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Original Articles: Cardiovascular

Enlargement of the Small Aortic Root During Aortic Valve Replacement: Is There a Benefit?

^a Division of Cardiac Surgery, University of Ottawa Heart Institute, Ottawa, Ontario, Canada
^b Department of Epidemiology, University of Ottawa, Ottawa, Ontario, Canada

Accepted for publication July 23, 2007.

^_* Address correspondence to Dr Ruel, University of Ottawa Heart Institute, 40 Ruskin St, Suite 3403, Ottawa, Ontario, K1Y 4W7, Canada (Email: mruel{at}ottawaheart.ca).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment References

 
Background: Aortic root enlargement (ARE) at the time of aortic valve replacement (AVR) is an often proposed but still unproven technique to prevent prosthesis-patient mismatch. To evaluate the risks and benefits of ARE, we examined the outcomes of patients with small aortic roots who underwent AVR with or without the use of ARE.

Methods: Patients (n = 712) with small aortic roots who underwent AVR were prospectively followed (follow-up, 3,730 patient-years; mean, 5.2 ± 4.1 years). All patients had a small aortic annulus that would have led to the insertion of an aortic prosthesis of 21 or less in size. Multivariate techniques were used to compare outcomes between patients who underwent AVR alone (n = 540) versus AVR plus ARE (n = 172).

Results: Aortic cross-clamp times were 9.9 minutes longer in the AVR+ARE group (p = 0.0002). There were no differences in reopening or stroke rates or perioperative mortality (all p = not significant). All patients in the AVR-alone group received size 19 to 21 prostheses, whereas 51% of the AVR+ARE patients received size 23 prostheses. Postoperative gradients were reduced (p < 0.01) and indexed effective orifice areas were larger (p < 0.0001) in the AVR+ARE group. While the incidence of postoperative prosthesis-patient mismatch (indexed effective orifice area 0.85 cm²/m²) was lower in the AVR+ARE group (p < 0.0001), the presence of mismatch did not significantly impact long-term outcomes after surgery. The ARE was associated with a trend toward better freedom from late congestive heart failure (p = 0.19), but not an improvement in long-term survival (p = 0.81).

Conclusions: For patients with small aortic roots, ARE at the time of AVR is a safe procedure that reduces postoperative gradients and the incidence of prosthesis-patient mismatch. However, ARE does not appreciably improve long-term clinical outcomes.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment References

 
The goals of aortic valve replacement (AVR) are to reduce pressure and volume overload on the left ventricle, relieve symptoms, and improve survival in patients with advanced aortic valve disease [1]. Ideally, postoperative transprosthetic pressure gradients should be minimal. However, high-pressure gradients may be encountered after surgery despite normally functioning prostheses, especially in patients who received small-sized prosthetic valves, and may result in postoperative left ventricular outflow tract obstruction and prosthesis-patient mismatch (PPM). First described by Rahimtoola in 1978, PPM is a condition in which the "effective prosthetic valve area, after insertion into the patient, is less than that of a normal valve" [2]. Subsequently, Pibarot and Dumesnil [3] defined PPM as a prosthetic valve effective orifice area (EOA) indexed to body surface area of 0.85 cm²/m² or less. We and others have documented worse postoperative outcomes in AVR patients with PPM, with less symptomatic improvement [4–6], less left ventricular mass regression [4, 6], and poor early and late survival after surgery [6–9].

Patients with small aortic roots, especially those with a large body surface area, are at high risk for having PPM after AVR. To minimize postoperative gradients and left ventricular outflow tract obstruction, several strategies have been developed to enlarge the small aortic root at the time of surgery, including the Nicks [10], the Konno [11], and the Manouguian [12] procedures. A number of cardiac surgery centers have reported their experience with aortic root enlargement (ARE) procedures, suggesting that these operations are both safe and feasible [12–15]. However, others have cautioned against the routine use of ARE because of its technical difficulty and its possible association with adverse outcomes [16, 17]. To our knowledge, data evaluating the effect of ARE on the incidence of postoperative PPM and late clinical outcomes are lacking. Therefore, the purpose of this study was to assess the risks and benefits of ARE by comparing the hemodynamic and clinical outcomes of patients with small aortic roots who underwent AVR with or without the use of ARE.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment References

