Ann Thorac Surg 2003;75:35-39
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Clinical and hemodynamic evaluation of small perimount aortic valves in patients aged 75 years or older
Nicola Vitale, MD, PhDa*,
Stephen C. Clark, FRCS (C/Th)a,
Alexander Ramsden, FRCSa,
Asif Hasan, FRCSa,
Colin J. Hilton, FRCSa,
Michael P. Holden, FRCSa
a Department of Cardiothoracic Surgery, Freeman Hospital, Newcastle-Upon-Tyne, United Kingdom
Accepted for publication August 2, 2002.
* Address reprint requests to Dr Vitale, Istituto di Cardiochirurgia, Policlinico, Piazza Giulio Cesare 11, 70124 Bari, Italy.
e-mail: nicola_vitale{at}lycos.co.uk
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Abstract
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BACKGROUND: There is the potential for iatrogenic aortic stenosis and poor quality of life when small aortic valve bioprostheses are used in elderly patients. The alternative is enlarging the aortic annulus to accommodate larger size prostheses, increasing operative mortality. It was hoped that bovine pericardial valves would improve hemodynamic performance in the smaller valve sizes.
METHODS: To determine long-term results and in vivo hemodynamic performance of small-size aortic Carpentier-Edwards bovine pericardial valves (Perimount) in elderly patients, we analyzed our follow-up and echocardiographic data from patients 75 years of age or older receiving isolated 19-mm and 21-mm Perimount valves. Ninety-four patients with a mean age of 77 ± 2.2 years were followed for 12 years. Seventeen patients with 19-mm and 25 patients with 21-mm Perimount valves underwent transthoracic echocardiograms.
RESULTS: Operative mortality was 6.3% (6 of 94). Twelve-year survival was 82.7%. Freedom from thromboembolism was 86.9% at 12 years. Two patients had anticoagulation-related bleeding. Overall New York Heart Association class decreased from 3 ± 1 to 1.6 ± 0.7 at the end of follow-up. Hemodynamic performances were satisfactory in both 19-mm and 21-mm Perimount valves, with low peak and mean transvalvular gradients and good effective orifice areas, orifice area indices, and performance indices.
CONCLUSIONS: Perimount aortic valve in the small aortic annulus has yielded excellent long-term results and hemodynamic performances. Perimount is a very satisfactory option in elderly patients. Implantation of a Perimount bioprosthesis avoids enlargement of the small aortic annulus, reducing mortality and morbidity associated with this procedure.
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Introduction
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The use of tissue valve prostheses has been advocated in an elderly population because of the reduction in the complications of thromboembolism and hemorrhage related to anticoagulation that were seen with mechanical prostheses [1–6]. The major complication of bioprostheses is structural valve degeneration, but its consequences are reduced in the elderly because most often the bioprostheses outlive patients [1–6].
The Carpentier-Edwards Perimount pericardial bioprostheses is a low-profile trileaflet valve composed of bovine pericardium. The hemodynamic characteristics of the pericardial bioprostheses have been reported to be better than those of porcine valves [7–9]. Nevertheless hemodynamic performance of small stent-mounted tissue valves may be suboptimal because the bulk of the valve itself as well as the stent and sewing cuff contribute to this.
The aim of the present study is the evaluation of long-term results and hemodynamic performances of the 19-mm and 21-mm Perimount aortic valves implanted in patients 75 years of age or older.
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Material and methods
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From 1988 to January 2000, 534 patients underwent isolated aortic valve replacement with Perimount pericardial valve. Of these, 94 patients (17.4%) 75 years of age or older received a 19-mm or 21-mm valve and were enrolled in the study. Associated coronary artery disease was not an exclusion criterion.
There were 66 men and 28 women with ages ranging from 75 to 85 years, with a mean of 77 ± 2.2 years. The clinical characteristics of patients are presented in Table 1.
Surgical technique
Approach to the heart was through a median sternotomy. Standard cardiopulmonary bypass was established with moderate systemic hypothermia (30°C). Myocardial protection was achieved by infusing crystalloid or cold-blood cardioplegia directly into the coronary ostia. Topical cooling was also used (4°C saline solution).
