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Frequency domain measures of heart period variability to assess risk late after myocardial infarction
J T Bigger1, J L Fleiss, L M Rolnitzky
1Department of Medicine, School of Public Health, Columbia University, New York, New York.
Insights
Spectral measures of heart period variability, assessed one year after myocardial infarction, significantly predict patient mortality. These findings highlight the prognostic value of heart rate variability in long-term post-infarction care.
Area of Science:
- Cardiology
- Medical Statistics
- Physiology
Background:
- Heart period (RR) variability spectral measures are known predictors of mortality within 30 days post-myocardial infarction.
- Prognostic significance of these measures taken later in recovery (beyond 3 months) remains unclear.
- Established spectral measures include ultra-low, very-low, low, and high-frequency power, total power, and the low-to-high frequency ratio.
Purpose of the Study:
- To investigate if spectral measures of heart period variability, assessed one year after myocardial infarction, can predict mortality.
- To evaluate the prognostic value of these heart rate variability metrics in patients who have survived the acute phase of infarction.
Main Methods:
- Utilized 24-hour electrocardiographic (ECG) recordings from patients in the Cardiac Arrhythmia Pilot Study (CAPS) who survived for one year post-infarction.
- Computed 24-hour power spectral density using fast Fourier transforms.
- Calculated six spectral measures and dichotomized values to maximize association with mortality.
Main Results:
- All six RR variability measures showed a strong, significant univariate association with mortality, with relative risks ranging from 2.5 to 5.6.
- Even after adjusting for clinical factors (age, functional class, ejection fraction, etc.) and ventricular arrhythmias, some heart period variability measures retained significant independent predictive power for all-cause mortality.
Conclusions:
- Spectral measures of heart period variability, when assessed one year after myocardial infarction, are significant predictors of death.
- These findings underscore the long-term prognostic utility of heart rate variability analysis in post-myocardial infarction patients.
Objectives:
To determine whether spectral measures of heart period (RR) variability predict death when measured late after infarction, we studied patients in the Cardiac Arrhythmia Pilot Study (CAPS) who survived for 1 year and had a 24-h electrocardiographic (ECG) recording made after the CAPS drug was washed out.
Background:
Four components of the heart period power spectrum--ultra low frequency (< 0.0033 Hz), very low frequency (0.0033 to < 0.04 Hz), low frequency (0.04 to < 0.15 Hz) and high frequency power (0.15 to < 0.40 Hz)--plus total power (1.157 x 10(-5) to < 0.40 Hz) and the ratio of low to high frequency power predict mortality when measured < 30 days after myocardial infarction. However, these variables increase to steady state values by 3 months after infarction and the prognostic significance of recovery values is unknown.
Methods:
The 24-h power spectral density was computed from ECG recordings made 1 year after infarction using fast Fourier transforms and the six measures listed were calculated. The values were dichotomized at cut points that maximized the association with mortality.
Results:
Each measure of RR variability had a strong and significant univariate association with mortality; the relative risks for these variables ranged from 2.5 to 5.6. After adjustment for age, New York Heart Association functional class, rales in the coronary care unit, left ventricular ejection fraction and ventricular arrhythmias, some measures of heart period variability still had a strong and significant independent association with all-cause mortality.
Conclusions:
Spectral measures of heart period variability, measured late after infarction, predict death.