Frequency domain measures of heart period variability to assess risk late after myocardial infarction

Abstract

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 wa, 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 10−5to <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.