Page 47 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Treatment of Arrhythmias

Oral sotalol, procainamide, or amiodarone is often heart rate. If immediate pacemaker therapy is not an
option, medical therapy can be attempted. An atropine
co-administered in order to slow conduction in
VetBooks.ir the atria, accessory pathways, and ventricles. In response test can help identify patients that would
benefit from such medical management. Following
dogs with drug-refractory AVRT and clinical signs,
radiofrequency ablation should be considered. injection of atropine IM or IV, the baseline heart rate
should increase by 50%–100% within 5–10 minutes
Treatment of bradyarrhythmias (initial worsening of AV block is a normal transient
Clinically significant bradyarrhythmias that typi- response). Patients experiencing at least a partial
cally require treatment involve sinus node dysfunc- response to atropine may be candidates for medical
tion (e.g., sinus bradycardia or sick sinus syndrome management of sinus bradycardia. Treatment
[SSS]), atrial standstill, or AV node conduction options include either vagolytics (e.g., probantheline
abnormalities (e.g., high-grade, second-degree or bromide), sympathomimetics (e.g., terbulatine), or a
third-degree AV block). Drugs commonly used to phosphodiesterase inhibitor (e.g., theophylline); for
treat bradyarrhythmias are listed in Table 4.2. drug doses, see Table 4.3. In animals with no clinical
signs, sinus bradycardia might be “waited out” with
Sinus bradycardia close monitoring.
Sinus bradycardia, beyond what occurs because of
normal vagal tone, can be due to conduction system Sick sinus syndrome (SSS)
disease (i.e., SSS) or secondary to an underlying Most dogs with SSS exhibit clinical signs ranging
systemic disease (i.e., Addison’s disease), electrolyte from exercise intolerance and lethargy (which may
abnormalities (i.e., hyperkalemia), drug toxicity be under-recognized by owners and mistakenly
(e.g., narcotics or overdosing of BBs, CCBs), or attributed to aging) to frequent syncope. If clinical
excessively increased vagal tone (i.e., secondary signs are intermittent, 24-hour Holter recordings are
to gastrointestinal or central nervous system often necessary to attribute the signs to SSS. Pace-
disease). Correction of the underlying condition maker therapy is typically required for syncopal or
or discontinuation of drugs may resolve secondary lethargic dogs with SSS. In animals without syncope
sinus bradycardia. Animals that are syncopal due to or with no, or only mild, clinical signs, watchful
bradycardia most likely require pacemaker therapy, waiting or medical management can be attempted
as oral drugs are not effective at accelerating the (see medical treatment of sinus bradycardia).

Table 4.2 Drugs for treatment of bradyarrhythmias
Drug Administration per os Intravenous Comments
administration
Atropine sulfate Dog and cat: Can cause transient worsening
0.02–0.04 mg/kg IV of AV nodal block
bolus or IM
Probantheline Dog: 0.25–5 mg/kg BID Can cause mydriasis,
bromide to TID constipation, dry mouth,
Cat: 0.25–0.5 mg/kg or keratoconjunctivitis sicca
7.5 mg/cat BID to TID
Terbutaline Dog: 1.25–5 mg/dog
BID to TID
Cat: 0.312–1.25 mg/cat
BID to TID
Theophylline Dog: 10–20 mg/kg BID Can cause restlessness and
Cat: 15–25 mg/kg SID anxiety, panting, nausea,
vomiting, diarrhea, polydipsia,
polyuria
Abbreviations: IV, intravenous; IM, intramuscular.

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