Syncope: signal-averaged ECG did not predict well which patients had inducible VT.

Clinical bottom line (level 1b)

  1. Around a sixth of patients with unexplained syncope had inducible VT on electrophysiologic studies.
  2. Signal-averaged ECG was not very helpful at predicting which patients had an inducible VT.
Steinberg et al: Journal of the American College of Cardiology 1994; 23: 99-106
Expires October 2004

The study

Setting: six university hospitals, USA

189 patients (aged mean 60 years, 63% male) one or more episodes of unexplained syncope

Excluded if
  • documented episode of sustained ventricular tachycardia (VT)
  • 12 lead ECG indicated bundle branch block or non-specific idioventricular conduction defect


    • All patients had antiarrhythmics stopped for at least five half-lives.
    Independent blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
    Reference standard:
    • sustained ventricular tachycardia (lasting 30 seconds or more, or with haemodynamic instability) stimulated by electrophyiosologic recording (three attempts)
    Diagnostic test: signal-averaged ECG, abnormal if any of the following:
    • duration of filtered QRS complex > 110 ms
    • root-mean-square voltage of terminal 40 ms of complex < 20 microV
    • low amplitude signal duration < 40 microV of terminal portion of root complex > 38 ms

    The evidence

    pre-test probability of VT: 15%, (95% CI: 9.8% to 20%)

    diagnostic test VT no VT LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    signal-averaged ECG 20 72 1.6
    (1.2 to 2.1)     		22% 0.52
    (0.28 to 0.94)     		8%
    total 28 161

    • logistic regression analysis on associated predictive factors for VT:
      • previous MI
      • abnormal signal-averaged ECG
      (no further data given)

    Comments

    1. Though patients may have inducible VT on electrophysiologic studies, does this mean VT is the cause of their syncope? EPS is a poor gold standard being an indirect measure of any cause of syncope.

    Citation

    1. Steinberg JS, Prystowsky E, Freedman RA, et al: Use of the signal-averaged electrocardiogram for predicting inducible ventricular tachycardia in patients with unexplained syncope: relation to clinical variables in a multivariate analysis. Journal of the American College of Cardiology 1994; 23: 99-106
    Contributor: Chris Ball and Clare Wotton, October 2000
    Reviewer:

    Clinical Question.
    Patient unexplained syncope
    Intervention or Exposure prevalence
    Outcome inducible VT on electrophysiologic studies