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J Thorac Cardiovasc Surg 2004;128:916-924
© 2004 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

Recurrent mitral regurgitation after annuloplasty for functional ischemic mitral regurgitation

^a Department of Thoracic and Cardiovascular Surgery, Biostatistics and Epidemiology
^b Department of Cardiovascular Medicine
^c The Cleveland Clinic Foundation, Cleveland, Ohio

Received for publication April 23, 2004; revisions received July 22, 2004; accepted for publication July 26, 2004.

^* Address for reprints: A. Marc Gillinov, MD, The Cleveland Clinic Foundation, 9500 Euclid Ave/Desk F24, Cleveland, OH 44195 (E-mail: gillinom{at}ccf.org).

	Abstract

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 
OBJECTIVES: We sought to characterize the temporal return of mitral regurgitation after annuloplasty for functional ischemic mitral regurgitation; to identify its predictors, particularly with respect to annuloplasty type; and to determine whether annuloplasty type influences survival.

METHODS: From April 1985 through November 2002, 585 patients underwent annuloplasty alone for repair of functional ischemic mitral regurgitation, generally with concomitant coronary revascularization (95%). A flexible band (Cosgrove) was used in 68%, a rigid ring (Carpentier) in 21%, and bovine pericardial annuloplasty (Peri-Guard) in 11%. Six hundred seventy-eight postoperative echocardiograms were available in 422 patients to assess the time course of postoperative mitral regurgitation and its correlates. Most echocardiograms were performed early after the operation (median, 8 days); 17% were performed at 1 year or beyond.

RESULTS: During the first 6 months after repair, the proportion of patients with 0 or 1+ mitral regurgitation decreased from 71% to 41%, whereas the proportion with 3+ or 4+ regurgitation increased from 13% to 28% (P < .0001); the regurgitation grade was stable thereafter. The temporal pattern of development of 3+ or 4+ regurgitation was similar for Cosgrove bands and Carpentier rings (25%) but substantially worse for Peri-Guard annuloplasties (66%). Small annuloplasty size did not influence postoperative regurgitation grade (P = .2), although Cosgrove bands were used in most patients receiving 26- and 28-mm annuloplasties. Freedom from reoperation was 97% at 5 years. Annuloplasty type was not associated with survival.

CONCLUSIONS: Although initial mitral valve replacement would eliminate the risk of postoperative mitral regurgitation, this strategy has been associated with reduced survival. Therefore the development of additional techniques is necessary to achieve more secure repair of functional ischemic mitral regurgitation.

The objectives of this study were to (1) characterize the temporal return of mitral regurgitation (MR) after annuloplasty alone for functional IMR; (2) to identify risk factors for the return of MR, particularly with respect to annuloplasty type; and (3) to determine whether annuloplasty type influences survival.

	Patients and methods

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 
Study group
From April 1985 through November 2002, 585 patients underwent annuloplasty alone for repair of functional IMR (see the "Definitions" section) at The Cleveland Clinic Foundation. All had at least 2+ (moderate) MR on echocardiography, left ventriculography, or both.

Concomitant procedures included coronary artery bypass grafting (585 [95%] patients) and tricuspid valve repair (62 [11%] patients). Patients who underwent a concomitant aortic valve procedure or left ventricular restoration were excluded.

Annuloplasty types included the Carpentier-Edwards Classic annuloplasty ring (n = 122 [21%]; Carpentier ring; Edwards Lifesciences, Irvine, Calif), the Cosgrove-Edwards annuloplasty system (n = 396 [68%]; Cosgrove band; Edwards Lifesciences), and bovine pericardial annuloplasty (n = 67 [11%]; Peri-Guard; Bio-Vascular, Saint Paul, Minn). Early in the series, Carpentier rings were used most commonly, and downsizing was inconsistent. Since 1997, most patients have received Cosgrove bands, with a practice of implanting 26-mm bands in women and 28-mm bands in men (see Electronic Appendixes 1 and 2 available at www.mosby.com/jtcvs). Median annuloplasty size was 28 mm for Cosgrove bands and 30 mm for Carpentier rings.

View larger version (17K): [in this window] [in a new window]   Annuloplasty type use by calendar year. Proportion of patients receiving Carpentier-Edwards classic annuloplasty ring (open circles), Cosgrove-Edwards annuloplasty system (filled circles), and Peri-Guard bovine pericardial annuloplasty (open squares) by year of operation.

