Thursday, December 19, 2013

Interobserver variations in the interpretation of ECGs concerning for STEMI

From a recent study:
A cross‐sectional survey was performed consisting of 36 deidentified ECGs that had previously resulted in putative STEMI diagnoses. Emergency physicians, cardiologists, and interventional cardiologists participated in the survey. For each ECG, physicians were asked, “based on the ECG above, is there a blocked coronary artery present causing a STEMI?” The reference standard for ascertaining the STEMI diagnosis was subsequent emergent coronary arteriography. Responses were analyzed with generalized estimating equations to account for nested and repeated measures. One hundred twenty‐four physicians interpreted a total of 4392 ECGs. Among all physicians, interreader agreement (kappa) for ECG interpretation was 0.33, reflecting poor agreement. The sensitivity to identify “true” STEMIs was 65% (95% CI: 63 to 67) and the specificity was 79% (95% CI: 77 to 81). There was a 6% increase in the odds of accurate ECG interpretation for every 5 years of experience since medical school graduation (OR 1.06, 95% CI: 1.02 to 1.10, P=0.01). After adjusting for experience, there was no significant difference in the odds of accurate interpretation by specialty—Emergency Medicine (reference), General Cardiology (AOR 0.97, 95% CI: 0.79 to 1.2, P=0.80), or Interventional Cardiology physicians (AOR 1.24, 95% CI: 0.93 to 1.7, P=0.15).
There is significant physician disagreement in interpreting ECGs with features concerning for STEMI. Such ECGs lack the necessary sensitivity and specificity to act as a suitable “stand‐alone” diagnostic test.

That last sentence may only be true when the popular formulaic approach to electrocardiographic interpretation is used. There are many well known STEMI mimics as well as examples of acute coronary occlusions that do not meet simplistic STEMI criteria (STEMI equivalents). Many such examples, recognizable by sophisticated observers, may have been ignored in this sample of physicians. The simplistic approach may be driven by todays STEMI performance incentives.

In the discussion section the authors correctly state:

However, the impetus for this study sprung largely from the notion that categorization of ECGs into dichotomous STEMI and not‐STEMI groups is often over‐simplified. This notion has importance particularly in respect to appropriateness criteria for STEMI team activation protocols. Many analyses of STEMI team activations categorize electrocardiographic ST segment elevations as a binary variable—present or not present. Such dichotomies fail to capture the graded nature of ST‐segment elevations and may grossly oversimplify the challenging task of diagnosing true STEMI patients from the much larger cohort of at‐risk patients presenting with chest pain or equivalent symptoms...
While these data speak to the difficult nature of discerning accurate from inaccurate STEMI diagnoses on the basis of ECGs alone, they also suggest that considering electrocardiographic ST elevations as a dichotomous variable for the purposes of catheterization activation protocols or appropriateness analyses may be insufficiently discerning.

The insufficiency of such a dichotomous approach is illustrated by outcomes and pathology data suggesting that the STEMI/NSTEMI distinction is baseless.

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