Assessment of annular distensibility in the aortic valve

OBJECTIVES: The recent introduction of transcatheter aortic heart valves into clinical practice has driven the need to develop methodologies to size such valves without access to the annulus in the manner hitherto possible with open heart surgery. To date, sizing has largely been done according to manufacturer-supplied guidelines based on transoesophageal echocardiography or multidetector computed tomography. We sought to examine how the diameter of the aortic valve annulus stretches under typical pressures encountered in normal and diseased states. In particular, we sought to measure how the area-derived diameter, Dcsa, i.e. the diameter derived from a cross-sectional area, varies with distending pressure. METHODS: We conducted testing on 14 explanted pig hearts. Placing each heart in a 37 C bath, an EndoFLIP EF-325 catheter (Crospon, Galway, Ireland) was introduced into the aortic valve transapically. The catheter allows intra-balloon pressure and up to 16 area-derived diameters to be measured simultaneously, thus permitting the shape of a lumen to be observed. By dividing the minimum area-derived diameter by distending pressure, a measure of distensibility (mm/mmHg) could be determined. Once the balloon was centred, balloon pressure was ramped between 100 and 200 mmHg, and the area-derived diameter was calculated at each pressure. RESULTS: Between 100 and 200 mmHg, the mean (SD) increase in diameter was found to be 3.0 (1.5) mm. Distensibility in the different hearts ranged from 0 to 0.05 mm/mmHg. In some cases, the diameter change over the pressure range was negligible, whereas in one case, the diameter change over the range was 5 mm. Whereas different nominal values of diameter are to be expected, a significant variation in the degree of distensibility was observed. CONCLUSIONS: Distensibility of the aortic valve annulus is highly variable. Measurement of this parameter in addition to nominal annulus diameter may suggest occasions where a larger transcatheter aortic-valve implantation valve than would be suggested by annulus diameter measurement alone, could be deployed safely with an objective of reducing regurgitation where the annulus is sufficiently distensible