- Email: [email protected]
Risk of strut fracture of Björk-Shiley convexo-concave valves
861
Risk of strut fracture of convexo-concave
Björk-Shiley valves
SiR,-The Lancet has published two articles this year, each defining subsets of patients with Bjork-Shiley convexo-concave (BSCC) heart valves who might be considered for elective, prophylactic valve replacement (Dr Birkmeyer and colleagues, Aug 29, p 520; and ref 1). Although Birkmeyer et al note that batches of high-risk valves of particular manufacturing date and process may yet be identified, manufacturing data were not requested by the authors of either article. Therefore, statistically significant relative hazard functions based on periods of manufacturing are not taken into account.z3 In conjunction with the US Food and Drug Administration, the manufacturer has re-assessed its data in the light of recently published cohort studies.I,3 Valve groups segregated by size, implant position (mitral or aortic), date of manufacture (for which weld date has been the traditional surrogate), and opening angle (60° or 70°) have been reviewed by consulting statisticians, an independent medical advisory panel, and departments of health in various countries. The table shows groups that have significantly different (95% confidence limits) estimated rates of fracture. BSCC VALVE RISK GROUPS
SIR,-Several groups of researchers have investigated the risk of outlet strut fracture of Bjork-Shiley convexo-concave valves. van de Graaf et all reported results of a population-based follow-up study in the Netherlands. In a response to this study, Bennett2 referred to a detailed analysis of 381 70° valves (then in press). By contrast with the Dutch study, Bennett reported that valve size was the only highly significant factor associated with strut fracture in a particular valve group. Once valve size was considered, neither age nor valve position was significant in strut fracture; this analysis was based on Cox multiple regression analysis with nine independent variables. That study has now been publishedand we would comment on the methodology used and the conclusions drawn. Our main comment concerns the method. The presentation of the Cox regression analysis does not include &bgr;-values or hazard ratio. What, therefore, was the magnitude of the risk factor? The statement that valve position is not a significant factor associated with strut fracture cannot be supported because the analysis of their data was far from flawless. The variables group I (early large-size [29-33 mm] valves), group II (late large-size [29-33] valves), and mitral location are entered together in the Cox model. Since 71 % of mitral valves and only 12% of aortic valves were large-size valves, the group variables and mitral location are highly correlated. If related variables are entered in a multivariate model the estimated coefficients for those variables may deviate considerably from the true value.’ Moreover, whether the group variables were entered as dummy variables, with group III as a reference, is obscure, and we doubt the meaning of the single log likelihood presented under step 0 (univariate analysis) in table vii. Bennett questioned the results from the Dutch study because of the small numbers in some groups. However, the 10-year actuarial fracture rates estimated by Bennett et al are also imprecise. Within subgroups only a small number of valves was followed up that long, and as a result the 95 % confidence intervals of the 10-year fracture rates are wide--eg, for large size aortic valves they were 3-2-19-6 and for large size mitral valves 50-178. Therefore, their conclusion that within valve-size groups fractures rates for aortic and mitral valves are similar is based on little evidence from the data. Lastly, we wonder how Bennett, studying the 70° valves, allows himself to recommend strategies for 60° valves carriers. Hardly any studies have been published about this difficulty for 60° valves. Department of Epidemiology, Utrecht University, 3511 CK Utrecht, Netherlands
Shiley Inc invites researchers to submit serial numbers of BSCC heart valves in their studies.
Individual
risk stratification
corresponding to each correct valve serial number will be provided in accordance with the table or newer valid information as it becomes available. In this way, the primary intent of both the investigators and the manufacturer to benefit BSCC heart valve
recipients will be kept uppermost. Heart Valve Research Center, 17672-B Cowan Avenue, Irvine, California 92714, USA
JAMES G. CHANDLER
Ash House, Fairfield Avenue, Staines, Middlesex, UK
ALEXIS POBEDONOSTZEFF
Shiley
1.
