By Sarah Handzel, BSN, RN
False positive STEMI diagnosis rates remain a relatively common problem in healthcare, and while it is better to be safe than sorry, false positive STEMI protocol activation can lead to significant and avoidable clinical and financial issues, both for the patient and for the healthcare system.
Twelve-lead ECG is an invaluable tool to help guide emergency management of suspected STEMI patients, but ECG misinterpretation has increased rates of unnecessary emergency coronary angiography, even as the recommended door-to-balloon time has shortened.
There is a critical need for better strategies to help healthcare providers, especially those on the front lines, rule out false positive STEMIs to avoid inappropriate cardiac catheterization laboratory (CCL) activation and subsequent treatment of the patient. Researchers continue to develop predictive tools and algorithms to help physicians make accurate and timely diagnoses and improve outcomes for those experiencing significant cardiac events.
The Problem of False Positive Diagnoses
Using data collected in 2014, the Journal of the American College of Cardiology has estimated that almost 20,000 primary percutaneous coronary interventions procedures are carried out each year following a STEMI diagnosis. According to research published in the Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, emergency coronary angiography is performed in up to 36% of suspected myocardial infarction cases as a result of false positive STEMI diagnosis using ECG.
It is important to keep in mind that several other cardiovascular conditions can mimic the ST-segment elevation traditionally associated with myocardial infarction. These include coronary spasm, left ventricular hypertrophy, myocarditis, and stress-induced cardiomyopathy. A study in Circulation: Cardiovascular Quality and Outcomes found that up to 18% of cardiac cath lab activations are cancelled as a result of ST-T segment changes that were not consistent with STEMI. Other frequent reasons for CCL cancellation were artifact, bundle branch block, and repolarization abnormalities.
Tools to Help Rule Out False Positive STEMI Diagnoses
Researchers are continually developing tools to help physicians prevent false positive STEMI diagnosis so that appropriate courses of treatment can be established.
First, identifying independent predictors of false positives can be helpful for ensuring an accurate diagnosis. In addition to absence of chest pain and tightness, Revista Española de Cardiología notes that other independent predictors may include:
- Advanced patient age
- Female sex
- History of myocardial infarction
- Presence of established complications
While these factors may, in fact, contribute to true STEMI cases, providers should keep in mind that any patient presenting with suspected STEMI and these predictors warrants additional evaluation with other diagnostic tools, such as ECG. But, as noted in the Circulation: Cardiovascular Quality and Outcomes study, artifact, ST segment elevation associated with left ventricular hypertrophy, and the presence of a bundle branch block may all complicate the diagnostic process, leading to inappropriate activation of the CCL.
Patient history of left bundle branch block (LBBB) was traditionally viewed as predictive of acute myocardial infarction (AMI). However, current ECG algorithms lack the sensitivity necessary to accurately diagnose MI in the presence of LBBB. A recent article in the Journal of the American Heart Association describes a new algorithm providers may use to achieve better diagnostic accuracy using new ECG criteria: the presence of ST depression greater or equal to 1mm (0.1mV) together with QRS polarity in any ECG lead, and the occurance of discordant ST deviation greater or equal to 1mm (0.1mV) in leads with low-voltage QRS.
The evaluation of these new ECG variables reveal that concordant ST deviations, including ST depression, are extremely specific for AMI. This new information may be used to avoid inappropriate CCL activation and utilization of other healthcare resources.
A False Positive Prediction Model
The same article in the Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine describes attempts to create a risk score model to help predict false positives. Several predictors for false positive STEMIs, such as age, atypical chest pain, and concave-morphology ST elevation, were assigned simplified scores to create a model for predicting false positives.
Physicians can use the risk score model to identify false positive STEMIs by calculating the area under the receiver operating characteristic (AUROC) curve. The overall risk scores range from 0 to 8, with a good level of accuracy for patients with an AUROC of 0.8 or more. Once STEMI is ruled out, common etiologies resulting in ECG abnormalities may include:
- Coronary spasm
- Primary rhythm disturbance
- Structural/valvular heart disease
Other causes, such as subarachnoid cerebral hemorrhage, massive gastrointestinal bleeding, and metabolic causes were also identified in the study that produced the risk score model.
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PreACT STEMI Algorithm
The American Heart Association developed a PreAct STEMI algorithm to improve systems of care for patients with ischemic symptoms and/or EMS suspicion of acute coronary syndrome/STEMI. Evaluation begins with a "clean" ECG obtained in the prehospital setting, which is later interpreted by a cardiologist or emergency physician. Next, the physician should determine whether the patient's symptoms warrant direction to the CCL, keeping in mind that some symptoms may actually result from other cardiovascular conditions and may not be predictive of STEMI. If immediate CCL activation is questionable, the patient should instead be directed to the emergency department for an expedited examination to determine if the patient should later proceed to the CCL.
Keeping Current Recommendations in Mind
While predictive models and STEMI algorithms can be very useful, it's still better to err on the side of caution with suspected STEMI patients. Current ACC/AHA Guidelines recommend that patients receive certain treatments, such as primary percutaneous coronary intervention, within 90 minutes of door-to-balloon time, while other treatments, such as thrombolytic therapy, should be initiated within 30 minutes.
Fast, accurate ECG interpretation remains an essential factor in diagnosis and treatment of STEMI. Physicians should not depend solely on technologies to make a definitive diagnosis; instead, they should consider these tools part of a multi-step evaluation process. Ultimately, it is the responsibility of the physician to make a timely and accurate STEMI diagnosis so the right course of treatment can be identified.
Sarah Handzel, BSN, RN, has been writing professionally since 2016 after spending over nine years in clinical practice in various specialties.
The opinions, beliefs, and viewpoints expressed in this article are solely those of the author and do not necessarily reflect the opinions, beliefs, and viewpoints of GE Healthcare. The author is a paid consultant for GE Healthcare and was compensated for creation of this article.