Assessment of Hemodynamics Properties of a New-Type Artificial Heart Valve Prosthesis Using Catheterization and Echocardiography

Transcription

1 American Journal of Hematology 81: (2006) Assessment of Hemodynamics Properties of a New-Type Artificial Heart Valve Prosthesis Using Catheterization and Echocardiography Y.J. Zeng, 1,4 * S.W. Xu, 2 Q. Wang, 3 Y. Chang, 4 A.Q. Dong, 2 R.K. Chen, 2 and X.J. Yu 1 1 Shantou Medical College, Shantou University, Shantou, , China 2 Department of Cardiovascular Surgery, The 2nd Hospital Affiliated to Medical College, Zhejiang University, Hangzhou , China 3 Rehabilitation Engineering Centre, The Hong Kong Polytechnic University, , China 4 Biomedical Engineering Center, Beijng University of Technology, China Objective: The objectives of this study were to assess the hemodynamic properties of the newly developed artificial heart valve prosthesis experimentally in laboratory simulation, in an animal model, and clinically in a human model and to compare the results measured by catheterization and echocardiography. Methods: (1) Laboratory simulation. The prosthesis was tested using a pulsatile flow simulator in the aortic position. Hydrodynamics parameters were automatically analyzed through a custom-designed data processing program. (2) Animal experiment. Six sheep subjected to mitral replacement with 21-mm-valve prosthesis were measured by open cardiac catheterization intraoperatively. Doppler echocardiography and open cardiac catheterization under dobutamine stress were performed in two sheep subjected to implantation 2.5 years ago. (3) Clinical patient observation. Observations were carried out on 14 patients with aortas replacement and 10 patients with bicuspid replacement using both doppler echocardiography and open cardiac catheterization. Results: (1) Laboratory simulation. The results showed that the value of the transvalvular gradient (DP) decreased with the increase of heart rate, and the values were not greater that 10 mm Hg at any given tissue annulus diameter. (2) Animal experiment. The mean DP value of the six sheep was 5.2 ± 1.7 mm Hg intraoperatively, while the corresponding DP value of the two sheep 2.5 years after implantation was 6.1 ± 0.3 mm Hg measured by open cardiac catheterization. (3) Clinical patient observation. The mean DP values in the aortic position measured by catheterization and echocardiography were and mm Hg, respectively. The gradients in the mitral position were and mm Hg, respectively. Conclusions: The results demonstrate that the new-type bileaflet heart valve prosthesis only generates a relatively low transvalvar gradient and thus has good hemodynamic properties. Am. J. Hematol. 81: , VC 2006 Wiley-Liss, Inc. Key words: heart valve prosthesis; cardiac valve replacement; hemodynamic INTRODUCTION Transvalvular pressure gradient (DP) of the artificial heart valve is defined as the pressure gradient produced due to the resistance of the valve orifice area against the blood stream when blood flows through the valve. It is regarded as one of the most important hemodynamics parameters to assess the functions of the artificial heart valve [1,2]. The new-type artificial heart valve prosthesis applied in this study is a solid pyrolytic carbon bileaflet heart transvalvuvar prosthesis, which is our VC 2006 Wiley-Liss, Inc. new achievement on an artificial heart valve in cooperation with Shanghai 901 Research Institute, China. In order to obtain understanding of this new *Correspondence to: Dr. Yan-Jun Zeng, Biomedical Engineering Center, Beijing University of Technology, Beijing , China. yjzeng@bjut.edu.cn Received for publication 29 May 2005; Accepted 31 August 2005 Published online in Wiley InterScience ( DOI: /ajh.20686

2 564 Zeng et al. type valve, relevant research on the hemodynamics properties of the transvalvular prosthesis was conducted using laboratory simulation, an animal model, and a clinical human model. MATERIALS AND METHODS Material The newly developed heart transvalvuvar prosthesis is made up of pyrolytic carbon and adopts a structure of bileaflet pump, including a valve frame and a pair of compressed bileaflet valves. When it starts to open, the central blood stream tends to be trifurcated. When it opens totally, the angle between vane and valve plane equals to 818. On the contrary, when the two valves are closed completely, the angle between each vane is The valve pivot and the valve frame are connected in a way like enarthroses. The pivot is located in the X-type blind hole. The rotation of the pivot drives blood to flow in the blind hole and sequentially washes the valve. Our new-type valves have five different types. The details are listed in Table I. Methods TABLE I. Orifice Diameter (OD) of the New-Type Heart Valve Prosthesis Type of valve prosthesis (mm) OD (mm) Laboratory Simulation. Four regularly used types (21 27 mm) of the artificial heart transvalvular were tested in this study. Three specimens of each type were selected for testing and the average values were calculated as the final results. According