HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Ulf Abdel-Rahman Anton Moritz Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kleine, P. Articles by Moritz, A. Search for Related Content PubMed PubMed Citation Articles by Kleine, P. Articles by Moritz, A. Related Collections Cardiac - physiology Valve disease

J Thorac Cardiovasc Surg 2002;124:925-932
© 2002 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease (ACD)

Effect of mechanical aortic valve orientation on coronary artery flow: Comparison of tilting disc versus bileaflet prostheses in pigs

From the Department of Thoracic & Cardiovascular Surgery^a and the Department of Biomedical Statistics,^b Johann-Wolfgang-Goethe University, Frankfurt/Main, Germany.

Study funding by: Medtronic Inc, Minneapolis, Minn.

Received for publication April 16, 2002. Revisions requested April 24, 2002; revisions received April 26, 2002. Accepted for publication April 27, 2002. Address for reprints: Peter Kleine, MD, Department of Thoracic & Cardiovascular Surgery, University Hospital, Theodor-Stern-Kai 7, 60596 Frankfurt/Main, Germany (E-mail: P.Kleine{at}em.uni-frankfurt.de).

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
Objective: Orientation for optimal systolic performance of tilting disc and bileaflet aortic valves was defined in previous studies. The present study investigates the influence of valve orientation on coronary artery flow in an animal model.
Methods: A rotation device holding either a Medtronic Hall tilting disc (n = 4; Medtronic, Inc, Minneapolis, Minn), a St Jude Medical bileaflet (n = 4; St Jude Medical, Inc, St Paul, Minn), or a Medtronic Advantage bileaflet (n = 3) aortic valve was implanted. The device allowed rotation of the valve without reopening the aorta. Flow through the left anterior descending coronary artery was measured preoperatively and at normal versus high cardiac output after weaning from extracorporeal circulation. Measurements were performed at the best and worst hemodynamic position, as defined previously.
Results: Coronary flow rates were similar in all animals preoperatively (26 ± 4.1 mL/min). After aortic valve replacement, left anterior descending flow increased significantly to 58.2 ± 10.6 mL/min. Highest flow rates at normal cardiac output were found in the optimum orientation, especially for the Medtronic valves (Medtronic Hall, 64 ± 8.7 mL/min; Medtronic Advantage, 64.6 ± 11.6 mL/min; St Jude Medical, 48.3 ± 10.3 mL/min), whereas the worst position demonstrated significantly lower left anterior descending flow, with no differences among valves (Medtronic Hall, 37.5 ± 1.3 mL/min; St Jude Medical, 35.7 ± 10.7 mL/min; Medtronic Advantage, 39.8 ± 10 mL/min). Left anterior descending artery flow increased significantly with higher cardiac output.
Conclusions: Coronary blood flow was significantly influenced by mechanical aortic valve implantation and the orientation of prostheses. For both valve designs, the previously defined optimum orientation with respect to pressure gradients and turbulence demonstrated the highest left anterior descending flow rates. Even in its optimum orientation, the St Jude Medical valve showed significantly lower coronary flow than the other valves.

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
Systolic and diastolic performance of tilting disc and bileaflet mechanical aortic valve substitutes have been investigated intensively in vitro ^1-3 and in vivo ^4-6 for the past 20 years. The in vitro studies usually did not incorporate the physiologic anatomy (angled outflow tract and sinuses of Valsalva), although these facts have an important effect on the flow conditions in the aortic root. ^7,8 Thus, in vivo studies reflect the complex reality, with a resulting asymmetric-eccentric flow and the highest flow velocities along the noncoronary cusp, ⁹ more precisely than in vitro studies.

