Assessment and comparison of the performance of cardiac valves.

A statistical method is presented to assess and compare cardiac valve performances. Patient survival and valve performances have been separated, and valve function and malfunction have been described in comprehensive and comparable terms. Formulas are proposed to calculate the significance of the difference between two survival probabilities as well as to calculate the instantaneous rate of events and the median remaining lifetime.

Long-term performance of 555 aortic homografts in the aortic position.

Long-term results with 555 aortic homografts used for isolated aortic valve replacement (AVR) between 1964 and 1986 were analyzed to assess valve performance and the time-related onset of valve-related events. The total follow-up was 2,931 patient-years. Twenty years after operation, overall survival was 51.6 +/- 8.1%, freedom from valve-related death was 67.1 +/- 8.9%, freedom from primary tissue failure was 12.4 +/- 4.8%, freedom from infective endocarditis was 82.7 +/- 4.3%, freedom from surgical technical failure was 88.1 +/- 2.3%, and freedom from all complications including valve-related death was 9.0 +/- 3.5%. The incidence of thromboembolism was 0.034% per patient-year (one potential event). Long-term results after homograft insertion for aortic stenosis were significantly better than those after insertion for aortic incompetence. It is concluded that the good quality of life and the median life expectancy, which extends more than 20 years after operation, make the homograft an excellent choice for AVR.

Viable and nonviable aortic homografts in the subcoronary position: a comparative study.

One hundred fifty-five freeze-dried, 63 frozen, and 337 Hanks'-antibiotic solution preserved or nutrient-antibiotic solution preserved homografts used for isolated aortic valve replacement have been followed for 1 to 20 years (mean, 5.3 years), a total of 2,931 patient-years of follow-up information. Overall survival, valve-related death, primary tissue failure, failure due to surgical technical error, infective endocarditis, and overall event-free survival have been assessed and compared. Overall survival 20 years after operation was 51.6% +/- 8.1% with a low incidence of sudden death. The method and length of preservation did not have any effect on the long-term performance or the mode of failure of the homografts. The rate of primary tissue failure was apparently higher with valves preserved in a solution containing calf serum, but the difference was not significant. It is concluded that long-term patient survival and quality of life after aortic valve replacement with a homograft are excellent. The current study, however, could not verify the existence of a significant difference between the three assessed methods of homograft preservation. Furthermore, it could not prove the importance of cellular viability or the existence of clinically significant immunological factors other than the calf serum content of the nutrient medium.

Long-term assessment of aortic valve replacement with autologous pulmonary valve.

Two hundred two autologous pulmonary valves were transplanted into the aortic position between 1967 and 1982 at the National Heart Hospital in London. The indication for operation was congenital or acquired aortic valve disease, and the patients were followed for periods from 1 to 4 years. The patients were not anti-coagulated, but the entire series has been completely free from thromboembolism or bleeding. The actuarial prediction of freedom from valve-related deaths was 82 +/- 6% at the end of the fourteenth year after operation; deaths were due to reoperations for technical failure and to infective endocarditis. Event-free survival of the autologous pulmonary valve in the aortic position was 73 +/- 6% after 14 years at risk. Valve failure resulted mainly from technical problems encountered during the early years of surgical experience. There was no macroscopic or histological evidence of calcification in any of the failed valves. The right ventricular outflow was reconstructed with an aortic homograft in the majority of patients; 81 +/- 5% of these homografts demonstrated event-free performance over a 12-year follow-up period. It is concluded that the long-term performance of a pulmonary autograft inserted for aortic valve disease is superior to that of any other valve substitute and that the operation offers an almost ideal means of aortic valve replacement in appropriate patients.

Potential flaws in the assessment of minor cerebrovascular events after heart valve replacement.

The specificity and sensitivity of the questionnaire method, whether through direct contact or via mail, in collecting information on thrombosis, embolism and bleeding after heart valve replacement were assessed by a critical analysis of methods currently in clinical use. The 16 questions contained in the standard questionnaire of the Albert Einstein College of Medicine searching for transient events were put to 1000 apparently healthy individuals. Additional questions related to risk factors such as previous heart valve replacement, any existing heart disease, hypertension, diabetes or current anticoagulant treatment for any reason were also asked. The male/female ratio was 54.9/45.1, and the mean age was 36.3 years with a range of 14-97 years. Eighty-five persons had one or more risk factors, 915 had none. A positive answer to at least one of the questions searching for TIA (transient ischemic attack) was given by 69.4% (n = 59) of those with, and by 54.8% (n = 501) without any risk factors. The total number of reported 'events' was 164 (1.93/person) for those with, and 1331 (1.45/person) for those without any risk factors. Four different follow up methods were applied to each of 123 patients after heart valve replacement: (a) regular follow up at an out-patient clinic, questionnaires sent at (b) six, (c) 18 and (d) 36 months after the start of the study. 57% of the transient and reversible events reported at the out-patient clinic were forgotten and not mentioned by the same patients in the 36 month questionnaire. One of the three permanent disabilities was also 'forgotten'.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative assessment of bioprosthesis durability in the aortic position.

