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Eur J Cardiothorac Surg 2004;26:1056-1057
© 2004 Elsevier Science NL
Letter to the Editor |
21, 5187 Cordova Bay Road, Victoria, BC, Canada V8Y2K7
Received 17 June 2004; accepted 27 July 2004.
* Tel.: +1-250-727-0355; fax: +1-250-727-0395. (E-mail: rfortune{at}telus.net).
I read with interest "Leaflet arrest in St Jude Medical (SJM) and CarboMedics valves: an experimental study" by Grattan and associates [1] which appeared in the EJCTS June, 2004. In this paper, the authors presented two cases in which SJM Masters series aortic valves were found to be in a ‘frozen’ position following implant.
The authors then developed an experimental model consisting of a pushrod which provided variable point pressure against the ring of the prosthesis directed at 180 degrees. Given our understanding of aortic root anatomy in both health and disease, I feel that the model in no way duplicates the forces on a prosthetic valve following aortic valve replacement.
The normal aortic root is usually 45% muscle and 55% fibrous tissue. Thus less than half of the annular area is contractile. The aortic root itself has been shown experimentally to expand during the isovolumic contraction phase, prior to ejection [2]. Also, Van Fenterghem has shown that during ejection, the basal segments adjoining the myocardium (NC-right and right-left basal lengths) shortened, whereas the aortomitral junction (left-NC basal length) lengthened [3]. Given the nature of a normal annulus then, only one pivot mechanism would be subjected to any contractile force, the other would be beside the fibrous components of the annulus and mitral valve, which expands.
Patients with long-standing aortic stenosis develop fibrosis and calcification which would negatively alter the contractility at the annular level. The authors then speculate that left ventricles generating pressures exceeding 200mmHg could result in dynamic leaflet arrest. This surely would be of greater clinical significance, as compared to their cases which occurred in cardioplegically arrested hearts, yet there is no significant reporting of this in the literature. They report that Jaggers showed one leaflet of a SJM standard valve leaflet to arrest following mitral valve replacement. If their hypothesis is correct, how do they explain the arrest of only one leaflet of the prosthesis in this situation? The authors describe a further experiment in which prosthetic valves are placed in the mitral position of a porcine midel. The normal mitral annulus may be capable of ‘two-point’ force loading. Once again, the contractile forces of a normal porcine mitral annulus bear no relationship to the contractile forces in a normal or diseased aortic annulus.
It is impossible to reconstruct the exact intra-operative environment that resulted in the immobile leaflets as reported. However, if the proper sizing technique is utilized in which the sizer passes freely through the annulus, it would not be possible for the valve to then malfunction due to ‘compressive forces’ because that is what proper sizing is supposed to achieve. It is well recognized, however, that tissue adjacent to the valve can result in valve malfunction. These can sometimes be difficult to visualize. In such occasions, the valve can be rotated as long as a proper debridement of the annulus has been undertaken beforehand. There, one can only assume that there were technical issues involved with the initial implants that resulted in the ‘frozen leaflets.’
Footnotes
1 Robert L. Fortune, MD is a surgical consultant to St Jude Medical. 
References
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