 
Patient Population and Follow-Up
This study focused on patients with small aortic roots. Patients (n = 712) with small aortic roots who underwent AVR were prospectively followed between 1989 and 2006 at the University of Ottawa Heart Institute. All patients were 18 years or older and had a small aortic annulus identified before or at surgery that would have led to the insertion of an aortic prosthesis of size 21 or smaller. Patients were excluded from the study population if they received stentless prostheses or if they received prostheses that are no longer commercially available. Patients were also excluded from the study population if they did not survive the perioperative period, except for the purposes of reporting procedural data and perioperative mortality rates. Of the 712 patients in this cohort, 540 patients underwent AVR and 172 underwent AVR plus ARE (AVR+ARE). After AVR, patients were assessed 6 months postoperatively and thereafter on an annual basis by a physician in a dedicated valve clinic. At each visit, patients underwent a medical history focused on the determination of functional status and the occurrence of valve-related complications, a physical examination, electrocardiogram, chest radiograph, complete blood count, serum chemistries, and international normalized ratio determinations when applicable. The methods of the valve clinic follow-up have been reviewed and approved by the University of Ottawa Heart Institute Human Research Ethics Board. Before 2004, a waiver of consent was granted by the Board. Since 2004, all valve clinic patients have provided explicit, fully informed consent for enrollment.

All patients were followed for at least one outpatient visit. Surgeries were performed between January 24, 1989, and August 4, 2006, and the closing interval for vital status determination was April 1 to May 5, 2007. The total follow-up for the entire cohort was 3,730 patient-years (mean, 5.2 ± 4.1 years; maximum, 17.5). The follow-up period for the patients who had AVR alone was 2,848 patient-years (mean, 5.3 ± 4.3 years; maximum, 17.5), and for the patients who had AVR+ARE, the follow-up was 883 patient-years (mean, 5.1 ± 3.8 years; maximum, 15.0).

Prostheses and Root Enlargement Procedure
The decision whether to perform an ARE was taken by the operating surgeon, depending on the patient’s age and comorbid conditions, the anatomy of the aortic root, and the surgeon’s judgment and comfort level. The ARE was performed based upon the techniques of Nicks and associates [10] and Manouguian and Seybold-Epting [12] using either autologous pericardium or Hemashield (Boston Scientific, Natick, Massachusetts) patches and 4-0 Prolene (Ethicon, Somerville, New Jersey). The ARE technique enabled the insertion of a prosthetic valve at least one size larger than the original annulus could accommodate. Prosthesis type and size were documented in all patients. Valve sizing and selection were performed with the sizers provided by each respective prosthetic valve manufacturer. Data were collected from operative records to audit technical details regarding the root enlargement procedures.

Echocardiograms
All patients underwent a complete M-mode, two-dimensional and Doppler transthoracic echocardiogram before and after AVR, and thereafter as clinically indicated. Measurements were documented from the M-mode recordings as per the recommendations of the American Society of Echocardiography [18]. The EOA for each prosthesis type and size was obtained from the literature of patients with normally functioning prostheses [5, 19, 20], and averaged if more than one published value was available. This was supplemented with phase I regulatory data provided by the valve manufacturer if published data were insufficient with respect to a specific prosthesis size. The indexed EOA was obtained by dividing the EOA by the patient’s body surface area at the time of operation. PPM was defined a priori as an indexed EOA of 0.85 cm²/m² or less, as this constitutes the most common definition of PPM in the literature [5, 19, 21]. To account for the differences between the sizes of the different prostheses used in this study, the actual internal and external diameters for each prosthesis type and size were determined from the literature [20].

