ECG of the Month

Mark Rishniw Veterinary Information Network, 777 W Covell Blvd, Davis, CA 95615

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 BVSc, PhD
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Lauren D. Brownell Bowmanville Veterinary Clinic, 2826 Hwy 2, Bowmanville, ON L1C 3K5, Canada

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 BSc, DVM
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Jennifer Jetton Lakehills Animal Health, 8997 FM 1283, Lakehills, TX 78063

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Lisa Henderson West River Veterinary Clinic, 106 2nd Ave NW, Hettinger, ND 58639.

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Mark D. Kittleson Veterinary Information Network, 777 W Covell Blvd, Davis, CA 95615

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 DVM, PhD

Three dogs were taken to 3 separate veterinary clinics for routine anesthetic procedures or clinical evaluations. The dogs included a 15-month-old 19-kg (42-lb) sexually intact female Boxer for which ovariohysterectomy was planned, a 6-year-old 12-kg (26-lb) neutered male mixed-breed dog that required an oral health assessment and treatment, and an 8-year-old 8-kg (18-lb) sexually intact female Shih Tzu that required evaluation because of coughing and syncope. The Boxer and mixed-breed dog were anesthetized, and ECG monitoring was performed during the scheduled procedures by means of multifunction monitors.a,b For both of those dogs, no complications during anesthesia were noted and they recovered from anesthesia uneventfully. The Shih Tzu was awake during the evaluation, and an ECG recording was obtained by means of a multifunction monitor.b Electrocardiographic recordings from the ECG monitors were obtained in all 3 cases.

ECG Interpretation

The ECG tracing obtained for the Boxer revealed a sinus rhythm with clipping of the R waves owing to an excessive gain (or sensitivity) setting. The sinus rate was approximately 75 beats/min (Figure 1). Fine decremental high-frequency oscillations were detected immediately after each P wave, and coarser decremental high-frequency oscillations were detected immediately after each QRS complex. For the mixed-breed dog, the ECG tracing revealed sinus tachycardia with a heart rate of approximately 150 beats/min (Figure 2). Depression of the ST segment was present. Fine incremental high-frequency oscillations were detected immediately after each P wave, and decremental high-frequency oscillations were detected immediately after each QRS complex. The ECG tracing obtained for the Shih Tzu revealed sinus tachycardia with a heart rate of approximately 160 beats/min (Figure 3). Depression of the ST segment was present. Coarse decremental high-frequency oscillations were detected immediately after each QRS complex (thick arrows)

Figure 1—
Figure 1—

Lead II ECG tracing obtained from an anesthetized 15-month-old Boxer undergoing ovariohysterectomy. The sinus rate is 75 beats/min. Notice the fine decremental oscillations immediately following each P wave (thin arrows) and QRS complex (thick arrows). The P-wave amplitude is 0.7 mV (reference limit, < 0.4 mV). Paper speed = 25 mm/s; 1 cm = 1 mV.

Citation: Journal of the American Veterinary Medical Association 244, 11; 10.2460/javma.244.11.1258

Figure 2—
Figure 2—

Lead II ECG tracing obtained from a 6-year-old small mixed-breed dog that was anesthetized for a dental procedure. The sinus rate is approximately 150 beats/min. Fine incremental high-frequency oscillations are evident immediately following each P wave (thin arrows), and decremental high-frequency oscillations are present immediately following each QRS complex (thick arrows). There is evidence of ST-segment depression. The upper trace is from a respiratory monitor; it is not known whether the monitor was connected to the patient at the time of ECG acquisition. Paper speed = 25 mm/s; 2 cm = 1 mV.

Citation: Journal of the American Veterinary Medical Association 244, 11; 10.2460/javma.244.11.1258

Figure 3—
Figure 3—

Lead III ECG tracing obtained from an 8-year-old female Shih Tzu undergoing evaluation because of coughing and syncope. The dog was awake during ECG monitoring. The sinus rate is approximately 160 beats/min. Coarse decremental high-frequency oscillations are present immediately following each QRS complex. Depression of the ST segment is evident. Paper speed = 25 mm/s; 2 cm = 1 mV.

Citation: Journal of the American Veterinary Medical Association 244, 11; 10.2460/javma.244.11.1258

In each ECG tracing, the fine oscillations were identified as a ringing (or ring) artifact. The ST-segment depressions observed for the mixed-breed dog and Shih Tzu were identified as high-pass filtering artifacts.

