Page 147 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answer 61 New Holter Monitoring ECG Cases

Answer 61
VetBooks.ir 1 ECGs 61a and 61b demonstrate two separate attempts at electrical cardioversion of atrial fibrillation.

• The beginning of each of the traces shows an irregular rhythm with a narrow (i.e., supraventricular)
QRS complex. Distinct P waves are not visible, but rather an undulating baseline representative of F
waves. Findings are consistent with atrial fibrillation.
• The arrowheads at the beginning of each of the tracings demonstrate appropriate “syncing” by
the cardioversion unit with the QRS complexes. A large, biphasic deflection represents the shock
delivery (blue arrow), which is synchronized with a QRS complex. The defibrillation attempt was
performed using a biphasic shock.
• ECG 61a was recorded during a shock of 2 J/kg. The shock is followed by three beats of a wide
complex tachycardia that likely is ventricular tachycardia, before resumption of atrial fibrillation.
Failure of successful conversion can be due to failure to depolarize >75% of the atrial myocardium
or if the cardioversion paddles are not in an optimal position on the dog’s chest. In these instances,
the cardioversion energy can be increased, the paddles can be repositioned, or both.
• ECG 61b demonstrates a subsequent and successful electrical conversion of atrial fibrillation of
the dog in ECG 61a. The beginning of the trace shows atrial fibrillation with synchronization
markers similar to ECG 61a, however, the seventh QRS complex is not appropriately identified
by the defibrillator and is missing a QRS marker. The energy required for cardioversion using a
biphasic defibrillator ranges between 0.5–3 J/kg. A shock of 3 J/kg (blue arrow) was delivered
directly after a QRS complex. A short run of ventricular tachycardia is then followed by a regular
supraventricular rhythm with distinct P waves (green arrows) and is most consistent with sinus
rhythm. Cardioversion commonly induces brief ventricular arrhythmias or pauses before atrial
fibrillation returns or sinus rhythm resumes. In this case, an increase in cardioversion energy from
2 to 3 J/kg resulted in successful termination of atrial fibrillation and sinus rhythm was restored.

61a ID: 20550628045415 9 Aug 2020 13:58:06 HR:122 Sp02:---Sync On Name:

Paddles ×1 2.5–30 Hz

1060827 25 mm/sec LP2034060827

61b Name: ID: 20550628045415 9 Dec 2023 18:06:32 HR:123 Sp02:---Sync On

Paddles ×1 2.5–30 Hz

25 mm/sec LP2034060827

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