Statistical Analyses
Clinical outcomes
Data were analyzed in Intercooled Stata 9.2 (Stata, College Station, Texas). Prosthesis hemodynamics and clinical outcomes were compared between small aortic root patients treated with AVR versus those treated with AVR and ARE. Continuous data are presented as a mean ± SD and were compared between groups using unpaired two-sided Student’s t tests for parametric data and Wilcoxon rank sum tests for nonparametric data. Categorical data are presented as proportions and were compared between groups using a Fisher’s exact test. Statistical significance was set at a p value of less than 0.05.

A composite congestive heart failure (CHF) endpoint was defined a priori as (1) New York Heart Association (NYHA) functional class III or IV for more than 4 consecutive weeks or (2) death for which the primary or main contributing diagnosis was CHF [5]. Clinical impressions were corroborated with physical examination, chest radiograph, electrocardiogram, and echocardiographic findings. Deaths from an unknown cause were not considered to result from CHF and were treated as a censored event if the patient had not previously experienced NYHA class III or IV symptoms. Nonparametric estimates of freedom from all-cause death and freedom from the composite CHF endpoint were determined using the Kaplan-Meier method and are reported as mean ± SE.

Multivariate analyses
Potential univariate predictors of outcomes were individually tested for equality with a log-rank test. To account for positive or negative confounding, multivariate Cox proportional hazards models were developed by incorporating all variables that had a p value of 0.20 or less on log-rank testing. Stepwise forward selection and backward elimination techniques were employed with p = 0.20 for entry and removal criteria. Risk factors (left ventricular dysfunction, age, atrial fibrillation, preoperative heart failure functional class, coronary artery disease, smoking, insulin-dependent diabetes mellitus, postoperative hypertension) for decreased survival and freedom from CHF after AVR that have been previously identified [5] were considered in each model. Effect modification between factors was tested with the use of interaction terms in the models. Scaled Schoenfeld residuals were employed to assess the Cox proportional hazard assumption for each variable. Stratified Cox analysis was applied if the proportional hazard assumption was not met for a particular factor. Hazard ratios (HR) are reported along with standard errors or 95% confidence intervals (CI).

	Results

Top Abstract Introduction Patients and Methods Results Comment References

 
Patient Characteristics
The preoperative characteristics of the AVR and AVR+ARE groups are presented in Table 1. Preoperative characteristics were equivalent between the groups, except patients in the AVR+ARE group were significantly younger (p = 0.03). Operative characteristics differed between the two groups, as demonstrated in Table 2. The ARE procedure was performed based on either the techniques of Nicks [10] (28.5%) or Manouguian [12] (71.5%). Patients in the AVR+ARE group were less likely to undergo intervention on the mitral or tricuspid valve (all p < 0.05). Baseline and operative factors that differed between the two groups with a p value of 0.20 or less were included in the multivariate analysis models examining long-term outcomes.

View larger version (32K): [in this window] [in a new window]   Fig 1. Postoperative transprosthesis gradients in patients with small aortic roots who underwent aortic valve replacement (AVR [shaded bars]) or AVR plus aortic root enlargement (ARE [open bars]). Both mean and peak transprosthetic gradients were significantly lower in the AVR plus ARE group.

View larger version (17K): [in this window] [in a new window]   Fig 2. (A) Survival and (B) freedom from New York Heart Association class III or IV congestive heart failure (CHF) or CHF death among patients with small aortic roots who underwent aortic valve replacement (AVR [dotted line]) or AVR plus aortic root enlargement (ARE [solid line]). After adjusting for potential confounders in the multivariate analysis, an ARE was associated with a trend toward better long-term freedom from CHF (p = 0.19) but not long-term survival (p = 0.81).

