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Ann Thorac Surg 2008;86:1799-1803. doi:10.1016/j.athoracsur.2008.08.019
© 2008 The Society of Thoracic Surgeons
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Original Articles: Adult Cardiac

Hemodynamic Evaluation and Midterm Outcome of Aortic Valve Replacement With Size 19 Perimount Prosthetic Valve

Pradeep Narayan, FRCS, Barnaby C. Reeves, PhD, Syad I.A. Rizvi, MRCS, Kayvan Shokrollahi, MRCS, Huda Ismail, MD, Gianni D. Angelini, FRCS, Angus Nightingale, MD, Massimo Caputo, MD*

Bristol Heart Institute, University of Bristol, Bristol, United Kingdom

Accepted for publication August 11, 2008.

Abbreviations and Acronyms AVR = aortic valve replacement; BSA = body surface area; CI = confidence interval; CO = cardiac output; EOA = effective orifice area; EOAI = effective orifice area index; LV = left ventricular; MAP = mean arterial pressure; MTG = mean transprosthetic gradient; PPM = patient-prosthesis mismatch; PTG = peak transprosthetic gradient

* Address correspondence to Dr Caputo, Bristol Heart Institute, University of Bristol, Bristol Royal Infirmary, Bristol, BS2 8HW, United Kingdom (Email: m.caputo{at}bristol.ac.uk).


   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background: We sought to investigate the effect of patient prosthesis mismatch on hemodynamic profile using dobutamine stress echocardiography, and to evaluate midterm survival of patients undergoing aortic valve replacement with 19-mm Perimount (Baxter Healthcare, Santa Ana, California) aortic prosthetic valves.

Methods: Between December 1, 1999, and August 17, 2005, 147 patients (mean age, 76.8 ± 5.51 years) had aortic valves replaced with 19-mm Perimount prostheses. Dobutamine stress echocardiography was performed in a subgroup of 24 patients (mean age, 76.6 ± 5.60 years). Univariable predictors of peak transprosthetic gradient (PTG) under maximum stress, adjusted for resting PTG, were investigated by regression. Survival in the whole cohort was described, and univariable predictors of survival were investigated by Cox regression.

Results: In the stress echocardiography subgroup, cardiac output (p < 0.0001), PTG (p < 0.0001), and effective orifice area index increased significantly (p = 0.002) under stress. Peak transprosthetic gradient under stress was strongly associated with PTG at rest (p < 0.0001). After controlling for PTG at rest, no other variables were associated with PTG under stress. In the whole cohort, mean duration of follow-up was 2.21 years; 23 patients died. Neither body surface area nor effective orifice area index was significantly associated with survival.

Conclusions: The 19-mm Perimount aortic prosthesis has acceptable hemodynamic performance. Transvalvular gradients were within a clinically acceptable range, both at rest and under stress. These findings suggest that patient-prosthesis mismatch is unlikely to cause a clinically important problem when the prosthesis is used, which is consistent with survival experience in the whole cohort.


   Introduction
Top
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
The proportion of patients presenting for aortic valve replacement (AVR) surgery who are elderly has increased in recent years and is likely to increase further in the future. Bioprosthetic valves are generally favored in the elderly to obviate or minimize the need for anticoagulation therapy. However, when operating on elderly patients, the surgeon is quite frequently confronted with a small aortic annulus. Particularly in female patients, there is still controversy about the optimal operative strategy, namely, is a small prosthesis in the aortic position acceptable or should the annulus be enlarged to minimize patient prosthesis mismatch [1]? One way of judging the acceptability of using a small prosthesis is to measure hemodynamic performance in vivo and to investigate whether patient-prosthesis mismatch (PPM) is associated with poor performance.

In patients undergoing aortic valve replacements, PPM is currently defined as moderate if the effective orifice area (EOA) index (EOAI) is less than 0.85 cm2/m2 but 0.65 cm2/m2 or greater, and severe if EOAI is less than 0.65 cm2/m2 [2]. Patient prosthesis mismatch is seen in 20% to 70% of aortic valve replacements, and has been associated with less regression of left ventricular (LV) mass after AVR, persistence of LV hypertrophy associated with PPM, inferior hemodynamics, a higher risk of cardiac events, and poorer survival after AVR [3]. Transprosthetic gradients are essentially determined by both the EOA and the transvalvular flow. Transvalvular flow in turn is related to cardiac output (CO) which, at rest, is largely determined by body surface area (BSA). Of note is that BSA contributes minimally to the variance in peak transprosthetic gradient (PTG) under stress. In fact, the main predictors of transprosthetic gradient are the intrinsic characteristics of each particular prosthesis [4].

