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Three Factors That Could Be Impacting Your ECG Interpretation

A physician smiles into the camera at a hospital while other clinicians gather in the background.

Importance of Conducting a Proper ECG

An ECG test may be the first thing you do if you suspect a patient has cardiac issues—and it may be the most important thing you do all day. If clinicians overlook the fundamentals in conducting proper ECGs, the resulting interpretations, diagnoses and patient treatment plans may be fundamentally impacted as well. A number of factors impact the data captured by an ECG, with consequences for how that data is then used in diagnosis and treatment decisions. Below are three important areas of concern and steps that can be taken to help ensure an accurate ECG interpretation.

Prep and Placement

High-quality ECG waveforms require good practices when prepping the patient and placing electrodes. If proper techniques have not been followed, ECG interpretation may be compromised even before it begins.

Capturing the electrical activity of the heart via electrodes is impacted by the fact that skin can be a poor conductor of electricity. For example, hair prevents electrode contact, dead skin does not conduct well, and oils, lotions and gels can leave a film. All of these sources of poor conductivity can lead to artifacts.

Good prep, therefore, consists of:

  • Clearing away hair
  • Removing lotions, powders and oils
  • Drying the skin for better electrode attachment
  • Abrading skin to remove dead skin cells

This approach to prepping patients may be met with some resistance from clinicians, due to longstanding processes or perceived limitations. To overcome such objections, consider the important implications:

  • Patients may have an ECG at any number of facilities at any time, so comparing new to previous ECGs requires consistency in prep practices.
  • Artifact has the potential to affect, or even misdirect, clinical decisions.
  • Most sources of artifact are preventable—addressing them can avoid the need for retesting.
  • Taking a few extra moments for patient prep can lead to higher quality exams the first time.

Proper electrode placement is also critical. In fact, when it comes to an inaccurate ECG interpretation, the top factor cited is precordial electrode misplacement.1 According to the ACC and AHA, 5% of all ECGs performed are done with a lead reversal.2 Some lead reversals can be difficult to discern as an error and may lead to physicians incorrectly identifying arrhythmia where there is none.3


ECG filtering removes noise from ECG recordings. In so doing, it’s intended to help physicians see waveform data more clearly, making ECGs easier to read and to interpret. While filtering can yield a clean-looking ECG, too much filtering can distort or remove authentic waveform data. The problem with overly filtered ECGs is that physicians may not know what they’re missing.

Filtering is beneficial if the filters are set to an appropriate threshold, and if the interpretive algorithm still looks at the original versus the processed waveform. Governing bodies like the ACC, AHA and HRS publish adult and pediatric guidelines providing guidance to:

  • Limit filtering so not to sacrifice potentially lifesaving waveform data
  • Clearly disclose filtering so physicians can more easily identify original vs. processed waveform data

All major ECG manufacturers offer filtering to reduce noise and provide clear ECG recordings, and most also offer interpretive algorithms to aid in decision support. Physicians need to be aware, however, of the filtering that takes place on any given ECG, and its potential impact on the interpretation.

Questions to ask include:

  • Are the filters set to the right threshold per ACC, AHA and HRS recommendations?
  • How can I tell what is original vs. processed waveform data?
  • Does the interpretation look at the original or the processed waveform?
doctor reviewing data on a monitor


An ECG is a visual representation of the electrical activity of the heart. The electrical stimulus of the heart occurs continuously, and in a repeated pattern to make the heart beat. To accurately represent this activity in digital form, a resting electrocardiograph is tasked with collecting enough data points to reproduce the analog signal as close to the original as possible.

The rate at which data points are sampled can have a significant impact with ECG waveforms that have fast-moving or high-frequency components. Examples of high-frequency information include:

  • Pacemaker spikes
  • High-frequency notches in the QRS complex
  • Notches in Left Bundle Branch Block ECGs

Therefore, it’s important to consider the following questions:

  • Does the sampling rate support a frequency response that is aligned with the published guidelines?
  • Is there any user intervention needed to enhance the pacemaker detection or display?

Accurate Diagnosis and Treatment

In addition to the skill of the practitioner reading the data, ECG interpretation depends on the quality of the data captured. Factors that have a critical impact on that data capture include filtering, sampling, patient prep and electrode placement. With a better understanding of these factors and their implications, steps can be taken to achieve results that can be trusted for diagnosis and treatment.


1. Kania, et al. The effect of precordial lead displacement on ECG morphology. Medical & Biological Engineering & Computing. 2014;52(2):109–119.
2. Kligfield, et al. Recommendations for the Standardization and Interpretation of the Electrocardiogram Part I: The Electrocardiogram and Its Technology. An AHA/ACC/HRS Scientific Statement. Circulation. 2007;115:1306-1324.
3. Adapted from M.A. Peberdy and J.P. Ornato, “Recognition of Electrocardiographic Lead Misplacements,” Am J Emerg Med 1993;11:4034 and Chou’s Electrocardiography in Clinical Practice pp. 586-597.