Manual Measurement of QT Dispersion in Patients with Acute Myocardial Infarction and Nondiagnostic Electrocardiograms

Objective: To determine whether manually measured QT dispersion (QTD) may be a useful diagnostic adjunct for acute myocardial infarction (AMI) in emergency department patients with chest pain (CP) and nondiagnostic initial electrocardiograms (ECGs). Methods: This was a retrospective review of a cohort of patients admitted to the coronary triage unit (CTU) at a large urban facility over a two‐year period (1997‐1999). Cases included all patients with nondiagnostic initial ECGs diagnosed as having AMI by enzymatic criteria. Controls consisted of patients admitted to the CTU who received a final diagnosis of “musculoskeletal pain” at discharge. The QT intervals were measured on the ECGs obtained on presentation. The ECGs were included only if the QT interval could be measured on at least eight out of 12 leads. The QTD was calculated as the difference between the longest and shortest QT intervals in all measured leads. All measurements and calculations were done by a single individual. The QTDs were compared for cases versus controls using 50 msec as a cutoff for the presence of AMI. Results: The study cohort consisted of 36 cases and 124 controls. The QTDs between the two groups were markedly different, with the mean for the cases at 85.5 msec [range: 40 to 200; ±standard deviation (SD) = 39.6] and for the controls 47.1 msec (range: 0 to 120; ±SD = 20.4). The unadjusted odds ratio (OR) of having a QTD greater than 50 msec in the setting of AMI and a nondiagnostic initial ECG in this cohort was 11.9 [95% confidence interval (95% CI) = 5.0 to 28.4; p < 0.0001] and was 12.5 (95% CI = 4.8 to 32.3; p < 0.0001) adjusted for age, gender, and ethnicity. Conclusions: Manually measured QTD is significantly greater in patients with AMI and nondiagnostic ECGs versus healthy controls with musculoskeletal CP. Along with other data, QTD may serve as a useful diagnostic and decision‐making tool in patients with acute CP and nondiagnostic ECGs.