Aortic root characteristics of human pulmonary autografts

Background-After pulmonary autograft replacement of the aortic valve and ro ot, the pulmonary artery (PA) wall is subjected to higher pressures. Concer n exists that this may lead to structural and functional changes in the imp lanted autograft and subsequent aortic root dilatation and neoaortic regurg itation. We therefore assessed root dimensions and neoaortic regurgitation, morphological structure, and mechanical behavior in patients who underwent the Ross operation. Methods and Results-Seventy-four patients who were randomized to undergo ao rtic valve replacement with an aortic homograft or a pulmonary autograft we re followed up echocardiographically for up to 4 years and had their aortic root dimensions measured at the level of the annulus, sinuses, and sinotub ular junction. In a separate series of 18 patients who underwent pulmonary autograft surgery and 8 normal organ donors, samples from the PA and aorta were analyzed for medial wall thickness, distribution of the staining of co llagen and elastin, and elastin fragmentation. Finally, stress-strain curve s were obtained from samples of the PA and aorta from 9 patients who underw ent pulmonary autograft surgery and from 1 patient in whom a 4-month-old au tograft was explanted, No patient in either group had aortic dilatation at any level of >20% or more than mild aortic regurgitation at up to 4 years o f follow-up. The aortic media was thicker in both autografts and normal don ors (P<0.01), and there was a trend for the PA media to be thicker in the a utograft group. Elastic fiber in all aortas showed little or no variation, whereas in the PA, there was considerable variation in fragmentation. Patie nts with higher preoperative PA pressures tended to have lower fragmentatio n scores (<chi>(2) P<0.01). The lower stiffness modulus, higher stiffness m odulus, and maximum tensile strength of the aorta was 34% to 38% higher tha n that of the PA (P<0.01); however, the 4-month-old autograft appeared to s how adaptation in mechanical behavior. Conclusions-In our series of patients, there was no significant progressive dilatation of the aortic root. We demonstrated differences in the anatomic structure and mechanical behavior of the PA in vitro and highlighted histo logical and mechanical modes of adaptation.