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Ann Thorac Surg 2006;81:1305-1309
© 2006 The Society of Thoracic Surgeons

Original article: Cardiovascular

Prevalence and Avoidance of Patient-Prosthesis Mismatch in Aortic Valve Replacement in Small Adults

Yoshimasa Sakamoto, MD, Kazuhiro Hashimoto, MD * , Hiroshi Okuyama, MD, Hiromitsu Takakura, MD, Shinichi Ishii, MD, Shingo Taguchi, MD, Hiroshi Kagawa, MD

Department of Cardiovascular Surgery, Jikei University School of Medicine, Tokyo, Japan

Accepted for publication October 17, 2005.

* Address correspondence to Dr Hashimoto, Department of Cardiovascular Surgery, Jikei University School of Medicine, 3-25-8 Nishishinbashi, Minato-ku, Tokyo 105-8461, Japan (Email: kaz-hashi{at}jikei.ac.jp).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
BACKGROUND: It is still controversial as to whether a small prosthesis should be inserted or a small aortic annulus should be enlarged to minimize patient-prosthesis mismatch (PPM). This retrospective study reviewed our strategy for avoiding PPM.

METHODS: Isolated or combined aortic valve replacement was performed in 181 patients, including 24 patients (13.3%) aged less than 65 years with a small aortic annulus (≤ 21 mm) who underwent enlargement of the annulus by the Manouguian (n = 18) or Nicks (n = 6) procedure. In patients aged 65 years or more, a Carpentier-Edwards Perimount pericardial (CEP) valve was implanted with few exceptions. We assessed our strategy for avoiding PPM by comparison with published normal reference values for the indexed effective orifice area.

RESULTS: A CEP valve was implanted in 53 patients, and St. Jude Medical (SJM) mechanical valves were used in 128 patients. A standard 21-mm SJM valve was only used in 4 patients and no 19-mm valves were employed. However, 19-mm CEP valves were used in 12 older patients with a small body surface area (1.43 ± 0.14 m2). No patient receiving an SJM valve had an indexed effective orifice area of 0.85 cm2/m2 or less, and PPM developed in only 2 (3.8%) of 53 patients receiving CEP valves. Consequently, the prevalence of PPM was 1.1%. The 10-year survival rates of patients receiving CEP or SJM valves with or without annular enlargement were similar.

CONCLUSIONS: The prevalence of PPM was low in patients more than 65 years old with a relatively small body size who received bioprosthetic valves. In patients less than 65 years old with a small annulus, the method of first choice for avoiding PPM is aortic annular enlargement.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
The main purpose of aortic valve replacement (AVR) is to reduce the pressure or volume load on the left ventricle and thus avoid the progression of left ventricular remodeling. Ideally, the postoperative transprosthetic pressure gradient and regurgitation will be minimal or around zero. However, a postoperative pressure gradient often persists, especially in patients who receive prostheses measuring 21 mm or less. Rahimtoola [1] first described the concept of patient-prosthesis mismatch (PPM) in 1978, and defined this as being present "when the effective prosthetic valve area, after insertion into the patient, is less than that of a normal valve." In patients undergoing AVR, PPM is currently defined as an effective orifice area indexed by body surface area (iEOA) of 0.85 cm2/m2 or less, and this is the generally accepted criterion [2, 3].

Previous studies have shown that patients with PPM achieve less symptomatic improvement because residual stenosis means there is no relief of left ventricular hypertrophy, and PPM also affects both short-term and long-term survival [4–7]. To minimize the occurrence of PPM, different surgical strategies can be tried depending on the patient's condition, including aortic root enlargement, supra-annular or high-performance prosthesis implantation, and the use of stentless bioprostheses, aortic homografts, or pulmonary autografts. To avoid PPM, we routinely perform supra-annular bioprosthesis implantation in patients aged 65 years or more with a small aortic annulus, whereas aortic root enlargement is done for patients less than 65 years old.

In recent decades, new high-performance prostheses have been invented for use with a small aortic annulus, and these have contributed to avoidance of PPM without the need for aortic annular enlargement. The aim of this study was to review our strategy of performing AVR with or without annular enlargement and to determine the incidence of PPM in our patients, particularly in a population with small build like the Japanese. We also discuss the possibility of avoiding PPM by using the newer high-performance valves.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
Study Population
Between October 1991 and December 2002, 181 adults who underwent isolated or combined AVR at our institution were enrolled in this study (Table 1). The mean age of the patients was 57.2 ± 13 years (range, 16 to 85), and they included 155 men and 26 women. Fifty-three patients underwent AVR with a Carpentier-Edwards Perimount pericardial bioprosthesis (model 2900; Edwards Lifesciences, Irvine, California). The remaining 128 patients received a St. Jude Medical (SJM) Standard mechanical prosthesis (St. Jude Medical, St. Paul, Minnesota). Concomitant surgical procedures were performed in 47 of the 181 patients, including coronary artery bypass grafting in 4 (2.2%) and mitral valve replacement in 39 (21.5%). Twenty-four patients (13.3%) underwent enlargement of a small aortic annulus (using the techniques of Manouguian [8] in 18 patients and Nicks [9] in 6 patients).


