Cardiac Arrhythmias

The clinical signs of an arrhythmia depend on how much it impairs cardiac output — how effectively the heart is pumping blood to the body. Signs range from absent to severe:

• No signs at all — the arrhythmia is discovered on routine examination or pre-anesthetic screening
• Episodic weakness or sudden collapse, often without warning (syncope)
• Exercise intolerance — tiring earlier than expected, reluctance to play or walk
• Intermittent wobbliness or appearing briefly confused, then recovering quickly
• Rapid, irregular, or very slow heart rate detected on examination
• Pale or gray gums during an episode — indicating temporarily reduced blood flow
• Sudden death in severe, untreated cases (particularly ventricular tachycardia and certain breed-related cardiomyopathies)

It is worth noting that many arrhythmias are intermittent — the pet may appear completely normal between episodes, which is why a single-snapshot ECG sometimes misses the problem and a 24-hour Holter monitor recording is needed.

Arrhythmias can arise from structural heart disease, systemic illness, electrolyte imbalances, or inherited electrical abnormalities. Common types and their typical settings include:

• Atrial fibrillation (AF) — the atria (upper heart chambers) fire chaotically instead of coordinating; common in giant-breed dogs (Irish Wolfhounds, Great Danes) and in any dog or cat with severely enlarged atria from advanced heart disease; produces a characteristically irregular heartbeat
• Ventricular premature complexes (VPCs) and ventricular tachycardia (VT) — abnormal beats arising from the ventricles (lower chambers); VPCs in small numbers are often benign, but runs of VT can degrade into ventricular fibrillation and sudden death; especially concerning in Doberman Pinschers, Boxers, and dogs with gastric dilatation-volvulus (bloat)
• Sick sinus syndrome — the heart's natural pacemaker (sinus node) fails to fire reliably, producing alternating fast and slow rhythms; miniature Schnauzers, Cocker Spaniels, and Pugs are predisposed
• Atrioventricular (AV) block — the electrical signal from the atria to the ventricles is delayed or completely blocked; third-degree (complete) AV block produces a very slow ventricular rate and often requires a pacemaker
• Bradycardia from systemic disease — severe hypothyroidism, hyperkalemia (elevated blood potassium, e.g., from Addison's disease), hypothermia, and certain drug toxicities can all depress the heart rate dangerously

Accurately characterizing an arrhythmia requires capturing the electrical rhythm — and the right tool depends on how often the abnormal rhythm is occurring:

• Electrocardiogram (ECG / EKG) — records the heart's electrical activity over several minutes; immediately identifies arrhythmias that are present at the time of the recording. This is the first test for any patient with a suspected rhythm abnormality.
• 24-hour Holter monitor — a lightweight, wearable ECG recorder that captures every heartbeat over a full day; essential for arrhythmias that happen intermittently, for screening Dobermans and Boxers annually for arrhythmic cardiomyopathy, and for assessing the frequency of VPCs before and after starting anti-arrhythmic medication
• Echocardiogram (cardiac ultrasound) — performed by Dr. D'Urso to determine whether the arrhythmia is secondary to underlying structural heart disease (enlarged chambers, reduced function) or is a primary electrical problem. This distinction changes treatment significantly.
• Blood panel and electrolytes — rules out metabolic causes such as hyperkalemia, hypothyroidism, or toxin exposure
• Blood pressure measurement — hypotension (low blood pressure) can both cause and result from arrhythmias

Not every arrhythmia needs treatment — the decision depends on the type of rhythm, its frequency, whether it is causing clinical signs, and the presence or absence of underlying heart disease. When treatment is indicated:

• Antiarrhythmic medications — sotalol, mexiletine, and lidocaine (IV for acute VT) are commonly used to suppress ventricular arrhythmias; diltiazem and digoxin are used for rate control in atrial fibrillation; the appropriate agent depends on the arrhythmia type and the patient's other conditions
• Pacemaker implantation — indicated for symptomatic sick sinus syndrome, high-grade second-degree AV block, and complete (third-degree) AV block where the ventricular escape rate is too slow to sustain normal activity. Pacemaker placement is a referral procedure performed at a veterinary specialty center; our team manages pre- and post-procedure cardiac care.
• Treating the underlying cause — correcting electrolyte imbalances, managing Addison's disease, stopping a causative drug, or treating the structural heart disease driving the rhythm problem
• Emergency management — ventricular tachycardia with hemodynamic compromise (pale gums, weakness, collapse) is a medical emergency; IV lidocaine and oxygen support are initiated immediately while the underlying cause is investigated

Holter monitoring is used to gauge the response to anti-arrhythmic therapy and guide dose adjustments over time.

Any pet that has fainted, collapsed, or shown episodes of sudden weakness should be evaluated the same day — these signs can indicate a dangerous arrhythmia that requires immediate treatment. Dogs of breeds known to carry arrhythmic cardiomyopathy (Doberman Pinschers, Boxers, Irish Wolfhounds) benefit from annual ECG or Holter screening even before symptoms develop, because sudden cardiac death can be the first outward sign of the disease. An irregular heartbeat heard by your regular veterinarian — or a murmur in a breed prone to ventricular disease — is a clear indication for cardiology evaluation and an echocardiogram. Dr. D'Urso interprets Holter recordings and echocardiograms on-site and can coordinate urgent care quickly when the situation demands it. Book an appointment to have your pet's heart rhythm evaluated.