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(Chest. 2000;118:1271-1277.)
© 2000 American College of Chest Physicians

Comparison of Aortic Valve Gradient During Exercise After Aortic Valve Reconstruction*

Thomas P. Graeter, MD; Michael Kindermann, MD; Roland Fries, MD; Frank Langer, MD and Hans-Joachim Schäfers, MD, FCCP

* From the Departments of Thoracic and Cardiovascular Surgery (Drs. Graeter, Langer, and Schäfers) and Cardiology (Drs. Kindermann and Fries), University Hospitals, Hamburg, Germany.

Correspondence to: Thomas P. Graeter, MD, Department of Thoracic and Cardiovascular Surgery, University Hospitals, 66421 Hamburg/Saar, Germany; e-mail: chtgrae{at}rz.uni-sb.de


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Purpose: Aortic valve preservation is a promising alternative to conventional composite replacement of aortic valve and ascending aorta. This approach may have a physiologic benefit compared with valve replacement similar to that seen in mitral valve reconstruction. We investigated aortic valve gradients at rest and during exercise in patients who had undergone valve-preserving aortic replacement and compared them with composite replacement of valve and aorta.

Methods: Four groups were studied: nine patients underwent composite valve replacement (group A: valve diameter, 23 to 27 mm), eight patients underwent remodeling of the aortic root (group B), and another nine patients had reimplantation of the aortic valve (group C). Healthy volunteers were studied as a control group (group D). Using continuous-wave Doppler echocardiography, all patients were examined on a bicycle ergometer for aortic valve gradients (0 to 75 W).

Results: There were no differences among the groups with respect to age, body surface, left ventricular end-diastolic diameter, fractional shortening, or left ventricular mass. Maximum resting gradients were significantly elevated in group A compared with groups B, C, and D (group A: 21.3 ± 7.1 mm Hg; group B: 9.0 ± 4.5 mm Hg; group C: 8.6 ± 3.7 mm Hg; group D: 4.9 ± 1.6 mm Hg; p < 0.05). At 75 W, group A exhibited significantly higher gradients than all other groups (group A: 31.3 ± 7.5 mm Hg; group B: 13.9 ± 6.6 mm Hg; group C: 12.8 ± 3.5 mm Hg; group D: 9.2 ± 1.9 mm Hg; p < 0.05). There was no significant difference among the other groups. Both valve-preserving groups had only insignificantly higher gradients than the control group.

Conclusion: Our data strongly support the suggestion that preserving the aortic valve restores nearly normal hemodynamic function of the aortic valve. Long-term observations will have to prove the clinical relevance of restoring physiologic aortic valve hemodynamics.

Key Words: aortic valve • exercise • gradients • reimplantation • remodeling


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Composite replacement of the aortic valve and the proximal aorta has become a standard operation for combined aortic dilatation and aortic valve disease.1 2 3 4 The prosthetic valve, however, is known for its elevated transvalvular gradient at rest as well as during exercise.5 6 Aortic valve-preserving operations are a promising clinical alternative to composite replacement of the valve and ascending aorta with reasonable results.2 7 Remodeling of the aortic root was first described by Sarsam and Yacoub,8 and reimplantation of the aortic valve was described by David and Feindel.9 Hemodynamic evaluations at rest have shown that preserved valves have a low transvalvular gradient.2 7 9 However, hemodynamic performance at rest is not truly representative of a patient’s daily activities. Theoretically, preserved valves should have a markedly superior hemodynamic performance compared with mechanical valves, particularly during conditions of exercise. We examined this hypothesis by comparing exercise hemodynamics in patients after composite replacement, remodeling of the aortic root, reimplantation of the aortic valve, or healthy volunteers.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
Four groups of individuals agreed to be studied, and informed consent was obtained from the patients. No patient contacted refused participation.

Group A consisted of nine patients after composite replacement of aortic valve and ascending aorta (Carbomedics; Hamburg, Germany). In group B, eight patients were examined after remodeling of the aortic valve. Group C consisted of nine patients who were studied after reimplantation of the aortic valve. As a control group, we used healthy young volunteers (group D, n = 10).

