Asian Annals
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Add to Personal Folders
Right arrow Download to citation manager
Right arrow Author home page(s):
Besim Yigiter
Right arrow Permission Requests
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Çam, N.
Right arrow Articles by Yigiter, B.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Çam, N.
Right arrow Articles by Yigiter, B.
Asian Cardiovasc Thorac Ann 1998;6:166-173
© 1998 Asia Publishing EXchange Pte Ltd

ORIGINAL CONTRIBUTION

Dobutamine Stress Test to Evaluate Different Sizes of Prosthetic Aortic Valves

Nese Çam, MD, Hakan Gerçekoglu, MD1, Seden Çelik, MD, Metin Gürsürer, MD, Gülsah Tayyareci, MD, Hasan Karabulut, MD1, Ahmet Narin, MD, Tuna Tezel, MD, Besim Yigiter, MD1

Department of Cardiology
1 Department of Cardiovascular Surgery Siyami Ersek Thoracic and Cardiovascular Surgery Center Istanbul, Turkey
For reprint information contact: Hakan Gerçekoglu, MD Department of Cardiovascular Surgery Siyami Ersek Thoracic and Cardiovascular Surgery Center Tünek Sok, Sözen Apt. 23/32 Göztepe, Istanbul 81080, Turkey Tel: 90 216 368 8574 Fax: 90 216 363 2879 Email: hgercekoglu{at}hotmail.com

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Dobutamine stress testing and Doppler echocardiography were used to assess hemodynamics in 27 patients aged 16 to 54 years with various sizes and types of aortic valve prosthesis. All patients underwent a symptom-limited treadmill exercise test within two days of the dobutamine test. There was no significant difference in ejection fractions and transvalvular gradients at rest and during dobutamine stress between St. Jude Medical, Medtronic-Hall, and Carbomedics valves. Exercise duration did not differ significantly among the different types of valve. When patients were classified by their underlying lesion, those with aortic stenosis and those with aortic insufficiency had similar ejection fractions and transvalvular gradients at rest and during dobutamine stress. The mean and peak transvalvular gradients at rest and during dobutamine stress were significantly different in patients with different valve sizes but the extent of the increase in gradients during stress was not significant. Linear regression analysis revealed that both peak and mean gradients during dobutamine stress could be predicted by the resting gradients. There was a negative correlation between valve size and gradients at rest and during stress, while there was a significant correlation between exercise duration and valve size. Dobutamine stress echocardiography was useful for studying hemodynamics in patients with aortic valve prostheses and the findings show that valvular size was the main determinant of exercise capacity.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Various noninvasive techniques have been used to evaluate prosthetic valve function.1 Hemodynamic alterations induced by pacing, isoproterenol, or exercise have been used to assess valve function.2,3 Although dobutamine stress echocardiography has found wide acceptance and application for identification of coronary artery disease,4–7 its use in the study of prosthetic valve function has only recently been reported.8,9 We performed dobutamine stress tests in 27 patients with mechanical aortic valve prostheses. Exercise capacity was assessed by a treadmill test. The aims of this study were: to evaluate the effectiveness and safety of dobutamine stress echocardiography in patients with prosthetic valves; to compare the hemodynamics of St. Jude Medical, Medtronic-Hall, and Carbomedics prosthetic valves at rest and during dobutamine stress; and to identify factors that might correlate with exercise duration. In addition, we compared the hemodynamics of valves greater than 21 mm in size with those of 21 mm or less, both at rest and during dobutamine stress testing.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Among patients who underwent aortic mechanical prosthetic valve implantation at our institution between 1989 and 1996, 42 were randomly selected and recalled for this study. Approval was obtained from the ethics committee and institutional review board of the hospital and informed consent was obtained from the patients or their legal representatives. Fifteen patients were excluded because of atrial fibrillation (n = 2), paravalvular leakage (n = 2), moderate or severe aortic regurgitation (n = 2), concomitant coronary artery surgery (n = 3), and inability to obtain technically adequate recordings (n = 6). The remaining 27 patients constituted the study group. The mean age of the study patients was 34.1 ± 9.3 years with a range of 16 to 54 years. There were 7 females and 20 males with a mean body surface area of 1.73 ± 0.13 m2. The underlying lesion was aortic insufficiency in 11 patients and aortic stenosis in 16. All patients were in New York Heart Association functional class I or II and the mean time interval from valve implantation was 42.4 months (range, 6 to 74 months). Carbomedics valves (Sulzer Carbomedics, Austin, TX, USA) were implanted in 11 patients; one had a 19-mm size, 5 had 21-mm, 2 had 23-mm, and 3 had 25-mm valves. Medtronic-Hall valves (Medtronic, Inc., Minneapolis, MN, USA) were inserted in 6 patients of whom 2 each had 20-mm, 21-mm, and 23-mm valves. St. Jude Medical valves (St. Jude Medical, Inc., St. Paul, MN, USA) were used in 10 patients; 4 had 19-mm, 3 had 23-mm, 2 had 25-mm, and 1 had a 27-mm valve.

