Increased Heart Rate Due to Premature Contractions in Dogs

Ventricular tachycardia is the medical term used to describe an increased heart rate. This increased heart rate can be hereditary irregular heartbeats (called arrhythmias) or may result from abnormalities of the heart. These abnormalities are typically associated with cardiomyopathy (heart disease), heart-valve disease, or myocarditis (inflammation of the heart). Ventricular tachycardia is more common in larger breeds with heart disease, such as Boxers, Doberman Pinschers, and German Shepherds. In these breeds, Boxers will typically show symptoms around 4-6 years of age, Doberman Pinschers from 3-6 years of age, and German Shepherds will develop as early as 12-16 weeks of age, though it will get more severe until 24-30 weeks of age. After 8 months, the severity should stabilize or begin to decrease. In other breeds, all age groups can be affected. Treatment options vary depending on the underlying cause, but can include surgery and administration of medicines by IV. Prognosis depends on the cause of the ventricular tachycardia, ranging from good to poor. In cases where onset of ventricular tachycardia is rapid, sudden death is possible.

Ventricular tachycardia refers to rapid heart rate and can be caused by arrhythmias that force the heart to contract more rapidly than it should. Possible symptoms include weakness, cough, trouble breathing, fainting, and rapid heart rate. 

Depending on the severity and other factors, ventricular tachycardia may not present any symptoms. In other cases, the following symptoms may be observed:

• Syncope (fainting)
• Weakness
• Trouble exercising
• Sudden death
• Tachycardia (rapid heart rate)
• Weak femoral pulses (typically measured by taking pulse at the inner thigh)
• Presence of heart murmur
• Cough
• Dyspnea (trouble breathing)
• Bluish discoloration of skin and tissue
• Cyanosis (decreased oxygen levels in red blood cells)
• Congestive heart failure (where the heart can’t pump enough blood to meet the body’s needs)

Types

Ventricular tachycardia is a problem with the heart in which the ventricular heart rate increases in speed. When this is caused by premature contractions, it is referring to irregular heartbeats, or arrhythmias, that cause the heart to contract more quickly than it should. These symptoms of heart problems can be hereditary or caused by heart abnormalities. 

• Cardiomyopathy (heart muscle disease)
• Congenital (present at birth) heart problems, such as subaortic stenosis (a defect at birth where the area just below the aortic valve is smaller than necessary)
• Chronic heart-valve disease
• Gastric dilatation (the stomach swells with gas/fluid, causing rotation around its volvulus, or short axis)
• Trauma
• Myocarditis (inflamed heart)
• Digitalis (heart medication) toxicity
• Heart tumors (benign or malignant)
• Pancreatitis (inflammation of the pancreas)

Diagnosis will vary depending on the underlying cause of the ventricular tachycardia and the symptoms your pet is presenting. The following diagnostic tests will be used to rule out other heart problems and determine the underlying cause of the condition.

• Physical exam
• Electrocardiogram; your veterinarian will analyze changes in the electrocardiogram. Specifically, three or more heart beats that are irregular and begin in the ventricle and cause quick contraction of the heart muscle in a row may be indicative of ventricular tachycardia.
• Echocardiogram (ECG), using an ultrasound to learn more about the heart and important blood vessels)
• Complete blood count
• 24-hour Holter monitoring, where your dog will wear a vest with a battery-powered ECG monitor is placed to record overall heart rate and rhythm

Treatment depends largely on the underlying cause of the condition, but may include:

• Correction of any instances of hypokalemia (low levels of potassium in the blood)
• Correction of any instances of hypomagnesemia (low levels of magnesium in the blood)
• If the condition results in the pet being unstable (unstable can be classified by an inability to stand, weakness, or syncope (frequent fainting), then they will be hospitalized and IV treatment will be administered while ECG monitoring is completed.
• After the irregular heart beat has been controlled and the pet has been stabilized, treatment may continue with oral medications
• In dogs where ventricular tachyarrhythmias (quick, abnormal ventricular heart beats) occurs, there is no present treatment to prevent sudden death.
• In most dogs, exercise restriction may not benefit the dog’s condition. With Boxers, excitement may increase the occurrence of ventricular tachycardia, so avoidance of situations that excite the dog should be attempted.
• If surgery is required, it is ideal that the cause of arrhythmias (irregular heartbeats) should be treated before any general anesthesia is administered. Using masks to administer anesthesia is not recommended. ECG monitoring should be done throughout all surgeries.
• Possible medicinal treatments include: lidocaine through IV administration, procainamide through IV administration, esmolol through IV administration, sotalol is typically effective in Boxers, a mexiletine and sotalol combination is typically most effective in German Shepherds

Recovery and management will vary depending on the cause, but many instances of ventricular tachycardia will require the following:

• Holter monitoring is preferred by many veterinarians for post-treatment monitoring. Holter monitoring allows the severity of ventricular tachycardia to be observed and reveals effectiveness of treatment. At minimum, 24-hour follow-up Holter monitoring will likely be used by your veterinarian to determine treatment effectiveness and control any arrhythmias.
• There are a few continuing monitoring techniques that are alternatives to Holter monitoring,  including electrocardiograms (where the electrical activity of the heart is recorded) and telemetry (where recordings of heart rate and rhythm are sent to a monitor through radio waves. However, these techniques aren’t as effective as Holter monitoring because ventricular premature contractions (arrhythmias that cause the heart to contract too quickly) and paroxysmal ventricular tachycardia (sporadic rapid heart rate) can occur through the day and therefore not be monitored.
• If your dog receives the heart medication digoxin, serum digoxin levels will need to be measured following a week of treatment to determine effectiveness.
• If your dog receives amiodarone, follow up should be done through serum chemistries that measure liver enzymes, typically around seven days following the start of the medicine.

Prognosis also depends largely on the cause of the condition. If the cause is metabolic, there is a fair prognosis. If the condition is related to heart disease, prognosis isn’t great due to the many complications that accompany heart disease and its tendency to worsen with time. If it associated to a type of cancer, prognosis is poor.