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a Division of Cardiac Surgery, Department of Anesthesia and Critical Care, Massachusetts General Hospital Heart Center, Boston, Massachusetts
b Cardiac Anesthesia Division, Department of Anesthesia and Critical Care, Massachusetts General Hospital Heart Center, Boston, Massachusetts
c Cardiology Division, Massachusetts General Hospital Heart Center, Boston, Massachusetts
Accepted for publication March 12, 2008.
* Address correspondence to Dr Agnihotri, Massachusetts General Hospital, Department of Surgery, Division of Cardiac Surgery, Box 642, 55 Fruit St, Boston, MA 02114 (Email: aagnihotri{at}partners.org).
| Adult cardiac surgery:
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| Abstract |
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Methods: Between 2002 and 2006, 391 patients with stenotic AV disease but no structural mitral valve disease underwent AVR without coronary artery bypass grafting. Excluded were 164 patients with combined aortic and mitral intervention, right heart surgery, or moderate to severe aortic insufficiency, to yield a final study group of 227 patients. Follow-up echographic evaluation of MR was obtained in 87 of 219 patients (40%) discharged alive without mitral valve intervention.
Results: Overall mortality was 3.5%. After AVR, intraoperative MR severity improved in 66% of patients. Independent predictors of lower postoperative MR were small left atrial size (p = 0.03), the presence of aortic insufficiency (p < 0.01), and preoperative congestive heart failure (p = 0.04). Prosthetic valve type or size was not an independent predictor of postoperative MR. After adjustment for intraoperative underestimation of MR grade, there was no difference between the postprocedural MR grade and the early or late follow-up MR grade (p = 0.6 and p = 0.8, respectively).
Conclusions: The results of this study support a conservative, tailored approach to concomitant mitral surgery in patients presenting for correction of aortic stenosis who demonstrate functional mitral regurgitation. Characteristics associated with resolution may allow for identification of patients most likely to benefit from mitral valve repair or replacement.
Patients who require surgical treatment of aortic stenosis often present with concomitant mitral regurgitation (MR). When the MR is severe, a double-valve operation with mitral valve repair or replacement is indicated. In most patients, MR is less severe and surgical decision making is influenced by an expectation that there will be a reduction in MR with relief of the gradient across the aortic valve (AV) [1].
Limited data exists on the incidence and resolution of secondary or "functional" MR in patients presenting with aortic stenosis. The objective of this study was to characterize the prevalence of concomitant MR and factors associated with its resolution.
| Patients and Methods |
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Patients with normal valve leaflets or otherwise normally functioning mitral valves despite mild calcification of the posterior annulus or leaflet were included in the study and were defined as having secondary or "functional" MR. We also included patients who underwent AVR with concomitant aortic annular enlargement procedures and atrial septal defect repairs. We excluded patients with structural mitral valve disease, mitral stenosis, combined procedures involving coronary artery bypass grafting (CABG), treatment of endocarditis, right heart valve procedures, and patients with a preoperative diagnosis of moderate or severe aortic insufficiency (AI) so that patients presenting with aortic stenosis as the primary indication for intervention were selected.
Preoperative, operative, and immediate postoperative data were obtained from a repository containing validated data elements through an internal auditing process. Additional information was obtained by review of the intraoperative echocardiograms. Patient mortality was defined as death within 30 days of operation. Morbidities were defined by The Society of Thoracic Surgeons data definitions document (version 2.51.1) [2]. Echocardiographic follow-up was obtained by querying the institutional echocardiographic database, patient records, and correspondence from referring cardiologists.
Echocardiography
Intraoperative, two-dimensional transesophageal echocardiography (TEE) was performed in all patients. Omniplane-3 Ultra-Band (Hewlett-Packard, Andover, MA) TEE probe (frequency, 2 to 7 mHz) transducers connected to Philips Sonos 5500 (Philips Medical Systems, NA, Bothell, WA) standard echocardiography consoles were used to perform the TEE studies. Previously recorded images were used to quantitatively assess the severity of functional MR immediately before and after surgical intervention. All measurements and assessments were performed on patients under general anesthesia.
One appropriately trained observer (E. W.) reviewed all echocardiograms. These results were verified by two expert echocardiographers (E. A., M. A.) to confirm accuracy. In addition to preoperative and postoperative MR grade, measurements were made of left atrial size, left ventricular wall thickness, and left ventricular internal diameter. The severity of MR was measured using the vena contracta method, as previously described [3].