DOPPLER ECHOCARDIOGRAPHY
Before dobutamine infusion, complete 2-dimensional M-mode and Doppler echocardiographic evaluation of the patients was performed with a Wingmed CFM-760 ultrasound system (Wingmed A/S, Oslo, Norway) using a 3.5-MHz transducer. Left ventricular end-systolic and end-diastolic dimensions as well as posterior and septal wall thicknesses were measured at the level of the chorda tendinea according to the American Society of Echocardiography recommendations.10 Biplanar left ventricular volumes were determined by planimetry of 2-dimensional recordings in the apical 4-chamber view. Left ventricular end-diastolic and end-systolic contours were traced with a video analysis system and ejection fractions were determined by Simpson's method.

Using the apical 5-chamber, the upper right parasternal, and the suprasternal windows, the maximal flow velocity across the prosthetic aortic valve was recorded. Recordings of velocity in the subaortic area were made in the 5-chamber view by color-flow mapping to position the pulsed sample in line with the flow. The sample was placed with its center below the start of flow acceleration, usually 0.5 cm below the plane of the ventricularaortic junction. The peak instantaneous transaortic gradient was calculated by the modified Bernoulli equation.11 In the majority of cases (89%), the best jet recordings were obtained from the apical window. The same acoustic windows were used before and at the peak level of dobutamine stress. Aortic valve area was calculated by the continuity equation using the sewingring diameter.12 In the parasternal long-axis view, measurement of left ventricular outflow tract diameter was performed in early systole using the inner edge-to-inner edge method.13,14 An average of the three largest diameters was calculated for each patient.

The presence and degree of prosthetic valve regurgitation was qualitatively assessed by pulsed wave, continuous, and color Doppler echocardiography from multiple windows. Doppler echocardiographic recording of the diastolic mitral flow was performed in the apical 4-chamber view by positioning the sample volume between the tips of the mitral leaflets. Isovolumetric relaxation time was derived from the interval between the end of the transaortic flow and the onset of the transmitral flow by simultaneous recording of both signals in continuous Doppler mode. Left ventricular ejection time was measured from the start of the opening to the start of the closing signal of the prosthesis.

After resting sequences were acquired, dobutamine infusion was started at a rate of 5 µg·kg-1·min-1 increasing every two minutes to 10, 20, 30, and 40 µg·kg-1·min-1. The end point was maximal dosage, a heart rate of 85% of the age-predicted maximal heart rate, or development of symptoms. If the target heart rate was not achieved by maximal dobutamine infusion alone, intravenous atropine in a dosage of 0.5 to 1 mg was given along with the dobutamine infusion. When the target heart rate was achieved, the Doppler echocardiographic measurements were recorded again. Throughout the dobutamine infusion, electrocardiographic changes were continuously monitored and the blood pressure was measured by sphygmomanometry every minute.

EXERCISE TEST
All patients underwent a symptom-limited treadmill exercise test with the Bruce protocol within two days of dobutamine stress echocardiography. Exercise was terminated when 85% of the age-predicted maximal heart rate was achieved or when symptoms of dyspnea or fatigue appeared.