View larger version (23K): [in this window] [in a new window]   Electronic Appendix 2. Annuloplasty ring size. Number of patients receiving each annuloplasty ring size.

Progression of MR after annuloplasty
Six hundred seventy-eight postrepair echocardiograms were available in 422 (75%) patients to assess the return of MR. These were obtained sporadically, with no set schedule for echocardiographic follow-up. Median time to postrepair echocardiography was 8 days; 75% (508) of echocardiograms were obtained within the first 2 months after the operation, and 17% (116) were obtained beyond 1 year. Patients who had a postoperative echocardiogram differed from those who did not; the latter were more likely to be in a higher preoperative New York Heart Association functional class, to have required preoperative intra-aortic balloon pump support, to have had a previous cardiac operation, and to have had more severe preoperative MR (see Electronic Appendixes 3 and 4 available at www.mosby.com/jtcvs).

Data analysis
Databases used in this study were approved by the institutional review board for use in research.

Selection bias
Because annuloplasty type was not selected randomly, factors associated with increased or decreased probability of a patient receiving a Carpentier ring rather than a Cosgrove band or a Peri-Guard repair rather than a Cosgrove band were identified (see Appendix 1 for variables used in analyses).¹⁰ From these 2 analyses, we calculated the probabilities of receiving (1) a Cosgrove band, (2) a Carpentier ring, and (3) a Peri-Guard repair (see Electronic Appendix 5available at www.mosby.com/jtcvs) for each patient. These probabilities were used as balancing scores to reduce selection bias in all analyses of outcome.^11,12

Factors influencing the return of MR
Factors influencing the temporal pattern of MR after annuloplasty were identified separately for the rapidly changing early period (first 6 months after repair) and the stable phase thereafter. In each case, type of annuloplasty and its balancing score were included in the analyses, regardless of statistical significance. Other factors were sought by using the candidate variables in Appendix 1.

Mitral valve replacement
Nonparametric and parametric¹³ methods were used to estimate freedom from mitral valve replacement after annuloplasty. The number of events was too small to compare annuloplasty type.

Survival
Nonparametric and parametric multiphase hazard-based methods¹³ were used to estimate survival. Risk factors associated with the 2 hazard phases resolved were identified by using multivariable analyses with bagging,¹⁴ according to the methodology described in Electronic Appendix 5.¹⁵ Variables indicating annuloplasty type and their balancing scores were included in each hazard phase.

Presentation
Mortality and survival estimates are accompanied by asymmetric 68% confidence intervals, which are comparable to ±1 SE.

	Results

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 
Progression of MR after annuloplasty
Although high-grade (3+ or 4+) MR was uncommon immediately postoperatively, the degree of MR changed rapidly during the first 6 months and then became relatively stable (Figure 1, A). Overall, 28% of patients had 3+ or 4+ MR 6 months after the operation (Figure 1, B). Six months after Peri-Guard annuloplasty, 66% of patients had 3+ or 4+ MR (Figure 2). In contrast, early and late grades of MR were similar in patients receiving Cosgrove bands and Carpentier rings; with each, approximately 25% of patients had 3+ or 4+ MR in the first 6 months after the operation (Figure 2).

View larger version (19K): [in this window] [in a new window]   Figure 1. Progression of MR after surgical annuloplasty overall. A, All grades of MR. Curves for each regurgitation grade represent average temporal prevalence, and they sum to 100% at each point in time. Numbers below the horizontal axis represent echocardiograms available at various time points, with the number of patients in parentheses. B, Prevalence of regurgitation grades 3+ or 4+. Symbols represent crude estimates of grouped raw data. Dashed lines are 68% confidence limits of average prevalence.

View larger version (19K): [in this window] [in a new window]   Figure 2. The effect of annuloplasty type on return of 3+ or 4+ mitral regurgitation. The number of echocardiograms available at various time points is indicated, with the number of patients in parentheses. Symbols represent crude estimates of grouped raw data. Carpentier, Carpentier-Edwards Classic annuloplasty ring; Cosgrove, Cosgrove-Edwards annuloplasty system; Peri-Guard, bovine pericardial annuloplasty.

