Relationship between Beat-to-Beat Variability of RT-Peak and RT-End Intervals in Normal Controls, Patients with Anxiety, and Patients with Cardiovascular Disease
Methods: In this study, we examined the relationship between the variability of beat-to-beat RTe (beginning of R-peak to T-end) and the variability of RTp (R-peak to T-peak) in the following groups: normal controls (n = 26), patients with anxiety (n = 26), and patients with cardiovascular disease with or without diabetes (n = 63). We obtained ECG sampled at 1024 Hz in lead II configuration in supine posture to obtain beat-to-beat interbeat interval (R–R) and RT-interval variability for 256 seconds.
Results: We found significant positive correlations (r = 0.8; P < 0.00001) in normal controls and patients with anxiety between the variability of RTeVI and RTpVI (RTe and RTp variability indices, respectively, corrected for the mean of RTe and RTp and the mean and the variance of R–R). These correlations were also statistically significant in the medically ill group but the r values were much smaller (r = 0.45 in various groups). The slopes were also significantly different between the two groups (P < 0.001). Bland–Altman plots also showed better agreement between the two measures in the controls and patients with anxiety compared to the group with cardiovascular disease.
Conclusions: These findings have methodological implications for studies comparing people with and without overt cardiovascular illness. While RTe or RTp variability index may be used interchangeably in normal controls and some patients with no overt cardiovascular problems, it may be more prudent to use both RTe and RTp variability indices in patients with cardiovascular illness. These indices, especially RTeVI, may provide different information about cardiac repolarization lability. Future studies should address the importance of the relative usefulness of these two measures especially in cardiac patients before and after successful treatment.
Document Type: Research Article
Affiliations: 1: Johns Hopkins University School of Medicine, Baltimore, MD 2: Institute of Cardiology, M.S. Ramaiah Institute of Cardiology, Bangalore, India 3: Friedrich Schiller University, Department of Psychiatry, Jena, Germany 4: University of Alberta, Edmonton, Canada 5: Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI
Publication date: July 1, 2007