Time to Treatment Influences the Impact of ST-Segment Resolution on One-Year Prognosis

Abstract

Background Early ST resolution after reperfusion is a prognostic indicator in acute myocardial infarction. Little information exists regarding the prognostic utility of ST resolution beyond 4 hours after fibrinolysis. Furthermore, the relation between time to treatment, ST resolution at 24 to 36 hours, and 1-year outcome has not been well studied. Accordingly, we undertook a prospective ECG substudy in the Assessment of the Safety and Efficacy of a New Thrombolytic (ASSENT-2) trial to examine this. Methods and Results Patients (n=13 100) were stratified into 3 ST-resolution categories, based on baseline and 24- to 36-hour ECGs: complete resolution (≥70%) in 6698 (51.1%) patients, partial resolution (30% to 70%) in 4610 (35.2%) patients, and no resolution (<30%) in 1792 (13.7%) patients; 1-year mortality rate was 5.1%, 8.0%, and 9.7%, respectively ( P <0.001). Among patients treated <2 hours after symptom onset, 55.6% had complete ST resolution, whereas 52.1% and 43% of patients treated between 2 to 4 hours and 4 to 6 hours, respectively, had complete ST resolution ( P <0.001). Within each category of ST resolution, patients treated <2 hours had lower 1-year mortality rates as compared with patients treated between 2 to 4 hours or >4 hours (3.8% versus 5.2% and 6.6%, P =0.002 in complete ST resolution; 5.7% versus 8.4% and 9.9%, P =0.001 in partial ST resolution; 7.1% versus 8.7% and 13%, P =0.006 in no resolution). The extent of ST resolution was closely and inversely correlated with 1-year mortality rates ( r =−0.963, P <0.001). Conclusions ST resolution at 24 to 36 hours after fibrinolysis is influenced by time to treatment and inversely related to 1-year mortality rates. Time to treatment further differentiates between high- and low-risk patients and further highlights the importance of reducing time delay to initiation of fibrinolysis in acute myocardial infarction.