Because of the flow profile in the aortic root, orientation of mechanical aortic valve substitutes has an important effect on the hemodynamic performance, and each valve design has its own optimal orientation. Animal studies must be performed in addition to in vitro setups to define this design-related optimal orientation. ¹⁰ In a previous animal study, ¹¹ optimal orientation for tilting disc (Medtronic Hall [MH]; Medtronic, Inc, St Paul, Minn) and bileaflet (St Jude Medical [SJM]; St Jude Medical, Inc, St Paul, Minn) valves was investigated. The MH valve showed almost physiologic hemodynamic performance with respect to downstream turbulence, with its major orifice facing the right posterior wall, the region of the noncoronary (posterior) cusp. The SJM valve could not achieve the almost physiologic results of the MH valve but was less susceptible to orientation. Its best results were obtained with one orifice oriented toward the right cusp. In this orientation the area of major flow was distributed equally among the 2 side orifices and the central slit.

After this animal study, the systolic performance of both valves was investigated in clinical studies. ^12-14 The tilting disc mechanism showed superior hemodynamic performance compared with that of the bileaflet mechanism with implantation of both valves in their optimum orientation. The superiority of the tilting disc mechanism was more pronounced in the smaller valves. The effect of valve orientation on the diastolic performance of mechanical aortic valves has not yet been investigated in such detail. It has been assumed that valve closure is determined exclusively on the basis of design and the valve-closure mechanism. Closing reflux and leakage flow both combine to create disturbed flow in the sinuses of Valsalva. ^15,16 The acute physiologic effect of these changes in aortic root flow pattern on coronary flow has not been fully elucidated. In one pilot study ¹⁷ it was demonstrated that flow velocities in the left anterior descending artery (LAD) increased significantly immediately after aortic valve replacement, but this study focused on the effect of cardioplegia and not on valve design or orientation. The present study investigates the effect of these factors on LAD flow immediately after mechanical aortic valve replacement in an animal model. It was hypothesized that a tilting disc valve demonstrating low systolic downstream turbulence at the level of the aortic root would allow a more physiologic diastolic coronary perfusion. Thus, it was assumed that valve orientation will not only influence systolic values but also coronary artery flow. A 21-mm MH tilting disc valve and a 23-mm SJM valve were chosen because these valve sizes offered equivalent pressure gradients in a previous study. ¹² Additionally, a newly designed bileaflet valve was investigated, a 23-mm Medtronic Advantage (MA) valve. This valve was chosen because it has a larger central slit and a reduced leakage flow compared with that of the SJM bileaflet valve substitute.

	Methods

Top Abstract Introduction Methods Results Discussion References

 
The animal study was performed according to the guidelines for animal experiments in Germany. The study comprised 11 healthy pigs with a body weight of 67 ± 5 kg. General anesthesia was achieved by administering fentanyl (1.5 µg · kg^-1 · h^-1) and propofol (2 mg/kg for initiation and 10 µg · kg^-1 · h^-1 for maintenance). Monitoring included electrocardiography, blood pressure, central venous pressure, pulmonary artery pressure, and blood temperature. Pulmonary capillary wedge pressure and cardiac output (CO) were measured intermittently, as mentioned below.

A median sternotomy was carried out in the usual manner. Measurement of hemodynamic parameters (heart rate, central venous pressure, blood pressure, pulmonary artery pressure, CO, and pulmonary capillary wedge pressure) was performed. In addition, the LAD flow rate before aortic valve replacement was measured with a perivascular ultrasound device (Transonic Flow-QC; Transonic Systems Inc, Ithaca, NY). The coronary artery was dissected in its middle segment, and a 2.5-mm flow probe (Transonic BF 2.5 SB) was placed and left in place for the remainder of the operation, providing continuous qualitative and quantitative measurement of LAD flow. ^18,19 Starting from the qualitative flow curves, total coronary flow was calculated by integral. The values mentioned in the "Results" section represent the calculated total coronary flow results.

Extracorporeal circulation was established by means of cannulation of one carotid artery and a 2-stage venous catheter. After crossclamping of the aorta, 1000 mL of St Thomas' Hospital solution was administered into the aortic root to achieve cardiac arrest, followed by 500 mL every 20 minutes administered directly into the coronary ostia. Normothermia was maintained during extracorporeal circulation. After complete dissection of the ascending aorta, the native valve was excised, and one of the 3 rotation devices was implanted with 3 running 4-0 Prolene sutures (Ethicon, Inc, Somerville, NJ).