STATISTICAL ANALYSIS
Continuous variables were expressed as mean values ± standard deviation. The unpaired Student's t test was performed to determine significant differences between mean values for the continuous variables. A p value of less than 0.05 was considered statistically significant. The association between variables was analyzed by means of linear regression analysis.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
DOBUTAMINE STRESS ECHOCARDIOGRAPHY
During the 27 dobutamine stress tests performed, 1 patient developed facial paresthesia and 3 patients had premature ventricular beats. No major life-threatening complications were noted. The highest dose of dobutamine required was 40 µg·kg-1·min-1 in 8 patients (with atropine added in 3). The target heart rate was achieved in 24 patients (89%). The mean rate-pressure product was 22.92 ± 2.02 beats per minute x mm Hg.

The treadmill exercise tests were performed without complications such as angina pectoris or arrhythmias. The rate-pressure product reached at maximal exercise was 23.79 ± 3.10 beats per minute x mm Hg. Four patients did not reach their target heart rate because of dyspnea or fatigue.

Table 1Go summarizes the Doppler echocardiographic findings according to valvular type. There was no significant difference in rest or exercise hemodynamics between St. Jude Medical, Medtronic-Hall, and Carbomedics valves. Valve areas and transvalvular gradients at rest and during dopamine stress testing were similar among the three types of valve. In addition, a comparison between different valve types of the same size revealed no significant difference (comparison was possible only for valves of 21, 23, and 25 mm). No significant difference in exercise duration among the valve types was observed.


View this table:
[in this window]
[in a new window]
  		Table 1. Rest and Exercise Parameters According to Valvular Type
 
When patients were classified by their underlying lesion, aortic stenosis and aortic insufficiency patients had similar resting (63.1% ± 9.1% versus 62.8% ± 13.1%) and dobutamine-stressed ejection fractions (68.8% ± 8.8% versus 66.2% ± 11.7%). Aortic stenosis and aortic insufficiency patients also showed similar valvular gradients at rest and during dobutamine stress. Exercise duration in patients with aortic insufficiency showed a trend towards higher values than the aortic stenosis group (8.6 ± 1.4 minutes versus 7.8 ± 1.9 minutes) but this was not statistically significant (Table 2Go).


View this table:
[in this window]
[in a new window]
  		Table 2. Rest and Exercise Parameters by Underlying Lesion
 
Mild aortic insufficiency was indicated by Doppler echocardiography in approximately 30% of these patients although none had auscultatory evidence of aortic insufficiency. There was no significant difference in the incidence of regurgitation detected among the three types of valve.

The mean gradient at rest did not exceed 30 mm Hg in the 14 patients with valves larger than 21 mm but during dobutamine stress testing the mean gradient exceeded 30 mm Hg in 3 of these patients (8.5%). In 13 patients with a 21-mm valve or smaller, the mean gradient at rest exceeded 30 mm Hg in 4 of them (31%) and during dobutamine stress testing the mean gradient exceeded 30 mm Hg in all except 3 patients (77%). The highest mean and peak gradients recorded during dobutamine stress testing in patients with valves greater than 21 mm and in the group with smaller valves were 42/64 mm Hg and 55/88 mm Hg respectively (Table 3Go).


View this table:
[in this window]
[in a new window]
  		Table 3. Parameters According to Valve Size
 
Peak and mean transvalvular pressure gradients and the increase in gradients during dobutamine stress testing are shown in Figures 1 and 2GoGo. In patients with larger than 21-mm valves, the mean and peak transvalvular gradients at rest were 19.2 ± 6.5 and 31.8 ± 7.2 mm Hg; during dobutamine stress testing, the mean and peak gradients increased to 30.1 ± 7.2 and 50.4 ± 10.9 mm Hg respectively. The percentage increases in mean and peak gradients were 64.3% ± 28% and 60.1% ± 30%. In patients with a 21-mm valve or smaller, the mean and peak gradients at rest were 25.6 ± 8.4 and 40.4 ± 11.2 mm Hg, increasing to 39.1 ± 9.5 and 63.9 ± 15.8 mm Hg during dobutamine stress testing. The percentage increases in mean and peak gradients were 61.8% ± 28.9% and 58.4% ± 20.2% respectively. During dobutamine stress testing, prosthetic valve gradients increased in all patients (p < 0.0001). Gradients at rest and during dobutamine stress testing were significantly higher in patients with smaller valves than in those with valves larger than 21 mm (p < 0.005) but the increase in gradients was not significantly different. Linear regression analysis revealed that both peak and mean gradients during dobutamine stress testing were predicted by the resting gradients (Figure 3Go). There was no significant correlation between resting transvalvular gradients and the increase in gradients during dobutamine stress testing. The duration of the valve implant did not correlate with gradients at rest or during dobutamine stress testing. There was also no significant correlation between maximal heart rate and gradients during dobutamine stress testing.



