Electrocardiographic Differentiation of Early Repolarization From Subtle Anterior ST-Segment Elevation Myocardial Infarction
Annals of Emergency Medicine,

Smith SW et al. – R–wave amplitude is lower, ST–segment elevation greater, and corrected QT interval (QTc) longer for subtle anterior ST–segment elevation myocardial infarction (STEMI) versus early repolarization. In combination with other clinical data, this derived and validated ECG equation could be an important adjunct in the diagnosis of anterior STEMI.

Methods
  • This was a retrospective study of patients with anterior STEMI (2003 to 2009) and early repolarization (2003 to 2005) at 2 urban hospitals, one of which (Minneapolis Heart Institute) receives 500 STEMI patients per year.
  • The authors compared the ECGs of nonobvious (“subtle”) anterior STEMI with emergency department noncardiac chest pain patients with early repolarization.
  • ST-segment elevation at the J point and 60ms after the J point, T-wave amplitude, R-wave amplitude, QTc, upward concavity, J-wave notching, and T waves in V1 and V6 were measured.
  • Multivariate logistic regression modeling was used to identify ECG measurements independently predictive of STEMI versus early repolarization in a derivation group and was subsequently validated in a separate group.

Results
  • Of 355 anterior STEMIs identified, 143 were nonobvious, or subtle, compared with 171 early repolarization ECGs.
  • ST-segment elevation was greater, R-wave amplitude lower, and T-wave amplitudeavg/R-wave amplitudeavg higher in leads V2 to V4 with STEMI versus early repolarization.
  • Computerized QTc was also significantly longer with STEMI versus early repolarization.
  • T-wave amplitude did not differ significantly between the groups, such that the T-wave amplitudeavg/R-wave amplitudeavg difference was entirely due to the difference in R-wave amplitude.
  • An ECG criterion based on 3 measurements (R-wave amplitude in lead V4, ST-segment elevation 60ms after J-point in lead V3, and QTc) was derived and validated for differentiating STEMI versus early repolarization, such that if the value of the equation ([1.196 x ST-segment elevation 60ms after the J point in lead V3 in mm]+[0.059 x QTc in ms]-[0.326 x R-wave amplitude in lead V4 in mm]) is greater than 23.4 predicted STEMI and if less than or equal to 23.4, it predicted early repolarization in both groups, with overall sensitivity, specificity, and accuracy of 86% (95% confidence interval [CI] 79, 91), 91% (95% CI 85, 95), and 88% (95% CI 84, 92), respectively, with positive likelihood ratio 9.2 (95% CI 8.5 to 10) and negative likelihood ratio 0.1 (95% CI 0.08 to 0.3).
  • Upward concavity, upright T wave in V1 or T wave, in V1 greater than T wave in V6, and J-wave notching did not provide important information.

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