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  		Table 1. Patient Characteristics
 
Surgical Procedure
A full midline sternotomy was employed in all patients. After establishing cardiopulmonary bypass and clamping the aorta, myocardial protection was provided by means of intermittent antegrade and retrograde blood cardioplegia. After resection of the native aortic valve cusps, the valve size was measured by using the sizer provided by each manufacturer. The CEP and SJM valves were implanted in the supraannular or intra-annular position with pledged-supported 2-0 polyester suture, using a noneverting and everting mattress suture technique, respectively. Our procedures for aortic annular enlargement have been described previously [10]. These were based on the techniques of Manouguian and associates [8] or Nicks and associates [9] and were selected for patients with a small aortic valve annulus less than 21 mm in diameter on direct measurement with the valve sizer.

Prediction of Patient-Prosthesis Mismatch
Patient-prosthesis mismatch was defined as a iEOA of 0.85 cm2/m2 or less on the basis of a previous study [2, 3]. The iEOA was calculated as the published in-vivo EOA value [11] divided by the patient's body surface area (BSA).

Statistical Analysis
Data were expressed as the mean ± SD and were compared by using an unpaired two-tailed t test. A probability value of less than 0.05 was considered to indicate statistical significance. The relationship between prosthesis size and the effective orifice area was evaluated by simple linear regression analysis. Analysis of cumulative survival and the event-free rates for thromboembolism, endocarditis, and reoperation was done by the Kaplan-Meier method, and curves were compared by the log-rank test.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
Long-Term Outcome
The average 10-year actuarial survival rate (including operative mortality) was 83.5% ± 6.5%, 87.5% ± 6.8%, and 91.9% ± 3.2% for patients with the CEP prosthesis, the SJM prosthesis without annular enlargement, and the SJM prosthesis with annular enlargement, respectively (p = 0.200; Fig 1). The incidence of thromboembolism, prosthetic valve endocarditis, and reoperation in these groups is listed in Table 2. There were no significant differences with respect to postoperative survival, thromboembolism, prosthetic valve endocarditis, and reoperation irrespective of the type of prosthesis and the AVR procedure.


Figure 1
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  		Fig 1. Actuarial survival rates with operative deaths included, for the Carpentier-Edwards Perimount pericardial (CEP) valve (diamonds), the St. Jude Medical (SJM) valve with enlargement (squares), and the SJM without enlargement (triangles).

 

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  		Table 2. Linearized Incidences of Valve-Related Complications
 
Correlation Between BSA and Prosthesis Size
The patients' BSA in this series ranged from 1.20 cm2 to 1.94 cm2, with an average of 1.57 cm2, which indicated small-built compared with a Western population. The implanted prosthetic valve size was well correlated with the BSA for both the mechanical and bioprosthetic valves (Fig 2). These relationship indicated that our choice of prosthesis size and our indications for enlargement of a small annulus were generally appropriate.


Figure 2
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  		Fig 2. Correlation of patient body surface area (BSA) and labeled prosthetic valve size. (A) Bioprosthetic valve. (B) Mechanical valve.

 
Incidence of Patient-Prosthesis Mismatch
Among the patients aged less than 64 years, 24 patients (18.8%) had a small aortic annulus and underwent the Manouguian procedure (n = 18) or the Nicks procedure (n = 6) for annular enlargement. No patient received an SJM valve less than 19 mm in size or had an iEOA of 0.85 cm2/m2 or less. Among the patients aged more than 65 years, 2 of 53 patients (3.8%) who underwent AVR with a CEP valve had PPM. These 2 patients both received a 19-mm CEP valve (Table 3). In 1 patient, the 19-mm CEP valve was required because of narrowing after reconstruction of the annulus with bovine pericardium to repair damage caused by infective endocarditis. Figure 3 illustrates the theoretical basis of avoiding PPM by achieving an iEOA0.85 cm2/m2. If a 23-mm SJM standard valve had not been implanted instead of a 19-mm valve in 18 patients and they had not received enlargement of a small annulus by Manouguian's procedure, all of them would have shown PPM after AVR. Figure 3 also demonstrates the possibility of avoiding PPM by using high-performance mechanical valves such as a 19-mm SJM HP or a 19-mm SJM Regent with a small outer sewing ring diameter and larger orifice area (Fig 4).


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  		Table 3. Estimation of Patient-Prosthesis Mismatch (P-PM): Carpentier-Edwards Perimount Pericardial Valve
 

Figure 3
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  		Fig 3. Avoidance of patient-prosthesis mismatch with aortic annular enlargements and high performance mechanical prostheses: SJM enlargement, 23 mm (solid line); SJM Regent, 19 mm (dotted line); SJM Hemodynamic Plus, 19 mm (dot-dashed line); and SJM Standard, 19 mm (dashed line). (BSA = body surface area; iEOA = indexed effective orifice area; SJM = St. Jude Medical.)

