title: Impaired exercise capacity predicts sudden cardiac death in a low-risk population: enhanced specificity with heightened T-wave alternans.
abstract: OBJECTIVE
  Because sudden cardiac death (SCD) is due to cardiac electrical instability, we postulated that prediction of this mode of death by exercise capacity will be enhanced by combined assessment with T-wave alternans (TWA), an index of repolarization abnormality.
  
  
  METHODS
  The Finnish Cardiovascular Study enrolled consecutive patients (n=2,044) with a routine clinically indicated exercise test. Exercise capacity was measured in metabolic equivalents (METs) and TWA by time-domain modified moving average method.
  
  
  RESULTS
  During 47.2+/-12.8-month follow-up (mean+/-SD) 120 patients died; 58 were cardiovascular deaths, and 29 were SCD. In multivariate analysis after adjustment for sex, age, smoking, use of beta-blockers, as well as other common coronary risk factors, the relative risk of patients whose exercise capacity was depressed (MET < 8) was 8.8 (95% CI 2.0-38.9, P=0.004) for SCD. The combination of low exercise capacity (MET < 8) and elevated TWA (> or =65 microV) yielded relative risks for SCD of 36.1 (6.3-206.0, P<0.001), for cardiovascular mortality of 21.1 (6.7-66.2, P<0.001), and for all-cause mortality of 7.8 (3.5-17.4, P<0.001) over patients with neither factor.
  
  
  CONCLUSIONS
  Reduced exercise capacity, particularly in combination with heightened TWA, indicating enhanced cardiac electrical instability, powerfully predicts risk for SCD in patients referred for exercise testing.
authors.affiliation: Medical School, University of Tampere, Tampere, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Minkkinen
authors.forename: Tuomo
authors.initials: T
authors.lastname: Nieminen
authors.forename: Richard L
authors.initials: RL
authors.lastname: Verrier
authors.forename: Johanna
authors.initials: J
authors.lastname: Leino
authors.forename: Terho
authors.initials: T
authors.lastname: Lehtimäki
authors.forename: Jari
authors.initials: J
authors.lastname: Viik
authors.forename: Rami
authors.initials: R
authors.lastname: Lehtinen
authors.forename: Kjell
authors.initials: K
authors.lastname: Nikus
authors.forename: Tiit
authors.initials: T
authors.lastname: Kööbi
authors.forename: Väinö
authors.initials: V
authors.lastname: Turjanmaa
authors.forename: Mika
authors.initials: M
authors.lastname: Kähönen
mesh_terms: D001145:Arrhythmias, Cardiac / Q000401:mortality / Q000503:physiopathology*; D016757:Death, Sudden, Cardiac / Q000453:epidemiology*; D004562:Electrocardiography; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D011379:Prognosis; D012189:Retrospective Studies; D012307:Risk Factors; D015996:Survival Rate / Q000639:trends; D013997:Time Factors