title: Reassessing the role of QTc in the diagnosis of autonomic failure among patients with diabetes: a meta-analysis.
abstract: OBJECTIVE
  A 1992 consensus statement on autonomic testing portrayed Bazett's heart rate-corrected QT interval (QT) prolongation as a specific yet insensitive indicator of diabetic autonomic failure. At that time, only a few small studies had evaluated the accuracy of QTc. To date, even fewer studies have evaluated whether its accuracy is influenced by patient characteristics.
  
  
  METHODS
  We critically appraised 17 studies reporting the sensitivity and specificity of QTc for diabetic autonomic failure. The studies represented 4,584 patients with diabetes (mean age 34.9 years, 46% female, 92% with type 1 diabetes, mean duration of diabetes 14.5 years). We summarized the accuracy of QTc prolongation for diabetic autonomic failure as an odds ratio (OR) (95% CI) and determined whether patient and study design characteristics influenced the accuracy of QTc prolongation by comparing summary receiver operating characteristic curves.
  
  
  RESULTS
  Autonomic failure, defined as > or =1.2+/-0.4 (mean +/- SD) abnormal of 2.0+/-1.6 administered cardiovascular reflex tests, was found in 26% (25-28) of patients. The pooled sensitivity and specificity of QTc > 441+/-8 ms for autonomic failure were 28% (26-29) and 86% (85-87), respectively. Autonomic failure was 2.26 times (1.90-2.70) more likely to be present in patients with than in patients without QTc prolongation. At 86% specificity, the sensitivity of QTc prolongation was 46 vs. 12% for men versus women (P = 0.0077), respectively, and, after adjustment for sex, 66 vs. 17% among patients aged 25 vs. 55 years (P = 0.1902) and 61 vs. 27% at thresholds of >420 vs. >460 ms, respectively (P = 0.2964).
  
  
  CONCLUSIONS
  QTc prolongation is a specific albeit insensitive indicator of autonomic failure. Although QTc prolongation is relatively accurate for men, accuracy may be even greater for young men at low QTc thresholds.
authors.affiliation: Northwest Center for Outcomes Research in Older Adults, Veterans Affairs Puget Sound Health Care System, Health Services Research and Development, Washington 98108, USA. ewhitsel@u.washington.edu
authors.forename: E A
authors.initials: EA
authors.lastname: Whitsel
authors.forename: E J
authors.initials: EJ
authors.lastname: Boyko
authors.forename: D S
authors.initials: DS
authors.lastname: Siscovick
mesh_terms: D000328:Adult; D001342:Autonomic Nervous System Diseases / Q000175:diagnosis*; D016206:Databases, Bibliographic; D003929:Diabetic Neuropathies / Q000175:diagnosis*; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D016239:MEDLINE; D008297:Male; D008875:Middle Aged