Unilateral Atrial Ectopic Rhythm in a Golden Retriever

Background: Atrial ectopic rhythm is a type of supraventricular arrhythmia, originating in two distinct points in the atrial region. In the electrocardiographic (ECG) tracing, it is represented by independent depolarizations of sinus P waves and ectopic P waves. The occurrence of this disorder is rare, and the diagnosis criteria are the presence of the described waves within the basal rhythm. In humans, there have been reports related to severe heart failure with an unfavorable prognosis. The present report aimed to describe the clinical case of a dog with unilateral atrial ectopic rhythm without any underlying cardiac disorder.Case: A 8-year-old male golden retriever was brought to a veterinary clinic for a preoperative evaluation for lipoma removal in the right forelimb. On clinical examination, the owner stated that the patient was active, with no signs of easy fatigue or cough. The canine displayed normophagy, normodipsia, normoquezia, and normouria. On physical examination, he demonstrated a lymphatic temperament with tachypnea. The temperature and capillary filling time were within the normal range, with a normokinetic pulse. Cardiac auscultation revealed a mild grade I/VI murmur in mitral focus and an 80-bpm heart rate. Respiratory auscultation revealed the presence of harshy lung sounds. The cough reflex was positive; the Piparote test, negative. The blood test showed no noticeable changes in blood count and serum biochemistry. Systemic systolic blood pressure was 120 mmHg. On radiographic examination, no evidence of heart or lung abnormalities were identified. After the clinical evaluation, an ECG examination was performed; a unilateral atrial ectopic rhythm was observed with different frequencies between atrial and ventricular rhythm and with P (164°) and P waves (80°). On echocardiographic examination, no morphological abnormalities were seen, though trivial mitral insufficiency was identified in a color Doppler study. Blood was collected to measure electrolytes to check for possible electrolytic abnormalities; the results were within the normal range. The patient was released for and remained stable throughout the procedure, maintaining the rhythm detected during the transoperatory time. Upon reassessment in a new ECG examination, the arrhythmia persisted, suggesting that a primary lesion in the atrial tissue was present.Discussion: An atrial ectopic rhythm diagnosis requires a detailed study with the aim of ruling out heart diseases that may affect the propagation of the cardiac stimulus. However, no morphological or functional abnormalities of note that justified triggering stimuli for the ectopic rhythm were observed. In addition, based on the echocardiographic evaluation, myocardial function was preserved, supporting the canine’s release for the procedure. The suspicion of hydroelectrolytic alteration and hypoxia was present after discarding structural causes, though it was discarded due to normal laboratory results. The presence of ectopic P waves was due to the non-interference in the sinus P’ waves; consequently, they were found in the sinus heart rhythm. Upon assessing the ectopic P wave frequency, the atrial rhythm frequency was higher than the heart rate, juxtaposing the different irregular intervals within the atrial cycle. The rhythm alone may explain that its severity can be linked to the physical findings. This indicated that they did not influence the presentation of ectopia since the cardiac output, controlled by the sinus rhythm part, was responsible for maintaining the rhythm and the demand of the organism; the electrical conduction system, responsible for atrial systole, represents 15-25% of the blood ejection for the ventricular filling. Patients with rhythm disorders as described need guidance and follow-up for the early detection of clinical signs resulting from the destabilization of the condition.Keywords: atrial dissociation, supraventricular arrhythmia, electrocardiogram, dogs