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Beat-to-beat electrocardiographic morphology variation in healed myocardial infarction
S A Ben-Haim1, B Becker, Y Edoute
1Cardiovascular Research Group, Rappaport Family Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Haifa, Israel.
Insights
Electrocardiogram (ECG) analysis reveals subtle variations in patients with myocardial infarction. These ECG morphologic variations may serve as future indicators of heart injury and electrical stability.
Area of Science:
- Cardiology
- Biomedical Engineering
- Signal Processing
Background:
- Myocardial infarction (MI) can lead to chronic myocardial ischemia and conduction abnormalities.
- Subtle electrocardiographic (ECG) variations may reflect underlying myocardial electrical instability.
- Quantifying these variations could provide new insights into post-MI cardiac health.
Purpose of the Study:
- To investigate beat-to-beat ECG morphologic variations in patients with healed Q-wave myocardial infarction compared to healthy controls.
- To explore the potential of these variations as quantitative indexes of myocardial injury and electrical stability.
Main Methods:
- High-fidelity ECG amplifiers were used to record ECGs from 49 men with healed Q-wave MI and 30 age-matched healthy men.
- Forty consecutive beats were averaged to obtain a stable ECG signal for variance calculation.
- Relative variance was computed in two frequency bands (4-40 Hz and 60-120 Hz) at QRS onset and offset.
Main Results:
- Patients with healed MI showed significantly lower relative variance at QRS offset in the low-frequency band (2.1 ± 0.5 vs. 2.5 ± 0.33, p < 0.02).
- Conversely, patients with healed MI exhibited significantly higher relative variance at QRS onset in the high-frequency band (1.95 ± 0.58 vs. 1.55 ± 0.35, p < 0.005).
- These findings suggest distinct patterns of electrical variability post-MI.
Conclusions:
- Changes in ECG variance at QRS onset and offset correlate with myocardial infarction.
- A model involving minor conduction abnormalities in chronically ischemic myocardium explains these observed variance changes.
- ECG variance analysis holds promise as a quantitative tool for assessing myocardial injury and electrical stability in ischemic heart disease.
Abstract:
Using high-fidelity electrocardiographic (ECG) amplifiers, we measured subtle beat-to-beat ECG morphologic variations at different phases of the ECG complex. The electrocardiograms were recorded from 49 men with a documented Q-wave myocardial infarction and from 30 age-matched normal men. Forty consecutive beats were averaged to achieve an average ECG signal from which variance could be calculated. The relative variance, defined as the ratio between the integrated variance of the examined window and the integrated variance of the ECG signal that was close to full cycle length, was calculated at QRS onset and at offset in 2 frequency bands (4 to 40 and 60 to 120 Hz). Patients with healed infarction had a relative variance of 2.1 +/- 0.5 (mean +/- standard deviation [SD]) at QRS offset (a window of 40 ms), which was significantly lower than that of the healthy volunteers: 2.5 +/- 0.33 (mean +/- SD; p less than 0.02) at the low-frequency band. At the high-frequency band, patients with healed infarction had a significantly higher relative variance than the control subjects at QRS onset: 1.95 +/- 0.58 vs 1.55 +/- 0.35 (mean +/- SD; p less than 0.005). A model based on the numerous minor conduction abnormalities that exist in the chronically ischemic myocardium is presented to explain the changes in variance at the onset and offset of the QRS. The variance changes described can eventually serve as quantitative indexes of myocardial injury and electrical stability in patients with ischemic heart disease.