The aortic Carpentier-Edwards Perimount pericardial bioprosthesis (Baxter Healthcare, Santa Ana, CA) has been reported to provide superior in vitro hemodynamic performance compared to first generation pericardial valves and porcine bioprostheses, both in the past [5] and more recently [6]. However, the latter report also found that, when using a 19-mm bioprosthesis (bovine or porcine), PPM occurred in 100% of the cases. Therefore, the authors recommended that an aortic root enlargement procedure, with implantation of a larger sized valve, should be carried out instead of AVR using a 19-mm valve [6]. Aortic root enlargement has been shown to be a safe procedure for patients with small aortic roots and leads to reduction of postoperative gradients and a lower incidence of PPM [7]. Either an anterior or posterior annular enlargement procedure may be performed in a patient with a small aortic root to allow for implantation of a larger valve. The posterior approach is the most commonly used aortic root enlargement procedure in adults and can increase the annular diameter by 2 to 4 mm [8].

Stress echocardiography in the context of prosthetic valve is solely for the hemodynamic performance of the valve. While exercise testing seems to be the most physiologic approach, quite often patients are either unwilling or indeed unable to conduct an exercise protocol; and dobutamine echocardiography has been shown to be a useful alternative, yielding results similar to those obtained with exercise [9].

The main objective of our study was to describe the in vivo hemodynamic performance of the 19-mm Perimount pericardial bioprosthesis using dobutamine stress testing.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
Patient Selection and Data Collection
Patients undergoing AVR with a 19-mm Perimount aortic valve between December 1999 until January 2004 were identified from our database (Patient Analysis and Tracking System; Dendrite Clinical Systems, London, United Kingdom). The main criteria among our surgeons for using a biological valve in the aortic position were as follows: age older than 65 years (but consideration is usually also given to patients' biological age); the likely need for another operation in future (eg, joint replacement); and intolerance of or disinclination to take warfarin. Data during a hospital admission are collected prospectively on all patients undergoing cardiac surgery and entered into the database. Patient characteristics were not considered when approaching patients to participate in the dobutamine stress echocardiographic testing. Patients were invited to undergo dobutamine stress echocardiography as part of their clinical management. However, only a minority took up the invitation, probably because the patients were elderly and often lived long distances from the tertiary hospital where they had their index operations and where the dobutamine stress echocardiography was being carried out. Written informed consent to undergo dobutamine stress echocardiography was obtained from each patient. Ethical approval for the study was obtained from the Local Ethics Committee.

Dobutamine Stress Protocol
Apical four-chamber views were obtained, and baseline Doppler measurements of transvalvular flow and gradients were recorded. Dobutamine was infused intravenously, starting at 5 µg · kg–1 · min–1 and with increments of 5 µg · kg–1 · min–1 every 15 minutes to a maximum of 20 µg · kg–1 · min–1. The electrocardiogram was monitored continuously, and blood pressure was measured at 5 minute intervals throughout the study.

Doppler Measurements and Calculations
All of the echocardiographic investigations were performed by a single experienced operator. Parasternal long-axis views were obtained, and an early systolic diameter of the left outflow tract was measured just below the bioprosthesis using an inner edge-to-edge technique; diameter was averaged over three measurements. The LV outflow tract cross-sectional area (CSA) was then calculated. Peak and mean velocities in the LV outflow tract were measured, and CO was derived from the equation:


Formula

where VTI is the velocity time integral in the left ventricular outflow tract and HR is heart rate per minute.

Continuous-wave Doppler was used to assess the flow velocity across the valve. Peak velocity was averaged from three velocity envelopes, and mean velocity was calculated by averaging the instantaneous velocities measured throughout the velocity complexes. The modified Bernoulli equation was used to calculate the mean transprosthetic gradient (MTG) and PTG and pressure drop across the bioprosthesis. Velocity ratio (VR) was calculated as the ratio of mean subaortic to mean transaortic velocity. A modified continuity equation was used to calculate the EOA as follows:


Formula

Two different methods were used to calculate the EOAI. For the entire sample, the EOAI was calculated as:


Formula

where EOA was taken to be 1.1 cm2 based on the in vivo hemodynamic data reported in the literature [10], and BSA is a patient's body surface area. In the subgroup of patients who underwent dobutamine stress testing, patient-specific values of effective orifice area (EOAIi) were measured and indexed using the same equation.

