Page 133 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answer 55 New Advanced-Level ECG Cases

Answer 55
VetBooks.ir 1 ECG 55a shows failure of the pacemaker to capture. The underlying rhythm is third-degree AV nodal

block. Ventricular pacing spikes (blue arrows) represent the electrical output from the pacemaker and
can be seen occurring at regular intervals (every 0.67 second) but without any pacing-induced QRS
complexes following each spike (ECG 55b). Because of the failure of the pacemaker to control heart
rate in the presence of the AV nodal block, ventricular escape beats have appeared (black arrows).
2 This patient collapsed because there were long periods of asystole occurring due to the loss of capture
from the malfunctioning pacemaker.
3 A chest radiograph and a pacemaker interrogation should be performed. The chest radiograph will allow
to see if the pacemaker lead is displaced or in its original position. The pacemaker interrogation assesses
electrical parameters such as output voltage and duration. Common causes of loss of capture include lead
dislodgement, insufficient pacing voltage or duration, or lead fracture. In this patient, radiographs confirmed
that the pacemaker lead was in place. The output voltage was increased, which resulted in successful and
consistent capture of the ventricle and creating a pacing-induced QRS complex.

55b

II

III

aVR

aVL

aVF

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