Proven Durability Research Articles

Incidental intracranial aneurysm

The management of of unruptured intracranial aneurysms is one of the most important issues confronting neurosurgeons today. The high mortality and morbidity associated with subarachnoid hemorrhage (SAH) has prompted interest in repair of aneurysms that are discovered before they have ruptured. A strong risk factor for intracranial aneurysm which causes SAH is a positive family history, polycystic kidney disease and patients who have survived a SAH. There is no cutoff size of aneurysm below which rupture is not possible. Presently there are no definitive guidelines in the management of incidental aneurysms and many centers consider each case individually with treatment offered for lesions more than 7 mm in diameter especially if patient is relatively young without major co-morbidities. Even though microsurgery offers the advantage of proven durability and higher rates of total aneurysm obliteration, the choice of treatment modality between open microsurgery and endovascular occlusion is flexibly adjusted to each case.

The Ross-Konno Procedure in Children: Outcomes, Autograft and Allograft Function, and Reoperations

The Ross aortic valve replacement with a modified Konno-type enlargement Ross-Konno procedure of the aortic annulus and subannular region allows an autograft aortic valve replacement for children with significant annular and subannular hypoplasia. The potential for growth and the proven durability of the autograft make the Ross-Konno procedure an ideal aortic valve replacement for this subgroup with multilevel left ventricular outflow tract obstruction. We reviewed our institutional midterm experience to assess autograft and homograft hemodynamics, and management after a Ross-Konno procedure. Between 1995 and 2005, 14 consecutive children (mean age, 6.4 +/- 5.9 years; range, 1 month to 17 years) underwent the Ross-Konno procedure. All children had severe to critical aortic stenosis or multilevel left ventricular outflow tract obstruction. There was 1 early and 1 late death with a mean follow-up of 5.7 +/- 3.6 years. Actuarial survival at 10 years was 86%. Three patients underwent right ventricular outflow tract reoperation for conduit replacement for homograft dysfunction and one patient required redo aortic root replacement with a mechanical valves for progressive aortic insufficiency. Freedom from right ventricular outflow tract and autograft reoperation at 10 years is 77% and 92%, respectively. Aortic annular dilation was not observed in all patients. Univariate and multivariate analysis identified no risk factors for autograft or homograft valve-related reoperation. The Ross-Konno procedure is an excellent technique to treat complex multilevel left ventricular outflow tract obstruction in children with significant annular and subannular hypoplasia. The autograft demonstrated durability without development of aortic stenosis or progressive dilation and a low incidence of developing progressive aortic insufficiency. Enlargement of the aortic annulus appear to parallel somatic growth in most instances.

Advances In Coronary Surgery

The first successful aortocoronary bypass operation was periormed in 1964 by Garrett, Howell, and DeBakey in Houston.26 That same year, Kolesov in Leningrad performed the first planned anastomosis between the left internal thoracic artery and the left anterior descending artery. 27 The future development of coronary angiography, cardiopulmonary bypass and cardioplegia helped coronary bypass surgery evolve from these first seminal events, and by the mid 1980s, coronary revascularization using cardiopulmonary bypass had become an accepted technique with durable outcomes.In July of 1979, Andreas Gruentzig launched the era of percutaneous coronary intervention (PCI) with the development of percutaneous transluminal coronary angioplasty. 28 Although outcomes were not as durable, the difference in morbidity and mortality made it an attractive alternative to surgery. The development of stent technology improved outcomes, and the introduction of drug-eluting stents in the new millennium dramatically reduced in-stent restenosis. As coronary bypass surgery continues to be refined, the challenge is to minimize the morbidity and mortality while preserving the proven durability of surgical revascularization.

Advances in Coronary Surgery

The first successful aortocoronary bypass operation was periormed in 1964 by Garrett, Howell, and DeBakey in Houston.26 That same year, Kolesov in Leningrad performed the first planned anastomosis between the left internal thoracic artery and the left anterior descending artery. 27 The future development of coronary angiography, cardiopulmonary bypass and cardioplegia helped coronary bypass surgery evolve from these first seminal events, and by the mid 1980s, coronary revascularization using cardiopulmonary bypass had become an accepted technique with durable outcomes. In July of 1979, Andreas Gruentzig launched the era of percutaneous coronary intervention (PCI) with the development of percutaneous transluminal coronary angioplasty. 28 Although outcomes were not as durable, the difference in morbidity and mortality made it an attractive alternative to surgery. The development of stent technology improved outcomes, and the introduction of drug-eluting stents in the new millennium dramatically reduced in-stent restenosis. As coronary bypass surgery continues to be refined, the challenge is to minimize the morbidity and mortality while preserving the proven durability of surgical revascularization.

