Singh-Ranger, Ravinder; (2000) Endovascular repair of abdominal aortic aneurysm; A morphological study. Masters thesis (M.S), UCL (University College London).

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Abstract

The longer-term efficacy and durability of endovascular repair (ER) are unknown. Preliminary, non-validated data suggest progressive shrinkage of the aneurysm sac and length follows successful ER. These alterations are also blamed for producing forces that disrupt device integrity. This study uses validated methods to document the morphological and dynamic changes affecting the aneurysm sac and neck after ER. Laboratory section: Six glass aneurysms with varying neck angulation and sac size were filled with known proportions of iodinated contrast media and deionized water. Volumes and linear dimensions were pre-determined with pyknometry and electronic callipers. Scanning with three-dimensional spiral CT angiography (3D SCTA) patient protocol produced near perfect correlation and agreement between true and scanned volumes and diameters. Inter- and intra-observer errors associated with clinical estimation of these parameters were also within acceptable range (<5% error). Volume appeared a more complete measure of sac morphology than diameter alone. Satellite technology for imaging arterial motion was validated by describing a glass aneurysm in terms of its volume. Acceptable reproduction was obtained combining multi-camera imaging with photogrammetric analysis. Clinical section: 88 patients treated with balloon-expanding PTFE or Talent selfexpanding endografts, were prospectively followed for 1-4 years post-ER. SCTA performed at day 5 and at 6 monthly intervals was used to record aneurysm neck diameters and length, aneurysm and endograft lengths, maximal sac diameters and sac volumes. ER produced a significant (P=0.02) increase in aneurysm volume (median PTFE 12.4 ml; Talent 15.1 ml at day 5) followed by marked shrinkage in Talent (median -40.8 ml by 1 year compared to preoperative) but not PTFE patients whose volumes remained unchanged. These alterations were not consistently followed by maximal diameter measurements and were later shown to be due to changes in intra-luminal thrombus volume. In PTFE patients, aneurysm length increased (median 3.2 mm; P=0.04) concomitantly with volume at day 5 followed by a second significant increase in both endograft and aneurysm lengths at 18 months (P<0.03). Median increases compared to preoperative values, were 16.4 and 14.6 mm respectively. Talent patients had no length changes. Neck diameters increased (P=0.03) immediately after deployment (PTFE mid-neck increase 2.5 min; Talent 3.1 mm). This continued for 6 months follow-up in Talent patients. No further change occurred with PTFE. Methods for filming arterial motion were developed. Attempts to quantify AAA neck motion are still in preliminary stages. It is concluded that aneurysm morphology post-ER is graft-specific (balloon vs self-expanding). Aneurysm length shrinkage does not cause endograft distortion as previously believed. This may be the result of an interaction between inherent graft weaknesses and repetitive differential motion with the aneurysm neck.

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