Page 49 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Treatment of Arrhythmias

with complete AVB can have “low-normal” HR due threshold for seizures in cats. The antiarrhythmic
effects of lidocaine are diminished in the presence
to a fast ventricular escape rhythm (120–140 bpm)
VetBooks.ir and no overt clinical signs, but typically over time of hypokalemia. Alternatives to lidocaine include
procainamide given as a slow IV bolus, as it may
(months to years) the escape rate tends to diminish
and once the HR drops below 100 bpm, cats start cause vomiting or hypotension due its negative
to show lethargy or syncope and may also develop inotropic effect, followed by a CRI. Refractory
congestive heart failure from chronic bradycardia. VT may be treated with potassium-blocking
At that point, pacemaker therapy is indicated, just antiarrhythmic agents, such as the IV form of water-
like in dogs. Due to cost, most cat owners elect soluble amiodarone-HCl (Nexterone). Nexterone is
medical therapy using beta agonists (Terbutaline), administered as an IV bolus infused over 10 min
but the efficacy is very limited. and is followed by a CRI. In cases of refractory VT,
magnesium supplementation (30 mg/kg slowly IV)
Treatment of ventricular arrhythmias (VAs) might also be beneficial.
The need for treatment of VA depends both on Other agents such as BBs can be given for additive
the hemodynamic consequences (i.e., hypotension antiarrhythmic effect. Esmolol or propranolol IV
causing weakness or fainting) and on the electrical boluses should be given judiciously because of the
instability of a rhythm (i.e., potential to degenerate negative inotropic effect of BBs. Oral sotalol with
into fatal ventricular fibrillation [VF]). Fainting or or without simultaneous use of IV drugs can help
weakness is usually due to ventricular tachycardia convert dangerous VT to sinus rhythm within
(VT) rather than single or paired VPCs. Hypotension 1–3 hours. The negative inotropic effect of the BB
produced by VT is related to the heart rate and component of sotalol should be considered.
duration of VT and cardiac contractility. In most Refractory VT, sometimes encountered in dogs
cases, sustained periods of VT >180–200 bpm are with myocarditis, myocardial infarction, or myo-
associated with clinical signs. The heart rate of VT is cardial neoplasia, might require electrical cardio-
also linked to the electrical propensity to degenerate version, as was previously described for AF.
into VF, which is more likely in the setting of VF is not amenable to medical antiarrhythmic
significant underlying heart disease. therapy, as organized cardiac electrical activity
Treatment may decrease clinical signs by slowing and function is absent, preventing delivery of
the heart rate of VT, shortening the duration of peripherally injected drugs to the heart. Therefore,
runs of VT, or, ideally, abolishing the VT entirely. electric defibrillation is the treatment of choice
However, no specific antiarrhythmic drug regimen for VF.
has been shown to prevent sudden death due to As previously mentioned, electrical cardioversion
VA. If systemic disease is present, it is important or defibrillation requires the patient to be anesthe-
2+
+
to correct electrolyte (K , Mg ) and acid–base tized or unconscious. The animal is placed in dorsal
disturbances, anemia, hypovolemia, or hypoxia, or lateral recumbency and self-adhesive defibril-
while managing the VA. Drugs commonly used for lation pads or handheld defibrillation paddles are
treatment of ventricular arrhythmias are presented applied on opposites sides of the chest following
in Table 4.3. application of conductive paste or gel. Different
energy dosages are required, depending on whether
Treatment of acute, life-threatening VT the unit is a biphasic (0.5–3 J/kg) or monophasic
Dogs and cats with VT and severe systemic defibrillator (2 J/kg: <7 kg BW; 5 J/kg: 8–40 kg
hypotension resulting in weakness or repeated BW; 5–10 J/kg: >40 kg BW). If the first shock is not
collapsing require immediate IV treatment, with effective, additional shocks of increasing energy are
the goals of conversion to sinus rhythm or slowing delivered.
of the VT rate. Intravenous treatment with a
sodium-channel blocker, typically lidocaine, is the Long-term therapy of VT
first choice for sustained VT. If lidocaine boluses To determine whether an antiarrhythmic drug
are effective, a constant rate infusion (CRI) of administered for long-term oral therapy of VA
lidocaine is started. Signs of lidocaine overdose is having (1) an antiarrhythmic effect, (2) an
include twitching, seizures, or vomiting, but side inadequate effect, or (3) a proarrhythmic effect,
effects dissipate rapidly because of the drug’s short Holter monitoring is recommended. A post-
half-life. Lidocaine is effective for VT in cats, treatment Holter recording, acquired 7–10 days
but should be used judiciously due to the lower after starting the drug, is evaluated for changes in
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