	Comment

Top Abstract Introduction Patients and Methods Results Comment References

 
The surgical management of the small aortic root at the time of AVR has been discussed in the cardiac surgery literature for more than 30 years. After initial attempts at supra-annular enlargement, the first report of aortic annular enlargement with a posterior incision was made by Nicks and colleagues [10] in 1970. Subsequently, in 1975, Konno and associates [11] demonstrated their surgical technique involving anterior annular enlargement for congenital aortic stenosis. In the late 1970s, Manouguian and Seybold-Epting [12] reported a novel enlargement technique through the commissure between the left and noncoronary sinuses of Valsalva [12]. These surgical strategies were developed with the objectives of implanting prostheses as large as possible to minimize postoperative gradients. Recent investigations documenting the adverse effects of postoperative PPM after AVR have renewed interest in the ARE operation [4–8, 19]. However, there remains a general perception among cardiac surgeons that ARE procedures increase the risk and technical difficulty of aortic valve surgery [16, 17].

Thus, the purpose of this study was to evaluate whether the addition of an ARE to an AVR in a patient with a small aortic root increases the perioperative risk and to determine whether it is associated with any clinical benefit. In this cohort of patients with small aortic roots followed annually after AVR, we observed that (1) the addition of an ARE to an AVR increased the aortic cross-clamp time, on average, by 9.9 minutes; (2) there was no significant increase in perioperative morbidity or mortality associated with the addition of an ARE; (3) patients with small aortic roots who underwent root enlargement procedures received larger prostheses, with lower postoperative gradients and larger EOAs; (4) patients who underwent ARE+AVR had a lower incidence of postoperative PPM, but the presence of PPM did not independently impact long-term outcomes; and (5) the addition of an ARE did not significantly improve long-term clinical outcomes among the entire cohort. Thus, patients with small aortic roots treated with ARE+AVR have better hemodynamic outcomes after surgery, without suffering an increased risk of perioperative morbidity or mortality. However, the ARE procedure did not appreciably improve long-term clinical outcomes after AVR.

Early reports of the ARE experience in the 1980s suggested that these operations were both safe and feasible, albeit at the expense of longer aortic cross-clamp times [12, 22, 23]. In 1997, however, Sommers and David [16] published a negative experience with the ARE procedure in a retrospective review of 530 patients who underwent AVR with Hancock II prostheses. Of this cohort, 98 patients underwent ARE in an effort to avoid postoperative PPM. The addition of an ARE increased the aortic cross-clamp time (by 11 minutes), increased the rate of perioperative reopening for bleeding (10.2% versus 6.7%, p = 0.23, AVR+ARE versus AVR), and increased the operative mortality rate (7.1% versus 3.5%, p = 0.10, AVR+ARE versus AVR) [16]. With similar long-term outcomes between the two groups, and yet increased early morbidity and mortality, there appeared to be no clinical advantage to the routine use of ARE at the time of AVR.

Recent experience with the ARE procedure has been more favorable, with reported operative mortality rates less than 4% in case series [13, 14]. Even in centers initially reporting high operative mortality rates, increasing experience has led to declining mortality rates (7.2% down to 2.9%) [16, 24]. The operative mortality during the era of the current study is higher than expected (6% to 7%), but this may be related to the surgical cohort (patients with small aortic roots), a high proportion of female patients, and a high proportion of patients requiring coronary revascularization. Both female sex and small prosthesis size have been demonstrated to increase AVR perioperative mortality [9]. Nevertheless, it appears that similar perioperative outcomes can be achieved in patients with small aortic roots undergoing AVR+ARE compared with AVR alone. The results of the current study demonstrate that, in experienced hands, there is no additional risk of perioperative bleeding or mortality with the addition of an ARE procedure at the time of AVR. The ARE procedure adds approximately 9.9 minutes of aortic cross-clamp time and 12.2 minutes of cardiopulmonary bypass time to the length of the operation.

