## 3 Discussion  
Transatrial approach for TTVIV is used in less than 4% of cases [6; 7; 8] as it is considered more invasive and technically difficult compared to the transfemoral and transapical route. [PERSON] et al., [PERSON] et al. and [PERSON] et al. consider that the transjugular access offers the most direct approach, especially in horizontally oriented TVs followed by the transfemoral route also feasible in two thirds of patients mainly with more vertically oriented TVs because of the technical advances in catheter steerability [9; 10; 11]. These two routes are preferred by most teams (96.72% of patients analysed by [PERSON] et al. in 2016) as they are the least invasive and do not need a surgical intervention for access [7]. The current case proves the safety, feasibility, and efficiency of the rarely used transatrial approach and pleads for its use in patients with unfavorable venous anatomy and severe stenosis of the degenerated tricuspid bioprosthesis complicating the access with the delivery system. The transjugular route did not offer a good angle to approach the TV in our patient and the marked angulation of the inferior vena cava when entering the right atrium precluded the transfemoral access to the degenerated TV bioprosthesis. For this procedure, we chose the Edwards Sapien 3 bioprosthesis, approved for valve-in-valve procedures, given the prior experience with this type of valve implanted in aortic position (transcatheter aortic valve implantation-TAVI) in more than 100 cases and its particular design associated with a low risk of paravalvular regurgitation after deployment. Figure 5: Transoesophageal echocardiography mid-oesophageal four-chamber incidence confirming the normal functioning the tricuspid bioprosthetic valve-in-valve with a maximum transvalvular gradient of 1.14 mmHg and a peak velocity of 0.53 m/s, suggesting substantial reduction in gradient severity after transcatheter valve implantation. Tricuspid valve-in-valve deployment is particularly difficult as transvenous pacemakers generally implanted across the valve could be dislodged when manipulating the delivery system. For this reason, we opted for a different method of rapid ventricular pacing using an intraventricular stiff guidewire as cathode with the anode placed subcutaneously. Rapid ventricular pacing was necessary to allow an accurate deployment in the setting of elevated right atrial pressures. We consider that transatrial access and direct pacing on Confida guidewire could increase procedural success. In the absence of ventricular pacing, TTVIV deployment is difficult. Particular attention was paid to manipulating catheters, the delivery system, and the guide wire, as the Sapien 3 valve was originally designed to navigate the aorta and to be deployed in the aortic annulus. The Confida stiff wire ensured the necessary support while navigating through the right atrium and the tricuspid valve, the steering potential of the system reducing trauma to right heart chambers. [PERSON] et al. performed the single multi-center study on the short-term (2016) and mid-term (2019) outcomes of TTVIV [6, 7]. They analyzed 306 patients who benefited both from Medtronic and Edwards valves implanted by tranjugular, transfemoral or, exceptionally, by transatrial approach. The patients were followed for a median of 15.9 months after implantation (0.1 to 90 months) in 80 centers. They proved the favorable outcome of the procedure as the 3-year mortality, reintervention, and TTVIV-related adverse outcomes rates were 17%, 12%, and 8% considering the severe status of patients that need TTVIV (NYHA III-IV heart failure, prior heart surgery, cardiovascular comorbidities, decompensated status). Given the severity of the disease and the poor outcome in the absence of redo valve replacement, the results are encouraging. TTVIV related complications (endocarditis, valve thrombosis) were reported in 16 cases (5.23%), valve function remaining stable in most patients [6, 7].