The rotation device containing the MH valve was implanted in 4 pigs, the SJM valve in 4 pigs, and the MA valve in the remaining 3 pigs. All valves were rotated alternately between the previously defined optimum and worst orientation with respect to systolic performance. Furthermore, each valve was alternately measured in the initial optimum and worst orientation to avoid the performance of measurements in the same succession.

Construction of the rotation devices
The rotation devices (Acutec, St Michael, Minn) were comparable with those used in previous experiments. ¹¹ They consisted of an outer conventional sewing ring and 2 inner rings, between which the rotation was performed with 2 monofilament lines. The 21-mm MH, 23-mm SJM, and 23-mm MA valves were fixed into the inner ring. After valve implantation, the 2 monofilament lines were passed through the aortic wall; pulling one monofilament line 2 cm led to a 45° rotation of the implanted valve without reopening of the aorta. The implanted rotation device holding the MH valve is shown in Figure 1.

View larger version (186K): [in this window] [in a new window]   Fig. 1. Implanted rotation device holding an MH tilting disc valve. Two monofilament lines (arrows) have been passed through the aortic wall. Pulling one of the lines 2 cm led to a 45° rotation of the implanted valve.

Optimum and worst position for the MH tilting disc valve ¹¹

View larger version (15K): [in this window] [in a new window]   Fig. 2. Optimum (A) and worst (B) orientation of the MH tilting disc valve. 12 In the hemodynamically best orientation, the major orifice faces the noncoronary cusp, the region of major flow during ejection. Rotation of 180° leads to the hemodynamically worst orientation. RCA, Right coronary artery; NCC, noncoronary cusp; LCA, left coronary artery.

Optimum and worst position for the SJM bileaflet valve ¹¹

View larger version (16K): [in this window] [in a new window]   Fig. 3. Optimum (A) and worst (B) orientation of the SJM bileaflet valve. 12 Optimum hemodynamics are achieved with one orifice facing the right cusp. The area of major flow is distributed equally to the 3 openings. Rotation of 90° leads to the worst orientation. RCA, Right coronary artery; NCC, noncoronary cusp; LCA, left coronary artery.

The aortotomy was closed with 2 lines of running 4-0 Prolene sutures. Subsequent reperfusion resulted in a satisfactory hemodynamic situation. Thus, all pigs could be successfully weaned from extracorporeal circulation with no or low dosages of inotropic support.

After decannulation, a complete series of the above-mentioned hemodynamic parameters and the LAD flow rates were measured at a constant CO (4.2 ± 0.4 L/min). The valves were then rotated into the opposite orientation. Again, the hemodynamic parameters and LAD flow rates were measured. The valves were repeatedly rotated between the different orientations to exclude the effect of time span between operation and measurements. CO was then increased to 5.9 ± 0.3 L/min with inotropic medication (0.36-0.48 µg · kg^-1 · min^-1 epinephrine) and administering additional intravenous volume. Hemodynamic parameters and LAD flow rates were again determined in both orientations.

Statistical analysis
As a first step of statistical analysis, Gaussian normal distributions of results obtained for hemodynamic parameters and LAD flow rates were tested by using the Dallal-Wilkinson corrected and Kolmogoroff-Smirnoff tests. ²⁰ If this could be verified as the result of a small deviation of results, differences between the valves were assessed with 2-sample t tests, analysis of variance, and multiple comparisons with the Scheffé test with 95% confidence limits. ²⁰ The commercially available statistical software BIAS was used to perform the statistical analysis.

