Prognostic Value of QTc Dispersion in Acute Myocardial Infarction

Abstract

Introduction Acute myocardial infarction (AMI) is linked to an increased risk of sudden cardiac death (SCD), with malignant ventricular arrhythmias, sustained ventricular tachycardia (VT) and ventricular fibrillation (VF), complicating STEMI (ST-segment elevation myocardial infarction) cases and accounting for a significant proportion of in-hospital SCDs. While advanced risk stratification techniques such as the GRACE (Global Registry of Acute Coronary Events) score depend on laboratory biomarkers and complex algorithms, their need for specialized equipment limits widespread use. Corrected QT (QTc) dispersion (QTd), the difference between the longest and shortest QT intervals on a 12-lead ECG, provides a simple alternative for assessing ventricular repolarization heterogeneity and predicting arrhythmic risk in AMI patients. Previous studies have assessed QTd in AMI populations, reporting associations with ventricular arrhythmias and mortality. However, the definition and measurement of QTd are subject to variability, with controversies surrounding manual versus automated measurement, correction formulas, and ECG lead selection, resulting in reported inter- and intra-observer variability. Methods A prospective observational study was conducted in an emergency and cardiac care setting, enrolling patients diagnosed with STEMI who underwent reperfusion therapy. Demographic data, clinical presentation, and medical history were recorded. Serial 12-lead ECGs were obtained at three time points: admission, post-reperfusion, and 24 hours later. QT intervals were measured manually using calipers, and the QTc interval was calculated using Bazett's formula. QTd was calculated as the difference between maximum and minimum QTc values across the ECG leads. To assess inter-observer variability, a randomly selected subset of ECGs was re-measured by a second cardiologist, and the intraclass correlation coefficient (ICC) was used to quantify agreement. Data analysis was performed using statistical software. Results The study population had a mean age of approximately 61 years, with a majority being male. QTd was significantly elevated in anterior wall myocardial infarction (AWMI) patients, with mean QTd values of 98.96 ± 2.95 ms at admission compared to 85.08 ± 17.02 ms in non-AWMI patients (p < 0.0001), particularly at admission and post-reperfusion. Inferior wall myocardial infarction (IWMI) patients exhibited an initial increase in QTd, which significantly reduced after reperfusion. Posterior wall myocardial infarction (PWMI) patients showed consistently lower QTd across all time points. While this was interpreted as correlating with fewer arrhythmic events, the study did not present actual data on arrhythmia frequency by infarct location. This lack of direct event correlation limits the strength of QTd as a prognostic marker. No significant variations were observed based on comorbidities. Conclusion QTd serves as a useful prognostic marker in AMI. Elevated QTd at admission is linked to a higher arrhythmic risk, particularly in AWMI. A reduction in QTd post-reperfusion supports its potential role in assessing therapeutic effectiveness. Routine QTd measurement may enhance risk stratification and inform clinical decision-making in AMI patients.

Keywords: acute myocardial infarction; electrocardiography; qtc dispersion; risk stratification; ventricular arrhythmias.

Figure 1. Study Design

Image Credits: Dr. Bilal Mohideen