The Ross/Konno procedure in neonates and infants: intermediate-term survival and autograft function

Background. The Ross procedure has been increasingly applied to neonates and infants. Addition of a modified Konno-type enlargement of the aortic annulus allows the application of this procedure to neonates and infants with significant annular hypoplasia. The potential for growth and the proven durability make the autograft an ideal aortic valve replacement. Methods. Between March 1993 and December 2000, 10 patients under 1 year of age underwent a Ross/Konno procedure at our institution (range, 2 to 349 days; median 16). All patients had severe to critical aortic stenosis. All patients required aortic annulus enlargement for size mismatch between the aortic and pulmonary valves. Results. There were no deaths at a median follow-up of 48 months (range, 1 to 74 months). All patients had none to mild aortic stenosis on Doppler echocardiography. Eight patients had a 0 to 1+ aortic insufficiency, 1 patient had a 2+ aortic insufficiency, and 1 patient had a 3+ aortic insufficiency. Aortic annular dilatation was not observed. Aortic sinus dilatation occurred initially (mean change in z-value: 0 to 12 months, +2.1) and then stabilized (mean change in z-value: 12 to > 36 months, +0.6). No patient required additional procedures for aortic valve disease. Two patients required three pulmonary allograft replacements. Conclusions. The Ross procedure with a modified Konno-type enlargement of the aortic annulus is an excellent approach to aortic valve disease in the neonate and infant. The procedure can be accomplished with low morbidity and mortality, and low rates of reoperation. The pulmonary autograft demonstrates durability without developing aortic stenosis, aortic insufficiency, or progressive dilatation. Enlargement of the aortic annulus parallels somatic growth.

Subclavian-to-Carotid Transposition for Coronary-Subclavian Steal Syndrome

The recurrence of myocardial ischemia has been well described to occur when a proximal subclavian artery stenosis develops in patients who have had coronary revascularization based on an internal mammary artery. Carotid-to-subclavian bypass distal to the mammary artery has been the traditional vascular reconstruction for these patients. Other interventions in the literature have included aorta-subclavian bypass, axilloaxillary bypass, and subclavian angioplasty or stent placement. This case report describes the use of a subclavian-to-carotid transposition for the treatment of a patient with symptomatic coronary-subclavian steal syndrome. A 56-year-old man was admitted with unstable angina. Eleven years previously he had undergone coronary revascularization with a left internal mammary artery (LIMA) to the left anterior descending artery and a vein graft to the right coronary artery. Cardiac catheterization at this time revealed a 90% stenosis in the midbody of the vein graft and a 90% stenosis of the proximal left subclavian artery with a 40 mm Hg gradient. The LIMA graft had no intrinsic abnormality. Atherectomy of the vein graft stenosis was performed with a 30% residual stenosis. The patient then underwent a subclavian-tocarotid transposition with a temporary shunt. The shunt was placed from the proximal common carotid to the distal subclavian to allow retrograde perfusion of the LIMA during occlusion of the subclavian artery. Transposition was performed with carotid occlusion in standard fashion. Follow-up angiography and duplex ultrasound confirmed a widely patent transposition. The patient remains asymptomatic 5 years later. The use of a subclavian-to-carotid transposition for treatment of the coronary-subclavian steal syndrome successfully corrected this patient's cardiac symptoms. Advantages of transposition over other forms of subclavian revascularization include (1) an all-autogenous reconstruction, (2) a single anastomosis, (3) proven long-term durability, and (4) subcutaneous surgical exposure. The main disadvantage of this technique is the potential need for a temporary shunt during occlusion of the proximal subclavian artery. Patients with retrograde flow in the LIMA could have the procedure performed without a shunt. The widespread use of subclavian angioplasty does not appear to be justified in these patients owing to recurrent stenoses after angioplasty as compared to the excellent long-term patency rates for subclavian-to-carotid transpositions.

Industrial Gas Turbine Performance Uprates: Tips, Tricks, and Traps

After industrial gas turbines have been in production for some amount of time, there is often an opportunity to improve or uprate the engine’s output power, cycle efficiency, or both. Typically, the manufacturer would like to provide these uprates without compromising the proven reliability and durability of the product. Further, the manufacturer would like the development of this uprate to be low cost, low risk, and result in an improvement in customer value over that of the original design. This Paper describes several options available for enhancing the performance of an existing industrial gas turbine engine, and discusses the implications for each option. Advantages and disadvantages of each option are given along with considerations that should be taken into account in selecting one option over another. Specific options discussed include dimensional scaling, improving component efficiencies, increasing massflow compressor zero staging, increasing firing temperature (thermal uprate), adding a recuperator, increasing cycle pressure ratio, and converting to a single shaft design. The implications on output power, cycle efficiency, off-design performance engine life or time between overhaul (TBO), engine cost, development time and cost, auxiliary requirements, and product support issues are discussed. Several examples are provided where these options have been successfully implemented in industrial gas turbine engines.