View larger version (15K):
[in this window]
[in a new window]
  		Figure 1. Peak gradient at rest, during dobutamine stress testing, and the increase in peak gradient during the test.

 


View larger version (15K):
[in this window]
[in a new window]
  		Figure 2. Mean gradient at rest, during dobutamine stress testing, and the increase in mean gradient during the test.

 


View larger version (15K):
[in this window]
[in a new window]
  		Figure 3. Linear regression analysis: (A) peak and (B) mean transvalvular pressure gradients during dobutamine stress testing correlated with the gradient at rest.

 
There was a negative correlation between valve size and peak gradients at rest and during dobutamine stress testing (Figure 4Go). In addition, mean gradients at rest and during dobutamine stress testing showed a significant negative correlation with valve size (at rest: r = –0.47, p < 0.005; for dobutamine stress: r = –0.57, p < 0.005). There was a considerable amount of scatter and overlap among peak and mean gradients obtained in valves of the same size.



View larger version (14K):
[in this window]
[in a new window]
  		Figure 4. Linear regression analysis showed that the peak gradients at rest (A) and during dobutamine stress (B) correlated with valve size.

 
There was a significant correlation between the duration of exercise and the valvular size (r = 0.81, p < 0.0001) as shown in Figure 5Go. There was no correlation between resting parameters of left ventricular function (including ejection fraction) or structure (left ventricular end-diastolic diameter, end-systolic diameter, and wall thickness) and exercise performance.



View larger version (8K):
[in this window]
[in a new window]
  		Figure 5. Linear regression analysis showed a significant correlation between exercise duration and valvular size.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Valvular prosthesis of various types and sizes have been implanted for many years in patients with aortic valve disease. Postoperative catheterization and Doppler echo-cardiography studies suggest that the hemodynamic performance of these devices can vary widely depending on the type and size of prosthesis being implanted as well as varying between individuals.15–20

It was suggested that a complete hemodynamic evaluation of prosthetic valves should include assessment of exercise hemodynamics.21–23 In order to evaluate the exercise hemodynamics of prosthetic valves, bicycle or treadmill exercise tests were performed and Doppler gradients were recorded immediately after exercise while the patients were in the supine position.21–22 The use of dobutamine stress echocardiography for this purpose has been reported only by Izzat and colleagues8,9 who applied the technique in evaluation of the hemodynamic performance of St. Jude Medical and Carbomedics 21-mm prostheses and in comparing small Carbomedics aortic valve prostheses (19 mm and 21 mm). They concluded that both groups had equally favorable hemodynamic performance. As with every echocardiographic examination, the evaluation of a prosthetic valve is sometimes limited by a poor window. This is even more frequent during exercise. The advantage of dobutamine stress is that it simulates the hemodynamic effect of isotonic exercise but does not depend on patient effort. Furthermore, diagnostic images can be obtained in nearly all patients because of the absence of patient motion as well as limited respiratory interference.

