This study demonstrates that ECGs concerning for STEMI lack the necessary sensitivity and specificity to be considered a reliable “stand‐alone” diagnostic test. The modest diagnostic accuracy and high interobserver disagreement in interpreting concerning ECGs for the presence of an acute coronary thrombotic lesion may help explain the high rates of “false positive” STEMI diagnoses recently reported by us and others.5,7,14
These data lend credibility to the notion that an increasing reliance on electrocardiograms as the sole tool for STEMI diagnoses, as may be done increasingly with telemedicine technology implementation, is associated with high levels of inaccurate diagnoses, particularly false positive STEMI diagnoses. Such findings reinforce the notion that the ECG is one of multiple modalities necessary to establish the STEMI diagnosis.
An emphasis on diagnostic sensitivity in ECG interpretation and resultant high rates of false positive errors, as suggested by this study, particularly among noncardiologists and younger providers are arguably less dangerous than false negative errors. Nevertheless, high rates of false positive diagnoses have the potential to significantly tax the human and capital resources invested in 24‐hour emergency STEMI programs and put patients at risk for unnecessary procedures. However, these data do suggest that diagnostic accuracy in interpreting potential STEMI ECGs is related to the experience of the interpreting physician; thus, targeted educational efforts may accelerate learning and help reduce unnecessary complications and health care expenditures. Of course, perfect diagnostic accuracy and a PPV of 100% is both unobtainable on a broad scale and undesirable because a certain number of “false positive” diagnoses are necessary to ensure appropriate diagnostic sensitivity.
While accuracy of physicians' interpretation does improve with physician experience, this was not true among the subgroup of “true positive” STEMI ECGs, suggesting that younger physicians are more likely to emphasize sensitivity. As compared to cardiologists, noncardiologists were also more likely to emphasize sensitivity with a corresponding decrement in specificity. However, in multivariable analyses, the odds of an accurate diagnosis of coronary artery occlusion were not significantly different based on specialty training. Among all physicians, the maximal height of the ST elevations, the number of leads with diagnostic ST elevations, and the lack of left ventricular hypertrophy all increased the odds of an accurate “true positive” STEMI diagnosis.
Improvements in telecommunication technologies and an increasing acceptance of telemedicine15
have led to a growing interest in remote prehospital STEMI diagnoses as a mechanism for expediting time to reperfusion.16–17
Such prehospital STEMI diagnoses allow for appropriate triage to designated heart centers and/or direct transport to the cardiac catheterization laboratory without evaluation in the ED.18–21
Implementation of telemedicine technologies is thus an extremely powerful and valuable process. However, remote STEMI diagnoses confirmed by ED physicians or cardiologists through telecommunication systems still rely largely on accurate interpretation of concerning ECGs from at‐risk patients with scant additional diagnostic information available. While prior small analyses have suggested that electronic transmission of prehospital ECGs to emergency physicians or cardiologists may improve the specificity of out‐of‐hospital STEMI diagnoses,22–23
two small observation studies of 7 and 15 interventional cardiologists respectively both demonstrated significant heterogeneity in interpretation of potential‐STEMI ECGs.24–25
Our data shed further light on the potential limitations of telemedicine strategies that rely predominantly on ECG interpretation for establishing the STEMI diagnosis. As such, these data may be useful in designing STEMI care systems that continue to leverage the advantages of telemedicine to improve patient care while recognizing the inherent limitations in diagnostic accuracy that may be associated with such technologies.
Given the implications of our data on improving regional primary PCI systems, we chose to evaluate the accuracy of physicians' ECG interpretations using the subsequent angiogram as the reference standard. One could choose, instead, to evaluate the appropriateness of the physicians' determinations relative to published criteria for electrocardiographic evidence of a myocardial infarction.12,26
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.27
Varying degrees of electrocardiographic ST segment elevation in the absence of culprit coronary artery lesions have been previously described5,12
and, notably, in this study the median height of the ST‐segment elevations among ECGs from patients without culprit lesions on angiography was 1.8 mm above the isoelectric T‐P segment. 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.
This study has a number of strengths. Each ECG is from a real STEMI team activation and each corresponding patient underwent diagnostic angiography, which provides a reference standard. Furthermore, we successfully recruited 124 physicians into this study and had very high rates of study completion. This study also has some inherent limitations. Pilot testing for this study suggested that enrolling such a large number of physicians and having them complete the task would require limiting the number of ECGs. In addition, it is recognized that culprit coronary occlusions may on occasion resolve spontaneously leading to a spurious disparity between the inciting ECG and the subsequent coronary arteriogram. While this is statistically unlikely to meaningfully affect our analysis, we did account for this possibility by accepting nonocclusive thrombotic coronary lesions or reduced TIMI blood flow without apparent culprit lesion as consistent with a STEMI diagnosis.
Additionally, our study was meant to assess practitioners' discernment among high‐risk ECGs and may not reflect lower‐risk conditions. Since each ECG was drawn from a patient who was sent for emergent coronary arteriography due to concern for a possible STEMI, our study ECGs were enriched for concerning characteristics relative to the population of ECGs evaluated in the ED as a whole. This enrichment will falsely decrease negative predictive values by artificially raising pretest probability and will decrease specificity since patients with low‐risk and “normal” ECGs not originally diagnosed with a STEMI clinically were not incorporated into the registry. Nevertheless, the NPV for all ECGs interpreted in a standard ED setting is of limited comparative use since it will always be high given the relatively low incidence of STEMIs in an unenriched population. As noted, increasing attention has also been afforded to “appropriateness” of STEMI team activations.8,12,28
Such criteria cannot be assessed in this study since appropriate activations are generally defined by considering ECG characteristics and an associated clinical scenario. Specific scenarios were not provided in this study in an effort to focus specifically on physicians' ECG interpretations.
In summary, physicians' accuracy in evaluating high‐risk ECGs for the presence of culprit coronary artery occlusions requiring activation of the STEMI team demonstrates only modest sensitivity and specificity and relatively high levels of interobserver disagreement. Such difficulties may explain higher than expected levels of inaccurate STEMI diagnoses. These findings should be considered when devising systems of care for potential STEMI patients. Directed educational efforts may aid in reducing inaccurate assessments of potentially concerning ECGs.