der Graaf Y, de Waard F, van Herwerden LA, Defauw J. Risk of strut fracture of 257-61 2 Hiratzka LF, Kouchoukos NT, Grunkemeier GL, Miller DC, Scully HE, Wechsler AS. Outlet strut fracture of the Bjork-Shiley 60° convexo-concave valve current information and recommendations for patient care. JAm Coll Cardiol 1988, 11: 1130-37. 3. Ericsson A, Lindblom D, Semb G, et al Strut fracture with Bjork-Shiley 70° convexo-concave valve: an international multi-institutional follow up study. Eur J Cardiothorac Surg 1992; 6: 339-46. van
Bjork-Shiley valves. Lancet 1992; 339:
YOLANDA VAN DER GRAAF ALE ALGRA
der Graaf Y, de Waard F, van Herwerden LA, Defauw J. Risk of strut fracture of Bjork-Shiley valves. Lancet 1992, 339: 257-61. 2. Bennett G. Bjork-Shiley valves Lancet 1992; 339: 815 3. Ericsson A, Lindblom D, Semb G, et al. Strut fracture with the Bjork-Shiley 70° convexo concave valve an international multi-institutional follow-up study. Eur J Cardiothorac Surg 1992, 6: 339-46. 4. Kleinbaum DG, Kupper LL, Morgenstem H. Epidemiologic research. Belmont, Lifetime Learning Publications, 1982. 428. 1.
*Shipped but not returned, therefore presumed implanted Unless otherwise specified, first month shown= from 1 st day of month, second month= to last day (eg Jan 1, 1980-Dec 31, 1980)
MARJON KALLEWAARD
van
Colonisation of oropharynx with staphylococci after penicillin in neutropenic patients
SIR,-Coagulase-negative staphylococci (CNS) are an increasing of bacteraemias in neutropenic patients, supposedly because of extensive use of intravascular devices. In our studies of infection prophylaxis during neutropenia after chemotherapy, we found that colonisation of the oropharynx may have a role. During 39 episodes of neutropenia (neutrophilic granulocytes <0-5 x109/1) in 21 patients treated for leukaemia, we used the following prophylactic antibiotics to prevent infections with gram-negative bacilli, Staphyloccocus atirezis, or yeasts: oral pefloxacin, trimethoprim orally or as nasal ointment, oral fluconazole, and oral amphotericin B. Our experience2 and that of others3 is that bacteraemias with viridans streptococci remain a problem. Therefore we treated 6 patients in the first 15 episodes empirically with benzylpenicillin if they had a high temperature; in the other 24 episodes we added phenoxymethylpenicillin orally for 10 days to the prophylactic regimen of 15 patients who were treated with high-dose cytarabine. cause
Risk of strut fracture of convexo-concave
Björk-Shiley valves
SiR,-The Lancet has published two articles this year, each defining subsets of patients with Bjork-Shiley convexo-concave (BSCC) heart valves who might be considered for elective, prophylactic valve replacement (Dr Birkmeyer and colleagues, Aug 29, p 520; and ref 1). Although Birkmeyer et al note that batches of high-risk valves of particular manufacturing date and process may yet be identified, manufacturing data were not requested by the authors of either article. Therefore, statistically significant relative hazard functions based on periods of manufacturing are not taken into account.z3 In conjunction with the US Food and Drug Administration, the manufacturer has re-assessed its data in the light of recently published cohort studies.I,3 Valve groups segregated by size, implant position (mitral or aortic), date of manufacture (for which weld date has been the traditional surrogate), and opening angle (60° or 70°) have been reviewed by consulting statisticians, an independent medical advisory panel, and departments of health in various countries. The table shows groups that have significantly different (95% confidence limits) estimated rates of fracture. BSCC VALVE RISK GROUPS
SIR,-Several groups of researchers have investigated the risk of outlet strut fracture of Bjork-Shiley convexo-concave valves. van de Graaf et all reported results of a population-based follow-up study in the Netherlands. In a response to this study, Bennett2 referred to a detailed analysis of 381 70° valves (then in press). By contrast with the Dutch study, Bennett reported that valve size was the only highly significant factor associated with strut fracture in a particular valve group. Once valve size was considered, neither age nor valve position was significant in strut fracture; this analysis was based on Cox multiple regression analysis with nine independent variables. That study has now been publishedand we would comment on the methodology used and the conclusions drawn. Our main comment concerns the method. The presentation of the Cox regression analysis does not include &bgr;-values or hazard ratio. What, therefore, was the magnitude of the risk factor? The statement that valve position is not a significant factor associated with strut fracture cannot be supported because the analysis of their data was far from flawless. The variables group I (early large-size [29-33 mm] valves), group II (late large-size [29-33] valves), and mitral location are entered together in the Cox model. Since 71 % of mitral valves and only 12% of aortic valves were large-size valves, the group variables and mitral location are highly correlated. If related variables are entered in a multivariate model the estimated coefficients for those variables may deviate considerably from the true value.’ Moreover, whether the group variables were entered as dummy variables, with group III as a reference, is obscure, and we doubt the meaning of the single log likelihood presented under step 0 (univariate analysis) in table vii. Bennett questioned the results from the Dutch study because of the small numbers in some groups. However, the 10-year actuarial fracture rates estimated by Bennett et al are also imprecise. Within subgroups only a small number of valves was followed up that long, and as a result the 95 % confidence intervals of the 10-year fracture rates are wide--eg, for large size aortic valves they were 3-2-19-6 and for large size mitral valves 50-178. Therefore, their conclusion that within valve-size groups fractures rates for aortic and mitral valves are similar is based on little evidence from the data. Lastly, we wonder how Bennett, studying the 70° valves, allows himself to recommend strategies for 60° valves carriers. Hardly any studies have been published about this difficulty for 60° valves. Department of Epidemiology, Utrecht University, 3511 CK Utrecht, Netherlands
Shiley Inc invites researchers to submit serial numbers of BSCC heart valves in their studies.