	Results

Top Abstract Introduction Methods Results Discussion References

 
The preoperative data did not vary significantly among animals. Heart rate was 95 ± 7 beats/min, and the other hemodynamic parameters were within normal ranges. The mean LAD flow rate was 25.9 ± 3.2 mL/min, without differences among valve groups. The mean CO was 4.2 ± 0.6 L/min. Aortic valve replacement could be performed without complications at a mean crossclamp time of 52 ± 9 minutes. Bypass time was 102 ± 11 minutes and did not show any significant differences among the 3 implanted valve groups. Figure 4 demonstrates the results of LAD coronary flow rate measurements in the different orientations postoperatively at normal and high COs. The results for normal CO were obtained at the following stable hemodynamic parameters. For MH valves, heart rate was 103 ± 6 beats/min, systolic blood pressure was 100 ± 9 mm Hg, diastolic blood pressure was 53 ± 6 mm Hg, and CO was 4.1 ± 0.4 L/min. For SJM valves, heart rate was 107 ± 9 beats/min, systolic blood pressure was 107 ± 10 mm Hg, diastolic blood pressure was 58 ± 8 mm Hg, and CO was 4.3 ± 0.6 L/min. For MA valves, heart rate was 106 ± 5 beats/min, systolic blood pressure was 106 ± 9 mm Hg, diastolic blood pressure was 55 ± 6 mm Hg, and CO was 4.3 ± 0.5 L/min. After these measurements, CO was increased to a higher output (mean, 5.9 ± 0.3 L/min). Again, stable hemodynamic conditions were achieved, with an increased heart rate of 107 ± 11 beats/min, a mean systolic pressure of 132 ± 12 mm Hg, and a mean diastolic pressure of 73 ± 13 mm Hg. There were no significant hemodynamic differences among groups.

View larger version (29K): [in this window] [in a new window]   Fig. 4. Coronary flow rates for the MH (A), SJM (B), and MA (C) valves. After aortic valve replacement, each individual animal demonstrated a significant increase in coronary flow from preoperative values. The highest LAD flow rates were obtained in the optimum orientation (best), whereas rotation into the worst orientation led to significantly lower flow. Increase of CO from normal (NO) to high (HO) values led to a further increase of coronary flow. The valves were repeatedly rotated between the different orientations to increase reproducibility of results.

View larger version (14K): [in this window] [in a new window]   Fig. 5. Qualitative measurement of the LAD coronary artery flow after aortic valve replacement with the 21-mm MH valve in the best orientation, from which peak and total coronary flow were calculated. The main portion of coronary flow remains during diastole (D), with a smaller peak during systolic (S) ejection (arrow). Similar results were obtained with other orientations and also with the SJM and MA valves.

MA bileaflet valve
Preoperative LAD flow was slightly higher in the animals with MA valves (28.3 ± 3.8 mL/min), but this difference was not significant. The postoperative results were more comparable with those of the MH tilting disc valve than with those of the SJM valve. At normal CO, LAD flow increased to 64.7 ± 11.0 mL/min (P <.001) in the optimum and 47.0 ± 14.7 mL/min (P <.05) in the worst orientation. This difference between best and worst orientation was also significant (P <.05). For the MA valve, a higher CO again led to an increase in LAD flow rates (113.7 ± 14.1 mL/min in the optimum and 78.3 ± 18.6 mL/min in the worst orientation).

All results regarding LAD flow rates at normal and high COs for the 3 valves are summarized in Table 1.

After rotation of all valves into their worst position, LAD flow rates were similar in all valve designs, with no statistical differences either at low or high CO.

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The flow profile of the aortic root is characterized by an asymmetric-eccentric flow, with the highest flow velocities along the noncoronary cusp. ⁹ This flow distribution, as well as the anatomic characteristics (angled outflow tract and vortex formation of cardiac muscle fibers leading to a spiral ejection pattern), have not been duplicated in the majority of in vitro studies from which most information regarding hemodynamic performance of mechanical aortic valve substitutes has been obtained. Thus, in vivo studies have an increased importance in determining the expected clinical hemodynamics of aortic valves. In previous animal and clinical studies ^11-14 the systolic hemodynamic performance of 2 different mechanical valves (ie, the MH valve, representing the asymmetric tilting disc design, and the SJM valve, representing the symmetric bileaflet design) have been investigated to determine their characteristics under conditions of natural eccentric flow. For both valve types, an optimal orientation with respect to downstream turbulence and transvalvular pressure gradients has been determined. The tilting disc valve showed the best results, with its major orifice facing the noncoronary leaflet. This corresponds to results obtained earlier. ¹⁸ The optimal orientation of the bileaflet valve was achieved with one of the leaflets oriented toward the right cusp. Because of its asymmetric design matching the natural eccentric flow, the MH valve guaranteed superior results in its optimum orientation compared with the SJM valve. These studies did not focus on diastolic valve performance (amount of leakage flow and closing characteristics of the different valve designs).