Survival
There were 37 hospital deaths (6.3%); survival was 82% at 1 year and 60% at 5 years. After accounting for other factors, neither annuloplasty type nor size was associated with time-related survival (see Electronic Appendix 6 available at www.mosby.com/jtcvs).

	Discussion

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

Progression of MR after annuloplasty
Functional IMR results from alterations in ventricular and annular geometry that decrease leaflet coaptation. Annuloplasty increases leaflet coaptation by decreasing the septal-lateral (anterior-posterior) dimension of the mitral annulus,² which does not address all mechanisms of functional IMR.¹⁶

Annuloplasty alone does not ensure successful and durable elimination of MR.^5-9,16-18 Previous reports document that 17% to 29% of patients experience early or late return of 2+ or greater MR.^5-9,16-18 However, these studies are small, and follow-up is limited, precluding detailed characterization of the temporal pattern of MR return. Furthermore, comparison between studies might be problematic because of different grading systems (eg, Is moderate MR defined as 2+ or 3+?).

Analysis of 678 postoperative echocardiograms obtained from a few days to 8 years postoperatively enabled us to examine the course of MR after annuloplasty. Most echocardiograms were obtained within 1 year of the operation, when estimates of MR degree are most reliable. MR is dynamic in the first 6 months after the operation and stabilizes thereafter.

Risk factors for return of MR
Some studies have demonstrated that various forms of suture annuloplasty are less durable than a prosthetic band or ring,^5,7,8 but von Oppell and colleagues¹⁷ report no difference. Posterior suture annuloplasty with pericardial buttressing used in this study failed to provide durable repair. The pattern of MR return was similar to that for Cosgrove bands and Carpentier rings. Few other reports compare different prosthetic annuloplasty techniques. In a smaller study with follow-up extending to only 6 weeks postoperatively, Aklog and associates⁹ found that complete resolution of IMR was more likely with Carpentier rings than with Cosgrove bands, although, as in our study, the prevalence of residual 2+ MR or greater was similar.

Recent experimental and human data confirm that the anterior mitral annular dimension and intertrigonal distance dilate in IMR.^19-21 Some have suggested that this supports use of a complete remodeling annuloplasty in patients with IMR.^20,21 However, it is reduction of the septal-lateral dimension that is most important.² Prosthetic ring or band annuloplasty more effectively reduces this diameter than does suture annuloplasty,⁷ perhaps explaining the difference in efficacy between these 2 techniques. However, data examining the effect of different prosthetic annuloplasty techniques on septal-lateral diameter are lacking.

In addition to debate over annuloplasty type, there is considerable discussion about annuloplasty size in patients with functional IMR. Most surgeons advocate an undersized annuloplasty to achieve the greatest reduction in septal-lateral dimension.^4,22,23 In patients with ischemic and nonischemic cardiomyopathies, Bolling and coworkers^22,23 have achieved excellent early and midterm results with an undersized flexible annuloplasty ring. However, there are few available data to answer the following question: How small should the annuloplasty be? Like Tahta,⁶ Aklog,⁹ and their colleagues, we found poor correlation between annuloplasty size and the return of MR. However, most of our patients received small annuloplasties (label size of 26, 28, or 30 mm); it is possible that had more patients received larger-sized annuloplasties, a difference in durability might have been detected. In addition, no patient received a 24-mm annuloplasty, and those in whom a Carpentier ring was inserted received the largest sizes. Therefore, the effect of small remodeling rigid annuloplasty (Carpentier ring) could not be examined.

Several clinical factors were associated with the return of MR. These included a higher grade of preoperative MR and more severe left ventricular dysfunction. Von Oppell and colleagues¹⁷ found that these factors increased the risk of MR recurrence after suture or ring annuloplasty, and Aklog and associates⁹ identified a higher grade of preoperative MR as a risk factor for greater postoperative MR. Others have failed to confirm these relationships.⁶ Jet direction also influenced repair durability; a central jet might indicate restriction of both the anterior and posterior leaflets, causing more severe leaflet tenting and making restoration of coaptation less probable.²⁴

Mitral valve replacement
Although return of MR was common, mitral valve replacement was not. There are several possible explanations for this observation. First, because nearly half of the patients died within 5 years of the operation, the competing risk of death might have limited the number of patients available for reoperation. Second, IMR after annuloplasty might be considered inconsequential compared with the underlying myocardial disease. Third, surgeons might be hesitant to perform a second or third cardiac operation in these elderly, high-risk patients.

