Page 109 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answer 40 ECG Cases

Answer 40
VetBooks.ir 1 ECG 40 shows sinus rhythm with criteria for left ventricular enlargement and a motion artifact.

2 • The heart rate is 115 bpm. The P waves are normal in amplitude and duration. Note that the ECG
was performed with a sensitivity setting of 5 mm/mV, which results in complexes half their normal
size. Thus, the R wave amplitude is increased at 4.0 mV (normal: <3.0 mV in large breed dogs) and
the QRS duration is prolonged at 70 ms (normal: <60 ms). Both of these findings are consistent with
left ventricular hypertrophy. Based on the dog’s age and breed and presence of a continuous murmur,
a patent ductus arteriosus is the most likely cause of the left heart hypertrophy.
• The fourth complex from the left is a result of movement artifact. At first inspection, the ECG
complex appears to have a morphology similar to the surrounding QRS complexes and to arrive
earlier than expected, thereby suggesting that it is a supraventricular or atrial premature beat.
However, two characteristics indicate that it is an artifact. First, the “QRS complex” does not have
a characteristic T wave following it similar to all the other beats, and second, the “QRS complex” is
absent from lead I. It is impossible for the heart to depolarize (forming a QRS complex) and not to
repolarize (forming a T wave), and it would be highly unlikely that a true QRS complex would not
be detected in all leads. Based on the orientation of leads I, II, and III (see Section 1, Fig. 1.1), artifact
generated by the left hind limb (in this case movement of the leg) will cause artifact in leads II and III,
which both use the left hind limb as one pole of the ECG recording, but be absent in lead I, which
uses the left and right forelimbs for its ECG recording.
• Electrocardiographic artifact is common in dogs and cats and careful inspection of the ECG is needed
to avoid misinterpretation of these deflections.

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