Myocardial infarction (MI) remains under-recognized in chronic lung disease (CLD) patients. Rehabilitation health professionals need accessible clinical measurements to identify the presence of prior MI in order to determine appropriate training prescription. The aim of the study was to estimate prior MI in CLD patients entering a pulmonary rehabilitation program, as well as its association with heart rate parameters such as resting heart rate and chronotropic response index. This was achieved through a retrospective cohort design in a pulmonary rehab outpatient centre involving 85 patients.
Electrocardiograms at rest and peak cardiopulmonary exercise testing, performed before pulmonary rehabilitation, were analyzed. Electrocardiographic evidence of prior MI, quantified by the Cardiac Infarction Injury Score (CIIS), was contrasted with reported myocardial events and then correlated with resting heart rate and chronotropic response index parameters.
Sixteen CLD patients (19%) demonstrated electrocardiographic evidence of prior MI, but less than half (8%) had a reported MI history (P < .05). The Cohen’s kappa test revealed poor level of agreement between CIIS and medical records (kappa = 0.165), indicating that prior MI diagnosis was under-reported in the medical records. Simple and multiple regression analyses showed that resting heart rate but not chronotropic response index was positively associated with CIIS in our population (R2 = 0.29, P < .001). CLD patients with a resting heart rate higher than 80 beats/min had approximately 5 times higher odds of having prior MI, as evidenced by a CIIS ≥20.
CLD patients entering pulmonary rehabilitation are at risk of unreported prior MI. Elevated resting heart rate seems to be an indicator of prior MI in CLD patients; therefore, careful adjustment of training intensity such as intermittent training is recommended under these circumstances.