The origin and development of three new mechanical valve designs: toroidal disc, pivoting disc, and rigid bileaflet cardiac prostheses

Modern concepts from old ideas in manufacture of cardiac valve prostheses

In reviewing the history of mechanical prosthetic valves, it appears evident how many improvements and technical advances have been obtained in this field. Looking to the past, it must also be underlined how some old concepts, which can be considered quite revolutionary for those years, clearly indicate the great skill and ingenuity of those who conceived them. Old ideas have been revitalized by modern concepts, and this is exemplified when considering the developments of bileaflet and sutureless prostheses.

Innovation According to C. Walton Lillehei

C. Walton Lillehei (1918-1999) represents the most distinguished American surgeon of his time and perhaps the greatest surgeon in history. As his mentor, Owen H. Wangenesteen (1898-1981), so accurately declared, Walt Lillehei was "one of the surgical immortals." Indeed, similar words were echoed by the famous cardiac surgeon, Denton A. Cooley (b. 1920), who said, "Hardly any other cardiac surgeon has introduced a greater number of innovative techniques and concepts." Born in Minneapolis, Lillehei attended the University of Minnesota, where he completed his college, medical, physiology, and surgical studies. Because of his extraordinary contributions to make open heart surgery feasible and safe, he is considered the father of open heart surgery. Many other contributions followed the initial innovations, particularly the use of the bubble oxygenator, the total intracardiac repair of tetralogy malformation, the use of myocardial electrodes for treating complete heart block, and the development of three cardiac valve prostheses, among other discoveries. The noted Minnesota surgeon was an innovator for his entire professional career. He believed in innovation and practiced innovation in any way possible. "Determination, persistence, and stubbornness" were, according to Lillehei, "the most important components of research and successful discovery."

Mechanical heart valves: 50 years of evolution

The past 50 years have witnessed remarkable progress in the development of safe, hemodynamically favorable mechanical heart valves. Starr-Edwards aortic and mitral ball valves introduced in the mid-1960s, continue to be used successfully worldwide. More than 100,000 Omniscience and Omnicarbon tilting-disc valves have been implanted since 1978 with essentially no mechanical failure; similar results have been obtained with more than 300,000 Hall-Kaster and Medtronic-Hall tilting-disc valves over the past 25 years. Pyrolytic carbon, originally used to encapsulate nuclear fuel rods, has been adapted for the fabrication of discs, leaflets and the housings for more than 2 million mechanical valves. The St. Jude bileaflet valves, totally fabricated from pyrolytic carbon, have remained virtually unchanged in design since their introduction in 1977. More than 1.3 million of these valves have been implanted worldwide with virtually no reported failures of the carbon leaflets or housings. Similarly, pyrolytic carbon bileaflet Carbomedics valves have been implanted in more than 500,000 patients since 1986. Now, 50 years after Dr Gibbon's seminal achievement, patients with debilitating valve disease can have elective valve replacement (mechanical or tissue) with an operative mortality approaching 1% to 2% and a low lifetime complication rate.

Clinical outcome in patients with 19-mm and 21-mm St. Jude aortic prostheses: comparison at long-term follow-up

BACKGROUND

Small-sized prostheses for aortic valve replacement may result in residual left ventricular outflow tract obstruction. Aim of the study was to verify whether implantation of 19-mm versus 21-mm St. Jude Medical standard prostheses (St. Jude Medical, Inc, St. Paul, MN) influences long-term clinical outcome.

METHODS

Two hundred twenty-nine patients who underwent aortic valve replacement with 19 mm (group 1, 53 patients) or 21-mm St. Jude Medical standard prostheses (group 2, 176 patients) were included in the study. Mean follow-up of current survivors was 10+/-4 years.

