Doppler-Echocardiographic Assessment of Carbomedics Prosthetic Valves in the Mitral Position

Transcription

1 Doppler-Echocardiographic Assessment of Carbomedics Prosthetic Valves in the Mitral Position Chee-Siong Soo, MRCP, Mestres Ca, MD, Monica Tay, Joon-Kuan Yeoh, MRCP, Eugene Sim, FRCS, and M. Choo, FRCP, Kuala Lumpur, Malaysia, and Singapore We prospectively studied 37 consecutive patients implanted with the Carbomedics prosthetic heart valve in the mitral position (without clinical evidence of prosthetic valve dysfunction) with two-dimensional and Doppler echocardiography. The peak mitral prosthetic gradient ranged from 4.60 to (mean 8.97 ± 2.29) rom Hg; mean mitral prosthetic gradient ranged from 1.67 to 6.18 (mean 3.24 ± 0.95) rom Hg; pressure half-time derived mitral valve area ranged from 1.67 to 5.30 (mean 2.70 ± 0.80) cm 2 These values compare favorably with that of another bileaflet valve (i.e., the St. Jude Medical valve). There was a wide overlap in peak and mean transmittal gradients, even with the valves of the same size, with a significant but weak inverse relationship between peak mitral gradients and valve size (p = 0.03, r = ). The performance index showed a smaller range of values, again with a significant but weak inverse relationship with valve size (p = 0.001, r = -0.54). The inverse relationship between valve size and peak mitral gradient and performance index should be borne in mind when analyzing Doppler hemodynamic data. ( J AM Soc EcHOCARDOGR 1994;7: ) The Carbomedics prosthetic heart valve ( CPHV) was introduced into clinical practice in 1986 (Carbomedics, nc., Austin, Texas). t is a bileafiet pyrolite-covered valve with presumed good hemodynamic performance and has been used in our unit since n vitro testing results showing good hemodynamic performance of the valve are readily available from the manufacturer's brochure, but because there is litde published data on its in-vivo performance in human beings, we used Doppler echocardiography to study the hemodynamic characteristics of the valve in 37 patients after mitral valve replacement. We also compare by use of the pooled data in the published literature the hemodynamic characteristics of the CPHV with that of another bileafiet valve, the From the Department of Medicine, Universiti Malaya, Kuala Lumpur, and the Cardiac Department, National University Hospital, Singapore. Reprint requests: Dr. Chee-Siong Soo, J abatan Perubatan, Fakulti Perubatan, Universiti Malaya, Kuala Lumpur, Malaysia. Copyright 1994 by the American Society ofechocardiography /94$ /l/50170 Table 1 Primary orifice areas without the leaflets in place for the Carbomedics Prosthetic Heart Valve (CPHV) and St. Jude Medical (SJM) valve Size (TAD in mm) CPHV (cm 2 ) &1M (em,) NA 5.18 TAD, Tissue annulus diameter; NA, not available (information not provided by manufacturer). St. Jude Medical (SJM) valve (St. Jude Medical, nc., St. Paul, Minn.). The SJM valve, which has been approved for clinical use in the United States, permits flow through the center of the prosthesis and has been shown to have excellent hemodynamic performance.1 3 n our institution, the CPHV is the bileafiet valve prosthesis used almost exclusively because of significant cost advantages over the SJM valve. 159

