Heart Beat Problems (Premature Complexes) in Dogs

A premature complex is a specific type of heart arrhythmia characterized by a premature beat of the heart. This disorder can come from the ventricles themselves (ventricular) or from the tissues above the ventricles (supraventricular). Although heart disease is a common cause of premature complexes in canines, it is not the only disease or disorder that can induce a premature complex to form. If this disorder persists after underlying causes are eliminated antiarrhythmic medications may be prescribed in an attempt to prevent more troublesome arrhythmias from developing.

An arrhythmia characterized by a premature P-wave depolarization, which causes a premature heartbeat followed by a skipped beat. Premature complexes may be indicative of underlying disorders.

Unless the underlying cause of the disorder is a congenital disorder, this disorder is more likely to strike older dogs than younger. Many of the symptoms are related to congestive heart failure, which may cause premature complexes or occur concurrently.

• Abdominal distention
• Congestive heart failure
• Cough
• Cyanosis (blue tinge to skin and mucous membranes)
• Difficulty breathing
• Lethargy
• Muscle wasting, especially of the forelegs and shoulders
• Slowed heart rate
• Sudden death
• Syncope (fainting)

Types

Premature complexes, also known as premature beats, can be broken into two broad categories based on where they originate from.

Supraventricular

• These disorders originate from the tissue above the ventricles and the majority of supraventricular premature beats are atrial in origin
• Disorders that would fit into this category would be atrial premature complexes and junctional premature complexes 

Ventricular

• The cardiac impulse for this variety of the disorder is initiated within the ventricles themselves rather than in a sinus node
• A ventricular premature complex is sometimes referred to as a skipped beat
• If too many ventricular premature complexes fire off too rapidly it can cause the canine to go into a tachycardic state

There are many conditions that can cause a premature complex to develop:

• Acidosis
• Anemia
• Atrial dilation
• Blood loss
• Cardiac neoplasia
• Cardiomyopathy
• Congestive heart failure
• Endocarditis
• Gastric dilation and volvulus (GDV)
• Genetically predisposed disorders
• Boxer - Arrhythmogenic right ventricular cardiomyopathy
• Doberman - Occult dilated cardiomyopathy
• German Shepherd -Juvenile ventricular arrhythmia 
• Hypocalcemia
• Hypokalemia
• Hypomagnesemia
• Immune-mediated disease
• Tick-borne disease
• Toxins (antiarrhythmic agents, barbiturates, Digoxin, Doxorubicin, Grepafloxacin, Sparfloxacin)

Your veterinarian will start by getting a history of symptoms and a physical evaluation. During the physical evaluation, specific attention will be paid to the sound of the heart and the color of the skin and mucous membranes. A distinctive gallop-like three beat rhythm can be heard with a standard stethoscope. A biochemistry profile, complete blood count, and urinalysis will be requested as well to help determine why the premature complex has developed. X-ray or ultrasound imaging of the chest or the abdominal area may be warranted, depending on the other results. ECG (electrocardiogram) technology provides the best option to diagnose a specific rhythm abnormality, and in many cases, an ambulatory ECG device can be strapped to your dog so that it can take readings over 24-48 hours. The ECG will generally pick up a premature P-wave that is different in size or configuration, causing the next beat to skip.

The first course of action for this disorder is to treat any underlying conditions that may be affecting the canine. Treatments can range from oral supplementation with magnesium to surgical intervention, depending on the conditions involved. Once any underlying causes have been addressed mild cases of this disorder may require observation rather than treatment. By themselves, the premature beat may not cause any serious problems unless they are frequent or the patient is at risk for developing another type of arrhythmia such as atrial fibrillation. If treatment is not recommended the patient should be re-evaluated on a regular basis to ensure the more serious arrhythmias do not develop. More critical cases will require medication to stabilize the beats. 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, sotalol, diltiazem, propranolol, or atenolol.

Your pet will most likely require more frequent visits to the veterinarian for monitoring of the heart rate and rhythm, even with mild cases of this arrhythmia. Premature complexes can resolve on their own or increase in frequency. Increases in frequency can deteriorate into more severe types of irregular heartbeats such as atrial fibrillations. If tachycardia accompanies the premature complex the chances that the patient will develop a more severe arrhythmia is increased and medication is more likely to be recommended. Although the medications to control the irregular heartbeats are helpful, the condition can still worsen as underlying conditions progress.