Heart Beat Problems (Fibrillation and Flutter) in Dogs

Atrial fibrillation and flutter are irregular contractions and twitching of the atria, the top two chambers of the heart. Atrial flutter involves the entire atria muscle, whereas fibrillation is a disorder that affects the individual fibers of the heart muscle. Diagnosis of this disorder is usually made using an ambulatory ECG machine that straps onto the patient and is worn for 24-48 hours. In most cases, antiarrhythmic medications are suitable for managing the inconsistent heart rate.

The irregular twitching and contractions of the atria muscles or specific fibers within the atria muscles causing interruptions and irregularity to the heart rate.

Many of the symptoms of fibrillation and flutter in the heart are related to congestive heart failure, a condition in which the heart cannot pump enough blood to meet the needs of the body. Signs may worsen with exercise.

• Coughing
• Cyanosis (bluish color of skin or mucous membranes)
• Difficulty breathing 
• Erratic heart rhythm (heard by stethoscope)
• Exercise intolerance
• Lethargy
• Pulse deficit (pulse and heart rate do not match)
• Rapid breathing
• Syncope (fainting)
• Variable pulse quality
• Weakness

Types 

Atrial fibrillation

• A rapid and irregular contraction or twitching of the heart muscle fibers involving the upper two chambers of the heart, the atria 

Primary atrial fibrillation

• This is atrial fibrillation without any underlying heart disease
• It is generally uncommon although larger dogs are at a slightly increased risk

Secondary atrial fibrillation

• A secondary atrial fibrillation has an underlying heart disease which is triggering the fibrillation 

Atrial flutter

• Involves the entire muscle of the atria and tends to be more rapid than with atrial fibrillation
• The baseline of an ECG will have a distinctive pattern of regular saw-like waves

There are several diseases and disorders that can trigger either atrial flutter or atrial fibrillation. 

• Atrial fibrosis
• Breed disposition- any large dog, but especially Great Dane, Doberman Pinscher, Newfoundland, Irish Wolfhound, Boxer
• Congenital heart disease
• Congestive heart failure
• Degenerative heart valve disease
• Digoxin toxicity
• Dilated cardiomyopathy
• Endocarditis
• Hypertrophic cardiomyopathy
• Hypomagnesemia
• Mitral valve endocardiosis
• Prolonged tachycardia
• Pulmonary hypertension

Your veterinarian will start by getting a history of symptoms and a physical evaluation. During the physical evaluation, particular attention will be paid to the heart sounds and the color of the skin and mucous membranes. A standard stethoscope will reveal an erratic heartbeat that has been described as sounding like “tennis shoes in a dryer”. A biochemistry profile, complete blood count, and urinalysis will be requested as well to help determine if there is an underlying cause and what it might be. X-ray or ultrasound imaging of the chest area may be warranted, depending on the other results. ECG (electrocardiogram) technology provides the best option to diagnose atrial fibrillation and flutter. An ambulatory ECG device can be strapped to your dog so that it can take readings over 24-48 hours which gives your veterinarian which is required for in order to get a clear picture of the heart’s rhythms.

The aim of treating fibrillation or flutter of the atria is to return the heart to its normal rhythm. With humans, an electric shock is given to the heart in order to reset the rhythm of the heart back to a steadier rhythm. This treatment, electrocardioversion, is less effective on canines and although it is still available as a treatment option, medications designed to slow the heart rate are more often recommended. Although digoxin can result in digoxin toxicity in a few cases, it is still an effective medication in many instances and is often a preferred treatment for irregular heartbeats. Other medications could include mexiletine, procainamide, sotalol, high-dose oral quinidine, diltiazem, propranolol, or atenolol. If the heart rate remains high after treatment, the veterinarian may consider adding in an adrenergic blocker such as esmolol. If the atrial disturbance is caused by an underlying heart condition, this condition will also need to be addressed.

Your veterinarian will probably want to follow-up with additional ambulatory ECG testing for 24-48 hour intervals to verify that the heart is beating more normally and the medication is properly regulating the muscle movement. If your pet’s heart arrhythmia does not have an underlying heart disease or disorder the medication usually clears up the symptoms. If there is an underlying heart condition the prognosis can be much more guarded depending on the severity of the condition of the heart. Echocardiography and radiography testing may also be done to determine the need for other medications in the event that the atrial fibrillation or flutter is not being managed with the current medications.