Published durability results of porcine and pericardial bioprostheses in the aortic position have been reviewed for the purpose of a qualitative comparison between these valve types, and also with previously reviewed series of homograft valves. Porcine bioprostheses exhibit a wide range of failure curves, with a characteristic Weibull-shaped pattern. Patient characteristics must account for the majority of differences seen among the series. Newer series generally contain older patients and have better results. A second generation pericardial valve has distinctly better durability than a previously discontinued pericardial model, and appears to be as durable as that of the best porcine valve series. Homograft valves using cold antibiotic storage have durability results approximately equal to porcine valves, but with younger patients on the average. The results with cryopreserved valves may be comparable, but insufficient long term information is available. To make these qualitative comparisons quantitative would require a formal analysis which takes age and other patient-related characteristics into account.

Comparison of structural valve failure among different 'models' of homograft valves.

Aortic homograft valves are accepted as excellent valve substitutes in the aortic position. Compared to stented bioprostheses, they are considered to have better hemodynamics and a zero or negligible thrombogenicity. Their perceived major single shortcoming is limited durability, but there is apparent broad variation within published data in this respect. Study of the relevant literature reveals important differences between procurement, sterilization and preservation of the individual series refuting any attempt at making a scientifically valid comparison of overall performances. Surgical method and patient selection are further sources of variation among reported long term results. Nevertheless, it appears that (a) cryopreservation produces results at least as good as those of other preservation methods, and (b) the worst results are those of series with the longest follow up. However, the good results with cryopreserved valves are reported in series with limited length of follow up. Because of the many variable factors associated with the use of homograft valves, a comprehensive set of definitions should be introduced, accepted and adhered to in reporting results.

Prosthetic valve function under simulated low cardiac output conditions: preliminary observations.

An experimental protocol was developed and a series of laboratory experiments started to assess the function and behaviour of replacement valves under simulated low cardiac output, that is low flow and low pressure conditions. The Helmholtz Institute's pulse duplicator (1) and instrumentation were carefully tuned in order to achieve accurate and reproducible delivery of the required extremely small stroke volumes. A pilot study was completed with 27 mm St. Jude Medical and CarboMedics bileaflet valves and Wessex porcine bioprostheses, three each, in the simulated aortic position. The results of these experiments suggest that the performances of the two bileaflet prostheses are inadequate if the flow is less than 2.0 l/min; the porcine bioprosthesis needs relatively low flow to start proper function, but its stenotic nature soon becomes apparent; increase in pressure without a corresponding increase in flow has a deleterious effect on valve performances by increasing regurgitation; increasing pulse rate is inversely correlated with valve efficiency; and there is no "all-or-none" cut off point between functional and non-functional situation for the tested devices; there is a semilogarithmic relation between increasing flow and valve performance. The clinical consequences are manifold and may be related both to the stabilization of circulation and to the increased thromboembolic risk during the early postoperative period.

Heterologous antigenicity induced in human aortic homografts during preservation.

A series of rabbit experiments has been carried out to investigate the potential antigenicity of the heat-treated foetal calf serum which is commonly used to enhance viability of preserved aortic homograft valves. In all presensitised animals, the calf serum content of the nutrient medium which infiltrated the aortic wall during preservation provoked a heavy second-set reaction. It is concluded that heat-treated foetal calf serum is a potent heterologous antigen and should not be used for preserving human tissue selected for transplantation.

[Membrane diffusion of paracetamol]. / A paracetamol membrándiffúziós vizsgálata.

A study was made of how different cyclodextrin (CD) derivatives, such as alpha-CD, beta-CD, gamma-CD, dimethyl-beta-CD and random-methyl-beta-CD, influence the diffusion of paracetamol. For interpretation of the phenomena, dissolution rate investigations, measurements of surface tension and determinations of partition coefficients were also performed. It was established that paracetamol has a low diffusion ability. It was also found that the different CD derivatives exert their influence in diverse ways, which depend on, among others, the cyclodextrin ratio and the mode of preparation of the product. These complementary examinations are useful for an explanation of the phenomena.