Supraventricular (Atrial) tachycardia

© Rand, J (2006) Problem-based feline medicine. Saunders Elsevier, Sydney

The arrhythmia from anywhere above and including the atrioventricular node. Supraventricular (atrial) tachycardias (SVT) most commonly result from primary myocardial disease. There arrhythmias are most commonly seen in association with hypertrophic or restrictive cardiomyopathies.

Clinical signs

In the majority of patients, clinical signs are related to the underlying disease such as cardiomyopathy rather than the tachycardia, and include a heart murmur, dyspnoea, weakness, collapse and lameness, paralysis or paresis from systemic thromboembolism.

Clinical signs related to a fast heart rate (> 280 bpm) include restlessness, tachypnoea, open-mouth breathing, poor pulse quality and delayed capillary refill time.

Diagnosis

Based on clinical signs including heart rate above 220 bpm, normal cardiac rhythm, normal QRS complexes on ECG (P waves may be buried in the S-T segment), the arrhythmi may be sustained or occur in paroxysms.

Differential diagnosis

Sinus tachycardia - looks identical to SVT on ECG but has lower heart rate. Sinus tachycardia has normal P waves.

Treatment

If the patient is symptomatic (hypotension, cardiogenic shock, collapse) for the arrhythmia, then treatment is required. The following drugs can be used in succession and are written in order of preference if the previous drug is not effective.

1) Diltiazem (calcium channel blocker) at 0.1-0.3 mg/kg IV slow bolus over 3-5 mins, then repeated if necessary in 5-10 mins if sustained SVT. After IV bolus an IV constant rate infusion at 5-20 ug/kg/min. Diltiazem is compatible with most IV fluids.

2) Esmolol at 250-500 ug/kg IV bolus given slowly over 1 min. Followed by constant rate IV infusion at 50-200 ug/kg/min. Esmolol is compatible with 5% dextrose.

3) Propanolol at 20 ug/kg/min slow IV bolus over 5 mins. Propanolol can be given up to a total dose of 100 ug/kg in repeated boluses.

If the patient is asymptomatic for arrhythmia, the following schedule can be employed

1) Atenolol at 6.25-12.5 mg/cat PO q 12hrs.

2) Diltiazem at 7.5-15 mg/cat PO q 8 hrs

3) Propanolol at 2.5-5 mg/cat PO q 8-12 hrs

4) Sotalol at 10-20 mg/cat PO q 12hrs