Download Ventricular Fibrillation and Cardiac Arrest

Ventricular Fibrillation and
Cardiac Arrest
Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)
BASIC INFORMATION
Description
Ventricular fibrillation is spasm or vibration of the heart, with no
effective heartbeats. It may arise when a ventricular premature
contraction (VPC) falls on the beat before it, causing the heart’s
electrical conduction system to malfunction. As a result, the heart
does not contract effectively, and blood is not pumped to the body.
In a short time, the heart stops. Cardiac arrest occurs when ventricular fibrillation starts and the pumping of blood stops.
Cardiopulmonary Resuscitation.) An electrocardiogram (ECG)
is needed to confirm that the heart is in ventricular fibrillation. All
other tests are postponed until after successful resuscitation has
occurred.
An animal that is successfully resuscitated requires numerous diagnostic procedures to search for a cause and evaluate the
effects of the arrest, including laboratory tests, chest and abdominal x-rays, and an echocardiogram (heart ultrasound). Further testing is based on the test results.
Causes
Problems in the body that cause the ventricles of the heart to become
irritated can result in VPCs and ventricular tachycardia. These
abnormal rhythms (arrhythmias) can lead to ventricular fibrillation.
Examples of such problems include being hit by a car (bruising
of the heart), gastric dilation, surgery, pancreatitis, hyperthyroidism (cats), serious infections (sepsis), severe changes in the body’s
electrolytes (potassium, calcium, magnesium), tumors, and drugs
(digoxin, antiarrhythmic drugs, opioids, tricyclic antidepressants).
Other potential causes include decreased blood volume (from
bleeding or dehydration), decreased oxygenation of the blood
(from respiratory or cardiac problems), decreased blood glucose
levels, hypothermia, elevated blood potassium levels, drugs, head
trauma, fluid in the sac around the heart, air in the chest, blood
clots, and many others.
Heart diseases can also be a cause. Unlike people, dogs and cats
rarely have “heart attacks” in which the blood supply to an area of
heart muscle is cut off and the heart muscle dies. In animals, ventricular fibrillation and cardiac arrest are more likely to occur with
diseases such as dilated cardiomyopathy in big dogs, congenital
heart diseases (subaortic or pulmonic stenosis), or advanced valvular disease in small dogs.
Clinical Signs
Signs of underlying disease or fainting episodes may be present in
some animals. Other animals have no signs of an abnormal heart
rhythm until they suddenly die from ventricular fibrillation. In
these cases, the animal initially collapses, becomes unresponsive,
and stops breathing. No heartbeat can be felt through the chest
wall, and no pulses can be felt in the neck or rear legs.
Diagnostic Tests
An animal that has gone into cardiac and respiratory arrest needs
immediate emergency care and resuscitation. (See the handout on
TREATMENT AND FOLLOW-UP
Treatment Options
The only treatment for ventricular fibrillation and cardiac arrest is
cardiopulmonary resuscitation (CPR) done by a veterinary team.
You can attempt to breathe for your animal through its mouth and
do chest compressions, but these are rarely successful. If you find
the animal collapsed, seek immediate veterinary care. If CPR is
successful, additional therapy is started based on the cause of the
cardiac arrest. The animal will remain hospitalized for further
treatment and observation.
Follow-up Care
If the animal survives, the type and frequency of follow-up visits
depend on the underlying cause of the cardiac arrest and the treatment required.
Prognosis
Prognosis is very poor for an animal that has suffered cardiac
arrest from ventricular fibrillation. Even if the arrest occurs in a
veterinary hospital, very few patients are successfully resuscitated
and live to leave the hospital.
About 30% of people who are observed to have a cardiac arrest
in the hospital are successfully resuscitated. Of that 30%, only
about 10% ever leave the hospital. The most successful resuscitations are usually those done on humans who have suffered a drug
overdose, drowning, or electrocution. In animals, the rate of successful resuscitation is much lower.
Prognosis also depends on the cause of the cardiac arrest and
how well that problem can be treated. Animals that arrest once
tend to arrest again within a short period of time unless the underlying cause is treated successfully. Cats that suffer a cardiac arrest
may be blind for 1-3 weeks from lack of oxygen to the brain, but
some will recover their eyesight.
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.