Page 125 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answer 51 New General-Level ECG Cases

Answer 51
VetBooks.ir 1 The heart rate is irregular with an average rate of approximately 115 bpm. There appears to be

occasional normal sinus beats (blue arrows) and frequent single ventricular premature beats (blue
arrowheads) (ECG 51b). The PR interval of the third and sixth sinus beats (green bar), which
immediately follow a VPC, appear prolonged at 0.16 second and 0.17 second, respectively. After
the fourth VPC, there is a P wave (green arrowhead) without a QRS complex, indicating AV nodal
block. The ECG findings are most consistent with sinus rhythm with single VPCs and concealed AV
nodal conduction. Concealed AV nodal conduction refers to the assumption that the VPC was able
to retrograde conduct into the AV node and partially or fully depolarize the AV nodal tissue, which
resulted either in slow AV nodal conduction of the subsequent sinus beat (first-degree AV nodal block)
or intermittent failure of the sinus impulses to traverse the AV node and cause a subsequent QRS
complex (second-degree AV nodal block). The term “concealed” refers to the fact that the depolarization
of the AV node is not actually detected on the ECG, only the effect that it has on subsequent sinus beats.
2 Concealed AV nodal conduction is relatively common in the presence of VPCs and contributes to
the pauses following VPCs. No specific treatment is needed to address concealed conduction and the
occasional dropped P wave. The VPCs can be due to underlying heart disease, such as cardiomyopathy
or valvular disease or secondary to extracardiac causes such as abdominal disease or other systemic
conditions.

51b
I

II

V

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