The diagnoses leading to the operation were similar in groups B and C, with all patients having either acute aortic dissection type A or an ascending aortic aneurysm combined with aortic valve regurgitation. In group A, most patients suffered from aortic valve stenosis coupled with an ascending aortic aneurysm (Table 1 ).


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  		Table 1.. Preoperative Diagnosis Leading to Operation*

 
To achieve stable hemodynamic conditions, selected patients were studied >= 12 months after their operation. With respect to the size of the implanted valve, we chose patients with a valve diameter of >= 23 mm. In the valve-sparing groups, only patients with tricuspid valves were asked to participate. In groups B, C, and D, the diameter of the valve was measured by echocardiography. Left ventricular end-diastolic diameters and fractional shortening were similar in all groups. The thickness of the interventricular septum was less in the control group, but almost identical in the other groups. The aortoventricular diameter measured by echocardiography showed the highest values in the control group, whereas diameters were minimally larger in group C compared with group B. These differences were not significant (Table 2 ). Preoperative left ventricular ejection fraction as measured during angiography was similar in all groups.


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  		Table 2.. Resting Hemodynamics*

 
Aortic valve hemodynamics were evaluated at rest and during exercise.

Operative Procedures
In patients with ascending aortic aneurysm and aortic valve stenosis, composite replacement of the aortic valve and ascending aorta was performed in typical fashion.1

In the presence of moderate dilation of the aortic root (sinotubular diameter < 5 cm, aortoventricular diameter < 3 cm) and aortic valve regurgitation caused by aortic dilatation or aortic dissection type A, a remodeling approach of the aortic root was chosen. The aortic sinuses were excised, and a Dacron graft was then chosen with a diameter corresponding to that of the aortoventricular junction. One end of the graft was configured so that the edges resembled the insertion lines of the aortic valve leaflets. The graft was then sutured to the aortic valve insertion, thus remodeling the aortic root.8

If severe root dilatation was present (sinotubular ridge > 5 cm, aortoventricular junction > 3 cm), a reimplantation approach was chosen. After excision of the sinuses, the aortic root was mobilized to the level of the aortoventricular junction. A Dacron graft was chosen according to the maximum height of the aortic valve leaflets, leaving approximately 40% of leaflet height for coaptation. The graft was anchored in the aortoventricular junction, and the valve was reimplanted within the graft in typical fashion.9

Aortic cross-clamp time was shortest in composite replacement (63 ± 14 min); however, only the difference to valve reimplantation was statistically significant (p < 0.05; Table 3 ). Accordingly, the time on bypass was longest in group C, significantly higher compared with group A (p < 0.05).


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  		Table 3.. Prestudy and Intraoperative Demographic Data*

 
Partial arch replacement was performed as required in nine patients (group A, n = 1; group B, n = 5; group C, n = 3). One patient underwent total arch replacement (group C).

Additional coronary surgery was required in three patients in the remodeling group and one patient in the reimplantation group. Another patient in the reimplantation group had concomitant mitral valve repair.

Patients in the valve-sparing groups had no previous cardiac surgery. In the composite group, two patients had previous aortic valve replacement, and another had supracommissural aortic replacement.

Hemodynamic Assessment
The Ultramark 9 (Advanced Technology Laboratories; Bothell, WA) was used for all measurements. Left ventricular end-systolic and end-diastolic dimensions and thickness of left ventricular posterior wall and interventricular septum were assessed in the short axis of a parasternal view by multiple M-mode measurements with calculation of fractional shortening.

Aortic valve maximum Doppler echocardiographic velocity was measured with a continuous-wave transducer (ATL 2.00 MHz CW, PN 4000–0307-03; Advanced Technology Laboratories). Particular care was taken to obtain the highest possible velocity by variation of the acoustic window and transducer orientation. The modified Bernoulli equation was used to calculate peak gradients (P = 4 x V2, where V is the peak transvalvular flow velocity), and mean pressure gradients were obtained by averaging the cardiac cycle measurement that resulted in the highest peak gradient. For semiquantitative measurement of aortic valve insufficiency at rest, the diameter of the regurgitation jet in relation to the left ventricular outflow tract was used as well as the intensity and decrease of the regurgitation signal in the continuous-wave Doppler echocardiography.10 11 Regurgitation was quantified into five grades: 0, none; 1, minimal (regurgitation jet or left ventricular outflow tract < 5%); 2, mild (5 to 10%); 3, moderate (10 to 40%); and 4, severe insufficiency (> 40%).