 

Figure 4
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  		Fig 4. Geometry of the St. Jude Medical (SJM) valves. (HP = Hemodynamic Plus.)

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
Making an appropriate choice of the prosthesis is one of the most important points in surgery for heart valve disease. The surgical procedure differs for each patient, not only because of the size of the aortic annulus but also because of the patient's age, level of activity, etiology, expected survival time, and complications. In the case of aortic valve disease, especially aortic stenosis, the age of the candidates for valve replacement has increased markedly in recent years. Thus, in our department, the mean age of the patients who underwent AVR was 66 years in 2002 versus 44 years during the 1980s. Since 1995, our first choice for patients aged more than 65 years old has been a bioprosthesis at the aortic position because of the excellent long-term results reported in Western countries [12–20]. Nevertheless, the risk of eventual tissue valve failure still exists, and longer follow-up may be necessary to prove the value of these prostheses compared with mechanical valves in a country like Japan with a long life expectancy.

Some studies have found a higher prevalence of PPM in patients receiving aortic bioprostheses compared with our results. Eichinger and coworkers [21] reported that there was mismatch in 100% of patients receiving a 19-mm valve and concluded that neither bovine nor porcine stented bioprostheses measuring 19 mm in diameter could be recommended, except in patients with a high risk of aortic root enlargement or those with such a small BSA that mismatch did not occur. In our experience, PPM only affected 4% of the patients who received a 19-mm CEP valve. We previously reported that the 19-mm CEP valve is a reliable option for elderly Japanese patients with a small aortic annulus [22]. Our results showed that the mean pressure gradients measured directly in the catheter laboratory was only 12.0 ± 4.9 mm Hg after implantation of a 19-mm CEP in patients with a BSA of 1.39 ± 0.11 m2. The reason was presumably that our elderly patients had a BSA almost equal to that in the previous report [22], and most of them were able to receive a small bioprosthesis without PPM. This study showed the suitability of the CEP valve for patients aged more than 65 years, not only with regard to the midterm outcome but also with regard to avoiding PPM.

For patients aged less than 65 years, mechanical valves were the first choice in this series. We routinely performed aortic annular enlargement by methods such as the Manouguian [8], Nicks [9], and Konno [23] procedures to avoid PPM and found that the Manouguian procedure was most useful for reoperation or double valve replacement [10]. Based on our previous study that revealed smaller regression of left ventricular mass after AVR with a 21-mm Bjork-Shiley valve [24], our strategy changed in 1991 to the performance of AVR without using 19-mm and 21-mm standard mechanical valves if possible. In this series, there would have been mismatch in 26 (14.4%) of the patients who underwent AVR if they had received a standard small mechanical valve and we had not performed aortic annular enlargement. The Manouguian procedure made it possible to gain an increment of two valve sizes and avoid PPM by implantation of 23-mm SJM standard valves in all of these patients. The Manouguian procedure was relatively successful [10], and the 10-year actuarial survival rate (including operative mortality) was similar among patients receiving CEP valves and SJM valves with or without annular enlargement. On the other hand, Sommers and David [25] and Carrier and associates [26] have reported that the operative mortality rate after aortic annular enlargement was twice that after standard AVR. In patients with a small aortic annulus, either annular enlargement or insertion of hemodynamically improved new prosthetic valves have been proposed to minimize the transprosthetic gradient.

Recently, the patients who need AVR are becoming older and thus have more complications and risk factors. In a patient aged 65 years or more with a small BSA, the surgeon may be unable to perform either supra-annular implantation of a bioprosthesis or aortic annular enlargement owing to the increased operative risk, but might be able to choose a high-performance bileaflet prosthesis with a small outer diameter and large iEOA, as shown in Figures 3 and 4. The calculation of the projected iEOA before operation could be useful strategy to decrease and avoid PPM in patients with larger body size. Effective orifice area of the new high-performance 19-mm SJM Regent valve is the almost same as the orifice of a 23-mm SJM standard valve. We think it reasonable to suggest that a 19-mm SJM Regent valve be used in a patient with a BSA of less than 2.0 m2.

In conclusion, our experience of AVR (including double valve replacement) indicated that few patients developed PPM, especially those aged more than 65 years old with a relatively small BSA who were able to receive bioprosthetic valves. In patients less than 65 years old with a small aortic annulus, the method of first choice for avoidance of PPM is aortic annular enlargement, but it may also be possible to use a high-performance bileaflet mechanical prosthesis as an alternative.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

  1. Rahimtoola SH. The problem of valve prosthesis-patient mismatch Circulation 1978;58:20-24.[Abstract/Free Full Text]
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