2 160 Soo et al. Journal of the American Society of Echocardiography March-April 1994 Table 2 Comparison of mitral bileaflet valve prostheses Size Peak gradient Prosthesis type (mm) No. (mmhg) Carbomedics ± ± ± ± 1.63 Total ± 2.29 Carbomedics ± ± ± ± ± 3.2 SJM ± 3.06 (pooled data)' ± ± 4.49 Total 9.98 ± 3.62 Mean gradient (mmhg) 3.60 ± ± ± ± ± ± ± ± L3 3.3 ± ± LS 5.00 ± ± L ± 3.00 Half-time (msec) MVA{cm 2 ) P 79 ± ± ± ± ± ± ± ± ± ± ± Ll ± ± ± ± L3 81 ± ± ± ± ± ± L85 ± ± ± ± ± ± ± 0.40 Note: There is no comparable published data for the performance index (P) (using Doppler derived MVA to substitute for the effective orifice area) of the St. Jude Medical valve. MATERALS AND METHODS Patient Group Between December 1988 and September 1991, all patients who had mitral valve replacement (MVR) with the CPHV were studied if ( 1) the referring physician and the patient consented to echocardiographic assessment after surgery, and (2) there was no clinical evidence of valvular malfunction-the patients being clinically stable after surgery and having no auscultatory findings of prosthetic valvular regurgitation. All the patients were studied between July 1990 and September 1991 with two-dimensional and Doppler echocardiography at a mean interval of 187 ± 206 days after surgery. Thirty-seven patients (18 men and 19 women) were included in the study: twenty-three patients underwent MVR, four patients underwent MVR and coronary artery bypass graft surgery, seven patients underwent MVR and aortic valve replacement (A VR), one patient underwent MVR and tricuspid annuloplasty, one patient underwent MVR, AVR and tricuspid annuloplasty, and one patient underwent MVR, A VR and coronary artery bypass graft surgery. The mean age was 46 years, with a range of 15 to 68 years. nformation on the prosthetic valve type, size, and location was obtained from the operative reports. Two patients were excluded from the study because one had severe paravalvular leak and the other had severe microangiopathic hemolytic anemia after surgery. Both patients required repeat surgery. Surgery The surgical technique was similar in each case: standard cardiopulmonary bypass technique with cold potassium cardioplegia and moderate systemic hypothermia. The prosthesis was implanted with interrupted pledget-supported mattress sutures. After surgery, all patients received anticoagulation with warfarin keeping the international normalized ratio between 2.5 to 4.0. nstrumentation A Hewlett-Packard Sonos 1000 echocardiographic machine with a 2.5 MHz transducer (Hewlett-Packard, Andover, Mass.) was used to perform the studies. Real-time two-dimensional echocardiographic studies in all the standard views were done to evaluate the prosthetic valve followed by two-dimensional echo-directed Doppler interrogation of the prosthetic valve. Continuous wave Doppler, pulsed Doppler, and color flow imaging modalities were used to interrogate flow across the prosthetic valve and look for prosthetic and paravalvular regurgitation as well as the presence of left ventricular outflow tract obstruction. All study information was recorded on super-vhs tape, and velocity recordings with spectral analysis were also recorded on paper at speeds of 50 to 75 mm/ sec.

