TOPLINE:

Among patients hospitalised with myocardial infarction (MI), those with expiratory carbon monoxide (CO) levels exceeding 11 ppm had significantly increased risks for 1-year all-cause death and other adverse outcomes.

METHODOLOGY:

• Researchers conducted a prospective study to assess whether expiratory CO levels influenced clinical outcomes in patients with MI.
• They included 717 adults (mean age, 63.6 years; 74.8% men) admitted to intensive cardiac care unit for MI with a culprit lesion across 39 French centres in April 2021.
• Expiratory CO levels were measured within 2 hours of admission, with levels > 11 ppm classified as elevated and levels ≤ 11 ppm classified as low.
• The primary outcome was the occurrence of 1-year all-cause death. Secondary outcomes were 1-year major adverse cardiovascular events and in-hospital major adverse events.

TAKEAWAY:

• Overall, 11% of patients had elevated CO levels; these patients had higher rates of 1-year all-cause death than those with low CO levels (16.5% vs 5.2%; P < .001).
• Elevated CO levels were independently associated with an increased risk for 1-year all-cause death across three models (hazard ratio, 3.6-6.3; P ≤ .001 for all three models).
• More patients with elevated vs low CO levels experienced 1-year major adverse cardiovascular events (19.0% vs 6.8%) and in-hospital major adverse events (25.3% vs 4.7%; P < .001 for both).
• Nearly 85% of patients with elevated CO levels were active smokers; elevated CO levels remained significantly associated with a high risk for 1‑year all-cause death after adjusting for smoking status.

IN PRACTICE:

"Regarding therapeutic opportunities apart from quitting smoking, an initial treatment with oxygen might be helpful in patients with MI who have CO levels > 11 ppm upon arrival to hospital, as recommended for CO poisoning," the researchers wrote.

SOURCE:

This study was led by Antoine Léquipar, Université Paris Cité, Paris, France. It was published online on October 07, 2025, in the European Journal of Preventive Cardiology.

LIMITATIONS:

Researchers could not determine whether CO directly affected prognosis or served as a surrogate marker. The pathophysiologic mechanisms behind poor outcomes in patients with elevated CO levels remained unclear. Data on types of smoking were limited, and patients who only used electronic cigarettes were classified as non-smokers.

DISCLOSURES:

This study received an unrestricted grant from the Foundation "Coeur et Recherche." The authors reported having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.