Sinus tachycardia

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

This arrhythmia originates from the sinoatrial node, the normal pacemaker of the heart. It results from increased sympathetic tone. The causes of increased sympathetic tone include stress, fever, pain, metabolic disease (hyperthyroidism), hypovolemia, thromboembolic disease, shock and anaemia.

Clinical signs

In the majority of patients, clinical signs are related to the underlying disease. 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

The diagnosis is based on physical examination and an ECG, which shows regular heart rhythm, a P wave for every QRS complex with a constant P-R interval.

Differential diagnosis

Supraventricular tachycardia including atrial tachycardia, AV nodal re-entrant tachycardia, atrial flutter with 2:1 conduction need to be differentiated from sinus tachycardia on the ECG. Excessive heart rate (>250 bpm) is more likely to be supraventricular tachycardia. Supraventricular tachycardia may have abnormal P wave morphology or lack P waves compared to sinus tachycardia where P waves are normal.

Treatment

Before initiating treatment, determine the underlying aetiology and treat appropriately. If associated with low systemic blood pressure and the cause is not hypovolemia, shock or blood loss, and systolic myocardial function is preserved, consider heart rate control with Atenolol (6.25-12.5 mg/cat PO q 12hrs), or diltiazem (7.5-15 mg/cat PO q 8 hrs).

Prognosis

Most cats have a favourable outcome, depending on aetiology.