After excision of the valve, the aortic annulus was debrided of residual calcium, and the Perimount valve was placed in the supraannular position with the footplate of the valve inserted within the annulus with interrupted sutures of 2-0 Ethibond (Ethicon, Brussels, Belgium).
Warfarin was given to patients in sinus rhythm for the first 3 months postoperatively, then aspirin at a dose of 150 mg. Patients in chronic atrial fibrillation were kept on the warfarin regimen. The international normalized ratio level was between 2.5 and 3.5.
Follow-up
Events during the follow-up were defined according to the guidelines for reporting valve-related mortality and morbidity [10]. Postoperative records were determined from patient records. In addition patients were interviewed over the phone before the closing date of follow-up. Those patients not seen in outpatient clinic or interviewed were considered lost to follow-up. Five patients were lost, so the follow-up was 94.3% complete. The total length of follow-up was 370.58 patient-years with a mean of 4.6 ± 2.2 years.
Echocardiography
Echocardiograms were performed at the discretion to the referring cardiologist. Doppler echocardiography at rest was obtained from apical and parasternal long-axis views. The ultrasonography window from which the highest velocities were obtained was selected and used for Doppler evaluation.
Flow velocity in the left ventricular outflow tract and across the valve was measured by means of pulsed and continuous wave Doppler, respectively. The modified Bernoulli equation was used to calculate peak and mean pressure gradients across the prosthesis. Color Doppler was used to visualize and quantify the amount and site of prosthetic valve regurgitation.
Doppler measurements and calculations
where V2 is prosthetic peak velocity in meters per second measured with continuous-wave Doppler and V1 is peak velocity proximal to valve in meters per second, measured with pulsed-wave Doppler.
where VTI2 is prosthetic velocity time integral measured with continuous-wave Doppler, and VTI1 is proximal velocity time integral measured with pulsed-wave Doppler, calculated by on-line averaging.
Effective orifice area
The effective orifice area (EOA) is an index of how well a valve design uses its geometric orifice area. It was calculated with the continuity equation by the simplified peak velocity method as CSA (PkVLVOT/PkVAo), where CSA is the subvalvular cross-sectional area, and PkVLVOT and PkVAo are the maximal velocity in the left ventricular outflow tract and across the valve, respectively. The cross-sectional area was calculated by measuring the left ventricular outflow tract just below the prosthetic ring using an edge-to-edge method.
Effective area index
The effective area index (EAI) is a measure of how well the EOA of the valve matches the body surface area (BSA). It is calculated as EAI = EOA/BSA. This index was used to detect mismatch between valve size and BSA. According to Pibarot and Dumesnil [11], it would appear that an indexed prosthetic valve area of approximately 0.85 cm2/m2 would be adequate to minimize the postoperative gradient.
Geometric orifice area index
This index is a measure of how well the geometric orifice area (GOA) of the valve matches the body surface area. It is calculated as GOA/BSA. The GOA is provided by the manufacturer, being 2.14 cm2 for the 19-mm valve and 3.14 cm2 for the 21-mm valve.
Statistical analysis
Time-related events were analyzed by the Kaplan-Meier method. Percentages of freedom from events are presented with standard error of the mean and confidence intervals. Comparisons between curves were performed by the Wilcoxon test. A p 
0.05 was considered significant. Data were analyzed with the statistical package SAS (SAS Institute, Del Mar, CA).
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Results
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Of the 94 patients, 69 patients (73.4%) received a 21-mm and 25 patients (26.5%), a 19-mmm aortic Perimount valve. Seventeen patients (18%) had concomitant coronary artery bypass grafting. The cardiopulmonary bypass and cross-clamping times were 94.7 ± 29 minutes and 68 ± 21 minutes, respectively. The operative mortality was 6.3% (6 of 94). Five patients died of low output syndrome and 1 patient of intractable bleeding. Two patients were reopened for bleeding.
Long-term follow-up
Of the 83 patients entered in the follow-up, 6 patients (7.2%) died. Two patients died of heart failure in peripheral hospitals; no signs of valve malfunction were found at clinical examination. Two patients died of cancer, and 2 patients died as a consequence of stroke. The Kaplan-Meier survival was 82.8% at 11 years (Fig 1). In patients with BSA less than 1.7 m2 the estimate of freedom from late death was 86%, whereas in patients with BSA more than 1.7 m2 the freedom from death was 73%. There was not a statistically significant difference (p = 0.08) between the two outcomes.
