CV benefit of intensive BP lowering may be associated with air pollution exposure
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Exposure to ambient particulate matter less than 2.5 µm may affect CV benefits from intensive BP lowering, according to a post hoc analysis of the SPRINT trial presented at the American College of Cardiology Scientific Session.
This presentation was the first-place winner in the Young Investigator Awards in Clinical Investigation session at the virtual meeting.
Data from the SPRINT trial
Researchers analyzed data from 9,286 patients from the SPRINT trial who were aged at least 50 years who had a systolic BP between 130 mm Hg and 180 mm Hg and were taking either no medications or up to four medications. Patients also had at least one of these risk factors: chronic kidney disease, presence of clinical or subclinical CVD not including stroke, aged at least 75 years and a Framingham risk score for 10-year CVD risk of at least 15%.
“Fine particulate matter includes really small molecules of less than 2.5 µm,” Sadeer G. Al-Kindi, MD, cardiologist at Harrington Heart and Vascular Institute at University Hospitals in Cleveland and a clinical instructor at Case Western Reserve University School of Medicine in Cleveland, said during the presentation. “It’s considered to be the most important environmental risk factor, contributing to global cardiovascular mortality, and possibly one of the mechanisms that mediate the effects on cardiovascular disease is through blood pressure.”
The primary outcome was a composite of MI, stroke, non-MI ACS, HF and CV death.
Each patient underwent an exposure assignment, during which researchers linked annual information on particulate matter exposure of less than 2.5 µm (PM2.5) to patients based on their ZIP code.
The mean PM2.5 was 9.5 µg/m3. There were 1,310 patients who lived in an area above the Environmental Protection Agency threshold, which was close to 12 µg/m3.
BP did not differ between the intensive and standard BP groups at any time point based on the quintiles of PM2.5.
In the lowest quartile of PM2.5, there was no difference in intensive BP lowering and standard BP lowering (HR = 1; 95% CI, 0.72-1.41). In contrast, there were substantial differences between the two groups in the highest quintile of PM2.5 (HR = 0.53; 95% CI, 0.36-0.79).
When researchers assessed individual components of the primary outcome, there were no differences across the quartiles of PM2.5 with regard to MI (P for interaction = .38), HF (P for interaction = .36) and CV death (P for interaction = .32). Differences were observed between intensive and standard BP groups for non-MI ACS (P for interaction = .025) and stroke (P for interaction = .01).
When PM2.5 was treated as a continuous variable, there was an interaction between PM2.5 and reduction in CV events with intensive BP lowering (P for interaction = .047).
“We conclude that ambient air pollution may influence the benefit of intensive blood pressure lowering,” Al-Kindi said during the presentation. “Intensive blood pressure lowering is especially beneficial in patients who live in areas and neighborhoods with high PM2.5 exposure levels. Intensive blood pressure lowering may diminish cardiovascular adverse effects of PM2.5 pollution.”
Al-Kindi emphasized that this analysis has limitations and should be interpreted with caution. He said, “This is a nonspecified post-hoc analysis utilizing satellite-based estimates of PM2.5 exposure, which has many limitations. The SPRINT trial was not powered to identify differences within subgroups. Nevertheless, the study adds to our understanding of air pollution effects on human health and identifies ways to mitigate these effects.”
Future research
During the discussion, Al-Kindi mentioned some next steps regarding research in this area. He said: “Yes, there is a clear epidemiologic association between air pollution and cardiovascular risk. Whether this risk can be mitigated by reducing air pollution levels is not very clear. There is emerging evidence right now in mice models but also in humans to suggest that if you use an air filtration intervention, for example, whereby you give people masks or you give them some nasal filters, there are some home filters that can reduce their risk of hypertension, so it did reduce their blood pressures. ... That translates to significant changes in biomarkers and inflammation. The next question is whether a large-scale trial in patients who have acute coronary syndrome, acute heart failure or even heart transplant patients, whether that can translate into clinical benefit.” – by Darlene Dobkowski
Reference:
Al-Kindi SG, et al. Young Investigator Awards: Clinical Investigations. Presented at: American College of Cardiology Scientific Session; March 28-30, 2020 (virtual meeting).
Disclosure: Al-Kindi reports no relevant financial disclosures.