RESULTS

Operative mortality was 7.5% in group 1 and 8.5% in group 2. At discharge, an important patient-prosthesis mismatch (effective orifice area index < or = 0.60 cm2/m2) was present in 18% of group 1 versus 5% in group 2 (p = 0.004). Among patients with body surface area less than 1.70 m2, such mismatch was present in 15% of group 1 versus 2% of group 2 (p = 0.008). At last follow-up New York Heart Association (NYHA) functional class (p < 0.001), left ventricular mass reduction (p = 0.02), mean (p = 0.002) and peak transprosthetic gradients (p < 0.001), and effective orifice area index (p = 0.005) were significantly better in group 2. Freedom from sudden death (92%+/-5% vs 99%+/-1%, p = 0.01), valve-related death (84%+/-6% vs 90%+/-5%, p = 0.02), and cardiac events (56%+/-13% vs 86%+/-4%, p = 0.008), were significantly lower in group 1. Effective orifice area index was an independent predictor of late cardiac events.

CONCLUSIONS

Although long-term results after aortic valve replacement with small-sized St. Jude Medical standard prostheses are satisfactory, 19-mm valve recipients show a high prevalence of important patient-prosthesis mismatch with less evident functional improvement and higher rate of cardiac events, suggesting a very cautious use of this prosthesis.

Impact of size mismatch and left ventricular function on performance of the St. Jude disc valve after aortic valve replacement

BACKGROUND

The hemodynamic function of the St. Jude valve may change relative to changes in left ventricular function after aortic valve replacement for aortic stenosis. From theoretical reasons one may hypothesize that prosthetic valve hemodynamic function is related to left ventricular failure and mismatch between valve size and patient/ventricular chamber size.

METHODS

Forty patients aged 24 to 82 years who survived aortic valve replacement for aortic stenosis with a standard St. Jude disc valve (mean size, 23.5 mm; range, 19 to 29 mm) were followed up prospectively with Doppler echocardiography and radionuclide left ventriculography preoperatively and 9 days, 3 months, and 18 months after the operation with assessment of intravascular hemolysis at 18 months. Follow-up to a maximum of 7.4 years (mean, 6.3 years) was 100% complete.

RESULTS

Left ventricular muscle mass index decreased from 198 +/- 62 g.m-2 preoperatively to 153 +/- 53 g.m-2 at 18 months (p < 0.001), paralleled by a significant increase in left ventricular ejection fraction, peak ejection rate, and peak filling rate; only 18% of the patients had normal left ventricular muscle mass index and only 32% normal ventricular function (normal left ventricular ejection fraction, peak ejection rate, peak filling rate, early filling fraction, and late filling fraction during atrial contraction) at 18 months. Prosthetic valve peak Doppler gradient dropped from 20 +/- 6 mm Hg at 9 days to 17 +/- 5 mm Hg at 18 months (p < 0.05). Reduction of left ventricular muscle mass index was unrelated to peak gradient and size of the valve. Peak gradient at 18 months rose with valve orifice diameter of 17 mm or less (by 6 mm Hg), orifice diameter/body surface area of 9 mm.m-2 or less (by 5 mm Hg), left ventricular enddiastolic dimension (by 23 mm Hg per 10 mm increase), and impaired ventricular function (by 3 mm Hg). All but 2 patients (5%) had intravascular hemolysis; none had anemia. Two patients with moderate paravalvular leak had the highest serum lactic dehydrogenase levels; 4 patients with trivial leak had higher serum lactic dehydrogenase levels than those without leak. Serum lactic dehydrogenase levels rose with moderate paravalvular leak, impaired ventricular function, and valve orifice diameter. Six patients with trivial or moderate paravalvular leak had a cumulative 7-year freedom from bleeding and thromboembolism of 44% +/- 22% compared with 87% +/- 5% for those without leak (p < 0.05).

CONCLUSIONS

The peak gradient of the St. Jude aortic valve dropped marginally over the first 18 postoperative months in association with incomplete left ventricular hypertrophy regression and marginal improvement of ventricular function. Mismatch between valve size and ventricular cavity size or patient size and impaired function of a dilated ventricle significantly compromised the performance of the St. Jude valve. Probably explained by platelet destruction or activation, paravalvular leak was related to bleeding and thromboembolic complications.