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ECG Data Capture and Interpretation: Critical Factors for Accurate Results

doctor reviewing data on a monitor

Introduction

A resting ECG is the standard of care for the initial assessment of many heart conditions — and it may be the most important thing you do for your patients in a day. It’s imperative that everyone involved in your ECG workflow is aware of and compliant with the key fundamentals. If overlooked, the data captured by your ECG could be impacted, with consequences for resulting interpretations, diagnoses and patient treatment plans.

When was the last time you reexamined how you prepare for and conduct ECG exams to ensure the best possible outcome? If it’s been a while, here are some factors to consider that could be impacting your results.

Electrode Storage And Selection

An ECG is only as good as the waveform acquired. That’s why each aspect of the exam is important, even down to how the electrodes themselves are handled and applied. A dry electrode with inadequate gel can reduce conduction of the ECG signal, compromising the data acquired. In most instances, this is simply the result of improper storage and can be easily avoided by following manufacturer’s instructions and these simple guidelines:

  • Open and remove electrodes from their pouch only when patient prep is completed and apply electrodes immediately.
  • Store pouches with unused electrodes in a resealable zipper storage bag away from light and heat.
  • Be sure to check the expiration date on your electrodes before use.

In addition to proper storage, the type of electrodes used during an exam can make a difference — not all electrodes can be used with all ECG devices. Some tips to keep in mind are:

  • Select the correct electrode for the type of ECG exam you are performing.
  • Use one electrode brand at a time. Multiple electrode brands should not be mixed during a test as resistance may vary from one manufacturer to another. The best results can be achieved when there is equal signal from all electrodes.
  • Never manually adjust electrode size or shape, as this could impact readings.
  • For pediatric patients, use pediatric electrodes that have been designed by the manufacturer specifically for this patient population.

Prep and Placement

High-quality ECG waveforms require good practices when prepping the patient and placing electrodes. Even for the most experienced clinicians, periodically reviewing best practices is worthwhile. If proper techniques have not been followed, ECG interpretation may be compromised before it even begins. Following these guidelines for patient prep consistency can help minimize motion and electrostatic artifact. It can also help ensure accuracy and comparability between traces done at different times, or across facilities.

Improperly placed electrodes can potentially lead to mistaken interpretation, misdiagnosis of conditions and mismanagement of patient care.2

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Patient preparation best practices:

  • Clear away hair where electrodes will be placed to enhance contact and reduce patient discomfort during removal.
  • Clean the skin to remove lotions, powders or oils that can impede electrical conduction, and dry thoroughly to improve electrode attachment.
  • Abrade the skin to remove dead skin cells, reduce resistance and enable more of the ECG signal to reach the electrode.

Taking just a few extra moments for patient prep can lead to higher quality exams the first time. Proper electrode placement is also critical, as even the slightest deviation from the correct position can create clinically significant changes.1 Improperly placed electrodes can potentially lead to mistaken interpretation, misdiagnosis of conditions and mismanagement of patient care.2

When it comes to an inaccurate ECG interpretation, the top factor cited is precordial electrode misplacement.2 According to the ACC and AHA, 5% of all ECGs performed are done with a lead reversal.3 Some lead reversals can be difficult to discern as an error and may lead to physicians incorrectly identifying arrhythmia where there is none.4

Make sure to review proper electrode placement. Many manufacturers include visual placement guidelines right on the device.

Signal Interference Precautions

An ECG signal can be interrupted by various types of “noise,” producing artifacts that could impact the quality of your ECG data. Let’s review some types of signal interference to be aware of:

Electromagnetic interference (EMI)

Electromagnetic interference (EMI) is a consequence of the growing use of smartphones and wearable devices such as smart watches and activity trackers. A review of clinical literature on this topic shows that:

  • ECG systems can be vulnerable to interference generated by GSM mobile phones when placed too close (7.5 cm) to the electrodes on a patient.5
  • EMI was also detected when the phone was placed on top of the acquisition module.6
  • EMI was incorrectly diagnosed by clinicians, most frequently confused with atrial fibrillation, ventricular arrhythmias and pacemaker disfunction.6

To avoid this form of artifact, make sure the patient and anyone else present removes and turns off these electronic devices.

External Forces

External forces such as movement from nearby construction have been hypothesized to cause signal interference.

  • This could be a consideration if your ECG devices use highly sensitive algorithms such as the VERITAS® interpretation algorithm employed by Hillrom devices.
  • Like other anomalies that may occur during ECG acquisition, you may want to note in the patient record if such conditions exist during ECG acquisition.

ECG interpretation depends on the quality of the data captured, not just the skill of the practitioner reading the data. Some factors that have a critical impact on the data captured include filtering and sampling. With a better understanding of these factors and their implications, you can take appropriate steps to achieve ECG results you can trust for diagnosis and treatment decisions.

Filtering

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 interpret. Filters can be very beneficial, if set to an appropriate threshold, and if the interpretive algorithm still looks at the original versus the processed waveform.

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 you may not know what you’re missing. Physicians need to be aware of the filtering that takes place on any given ECG, and its potential impact on the interpretation.

Governing bodies like the ACC, AHA and HRS publish adult and pediatric guidelines 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

Ask Yourself These Questions:

  • 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?
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Sampling

An ECG is really just 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 heartbeat. 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 these data points are sampled can have a significant impact on ECG waveforms that have fast-moving or high-frequency components. Some examples of high-frequency information include:

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

Consider The Following:

  • 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?
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It Matters How You Measure

The data captured by your ECG directly impacts the resulting interpretations, diagnoses and patient treatment plans. Whether you are involved in ECG acquisition or interpretation, spending a little more time considering these critical factors can help improve the accuracy of the data collected and the resulting ECG interpretation.

References
  1. McCann K, Holdgate A, Mahammad R, and Waddington A. Accuracy of ECG electrode placement by emergency department clinicians. Emerg Med Australas. 2007; Oct;19(5):442-8. https://www.ncbi.nlm.nih.gov/pubmed/17919217
  2. Khunti K. Accurate interpretation of the 12-lead ECG electrode placement: A systematic review. Health Education Journal. 2013;73(5); 610-623. https://doi.org/10.1177/0017896912472328
  3. 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.
  4. 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.
  5. Baranchuk A, Kang J, et al. Electromagnetic interference of communication devices on ECG machines. Clin Cardiol. 2009. Oct; 32(10):588-92. doi: 10.1002/ clc.20459. https://www.ncbi.nlm.nih.gov/pubmed/19824066
  6. Buczkowski T, Janusek D, et al. Influence of Mobile Phones on the Quality of ECG Signal Acquired by Medical Devices. Measurement Science Review. 2013; 13(5):231-236. https://www.researchgate.net/publication/258698582_Influence_of_Mobile_Phones_on_the_Quality_of_ECG_Signal_Acquired_by_ Medical_Devices