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Heatwaves have life-threatening effects on heart failure patients

Patients who have suffered from heart failure are often placed on diuretic drugs to help them control the fluid levels in their bodies. Since the heart does not pump as efficiently in these patients, waste products accumulate in the body, causing shortness of breath and a build-up of fluid in the lungs, legs and abdomen. Diuretic drugs increase the production of urine in these patients so that they can avoid the negative effects of fluid retention. However, this gives rise to a potentially dangerous situation if these patients are exposed to the hot and dehydrating conditions of a heatwave.

Care of heart failure patients involves close monitoring of their weight on a daily basis in order to detect sudden swelling or edema, which is the main reason for hospital admission. The European Society of Cardiology (ESC) guidelines recommend educating patients to increase their diuretic dose or alert their healthcare team if they experience an increase in breathlessness or swelling, or a sudden unexpected weight gain of more than 2 kg in three days.  These conditions could indicate that the heart is under strain or that the dosage of diuretic medication needs to be increased. 

Heart failure patients are not commonly instructed to look out for instances of weight loss, a situation that could be dangerous in times of hot temperatures, state the authors of a new study. “When healthy people drink more fluids during hot weather, the body automatically regulates urine output. This does not apply to patients with heart failure because they take diuretics,” explained study author Professor François Roubille of Montpellier University Hospital, France.

The nationwide study conducted in France linked hot temperatures during the 2019 heatwave with weight loss in heart failure patients. This may potentially indicate dehydration and is associated with a worsening condition in these patients who will not be aware of the danger if they are focused on monitoring their weight for increases only. The findings are published in ESC Heart Failure, the open access journal of the Heart Failure Association (HFA) of the European Society of Cardiology.

“This study is the first to show a strict relationship between ambient temperature and body weight in heart failure patients,” said Professor Roubille. “The finding is timely given the heatwaves again this year. The weight loss we observed in people with heart failure may lead to low blood pressure, especially when standing up, and renal failure, and is potentially life-threatening. With rising temperatures forecast for the future, clinicians and patients should be ready to reduce the dose of diuretics when weight loss occurs.”

The study made use of a national telemonitoring system to examine the relationship between body weight and air temperature in heart failure patients between 1 June and 20 September 2019. During this time, two heatwaves occurred, one at the end of June and the other at the end of July. The participants included 1,420 patients with chronic heart failure who weighed themselves every day using a connected scale that automatically sent their data to the clinic. They also reported daily symptoms such as edema, fatigue, breathlessness and coughing by answering questions on a personal device (e.g. smartphone, tablet) that also sent their answers automatically to the clinic.

Data that was collected remotely in this way was combined with measurements of daily noontime temperatures from the closest weather station to each patient’s home. The researchers analyzed the association between patient weight, ambient temperature on the same day, and temperature two days prior to the weight measurement. The negative relationship between temperature and weight was very strong, with weight decreasing as temperature increased. The strongest relationship was found between a patient’s weight and the ambient temperature two days prior to the weight measurement. 

“The weight loss we observed during the heatwave was clinically relevant. Patients weighing 78 kg lost 1.5 kg in a short period of time. We were surprised to see that weight dropped with hot temperatures, as we had expected the opposite. For this reason, the telemonitoring system was programmed to alert clinicians when patients gained weight,” said Professor Roubille.

“Given the expectation of more heatwaves, telemonitoring systems also need to alert clinicians of weight loss in heart failure patients. In addition, systems could notify patients losing weight that it may be due to the heat and they should contact their healthcare provider about reducing the dose of diuretics. For heart failure patients not monitored remotely, a good rule of thumb would be to contact a healthcare professional if weight drops by 2 kg during a heatwave for advice on adjusting diuretic medication. Reacting early should help us to prevent complications.”

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By Alison Bosman, Staff Writer

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