Our study has documented the hemodynamic benefit of the ARE in patients with small aortic roots undergoing AVR. The ARE procedure enabled the insertion of larger prosthetic valves (size 23 in more than half the patients), reduced postoperative gradients, and reduced the incidence of postoperative PPM. The concept of PPM was first introduced by Rahimtoola [2] in 1978 to describe the condition in which the prosthetic valve orifice area is less than that of the native human valve. Subsequent studies examining the physiologic sequalae of PPM have fostered the recommendation that the indexed EOA of an aortic prosthesis should ideally be greater than 0.85 cm²/m² to minimize postoperative gradients and improve clinical results [19]. There continues to be controversy in the literature as to the relevance of PPM. In the current study, we found that ARE reduced the incidence of postoperative PPM, but PPM did not significantly impact long-term outcomes after AVR, regardless of whether patients underwent ARE. Earlier work from our group has demonstrated that PPM is an independent predictor of adverse outcomes after AVR specifically in patients with preoperative left ventricular dysfunction or low-gradient aortic stenosis [4, 6]. However, we did not have enough statistical power in the present study to focus on the outcomes of these patients.

Previous ARE studies have produced conflicting results when comparing outcomes in patients who underwent AVR+ARE to those who underwent AVR alone [13, 16]. In 1996, Kitamura and colleagues [13] reported a series of 45 patients with small aortic annuli (19 mm) who underwent AVR with or without ARE procedures. Although early mortality was similar between the two groups (3.6% versus 5.9%, p = not significant, AVR+ARE versus AVR), 10-year survival (85.7% versus 62.7%, p < 0.10, AVR+ARE versus AVR) and 10-year freedom from valve-related events (81.0% versus 58.8%, p < 0.05, AVR+ARE versus AVR) were improved in the AVR+ARE group, suggesting that long-term outcomes may be superior after AVR with ARE [13]. In the current study, we found that the addition of ARE for patients with small aortic roots was associated with a trend toward better long-term freedom from CHF (HR: 0.6; 95% CI: 0.3 to 1.3; p = 0.19), but not long-term survival (HR: 1.1; 95% CI: 0.7 to 1.6; p = 0.81) after AVR.

Whether ARE procedures improve the long-term outcomes in patients with small aortic roots can not definitively be determined in the absence of prospective data. However, we believe that a randomized controlled trial prospectively evaluating the ARE operation is unlikely ever to be conducted. Complicating the issue, enlargement of the aortic root is generally applied to patients with small aortic roots who are deemed to be good operative candidates with prospects for excellent long-term survival [16]. In the current study, the AVR+ARE patients were significantly younger compared with those who underwent AVR without root enlargement. In contrast, high-risk AVR patients with lower probability of long-term survival, as well as those with long cross-clamp times due to concomitant procedures (namely, mitral surgery), may be less likely to undergo aortic root enlargement. Although multivariate analyses were used in this study, confounding by indication, a form of selection bias, can not be fully accounted for by multivariate analyses [7].

Limitations
Other strategies have been described for the management of the small aortic root at the time of AVR, including the use of stentless valves [25]. However, the ARE procedure is the favored approach at our institution, thus limiting our ability to draw comparisons to other techniques. Group differences and known confounders were controlled for in this observational study by using multivariate analysis. Despite the sample size and statistical adjustments applied, however, unmeasured or unknown confounders may have influenced the results. Moreover, the Cox proportional hazards regression method requires an assumption of independent censoring that may not always be met. In this regard, it is possible that patients lost to follow-up after a number of visits may have had subsequent outcomes that were not accounted for in the analyses. Finally, like that of other observational cohorts, the results of these analyses may not be generalizable to all patients with small aortic roots who have undergone AVR at other centers because this study represents a single institution’s experience.

In conclusion, for patients with small aortic roots, the addition of an ARE procedure at the time of AVR slightly increases the length of the operation, but does not increase perioperative morbidity or mortality. The ARE procedure improves postoperative transprosthesis gradients and reduces the incidence of PPM after surgery. However, ARE does not appreciably improve long-term clinical outcomes for patients with small aortic roots undergoing AVR.

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Top Abstract Introduction Patients and Methods Results Comment References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Alexander Kulik Roy G. Masters Fraser D. Rubens Paul J. Hendry Thierry G. Mesana Marc Ruel Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kulik, A. Articles by Ruel, M. Search for Related Content PubMed PubMed Citation Articles by Kulik, A. Articles by Ruel, M. Related Collections Valve disease Related Article