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Fig 1. Long-term freedom from death with and without operative mortality calculated by the Kaplan-Meier method. The dashed lines represent the confidence intervals. The table shows freedom rates without operative mortality. Survival estimates and patients at risk at observational times are also shown in the table. (Pts = patients.)
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A total of 11 cerebral thromboembolic events were observed in 8 patients. One patient had two transient ischemic attacks whereas one patient had three transient ischemic attacks. The international normalized ratios were in the low therapeutic range in all episodes. The Kaplan-Meier estimate of freedom from thromboembolism was 86.6% (Fig 2).
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Fig 2. Long-term freedom from thromboembolism calculated by the Kaplan-Meier method. Survival estimates and patients at risk at observational times are shown in the table. (Pts = patients.)
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Of the 23 patients taking warfarin for atrial fibrillation, 2 patients had a gastrointestinal bleeding that required hospitalization. At the time of the event, 2 years after operation, their international normalized ratios were 4.3 and 4.5, respectively.
One patient with a 21-mm valve experienced endocarditis 2 years after operation and underwent successful valve re-replacement with a new 21-mm Perimount valve.
At the end of the follow-up the New York Heart Association (NYHA) functional class of the patients improved as shown in Figure 3. All patients are reported well with a very satisfactory quality of life. In detail, patients in NYHA functional class I are able to carry out their daily routine and also some physical activity like a walk, or a game of golf in the younger patients. Patients in class II carry out their daily duties but do not exercise. Those 11 patients in NYHA class III are limited to indoor light activity.
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Fig 3. Comparison of New York Heart Association (NYHA) functional status of the 83 patients preoperatively and postoperatively (time of follow-up). The mean indicates the preoperative and postoperative mean NYHA class. (Preop = preoperatively; Postop = postoperatively; SD = standard deviation.)
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Echocardiography
Echocardiographic measurements at rest were collected at 14 ± 3.2 months after operation from 17 and 25 patients with 19-mm and 21-mm Perimount valves, respectively. Results are shown in Table 2.
With regard to the NYHA functional class of the 17 patients with 19-mm Perimount valves, 5 patients were in class I, 10 patients in class II, and 2 patients in class III. The EAI of these latter 2 patients was 0.83 and 0.87. Of the 25 patients with 21-mm Perimount valves, 12 patients were in NYHA class I, 10 patients in class II, and 3 patients in class III. The EAI of these latter 3 patients was 0.86, 0.90, and 0.89.
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Comment
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In the present study we have shown that elderly patients with a small aortic root who underwent implantation of a 19-mm or 21-mm Perimount valve had excellent long-term survival and event-free survival. These outcomes can be favorably compared with series of patients with Perimount aortic valves of larger diameter, as well as with patients with Intact or Mosaic bioprostheses [1–6, 12, 13]. In our patients with 19-mm valve there was no need for aortic root enlargement, and this contributed to keep the operative mortality (6%) within the expected rates for aortic valve replacement [1–5]. Enlarging the aortic root in a senescent aorta may be technically very challenging if we consider that most of the valves as well as the roots are heavily calcified. In our series there were several patients with calcified and frail aortic root; any more extensive procedure like aortic root enlargement would have meant increasing even further the risk of intraoperative bleeding. One of the operative deaths in our series was a result of uncontrollable bleeding from a porcelain aorta. In their series of patients with 19-mm Perimount aortic valves, Carrier and associates [12] reported an operative mortality of 12% in patients undergoing aortic root enlargement compared with an operative mortality of 6% in patients receiving the Perimount valve only. Sommers and David [14] reported that operative mortality was twice as high with patch enlargement of the aortic annulus compared with isolated valve replacement in middle-aged patients. Although hospital mortality was increased with aortic annulus enlargement, they recommend this technique to prevent patient–prosthesis mismatch [14]. Our results suggest that, unless for an extremely small annulus, there is no significant advantage to the use of an annulus enlargement technique in elderly patients in whom hospital mortality could be even higher than previously reported by Sommers and David [14] without a significant benefit in midterm survival and in survival free from valve-related complications.
