sweating responses were not impaired. Their studies also showed that CHF patients exhibit impaired thermoregulatory responses to heat exposure, possibly facilitated by lower skin blood flow (Green et al.). This research suggests that there may be some benefit of hotter weather for individuals with CHF. An earlier study conducted by Westheim et al. (1992) examined the increase in haemodynamic stress and neurohormonal activation of CHF patients during winter months, and suggested that these stresses increase CHF rates in colder winter months.
Inglis et al. demonstrated obvious seasonal variations in CHF-related morbidity and mortality in a cohort of patients located in the southern hemisphere. As human activity continues to alter the earth’s climate, temperatures will increase across the globe. Their research suggests that a decrease in cold stress due to global warming may be a comforting prospect for individuals with CHF-related conditions. The relationship between temperature change and CHF-related morbidity and mortality may present an atypical health benefit for a large portion of the global population. —Dylan Farrell