Page 119 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition
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Answer 48 New General-Level ECG Cases
Answer 48
VetBooks.ir 1 ECG 48 shows second-degree AV nodal block.
2 The ventricular rate during sinus rhythm is approximately 135 bpm. There are P waves without
subsequent QRS complexes, indicating a failure of the sinus impulses to travel through the AV node and
depolarize the ventricles.
3 The PR interval of the sinus beat preceding the dropped P waves is 0.16 seconds (4 mm × 0.04 sec/mm).
This PR interval is the same as the other sinus beats and the second-degree AV nodal block is further
described as type II, wherein the PR interval is not increased in the beats prior to the dropped P wave.
4 The dropped P waves are relatively infrequent and no clinical signs are necessarily expected; however,
the owner should be queried further about subtle changes in the dog’s activity and behavior. The
presence of second-degree AV nodal block raises suspicion of underlying AV node disease. Diagnostic
options include watchful waiting and recheck ECG in 3–6 months or ambulatory ECG (Holter)
monitoring to better characterize the frequency and severity of the AV nodal block over a 24- or
48-hour time period.
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