Page 236 - Clinical Small Animal Internal Medicine

204 Section 3 Cardiovascular Disease

prevent worsening of ventricular arrhythmias and low it should not be combined with other beta‐blockers. It is
VetBooks.ir magnesium concentrations may result in hypokalemia the first choice for boxers with arrhythmogenic right
ventricular cardiomyopathy.
that is nonresponsive despite adequate supplementation.
Amiodarone is a drug that appears to be very effective
Other alternatives, such as synchronized cardioversion,
esmolol or precordial thump, can be attempted if the for refractory arrhythmias but it has been reported to
above therapies fail to improve hemodynamic stability. have significant and severe side‐effects. The low end of
Precordial thump for control of ventricular arrhyth- the dosage range should be used first and uptitrated only
mias was previously recommended as an initial maneu- if necessary. There are many side‐effects to the chronic
ver in the treatment of ventricular tachycardia (VT) or use of amiodarone. It may cause a hepatopathy, so liver
ventricular fibrillation, but is now only considered for enzymes should be evaluated before starting and peri-
patients with witnessed, monitored and unstable VT odically while receiving amiodarone and any time ano-
resulting in cardiac arrest/asystole. A precordial thump rexia develops. It may also cause neutropenia of unknown
is a very carefully aimed blow with the fist to the chest clinical significance and neurologic signs, and/or ataxia,
with the intent to interrupt a life‐threatening rhythm. especially at higher doses and with prolonged use.
The thump is thought to produce an electrical depo- Amiodarone can be combined with a beta‐blocker.
larization of 2–5 joules, but is only effective if used Additionally, it does not appear to have significant nega-
near the onset of ventricular fibrillation. The precor- tive inotropic effects and is thus safe to use in patients
dial thump for VT remains controversial as precordial with ventricular dysfunction. The authors have not used
blows can trigger ventricular fibrillation (i.e., commo- this drug in cats.
tio cordis). It should only be used for asystole or ven- Mexiletine is another useful antiarrhythmic agent, but
tricular fibrillation when a defibrillator is unavailable has become increasingly more difficult to find for veteri-
for use. nary patients and has several times come off the market.
It is often used in combination with atenolol or sotalol
for refractory arrhythmias or as an initial antiarrhythmic
Chronic Therapy of Ventricular Tachycardia
agent for dogs with systolic dysfunction. The authors
All chronic antiarrhythmic agents have the potential to have not used mexiletine as an antiarrhythmic in cats.
act as proarrhythmics, so their use should be monitored. Although antiarrhythmics are usually successful at
This is ideally done by obtaining a 24‐hour Holter controlling clinical signs in animals with ventricular
recording before and 8–15 days after initiation of antiar- arrhythmias, their ability to decrease the risk for sudden
rhythmics. If worsening arrhythmias develop, then a death is uncertain. Recently, the use of implantable car-
proarrhythmic effect should be considered as an under- dioverter defibrillators (ICD) has been investigated in
lying etiology. In addition, all antiarrhythmic agents have dogs. These devices, which have similarities with pace-
significant toxicity profiles. In both dogs and cats, the makers, are extensively used in people to terminate life‐
authors’ first choice for chronic ventricular arrhythmia threatening episodes of ventricular tachycardia or
therapy is sotalol. Although not a pure beta‐blocker, fibrillation with high‐energy electrical shocks. Accurate
sotalol has significant beta‐blocking effects, and should detection of arrhythmias amenable to electrical therapy
therefore be used with caution and slowly uptitrated in is, however, still challenging in dogs. Advances in ICD
dogs with significant ventricular systolic dysfunction, technology and programmability may help to expand
such as those with dilated cardiomyopathy. In addition, their use in veterinary medicine.