Survival
As in other studies of patients with IMR, survival was limited.^1-3 Although our previous study demonstrated that pericardial annuloplasty reduced survival in patients with IMR undergoing mitral valve repair, the analysis included patients with all forms of IMR, including papillary muscle pathology. In contrast, this study focuses on that subset of patients with functional IMR, and in this population we found little association between annuloplasty type and survival. These results do not preclude a survival effect of other annuloplasty techniques not used in this study. In fact, comparing suture annuloplasty with a remodeling ring, Grossi and coworkers⁵ demonstrated reduced survival with suture annuloplasty. However, other studies have failed to identify annuloplasty type as a risk factor.^9,17

Limitations
Most of this study's findings are based on analysis of postoperative echocardiograms. Systematic scheduling of echocardiographic follow-up is not possible outside a clinical trial.^1,6,9 Although most patients had a predischarge echocardiogram, late echocardiograms were obtained sporadically at the cardiologists' discretion. Comparing patients who received postoperative echocardiograms with those who did not revealed some differences (see Electronic Appendixes 3 and 4). Patients without postoperative echocardiograms had a higher degree of preoperative MR, a factor related to more severe postoperative MR. This suggests that high-grade postoperative MR might be underestimated. Most echocardiograms were obtained in the first year after the operation, the time of greatest change in MR grade. However, 17% of echocardiograms were obtained beyond that point, providing sufficient data to characterize the temporal pattern of MR.

Because this was not a randomized study, there were differences among patients receiving different annuloplasty types. Multivariable analyses and balancing scores were used to account for these differences.

It is possible that detailed analysis of preoperative echocardiographic dimensions will reveal quantifiable risk factors for annuloplasty failure. In fact, Calafiore and associates²⁴ has suggested that excessive leaflet tenting jeopardizes repair.

We cannot address in a formal fashion the relationship between progression of MR and survival. Others have suggested that MR recurrence jeopardizes survival,^9,17 but to our knowledge, statistical methodology to test this hypothesis properly does not exist. Both recurrent MR and death are outcomes of surgical intervention. Examination of their interdependence and their relationship to surgical technique requires the development of novel statistical methodology.

Clinical inferences
A prosthetic annuloplasty band or ring should be used in patients with functional IMR. During the first 6 months thereafter, patients should be followed closely by using echocardiography. Although initial mitral valve replacement would eliminate the risk of postoperative MR, this strategy is associated with reduced survival in most patients with IMR.¹ Therefore, development of additional techniques is necessary to achieve more secure repair of functional IMR.

Discussion
Dr D. Craig Miller (Stanford, Calif). Thank you, Dr McGee, for a very fine presentation. You should be proud. Number one, I would like to compliment The Cleveland Clinic Foundation for your honesty. This is an important contribution.

Unlike mitral valve prolapse, in which the standard of care is to leave zero or negligible residual MR after repair, surgeons have played ostrich for far too long in overlooking the repair failures that we leave behind in patients with IMR. Why have we overlooked these shortcomings? For one, in many cases we most likely were just glad to have a survivor.

The debate about whether you should intervene in those cases with moderate IMR when you are performing coronary revascularization remains open, but most of the world now thinks you should do something to the valve if the degree of MR is more than 2+ on a preoperative transthoracic echocardiogram.

I have one minor quibble—despite being a believer in Gene Blackstone's statistical magic—which concerns the echocardiographic data. The median time for all echocardiographic studies was only 8 days postoperatively; you had an echocardiogram within 2 months in 75% of patients but beyond 1 year in only 17%. Yet your curves showing the recurrent rates of MR were drawn way out to 4 and 5 years, and I did not see any confidence levels or variability of the estimates, which I would expect from Dr Blackstone. Are you not extrapolating beyond what the data set reliably allows?

Dr McGee. Thank you very much for your comments, Dr Miller. We are all very much indebted to you for furthering our understanding of the complex functional anatomy of the mitral valve.

