QT dispersion in the risk stratification of patients with unstable angina: correlation with clinical course, troponin T and scintigraphy

Abstract

Objective — This study sought to evaluate the potential prognostic usefulness of QT dispersion (QTd) in patients with unstable angina.

Methods and results — QTd was calculated and plasma troponin T (TnT) level was measured and rest perfusion imaging with Tc-99m sestamibi was performed in 62 patients admitted with chest pain at rest. All patients had a follow-up during one month in order to assess cardiac events. Cardiac events occurred in 41 patients (no deaths, 11 myocardial infarctions (MI), 4 urgent and 26 planned revascularizations).The mean QTd in patients with cardiac events was significantly higher than in those without cardiac events (68 ± 28 vs. 54 ± 14 ms; p = 0.01).When patients were divided into subgroups according to the cardiac events, the mean QTd in MI and revascularization were 90 ± 25 ms and 60 ± 25 ms, respectively. QTd in patients with MI was higher than in patients without cardiac events (p = 0.001). There was no significant difference in QTd between the revascularization subgroup and patients without cardiac events. Nineteen patients with elevated TnT had a greater QTd compared to patients with normal TnT (74 ± 29 vs. 56 ± 20 ms; p = 0.008). Additionally, the mean QTd in 46 patients with perfusion defects was slightly higher than in patients without (66 ± 27 vs. 53 ± 17 ms; p = 0.03).There was also a moderate correlation between QTd and the number of perfusion defects (r = 0.31, p = 0.01). On the other hand, most of the patients who had a MI or urgent revascularization had a QTd greater than 75 ms.

Conclusion — The measurement of QTd in patients with unstable angina may help to stratify patients at high risk for cardiac events, in particular MI and urgent revascularization.

Key Words:

• QT dispersion
• unstable angina
• troponin T
• SPECT