Supraventricular Tachycardia in Dogs
Supraventricular tachycardia (SVT) in dogs refers to an abnormally rapid heartbeat originating above the heart’s ventricles. This can occur even during times of rest or low activity, not just during exercise, illness, or stress. A persistently high heart rate, as observed in SVT, can lead to progressive myocardial (heart muscle) failure and eventually congestive heart failure.
SVT might not always be noticed if it occurs sporadically. However, when there are repetitive premature electrical depolarizations in the heart originating from a site other than the sinus node (the heart’s natural pacemaker), such as in the atrial muscle or atrioventricular nodal tissue, the condition can pose a serious health risk.
Symptoms and Types
- Slow SVT or rare occurrences of SVT
- No apparent clinical signs observed.
- Fast SVT (heart rate exceeding 300 beats per minute)
- Weakness
- Fainting
- Congestive heart failure (CHF)
- Coughing
- Abnormal breathing
Causes
SVT can be triggered by various factors, such as:
- Heart disease
- Digoxin toxicity
- Systemic disorders
- Electrolyte imbalances
- Abnormal automaticity in an ectopic focus (when the heart beats prematurely or outside the normal parameters)
- In some cases, dogs may develop SVT due to a genetic predisposition or for reasons that remain unknown.
Diagnosis
Your veterinarian will conduct a comprehensive physical examination of your dog, considering the background history of symptoms provided by you. Standard laboratory tests, including a biochemical profile, complete blood count, urinalysis, and electrolyte panel, will be performed to rule out systemic disease, cancer, and electrolyte imbalances.
An electrocardiogram (EKG) recording will be utilized to assess the electrical currents in the heart muscles, potentially identifying abnormalities in cardiac electrical conduction, which is essential for the heart’s contraction/beat. An EKG (with Doppler studies) can also help your veterinarian determine the type and severity of any underlying heart disease, as well as evaluate myocardial function in dogs with primary SVT.
Additionally, long-term ambulatory (Holter) recording of the EKG may be employed to detect SVT attacks in cases of unexplained fainting. Event (loop) recorders may also identify paroxysmal SVT in dogs experiencing infrequent episodes of syncope (fainting).
Treatment
Dogs exhibiting sustained SVT or symptoms of congestive heart failure should be promptly hospitalized. Various non-pharmacologic emergency interventions may be employed, including vagal maneuvers, precordial thump, and/or electrical cardioversion. Precordial thump administration successfully terminates SVT in over 90 percent of cases, although the rhythm may only be temporarily disrupted.
To administer a precordial thump, the dog is positioned on its right side, and the affected region is gently “thumped” with a fist while simultaneously monitoring the EKG.
Recovery and Management
Your veterinarian will arrange follow-up appointments for your dog as necessary to manage the SVT and/or any underlying heart disease with prescribed medication and/or dietary adjustments. You will be advised to feed your dog a low-sodium diet and limit its activity until further guidance. Short, low-impact outdoor walks are recommended during this period.
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