The American Society of Echocardiography guidelines for evaluation of the severity of MR state that a vena contracta width (VCW) of less than 0.3 cm is considered a mild lesion, and a VCW of 0.7 cm or more is severe [4]. Values within these parameters are moderate lesions. A midesophageal 4-chamber view (transducer angle, 0° to 20°) and the midesophageal long-axis view (transducer angle, 120° to 135°) were used to obtain the VCW measurements. Left atrial size was measured from the midesophageal 4-chamber view from the lateral wall to the interatrial septum, and inferior left ventricular wall thickness and internal diameter were measured from the transgastric, short-axis view at end-diastole. Trabeculae carnea and papillary muscles were excluded for wall thickness measurements. At least three measurements were taken, and the mean value was calculated [5].
Aortic Valve Orifice Area
The in vivo valve area for the prosthetic AV was estimated using the effective orifice area (EOA) and geometric orifice area (GOA) of the valve prosthesis. The EOA was derived from the manufacturer's published values of projected in vivo EOA. This value was indexed to body surface area to yield the indexed effective orifice area (iEOA) of the valve. The GOA was also considered as a potentially important variable. It was calculated using the internal diameter of the valve (GOA =
x inner ring radius2). Indexing to the body surface area yielded the indexed geometric orifice area (iGOA) [6].
For the purposes of seeking relationships in valve size selection and outcomes, including resolution of MR, the iEOA and iGOA were both considered to be continuous variables. To facilitate tabular representation, an iEOA of less than 0.65 cm2/m2 and an iGOA of less than 1.2 cm2/m2 were defined as "patient-prosthesis mismatch" in the present study [7–9]. EOA and GOA values used in this study were consistent with those used in other studies (Appendix) [10].
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2 analysis of binary variables was performed. Logistic multivariable regression analysis with stepwise forward selection was used for binary outcomes, and linear multivariable regression was used for modeling of continuous outcomes. Criteria for entry and retention into multivariable models were set at the 0.1 and 0.05 confidence level, respectively. Only variables significant at the 0.1 level were considered for the multivariable analyses. A second logistic regression analysis was conducted to determine the factors associated with achieving postoperative mild MR. For this analysis, the 227 patients with isolated AVR were considered. A depiction was created from the regression equation, and 70% confidence intervals were applied. For multivariable analysis, missing data or variables were standardized to the mean of the known group.
In a secondary exploratory analysis, we assessed the pattern of change in mitral valve regurgitation grade for 87 patients (40%) discharged alive who had no procedure performed on the mitral valve and in whom we were able to obtain follow-up echocardiography evaluation of the mitral valve. To be consistent with follow-up echocardiography reports, mitral valve regurgitation grade was defined in four categories as none/trace, mild, moderate, and severe. A mixed-effects ordinal logistic regression model [11] was used to account for the correlation between repeated echocardiography measurements and was calculated using the NLMIXED procedure in SAS 9.1 software (SAS Institute, Cary, NC). We defined five time points for echocardiography measurements: baseline (preoperative), intraoperative preprocedure, intraoperative postprocedure, early follow-up (<30 days), and late follow-up (700 ± 506 days). Values of p < 0.05 were considered to be statistically significant.
| Results |
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Early and Late Follow-Up Change in MR
Amongst the 87 patients (40%) discharged alive who had no procedure performed on the mitral valve and in whom late echocardiographic information was available, the relationship of pre- and postoperative transthoracic echocardiographic (TTE) to intraoperative transesophageal echocardiographic (TEE) assessment of MR was investigated. In this group, more patients presented moderate MR in the preoperative TTE (19.9%) compared with the intraoperative preprocedural TEE (9.9%) (odds ratio [95% confidence interval]: 3.28 [1.65–6.52]; p = 0.01). The intraoperative underestimation of MR grade was estimated by the preoperative–intraoperative preprocedural difference in the MR grade. After adjustment for this underestimation, there was no difference between the postprocedural presence of moderate MR (7.1% by TEE) and the early (OR 0.74 [0.23–2.40]; p = 0.6) or late (OR 1.15 [0.42–3.13]; p = 0.8) follow-up presence of moderate MR. Moreover, the MR grade did not progress to "severe" in any patient during early or late follow-up.
| Comment |
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Decisions regarding surgical treatment are challenging given incomplete information. Without mitral intervention, there is evidence to suggest that relief of the AV gradient alone should cause immediate improvement in left ventricular pressure, with some reduction in MR. Additional benefit may be achieved over time with regression of left ventricular hypertrophy and resolution of volume overload. Avoiding unnecessary additional operations in these patients may reduce morbidity, especially given the sensitivity of the hypertrophied heart to ischemia.
