The prognostic value of expiratory carbon monoxide level for outcome prediction after myocardial infarction.

Aims: To assess the prognostic value of expiratory carbon monoxide (CO) levels in patients admitted for myocardial infarction (MI).

Methods and results: In this prospective study, expiratory CO levels were measured upon admission in consecutive patients hospitalized for MI across 39 centres. The primary outcome was 1-year all-cause death. Secondary outcomes included 1-year major adverse cardiac events (MACEs: cardiovascular death and recurrent MI) and in-hospital major adverse events (MAEs: death, severe ventricular arrhythmia, cardiogenic shock, and the need for mechanical ventilation). The prognostic value of expiratory CO levels was further evaluated using machine learning (ML) analysis. Among 717 patients (64 ± 13 years; 75% males; 33% active smokers; 43% ST-elevation MI), elevated expiratory CO levels (>11 ppm) were found in 79 patients (11%). Patients with elevated CO levels had a higher rate of 1-year all-cause mortality compared with those without (16.5% vs. 5.2%, P < 0.001). Elevated CO levels were independently associated with 1-year all-cause death across various adjustment models: comorbidities [odds ratio (95% confidence interval): 3.6 (1.7-7.5)], clinical parameters of in-hospital severity [4.5 (2.3-8.8)], and respiratory parameters [6.3 (3.1-12.8)]. Elevated CO levels were also independently associated with a significant increase in 1-year MACEs and in-hospital MAEs. Machine learning analysis identified CO level as one of the most important predictors of adverse events, compared with other known prognosticators.

Conclusion: This is the first study to demonstrate that elevated expiratory CO levels upon admission are independently associated with an increased risk of 1-year all-cause mortality, 1-year MACEs, and in-hospital MAEs in patients hospitalized for MI.