Diastolic function of mechanical aortic valves, focusing on the disturbed flow distribution in the sinuses of Valsalva, has not yet been intensively investigated in vivo. Thus, most information regarding the closing phase has been obtained in vitro without duplicating the physiologic flow conditions, even though some setups included a reconstruction of the sinuses. ¹⁹ These studies reported a relatively large closing reflux and leakage flow across the closed SJM valve, whereas the MH valve has only a small closing reflux and leakage flow. ^1,2 The in vitro data from the MA bileaflet valve have not been published yet.

Several clinical studies have demonstrated dramatic changes in coronary blood flow in patients with aortic stenosis, as well as in those with aortic regurgitation, which normalize to a certain extent after aortic valve replacement ^21,22 but remain pathologic under stress conditions. ²³ It was demonstrated that aortic valve replacement, including extracorporeal circulation and administration of cardioplegic solution, immediately leads to increased coronary flow, which persists for at least 20 hours postoperatively. ^17,24 This can be explained by a lower coronary artery resistance after extracorporeal circulation, which depends on the type of cardioplegic solution. ²⁵

The present study did not focus on the effect of aortic valve replacement itself on coronary artery flow but on the role of valve orientation and design. It has been demonstrated before that valve design and orientation have an effect on turbulence downstream. ¹¹ This was observed approximately 4 cm downstream from the valve. We did not investigate flow in the sinuses of Valsalva, from which the coronary arteries arise, but a change in flow pattern here can be expected as a consequence of the disturbed flow further downstream.

In all 3 valves the hemodynamically optimal orientation, which was previously defined with respect to systolic parameters, such as pressure gradients or downstream turbulence, showed the highest LAD flow rates. Implantation of the MH valve in the optimum orientation, which was accompanied by the most physiologic flow with respect to downstream turbulence during ejection, ¹¹ now led to the highest LAD flow rates. This might be explained by a correlation between low aortic root turbulence and coronary flow rate. This is further supported by the fact that the SJM valve, which did not achieve the almost physiologic low turbulence pattern, even in the optimal orientation, demonstrated significantly lower LAD flow rates compared with those of the MH valves. The increased closing reflux and leakage flow observed in previous studies ²⁶ might further explain these results. Little information has been obtained yet for the new MA bileaflet valve because downstream turbulence in vivo has not been measured, but its larger central orifice might cause less resistance to eccentric flow, and closing volume was reported to be less than that of the SJM, which might explain the significantly increased coronary flow in the MA valve compared with in the SJM valve. Further studies are needed to investigate whether the rather moderate design changes between the 2 bileaflet valves account for the measured differences in coronary flow. The reason for the significant differences regarding LAD flow in different orientations was not determined in the present study because downstream turbulence for the MA valve has not yet been measured. It remains unclear how the coronary artery flow pattern and flow reserve influence the long-term course in the presence of a mechanical aortic valve because only the acute changes immediately after valve replacement were investigated. It has been demonstrated, in a clinical study, that coronary flow is altered in patients with mechanical aortic valve substitutes. ²⁴ This might have an effect on the late course of ventricular function after valve replacement. A clinical study focusing on valve design and orientation will be necessary to further elucidate the effect of the coronary flow alterations after valve replacement.

