To analyze the relation between prolonged QT interval and mortality in patients with ST-elevation myocardial infarction and complementarity with Killip, Thrombolysis in Myocardial Infarction (TIMI) and Acute Physiology and Chronic Health Evaluation-II (APACHE-II) scales.
A nested cohort case–control study was conducted in a Spanish hospital. The cohort consisted of patients with ST-elevation myocardial infarction admitted between 2008 and 2010 (n = 524). The cases were the patients who died (n = 38) and the controls (n = 81) were a random sample of those who survived (one of every six).
The corrected QT (QTc) interval of first ECG (prehospital-or-hospital admission) was prolonged in 18 of the 35 patients who died (51.4%) and in 12 of the controls (16.7%; P < 0.001). APACHE-II, TIMI and Killip scores were higher in the patients who had died (P < 0.001). Mortality with prolonged QTc (19.3%) was 20%, and 4.5% were with normal QTc (80.7%; P < 0.001).
Logistic regression showed a relation between mortality with prolonged QTc and TIMI [odds ratio (OR) 3.57(1.16–10.97)]. A second model was constructed with APACHE-II and prolonged QTc [OR 6.47(1.77–23.59)]; receiver operating characteristic (ROC) curve area [0.92(0.87–0.97)], and individually, for APACHE-II was 0.88 (0.81–0.95). A new score was constructed: QTc (not prolonged: 0 points, prolonged: 7 points), age (<65 years: 0 points, 65–74 years: 6 points, ≥75 years: 9 points), Killip (I: 0 points, II–III: 4 points, IV: 17 points). ROC area: 0.88.
Hospital mortality was higher with prolonged QTc at prehospital-or-hospital admission, given equal Killip, TIMI and APACHE values. Discrimination of Killip, TIMI and APACHE values can be improved with prolonged QTc. Discrimination of a model including Killip, age and prolonged QTc is quite good. We have made a new simple prognostic scale with these variables.