Atrial tachycardia

From Dog

Atrial tachycardia is a common cardiac abnormality of dogs characterized by supraventricular impulses originating from outside the sinoatrial node.

This condition is thought to be due to an abnormal automatic focus within the atrium, often a result of atrial fibrosis due to underlying cardiac pathology[1] that interrupts contiguity between the SA node and the surrounding atrial myocardium[2], or triggered by sympathovagal discharges from the autonomic nervous system[3].

Causes include:

With atrial tachycardia, cardiac compensation for this phenomenon occurs by re-entrant circuits which allow the impulse to re-stimulate the atrium and to pass down to the ventricle.

In most dogs, this condition is associated with congestive heart failure, and clinically affected dogs invariably present with dyspnea, coughing and exercise intolerance in association with a failing heart. A regular or intermittently irregular heart beat can be discerned, with a concomitant gallop rhythm. Although atrial tachycardia may be the result of atrial myocardial disease, the risk of developing atrial thromboembolism does not appear evident in dogs compared with human patients[4].

Diagnosis can be established on ECG studies, particularly a 24-hr ambulatory Holter, and echocardiography.

The ECG features of this condition is rapid heart rate (>160 beats per minute) and diminished size of P wave preluding a rapid succession of QRS complexes, followed by normal sinus rhythm. This ectopic rhythm is caused by rapid firing of two or more ectopic atrial foci.

A differential diagnosis would include sinus tachycardia and atrial flutter.

Treatment usually requires atenolol, digoxin or verapamil.

Prognosis is often guarded to to severe underlying cardiac disease.

References

  1. Nakatani Y et al (2013) Tranilast prevents atrial remodeling and development of atrial fibrillation in a canine model of atrial tachycardia and left ventricular dysfunction. J Am Coll Cardiol 61(5):582-588
  2. Nakao S et al (2012) The anatomical basis of bradycardia-tachycardia syndrome in elderly dogs with chronic degenerative valvular disease. J Comp Pathol 146(2-3):175-182
  3. Park HW et al (2012) Neural mechanisms of atrial fibrillation. Curr Opin Cardiol 27(1):24-28
  4. Nishida K et al (2012) Atrial fibrillation-associated remodeling does not promote atrial thrombus formation in canine models. Circ Arrhythm Electrophysiol 5(6):1168-1175