Statistical Analysis
Characteristics of patients who had a Perimount 19-mm valve were tabulated. For the subgroup who underwent stress testing, estimates of mean valve performance measurements at rest and stress are reported, together with estimates of differences (ie, mean under maximum stress minus mean at rest). The primary measure of hemodynamic performance was transprosthetic gradients; other measures of hemodynamic performance and midterm survival were secondary outcomes.

Paired t tests (two-tailed) were used to assess whether there were significant changes in mean arterial pressure (MAP), CO, EOAIi, MTG, and PTG under maximum stress; other variables are derived from these and are therefore not independent, so these were not tested. Regression models adjusted for resting MTG and PTG investigated univariable predictors of MTG and PTG under maximum stress.

For the entire sample, vital status and dates of death, where applicable, were obtained through the UK National Health Service Strategic Tracing Service. Survival was described by a Kaplan-Meier graph, and univariable predictors of survival were investigated by Cox regression. Multivariable survival analysis could not be carried out because of the limited number of deaths (n = 23).


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
A total of 147 patients underwent AVR with a 19-mm Perimount valve in our institution between December 1999 and August 2005, and 24 of those were recruited for dobutamine stress echocardiography (Table 1). A total of 8 cardiac surgeons was responsible for operations on the entire cohort.


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  		Table 1 Characteristics of All Patients in Cardiac Surgery Database Who Had Perimount 19-mm Valve Prosthesis (n = 147) and Subgroup Who Participated in Dobutamine Stress Test (n = 24)
 
The subgroup who consented to undergo stress testing were less likely to have had combined valve replacement and coronary surgery (p = 0.03) and, on average, had had their operations longer ago (p = 0.0004). As the subgroup was inevitably recruited from survivors, these differences are not remarkable. In other respects, the subgroup did not appear different from the whole group.

Dobutamine Stress Test
All relevant measurements at rest and under maximum stress are summarized in Table 2. As described above, the statistical significance of differences between rest and stress were tested only for MAP, CO, MTG, PTG, and EOAIi. Mean arterial pressure decreased significantly under stress (mean difference, –17.0 mm Hg; 95% confidence interval [CI]: –23.4 to –10.6, p < 0.0001). Cardiac output (mean difference, 3.69 L/min; 95% CI: 2.86 to 4.52, p < 0.0001), MTG (mean difference, 4.21 mm Hg; 95% CI: 2.00 to 6.43, p = 0.0007), PTG (mean difference, 32.1 mm Hg; 95% CI: 25.5 to 38.7, p < 0.0001), and EOAIi (mean difference, 0.14 mm2, 95% CI: 0.06 to 0.22, p = 0.002) increased significantly under stress.


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  		Table 2 Estimates of Mean Valve Variables at Rest and Under Stress a
 
The PTG under stress was strongly associated with PTG at rest (p < 0.0001). In regression models that adjusted for PTG at rest, only MAP at rest showed any evidence of being significantly associated with PTG under stress (–0.43 mm Hg change in PTG under stress for every mm Hg increase in MAP at rest; 95% CI: –0.91 to 0.04, p = 0.07) but adding this covariate did not significantly improve the fit of the model. The model that included only resting PTG as a covariate fitted the data well (r2 adj = 0.41, F = 17.2, df = 1 and 22, p = 0.0004), allowing prediction of PTG from the following equation:


Formula

Thus, EOAIi was not associated with PTG under stress (5.23 mm Hg change in PTG under stress for a unit change in EOAIi; 95% CI: –35.1 to 45.6, p = 0.79).

The MTG under stress was also strongly associated with MTG at rest (p < 0.0001). In regression models that adjusted for MTG at rest, no other variables were significantly associated with PTG under stress. The model that included only resting PTG as a covariate fitted the data well (r2 adj = 0.92, F = 39.1, df = 1 and 22, p < 0.0001), allowing prediction of MTG from the following equation:


Formula

As for PTG, EOAIi was not associated with MTG under stress (–3.58 mm Hg change in MTG under stress for a unit change in EOAIi; 95% CI: –13.8 to 6.63, p = 0.47).