Repairing the degenerative mitral valve: Ten- to fifteen-year follow-up

From January 1969 to December 1992, mitral valve reconstructive operations were performed on 155 patients with degenerative mitral valve disease. There were 102 male and 53 female patients, with a mean age of 60.5 ± 9.2 years, a mean duration of symptoms of 3.8 ± 2.7 years, and 34% were in atrial fibrillation. All patients were in New York Heart Association functional classes III and IV before operation. The degree of mitral regurgitation was severe in 94% and moderate in 6%, and 50.9% of patients had moderate to severe impairment of left ventricular function. Emergency operation was undertaken in 7.1% of cases; 19% of patients underwent additional procedures. All patients had posterior mitral leaflet pathology and 19 patients had anterior mitral leaflet pathology. Ring annuloplasty was used in only 3% of cases. The operative mortality rate was 3.9%, 9% of patients had morbid events, and 4.5% of patients had repair failure within 6 months. All patients have been followed up with serial echocardiography for a mean time of 5.2 ± 0.3 years (range 0.5 to 24 years). Immediately after operation, 92.9% had no mitral regurgitation to mild mitral regurgitation. At last follow-up, 96.9% had no mitral regurgitation to mild mitral regurgitation by echocardiography and 98% of patients were in New York Heart Association functional classes I and II. The actuarial survival at 15 years was 46% ± 11%, freedom from reoperation was 84.9% ± 11%, freedom from infective endocarditis was 96.0% ± 11%, freedom from thromboembolism was 90.4% ± 11%, and freedom from all valve-related events was 36.7% ± 11%. It is well documented that repair of degenerative mitral valves offers excellent short-term and medium long–term benefits. This series represents the longest follow-up reported outside Europe. Our results beyond 10 years support our conclusion that an annuloplasty ring is not an absolute prerequisite for achieving successful repair of proven durability in most patients with degenerative mitral valve disease. (J T horac C ardiovasc S urg 1996;112:238-47)

Fixation of the acetabular component: The case for cement

This discussion intends to support the case for cemented fixation of the acetabular component in total hip arthroplasty (THA), in a carefully selected patient population over age 60. Our argument for the use of cemented sockets centers around the following four points: (1) the proven durability of cemented acetabular components, (2) decreased rate of polyethylene wear noted in all-polyethylene sockets, (3) high incidence of severe osteolysis in noncemented acetabular components, (4) issues of cost containment in THA. Each of these four points is discussed separately.

Long-term performance of Star-Edwards silastic ball valves and St Jude Medical bi-leaflet valves

Long-term performance of Starr-Edwards silastic ball (SESB, n = 168) and St Jude Medical bi-leaflet (SJMB, n = 93) valves in patients who were alive 30 days after implantation (1980-86) for aortic stenosis was compared. Mean follow-up was 3.0 years (0.1-7.9 years). The SESB and SJMB groups differed as regards female gender (18% vs 47%, P less than 0.0001), NYHA classes III-IV (59% vs 72%, P less than 0.05), coronary artery disease (CAD, 32% vs 62%, P less than 0.01) in patients with coronary arteriography (n = 82 and n = 55, respectively), and prosthetic annulus diameter (26 +/- 1 vs 23 +/- 2 mm, P less than 0.0001). Five-year survival +/- SE in SESB vs SJMB patients was: total population, 89 +/- 3% vs 80 +/- 6% (NS); coronary arteriography population, no CAD, 90 +/- 4% vs 100% (NS), and with CAD, 71 +/- 11% vs 60 +/- 13% (NS; P = 0.01 for CAD). Five-year event-free survival +/- SE in SESB vs SJMB patients was 95 +/- 2% vs 97 +/- 2% (NS) for thromboembolism, 95 +/- 2% vs 89 +/- 4% (NS) for coumadin-related haemorrhage, 98 +/- 1% vs 99 +/- 1% (NS) for endocarditis, 98 +/- 1% vs 94 +/- 5% (NS) for paravalvular leak, 88 +/- 3% vs 79 +/- 6% (NS) for all valve-related complications, and 98 +/- 1% vs 95 +/- 4% (NS) for prosthesis replacement. Thrombotic occlusion or structural failure were not observed. No patients without CAD experienced thromboembolic events. Cox regression analyses (in both total population and coronary arteriography population) of survival as well as the various complications revealed that the type of prosthesis did not have predictive influence. CAD was an independent risk factor for thromboembolism, haemorrhage, and all valve-related complications. Previous systemic hypertension was independently predictive of haemorrhage. The SESB and SJMB prostheses showed comparable and acceptable long-term performance. Only patient-related variables, notably CAD, influenced late results. The proven durability and relatively low price of the SESB valves together with the excellent haemodynamic performance of even small-sized SJMB valves should be considered in the light of the present results.

