Spectral analysis of RR and RT variabilities in patients with coronary artery disease

Background: As the duration of the Q-T interval is dependent upon the length of the preceding cardiac cycle, changes in QT interval duration mainly reflect, in normal subjects, the physiological beat-by-beat variability of the sinus node. However, little information is available on short-term QT variability in patients with an abnormal neural modulation of the sinus node. Methods: We analyzed, with autoregressive techniques, RR and R-T(apex), and R-T(end) variabilities in 12 patients after myocardial infarction, in 13 patients before and after percutaneous transluminal coronary angioplasty (PTCA), and in 10 age-matched controls. Results: No significant differences in mean value and variance of RR, R-T(apex), and R-T(end) interval among the three groups of subjects were observed. Spectral analysis of RR variability was characterized by signs of sympathetic activation with a predominance of low frequency (LF) component in patients after myocardial infarction (69 ± 5 nu) and before PTCA (74 ± 5 nu) in comparison to controls (50 ± 4 nu). Instead, spectral energy was equally distributed within LF and HF (high frequency) components of R-T(apex) and R-T(end) variabilities in the three groups of subjects. Conclusions: These data indicate that the predominance of LF(RR) in normalized units, indicating an increase of sympathetic modulation of sinus node activity in patients with coronary artery disease, are not accompanied by a parallel predominance of the LF component of R-T(apex) and R-T(end) variabilities. This difference reflects, in our opinion, a minor dependency of duration of ventricular repolarization from the preceding cardiac cycle in patients with coronary artery disease.