They say more evidence is needed to conclusively state that the two medicines indeed cause heart attacks on hot days.
A new study links beta-blockers to attacks on hot days. (Creative Commons)
Doubts have been cast on a study published in Nature that found two medications prescribed for heart patients to help limit their risk of cardiovascular disease, may also cause heart attacks on hot days.
A doctor contacted by South First claimed that more evidence was needed to establish this as a fact.
Hyderabad cardiologist Dr Prashant Rao said: “This is an hypothetical study. They have not ascertained that these medications are the cause of heart attack. Patients should not stop or change their medicines as their doctors will decide upon the cause. Let’s leave it to the doctors for now.”
The two medications are beta-blockers (medicines such as Propranolol) which may improve quality of life, and antiplatelet drugs (medicines such as clopidogrel) which may reduce the risk of heart attack. The results of the study suggest that these protective measures may also have an opposite effect on particularly hot days.
Though the researchers themselves were cautious in the interpretation of their findings as the research did not directly prove that these drugs caused the heart attacks in the heat.
The researchers investigated the data from the Augsburg Myocardial Infarction Registry in Germany from 2001 to 2014 for their analysis. A total of 2,494 cases were examined during the months of May to September.
The researchers found a significantly increased risk of nonfatal myocardial infarction on hot days compared with cooler control days in patients taking antiplatelet medications or beta-blockers, compared with patients not taking these drugs.
Antiplatelet use was associated with a 63 percent increase in risk, and beta-blockers use was associated with a 65 percent increase in risk. Patients who took both medications had a 75 percent higher risk.
The study also mentioned that non-users of these medications were not more likely to have a heart attack on hot days.
Also, the effect of medication use was stronger in the younger age group of 25-59 years than for older patients in the age group 60-74 years, even though the latter were more likely to have underlying coronary heart disease.
“The results suggest that heart attacks may become a greater risk for patients with existing cardiovascular diseases as climate change progresses and hot and very hot days become more frequent,” explained Dr. Alexandra Schneider, an author of the study.
The research findings do not directly prove that these drugs caused the heart attacks on hot days. However, based on these data, the scientists speculate that taking the medications makes it more difficult for the body to thermoregulate — adapt to high temperatures.
“The medication could actually make these patients more sensitive to heat exposure. However, it is also conceivable that the underlying severe heart disease explains both the prescription of the drugs and the higher sensitivity of these patients to heat,” reads the study.
“Until more studies are done, we should not generalise this finding. South India being a heat sensitive part of the country, we are only going to not prescribe these medicines after we have clear epidemiological evidence,” Dr Rao told South First.
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