Page 77 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answers 16, 17 ECG Cases

Answer 16
VetBooks.ir 1 ECG 16 shows atrial flutter (AFL).

2 • The average heart rate is 120 bpm. The rhythm is irregular and there is a “sawtooth” baseline that
represents the AFL waves (F waves). The rate of the F waves is 425 bpm. The QRS complexes
are narrow and of normal morphology.
• AFL usually occurs in the presence of advanced cardiac disease, such as mitral valve disease or dilated
cardiomyopathy. AFL is often considered a more “organized” form of AF. The ventricular rate is
dependent on the conduction of the F waves through the AV node and is further described by the
ratio of F waves to QRS complexes (e.g., four F waves for every one QRS is described as 4:1). In cases
where the ventricular rate is rapid, medication to slow conduction through the AV node (e.g., digoxin,
diltiazem, and/or atenolol) can be used.
• The key points are the “sawtooth baseline” made up of F waves, the variable conduction of F waves
through the AV node, and the often rapid ventricular rate.

Answer 17

1 ECG 17 shows sinus arrest and junctional escape beats.
2 • There are eight beats of sinus rhythm at the start of the ECG tracing with normal P waves, QRS
complexes, and T waves. The heart rate is ~215 bpm and the rhythm is regular.
• Following the eighth beat, there is a 2.5-second period of sinus arrest that is terminated by a narrow
QRS complex without a P wave, consistent with a junctional escape beat. This is followed by another
sinus beat, a second period of sinus arrest, a second junctional escape beat, and then resumption of
sinus rhythm. Sinus arrest can be secondary to sinus node disease, cardiomyopathy, abnormal vagal
tone secondary to central nervous system, gastrointestinal, or respiratory disease, or drug toxicity
(i.e., beta-blockers). Extended periods of sinus arrest (typically >3–4 seconds in cats) can cause
clinical signs such as syncope or weakness.

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