During bicycle exercise, patients were sitting on a reclining seat at a 50° position (Ergo-Metrics 900 L; Ergoline; Bitz, Germany). The starting workload was 25 W, which was increased by 25 W every 3 min until symptomatic termination of the test occurred (dyspnea, muscular fatigue). To facilitate Doppler echocardiographic measurements during exercise, the chest site where optimum Doppler echocardiographic waveforms were recorded was marked before starting exercise. In case of unsatisfactory Doppler echocardiographic signal, the whole exercise unit was tilted slightly to the left side until optimal measurements were obtained. Measurements were taken during the last minute of each 3-min workload cycle. BP and heart rate were measured noninvasively every minute using a sphygmomanometer cuff fixed on the right arm.

Statistical Methods
Results were expressed as mean ± SD. A Mann-Whitney U test was used for comparative analysis of continuous variables in two groups of patients. Analysis of variance was used for comparisons among all four patient groups. Statistical significance was established at p < 0.05. Data were analyzed post hoc according to Bonferroni–Dunn.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
Clinical and demographic data of the patients and controls are shown in Table 3 . Sex distribution was similar in all groups. The age was significantly lower in the control group, but did not vary greatly among the other groups.

Systolic BP and corresponding heart rate at different exercise levels are demonstrated in Figures 1 , 2 . In all groups, they increased during bicycle exercise and returned to near normal values after 5 min of rest.



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  		Figure 1.. Heart rate (HR) at rest and exercise.

 


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  		Figure 2.. Systolic (syst) BP at rest and exercise.

 
All patients reached a 50-W workload. The 75-W exercise level was reached by seven of nine patients in group A, by seven of eight patients in group B, and eight of nine patients in group C.

Comparing the peak (Fig 3 ) and mean (Fig 4 ) pressure gradients during exercise, gradients were consistently higher in patients with composite valves and lowest in healthy volunteers. In group A, maximum resting gradients increased from 21.3 ± 7.1 mm Hg at rest to 31.3 ± 7.5 mm Hg at 75 W. This was significantly higher than in all other groups (p < 0.05). In the remodeling group, gradients increased from 9 ± 4.5 mm Hg at rest to 13.9 ± 6.6 mm Hg at 75 W. Resting values in the reimplantation group were 8.6 ± 3.7 mm Hg, which increased to 12.8 ± 3.5 mm Hg at 75 W. Slightly lower gradients were measured in the control group: 4.9 ± 1.6 mm Hg at rest and 9.2 ± 1.9 mm Hg at 75 W. Patients with reconstructed valves had minimally higher gradients than the control subjects at all exercise levels, but this was not statistically significant. Testing for between-group differences at rest and exercise demonstrated no statistical significance comparing groups B, C, or D, but the composite group had significantly higher values than all other groups (Bonferroni–Dunn, p < 0.05).



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  		Figure 3.. Maximum aortic valve gradients during different levels of exercise (*significantly elevated, p < 0.05).

 


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  		Figure 4.. Mean aortic valve gradients at rest and during exercise (*significantly elevated, p < 0.05).

 
Mean pressure gradients had the same tendency as peak gradients. They were higher in all groups during exercise, and again, the composite group exhibited significantly higher gradients than all other groups. Examining groups B, C, and D demonstrated only minor differences that did not reach statistical significance.


