Imaging, Valvular and Procedural Predictors
Heavy calcium volume has been identified as a predictor for pacemaker insertion in prior studies. However, different studies have used different parameters for the measurement of calcium burden including aortic valve calcium score, porcelain aorta, landing zone calcification, LVOT calcium, and mitral annulus calcification. In our analysis, high calcium volume in the area extending below LVOTlc and LVOTnc was found to be an important predictor. Our study also determined implant depth to be another major predictor suggesting the significance of higher deployment of the valve in the aortic area. Implant depth was reported in individual studies as either > 25% of stent frame below aortic annulus or > 6 mm length of an implant from the lower edge of the non-coronary cusp to the ventricular end of the prosthesis.
Increasing valve to aortic annulus oversizing ratios using multislice computed tomography (CT) is known to reduce the rate of paravalvular leak as the valve can fit better in the annulus (46). However, our analysis determined this size discrepancy, between the valve and the annulus, is associated with an increase in PPMI. The need for pre-dilatation balloon valvuloplasty has been substantially reduced as studies have shown direct TAVR is safe, feasible and has similar outcomes (35, 47). Our analysis shows that both pre and post balloon valvuloplasty are significant predictors of PPMI.
Since the introduction of TAVR, two valves have been widely used; the balloon-expandable ESV and the self-expandable MCRS. The rate of PPMI is markedly higher in the MCRS valve (44, 48). This higher rate has been attributed to the difference in stent design, long nitinol frame, and radial force exerted by the stent into the conduction tissue (49). The balloon-expandable technology has evolved from XT to S3, and the self-expandable technology has evolved to the Evolut R system. In the analysis of 12,381 patients from different trials and registries by Vlastra et al, new-generation BEV required PPMI less frequently when compared to the new-generation SEV (S3: 8.9% vs Evolut: 18.1%). This difference was greater in early-generation valves (ESV: 6.1% and XT: 7.5% vs MCRS: 21.2%) (44). The S3 valves were designed with a longer stent frame which lead to decrease in the paravalvular leak, but increased incidence of PPMI (7). Recently, modifications in the implantation technique by high deployment of the valve has led to a reduction in the rate of this complication (50).