Ventricular Standstill in Dogs - Symptoms, Causes, Diagnosis and Treatment

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Dog Laying Down

Ventricular standstill is a serious condition that can affect the heart of a dog. If this occurs in a dog it can have a fatal outcome. Knowing what this heart condition is and what it may mean for a dog that has it is beneficial for dog owners to understand.

What Is Ventricular Standstill in Dogs?

Ventricular standstill is also known as asystole. It occurs when parts of the heart, called the ventricles, stop working properly and emit no electrical signal on a machine designed to read these signals called an electrocardiogram. This signal on the electrocardiogram (ECG/EKG) is referred to as a QRS complex and is the visual representation of the electrical impulse going through the ventricles. It is seen as the main spike on an ECG tracing line or is often thought of as the visual heartbeat on the ECG monitor screen. When ventricular standstill occurs, a flat line is seen on an ECG because there are no electrical impulses occurring in the heart ventricles. It may also commonly be referred to as a type of cardiac arrest but a heart attack is something different.

Types of Heart Rhythms in Dogs

There are several different types of abnormal heart rhythms or arrhythmias that may be seen on an ECG of a dog. These different types of heart rhythms will produce different ECG line patterns or tracings. These different ECG tracings then help a veterinarian know what type of abnormal rhythm is present. Some of the most commonly seen include:

  • Sinus arrhythmias
  • Atrial fibrillation (A-fib)
  • Ventricular tachycardia (V-tach)
  • Atrioventricular blocks (AV block)
  • Ventricular premature complex (VPC)
  • Ventricular standstill (asystole)
  • Atrial standstill
adult white American bulldog sitting on couch
adult white American bulldog sitting on couch

Signs of Ventricular Standstill in Dogs

  • Collapse
  • No movement
  • No heartbeat
  • Sudden death

The signs of ventricular standstill in a dog are very apparent to a pet owner, even without the use of an ECG. Dogs who experience this heart problem will collapse since their heart is no longer pumping blood properly through their body. No movement will be seen from the dog and no heartbeat will be felt if you place your hand on the dog's chest.

Causes of Ventricular Standstill in Dogs

There are a few causes of ventricular standstill in dogs.

  • AV or SA node problems: The heart has four chambers in it that pump blood through the body and each chamber has valves that open and close. Electrical impulses from the heart's natural pacemaker, called the sinoatrial (SA) node, tell those valves when to open and close. When the body's pacemaker doesn't work properly or the signals are blocked at the atrioventricular (AV) node, these valves don't open and close so blood does not get pumped through the body. This lack of pacemaker activity or AV node action results in ventricular standstill and a flat line on an ECG monitor screen because there is no electrical activity to read.
  • High potassium: Referred to medically as hyperkalemia, extremely high potassium levels in the blood from under-active adrenal glands, obstructed or burst urinary bladders and urinary tracts, or other problems can cause ventricular standstill.
  • Heart disease: Major heart disease can cause the heart to malfunction and ventricular standstill may occur.
  • Systemic illness: Major illness and infection within the body can cause the heart to stop working properly and may result in ventricular standstill.

Diagnosing Ventricular Standstill in Dogs

If a dog has ventricular standstill it will most likely collapse and go into cardiac arrest. This is of course an emergency situation in which cardiopulmonary resuscitation (CPR) is often started but an ECG is often also connected to a dog at this time to gather insight into whether or not there is electrical activity in the heart. Ventricular standstill will be seen at this time on the ECG monitor screen as a flat line.

brown short coated medium sized dog on snow covered ground during daytime
brown short coated medium sized dog on snow covered ground during daytime
brown and white long coated dog
brown and white long coated dog
grey scale photography of dog sitting on ground
grey scale photography of dog sitting on ground

Occasionally dogs have episodes of something called syncope or fainting which may also result in ventricular standstill. This can be seen if an ECG is connected to the pet when the fainting or collapse occurs. These dogs may not go into cardiac arrest because the abnormal heart rhythm is only temporary but it is still a serious issue.

Treatment of Ventricular Standstill in Dogs

Ventricular standstill often requires CPR efforts in order to restart the heart's normal beating action, regardless of the cause of the arrhythmia. Medications, oxygen therapy, chest compressions, and more invasive CPR techniques may be utilized. It is important for dog owners to realize that the success rate of CPR is extremely at less than six percent, so CPR is unfortunately often unsuccessful, though.

If ventricular standstill occurs alongside intermittent fainting issues due to pacemaker issues within the body, an artificial pacemaker may be recommended to be surgically placed in your dog. This is not a common occurrence as ventricular standstill often occurs with cardiac arrest but it is a treatment for some dogs with occasional ventricular standstill.