Newly Created Canine Model of Sinus Node Dysfunction by Minimally Invasive Procedure

Objectives: Sick sinus syndrome (SSS) is a type of bradyarrhythmia that can lead to syncope. It is one of the most common causes of cardiac impairment necessitating pacemaker implantation. However, studies of SSS pathogenesis are neither comprehensive nor conclusive due to limited success in achieving a stable animal SSS model. Here, we report a reproducible canine SSS model by minimally invasive procedure.

Methods: Five beagles, weighing 9.0 ± 1.5 kg (range, 8.5–9.5) and aged 10 ± 1.5 months (range, 8–16), were used for the present study. Anesthetic induction followed premedication with propofol; the dogs were then intubated and ventilated with room air supplemented with oxygen to maintain normal oxygen saturation using a respirator. Anesthesia was maintained with isoflurane, supplemented with midazolam and fentanyl throughout the experiment. The arterial blood gases, electrolytes, and arterial blood pressure were measured. Body surface electrocardiographic leads were monitored for heart rate and cardiac rhythm assessment. After a right thoracotomy incision and right lung retracted, the pericardium was opened and the temporary pacemaker was sewn to the right ventricle. Radiofrequency (RF) ablation was performed around the superior vena cava–right atrial junction (site of the presumed location of the sinoatrial node) and the right azygos vein–right atrial junction using AtriCure RF ablation system.

Results: Clamp crushing with RF ablation of the SN region was successful in five of five attempts. After surgical removal of the SN region, the cardiac rhythm transitioned to sinus bradycardia ( < 60 bpm) or junctional rhythm with sick sinus syndrome (60 <  HR <  150 bpm). When sinus bradycardia occurred after SN removal, temporary pacing supplied the deficiency if the ventricular rate was less than 60 bpm.

Conclusion: Our study has shown the feasibility of creating a reliable and reproducible canine model of sinus node dysfunction. The technique using AtriCure RF was not troublesome and the result was good. Therefore, we can expect that it is useful for the study of experimental pharmacology and the technological development of pacemaker.