From Dog

Arrhythmia, both atrial (supraventricular) and ventricular are a common, and sometimes normal, activity of the canine heart.

Concerns arise when the severity of arrythmias leads to life-threatening atrial of ventricular fibrillation.

Types of arrhythmias include bradyarrhythmias (slow) and tachyarrhythmias (fast).

These heart beat irregularities may be observed during routine electrocardiogram studies and are commonly observed during postural changes associated with routine anesthesia[1] and many are thought to be non-pathological.

A number of arrhythmias are due to heart rate turbulence, defined as a return to normal beat after a ventricular premature complex which results from an abnormal baroreceptor response, and is commonly observed in the Boxer with mild and moderate subaortic stenosis[2] and dilated cardiomyopathy in the Boxer, Doberman Pinscher and Great Dane[3].

However, many canine arrhythmias are the result of underlying cardiac conduction disorders (e.g. atrial fibrillation[4]). These conduction disorders, which may be present without any evidence of valvular disease, are thought to arise as a result of decreased calcium channeling across the myocytes of the heart and defective cytosolic calcium removal following myocontractility, leading to increased refractory myocytes that become dyssynchronous with the majority of remaining cardiac myocytes[5]. Certain breeds, such as the German Shepherd[6] have such defective calcium channeling due to a genetic dysfunction of myocardial tissues, and in these cases, may lead to ventricular fibrillation, syncope or sudden death.

Common causes of ventricular arrhythmias include:

Routine ECGs, chest radiographs, echocardiography and serological testing of the cardiac biomarker NT-proBNP may help determine the underlying cause of the arrhythmia[16]. A 24-hour Holter electrocardiography may be required in difficult cases.

Medications which have shown effectiveness at controlling both supraventricular (atrial) and ventricular arrhytmias include atenolol and amiodarone[17].


  1. McMillan MW et al (2012) Potential Bezold-Jarisch reflex secondary to a 180° postural change in an anaesthetized dog. Vet Anaesth Analg 39(5):561-562
  2. Noszczyk-Nowak A (2012) Heart rate turbulence in mild-to-moderate aortic stenosis in boxers. Pol J Vet Sci 15(3):477-481
  3. Noszczyk-Nowak A (2012) Heart rate turbulence in healthy dogs and dogs with dilated cardiomyopathy. Pol J Vet Sci 15(3):469-475
  4. Watanabe I et al (2012) Linear catheter ablation of the right atrium for rapid atrial pacing-induced sustained atrial fibrillation in dogs. Int Heart J 53(6):375-382
  5. Iyer V et al (2012) Altered spatial calcium regulation enhances electrical heterogeneity in the failing canine left ventricle: implications for electrical instability. J Appl Physiol 112(6):944-955
  6. Jesty SA et al (2013) Cardiomyocyte calcium cycling in a naturally occurring German shepherd dog model of inherited ventricular arrhythmia and sudden cardiac death. J Vet Cardiol Feb 19
  7. Liu Y et al (2012) Extra- and intracellular recordings from the avjunction: discerning the mechanisms for irregular ventricular responses during supraventricular arrhythmias. Acta Cardiol 67(2):221-229
  8. Bourgonje VJ et al (2012) Relevance of calmodulin/CaMKII activation for arrhythmogenesis in the AV block dog. Heart Rhythm 9(11):1875-1883
  9. Green JL et al (2012) Preoperative thoracic radiographic findings in dogs presenting for gastric dilatation-volvulus (2000-2010): 101 cases. J Vet Emerg Crit Care (San Antonio) 22(5):595-600
  10. Jung S & Jandrey KE (2012) Hyperkalemia secondary to renal hypoperfusion in a dog with third-degree atrioventricular block. J Vet Emerg Crit Care (San Antonio) 22(4):483-487
  11. Perego M et al (2012) Isorhythmic atrioventricular dissociation in Labrador Retrievers. J Vet Intern Med 26(2):320-325
  12. Oliveira MS et al (2012) Heart rate variability parameters of myxomatous mitral valve disease in dogs with and without heart failure obtained using 24-hour Holter electrocardiography. Vet Rec 170(24):622
  13. Caldas IS et al (2013) Myocardial scars correlate with eletrocardiographic changes in chronic Trypanosoma cruzi infection for dogs treated with Benznidazole. Trop Med Int Health 18(1):75-84
  14. Billeter SA et al (2012) Invasion of canine erythrocytes by Bartonella vinsonii subsp. berkhoffii. Vet Microbiol 156(1-2):213-216
  15. Jin Q et al (2012) Ibutilide decreases defibrillation threshold by the reduction of activation pattern complexity during ventricular fibrillation in canine hearts. Chin Med J (Engl) 125(15):2701-2707
  16. Haßdenteufel E et al (2012) NT-proBNP as a diagnostic marker in dogs with dyspnea and in asymptomatic dogs with heart murmur. Tierarztl Prax Ausg K Kleintiere Heimtiere 40(3):171-179
  17. Pedro B et al (2012) Retrospective evaluation of the use of amiodarone in dogs with arrhythmias (from 2003 to 2010). J Small Anim Pract 53(1):19-26