Page 42 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Section 4

VetBooks.ir TREATMENT OF

ARRHYTHMIAS

The decision on whether or not and how to treat aortic thromboembolism, anemia, neoplasia, or
arrhythmias depends on factors such as a history drug reactions, in which case therapy should be
of collapse, the heart rate during an arrhythmia, aimed at correcting or managing the underlying
the presence and severity of underlying heart disease. Cats of any breed, age, or sex may
disease, and affected dog breed (predispositions experience arrhythmias but Maine Coon cats are
of most commonly affected breeds; for genetic VT predisposed to HCM and thus commonly reported
abnormalities, see Box 4.1), as well as the presence of to have arrhythmias. Single VPCs and APCs are most
various systemic diseases that potentially contribute commonly found on Holter recordings of cats with
to the presence of arrhythmias. HCM, but complex arrhythmias with sustained VT
Therapy of arrhythmias should not be instituted and SVT are also reported, while healthy cats rarely
without an ECG to provide a definitive diagnosis of show any ectopic beats. Occasionally, cats are
the nature of the arrhythmia. By auscultation alone, diagnosed with atrial fibrillation. Typically, these
some ventricular arrhythmias can be confused cats have advanced underlying heart disease with
with supraventricular arrhythmias such as atrial marked dilation of the atria.
tachycardia or atrial fibrillation, which warrant Clinical signs of arrhythmias are often hard to
very different treatment strategies. Ambulatory, identify in cats, with lethargy or collapse being most
long-term ECG recordings, such as 24-hour Holter suggestive of a possible arrhythmia. Congestive
monitoring, might be required to establish a definitive heart failure, aortic thromboembolism or signs of
diagnosis since many arrhythmias are intermittent hyperthyroidism should prompt a careful evaluation
and might not be documented during a short in- for arrhythmias as a sequalae to the primary disease
hospital ECG. (See Section 5 for Holter monitoring.) process, as this population is at greatest risk for
Post-treatment 24-hour Holter recordings are sudden death. Due to the cats poor tolerance for
highly useful for assessment of drug efficacy, and wearing Holters, most arrhythmias are monitored
also allow for detection of drug toxicity, such as by ECG only.
proarrhythmia (worsening ventricular arrhythmias)
or drug overdose, for instance, bradycardia or MECHANISMS OF ANTIARRHYTHMIC
pauses secondary to excessive AV block. Pauses, if DRUGS
they occur only during sleep or rest, are usually of Antiarrhythmic drugs target two general areas of
low concern. the heart because of their specific electrophysiologic
In addition to medical therapy, interventional properties:
techniques, such as radiofrequency ablation,
are a potentially curative treatment of certain 1. Sinoatrial (SA) and AV nodal tissue:
supraventricular arrhythmias (AFL, AVRT), but are Depolarization in these tissues is calcium-
only offered at certain veterinary specialty clinics. channel driven and sensitive to autonomic tone.
Cardiac arrhythmias in cats most commonly To treat arrhythmias that originate from the SA
are associated with underlying heart disease, such and AV nodal tissue, calcium-channel blockers
as HCM or RCM, where sudden cardiac death is (CCBs) and beta-blockers (BBs) are primarily
thought to be linked to the presence of complex used. The most commonly prescribed CCB for
arrhythmias. Arrhythmias can also occur secondary treatment of arrhythmias is diltiazem (available
to systemic disease, namely hyperthyroidism, PO and IV). The β1-selective BBs atenolol
electrolyte imbalances (i.e., hyperkalemia), feline and esmolol (IV only) are the most frequently
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