F100-PW-229 Higher Thrust in Same Frame Size

The F100-PW-229 fighter aircraft engine is a higher thrust derivative of the F100-PW-220 and in the same frame size. The engine was developed from the F100 Engine Model Derivative (EMD) Program and parallel IR&D efforts. The increased thrust was achieved by increasing the flow and pressure ratio of the two-spool compression system accompanied by an increase in turbine temperature. The increased length compression system was offset by an innovative design intermediate case and a reduced length combustor to maintain overall engine axial length. The –229 engine has a thrust-to-weight ratio of 8.0 with a 20–30 percent performance increase over the –220 model across the flight map. Significant improvements in maintainability have been incorporated while retaining the proven durability and operability features of the –220 engine. The Government-industry partnership is working well, continually providing increased performance engines for our first-line fighters.

Mechanical valves: A comparative analysis of the Starr-Edwards and Björk-Shiley prostheses

Despite the requirement of anticoagulation, mechanical valve prostheses offer the advantage of proven durability. We have compared the long-term results of 467 aortic valve replacements and 342 mitral valve replacements using the Starr-Edwards prosthesis with 110 aortic valve replacements and 105 mitral valve replacements using the Björk-Shiley prosthesis from 1973 through 1977. Improvement in New York Heart Association (NYHA) class was noted in greater than 80% of patients in all four groups. Long-term survival with mean follow-up over 5 years was not significantly different between respective groups. The probability of thromboembolic complications, however, was significantly higher (p less than 0.05) with the Starr-Edwards prosthesis in both the aortic and mitral positions. The probability of valve failure, although low for all groups, was significantly higher (p less than 0.05) in the Björk-Shiley mitral group due to late thrombotic occlusion. Use of the Starr-Edwards and Björk-Shiley prostheses is associated with satisfactory functional improvement and similar long-term survival rate. However, the increased risk of valve failure due to late thrombotic occlusion of the Björk-Shiley prosthesis should be considered when choosing a mechanical mitral prosthesis.

Enlargement of the aortic root or anulus with autogenous pericardial patch during aortic valve replacement: Long-term follow-up

Patch enlargement of the aortic root or anulus is a widely accepted technique when restrictive anatomy is encountered during aortic valve replacement. Patches made of prosthetic material have been used almost exclusively, and patches of autogenous pericardium have not received wide acceptance. Although pericardium is advantageous because of its low cost, ready availability, and ease of handling, its long-term durability has not been fully established. From 1965 to 1981, 96 patients had autogenous pericardial patches placed during aortic valve replacement at the Mayo Clinic. In 81 patients, the patches were placed solely in a supravalvular position to facilitate aortic closure, while in 15 patients, the patches were placed in both subvalvular and supravalvular positions, allowing for annular expansion and insertion of a larger prosthesis. In a mean follow-up of 5.4 years, none of the 92 operative survivors has had clinical evidence of sudden patch failure and none has had patch aneurysms detected by routine chest roentgenography. One patient required reoperation for a perivalvular leak at the point where the prosthesis had been sutured to the patch. Objective data concerning the late postoperative status of the patch were available on 48 patients: 24 underwent reoperation, 16 underwent two-dimensional echocardiography, two underwent aortic root angiography, and six underwent postmortem examination. Patch aneurysms were universally absent, and in every patient the patches were well incorporated into the adjacent tissues. This proven durability suggests that autogenous pericardium is a satisfactory patch material when required during aortic valve replacement.

A critical review of magnetic recording materials

A review of the methods of preparation and the relevant properties of materials which the authors consider suitable for incorporation in conventional magnetic recording surfaces such as tapes, disks, drums, strips, and cards is provided. This field is presently dominated by one material, gamma ferric oxide in fine particle form, and so it is not surprising that this material is discussed at greater length than its potential rivals. The reasons for this dominance are considered and found to be 1) the ability of gamma ferric oxide recording surfaces to perform adequately in the recording systems which have been developed so far, i.e., the magnetic properties of the oxide have apparently not been the limiting factors in the performance of recording systems; 2) the relative cheapness of the particles; 3) the existence of suitable binder systems of proven durability; and 4) the need for compatibility with existing recording devices.