3 Journal of the American Society of Echocardiography Volume 7 Number 2 Soo et al. 161 Doppler Evaluation of the Mitral Prostheses Mitral diastolic flow was evaluated from the cardiac apex, searching for signals with the most clearly defined profile and the highest obtainable velocities. The peak transmitral velocity (Vmax) was measured from the peak of the velocity envelope and was used to calculate the instantaneous peak transmitral gradient with the simplified Benoulli equation (gradient = 4v 2 ). 4 The mean diastolic gradient was calculated by planimetry of the diastolic signal, taking the mean of the instantaneous gradients. The mitral valve area (MVA) was calculated by the pressure half-time method (MV A = 220/pressure half-time). 4 The Hewlett-Packard analysis software was used for the computation of these values. Eighteen of 37 patients ( 49%) were in atrial fibrillation at the time of study, and in these patients, measurements from 10 cycles were obtained and the results averaged. Mitral regurgitation was analyzed by continuous wave Doppler, pulsed Doppler, and color flow imaging, and the severity of mitral regurgitation was graded by use of the method of Helmcke et al. 5 Left ventricular outflow tract obstruction was assessed by looking for systolic turbulence in the left ventricular outflow tract by both pulsed Doppler and color flow imaging techniques. Size and Dimensions of the Prosthetic Valve The size and dimensions for the tissue annulus diameter, orifice diameter, and primary orifice area were obtained from the manufacturer. The primary orifice area is the calculated area as determined from the orifice diameter; it is not synonymous with the effective orifice area, which is a measure of the area available for flow. Table 1 details the primary orifice areas without the leaflets in place for the CPHV and SJM valve. There is very little difference between the primary orifice area of the two valves. Performance ndex The performance index is a measure of how effectively the external dimension of the valve is used in providing forward flow, 6 normalized with respect to the valve size. Thus the performance index can be used to compare the performance of valves of different sizes. t is defined as the effective orifice area divided by the calculated primary orifice area. The performance index is derived from in vitro hydrodynamic studies that determine the effective orifice area. n this study, we are using the MVA from in Peak and Mean Mitral Dlalltollc Gradients vs Size of Mitral Proethesls i Vlllvea(mml ~ G Figure 1. Peak and mean mitral prosthetic gradients plotted against valve size. There was significant but weak inverse relationship between valve size and peak mitral prosthetic gradient (p = 0.03, r = ). There was no significant relationship between valve size and mean mitral prosthetic gradient (p = 0.19, r = ). vivo Doppler echocardiographic studies to approximate the effective orifice area. For the size 31 CPHV, the primary orifice area is assumed to be the same as that of the SJM valve, because there are no manufacturer's data on this and the primary orifice area of the two valves are very similar. Statistics All statistical studies were performed with Microsoft Excel 4.0 software program. Correlations between gradients and valve size were calculated by use of the least squares method of linear regression. RESULTS Peak Mitral Diastolic Gradient n the 37 patients with a CPHV, the peak gradient ranged from 4.60 to (mean 8.97 ± 2.29) mm (Table 2) Hg. n the study by Reisner and Meltzer, pooled data for the SJM valve showed peak gradients of 9.98 ± 3.62 mm Hg. 7 The peak gradients for different valve sizes are similar to the pooled data for the SJM valve. These data are also similar to data for

4 162 Soo et al. Journal of the American Society of Echocardiography March-Aprill994 Scatterplot of Peak Mitral Prosthetic Gradients vs Size of Mitral Prosthesis l12.00 i i !! ~ l! 8.00 c A Valve size (mmt Figure 2 Scatterplot of peak mitral prosthetic gradients versus size of mitral prosthesis. There is a wide range of gradients with great overlap between gradients from valves of different sizes. the CPHV in the study by Chambers et al. 8 A significant but weak inverse relationship existed between valve size and peak mitral prosthetic gradient (p = 0.03, r = -0.36) (Figure 1). There was a wide range of gradients with great overlap between gradients from valves of different sizes (Figure 2). Mean Mitral Diastolic Gradient The mean gradient in all patients ranged from 1.67 to 6.18 (mean 3.24 ± 0.95) mm Hg (Table 2). The mean gradients for different valve sizes are similar to the pooled data for the SJM valve. The data are also similar to data for the CPHV in the study by Chambers et al. 8 There was no significant relationship between valve size and mean mitral prosthetic gradient (p = 0.19, r = -0.22) (Figure 1). There was a narrower range of gradients but, again, there was great overlap between gradients from valves of different sizes (Figure 3). Pressure Half-time and MV A The MVA (calculated from the pressure half-time) in all patients ranged from 1.67 to 5.30 (mean 2.70 ± 0.80) cm 2 (Table 2). The MVA for different valve sizes are similar to the pooled data for the SJM valve and consistently showed a higher MV A than the data for the CPHV in the study by Chambers et al. 8 ; this is to be expected inasmuch as MVA in that study is derived from the continuity equation. There was no significant relationship between the valve size and Doppler determined mitral valve areas (p = 0.47, r = -0.12). Perfonnance ndex The performance index (MV A divided by manufacturer's primary orifice area in all patients ranged from 0.33 to 1.24 (mean 0.65 ± 0.22) (Table 2). There was a significant but weak inverse relationship between valve size and the performance index (p = 0.001, r = ). Mitral Paraprosthetic Regurgitation Only three of 3 7 patients ( 8%) had Doppler evidence of mitral regurgitation, all of which were mild in severity. These are small paraprosthetic jets seen on color Doppler and associated with readily obtainable