The parameters influencing exercise capacity and exercise hemodynamics of patients after aortic valve replacement has not been extensively studied. Tatineni and colleagues22 evaluated rest and exercise hemodynamics of St. Jude Medical and Medtronic-Hall prostheses by Doppler echocardiography. An increase in the ratio of peak to mean gradients from 21 ± 7:9 ± 4 mm Hg to 35 ± 12:15 ± 6 mm Hg was reported in 20 patients with a Medtronic-Hall aortic valve prosthesis. Mean valve size for their group was 24 ± 3 mm with only 2 patients having a 21-mm prosthesis. In patients with a St. Jude Medical aortic valve prosthesis, an increase in peak: mean gradients from 24 ± 7:11 ± 4 mm Hg to 41 ± l2:18 ± 7 mm Hg was found with exercise and they concluded that St. Jude Medical and Medtronic-Hall valves in the aortic position have similar resting and exercise hemodynamics. In our study, there was no significant difference in exercise duration and transvalvular gradients at rest and during dobutamine stress testing between St. Jude Medical and Medtronic-Hall valves, which is in agreement with the data of Tatineni and colleagues.22 Similarly, their findings agree with those in our study showing no difference in exercise duration and resting or exercise ejection fractions between patients with preoperative aortic stenosis and those with aortic insufficiency.

Regarding resting gradients across St. Jude Medical aortic prosthesis, five previous Doppler studies analyzing a total of 118 patients have reported a mean peak gradient of 24.5 mm Hg and a mean gradient of 12.5 mm Hg at rest.19,22,24–26 In our study, the mean and peak gradients at rest were higher than those reported previously. This may be due to the presence of a 19-mm prosthesis in 25% of our study group, whereas in previous studies, very few patients had valves smaller than 21 mm.

In the study by Chambers and colleagues27 on Carbomedics valves in the aortic position, mean gradients ranged between 6 and 9 mm Hg and peak gradients between 11 and 40 mm Hg. This is lower than our range for mean (12 to 34 mm Hg) and peak gradients (24 to 56 mm Hg) at rest in 11 patients with Carbomedics valves. We found an inverse correlation between valve size and both mean and peak gradients. Similar results have been reported in earlier studies.19,22,28 However, exercise data on small aortic valve prostheses have been reported infrequently. A negative influence of a small prosthesis on exercise capacity has been suggested to be the result of high gradients during exercise that are not always seen at rest.29 Tatineni and colleagues22 reported prosthesis size to be an independent predictor of exercise tolerance after aortic valve replacement. Our findings are consistent with these observations. Wiseth and colleagues21 assessed hemodynamics in 25 patients with a less than 21-mm aortic valve prosthesis. They reported an increase in gradients with exercise from 30 ± 8:16 ± 4 mm Hg (peak:mean gradient) at rest to 46 ± 12:24 ± 7 mm Hg during exercise. They emphasized that resting gradients in patients with less than 21-mm aortic valve prostheses were acceptable with only a moderate increase during exercise and in contrast to other studies, they concluded that the limitation of exercise capacity in these patients with small aortic prosthetic valves was likely to be due to other or additional factors than the moderate increase in gradients with exercise.

Paulis and colleagues30 evaluated the hemodynamic performance of small diameter Carbomedics aortic valves in patients with a mismatch between the prosthetic valve and body surface area, by means of Doppler echocardiography at rest and after isotonic exercise. Surprisingly, they observed that a 19-mm valve prosthesis had a significantly increased effective orifice area with exercise, whereas it was almost unmodified for the 21-mm valve. Peak resting gradients of 33.4 ± 13.2 and 25.4 ± 5.2 mm Hg for patients with 19-mm and 21-mm valves increased to 34.3 ± 14.5 and 34.9 ± 8.1 mm Hg respectively, with exercise. Therefore, in their study, only the 21-mm valve prosthesis showed a significant increase in peak and mean gradients. They concluded that small diameter Carbomedics valves have satisfactory hemodynamic performances even after strenuous exercise in patients with large body surface areas. In our study, there was only 1 patient with a 19-mm Carbomedics aortic prosthesis in whom the peak gradient increased from 43 mm Hg to 50 mm Hg during dobutamine stress testing. Our data were not sufficient for any conclusions.

