Dogs are favourite animals in cardiac research and many experiments were carried out to develop an artificial mitral valve. However, the artificial valves almost always produced fatal blood clots in these animals,(1) with the result that many surgeons were deterred from carrying out human trials.(2)
Like other experimental surgeons, Starr and Edwards encountered the familiar problem of blood clots but eventually decided on a "caged-ball" device.(3) Other designs were uniformly fatal to the animals and whilst 6 of the 7 dogs receiving the caged ball valve died within 17 days, one did survive for some months. Fortunately, the new valve proved far more successful in clinical trials where blood clotting was not a problem.(4) The surgeons concluded that "the marked propensity of the dog to thrombotic occlusion (blood clotting) or massive embolization from a mitral prosthesis is not shared by the human being."(5)
Starr and Edwards wanted to carry out further animal testing of their new caged ball device but could not use the valve that proved so successful in patients because it nearly always killed the dogs. Instead, they designed a different valve specifically for use in these animals! The modified valve did not kill the animals so frequently: even so, 78% still died within 46 days. It was noted that "species differences have therefore led to the use in this clinic of an unshielded ball valve for human mitral replacement and a shielded ball valve as the prosthesis of choice for further testing in the dog."(5)
The successful clinical application of another early design of mitral valve replacement cast further doubt on the value of animal research, since none of the dogs used in preclinical tests survived beyond 40 hours!(6)
1) A.V.Doumanian & F.H.Ellis, Journal of Thoracic & Cardiovascular Surgery, 1961,
2) G.H.A.Clowes Jr, Annals of Surgery, 1961, vol. l 54, 740.
3) A.Starr, American College of Surgeons, Surgical Forum, 1960, vol. 11, 258-260.
4) A.Starr & M.L.Edwards, Annals of Surgery, 1961, vol.l54, 726-740.
5) A.Starr & M.L.Edwards, Journal of Thoracic & Cardiovascular Surgery, 1961, vol.42, 673-682.
6) N.S.Braunwald et al, Journal of Thoracic & Cardiovascular Surgery, 1960, vol.40, 1-11.
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