Discussion

Ringing artifact is an oscillatory artifact created by notch filters used to remove 50- or 60-Hz interference from ECG recordings.1,2 Notch filters allow removal of narrow-band noise (such as 50- or 60-Hz frequencies), and ECG systems often incorporate a second-order infinite impulse response notch filter for that purpose. However, the impulse response of those filters is oscillatory, which can cause microvolt-level ringing artifacts (up to 40 μV) in regions of the signal (ECG wave) that have sharp transitions.1 Consequently, these artifacts occur mostly at the termination of the QRS complexes and occasionally at the termination of the P waves.

High-bandpass filters with higher frequency thresholds (eg, 0.5 Hz vs 0.05 Hz) can cause alterations in the ST segment, which can mimic ST-segment depression or elevation and lead to misdiagnosis.3 The ST-segment depression in the ECG tracings for 2 of the dogs of the present report was likely a result of such a filtering artifact.

Electrocardiographic monitors used for monitoring anesthetized patients are often heavily filtered to eliminate distortion created by movement or intraoperative use of electrical equipment (eg, cautery units) that require a power-line electric source. Consequently, such monitors are more likely to produce artifacts similar to those observed in the ECG tracings from the dogs of the present report than are diagnostic ECG machines that can be uncoupled from power-line electric sources and operated in rooms without other nearby electrical equipment or fluorescent lighting, thereby eliminating the need to apply aggressive filtering of the electrical signal.

Clinicians should recognize ringing artifact and ST-segment changes when performing ECG examinations with ECG monitors that use aggressive high-bandpass and notch filters and classify them as benign artifacts rather than ECG abnormalities. When uncertain whether ECG changes are artifactual, clinicians should perform another ECG examination with a diagnostic ECG machine for confirmation.

a.

BM3Vet, Bionet America Inc, Tustin, Calif.

b.

Cardell Veterinary Monitor 9500HD, Midmark Corp, Versailles, Ohio.

References

  • 1. Zhou X, Zhang Y. A hybrid approach to the simultaneous eliminating of power-line interference and associated ringing artifacts in electrocardiograms. Biomed Eng Online [serial online]. 2013;12:42. Available at: www.biomedical-engineering-online.com/content/12/1/42. Accessed Nov 11, 2013.

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  • 2. Luo S, Johnston P. A review of electrocardiogram filtering. J Electrocardiol 2010;43:486496.

  • 3. Buendia-Fuentes F, Arnau-Vives MA & Arnau-Vives A, et al. High-bandpass filters in electrocardiography: source of error in the interpretation of the ST segment. ISRN Cardiol [serial online]. 2012;2012:706217. Available at: www.hindawi.com/journals/isrn.cardiology/2012/706217/.

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  • Figure 1—

    Lead II ECG tracing obtained from an anesthetized 15-month-old Boxer undergoing ovariohysterectomy. The sinus rate is 75 beats/min. Notice the fine decremental oscillations immediately following each P wave (thin arrows) and QRS complex (thick arrows). The P-wave amplitude is 0.7 mV (reference limit, < 0.4 mV). Paper speed = 25 mm/s; 1 cm = 1 mV.

  • Figure 2—

    Lead II ECG tracing obtained from a 6-year-old small mixed-breed dog that was anesthetized for a dental procedure. The sinus rate is approximately 150 beats/min. Fine incremental high-frequency oscillations are evident immediately following each P wave (thin arrows), and decremental high-frequency oscillations are present immediately following each QRS complex (thick arrows). There is evidence of ST-segment depression. The upper trace is from a respiratory monitor; it is not known whether the monitor was connected to the patient at the time of ECG acquisition. Paper speed = 25 mm/s; 2 cm = 1 mV.

  • Figure 3—

    Lead III ECG tracing obtained from an 8-year-old female Shih Tzu undergoing evaluation because of coughing and syncope. The dog was awake during ECG monitoring. The sinus rate is approximately 160 beats/min. Coarse decremental high-frequency oscillations are present immediately following each QRS complex. Depression of the ST segment is evident. Paper speed = 25 mm/s; 2 cm = 1 mV.

  • 1. Zhou X, Zhang Y. A hybrid approach to the simultaneous eliminating of power-line interference and associated ringing artifacts in electrocardiograms. Biomed Eng Online [serial online]. 2013;12:42. Available at: www.biomedical-engineering-online.com/content/12/1/42. Accessed Nov 11, 2013.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. Luo S, Johnston P. A review of electrocardiogram filtering. J Electrocardiol 2010;43:486496.

  • 3. Buendia-Fuentes F, Arnau-Vives MA & Arnau-Vives A, et al. High-bandpass filters in electrocardiography: source of error in the interpretation of the ST segment. ISRN Cardiol [serial online]. 2012;2012:706217. Available at: www.hindawi.com/journals/isrn.cardiology/2012/706217/.

    • Search Google Scholar
    • Export Citation

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