Follow-Up
Mean duration of follow-up in the whole cohort was 2.21 years. Twenty-three patients with Perimount 19-mm valves died during follow-up. The Kaplan-Meier plot (Fig 1) shows the distribution of these deaths during follow-up, giving an estimated 3-year postoperative mortality of 20% (95% CI: 13% to 30%). It appears as though deaths occurred at a steady rate during follow-up, namely, at approximately 7% per year.


Figure 1
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  		Fig 1. Kaplan-Meier graph showing cumulative deaths from any cause over time.

 
Cox regression modeling investigated whether age, sex, BSA, combined coronary artery bypass graft surgery and number of distal anastomoses, New York Heart Association (NYHA) functional class, cross-clamp time, EOAI, and new need for postoperative hemodialysis were prognostic with respect to survival. Age, male sex, NYHA class, and cross-clamp time appeared to be associated with survival (Table 3), increasing the risk of death during follow-up. Neither BSA nor EOAI was significantly associated with survival. There were too few deaths during follow-up (n = 23) to permit more complex multivariable models to be fitted.


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  		Table 3 Univariable Estimates of Association of Potential Prognostic Factors With Survival
 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
The hemodynamic performance of the 19-mm Perimount pericardial bioprosthesis appears entirely satisfactory in our study. The average peak-to-peak gradients across the 19-mm Perimount valve both at rest and at maximal stress were in keeping with data reported from previous studies [11]. In our study, neither BSA nor EOAI (and therefore PPM) were significantly associated with survival.

The impact of PPM has been very extensively studied, and associations have been reported between PPM and short-term mortality [2] and LV wall regression [3]. The effect of PPM on valve-related mortality has also been described [12].

The effect of PPM on survival after AVR, and the mechanisms by which PPM affects survival, are poorly understood. The issue of PPM, therefore, still generates much controversy with respect to its clinical relevance and especially in relation to its effect on survival after operation. Evidence of an association between PPM and survival is inconsistent. Although it has been reported that PPM is a strong and independent predictor of cardiac events and poor survival [2, 3, 12, 13], there is also evidence to the contrary; that is, PPM or the use of a small prosthesis has no effect on survival after surgery [14, 15].

The average age of patients who received a 19-mm Carpentier-Edwards Perimount pericardial valve in this study was 76.6 years. Therefore, while accepting the principle of inserting the largest possible size of valve when performing an AVR, any survival advantage of a larger valve has to be weighed up against the increased operative risk from an aortic root enlargement procedure in these elderly and usually frail patients. It has been reported that the operative mortality rate after annular enlargement is twice that of a standard AVR [16]. Although aortic root enlargement may be a technically safe procedure in experienced hands, it is bound to increase the operative time and the bypass time; the latter by itself has been shown to be associated with adverse outcome if prolonged beyond 120 minutes [2]. In fact, prolonged cross-clamp time was found to be one of the important determinants of poor survival in our study (Table 3).

Other options to reduce PPM when confronted with a small aortic root are insertion of a stentless bioprosthesis or supra-annular insertion of a modern bioprosthesis like the Perimount Magna (Edward Lifesciences, Irvine, California). Insertion of a stentless prosthesis is technically more challenging and requires surgical experience with the technique to achieve mortality and morbidity rates similar to those for a stented bioprosthesis [17]. Owing to its smaller sewing ring and lower profile, a larger Perimount Magna valve can be used than would be possible using a standard Perimount valve. While the Magna valve was found to have superior hemodynamics at greater sizes, it was seen that in patients with an aortic annulus 18 to 20 mm in diameter, the implanted valve type and the implantation position did not affect the hemodynamic performance of the valve, or the incidence of PPM [17].

While PPM does pose a risk for valve-related events, this risk may be overshadowed by the fact that there is generally poor survival after AVR. It has been suggested that, in an elderly patient with BSA less than 1.5 m2, a 19-mm valve from any manufacturer is appropriate, and that even a patient with a larger BSA in this age group would probably be unlikely to suffer detrimental effects of PPM [12]. This point of view has been supported by other studies, too [2]. It has also been shown that in the elderly population, there is no survival benefit associated with the implantation of a larger size prosthesis compared with a 19-mm bioprosthetic valve [18].

