Comparison of attraction capabilities associated with high-speed, dual-pneumatic vitrectomy probes.

PURPOSE: To measure membrane attraction capabilities of enhanced 27-gauge, enhanced 25-gauge, and 23-gauge vitrectomy probes under various parameters. METHODS: A membrane-on-cantilever apparatus was used to measure membrane attraction for enhanced 27-, enhanced 25-, and 23-gauge UltraVit probes (n = 6 for each). The following parameters were evaluated: effects of cut rates and duty cycles on membrane attraction distances, and flow rates and vacuum levels required to attract a membrane at a fixed distance. RESULTS: The enhanced 27-gauge probe had the shortest attraction distance across all cutting speeds and duty cycles. To attract a membrane at a fixed distance, increasing vacuum was necessary with higher cutting rates and smaller probe gauges but flow rate remained relatively constant. The biased open duty cycle was associated with a longer attraction distance than 50/50 or biased closed modes. CONCLUSION: The shorter membrane attraction distance of the enhanced 27-gauge probe versus 23-gauge and enhanced 25-gauge probes may permit greater membrane dissection precision while providing improved access to small tissue planes. Equivalent fluid flow capabilities of the 27-gauge probe compared with the 23-gauge and 25-gauge probes may provide efficient aspiration. Surgeon selection of duty cycle modes may improve intraoperative fluid control and expand the cutter utility as a multifunctional tool.

Geometry and fusion of aortic valves from pulsatile flow ventricular assist device patients.

BACKGROUND AND AIM OF THE STUDY: Aortic valve commissural fusion is a process in which fibrous tissue is deposited at the aortic valve commissures, creating adhesion between leaflets and preventing opening. Fusion has recently been associated with the implantation of left ventricular assist devices (VADs), affecting upwards of 50% of patients in recent studies. Aortic incompetence has also been associated with pulsatile VAD use, but a specific structural mechanism has not been identified. The study aim was to measure aortic valve geometry and fusion in tissue samples from explanted hearts of VAD recipients and to identify features that might explain the development of aortic valve dysfunction. METHODS: The diameter, perimeter and thickness of the aortic root, as well as the height, edge length and thickness of each of the three aortic leaflets were measured in seven valves. Histological studies were performed of both fused and unfused leaflets. RESULTS: The aortic root geometry showed an elliptical aorta, with asymmetric leaflets. The right coronary leaflet had the greatest edge length, but was thinnest. The other two leaflets were smaller, but slightly thicker. Overall, the aorta and valve geometry was within the normal range. Fusion was found in five of the seven valves studied, and often observed in multiple leaflets. Fusion length correlated loosely with the time of VAD support. Tissue from both fused and unfused valves showed unilateral fibrosis in the leaflets, and a loss of the laminar tissue structure that was related to the duration of VAD support. CONCLUSION: These findings support previous observations that pathological changes occur in the aortic valves of VAD patients shortly after implantation. While the tissue exhibits abnormalities in the structure, the geometry does not show gross remodeling such as annular dilatation or leaflet lengthening that might precede the development of aortic valve dysfunction. These changes are associated with the development of aortic valve fusion, and may be related to the biomechanical changes introduced by the VAD.