Page 111 - Small Animal Internal Medicine, 6th Edition

CHAPTER 4 Cardiac Arrhythmias and Antiarrhythmic Therapy 83

Acute Therapy—Ventricular Tachyarrhythmias

CAT
DOG
VetBooks.ir IV Lidocaine (maximize β-blocker
dose if necessary)
Effective Ineffective
Ineffective Effective
Continue as Check serum K , Mg ; IV Lidocaine Continue as

needed (CRI); verify ECG Dx; try other (low dose) needed; monitor;
or try alternate drugs: procainamide, ± treat underlying
agent for PO β-blocker, or amiodarone, disease
therapy; monitor or sotolol, or mexiletine, Ineffective
or quinidine (see text)
Effective Effective
Effective Ineffective

Reevaluate ECG; treat underlying Try alternate agent;
Continue as disease and metabolic abnormalities; or continue most
needed; treat try another drug or drug combination; effective agent;
underlying try MgSO infusion supportive care
4
disease and monitoring
Effective Ineffective
FIG 4.3
A therapeutic approach to ventricular tachyarrhythmias. See Table 4.2 for drug doses and
text for more information. CRI, Constant-rate infusion; Dx, diagnosis; ECG,
electrocardiogram.

only the newer aqueous preparation (e.g., Nexterone; Baxter The patient’s clinical status, the underlying disease(s), the
International) should be used. Older amiodarone formula- success of the drug in controlling the arrhythmia, and the
tions can cause marked hypotension and hypersensitivity drug dosage (that is, whether it could be increased within
reactions because of the solvents used (see p. 95). Alterna- recommended dosage range) all influence the decision
tively, procainamide (IV or IM) or quinidine (IM or PO) can whether to continue or discontinue current treatment or
be tried next. Effects of a single IM or oral loading dose to use a different drug. Clinical status and results of diag-
should occur within 2 hours. If this is effective, lower doses nostic testing also guide decisions about chronic oral
can be given every 4 to 6 hours IM (or PO, if available). If therapy.
ineffective, the dose can be increased or another antiarrhyth- If the ventricular tachyarrhythmia appears refractory to
mic drug chosen. Quinidine is not given IV because of its initial treatment attempts, one or more of the following con-
hypotensive effects; it also is not recommended in patients siderations may be helpful:
on digoxin or that have prolonged QT intervals. If the
arrhythmia has not been controlled, a β-blocker can be 1. Reevaluate the ECG—could the rhythm have been incor-
added. rectly diagnosed initially? For example, SVT with an
Cats with frequent ventricular tachyarrhythmias usually intraventricular conduction disturbance (aberrant ven-
are given a β-blocker first. Alternatively, low doses of lido- tricular conduction) can mimic ventricular tachycardia.
caine can be administered. However, cats can be quite sensi- In such cases, IV diltiazem is usually more effective than
tive to the neurotoxic effects of this drug. Procainamide or lidocaine.
++
+
sotalol also can be used. 2. Reevaluate the serum K (and Mg ) concentration.
Digoxin is not used to treat ventricular tachyarrhythmias. Hypokalemia reduces the efficacy of class I antiarrhyth-
It can predispose to the development of ventricular arrhyth- mic drugs (such as lidocaine, procainamide, quinidine)
mias. Patients with heart failure and/or supraventricular and can predispose to the development of arrhythmias. If
+
arrhythmias that are being treated with digoxin and that the serum K concentration is less than 3 mEq/L, KCl can
+
develop frequent or repetitive VPCs may need additional be infused at 0.5 mEq/kg/h; for serum K between 3 to
antiarrhythmic drug therapy (e.g., lidocaine) or digoxin 3.5 mEq/L, KCl can be infused at 0.25 mEq/kg/h. A
+
withdrawal, as well as serum digoxin measurement. Ancil- serum K concentration in the high normal range is the
+
++
lary KCl supplementation (if serum K ≤ 4 mEq/L) with or goal. If the serum Mg concentration is less than 1 mg/
without MgSO 4 can increase antiarrhythmic efficacy. dL, MgSO 4 or MgCl 2 , diluted in D 5 W, can be administered
Close ECG and patient monitoring and further diagnos- at 0.75 to 1 mEq/kg/day by CRI.
tic testing should follow initial therapy. Total suppression 3. Try amiodarone (IV), sotalol (PO), or a β-blocker in con-
of persistent ventricular tachyarrhythmias is not expected. junction with a class I drug (such as esmolol, propranolol,