Seasonal variations linked to heart failure

An association between winter months and an increase in heart failure has been confirmed by Sally Inglis, a PhD student at The University of Queensland’s School’s of Medicine and Nursing.

Working with a team of researchers from the Departments of Clinical Pharmacology and Cardiology at the Royal Adelaide Hospital, Ms Inglis examined the seasonal differences in hospital admissions and deaths in 2961 patients with chronic heart failure residing in South Australia over the period July 1994 to June 2004.

“After examining the results it was clear that heart failure-related hospitalisations peaked in winter and were lowest in summer," Ms Inglis said.

"Similarly, deaths in those diagnosed with heart failure were higher in winter and lowest in summer.

“Those aged 75 years or older were most at risk of seasonal variations and what was also interesting was that the lowest rate of hospitalisations and deaths was seen in the hottest months of Adelaide (January and February) when temperatures can reach peaks of above 30°C for many days.”

Ms Inglis’s research has attracted international attention. She has just returned from Italy where she presented her findings at the European Society of Cardiology Heart Failure Congress in Milan. And her research paper will be published this month in the European Journal of Heart Failure.

This research is important because it represents one of the first studies to formally identify the global phenomenon of seasonal variations in heart failure in a Mediterranean-style climate comprising of mild winters and warm to hot summer months.

The phenomenon of seasonal variations in heart failure events is well described in the northern hemisphere.

“It was interesting how similar our findings were to those from other climates," she said.

"The climates in which this phenomenon has been previously studied are quite different to that of Adelaide.

"We were surprised that these patients from Adelaide seemed to be able to tolerate the hot summer temperatures in Adelaide without an increase in hospitalisations or deaths which has been reported in some northern hemisphere studies during heat waves.”

Ms Inglis said the findings demonstrated that there are differences in the demand on health services according to the time of the year.

She said the extra pressure exerted on the healthcare system (GPs and hospitals in particular) by these patients with chronic heart failure along with the other “normal” winter increase in the rest of the population could push resources and staff to their limits.

The findings indicated that these patients needed to be paid careful attention in terms of their management in the period before times of higher risk of hospitalisation and death (winter). They needed to be adequately prepared to face this period of increased risk, she said.

“In patients with diagnosed chronic heart failure, these findings further confirm the real risk facing these patients during colder months," Ms Inglis said.

"Patients and their health care providers need to be aware of this and take adequate preventative measures to reduce the risk.”

The actual mechanisms and factors which may contribute to this pattern observed were not fully understood. There could be a combination of physiological, lifestyle and environmental factors which played a part in the vulnerability to colder weather and tolerance to warmer weather observed.

She said further research to be undertaken would allow greater understanding of these factors.

Ms Inglis is supported by the National Health and Medical Research Council and National Heart Foundation of Australia.

(Source: European Journal of Heart Failure: University of Queensland: July 2008)