Limitations
There are limitations to this study inherent to this type of investigation. It is a retrospective review based on prospectively collected data. We examined data from three surgeons performing both types of aortic valve implantation concurrently, but there may be remaining bias despite inverse probability weighting. Early in the experience with SLV there was a conscious decision to place the valve in older and sicker patients. As the outcomes were shown to be good and experience improved, the SLV was used in a wider patient population. There was also on ongoing learning curve and changes to the implantation technique, as evidenced by decreasing need for PPM.