Page 111 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 41, 42 ECG Cases

Answer 41
VetBooks.ir 1 ECG 41 shows sinus bradycardia (SB).

2 • The heart rate ranges from 44 bpm to 70 bpm. The rhythm is slightly irregular.
• There is a normal P wave, QRS complex, and T wave for every beat.
• Causes of SB include high resting vagal tone, sinus node dysfunction, electrolyte abnormalities (i.e.,
hyperkalemia), central nervous system disease, hypothermia, and drugs (e.g., anesthestics, sedatives,
opioids).
• In this case, the cause of the SB is likely related to high resting vagal tone as the irregularity is
suggestive of sinus arrhythmia. If so, a normal response to exercise or administration of atropine
should be an increase in the heart rate and regularity. Failure to respond to these stimuli can signal
underlying conduction system disease.

Answer 42

1 ECG 42 shows VT degenerating into VF.
2 • The first two QRS complexes (A) are the result of an artificial pacemaker with a rate of 100 bpm. The
rhythm changes into a rapid and polymorphic VT, before it degenerates into VF (B).VF is characterized
by low amplitude and disorganized electrical activity of the heart where the ECG deflections constantly
change in shape, direction, and amplitude. Normal P–QRS–T waves are not discernible during VF. In
this example the fibrillatory waves appear relatively coarse. Typically, the amplitude of coarse fibrillation
becomes progressively lower with ever-finer oscillations detected on the ECG.
• During VF, the ventricular muscle twitches randomly, rather than contracting in a coordinated
fashion. Subsequently the ventricles fail to pump blood into the systemic and pulmonary circulation.
VF causes loss of consciousness within seconds, as cardiac output totally ceases, and the rhythm is
fatal if not treated immediately. External electrical defibrillation is the most successful method to
terminate VF and help restore a more effective rhythm.

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