Page 69 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition
P. 69
Answer 10 ECG Cases
Answer 10
VetBooks.ir 1 ECG 10 shows sinus arrhythmia.
2 • The average heart rate is ~90 bpm. The rhythm is regularly irregular and there is a P for every QRS
and QRS for every P. The amplitude and duration of the P and QRS complexes are normal.
The MEA is normal.
• Sinus arrhythmia is similar to sinus rhythm with respect to average heart rate and the normal
sequence of cardiac depolarization. Sinus arrhythmia differs from sinus rhythm in that the heart rate
demonstrates phasic changes that are often (but not always) related to respiration. Higher rates are
noted during inspiration and slower heart rates during expiration (respiratory sinus arrhythmia).
• Changes in size and shape of the P wave (arrows) is termed wandering pacemaker and can occur during
sinus arrhythmia. The P wave amplitude is greater during faster heart rates and smaller during slower
heart rates.
• Vagolytic stimuli (e.g., exercise, atropine) reduces or eliminates sinus arrhythmia.
• The key points are the phasic irregularity and normal rate, sequence, and morphology of the
P–QRS–T waves.
10
I
II
III
aVR
aVL
aVF
56
