ECG interpretation is a core and fundamental skill of emergency medicine. Emergency physicians are expected to provide expert ECG interpretation quickly in a busy emergency department environment and initiate emergent and life-saving interventions base on those interpretations.

Mistakes in ECG interpretation can have detrimental consequences and ultimately result in patient harm. A Canadian study published in the European Heart Journal in 2008 examined patients from 51 hospitals included in the Canadian Acute Coronary Syndrome registry that had been hospitalized with ACS, and also had an interpretable initial ECG. Essentially what they found was when there was disagreement between the core lab and the local hospital regarding the ECG interpretation, that these patients were less likely to receive acetylsalicylic acid (ASA), heparin, and ultimately reperfusion therapy. Additionally, after adjusting for other validated prognostic factors, site-unrecognized ST-elevation was independently associated with higher 1-year mortality (OR of 2.21)

So knowing that our interpretations matter, how competent are physicians as a whole at the interpretation of ECGs? This question was recently investigated and answered in the fall of 2020 and published within JAMA.² They completed a systematic review and synthesized all the available literature on physician accuracy of ECG interpretation. They included 78 studies with more than 10000 participants. Overall the pooled accuracy was 42% among medical students, 56 % among residents, 69% among practicing physicians, and 75% amongst cardiologist and cardiology fellows. Although we do see that performance improves with training, these findings suggest that ECG interpretation deficiencies exist for all levels of training.

This begs the question if literature suggests that there are deficiencies in our skills set, and what we do is critical, can perhaps the computer interpretation help us and improve our interpretation skills?

How Computer ECG Interpretation works

The acquisition of data from the patient to the final computer readout is a complex pathway that occurs rapidly at the bedside.

An overview of the ECG signal acquisition pathway is paramount to a better understanding of how these programs work, and this can be grossly simplified into three steps.

• • SIGNAL ACQUISITION:
    • Leads are placed on the patient. As inputs, the machine receives patient age and sex. No further clinical history or physical examination is provided or input into the pathway.
    • This step is one of the most crucial steps of the process as any errors at this stage can have unintended and downstream consequences. Such errors include:
      • Patient movement leading to the increased artifact
      • Or inadvertent lead reversal or misplacement.

• • DATA PROCESSING:
    • The incoming analog electric signals are digitized.
    • From there this digitized signal undergoes a series of steps to process it and make it presentable for the computer interpretation algorithm.
    • These steps include:
      • Noise filtering and elimination of artifact.
      • ECG measurements are performed.
      • Reliable measurement of rate, axis, and intervals.

• • COMPUTER INTERPRETATION:
    • The processed data can then be passed through a series of algorithms that ultimately results in a final computer output and interpretation.
    • These computer interpretation algorithms are proprietary and vary depending on which software is being utilized.

In fact, these computer interpretations can produce quite varying results. The algorithms in which they employ are not standardized amongst providers. There is limited collaboration amongst creators, and the algorithms may be tested against limited populations not necessarily representative of the local population in which they are utilized.

The aforementioned issues were reviewed in detail in 2017 in the Journal of the American College of Cardiology by Dr. Schlapfer and the late Dr. Wellens.³ They raised several concerns regarding the state of these computer interpretation programs, and additionally, they also recommended improved training for physicians. And so as part of these recommendations, we will proceed from here to further unravel the strengths and limitations of the computer⁴computer are as follows:

Strengths and Limitations of the Computer ECG Interpretation

The primary strengths of the computer interpretation are as follows:

• • RATE, AXIS, AND INTERVAL CALCULATION:
    • In a good tracing, in the absence of an artifact, the computer fairly reliably calculates rate, PR interval, QRS duration and QTc

• • NORMAL, AND SINUS RHYTHM DETECTION:
    • With exception⁵, the computer is good at the identification of sinus rhythm⁶, and the identification of normal ECGs.⁷ Beyond sinus rhythm, the machine is much less reliable and rhythm interpretation should be interpreted cautiously.
    • Additionally, a computer interpretation of normal does not replace intense scrutiny by an over-reading physician at this time.

The primary limitations of the computer with some relevance to emergency physicians are as follows:

• • ATRIAL FIBRILLATION:
    • Computer interpretation algorithms in their present form have been shown to overcall atrial fibrillation, and in some cases lead to unnecessary consultation, admission, and pharmacologic intervention.^8,9
    • Emergency physicians have been shown to fall victim to this phenomenon. Cardiologists who clinically integrate bedside information, more often correct an erroneous computer interpretation.⁴

• • STEMI:
    • Although some studies have shown good specificity for the computer in the diagnosis of STEMI,¹⁰ more recent work has highlighted it’s poor sensitivity.¹¹ In addition to poor sensitivity, the computer will routinely miss STEMI equivalents and subtle signs of ischemia.

• • QTc:
    • It has been noted in the literature that the widely adopted Marquette 12SL, although appropriately calculating the QTc interval, will often fail to include an interpretative statement in the setting of a prolonged QTc value.¹²
    • Always visually inspect the QT interval, and then take a look at the reported QTc interval. Consider manual calculation if clinical concern.

• • PACEMAKER DETECTION: 
    • The computer has been shown to struggle with pacemaker detection.¹³

What does the Literature say: Do Computer-Based ECG Interpretations Affect Our thinking?

From the literature, there have been a number of small and heterogeneous studies examining the impact of the computer on our decision-making.^14-16

Although difficult to draw any firm conclusions, I think there is a trend that for experienced interpreters; the computer makes them much stronger. However for novice interpreters, computer interpretation can lead you astray, and you may fail to recognize help even when it’s provided.

Suggested Approach for Use of Computer ECG Interpretation

Not willing to completely dismiss any and all help that the computer provides. Find below a suggested approach for the incorporation of the computer algorithm into your own practice. This method was adapted from the work of Dr. Ken Grauer.¹⁷

The most important aspect is to not look at the computerized report initially and to cover it up. From there complete the following:

• • INTERPRET
    • Interpret the ECG as you normally would.
    • Use whatever standard approach you are comfortable.

• • MATH
    • Utilize the computer for its interval calculation prowess. It will make you faster.

• • PEEK
    • Finally, review the computer interpretation, and systematically review each interpretive statement provided by the computer.
    • This is where the potential lies for the novice interpreter, is that it provided a second opinion and systematically makes you review your own interpretation.