Despite these observations, some groups recommend an aggressive approach to operating on the mitral valve. Supporting this idea is the observation that double-valve operations for aortic stenosis and secondary MR are low risk and have impressive results [12]. The use of aggressive therapy is further supported by data showing that concomitant moderate to severe MR does not improve in half the patients and that it is increased in a small subgroup of patients [13–15]. Another study observed that no difference in survival, but isolated AVR for patients with preoperative MR exceeding 2 had increased composite end points of CHF and reintervention. These authors identified several important risk factors, including left atrial size exceeding 5 cm, AV gradient of less than 60 mm Hg, and atrial fibrillation [16]. On the other extreme, some believe that repair or replacement is unnecessary unless patients clearly demonstrate severe MR. Several reports have documented minimal or no impact on early morbidity when there is no intervention on the mitral valve [1, 17–19].
Other recent reports have included patients with mixed mitral pathology, or concomitant CABG [20]. These factors may complicate the interpretation of changes in MR in the isolated AVR population. In a previous analysis, we documented a reduction in MR by CABG alone [21]. In the case of patients with structural mitral valve disease, it is generally known that the degree of benefit from isolated AVR will be limited, and we did not include this population in the present study.
In an attempt to provide information for surgical decision making, the current analysis identified several characteristics that were independently associated with changes in MR:
It has previously been argued that the concept of patient-prosthesis mismatch may affect the success of corrective AV operations [7, 8, 23]. Our study supports previous work documenting the lack of relationship between indexed valve size with death and postoperative functional recovery [24, 25]. The choice of valve size did not appear to impact the resolution of MR. In addition, iEOA was not associated with increased early death nor was it an independent risk factor by multivariable analysis. Performance of aortic root enlargement was unrelated to the risk of death or reduction in MR in our small study population.
Previous studies have used categoric measurements of MR that have been less precise than those used in this study. Because categoric classifications are often too coarse to allow optimal decision making and are prone to observer error and bias, it is important for the surgeon to obtain a quantitative assessment of MR. Our approach was to measure the degree of MR using the VCW method, which has been validated with TEE and is an accepted method that provides an accurate quantitative assessment of the degree of MR for both central and eccentric jets [3, 5, 25]. The VCW is especially appropriate in the operative setting because its accuracy is less dependent on loading conditions [3, 4, 26].
The principal limitation of this study is that it is primarily based on an intraoperative assessment of the MR, with limited postoperative follow-up data. Previous reports have demonstrated that echocardiographic data obtained 10 minutes postoperatively were comparable with data acquired after 1 day [25]. We recognize that the remodeling that occurs after AVR may lead to delayed changes that cannot be immediately observed. Late changes in preload or afterload associated with general anesthesia are additional limitations to interpretation of this study.
In addition, variability of quality and completeness of the recorded echocardiographic studies limited our ability to obtain a complete set of all four desired echocardiographic measurements in 20% of the patients. In these patients, the echocardiographic results did not allow a full set of variables because the goal was to extract the maximum amount of data without including data that were not clearly recorded. As a retrospective study, follow-up echocardiography measurements were incomplete and opportunistic. These were performed in the context of a routine follow-up by the referring cardiologist. Given that an echocardiographic examination may be more likely in the context of unexpected physical examination findings or clinical course, this may represent a biased sample of the overall study population. If so, this bias should tend to make regurgitation appear more likely than it would be in a complete sample.
In conclusion, the results of this study support a conservative, tailored approach to concomitant mitral surgery in patients presenting for correction of aortic stenosis who demonstrate functional regurgitation. Mitral annuloplasty or replacement appears warranted in patients with severe regurgitation. Mitral operations may be avoided in essentially all cases of mild regurgitation. For the large group of patients with moderate regurgitation, identified patient characteristics may aid in selection of patients for whom more aggressive surgical treatment is warranted.
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| Acknowledgments |
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| References |
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