An arrhythmia is any deviation from the heart’s normal rhythm. Some are incidental findings on routine exams and require no treatment. Others are dangerous and can cause fainting, collapse, or sudden death. Sorting the two apart requires a cardiology evaluation, an ECG, and often a 24-hour Holter monitor to catch rhythms that come and go.

The common types of arrhythmia.

Arrhythmias are broadly categorized as tachyarrhythmias (heart rate too fast), bradyarrhythmias (heart rate too slow), and conduction disturbances (signals not moving through the heart normally). Each type has specific causes, symptoms, and treatments.

• Atrial fibrillation — rapid, irregular firing of the top chambers, common in large-breed dogs with heart disease
• Ventricular arrhythmias — premature beats or runs from the bottom chambers, can be dangerous if frequent
• Sick sinus syndrome — an unreliable natural pacemaker, causes pauses and syncope
• Third-degree AV block — complete disconnect between top and bottom chambers, life-threatening
• Supraventricular tachycardia — rapid rhythms originating above the ventricles
• Boxer ARVC — genetic ventricular arrhythmia in Boxers with associated cardiomyopathy

Signs that suggest an arrhythmia.

Sometimes arrhythmias are silent and detected only by ECG. When they cause symptoms, the most common are exercise intolerance, weakness, fainting or collapse, and irregular pulses on physical exam.

Certain breeds are at particular risk. Boxers can develop arrhythmogenic right ventricular cardiomyopathy (ARVC), which produces ventricular arrhythmias and increases the risk of sudden death. Dobermans with DCM develop ventricular arrhythmias as part of their disease. Screening these breeds with a Holter monitor is often part of proactive cardiac care.

Diagnosis and treatment.

The two most useful diagnostic tools are ECG (a snapshot of the heart’s rhythm) and Holter monitor (24 hours of continuous rhythm recording at home). Echocardiography identifies any underlying structural disease. Blood tests rule out metabolic contributors like electrolyte disturbances or thyroid disease.

Treatment depends on the type and cause. Options include anti-arrhythmic medications, pacemaker implantation for bradyarrhythmia’s, and in select cases, catheter ablation of the abnormal pathway. Dr. Dos Santos’s advanced training in interventional electrophysiology means we can offer procedures once available only at academic centers.

Frequently asked questions

Are all arrhythmias dangerous?

No. Some arrhythmias — like respiratory sinus arrhythmia in dogs — are normal and require no treatment. Others are dangerous and can cause collapse or sudden death. A cardiology evaluation distinguishes the two.

Can my pet exercise with an arrhythmia?

It depends entirely on the type and cause. Some arrhythmias have no impact on exercise capacity; others require activity restriction until treated. Your cardiologist will give specific guidance.

What is catheter ablation?

Catheter ablation is a procedure where a thin catheter is passed through blood vessels to the heart, and a specific area of abnormal electrical activity is treated (usually with heat or cold). It’s available for select arrhythmias at specialty centers — Dr. Dos Santos is one of a small number of veterinary cardiologists with this training.

Are arrhythmias inherited?

Many are. Boxer ARVC, Doberman DCM-associated arrhythmias, and Great Dane atrial fibrillation all have genetic bases. Screening at-risk breeds is a key part of preventive cardiac care.

How is arrhythmia response to medication monitored?

Follow-up ECGs and Holter monitors track whether the medication is controlling the arrhythmia. Blood levels of some medications may also be checked.