Rotation of the valves into their worst orientation led to a major reduction of LAD flow in all 11 implanted prostheses, eliminating any significant differences among the valves. The reduction in LAD flow was highest in the asymmetrically constructed MH valve and reached statistical significance. The requirement for optimum orientation of this valve design has been demonstrated before with respect to turbulence and pressure gradients. This supports the hypothesis that there is a correlation between low aortic root turbulence and high coronary flow rate. Thus, mechanical valve orientation might indirectly influence diastolic coronary artery flow, even with the valve being closed by determining the systolic disturbance of aortic root flow pattern. The advantage of the SJM in the worst orientation with respect to systolic performance, however, did not translate to a higher LAD flow rate, probably because of the increased back flow of this valve. For the SJM valve, rotation did not lead to a significant reduction of coronary artery flow, and again, the low susceptibility to rotation was observed. Although this acute study has shown higher coronary flow with the optimally orientated MH valve, the long-term effect of this phenomenon has not been investigated because an elevated coronary flow rate does not necessarily mean a benefit but also might indicate increased cardiac work or oxygen consumption.

The authors wish to encourage other research groups to further investigate the explanation for changes in coronary flow after aortic valve replacement, especially focusing on the chronic course and the clinical effect of our findings.

The present pilot study showed that mechanical valve orientation plays an important role in overall valve performance not only by influencing systolic performance of the implanted substitutes but also by significantly changing coronary flow rates during diastole.

The present study was designed to provide initial information regarding the effect of mechanical aortic valve replacement with different prostheses in different orientations. Thus, a limited number of animals were included in the study. Also, no control animals were included to evaluate the effect of cardioplegia alone on coronary artery flow. Furthermore, the study could not provide a definite answer to the question of why coronary blood flow in the closed occluder phase of the valve was affected by rotation. Further investigation of the chronic course of coronary artery flow at least 24 hours postoperatively should be performed to help answer this question.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Yoganathan AP, Woo YR, Sung HW. Turbulent shear stress measurements in the vicinity of aortic heart valve prostheses. J Biomech. 1986;19:433-42.[Medline]
   
2. Reul H, van Son JAM, Steinseifer U, Schmitz B, Schmidt A, Schmitz C, et al. In vitro comparison of bileaflet aortic valve prostheses. J Thorac Cardiovasc Surg. 1993;3:412-20.
   
3. Stein PD, Walburn FJ, Sabbah HN. Turbulent stresses in the region of aortic and pulmonary valves. J Biomech Eng. 1982;104:238-44.[Medline]
   
4. Butchard EG, Hui-Hua L, Payne N, Buchan K, Grunkemeier GL. Twenty years' experience with the Medtronic Hall valve. J Thorac Cardiovasc Surg. 2001;121:1090-100.[Abstract/Free Full Text]
   
5. Skoularigis J, Essop MR, Skudicky D, Middlemost SJ, Sareli P. Frequency and severity of intravascular hemolysis after left-sided cardiac valve replacement with Medtronic Hall and St. Jude Medical prostheses, and influence of prosthetic type, position, size and number. Am J Cardiol. 1993;74:587-91.
   
6. Hasenkam JM, Pedersen EM, Östergaard JH. Velocity fields and turbulent stresses downstream of biological and mechanical aortic valve prostheses implanted in pigs. Cardiovasc Res. 1988;22:472-83.[Medline]
   
7. Falsetti HL, Caroll RJ, Swope RD, Chen CJ. Turbulent blood flow in the ascending aorta of dogs. Cardiovasc Res. 1983;17:529-37.
   
8. Nygaard H, Paulsen PK, Hasenkam JM, Pedersen EM. Turbulent shear stresses in three mechanical aortic valve prostheses in human beings. J Thorac Cardiovasc Surg. 1994;2:438-46.
   
9. Nygaard H, Paulsen PK, Hasenkam JM, Kromann-Hansen O, Pedersen EM, Rovsing PE. Quantitation of the turbulent shear stress distribution of normal, diseased and artificial valve prostheses in human beings. J Thorac Cardiovasc Surg. 1992;6:609-17.
   