To answer your question, it is true that most of our echocardiograms were early, and 17%, as you mentioned, were after 1 year, but we did have points out to that far, and we believe our data. In addition, the echocardiograms that were obtained sporadically were done so in symptomatic patients, and it also seemed to be in patients who had more complex jets. Therefore it is likely that we were somewhat pessimistic in the return of MR, and if there is any error, it is going to be an overestimate of recurrent MR.

Dr Miller. Were these postoperative studies all Cleveland Clinic echocardiograms?

Dr McGee. Yes, they were all Cleveland Clinic echocardiograms, and they were all transthoracic studies.

Dr Miller. That explains why you do not have too many late studies, even though many were probably done elsewhere. I could turn your argument against you and speculate that this is actually an overly rosy estimate of the recurrent rate of IMR because you do not have complete echocardiographic follow-up information. Perhaps those with more severe recurrent MR and poorer left ventricular (LV) function had succumbed and therefore did not return to get a Cleveland Clinic Foundation postoperative echocardiogram. But that is an imponderable result, so let's drop it for now.

On your echocardiographic studies, were there any substantial mitral gradients? This is pertinent because in Dr Rankin's and Dr Glower's article, they were using 24- to 26-mm rings. What was the average mitral mean gradient? Are we creating any important degree of functional mitral stenosis by using these teeny rings?

Dr McGee. To my knowledge, there were not any gradients created by overdownsizing.

Dr Miller. Finally, in 2002-2003, use of the Cosgrove band dipped, whereas use of the Carpentier-Edwards Classic ring increased. What is the current practice today since the completion of this study?

Dr McGee. That would depend on which surgeon you spoke with.

Dr Miller. A very prudent answer; that is what I thought you would say.

Regarding the reoperation rate, it is low, with 97% free at 5 years, and you give us 3 reasons in the article why that might be so. Interestingly, that was the identical number Dr Glower just presented. But is it really fair to compare reoperation rates after repair for prolapse with reoperation for IMR? That is an apples to oranges comparison and just does not compute. I would wager that many patients with recurrent MR were just too sick or too old or both to even consider reoperating on them, which is distinctly different than younger patients after prolapse repair; this might be the main reason why even though 25% had severe MR 6 months later, more did not undergo reoperation. Would you agree?

Dr McGee. Yes, sir.

Dr Miller. That represents good judgment.

Dr Bruce W. Lytle (Cleveland, Ohio). I would like to interject something here. The interesting thing about it is, though, that the unadjusted survival rate of these patients is also identical to the unadjusted survival rate of Dr Glower's and Dr Rankin's patients, which is 55% at 5 to 6 years. Therefore whatever is going on there, these are very similar groups of patients in terms of survival.

Dr Miller. That is a good point, Bruce.

Finally, if we can break through our denial, which is always tough for a surgeon, and accept that simple ring annuloplasty is not enough for patients with IMR, is there anything we can add to a ring at the ventricular level to improve things, such as a Coapsys device or other method of LV reshaping? Or should we swallow our pride and do a straightforward, quick, and reliable total chordal-sparing mitral valve replacement with a bioprosthesis? Recall that 4 years ago at this meeting, the Cleveland Clinic group actually showed a 7-year survival advantage for mitral valve replacement over repair in the sickest of the 5 quintiles.

Dr McGee. That is a very good point.

I think there are some reports of chordal lengthening, but that currently is not done at the Cleveland Clinic. In certain patients I think a chordal-sparing mitral valve replacement is a good treatment. The majority of patients with ischemic MR, I think, will benefit from a ring annuloplasty, but patients with bileaflet tethering, severe LV dysfunction, and very complex jets, who are extremely sick, would most likely be best served by a chordal-sparing replacement with a bioprosthetic valve.

Dr Miller. I agree, and they certainly do not live long enough to need a mechanical valve. Historically, the very poor results we all remember after mitral valve replacement and coronary artery bypass grafting from decades ago might have been due to suboptimal myocardial protection and cutting out the whole valve and subvalvular apparatus.

Dr David Adams (New York, NY). Just another comment about apples and oranges. You used your Carpentier rings predominantly early in the late 1980s. You were not downsizing; your histograms showed your average size was 30 mm, and more were 30, 32, and 34 mm. The majority of your Cosgrove bands were size 26 and size 28 mm. It appears you had a different strategy in terms of size selection over the period of the study. Could you comment on that and how you think that might affect your direct comparison of the 2 rings?