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
To preserve the native aortic valve, two valve-sparing procedures have been proposed for patients with aortic regurgitation and dilatation of the ascending aorta. Sarsam and Yacoub8 introduced remodeling of the aortic root, whereas David and Feindel9 chose the more aggressive approach of reimplanting the aortic valve in a vascular graft. Low resting aortic valve gradients have been reported for both procedures.2 7 9 These gradients are comparable to those reported for pulmonary autografts.12 It has been emphasized that the physiologic function of the pulmonary autograft becomes particularly apparent during conditions of exercise. Nevertheless, the Ross procedure involves a two-valve operation with an unproved prognosis and a higher operative risk owing to more extensive surgery. The prognosis in remodeling or reimplantation procedures is encouraging in midterm follow-ups, but involving only one valve, the operative risk in our opinion is slightly lower. Until now, to our knowledge, hemodynamic exercise studies after aortic valve reimplantation or root remodeling have not been published.

Simultaneous Doppler and catheterization studies have shown that continuous-wave Doppler ultrasound can accurately predict pressure gradients across prosthetic valves in the aortic position.6 Comparing invasively measured gradients with Doppler gradients, a continuous overestimation of the gradient by Doppler echocardiography is seen. As this is a systematic overestimation affecting all measurements, it does not reduce the clinical significance of the results.6 Cardiac output greatly influences the measurement of aortic valve gradients. We did not measure cardiac output by echocardiography, as this is another flow-dependent variable and therefore prone to the same systematic error as gradient measurements. Considering that BP and heart rate increased adequately and similarly during exercise in all groups, we assumed a similar rise of cardiac output. This theory is further supported by the fact that left ventricular resting variables imply normal function in all groups and no patient had to break off the exercise because of angina or dyspnea. Nevertheless, this is a limitation of this study.

Our control measurements were compatible with the results of healthy volunteers in the group studied by Oury et al.12 We found a resting peak gradient of 20 ± 7 mm Hg (mean gradient, 11 ± 4 mm Hg) in nine patients after composite replacement. Previously reported peak gradients at rest and exercise for normally functioning composite valves are comparable to our findings.2 13 As the results of these two groups are comparable to the findings of others, this is an indication for a similar and reproducible setup. Again, compared with the data currently available, resting gradients in our patients have been in a very similar range.2 7 9 12 We measured mean gradients of 8 ± 4 mm Hg (group B) and 7 ± 3 mm Hg (group C) at a workload of 50 W. In comparison with healthy young men, these gradients were only slightly and not significantly elevated (Fig 3 , 4) . Taking into account the significantly lower age in the control group might explain lower gradients in this group, as natural aortic valve performance worsens with age.

Thus, rest and exercise values of the reconstructed valves are only slightly higher than in the control group, but significantly lower compared with mechanical replacement of the aortic valve, implying an almost normal physiologic behavior. Transvalvular gradients were minimally higher in the remodeling group compared with the reimplantation group, but these differences were not statistically significant and may be physiologically negligible.

Westaby et al14 and Jin et al15 demonstrated that left ventricular remodeling after aortic valve replacement occurs within the first 6 months. We therefore chose patients >= 1 year postoperatively to have stable hemodynamic conditions. Postoperative data on left ventricular function or muscular hypertrophy revealed no significant differences among the groups, although the valvular gradient in the composite group was drastically elevated.

One variable influencing transprosthetic flow is the shape and surface of the valve. During exercise, a possible increase of effective orifice area may also be of importance, but data concerning this issue are conflicting and methodologically problematic inasmuch as formulas for calculation of effective orifice area are flow dependent.16 The diameter of the aortoventricular junction in the valve-sparing groups was almost 2 mm wider in the reimplantation group. This might explain the minimal difference in gradients between the valve-sparing groups, as the aortic valve gradient decreases with increasing valve diameter.17

Another part of the hemodynamic performance after valve replacement addresses the distensibility of the aortic root.18 In groups A and C, the ascending aorta is completely replaced, whereas in group B, there are remnants of the aortic wall close to the insertion lines of the aortic valve. This would, in fact, favor the remodeling procedure, but gradients in this group were similar or even slightly higher than in the reimplantation group. Although the aortic root in valve-sparing aortic replacement is lacking natural elasticity, both groups demonstrated almost physiologic aortic valve function.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
The hemodynamic performance of the aortic root repaired by valve-preserving approaches (remodeling or reimplantation) is only slightly inferior to that of natural valves in healthy young men. Our data strongly support the suggestion that preservation of the aortic valve leads to essentially physiologic hemodynamics. Long-term observations will have to prove the clinical relevance of restoring physiologic aortic valve hemodynamics.

