Ventricular Standstill in Dogs

When the heart stops, even for a few seconds, it can upset the rhythm of the heart, in that restoration to proper activity is disturbed. With ventricular standstill, the heart appears to function normally but has episodes of stopping for a few seconds at a time, at irregular intervals. Also called pulseless electrical activity and asystole, this loss of cardiac output takes place in the bottom chambers of the heart. The bottom two chambers are called the ventricles. The top two chambers are known as the atria; atrial standstill is another condition of the heart altogether.

Ventricular standstill occurs when there is an absence of ventricular activity in the heart for more than a few seconds. This condition can lead to the full stoppage of the heart, known as cardiac arrest.

The most obvious sign you will see your dog display if he has ventricular standstill is episodic fainting. This symptom should be taken as a serious event, and it is imperative that you get your canine companion to the veterinary clinic without delay.

• Your dog may have short episodes of fainting, but after the occurrence continues to act normally as if nothing happened
• You may notice times of lethargic behavior due to low oxygen levels
• He may collapse with loss of consciousness
• Your pet could experience complete cardiac arrest and death

Types

Ventricular standstill can be classified in two ways.

Primary

• The condition has developed on its own

Secondary

• Other factors have led to the event

The asystole, or absence of activity in the ventricle chambers of the heart, results in the blood not being pumped rhythmically as it should into the lungs and the body. 

Primary

• Ischemia (lack of blood flow to the heart, and thereby lack of oxygen as well)
• Degeneration of the sinoatrial node (the natural pacemaker of the heart)or AV node (receives impulses from the sinoatrial node)
• Cardiac disease

Secondary

• Effect of a medication
• Electrolyte imbalances
• Acidosis
• Cardiogenic shock (the heart is damaged and unable to pump blood to the organs of the body)
• Resulting from untreated or undiagnosed ventricular tachycardia or ventricular fibrillation
• Resulting from other systemic diseases

If your pet arrives at the clinic in a state of distress or is suffering from repeated fainting episodes, the veterinary team will concentrate on addressing the immediate problem, attempting to maintain the proper rhythm and function of the heart. You will be asked pertinent questions related to ventricular standstill.

• How often has your dog been having the fainting episodes?
• How long does the syncope event last?
• Are they very sporadic, or do they occur often?
• How does he appear when he awakens from the faint?
• Does he seem tired or lacking in his normal energy level?
• Has he been ill lately?
• Is he on medication?

A physical examination, involving listening to the heart, lungs, and rate of pulse will take place. A complete blood count, biochemistry profile and urinalysis are tests that normally follow the diagnostic protocol. Diagnosing a case of ventricular standstill can be complex, and may result in additional tests.

• Electrocardiogram to verify the heart rhythm
• Echocardiogram to view the heart
• Fine needle aspirate of fluid
• Cytology will evaluate cells and proteins
• Radiograph to view the heart and lungs
• Holter test (a 24 hour ECG monitor put on the dog to track the heart rhythm and possibly denote an AV block, for example)

Once your pet has been stabilised and definitive diagnosis has been made, your veterinarian will assist you in further decision making in regards to treatment. If there is an underlying disease process or an electrolyte imbalance causing the problem, treatment could be as simple as correcting the initial problem or managing the illness that is contributing to the ventricular standstill.

If the diagnosis shows a primary cause, resolution could be more difficult.   Documentation shows the successful implantation of a pacemaker is a possibility you can discuss with your veterinarian. This choice of treatment will most likely involve a visit to a specialist, well versed and knowledgeable in ventricular standstill and additional heart abnormalities.

Studies have shown that despite some canines who have experienced complications due to pacemaker implantation, the majority of dogs who have gone through the procedure have gone on to lead a healthy life. Having a pacemaker does involve significant follow up to verify the functioning of the device and to ensure that the ventricular standstill is under control.

For those pets whose treatment involves care and resolution of an ongoing illness, ventricular standstill could be something that recurs.