Clinical outcome predicted by coronary flow reserve in patients with a prior myocardial infarction

Background Survivors of myocardial infarction (MI) are at a 30% risk of new major adverse cardiovascular events (MACE) including death, myocardial infarction and stroke. Coronary flow reserve (CFR) is a strong and independent predictor of MACE. Purpose The aim was to evaluate the importance of impaired CFR as a predictor of MACE in this patient group, which aids in the development of personalised medicine for high-risk individuals with prior MI. Methods PROFLOW (PROspective evaluation of coronary FLOW reserve and molecular biomarkers in patients with established coronary artery disease) is a prospective, exploratory study with 3 years follow-up. We used information from the SCAAR (Swedish Coronary Angiography and Angioplasty Registry) to identify high-risk patients with a history of type-1 MI. We measured CFR non-invasively in the left anterior descending artery (LAD) using transthoracic Doppler echocardiography. Coronary flow velocity was first measured at rest and then at maximal flow after induction of hyperaemia by intravenous infusion of adenosine (140 μg/kg/min). An adjusted time-to-event analysis using Cox regression was used to evaluate a dichotomized CFR, low (≤ 2.5) versus high (> 2.5), in relation to MACE. Results We included 582 patients with a measurable CFR value at baseline with a large portion suffering from low (≤ 2.5) CFR (42.1%). The patients in the low CFR group were slightly older, 69.5 vs. 67.7 with a higher percentage of women, 22.9% vs. 14.8%, and a larger proportion with incomplete revascularization, 31.0% vs. 20.2%. More patients in the high CFR group were prescribed ticagrelor 17.2% vs. 6.9%. The groups were fairly balanced on the majority of other factors. In a multivariable Cox model, lower CFR showed a higher hazard rate for MACE 1.89 CI (1.14 3.13). There were no significant interactions for any of the subgroups: age, sex, hypertension, diabetes, smoking, history of stroke or CABG. Conclusions In patients with prior MI, a lower CFR value was associated with a higher adverse MACE rate.