Development of a transseptal puncture technique in horses : exploring the transhepatic and jugular vein approach

Introduction: The advent of advanced electrophysiological procedures such as 3D electro-anatomical mapping and radiofrequency ablation currently allows for diagnosis and treatment of right atrial arrhythmias in horses.1,2 In contrast, left atrial arrhythmias are scarcely studied3 due to the perilous arterial approach that is needed to access the left atrium. In small animal and human medicine, the transseptal puncture, which is performed via the femoral vein, is a commonly used technique to access the left atrium via the oval fossa in a safe and efficient way. In human medicine, the transhepatic approach has been reported as an alternative to the femoral approach, as the oval fossa is accessed from a similar direction and ensures similar catheter manipulations. Indeed, a caudal approach towards the oval fossa is favourable to position the puncture assembly into the pouchlike anatomy of the oval fossa and direct it towards the left atrium. In contrast, the majority of catheterizations in horses is performed via the jugular vein, which implies a cranial instead of a caudal access to the heart. Moreover, fluoroscopy, which is most commonly used to perform the transseptal puncture in small animals and humans, provides limited to no imaging guidance to allow catheter manipulation in horses due to the size of the equine thorax. Similarly, computed tomography or magnetic resonance imaging cannot be used either to provide insight into the detailed anatomy of the interatrial septum in an adult horse. Therefore, the goal of this study was to develop a transseptal puncture protocol using a transhepatic and a jugular vein approach under ultrasound guidance. Methods: All horses in the study were donated for scientific research and owner informed consent was obtained. In 17 horses, a transseptal puncture was performed under general anaesthesia: in nine horses the jugular vein approach was performed, in six horses both the jugular vein and transhepatic approach was performed, and in two horses the transhepatic approach was performed. For the jugular vein approach, a 0.035″ J-tipped or pigtail guidewire followed by 8.5F steerable sheath-dilator assembly was introduced via the right jugular vein and positioned in front of the oval fossa. For the transhepatic approach, a puncture site for transhepatic access was determined on the left or right abdominal wall by locating a clearly visible hepatic vein of at least 8mm in diameter using transthoracic ultrasound. The hepatic vein was punctured using a 9cm long 18G needle, allowing the introduction of a 0.032″ guidewire and subsequent dilator and 8.5F steerable sheath and positioning in front of the oval fossa. The 0.032″ guidewire was then exchanged for a 0.035″ J-tipped or pigtail guidewire. For both approaches, the procedure continued with positioning of the distal tip of the guidewire against the oval fossa and puncture by applying radiofrequency energy on the guidewire, after which dilator and sheath were advanced into the left atrium. The entire procedure was guided using transthoracic and intracardiac echocardiography, and continuous ECG-monitoring was performed. The horses were euthanized at the end of the procedure and lesion size and permeability were evaluated post-mortem. Results: In 13/17 horses, a successful transseptal puncture was achieved, accounting for 14/15 jugular vein approaches and 5/8 transhepatic approaches (total of 23 punctures). In four horses, the transhepatic puncture was performed on the right side, in the other four on the left side. On post-mortem evaluation, permeable lesions of 1-5 mm were visible in all horses in the oval fossa on the right atrial side and ventral to pulmonary vein ostium III on the left atrial side. The most challenging part of the procedure was the over-the-wire insertion of the dilator-sheath assembly into the left atrium due to the thickness of the equine interatrial septum and limited catheter support. In five horses, atrial fibrillation was already present before the puncture, in 12 procedures paroxysmal atrial fibrillation or paroxysmal atrial tachycardia occurred in response to the puncture and in one horse persistent atrial fibrillation developed. Procedural failure in four horses was due to inability to advance dilator-sheath assembly (N=2), termination of the procedure due to technical failure (N=1), and inability to advance the guidewire towards the heart during a transhepatic approach (N=1). Ultrasound guidance, and especially intracardiac echocardiography (Figure 1), was adequate to guide the procedure. Limitations: Although care was taken to perform the second puncture on another location in the oval fossa in the horses in which both methods were applied, it cannot be excluded that the second puncture was realised via the first puncture site. Not all procedures were performed with the same devices. Post-operative complications could not be evaluated as the horses were euthanized for reasons not related to the study. Conclusion: Both transseptal puncture techniques allowed to access the left atrium in a minimally invasive way. Further research is needed to establish in which cases which approach would be most appropriate, to investigate which devices yield the most effective results and to determine post-operative complication rate.

Publication year:2022

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