to ISO and GB standard, the testing of the valves was performed under a simulated condition of human physiological circulation. The pulsatile flow simulator is composed of three parts, i.e., a digital DC motor, a testing antrum of atria, aorta, and left ventricular, and an adjustable post load system. Physiological pressure sensors were fixed at 1 cm upper and 15 cm downstream to the aorta, respectively, to measure the left ventricle and aorta pressure. The sampling period was 50 ms. A total of 128 points were sampled during each simulated cardiac cycle, and 10 continuous cardiac cycles were collected. The hemodynamic parameters such as transvalvular pressure gradients (DP), average discharge (Q), average aorta pressure (PA), effective orifice area (EOA), flow volume of valve closing (CLV), and let-out flow volume (LEV) were analyzed automatically by a customer-designed processing program. The experiment liquid was normal saline-glycerine mixture with a density of g/cm 3 and a concentration of 3.5 Cp. Animal Experiment. In this study, 15 sheep (5 6 months old, weight kg) underwent the mitral replacement operation using the open cardiac catheterization. The 21-mm valve was selected for the experiment. Six sheep with a good match between the artificial heart valve and the original mitral valve were selected for hemodynamic measurement. After the external circulation ended and blood pressure and heart rate approached a stable state, the bicatheter method was applied to determine the transvalvular pressure gradients. An 18G needle was punctured into the right and left ventricles directly. Their ventricular gradients were recorded using multifunctional monitor (Drage 1904). The average value of three cardiac cycles was calculated. Meanwhile, the cardiac output (CO) was examined by the method of heat dilution. Two sheep survived for 30 months and their transvalvular gradients were first measured using Doppler echocardiography and then using the open cardiac catheterization under dobutamine stress, the transvalvular gradient between the right and left ventricular pressures was obtained, as well as cardiac output. Intravenous injection of dobutamine was conducted every 15 min for three times with a dose of 5, 10, and 20 mg/kg/min, respectively. The transvalvular pressure gradients were determined using the improved Bernoulli formula. Clinical Patient Observation. A total of 62 patients (24 male, 38 female, age ranged from 20 to 26) with disease history ranging from 2 to 26 years were performed for the valve replacement operation and 72 pieces of the new type artificial heart valve prosthesis were used. Thirty-eight patients were subjected to the bileaflet replacement, 15 to mitral valve replacement, and 9 to aorta valve replacement. We measured the values of the transvalvular pressure gradients of 14 aorta valves and 10 mitral valves. Two methods were used in this study. (1) In open cardiac catheterization the bicatheter method recorded the right and left ventricular gradients when the external circulatory system ended and the blood pressure and heart rate of patient became stable. For patients with sinoatrial heart rate, the average value of three cardiac cycles was measured, while the average value of six cardiac cycles was measured for patients with atrial fibrillation heart rate. Moreover, the cardiac output was measured using the heat dilution method. (2) In Doppler echocardiography we performed echocardiography check during or after the operation and calculated the transvalvu-

3 Assessment of Hemodynamic Properties of an Artificial Heart Valve 565 TABLE II. Hemodynamic Data of Six Sheep Measured after Heart Catheterization with the 21-mm New Heart Valve Prosthesis Serial no. of sheep CO (L/min) Left ventricular diastole pressure (mm Hg) Left atrial pressure (mm Hg) DP (mm Hg) Fig. 1. Mean pressure gradient (DP) of the new heart valve prosthesis with four different sizes (21 27 mm) were measured by changing pulsating frequency to 55, 75, and 100 per minute, respectively, under a physiological circulation simulation with a cardiac output of 4 L/min. TABLE III. Hemodynamic Data of the 21-mm New Prosthetic Valve Measured by Echocardiography 2.5 Years after the Implantation Operation Serial no. of sheep Mean CO (L/min) DP (mm Hg) Fig. 2. Mean pressure gradient (DP) as a function of pulse rate for the new heart valve prosthesis with four different sizes (21 27 mm). lar pressure gradient according to the improved Bernoulli formula. RESULTS Laboratory Simulation Result For a simulation of physiological circulation with a cardiac output of 4 L/min in this study, the mean pressure differences under different pulsating frequency of 55, 75, and 100 per minute were measured (Figs. 1 and 2). It is shown that there are obvious changes in transvalvular pressure gradient for the different types of valves (type mm). Moreover, the DP values of all valves decreased with the increase of heart rate from 55 to 100 per minute and the values ranged from 9.54 to 1.11 mm Hg. Animal Experiment Result Six sheep were observed