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Hot Weather MI Risk Hinted for Antiplatelets, Beta Blockers

Patients who take beta blockers or antiplatelet agents are lowering their risk for cardiovascular events, but the protection may fall short for those who spend time outdoors on hot summer days, hints a limited analysis published as a letter this week in Nature Cardiovascular Research.

Patients taking either a beta blocker or antiplatelet, or both medications together, appeared at elevated risk for nonfatal acute myocardial infarction (MI) specifically on days when the weather turned hot, suggests the registry cohort study that covered 14 years of clinical and meteorologic data.

“The take-away message is not that patients should stop using these two medications, by no means. We’re raising cautions for patients taking them, to watch out for themselves during high-heat days,” lead author Kai Chen, PhD, Yale School of Public Health, New Haven, Connecticut, told theheart.org | Medscape Cardiology.

“We’re not giving the message that these drugs have harmful effects” because the nature of the links between the medications and MI in the study, with its potential for confounding, remain unknown, said Chen, from the Department of Environmental Health Sciences and Yale Center on Climate Change and Health.

For example, patients who take beta blockers or antiplatelets tend to be sicker than patients not on the drugs, which could make heat-related MI more likely, and the drugs wrongly appear to be culprits, he observed. The analysis contained signals that could support either scenario.

The study is based on cases of nonfatal MI in Augsburg, Germany that are part of the MONICA-KORA MI registry. The odds of a heat-related nonfatal MI, it suggests, were increased 63% among patients taking antiplatelets and by 65% among those on beta blockers, compared with those not on these drugs. The odds went up by 75% among those on both drug classes, but the risks weren’t raised in patients not taking them.

Rising Heat-related MI

Chen said analysis was inspired by a 2019 report — also based on MONICA-KORA, from many of the same authors and using similar methods to track events by daily air temperature — that showed a rising trend for heat-related MI and declining rate for MI related to cold weather from 1987 to 2014. A next step, he figured, would be to determine whether the MI risk trends were associated with any cardiovascular medications.

The current study’s signal of risk related to antiplatelets and beta blockers did not emerge for ACE inhibitors, calcium-channel blockers, or diuretics. Statins showed a link to increased nonfatal MI risk, but solely among participants younger than 60 years, who were also far less likely to have pre-existing coronary heart disease (CHD). He and his colleagues chose not to highlight that finding, Chen said, because the age subgroup analysis was grossly underpowered.

The overall analysis involved 2494 cases of nonfatal MI that occurred during the warmer months — May to September — from 2001 to 2014. It was limited to nonfatal cases — those with at least a month of survival after hospital admission — because of insufficient data on medication use associated with fatal MIs, the report states.

Nonfatal MIs were defined as heat-related if they struck on days reaching the 95th percentile for temperature across the 14 years, in this case 24.2 °C (about 75.6 °F), relative to the average temperature of lowest nonfatal MI risk across the cohort, 7.5 °C (about 45.5 °F).

Patients served as both cases and their own controls, in that air temperature exposures on the day of their MI (case day) were compared with the remaining same days of the week in the same calendar month (control days). That approach, the report states, “automatically controls for long-term time trends, seasonality, day of the week, and time-invariant confounders (for example, pre-existing cardiovascular disease).”

The odds ratio (OR) for heat-related MI for patients on antiplatelets was 1.63 (95% CI, 1.07 – 2.46), and for antiplatelet nonusers was 0.94 (95% CI, 0.68 – 1.29). The difference between the two ratios was significant (= .04).

The corresponding OR for patients taking beta blockers was 1.65 (95% CI, 1.11 – 2.45), and for nonusers of beta blockers was 0.90 (95% CI, 0.64 – 1.26). Again, the OR difference was significant (P = .02).

The ORs for users of both medication classes and nonusers of either med class, respectively, were 1.75 (95% CI, 1.12 – 2.73) and 0.84 (95% CI, 0.59 – 1.19). The latter OR was significantly lower than former (P = .01).

In a sign that antiplatelet and beta blocker use might have been just a marker for sicker patients who were more vulnerable to heat-related MI, Chen said, the nonfatal MI risk was significantly elevated (OR, 2.17; 95% CI, 1.40 – 3.38) among patients with pre-existing CHD, but not among those free of pre-existing CHD (OR 0.88; 95% CI, 0.65 – 1.20); the odds difference was P < .01.

That signal of confounding by indication is somewhat countered, the report states, by variations in nonfatal MI risk by age group. The increased chances of an event seen overall in relation to beta blockers and antiplatelets were more pronounced among the 39% of patients 25 to 59 years (< .01). That’s in spite that group’s lower CHD prevalence. The risk elevation solely among the older patients was attenuated and rendered nonsignificant, even with their greater CHD burden, the report notes.

The report speculates on a potential mechanism by which beta blockers, at least, might conceivably raise the risk for heat-related MI. “Beta-receptor blockers inhibit skin vasodilation, resulting in reduced heat dissipation through convection and, at the same time, could intensify the blood-pressure-lowering effect of other anti-hypertensive drugs, which then could lead to syncope.”

Beta blockers, Chen said, “can mechanistically make people more vulnerable to heat. That’s one potential explanation. Or it could be that these people taking the medications are just sicker. Whatever the reasons, the phenomenon we observed is that these patients taking these two medications are at higher risk during high-temperature days.”

Chen and the other authors declare no competing interests.

Nat Cardiovasc Res. Published online August 1, 2022. Letter

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