The above reports are in keeping with the conclusions we draw from this study. The hemodynamic performance of the valve was shown to be entirely satisfactory and survival was consistent with the contemporary literature. Therefore, although aortic root enlargement and insertion of larger sized prosthesis with avoidance of PPM has a theoretical advantage, use of the 19-mm bioprosthetic valve in elderly patients appears safe and justified.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
This study was carried out with the support of funding from the British Heart Foundation and the Garfield Weston Trust.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Sakamoto Y, Hashimoto K, Okuyama H, et al. Prevalence and avoidance of patient-prosthesis mismatch in aortic valve replacement in small adults Ann Thorac Surg 2006;81:1305-1309.[Abstract/Free Full Text]
  2. Blais C, Dumesnil JG, Baillot R, Simard S, Doyle D, Pibarot P. Impact of valve prosthesis-patient mismatch on short-term mortality after aortic valve replacement Circulation 2003;108:983-988.[Abstract/Free Full Text]
  3. Pibarot P, Dumesnil. Prosthesis-patient mismatch: definition, clinical impact and prevention Heart 2006;92:1022-1029.[Abstract/Free Full Text]
  4. Izzat MB, Kadir I, Reeves B, Wilde P, Bryan AJ, Angelini GD. Patient prosthesis mismatch is negligible with modern small size aortic valve prosthesis Ann Thorac Surg 1999;68:1657-1660.[Abstract/Free Full Text]
  5. Yoganathan AP, Woo YR, Sung HW, Williams FP, Franch RH, Jones M. In vitro hemodynamic characteristics of tissue bioprostheses in the aortic position J Thorac Cardiovasc Surg 1986;92:198-209.[Abstract]
  6. Eichinger WB, Botzenhardt F, Keithahn A, et al. Exercise hemodynamics of bovine versus porcine bioprostheses: a prospective randomized comparison of the mosaic and perimount aortic valves J Thorac Cardiovasc Surg 2005;129:1056-1063.[Abstract/Free Full Text]
  7. Kulik A, Al-Saigh M, Chan V, et al. Enlargement of the small aortic root during aortic valve replacement: is there a benefit? Ann Thorac Surg 2008;85:94-101.[Abstract/Free Full Text]
  8. Desai ND, Christakis GT. Bioprosthetic aortic valve replacement: stented pericardial and porcine valvesIn: Cohn LH, editor. Cardiac surgery in the adult. 3rd edition. New York: McGraw-Hill; 2007. pp. 857-894.
  9. Kadir I, Walsh C, Wilde P, Bryan AJ, Angelini GD. Comparison of exercise and dobutamine echocardiography in the haemodynamic assessment of small size mechanical aortic valve prosthesis Eur J Cardiothorac Surg 2002;21:692-697.[Abstract/Free Full Text]
  10. Khan SS, Siegel RJ, DeRobertis MA, et al. Regression of hypertrophy after Carpentier-Edwards pericardial aortic valve replacement Ann Thorac Surg 2000;69:531-535.[Abstract/Free Full Text]
  11. Cosgrove DM, Lytle BW, Gill CC, et al. In vivo hemodynamic comparison of porcine and pericardial valves J Thorac Cardiovasc Surg 1985;89:358-368.[Abstract]
  12. Rao V, Jamieson WRE, Ivanov J, Armstrong S, David TE. Prosthesis-patient mismatch affects survival after aortic valve replacement Circulation 2000;102(19 Suppl 3):III5-III9.[Medline]
  13. Tasca G, Mhagna Z, Perotti S, et al. Impact of prosthesis-patient mismatch on cardiac events and midterm mortality after aortic valve replacement in patients with pure aortic stenosis Circulation 2006;113:570-576.[Abstract/Free Full Text]
  14. Medalion B, Blackstone EH, Lytle BW, White J Arnold JH, Cosgrove DM. Aortic valve replacement: is valve size important? J Thorac Cardiovasc Surg 2000;119:963-974.[Abstract/Free Full Text]
  15. Hanayama N, Christakis GT, Mallidi HR, et al. Patient prosthesis mismatch is rare after aortic valve replacement: valve size may be irrelevant Ann Thorac Surg 2002;73:1822-1829.[Abstract/Free Full Text]
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  17. Botzenhardt F, Eichinger WB, Bleiziffer S, et al. Haemodynamic comparison of bioprosthesis for complete supra-annular position in patients with small aortic root annulus J Am Coll Cardiol 2005;45:2054-2060.[Abstract/Free Full Text]
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Gianni D. Angelini
Massimo Caputo
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