We found a significant heterogeneity within each valve size and an overlap in peak as well as mean gradients among the various valve sizes. Several studies have demonstrated that although an inverse relationship exists between valve size and gradients, there was a significant overlap between gradients of a particular valve type and size as well as among various sizes of the same valve.18,19,25,28,31 This was explained by the dependence of transvalvular gradient on several factors in addition to the effective flow area: left ventricular function; heart rate; cardiac output; and flow period (systolic ejection period and diastolic filling period).32 Wide variations in these parameters explain the wide variation in pressure gradients that can be expected when studying a diverse group of patients.

In this study, gradients recorded during dobutamine stress testing did not correlate with maximal heart rate. This is in contrast to what has been demonstrated with mitral valve prostheses where there was a linear correlation with heart rate.33 A similar finding has been reported recently by Wiseth and colleagues.21 The gradients observed in the present study are higher than those previously reported, which may be due to the following reasons: (1) As the gradients we obtained were not corrected for left ventricular outflow tract velocities in the Bernoulli equation, they represent some overestimation. During exercise, left ventricular outflow tract velocities may increase, especially in patients with a narrow outflow tract. An inverse relationship between the left ventricular outflow tract diameters and velocities in patients with aortic valve prosthesis has been reported.27 Therefore, the difference between gradients with and without correction for left ventricular outflow tract velocities in the Bernoulli equation may be even greater during exercise. (2) Most studies on the exercise hemodynamics of aortic prostheses have used an upright exercise test followed by an immediate postexercise Doppler recording after the patient has assumed the supine position. In the study by Wiseth and colleagues21, a 16% decrease in heart rate was noted during the first minute after exercise; further decreases in heart rate of 7% and 5% were recorded. This demonstrates that an important change in hemodynamics, including prosthesis gradients, occurs in the very early postexercise period. In our study, Doppler gradients were recorded immediately on achieving the target heart rate and there was not even a slight delay that could influence the result. (3) Recent studies suggest that all prosthetic valves are at least mildly stenotic and may cause relatively high gradients in spite of normal prosthetic function; such gradients may be due to a mismatch between the effective orifice area of the prosthesis and the patient's body surface area.34–37 Dumesnil and colleagues35 emphasized that for aortic prostheses, an indexed prosthetic valve area greater than 0.9 cm2·m–2 would be a minimal requirement to limit the postoperative gradient. In our study group, among 14 patients with less than 21-mm valves, the effective area index was inadequate in 10 patients. For the whole group (<21-mm valves) the effective area index was 0.74. Therefore, in our study group, especially for patients with small aortic prostheses, the high transvalvular gradients may be due to a mismatch between the valve prosthesis and body surface area.

We concluded that the dobutamine stress test is a simple, safe, and readily available method for evaluating hemodynamics in aortic prostheses by echocardiography. St. Jude Medical, Carbomedics, and Medtronic-Hall valves had almost similar hemodynamics at rest and during dobutamine stress testing. Valvular size was the main determinant of exercise capacity.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Kottler MN, Mintz GS, Panidis I, Marganroth J, Segal BL, Ross J. Noninvasive evaluation of normal and abnormal prosthetic valve function. J Am Coll Cardiol 1983;2:151–73.[Abstract]

  2. Thormann J, Gottwik M, Schlepper M, Hehrlein F. Hemodynamic alterations induced by isoproterenol and pacing after aortic valve replacement with the Björk-Shiley or St. Jude Medical prosthesis. Circulation 1981;63:895–904[Abstract/Free Full Text]

  3. Björk VO, Böök K, Holmgren A. Significance of position and opening angle of the Björk-Shiley tilting-disc valve in mitral surgery. Scand J Thorac Cardiovasc Surg 1973; 7:187–201.[Medline]

  4. Fung AY, Gallagher KP, Buda AJ. The physiologic basis of dobutamine as compared with dipyridamole stress interventions in the assessment of critical coronary stenosis. Circulation 1987;76:941–7.