after the open cardiac catheterization operation. The mean transvalvular pressure gradient of the 21-mm artificial heart valve prosthesis was 5.2 ± 1.7 mm Hg (Table II). The hemodynamic properties of the artificial valve prosthesis of two sheep survived for 2.5 years after the replacement operation were measured using both the open cardiac catheterization and Doppler echocardiography (Tables III and IV). It was noted that the weights of sheep Nos. 11 and 13 grew from 45 to 58 kg and from 52 to 75 kg in 2.5 years, respectively, since sheep were in the growth period when the implantation operation was carried out. As a result, with a different dosage of dobutamine, the transvalvular pressure gradients increased with increasing the cardiac output when the subjects were at rest. The results indicate that the growth of the testing animal may lead to a relatively narrow artificial heart valve. Clinical Result The mean pressure gradient of 14 aorta valves measured by open cardiac catheterization and echocardiography is and mm Hg, respectively (Table V). Among the 10 pieces of bicuspid valve, the mean pressure gradient of 5 pieces of the 25-mm artificial valves measured by these two methods are 2.1 ± 0.9 and 5.3 ± 1.9 mm Hg, respectively, while the mean values of DP of the other 5 pieces of the 27-mm valves are 1.1 ± 0.9 and 4.1 ± 1.2 mm Hg, respectively. DISCUSSION Transvalvar pressure gradient is one of the most important hemodynamics parameters [1,2] to assess the functions of the artificial heart valve. For a new

4 566 Zeng et al. TABLE IV. Hemodynamic Data of the 21-mm New Prosthetic Valve Measured by the Bicatheter Method with Different Dobutamine Stresses for the Two 2.5-years Survived Sheep at Rest Test under dobutamine stress At rest 5 mg/kg/min 10 mg/kg/min 20 mg/kg/min Serial no CO (L/min) Left ventricular diastole pressure (mm Hg) Left atrial pressure (mm Hg) DP (mm Hg) TABLE V. Hemodynamic Data of the New-Type Prosthetic Valve at the Aortic Position Measured by Catheterization and Echocardiography Type of valve prosthesis (mm) 21 (n ¼ 4) 23 (n ¼ 6) 25 (n ¼ 4) DP (mm Hg) Catheterization 6.24 ± ± ± 0.14 Echocardiography 9.42 ± ± ± 2.40 CO (L/min/m 2 ) Catheterization 2.55 ± ± ± 0.58 Echocardiography 2.84 ± ± ± 0.22 Note. n, number of cases. developed artificial transvalvular, the lower the transvalvular pressure gradient is, the better its properties are. It will approach an ideal condition if the value of the gradient equals zero [3,4]. However, the clinically used transvalvular at present has an obvious pressure gradient [1 4]. Since it is influenced by many factors, its value changes in a wide range. Transvalvulars with different types and sizes have different mean pressure gradients. Even the transvalvulars with the same type and size implanted in different patients may perform differently. In general, the normal transvalvular pressure gradient should be lower than 40 mm Hg [5]. At present, the pressure gradient of the advanced transvalvular prosthesis is below 20 mm Hg approximately [6,7]. It has been demonstrated that the effective orifice area and cardiac output are the most significant factors affecting pressure gradients when the bileaflet heart transvalvular prosthesis is applied [5 7]. The larger effective orifice area generates less impedance when the blood flow circulates through the valve. Consequently, the pressure gradient decreases. Given that the effective orifice area is fixed, cardiac output becomes the main factor. Clinically, the pressure gradient will increase obviously when a small transvalvular prosthesis is implanted in a patient with a large body surface area. This phenomenon is known as relative narrow. It has been indicated that the pressure gradient increases with increment of cardiac output. Therefore, the measurement of the pressure gradients under various blood flow conditions should be considered to evaluate the normal value of the pressure gradient. Izzat et al. applied echocardiography with dobutamine stress, instead of motion experiment, to measure the pressure gradients under different conditions in the blood stream and achieved satisfying results [6]. Invasive catheterization and noninvasive Doppler echocardiography are two main approaches to determine the transvalvular pressure gradient. Cardiac catheterization can be performed during open cardiosurgery and the gradient between the two cardiac chambers is measured directly. Otherwise, the cardiac chamber pressures of the artificial valves can be measured using the bicatheter method, and then the transvalvular pressure gradient is calculated and equals the difference of the two pressures. The catheterization is recognized as the gold standard [8] due to its direct reflection of the transvalvular pressure gradient. Especially for new valves, it is irreplaceable. However, it is not easy for this method to be used regularly in a clinic because of its destructively intrusive property. Since Holen et al. first applied Doppler echocardiography to determine the pressure gradient of the mitral transvalvular prosthesis in 1979 [9], more and more attention has been focused on echocardiography for the assessment of the function of implanted transvalvular gradients. Previous studies have demonstrated that the results of the pressure gradient measured by echocardiography and catheterization are not equal, that is, the value of the pressure gradient measured by echocardiography is higher than that of catheterization, although there is a strong correlation between these two methods [10,11]. Ihlen et al. used the noninvasive method to measure 73

