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Ventricular Arrhythmias 1035

• Ventricular escape beats and VPCs often look
identical. Ventricular escape beats occur at
VetBooks.ir II 40-100 beats/min for cats) or after a pause Diseases and Disorders
slow heart rates (20-40 beats/min for dogs,
and are typically associated with second- or

pause/arrest. They are saving the heart from
VENTRICULAR ARRHYTHMIAS Lead II ECG for a dog with ventricular tachycardia: 50 mm/s, 10 mm/ third-degree atrioventricular block or sinus
mV. The ventricular tachycardia is monomorphic (ventricular premature complexes all of the same shape) and arrest and should never be treated with
extremely rapid (375 beats/min) in this critically septic dog. ventricular antiarrhythmics. In contrast,
VPCs occur prematurely and are therefore
in addition to the heart’s usual rhythm.
II • The most common correctable underlying
causes of ventricular arrhythmias are hypo-
kalemia, hypoxia, GDV, abdominal masses,
anemia, metabolic acidosis, and pain.
• The most common treatable but noncorrect-
able causes of ventricular arrhythmias are
VENTRICULAR ARRHYTHMIAS Single-lead ECG for a dog with immune-mediated hemolytic anemia and
an ausculted arrhythmia: 50 mm/s, 5 mm/mV. The fifth beat is a normal sinus beat; the remaining beats are of cardiomyopathy and degenerative valvular
ventricular origin. Despite the ventricular arrhythmia, the rate is not rapid (115 beats/min) and likely only slightly heart disease.
faster than the underlying sinus rate. This is an accelerated idioventricular rhythm, a benign rhythm that does • Ventricular arrhythmias most commonly are
not require therapy beyond proactive treatment of its inciting cause (here, anemia). manifestations of an underlying disorder.
Attempting to eliminate ventricular arrhyth-
hypokalemia. Hypomagnesemia can also Possible Complications mias with antiarrhythmic drugs in a stable
promote dysrhythmias. For patients who Uncontrolled ventricular arrhythmias may animal is analogous to shooting the mes-
do not convert, the authors will use the progress to ventricular flutter and ventricular senger. Rather, the underlying cause needs to
following: fibrillation (cardiac arrest), but normalization of be addressed. Perhaps no antiarrhythmic drug
○ Sotalol 0.5-2 mg/kg PO q 12h (dogs); the ECG to sinus rhythm using antiarrhythmic is as beneficial to a patient with ventricular
10-20 mg/CAT PO q 12h for patients who drugs alone has never been shown to improve arrhythmias as correction of the underlying
are clinically stable the prognosis for survival. Complications cause.
○ Amiodarone (Nexterone) 3 mg/kg bolus can be minimized by treating/correcting
over 15-20 minutes (dogs only); can be inciting factors and reserving ventricular Prevention
followed with IV CRI at 0.5 mg/kg/min antiarrhythmic drugs for cases in which overt Ventricular arrhythmias are clues to a primary
(dogs only) signs such as syncope are present or in which cardiac or systemic disturbance. Preventing
a very high rate (e.g., > 220 beats/min in dogs, them relies on identifying and managing the
Chronic Treatment > 260 beats/min in cats) is present despite underlying disease whenever possible.
• Ongoing management of the underlying management or correction of the underlying
cause cause. Technician Tips
• Oral antiarrhythmic drugs may be used Impostors of ventricular arrhythmias are
for treating rapid and/or clinically overt Recommended Monitoring common on in-hospital telemetry monitors,
(syncopal) ventricular arrhythmia. Options • ECG as dictated by clinical evaluation; but ventricular arrhythmias are an important
include one of the following: monitoring ranges from continuous ECG signal requiring attention. Unusual-appearing
○ Sotalol 0.5-2 mg/kg PO q 12h (dogs); with VT in an unstable, hospitalized animal heartbeats on an ECG monitor should be
10-20 mg/CAT PO q 12h; for small to periodic ECG or Holter monitoring printed and reviewed with the attending
patients, can be compounded as a liquid during recheck visits in stable animals veterinarian.
formulation (e.g., 10 mg/mL). Clinical • Follow-up tests as listed for initial diagnosis
efficacy appears similar to tablet formula- to monitor underlying condition Client Education
tion and stable for up to 2 months. Ventricular arrhythmias are serious disturbances
○ Mexiletine 4-8 mg/kg PO q 8h and sotalol PROGNOSIS & OUTCOME of the cardiac rhythm. Their impact can range
(see dose above) or atenolol 0.2-0.75 mg/ from minimal to life-threatening, and sudden
kg PO q 12h (dogs) • Ventricular arrhythmias that occur at a faster cardiac death is always possible when an
○ Amiodarone 10 mg/kg PO q 12h for 1 rate are more likely to produce clinical signs animal has a disorder that causes ventricular
week (loading), then 5-8 mg/kg PO q 24h and carry a more guarded prognosis than arrhythmias.
(dogs) slower ventricular arrhythmias.
○ Atenolol (cats) 6.25-12.5 mg/CAT PO q • Ventricular arrhythmias that fail to respond SUGGESTED READING
12-24h to correction of the underlying problem (or Côté E: Electrocardiography and cardiac arrhythmias.
for which the underlying problem cannot In Ettinger SJ, et al, editors: Textbook of veterinary
Nutrition/Diet be corrected) usually indicate cardiac mani- internal medicine, ed 8, St. Louis, 2017, Elsevier,
Administration of long-chain omega-3 fatty festations of a serious problem that carries pp 1171-1187.
acids from fish oils (EPA, DHA) may reduce the a guarded short-term prognosis. Long-term AUTHORS: Amara H. Estrada, DVM, DACVIM; Ashley
number of VPCs. Effect on mortality unknown. prognosis depends on the exact nature of the E. Jones, DVM, DACVIM
underlying problem. EDITOR: Meg M. Sleeper, VMD, DACVIM
Behavior/Exercise
Exercise and the associated sympathetic drive PEARLS & CONSIDERATIONS
may precipitate arrhythmias, but quality of life
must also be strongly considered. Comments
• Virtually any disease or disorder, if sufficiently
Drug Interactions severe to have systemic effects, can cause
Digoxin can cause ventricular arrhythmias. ventricular arrhythmias.

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