Electrocardiographic repolarization measurements at rest and during exercise in normal subjects and in patients with coronary artery disease
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K G Lax1, P M Okin, P Kligfield
1Department of Medicine, New York Hospital-Cornell Medical Center, New York 10021.
Insights
Electrocardiogram (ECG) repolarization measures, like QTc, show moderate sensitivity for detecting heart disease during exercise. However, the standard deviation of J-point to T-wave peaks (SD-SoTm) offers a more reliable indicator, even in cases with false-negative stress tests.
Area of Science:
- Cardiology
- Exercise Physiology
- Biomedical Engineering
Background:
- Electrocardiographic (ECG) repolarization measures assess cardiac electrical activity.
- Assessing repolarization during exercise is crucial for diagnosing ischemic heart disease.
- Normal values for ECG repolarization during exercise are needed for accurate interpretation.
Purpose of the Study:
- To establish normal values for ECG repolarization duration and dispersion during treadmill exercise.
- To evaluate the behavior of these measures during exercise-induced ischemia in men with coronary artery disease (CAD).
- To compare the diagnostic utility of temporal repolarization measures (e.g., QTc) versus dispersion measures (e.g., SD-SoTm).
Main Methods:
- Collected data on 94 healthy men and 79 men with proven CAD or stable angina.
- Measured simple and rate-corrected ECG repolarization parameters during treadmill exercise.
- Analyzed the standard deviation of J-point to T-wave peaks across precordial leads (SD-SoTm).
- Compared repolarization measures between normal subjects and patients at matched and peak exercise heart rates.
Main Results:
- Rate-corrected temporal repolarization measures (QTc) showed moderate sensitivity for disease, dependent on exercise heart rate criteria.
- Sensitivity of QTc declined when using matched heart rate data.
- SD-SoTm, a measure of precordial repolarization dispersion, was independent of exercise heart rate in normal subjects.
- Elevated SD-SoTm at peak exercise was observed in 38% of men with CAD, including those with false-negative stress tests.
Conclusions:
- Standard deviation of J-point to T-wave peaks (SD-SoTm) is a more reliable indicator of exercise-induced ischemia than temporal repolarization measures like QTc.
- SD-SoTm can detect coronary artery disease in patients with normal resting ECGs and even in those with false-negative exercise stress tests.
- This dispersion measure offers improved diagnostic potential for identifying significant coronary artery disease during exercise testing.
Abstract:
Normal values for simple and rate-corrected measures of the duration and dispersion of electrocardiographic (ECG) repolarization during treadmill exercise were obtained in 94 clinically normal men, and the behavior of these measures during ischemia was examined in 79 men with catheterization-proven disease or with stable angina, all of whom had normal resting ECGs. Temporal measures of repolarization, exemplified by QTc, were found to be moderately sensitive for disease only when highly specific criteria were derived from data at peak exercise heart rates that were significantly higher in normal subjects than in patients; sensitivities of rate-corrected measures declined markedly when criteria were derived from matched heart rate data in normal subjects. In contrast, the standard deviation of the mean measured J-point to T-wave peaks across the V1 to V6 precordial leads (SD-SoTm), a measure of precordial dispersion of repolarization, was unrelated to exercise heart rate in normal subjects; SD-SoTm exceeding the 95% value at matched intraexercise heart rates in normal subjects was found at peak exercise in 38% of men with coronary disease, including some patients with otherwise false-negative standard exercise test responses.