What is an arrhythmia?

Normally, an impulse begins in the sinoatrial node and travels through the atria, atrioventricular node and ventricles in sequence. Abnormal impulse generation or conduction can cause fast rhythms (tachycardia), slow rhythms (bradycardia) or irregular beats.

Some arrhythmias cause no symptoms, while others can cause fainting or sudden death during exercise. Type and frequency need assessment. An in-clinic ECG may capture an arrhythmia, but intermittent events may only occur at home; a 24-hour Holter supplements the examination.

Pets at higher risk

Any pet can develop an arrhythmia, but assessment takes particular priority for:

  • Dogs or cats with MMVD, DCM, HCM, RCM or other heart disease
  • Breeds with known arrhythmogenic right ventricular cardiomyopathy or DCM risk, such as Boxers and Dobermans
  • Any pet with even one episode of fainting or sudden unsteadiness during exercise
  • Older dogs and cats, with possible AV block or slow arrhythmias
  • Irregular beats detected before anesthesia or noncardiac surgery
  • Concurrent electrolyte abnormalities, thyroid disease or chronic kidney disease

What signs should I watch for?

These signs may suggest an arrhythmia. Report even a single occurrence, including circumstances, duration and recovery.

  • Fainting — sudden collapse followed by rapid recovery of consciousness
  • Unsteadiness or brief loss of balance during exercise or excitement
  • Slow recovery and prolonged panting after a gentle walk
  • An apparent skipped beat felt while holding your pet
  • Briefly pale or blue gums or tongue
  • Sudden waking and restlessness, rarely associated with a severe tachycardia episode

Fainting is a strong reason to assess rhythm

Fainting suggests a brief period of inadequate blood flow to the brain, rather than simple dizziness. Arrhythmia is not the only possible cause, but its potential importance warrants considering a 24-hour Holter alongside an in-clinic ECG.

Diagnosis — ECG and Holter

An arrhythmia must be recorded to identify it. A staged approach helps avoid missing events absent during a clinic visit.

  1. Auscultation and pulse assessment

    Check heart rate, regularity and pulse deficits. A mismatch between audible heartbeats and femoral pulses may be the first clue.

  2. In-clinic 12-lead ECG

    A standard 12- or 6-lead ECG assesses P waves, QRS complexes and QT intervals and classifies recorded rhythms. Waveform features help determine the type and clinical significance.

  3. 24-hour Holter monitoring

    A patch recorder on the chest captures every beat during daily life for 24 hours. It can identify intermittent arrhythmias, nighttime bradycardia and exercise-related tachycardia missed in the clinic, supporting assessment of fainting and exercise intolerance.

  4. Echocardiography

    Assess structural disease underlying the arrhythmia, such as MMVD, DCM or HCM. The combination of rhythm type and underlying condition determines treatment.

  5. Blood tests / Blood pressure / Thyroid

    Assess electrolytes such as potassium, thyroid and kidney function, and blood pressure. Noncardiac causes, including electrolyte imbalance and hyperthyroidism, require an integrated assessment.

Types of arrhythmia

Arrhythmias are grouped by where they originate and whether the rate is fast or slow. Management differs substantially by type.

Type Examples Management approach
Supraventricular tachyarrhythmias Atrial fibrillation, paroxysmal supraventricular tachycardia and others Assess underlying disease and use medication to control ventricular rate
Ventricular tachyarrhythmias Ventricular premature complexes (VPCs) and ventricular tachycardia (VT) Assess burden with Holter monitoring and consider antiarrhythmics
Bradyarrhythmias AV block, especially third-degree, and sick sinus syndrome (SSS) Consider pacemaker referral when accompanied by fainting or exercise intolerance
Conduction abnormalities Left or right bundle branch block (LBBB/RBBB), intraventricular conduction delay Often need no treatment in isolation; focus on underlying assessment
Noncardiac causes Electrolyte abnormalities, hyperthyroidism or medication effects Correct the underlying cause first rather than relying on cardiac medication

This table is an owner-oriented summary. The veterinarian classifies and treats the rhythm using ECG and Holter results.

Treatment and management by type

Management considers both arrhythmia risk and the stage of underlying heart disease. We follow this stepwise approach.

Medication according to type and burden

A high VPC burden or recurrent VT may warrant antiarrhythmics. Atrial fibrillation treatment focuses on rate control. Concurrent heart failure requires its own combination therapy. Kidney function, electrolytes and blood pressure guide dose adjustments.

Bradyarrhythmias and pacemaker referral

Medication has limited benefit in symptomatic third-degree AV block or sick sinus syndrome, so pacemaker implantation may be considered. We offer outpatient care and daytime hospitalization and refer implantation to cooperating centers. We provide assessment before and follow-up after the procedure.

Treating underlying heart disease alongside the rhythm

We also manage the stage of structural disease such as MMVD, DCM, HCM or RCM. Coordinating both aspects helps reduce arrhythmia burden.

Home monitoring and reassessment

Even brief notes on the time, circumstances and duration of fainting or exercise intolerance help assess treatment. A repeat Holter after medication is introduced allows quantitative comparison of arrhythmia burden.

Frequently asked questions

Why recommend a Holter if the clinic ECG was normal?
An in-clinic ECG usually records only one to two minutes. Intermittent events may be missed, so a Holter records the full day's heartbeats as a complementary test.

Can my pet walk and eat normally during Holter monitoring?
Yes. This noninvasive chest-patch recorder is most useful when normal walking, meals and play continue. Avoid bathing so the patches stay attached.

Does one fainting episode really need testing?
Even one episode is a strong reason for rhythm assessment. It may have another cause, but if arrhythmia is responsible, the next event could be more severe. Prompt assessment is safer.

Can you implant a pacemaker?
We provide outpatient care and daytime hospitalization. Implantation takes place at cooperating centers with procedural and 24-hour inpatient facilities. We provide ECG, Holter and ultrasound assessment beforehand, then regular follow-up and medication care.

Does respiratory sinus arrhythmia in a dog need treatment?
Respiratory sinus arrhythmia is a normal variation in heart rate with breathing and needs no treatment. A different pattern of missed beats or other symptoms warrants assessment.

Can cats have Holter monitoring?
Yes, although tolerance of handling and patches varies. We fit the device with minimal restraint and explain home observations.

References

These external resources explain ECG, Holter and other rhythm assessments. They do not define our services or an individual prescription.

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