title: Relationship between beat-to-beat variability of RT-peak and RT-end intervals in normal controls, patients with anxiety, and patients with cardiovascular disease.
abstract: BACKGROUND
  Some studies suggest that it is important to take the end of "T" wave to quantify QT-interval variability, which signifies cardiac repolarization lability, as there is substantial and important information beyond the peak of the T wave on the surface electrocardiogram.
  
  
  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.
authors.affiliation: Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI, USA. Vikramyershr@yahoo.com
authors.forename: Vikram Kumar
authors.initials: VK
authors.lastname: Yeragani
authors.forename: Ronald
authors.initials: R
authors.lastname: Berger
authors.forename: Nagaraj
authors.initials: N
authors.lastname: Desai
authors.forename: Karl Juergen
authors.initials: KJ
authors.lastname: Bar
authors.forename: Pratap
authors.initials: P
authors.lastname: Chokka
authors.forename: Manuel
authors.initials: M
authors.lastname: Tancer
mesh_terms: D000328:Adult; D001008:Anxiety Disorders / Q000503:physiopathology*; D002318:Cardiovascular Diseases / Q000503:physiopathology*; D016022:Case-Control Studies; D003920:Diabetes Mellitus / Q000503:physiopathology; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D015203:Reproducibility of Results; D016683:Supine Position