Influence of inflation pressure and balloon size on the development of intimal hyperplasia after balloon angioplasty: A study in the atherosclerotic rabbit

Abstract

To evaluate the effect of balloon size and inflation pressure on acute and subsequent outcome following balloon angioplasty (BA), 70 New Zealand white rabbits with bilateral femoral atherosclerosis were assigned to four groups: group 1, oversized balloon, low inflation pressure (n = 35 vessels; balloon size, 3.0 mm/inflation pressure, 5 atm); group 2, oversized balloon, high inflation pressure (n = 36; 3.0 mm/10 atm); group 3, appropriate size, low inflation pressure (n = 17; 2.5 mm/5 atm); and group 4, appropriate size balloon, high inflation pressure (n = 19; 2.5 mm/10 atm). Angiograms were obtained before, 10 minutes after, and 28 days after BA and read by two blinded observers using electronic calipers. The in vivo balloon-to-vessel ratio was measured for each group. There were eight non-BA controls. Rabbits were sacrificed either immediately (n = 34) or at 28 days after BA (n = 36), with the femoral vessels pressure perfused for histologic and morphometic analysis. The latter was performed at 28 days only. Absolute angiographic diameters increased in all groups immediately after BA (p < 0.01). Acute angiographic success, defined as greater than 20% increase in luminal diameter, was higher using high inflation pressure (group 2, 32/36 [89%] and group 4, 16/19 [84%] vs group 1, 23/35 [66%] and group 3, 9/17 [53%]; p < 0.05). A 3.0-mm balloon resulted in significant oversizing irrespective of inflation pressure (balloon-to-vessel ratio, 1.5 ± 0.1 vs 1.1 ± 0.1 to 1, for the 2.5-mm balloon). Vessels exposed to high inflation pressure had a significantly higher incidence of mural thrombus, dissection (p < 0.01), and medial necrosis versus low pressure (p < 0.05). At 28 days, the rates of restenosis (defined as greater than 50% loss of initial gain) were 14/20 (70%), 11/16 (69%), 5/10 (50%), and 5/10 (50%) for groups 1 through 4 (p = NS; a trend in favor of the groups using an oversized balloon). There was an increase in the degree of intimal hyperplasia by morphometric analysis in all groups, being most marked in group 2 (oversized balloon and high inflation pressure, 1.7 ± 0.9 vs 0.5 ± 0.2 mm for controls, p < 0.001). We reached two conclusions. First, all protocols resulted in a significant increase in luminal diameter immediately after angioplasty with the highest success rate in vessels subjected to high pressure dilatation. Second, the combination of high inflation pressure and an oversized balloon caused the most extensive vessel-wall damage early after BA and the greatest degree of intimal hyperplasia at 28 days. Thus, oversizing the balloon with high inflation pressure may represent a factor causing restenosis following BA.