Relationship between the QTc interval at hospital admission and the severity of the underlying ischaemia in low and intermediate risk people studied for acute chest pain.

Background: The corrected QT interval (QTc) is prolonged in the setting of acute coronary artery disease. However, very little data are available concerning the relationship between the QTc obtained soon after an episode of acute chest pain (ACHP) and the magnitude and severity of the myocardial ischaemia objectified in subsequent stress tests (STS).
Methods: This was a prospective and observational study in which we investigated the relationship between the QTc determined on the hospital admission electrocardiogram (AQTc) using Bazett's formula and the results of the STS performed subsequently in 206 patients consecutively admitted to the Emergency Department for ACHP without persistent ST-elevation.
Results: The mean AQTc was 456+/-60 ms. There were 88 (42%) individuals with a moderately or severely abnormal STS. The AQTc was longer in the patients with a moderately or severely abnormal STS: 490+/-52 versus 430+/-56 (p<0.001) and was correlated with the probability of the patient having a moderately or severely abnormal STS (c=0.84; p<0.001). The best cut-off point was 450 ms (sensitivity, specificity and negative predictive value: 81, 77 and 84 %). Patients with AQTc>or=450 had a higher frequency of moderately or severely abnormal STS (73 versus 16%; OR: 2.9; 95% CI: 2.1-4.1; p<0.001). After adjusting for age, sex, cardiac risk factors, cardiac history, QRS duration, ST-depression, troponin I release and pre-STS medical treatment, AQTc>or=450 remained as an independent predictor (OR: 12; 95% CI: 6-24; p<0.001).
Conclusions: In patients studied for ACHP, the QTc on the hospital admission electrocardiogram correlates with the underlying myocardial ischaemia. AQTc>or=450 ms selects a group of people at risk of presenting a moderately or severely abnormal STS, regardless of ST abnormalities and troponin release.