Page 113 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 43, 44 ECG Cases

Answer 43
VetBooks.ir 1 ECG 43 shows a junctional escape complex.

2 • The first three beats appear sinus in origin with a rate of 120 bpm. After these beats there is a
period of sinus arrest/pause of approximately 1.4 seconds, followed by a junctional escape beat with
a different P wave configuration. The QRS configuration of the junctional escape beat is normal.
• Junctional escape beats occur when the rate of the sinus rhythm slows below the intrinsic rate of the
junctional escape rhythm (typically 40–80 bpm). The P wave of the escape beat is typically different
from that of the sinus beat, indicating its origin from the escape focus rather than the sinus node.
• Escape rhythms should never be suppressed, rather the underlying cause of the bradycardia should be
investigated.
• The key points are normal QRS complexes with negative or altered P wave configuration occurring
after periods of bradycardia or asystole.

Answer 44

1 ECG 44 shows sinus rhythm.
2 • The average heart rate is 200 bpm. The rhythm is regular with normal P (blue arrows), QRS
(black arrows), and T waves (green arrows).
• Sinus rhythm represents a normal sequence of atrial and ventricular depolarization that occurs
at a normal heart rate. Beats are initiated by depolarization of the SA node, followed by atrial
depolarization (P wave), AV node depolarization (PR interval), and ventricular depolarization (QRS
complex) and repolarization (T wave). The normal T wave in cats is often very low voltage and may
not be visualized at all.
• In cats, the rate of sinus rhythm is typically 120–240 bpm.
• Note that in the cat with normal sinus rhythm, the polarity of the QRS complexes is positive in leads
II and aVF, indicating a normal MEA.

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