Received for publication November 11, 1999. Accepted for publication May 15, 2000.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

  1. Bentall, H, DeBono, A (1968) A technique for complete replacement of the ascending aorta. Thorax 23,338-339[ISI][Medline]
  2. Borst, HG, Laas, J (1993) Surgical treatment of thoracic aortic aneurysms. Adv Card Surg 4,47-87[Medline]
  3. Bachet, J, Termingnon, JL, Goutot, B, et al (1996) Aortic root replacement with a composite graft: factors influencing immediate and long term results. Eur J Cardiothorac Surg 10,207-213[Abstract]
  4. Gott, VL, Gillinov, AM, Pyeritz, RE, et al (1995) Aortic root replacement: risk factor analysis of a seventeen year experience with 270 patients. J Thorac Cardiovasc Surg 105,435-438[Abstract]
  5. Hachida, U, Koyanagi, H, Nonoyama, M, et al (1998) Serial hemodynamic study after aortic valve replacement in patients with narrow aortic roots. J Heart Valve Dis 7,81-85[ISI][Medline]
  6. Burstow, DJ, Nishimure, RA, Bailey, KR, et al (1989) Continuous Doppler echocardiographic measurements of prosthetic valve gradient: a simultaneous Doppler catheter correlative study. Circulation 80,504-514[Abstract/Free Full Text]
  7. Schäfers H-J, Fries R, Langer F, et al. Valve preserving replacement of the ascending aorta: remodeling vs reimplantation. J Thorac Cardiovasc Surg 2000 (in press)
  8. Sarsam, MA, Yacoub, M (1993) Remodeling of the aortic valve annulus. J Thorac Cardiovasc Surg 105,435-438
  9. David, TE, Feindel, CF (1992) An aortic valve sparing operation for patients with aortic incompetence and aneurysm of the ascending aorta. J Thorac Cardiovasc Surg 103,617-622[Abstract]
  10. Nishimura, RA, Vonk, GD, Rumberger, JA, et al (1992) Semiquantification of aortic regurgitation by different Doppler echocardiographic techniques and comparison with ultrafast computed tomography. Am Heart J 124,995-1001[CrossRef][ISI][Medline]
  11. Wilkenshoff, UM, Kruck, I, Gast, D, et al (1994) Validity of continuous wave Doppler and color Doppler in the assessment of aortic regurgitation. Eur Heart J 15,1227-1234[Abstract/Free Full Text]
  12. Oury, JH, Doty, DB, Oswalt, JD, et al (1998) Cardiopulmonary response to maximal exercise in young athletes following the Ross procedure. Ann Thorac Surg 66(suppl),S153-S154
  13. Strike, PC, Edwards, TJ, Gardiner, D, et al (1998) Functional hemodynamic assessment of the 21 mm and 23 mm Carbomedics Top Hat aortic prosthetic valve. J Card Surg 13,98-103[CrossRef][ISI][Medline]
  14. Westaby, S, Amarasena, M, Long, V, et al (1995) Time related hemodynamic changes after aortic replacement with the Freestyle stentless xenograft. Ann Thorac Surg 60,1633-1639[Abstract/Free Full Text]
  15. Jin, XY, Westaby, S, Gibson, DG, et al (1997) Left ventricular remodelling and improvement in Freestyle stentless valve hemodynamics. Eur J Cardiothorac Surg 12,63-69[Abstract]
  16. Schwammenthal, E, Vered, Z, Rabinowitz, B, et al (1997) Stress echocardiography beyond coronary artery disease. Eur Heart J 18(suppl D),130-137
  17. Sintek, CF, Fletcher, AD, Khonsari, S (1995) Stentless porcine aortic root: valve of choice for the elderly patient with small aortic root? J Thorac Cardiovasc Surg 109,871-876[Abstract]
  18. Brewer RJ, Deck JD, Capat ID, et al. The dynamic aortic root: its role in aortic valve function. J Thorac Cardiovasc Surg 1976; 72:413–417



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