10. Travis BR, Heinrich RS, Ensley AE, Gibson DE, Hashim S, Yoganathan AP. The hemodynamic effects of mechanical valve type and orientation on fluid mechanical energy loss and pressure drop in in vitro models of ventricular hypertrophy. J Heart Valve Dis. 1998;7:345-54.[Medline]
    
11. Kleine P, Perthel M, Nygaard H, Hansen SB, Paulsen PK, Riis C, et al. Medtronic Hall versus St. Jude Medical mechanical aortic valve: downstream turbulence with respect to rotation in pigs. J Heart Valve Dis. 1998;7:548-55.[Medline]
    
12. Kleine P, Hasenkam JM, Nygaard H, Perthel M, Wesemeyer D, Laas J. Tilting disc versus bileaflet aortic valve substitutes: intraoperative and postoperative hemodynamic performance in humans. J Heart Valve Dis. 2000;9:308-12.[Medline]
    
13. Kleine P, Perthel M, Hasenkam JM, Nygaard H, Hansen SB, Laas J. Downstream turbulence and high intensity transient signals (HITS) following aortic valve replacement with Medtronic Hall or St. Jude Medical valve substitutes. Eur J Cardiothorac Surg. 2000;17:20-4.[Abstract/Free Full Text]
    
14. Kleine P, Perthel M, Hasenkam JM, Nygaard H, Hansen SB, Laas J. High intensity transient signals (HITS) as parameter for optimum orientation of mechanical aortic valves. Thorac Cardiovasc Surg. 2000;48:360-3.[Medline]
    
15. Bodnar E, Reul H, Schmitz B. Prosthetic valve function under simulated low cardiac output conditions: preliminary observations. J Heart Valve Dis. 1993;2:348-51.[Medline]
    
16. Yoganathan AP, Chaux A, Gray RJ, Woo YR, DeRobertis M, Williams FP, et al. Bileaflet, tilting disc and porcine aortic valve substitutes: in vitro hydrodynamic characteristics. J Am Coll Cardiol. 1984;3:313-20.[Medline]
    
17. Jin XY, Gibson DG, Pepper JR. The effects of cardioplegia on coronary pressure-flow velocity relationships during aortic valve replacement. Eur J Cardiothorac Surg. 1999;16:324-30.[Abstract/Free Full Text]
    
18. Olin CL, Bonfim V, Halvazulis V, Holmgren AG, Lamke BJ. Optimal insertion technique for the Björk-Shiley valve in the narrow aortic ostium. Ann Thorac Surg. 1983;36:367-76[Free Full Text]
    
19. Walker PG, Pedersen EM, Oyre S, Flepp L, Ringgaard S, Heinrich RS, et al. Magnetic resonance velocity imaging: a new method for prosthetic heart valve study. J Heart Valve Dis. 1995;4:296-307.[Medline]
    
20. Sachs L. Angewandte Statistik. 8th ed. Heidelberg: Springer-Verlag; 1997. p. 345-56.
    
21. Hildick-Smith DJ, Shapiro LM. Coronary flow reserve improves after aortic valve replacement for aortic stenosis: an adenosine transthoracic echocardiography study. J Am Coll Cardiol. 2000;36:1889-96.[Medline]
    
22. Tamborini G, Barbier P, Doria E, Galli C, Maltagliati A, Ossoli D, et al. Influences of aortic pressure gradient and ventricular spetal thickness with systolic coronary flow in aortic valve stenosis. Am J Cardiol. 1996;78:1303-6.[Medline]
    
23. Takeuchi M, Nakashima Y. Effect of aortic valve replacement on coronary flow velocity during metabolic stress in a patient with aortic stenosis. Catheter Cardiovasc Diagn. 1997;40:287-90[Medline]
    
24. Jin XY, Gibson DG, Pepper JR. The relationship of myocardial stroke work to coronary flow velocity immediately after aortic valve replacement. Ann Thorac Surg. 1999;67:705-10.[Abstract/Free Full Text]
    
25. Kober IM, Obermayr RP, Brull T, Ehsani N, Schneider B, Spieckermann PG. Comparison of the solutions of Bretschneider, St. Thomas' Hospital and the National Institutes of Health for cardioplegic protection during moderate hypothermic arrest. Eur Surg Res. 1998;30:243-51.[Medline]
    