  5. Mannering D, Cripps T, Leech G, et al. The dobutamine stress test as an alternative to exercise testing after acute myocardial infarction. Br Heart J 1988;59:521–6.[Abstract/Free Full Text]

  6. Berthe C, Pierard LA, Hiernaux M, et al. Predicting the extent and location of coronary artery disease in acute myocardial infarction by echocardiography during dobutamine infusion. Am J Cardiol 1986;58:1167–72.[Medline]

  7. Sawada SG, Segar DS, Ryan T, et al. Echocardiographic detection of coronary artery disease during dobutamine infusion. Circulation 1981;83:1605–14.[Abstract/Free Full Text]

  8. Izzat MB, Birdi I, Wilde P, Bryan AI, Angelini GD. Comparison of hemodynamic performances of St. Jude Medical and Carbomedics 21-mm aortic prostheses by means of dobutamine stress echocardiography. J Thorac Cardiovasc Surg 1996;111:408–15.[Abstract/Free Full Text]

  9. Izzat MB, Birdi I, Wilde P, Bryan AI, Angelini GD. Evaluation of the hemodynamic performances of small Carbomedics aortic prostheses using dobutamine stress Doppler echocardiography. Ann Thorac Surg 1995;60:1048–52.[Abstract/Free Full Text]

  10. Shan DJ, De Maria A, Kyssla J, Weyman A. The committee on M-mode standardization of the American Society of Echocardiography recommendations regarding quantitation in M-mode echocardiography. Results of a survey of echocardiographic measurements. Circulation 1987;58:1072–85.[Abstract/Free Full Text]

  11. Williams GA, Nelson JG, Kennedy HL, Labovitz AJ. Value of multiple echocardiographic views in the evaluation of aortic stenosis in adults by continuous wave Doppler. Am J Cardiol 1985;55:445–9.[Medline]

  12. Skjaerpe T, Hegrenaes L, Hatle L. Noninvasive estimation of valve area in patients with aortic stenosis by Doppler ultrasound and two-dimensional echocardiography. Circulation 1985;72:810–8.[Abstract/Free Full Text]

  13. Zoghbi WA, Farmer KL, Soto JG, Nelson JG, Quinones MA. Accurate noninvasive quantification of stenotic aortic valve area by Doppler echocardiography. Circulation 1986; 73:452–92.[Abstract/Free Full Text]

  14. Lewis JF, Kuo LC, Nelson JG, Limacher MC, Quinones MA. Pulsed Doppler echocardiographic determination of stroke volume and cardiac output: clinical validation of two new methods using the apical window. Circulation 1984;70:425–31.[Abstract/Free Full Text]

  15. Nitter-Hauge S, Semb B, Abdelnoor M, Hall KV. A five-year experience with the Medtronic-Hall disc valve prosthesis. Circulation 1983; 68(Suppl II):II-169–74.

  16. Cosgrove DM, Lytle BW, Gill CC, et al. In vivo hemodynamic comparison of porcine and pericardial valves. J Thorac Cardiovasc Surg 1985; 89:358–68.[Abstract]

  17. Khan SS, Mitchell RS, Derby GC, Oyer PE, Miller DC. Differences in Hancock and Carpentier-Edwards porcine xenograft aortic valve hemodynamics. Effects of valve size. Circulation 1990; 82(Suppl IV):IV-117–24.

  18. Reisner SA, Meltzer RS. Normal values of prosthetic valve Doppler echocardiographic parameters: a review. J Am Soc Echocardiogr 1988;1:201–10.[Medline]

  19. Cooper DM, Stewart WJ, Schiavone WA, Lombardo HP, Lytle BW, Loop FD. Evaluation of normal prosthetic valve function by Doppler echocardiography. Am Heart J 1987; 114:576–9.[Medline]

  20. Sagar KB, Wann LS, Paulsen WHJ, Romhilt DW. Doppler echocardiographic evaluation of Hancock and Björk-Shiley prosthetic valves. J Am Coll Cardiol 1986;7:681–7.[Abstract]

  21. Wiseth R, Levang OW, Tangen G, Rein KA, Skjaerpe T, Hatle L. Exercise hemodynamics in small (< 21 mm) aortic valve prosthesis assessed by Doppler echocardiography. Am Heart J 1993; 125:138–46.[Medline]

  22. Tatineni S, Barner HB, Pearson AC, Halbe D, Woodruff R, Labovitz J. Rest and exercise evaluation of St. Jude Medical and Medtronic-Hall prostheses. Circulation 1989; 80(Suppl I):I-16–23.