This suggestion is based on the observation that at the end of the follow-up there was an improvement of NYHA functional class; preoperatively the mean NYHA class was 3 ± 1 whereas at the closing time of follow-up the NYHA class was 1.6 ± 0.7. Furthermore, when interviewed, patients declared they were leading active lives for their age and could take part in activities they could not do before the operation.
With regard to morbidity, thromboembolism was the most frequent complication by far. All the events occurred in patients receiving anticoagulant for atrial fibrillation. We prefer to anticoagulate our patients with tissue valves for the first 3 months postoperatively because the thromboembolic risk outweighs the risk of bleeding in this group of patients according to our unpublished audit data. The 86.6% rate of freedom from thromboembolism in our patients was similar to that observed in the series of Poirier and Cosgrove, being 88% in both studies [1, 5]. Thromboembolic rates in patients with aortic pericardial valves parallel those observed in patients with aortic porcine valves [1–6, 13].
No tissue failure was observed in our series, confirming once again that the pericardial valve is a valid option for the elderly patient needing aortic valve replacement. This outcome was in accordance with previous reports in which 100% freedom from structural degeneration was observed more than 14 years in an elderly subgroup of patients with aortic pericardial valves [1–5]. On the other hand, the same report noted that patients of intermediate age had a 92% freedom rate from valve failure whereas the youngest patients reached a 90.2% freedom rate [1].
As far as hemodynamic performances are concerned, both the 19-mm and 21-mm Perimount aortic valves exhibited good performances at rest.
Peak and mean transvalvular gradients are still the variables most frequently used to characterize a prosthetic heart valve. In our patients both the 19-mm and 21-mm Perimount valves showed satisfactory peak and mean gradients. This outcome is in accordance with the results found by McDonald and coworkers [8] and Takakura and coworkers [15] in series of patients with Perimount aortic valves of the same outer diameters. On the other hand, gradients in our patients with 21-mm Perimount valves were higher than those recorded in patients with a Mosaic valve of the same size [13–16]. Measurements of pressure gradients across different types of bioprosthetic and mechanical valves are reported to correlate well with catheter-derived gradients [7]. Further, bioprosthetic aortic valves have a central flow, which simplifies assumptions and measurement of velocities.
With regard to EOA, we found adequate valve areas in both sizes. Our data are similar to those reported by other authors [8, 15], although there are differences in the method of measurement. In our series we applied an edge-to-edge method for the calculation of the cross-sectional area, and in patients with a hypertrophic ventricular septum this may reduce EOAs. On the other hand some authors report valve areas calculated taking into account the valve prosthesis diameter as provided by the manufacturers. Both methods are accepted and validated against catheter-derived valve areas [9]. Nonetheless we prefer the edge-to-edge method as this provides information that take into account the pathologic characteristics of the left ventricle.
According to Pibarot and Dumesnil [11], an EAI of 0.85 or above could be considered adequate in patients with stented tissue valves. The mean EAI of our patients with 21-mm Perimount valves was 0.88 and was similar to the valve area indices of patients with 21-mm Perimount or Mosaic valves reported in other series [13, 16]. The EAI in the 17 patients with Perimount 19-mm valves may be considered inadequate, although no sudden death was observed and 1 of the 2 patients in NYHA class III has associated ischemic heart disease. The patient–prosthesis mismatch observed in our group of patients was found also in other series of patients with Mosaic 19-mm valves [13, 16].
We acknowledge the limitations of our study regarding the retrospective design and the small number of patients who underwent postoperative control echocardiograms.
In conclusion, the Perimount tissue valve in the small aortic annulus has yielded excellent long-term results and good hemodynamic performances. Therefore this prosthetic device is a very satisfactory option in elderly patients necessitating aortic valve replacement. Implantation of a Perimount bioprosthesis avoids enlargement of the small aortic annulus, reducing mortality and morbidity associated with this procedure.
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Acknowledgments
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The authors gratefully acknowledge the help of Angela Lillo, BS, for statistical analysis.
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References
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Abstract
Introduction