Individual
risk stratification
corresponding to each correct valve serial number will be provided in accordance with the table or newer valid information as it becomes available. In this way, the primary intent of both the investigators and the manufacturer to benefit BSCC heart valve
recipients will be kept uppermost. Heart Valve Research Center, 17672-B Cowan Avenue, Irvine, California 92714, USA
JAMES G. CHANDLER
Ash House, Fairfield Avenue, Staines, Middlesex, UK
ALEXIS POBEDONOSTZEFF
Shiley
1.
der Graaf Y, de Waard F, van Herwerden LA, Defauw J. Risk of strut fracture of 257-61 2 Hiratzka LF, Kouchoukos NT, Grunkemeier GL, Miller DC, Scully HE, Wechsler AS. Outlet strut fracture of the Bjork-Shiley 60° convexo-concave valve current information and recommendations for patient care. JAm Coll Cardiol 1988, 11: 1130-37. 3. Ericsson A, Lindblom D, Semb G, et al Strut fracture with Bjork-Shiley 70° convexo-concave valve: an international multi-institutional follow up study. Eur J Cardiothorac Surg 1992; 6: 339-46. van
Bjork-Shiley valves. Lancet 1992; 339:
YOLANDA VAN DER GRAAF ALE ALGRA
der Graaf Y, de Waard F, van Herwerden LA, Defauw J. Risk of strut fracture of Bjork-Shiley valves. Lancet 1992, 339: 257-61. 2. Bennett G. Bjork-Shiley valves Lancet 1992; 339: 815 3. Ericsson A, Lindblom D, Semb G, et al. Strut fracture with the Bjork-Shiley 70° convexo concave valve an international multi-institutional follow-up study. Eur J Cardiothorac Surg 1992, 6: 339-46. 4. Kleinbaum DG, Kupper LL, Morgenstem H. Epidemiologic research. Belmont, Lifetime Learning Publications, 1982. 428. 1.
*Shipped but not returned, therefore presumed implanted Unless otherwise specified, first month shown= from 1 st day of month, second month= to last day (eg Jan 1, 1980-Dec 31, 1980)
MARJON KALLEWAARD
van
Colonisation of oropharynx with staphylococci after penicillin in neutropenic patients
SIR,-Coagulase-negative staphylococci (CNS) are an increasing of bacteraemias in neutropenic patients, supposedly because of extensive use of intravascular devices. In our studies of infection prophylaxis during neutropenia after chemotherapy, we found that colonisation of the oropharynx may have a role. During 39 episodes of neutropenia (neutrophilic granulocytes <0-5 x109/1) in 21 patients treated for leukaemia, we used the following prophylactic antibiotics to prevent infections with gram-negative bacilli, Staphyloccocus atirezis, or yeasts: oral pefloxacin, trimethoprim orally or as nasal ointment, oral fluconazole, and oral amphotericin B. Our experience2 and that of others3 is that bacteraemias with viridans streptococci remain a problem. Therefore we treated 6 patients in the first 15 episodes empirically with benzylpenicillin if they had a high temperature; in the other 24 episodes we added phenoxymethylpenicillin orally for 10 days to the prophylactic regimen of 15 patients who were treated with high-dose cytarabine. cause