title: Heart rate variability from 24-hour electrocardiography and the 2-year risk for sudden death.
abstract: BACKGROUND
  Low heart rate variability has been implicated as a risk factor for sudden death. However, no large epidemiological studies using sudden death as an outcome event have been reported.
  
  
  RESULTS
  A total of 6,693 consecutive patients who underwent 24-hour ambulatory ECG were followed up for 2 years; of these, 245 patients died suddenly. Clinical data at the time of 24-hour ambulatory ECG were collected for all patients who died suddenly and for a random sample of 268 patients from the study cohort. In all patients in sinus rhythm with or without occasional supraventricular arrhythmias at the 24-hour ECG (193 patients who died suddenly and 230 patients from the sample), heart rate variability parameters were derived. Patients with low short-term RR interval variability (mean during 24 hours of per-minute standard deviations [SD] of RR intervals < 25 msec) had a 4.1-fold higher risk (95% confidence interval [CI], 2.6, 8.1) for sudden death than patients with high short-term variability (> or = 40 msec); after adjustment for age, evidence of cardiac dysfunction, and history of myocardial infarction, the relative risk was 2.6 (95% CI, 1.4, 5.1). The crude relative risk of long-term RR interval variability (SD during 24 hours of per-minute means of RR intervals < 8 msec) was 4.4 (95% CI, 2.6, 7.7); after adjustment for the same risk factors, it was 2.2 (95% CI, 1.2, 4.1). Patients with a minimum heart rate > or = 65 beats per minute had a double risk of sudden death compared with those with a minimum heart rate < 65 beats per minute (adjusted relative risk, 2.1; 95% CI, 1.3, 3.6).
  
  
  CONCLUSIONS
  These findings support the theory that patients with low parasympathetic activity (low short-term RR interval variability) have an increased risk for sudden death independent of other risk factors.
authors.affiliation: Department of Cardiology, Erasmus University, Rotterdam, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Algra
authors.forename: J G
authors.initials: JG
authors.lastname: Tijssen
authors.forename: J R
authors.initials: JR
authors.lastname: Roelandt
authors.forename: J
authors.initials: J
authors.lastname: Pool
authors.forename: J
authors.initials: J
authors.lastname: Lubsen
mesh_terms: D001341:Autonomic Nervous System / Q000503:physiopathology*; D015331:Cohort Studies; D016757:Death, Sudden, Cardiac / Q000453:epidemiology*; D015716:Electrocardiography, Ambulatory; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012044:Regression Analysis; D012307:Risk Factors; D013997:Time Factors