Need for New Pacemaker
The risk factors for development of high-grade heart block requiring permanent pacemaker in observational studies include use of SE valve and pre-existing right bundle branch block.34 In patients receiving the SE valve, the risk of requiring a permanent pacemaker can be as high as 42.5 % whereas the risk of this complication for BE valve is similar to that observed after balloon valvuloplasty or surgical valve replacement in clinical trials.35 Similar results were reproduced in the CHOICE trial, where 37.6 % of SE patients required a new pacemaker as compared to 17.3 % in the BE group.20 Higher incidence of significant heart block in SE valve patients could be explained by the interaction of its nitinol frame with the interventricular septum. Radial forces of the CoreValve stent are greater on the LVOT, especially if the LVOT diameter is small or tissue stiffness is high. Excessive radial force, especially in low implants, may contribute to heart block.36 Furthermore, SE CoreValve implantation is associated with a higher incidence of new left bundle branch block when compared to BE valve implantation and surgical valve replacement.37 Newer generation repositionable SE devices may help in reducing the pacemaker rate with a more targeted implantation.
Rare Complications
Occlusion of coronary artery ostia is a rare but life-threatening cause of ischaemia and hypotension following TAVI, with the majority of such complications reported after BE valve implantation. A recent large series reported an incidence of 0.81 % for BE versus 0.34 % for SE valves (p=0.02).38 Factors predisposing to coronary artery occlusion include small aortic sinuses, aortic annulus to coronary ostium distance less than 1 cm and significant asymmetric valve calcification. This complication was also reported to be more frequent in women and in patients with prior surgical bioprosthesis. In the randomised CHOICE trial, two patients belonging to the BE group had coronary obstruction as opposed to none in the SE group.20 Annulus rupture is another rare life-threatening complication and risk factors include BE valve implantation, small annular size, bulky calcification and aggressive predilatation.39,40 The reported incidences of valve embolism, valve malpositioning and need for more than one valve implantation are higher with SE valves.41 Implantation of ≥ 2 valves was higher in the SE group in the CHOICE trial (5.8 % for SE versus 0.8 % for BE).20 However, nearly half of BE valve embolisations occur towards the left ventricle as opposed to SE valves, which usually require surgery and are associated with a high mortality rate.4 BE valve embolisations are generally caused by anatomic and technical factors, which may be avoided with procedural planning. In recent years, a few cases of valve thrombosis with both BE and SE valves have been reported.
Valve Durability
Valve durability is important for the expansion of TAVI to younger patients, and both prosthesis types have been found to be durable in short- and intermediate-term studies. Toggweiler et al.42 evaluated the long-term haemodynamic changes of BE valves at five years’ follow-up and observed a decrease in mean aortic valve area of 0.06 cm 2/year and an increase in mean transvalvular gradient of 0.27 mmHg/year with no cases of structural valve failure. Similarly, the CoreValve CE Pivotal Study demonstrated excellent durability at four years in patients who were treated with the SE CoreValve System.7