Page 127 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Answer 52 New Advanced-Level ECG Cases

Answer 52
VetBooks.ir 1 The heart rate at the beginning of the recording is 250 bpm and at the end of the recording is

110 bpm. The first part of the recording is best described as a “wide complex” tachycardia, which
could be due to ventricular tachycardia or supraventricular tachycardia with a concurrent conduction
abnormality, such as a left bundle branch block. In the second half of the recording, the tachycardia
is disrupted, resulting in a marked decrease in heart rate and P waves are visible preceding each
QRS complex, indicating the sinus node to be the origin of these beats. The QRS complexes of the
sinus beats appear identical to the QRS complexes during the supraventricular tachycardia and are
abnormally wide (0.10 second), consistent with a left bundle branch block. Thus, the most likely ECG
diagnosis is supraventricular tachycardia with a left bundle branch block. This type of wide complex
supraventricular tachycardia is difficult to distinguish from ventricular tachycardia up until the point
when the tachycardia is disrupted and P waves become apparent.
2 Left bundle branch block is usually associated with clinically important heart disease. Supraventricular
tachycardia is often the result of underlying heart disease, especially diseases that are typified by
atrial enlargement, such as mitral valve disease or dilated cardiomyopathy. Vagal maneuvers such
as ocular pressure can be used to acutely disrupt supraventricular tachycardia and help distinguish
supraventricular vs. ventricular tachycardia. Weakness, activity intolerance, or syncope can occur
secondary to the tachycardia, especially if underlying myocardial disease is present. Treatment might
include drugs that slow AV nodal conduction, such as diltiazem or atenolol, to reduce the ventricular
heart rate.

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