Page 75 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 14, 15 ECG Cases

Answer 14
VetBooks.ir 1 ECG 14 shows normal sinus rhythm with baseline artifact.

2 • The heart rate is 200 bpm, likely in response to being handled for ECG acquisition. The P–QRS–T
complexes are normal and the MEA is normal.
• The diastolic intervals after the third and fourth QRS complex, the sixth and eighth, as well as the
eleventh and twelfth QRS complexes show small, high-frequency undulations, most easily discerned
in leads II and aVF. These undulations are not an arrhythmia, but the consequence of the cat purring,
causing a repeatable, breathing-associated artifact in this ECG. This type of artifact can often be
mistaken as AF, but the presence of P waves precludes this diagnosis. In dogs, panting or shivering
are common causes of similar artifacts. Other causes of ECG artifact include electrical current 60 or
50 Hz interference, due to poor grounding of the ECG machine or any other electronic equipment
connected to the patient. The 60 Hz cycle interference can also mimic AF, and all other electronic
equipment in the room may need to be unplugged to avoid this artifact.

Answer 15

1 ECG 15 shows complete or third-degree AV nodal block.
2 • The ventricular heart rate is 35 bpm. There is complete AV dissociation, with the P waves having no
relationship to the QRS complexes and the atrial and ventricular rates are independent of each other.
In complete AV block, the atrial rate (P–P interval) is always faster than the ventricular rate, and P
waves should have ample opportunity to conduct to the ventricles, but fail to do so. In third-degree
(complete) AV block, the ventricular escape rhythm is usually slow and regular, and approximately
40–60 bpm in dogs and 80–120 bpm in cats.
• The etiology of most cases of third-degree AV block is unknown, but age-related degeneration of the
AV node or acute myocarditis are two possible causes.
• Most dogs with third-degree AV block show signs of weakness, lethargy, activity intolerance, or
syncope, and require artificial pacemaker implantation. In cats, the more rapid ventricular escape rate
often permits normal quality of life without the need for any specific therapy.

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