26. Chambers J, Fraser A, Lawford P, Nihoyannopoulos P, Simson J. Echocardiographic assessment of artificial heart valves: British society of echocardiography position paper. Br Heart J. 1994;71(suppl):6-14.[Free Full Text]
    

This article has been cited by other articles:

				V. Mannacio, L. Di Tommaso, V. De Amicis, P. Stassano, and C. Vosa Coronary perfusion: Impact of flow dynamics and geometric design of 2 different aortic prostheses of similar size J. Thorac. Cardiovasc. Surg., May 1, 2012; 143(5): 1030 - 1035. [Abstract] [Full Text] [PDF]

				J. Kempfert, A. J. Rastan, F. Beyersdorf, M. Schonburg, G. Schuler, S. Sorg, F.-W. Mohr, and T. Walther Trans-apical aortic valve implantation using a new self-expandable bioprosthesis: initial outcomes Eur J Cardiothorac Surg, November 1, 2011; 40(5): 1114 - 1119. [Abstract] [Full Text] [PDF]

				W. B. Eichinger, I. Hettich, S. Bleiziffer, R. Gunzinger, A. Hutter, R. Bauernschmitt, and R. Lange Intermittent regurgitation caused by incomplete leaflet closure of the Medtronic ADVANTAGE bileaflet heart valve: Analysis of the underlying mechanism J. Thorac. Cardiovasc. Surg., September 1, 2010; 140(3): 611 - 616. [Abstract] [Full Text] [PDF]

				M. van't Veer, B. van Straten, F. vande Vosse, and N. Pijls Influence of orientation of bi-leaflet valve prostheses on coronary perfusion pressure in humans Interact CardioVasc Thorac Surg, October 1, 2007; 6(5): 588 - 592. [Abstract] [Full Text] [PDF]

				W. Hassanein, A. Albert, I. Florath, Y. Y. Hegazy, U. Rosendahl, S. Bauer, and J. Ennker Concomitant aortic valve replacement and coronary bypass: the effect of valve type on the blood flow in bypass grafts Eur J Cardiothorac Surg, March 1, 2007; 31(3): 391 - 396. [Abstract] [Full Text] [PDF]

				F. Bakhtiary, O. Dzemali, T. Wittlinger, A. Moritz, and P. Kleine Reply to the editor. J. Thorac. Cardiovasc. Surg., September 1, 2006; 132(3): 727 - 728. [Full Text] [PDF]

				F. Bakhtiary, M. Schiemann, O. Dzemali, T. Wittlinger, M. Doss, H. Ackermann, A. Moritz, and P. Kleine Stentless bioprostheses improve postoperative coronary flow more than stented prostheses after valve replacement for aortic stenosis J. Thorac. Cardiovasc. Surg., April 1, 2006; 131(4): 883 - 888. [Abstract] [Full Text] [PDF]

				S. Mottl-Link, I. Wolf, M. Hastenteufel, S. Witte, H.-P. Meinzer, S. Hagl, and R. De Simone Non-invasive assessment of differences between bileaflet and tilting-disc aortic valve prostheses by 3D-Doppler profiles Interact CardioVasc Thorac Surg, October 1, 2005; 4(5): 383 - 387. [Abstract] [Full Text] [PDF]

				R. De Paulis, F. Tomai, F. Bertoldo, A. S. Ghini, R. Scaffa, P. Nardi, and L. Chiariello Coronary flow characteristics after a Bentall procedure with or without sinuses of Valsalva Eur J Cardiothorac Surg, July 1, 2004; 26(1): 66 - 72. [Abstract] [Full Text] [PDF]

				Y. Wu, R. Gregorio, A. Renzulli, F. Onorati, M. De Feo, G. Grunkemeier, and M. Cotrufo Mechanical heart valves: Are two leaflets better than one? J. Thorac. Cardiovasc. Surg., April 1, 2004; 127(4): 1171 - 1179. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Ulf Abdel-Rahman Anton Moritz Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kleine, P. Articles by Moritz, A. Search for Related Content PubMed PubMed Citation Articles by Kleine, P. Articles by Moritz, A. Related Collections Cardiac - physiology Valve disease