5 Assessment of Hemodynamic Properties of an Artificial Heart Valve 567 patient implanted with a CarboMedics bileaflet valve prosthesis and used catheterization to measure the pressure gradient of 27 patients [11]. The results showed that the pressure gradients measured noninvasively were 4.3 ± 4.8 mm Hg higher than those measured by an invasive method. This study found similar results in that the gradient value measured by echocardiography was 3 mm Hg greater than that by catheterization. Here are three possible factors causing a higher value of the gradient using echocardiography: (1) There is a localized pressure gradient, which can recover rapidly, existing between the two leaves of bileaflet valve [12]. When echocardiography is used to measure the transvalvular pressures of the valve planes, the pressure gradient will be included. The catheter is located at least 2 cm farther away from the artificial transvalvular in general, so the localized interleaf pressure gradient will already recover. (2) For echocardiography measurement, the transvalvular pressure gradient is calculated using the Bernoulli formula DP ¼ 4(V 2 2 V2 1 ). The speed V 1 under the valve is usually ignored in the calculation. Therefore, the transvalvular pressure gradient is greater than the real value [3]. The two methods are performed during different periods of the cardiac cycle, that is, catheterization is conducted during the ventricular presystole while echocardiography is performed during postsystole. In order to reduce the variation between the two methods, some researchers suggested that it would be feasible to use the mean transvalvular pressure gradient as a parameter [12]. The results of this study demonstrate that the new type bileaflet artificial heart valve performs well in hemodynamic experiments. The measured transvalvular pressure gradient is from 9.54 to 1.11 mm Hg, less than 10 mm Hg. In the animal experiment, the transvalvular pressure gradients of six pieces of 21- mm implanted valves are also less than 10 mm Hg. Only the maximum gradient of two sheep survived 2.5 years after implantation approached to a higher value, 17.8 mm Hg, which may possibly be induced by weight gain. This indicates that the replacement of an artificial heart valve that does not match the weight of the sheep will cause the relative narrow phenomenon for the artificial heart valve. Moreover, the clinical information illustrated the low pressure gradient (<10 mm Hg) measured by either catheterization or echocardiography. In summary, this study demonstrates that the newly developed bileaflet heart valve prosthesis has a good hemodynamic property. REFERENCES 1. Akins CW. Mechanical cardiac valvular prostheses. Ann Throrac Surg 1991;52: Akins CW. Results with mechanical cardiac valvular prostheses. Ann Thorac Surg 1995;60: Wilkins GT, Gillam LD, Kritzer GL, et al. Validation of continuous-wave Doppler echocardiographic measurements of mitral and tricuspid prosthetic valve gradients: a simultaneous Doppler-catheter study. Circulation 1986;74: Chai YZ, editor. Cardiac valvular prostheses and cardiac valve replacement. Peking: People s Medical Publishing House; p Labovitz AJ. Assessment of prosthetic heart valve function by Doppler echocardiography. Circulation 1989;80: Izzat MB, Birdi I, Wilde P, et al. Comparison of hemodynamic performance of St. Jude Medical and CarboMedics 21mm aortic prostheses by means of Dobutamine stress echocardiography. J Thorac Cardiovasc Surg 1996;111: Rashitan MY, Stevenson DA, Allen DT, et al. Flow characteristics of four commonly used mechanical heart valves. Am J Cardiol 1986;58: Cooper DM, Stewart WJ, Schiavone WA, et al. Evaluation of normal prosthetic valve function by Doppler echocardiography. Am Heart J 1987; Holen J, Simonsen S, Froysaker T. An Ultrasound Doppler technique for the noninvasive determination of the pressure gradient in Bjork-Shiley mitral valve. Circulation 1979;59: Baumgartner H, Khan S, DeRobertis M, et al. Effect of prosthetic aortic valve design on the Doppler-catheter gradient correlation: an invitro study of normal St. Jude. Medtronic-Hall, Starr-Edwards and Hancock valves. J Am Coll Cardiol 1992; 19: Ihen H, Molstad P, Simonsen S, et al. Hemodynamic evaluation of the CarboMedics prosthetic heart valve in aortic position: comparison of noninvasive and invasive techniques. Am Heart J 1992; Laske A, Jenni R, Maloigne M, et al. Pressure gradients across bileaflet aortic valves by direct measurement and echocardiography. Ann Thorac Surg 1996;61:48 57.