Respiratory rate predicts outcome after acute myocardial infarction: a prospective cohort study

Abstract

Aims: Risk stratification after acute myocardial infarction (MI) remains imperfect and new indices are sought that might improve the post-MI risk assessment. In a contemporarily-treated cohort of acute MI patients, we tested whether the respiratory rate provides prognostic information and how this information compares to that of established risk assessment.

Methods and results: A total of 941 consecutive patients (mean age 61 years, 19% female) presenting with acute MI were enrolled between May 2000 and March 2005. The last follow-up was performed May 2010. Main outcome measure was total mortality during a follow-up period of 5 years. Patients underwent 10-min resting recordings of the respiratory rate within 2 weeks after MI in addition to the measurement of the left ventricular ejection fraction (LVEF) and standard clinical assessment including the GRACE score. During the follow-up, 72 patients died. The respiratory rate was a significant predictor of death in univariable analysis (hazard ratio 1.19 per 1/min, 95% confidence interval: 1.12-1.27) as was the GRACE score [1.04 (1.03-1.05) per point], LVEF [0.96 (0.94-0.97) per 1%], and the diagnosis of diabetes mellitus [2.78 (1.73-4.47)], all P < 0.0001. On multivariate analysis, the GRACE score (P < 0.0001), respiratory rate (P < 0.0001), LVEF (P = 0.013), and diabetes (P = 0.016) were independent prognostic markers.

Conclusion: The respiratory rate provides powerful prognostic information which is independent and complementary to that of existing risk assessment. Simple and inexpensive assessment of the respiratory rate should be considered a complementary variable for the assessment of risk after acute MI.

Keywords: GRACE score; Left ventricular ejection fraction; Myocardial infarction; Respiration rate; Risk assessment.