Download Ventricular Premature Contractions and Tachycardia

Ventricular Premature Contractions
and Tachycardia
Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)
BASIC INFORMATION
Description
Ventricular premature contractions (VPCs) are beats that originate from the large chambers of the heart (ventricles). They occur
before the heart has time to fill adequately and alter the pattern of
the heartbeat, which can decrease the ability of the heart to pump
blood effectively.
Ventricular tachycardia (VT) arises when three or more VPCs
occur in a row. The longer and faster the VT, the more the pumping
effectiveness of the heart is affected, and the less blood is received
by the body. If one of the abnormal beats occurs at the wrong time,
it can stop the heart and the animal dies.
A few VPCs can occur daily in normal dogs and cats, but if
VPCs become frequent and arise from multiple places in the ventricles, then serious problems can develop.
Causes
Problems in the body that cause the ventricles to become irritated
can generate these abnormal heart rhythms (arrhythmias). Examples
include being hit by a car (bruising of the heart), gastric dilation,
surgery, pancreatitis, hyperthyroidism (in cats), serious infections
(sepsis), severe changes in the body’s electrolytes (potassium, calcium, magnesium), tumors, and drugs (digoxin, antiarrhythmic
drugs, opioids, tricyclic antidepressants). Sometimes the cause cannot be found.
Heart diseases can also cause these arrhythmias. Dilated cardiomyopathy in big dogs, congenital heart diseases (such as subaortic or pulmonic stenosis), and advanced valvular disease in small
dogs can result in ventricular arrhythmias. Doberman pinschers,
boxers, and German shepherd dogs can develop these arrhythmias
as a part of heart diseases specific to their breed.
Clinical Signs
Signs are mainly related to the underlying disease, especially if the
VPCs are infrequent. If the VPCs are frequent, fast, and constant
(VT), then the animal may experience weakness, fainting episodes,
intermittent rapid breathing, or sudden death. In boxers, fainting
during exercise, stress, or excitement may be the only sign.
Diagnostic Tests
An electrocardiogram (ECG) is necessary to diagnose these
arrhythmias. If an animal is having fainting episodes and the ECG
is normal, then a 24-hour Holter monitor or an event monitor may
be needed to document the frequency and severity of the arrhythmia. (See the handout on Electrocardiography.) Once VPCs
or VT is diagnosed, extensive testing is done to find the cause.
Laboratory tests, chest and abdominal x-rays, and an echocardiogram (heart ultrasound) are usually done first. Depending on their
results, further tests may be necessary.
TREATMENT AND FOLLOW-UP
Treatment Options
Whether the VPCs or VT are treated depends on the frequency of
the beats (single, infrequent beats are not treated); the rate at which
they are occurring (VT is treated); the appearance of the beats (the
more bizarre and closer to other beats, the more likely they are to be
treated); and the animal’s symptoms (fainting animals are treated).
Boxers, Doberman pinschers, and German shepherd dogs with
VPCs are treated, because sudden death can occur in these breeds.
Dogs with serious arrhythmias must be hospitalized and treated
with intravenous lidocaine to stabilize the heart rhythm. Lifethreatening ventricular arrhythmias are less common in cats, and
hospitalization is primarily needed to treat the underlying problem
rather than the arrhythmia.
Once the heart rhythm has been stabilized, several different
drugs may be used orally. Sometimes the dog must be switched
from one drug to another to control the arrhythmia. Ideally, Holter
monitoring is done before and during therapy to evaluate the drug’s
effectiveness. Oral drugs used in dogs include sotalol, mexiletine,
mexiletine-atenolol combinations, and sotalol-mexiletine combinations. Amiodarone is used as a last resort (because of its multiple side effects) and requires referral to a veterinary specialist for
its administration. Cats may be given atenolol or sotalol.
Follow-up Care
Frequent ECGs and, ideally, Holter monitoring are performed
to assess the response to treatment. The duration of the therapy
depends on the underlying problem. If the underlying disease process cannot be cured, the animal often remains on antiarrhythmic
therapy indefinitely. Boxers, Doberman pinschers, and German
shepherd dogs are usually treated for the rest of their lives.
Prognosis
If the underlying disease is curable, prognosis is excellent, because
ventricular arrhythmias usually disappear once the disease is
gone. With chronic diseases, prognosis depends on how well the
arrhythmia can be controlled. No drug can prevent sudden death in
all cases. Affected boxers may do well for more than a year with
controlled arrhythmias, but Dobermans may eventually develop
dilated cardiomyopathy. Arrhythmias in German shepherd dogs
can be hard to control, so their prognosis is more guarded.
IF SPECIAL INSTRUCTIONS HAVE BEEN ADDED, THEY WILL APPEAR ON THE LAST PAGE OF THE PRINTOUT.
Copyright © 2011 by Saunders, an imprint of Elsevier Inc. All rights reserved.