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A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis
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Beat-to-beat QT interval variability associated with acute myocardial ischemia

Taizo Murabayashi1, Barry Fetics, David Kass

  • 1Cardiology Division, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, MD, USA.

Journal of Electrocardiology
|January 12, 2002
PubMed

Insights

Myocardial ischemia destabilizes ventricular repolarization, significantly increasing QT interval variability (QTV). Heart rate variability (HRV) showed no significant change during ischemic events, suggesting QTV is a sensitive marker for ischemia-induced repolarization instability.

Area of Science:

  • Cardiology
  • Electrophysiology
  • Medical Signal Analysis

Background:

  • Beat-to-beat QT interval variability (QTV) measures the lability of ventricular repolarization.
  • Myocardial ischemia is suspected to destabilize ventricular repolarization, potentially increasing QTV.

Purpose of the Study:

  • To investigate the hypothesis that myocardial ischemia increases QTV.
  • To analyze the relationship between ischemic episodes and QTV in patients.

Main Methods:

  • Analysis of 2-hour, 2-lead digitized electrocardiogram (ECG) records from 68 patients in the European ST-T Database.
  • Automated determination of normalized QTV (QTVnorm), QT variability index (QTVI), and normalized heart rate variability (HRVnorm) for 5-minute epochs.
  • Comparison of QTV and HRV metrics during annotated ischemic and non-ischemic episodes.

Main Results:

  • QTVnorm was significantly higher during ischemic episodes compared to non-ischemic episodes (1.41 ± 0.77 vs. 0.88 ± 0.23, P < .0001).
  • The QTVI was also significantly higher during ischemic episodes (-0.051 ± 0.12 vs. 0.14 ± 0.31, P < .0001).
  • No significant difference in HRVnorm was observed between ischemic and non-ischemic episodes (1.22 ± 0.63 vs. 0.94 ± 0.18, P > .05).

Conclusions:

  • Acute myocardial ischemia is associated with increased lability in ventricular repolarization, reflected by enhanced beat-to-beat QTV.
  • QTV appears to be a more sensitive indicator of ischemia-induced repolarization changes than HRV.
  • Further research is warranted to explore the link between ischemic repolarization liability and the risk of arrhythmias.

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