  23. Jaffe WM, Coverdale HA, Roche AHG, Whitlock RML, Neutze JM, Barratt-Boyes BG. Rest and exercise hemodynamics of 20 to 23 mm allograft, Medtronic-Intact (porcine), and St. Jude Medical valves in the aortic position. J Thorac Cardiovasc Surg 1990;100:167–74.[Abstract]

  24. Weinstein IR, Marberger JP, Perez JE. Ultrasonic assessment of the St. Jude prosthetic valve. M-mode, two-dimensional and Doppler echocardiography. Circulation 1983; 68:897–905.[Abstract/Free Full Text]

  25. Panidis IP, Ross J, Mintz GS. Normal and abnormal prosthetic valve function as assessed by Doppler echocardiography. J Am Coll Cardiol 1986;8:317–26.[Abstract]

  26. Kisanuki A, Tei C, Arikawa K. Continuous-wave Doppler echocardiographic assessment of prosthetic aortic valves. J Cardiogr 1986;16:121–32.[Medline]

  27. Chambers J, Cross J, Deverall P, Sowton E. Echocardiographic description of the Carbomedics bileaflet prosthetic heart valve. J Am Coll Cardiol 1993;21:398–405.[Abstract]

  28. Williams GA, Labovitz AJ. Doppler hemodynamic evaluation of Starr-Edwards, Björk-Shiley, Hancock and Carpentier-Edwards cardiac valves. Am J Cardiol 1985; 56:325–32.[Medline]

  29. Teoh KH, Fulop JC, Welsel RD, Ivanov J, Tong CP, Slattery SA. Aortic valve replacement with a small prosthesis. Circulation 1987;76(Suppl III):III-123–31.

  30. Paulis RD, Sommariva L, Russo F, Tomai F, Tondo A, Pagliaricci C. Doppler echocardiography evaluation of the Carbomedics valve in patients with small aortic anulus and valve prosthesis-body surface area mismatch. J Thorac Cardiovasc Surg 1994;108:57–62.[Abstract/Free Full Text]

  31. Chafizadeh ER, Zaghbi WA. Doppler echocardiographic assessment of the St. Jude Medical prosthetic valve in the aortic position using the continuity equation. Circulation 1991;83:213–23.[Abstract/Free Full Text]

  32. Gabbay S, McQeen DM, Yellin EL, Frater WM. In vitro hydrodynamic comparison of mitral valve prosthesis at high flow rates. J Thorac Cardiovasc Surg 1978;76:771–87.[Abstract]

  33. Reisner SA, Lichtenberg GS, Shapiro JR, Schwarz KQ, Meltzer RS. Exercise Doppler echocardiography in patients with mitral prosthetic valves. Am Heart J 1989;118:755–9.[Medline]

  34. Dumesnil JG, Yoganathan AP. Valve prosthesis hemodynamics and the problem of high transprosthetic pressure gradients. Eur J Cardio-thorac Surg 1992;6:34–8.

  35. Dumesnil JG, Honos GN, Lemieux M, Beauchemin J. Validation and applications of indexed aortic prosthetic valve areas calculated by Doppler echocardiography. J Am Coll Cardiol 1990;16:637–43.[Abstract]

  36. Rahimtoola SH. The problem of valve prosthesis-patient mismatch. Circulation 1978;58:20–4.[Abstract/Free Full Text]

  37. Rahimtoola SH, Murphy E. Valve prosthesis-patient mismatch. A long-term sequel. Br Heart J 1981;45:331–5.[Abstract/Free Full Text]





This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Add to Personal Folders
Right arrow Download to citation manager
Right arrow Author home page(s):
Besim Yigiter
Right arrow Permission Requests
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Çam, N.
Right arrow Articles by Yigiter, B.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Çam, N.
Right arrow Articles by Yigiter, B.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
ANN THORAC SURG ASIAN CARDIOVASC THORAC ANN EUR J CARDIOTHORAC SURG
J THORAC CARDIOVASC SURG ICVTS ALL CTSNet JOURNALS