Dr McGee. Thank you, Dr Adams. Sizing is also a function of surgeon preference. Most surgeons downsize at least 2 sizes, but your point that the Cosgrove bands tended to predominate in the smaller sizes is well taken. That was corrected per the numbers, but we were not able to demonstrate a difference, as you pointed out.

Dr Robert Frater (Broxville, NY). Your title implies very distinctly a comparison between different techniques: 2 of them are very standard in being rigid rings, and the third is a technique that requires a great deal of art to make it work at all. You obviously have condemned the pericardial annuloplasty. Would it not be fairer to say that "in our hands we were not able to make the pericardial annuloplasty work" rather than saying, given your experience, that it is automatically for everybody else a bad technique?

Dr McGee. Thank you, Dr Frater. One of the problems with looking at the pericardial annuloplasties was that there did not seem to be a systematic way of sizing them, and there was a lot of variability in that. From our understanding, most were sized to a 26-mm sizer, but that is one of the problems. It is not a standardized method, and because of that, it is hard to reproduce.

Dr Alain Carpentier (Paris, France). Well, I just rise to give a small technical recommendation; that is, we all know that in ischemic valvular disease there is a predominant dilatation in the P3 area, and as pointed out by the previous speaker, you use, in this case, pledget-supported sutures. Another alternative that I like to use in this particular area is a double-roll suture. In other words, if you place 2 rolls of sutures, then you prevent the potential ring dehiscence.

Dr Thoralf Sundt III (Rochester, Minn). Did I understand one of your final slides to show no correlation between annuloplasty technique and survival?

Dr McGee. Yes, there was no difference in terms of survival when it was corrected.

Dr Sundt. When it was corrected?

Dr McGee. For patient factors.

Dr Sundt. Therefore, if there is a profound difference in residual MR according to technique and no difference in survival according to technique, does that not imply that there is no correlation between survival and correction of the MR?

Dr McGee. We did not look specifically at survival and recurrent MR, because after extensive discussions with Dr Blackstone, we are not aware of a way to do that with the current statistical methodology.

	Electronic Appendix 1

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 

	Electronic Appendix 5. Details of statistical models bias reduction

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

Three propensity scores (propensity for receiving Cosgrove band, Carpentier ring, and Peri-Guard annuloplasty) were calculated for each patient by solving the 2 simultaneous multivariable logistic regression equations. Two of the 3 scores and their transformations, where appropriate, were then forced into multivariable analyses as balancing scores to reduce selection bias.^10,12

	Temporal pattern of follow-up MR

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 
Longitudinal ordinal regression was used to analyze the repeated measurements of postoperative and follow-up MR grade (PROC GENMOD, SAS Institute).

	Factors influencing MR development

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 
For MR grade measurements made within 6 months of repair, and separately for those made after 6 months, we initially screened variables by using ordinary multivariable logistic regression (PROC LOGISTIC, SAS Institute) and the assumption of independence of observations, with liberal entry (0.2) and retention (0.12) criteria. Because of the limited capability of PROC GENMOD to explore multivariable relations, this analysis was performed simply to identify possible candidates for our repeated measurements model. These candidate variables and their transformations, if any, were entered simultaneously into a longitudinal logistic regression model (PROC GENMOD) and then eliminated one by one until all variables remaining had a P value of .1 or less.

	Survival

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 
A parametric model was used to resolve the number of phases of instantaneous risk of death (hazard function) and to estimate shaping parameters.¹³ Multivariable analysis was performed in the hazard function domain. Preoperative and intraoperative variables used in the analyses are listed in Appendix 1, and variable selection was by bootstrap bagging, with a retention criterion of a P value of .05 or less.¹⁴ Cosgrove band and Peri-Guard annuloplasty indicators were forced into each hazard phase (leaving Carpentier ring as the reference group), as were the two balancing scores.^10,12

Electronic appendixes are available online.

 

	Footnotes

 
Read at the Eighty-fourth Annual Meeting of The American Association for Thoracic Surgery, Toronto, Ontario, Canada, April 25-28, 2004.

	References

Top Abstract Patients and methods Results Discussion Electronic Appendix 1 Electronic Appendix 5. Details... Temporal pattern of follow-up... Factors influencing MR... Survival References

 

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