5 Journal of the American Society of Echocardiography Volume 7 Number 2 Soo et al ~ = 4.00! 3.00.! c: 2.oo Valve siz8 (mm, Figure 3 Scatterplot of mean mitral prosthetic gradients versus size of mitral prosthesis. There was a narrower range of gradients but again there was great overlap between gradients from valves of different sizes. jets on continuous wave Doppler echocardiography, as opposed to the normal pivotal leaks that are associated with low-intensity jets on continuous wave Doppler. The normal pivotal leaks are usually not seen on transthoracic echocardiography, but are readily seen on transesophageal study. 8 Left Ventricular Outflow Tract Obstruction n all 37 patients, there was no Doppler evidence of left ventricular outflow tract obstruction by the mitral valve prosthesis. DSCUSSON Doppler echocardiography is now routinely used to evaluate prosthetic valve function; it is noninvasive and gives accurate as well as reproducible results. Simultaneous Doppler-catheter correlative studies in mitral prostheses have shown an excellent correlation between the two techniques for both maximal (r = 0.96) and mean pressure gradients (r = 0.97); the investigators did not compare valve areas derived from Doppler with valve areas derived from direct hemodynamic measurements. 9 Doppler derived hemodynamic data also enable us to ( l) compare the relative performance of the various valves, and (2) detect abnormal or dysfunctioning prosthetic valves. Most of these studies have used the clinical assessment of patient status to establish normal values for prosthetic valves and subsequent changes in the Doppler hemodynamics when the patient becomes symptomatic. lo,u Transvalvular Gradients n our study, we have found wide individual variations in the peak and mean pressure gradients, even for valves of the same size, with a significant but weak inverse relationship between peak mitral gradients and valve size. This is consistent with the results of similar published studies. 12 This wide variability is because the transmitral gradient is dependent on several factors in addition to the effective flow area: left ventricular function, heart rate, cardiac output, and flow period. However, for the individual patient, these measurements are quite reproducible on serial

6 164 Soo et al. Journal of the American Society of Echocardiography March-Aprill994 studies if the patients are clinically stable. Hence, a baseline study after valve replacement might help subsequent assessment when the patient becomes symptomatic. The peak and mean mitral prosthetic gradients in the CPHV and the SJM valve are quite similar. Mitral Valve Area and Performance ndex The effective mitral orifice area (derived from the pressure half-time method) showed a narrower range of values; again, the MV A of the CPHV and the SJM valve are quite close. The pressure half-time method often overestimates the MV A compared with the MV A obtained with the continuity equation method 8 13 (this is seen by comparing the MVA in our study with the MV A in the study by Chambers et al). 8 However, there is sufficient correlation to allow clinical decisions to be made with reasonable certainty. The performance index also showed a narrower range of values, with a significant but weak inverse correlation with the valve size. The performance index values obtained may often be an overestimate because it is based on the pressure half-time-derived MV A. t cannot be directly compared with the in vitro hydrodynamically determined performance index. Mitral Paraprosthetic Regurgitation This frequency of 8% (ll% for the CPHVs in the study by Chambers et al. 8 ) was similar to the 9% frequency of mild paraprosthetic mitral regurgitation reported by Cooper et al. 14 Transthoracic echocardiographic detection of mitral prosthetic regurgitation is limited by technical factors including increased distance of the left atrium from the transducer and masking of the regurgitant jet by the prosthesis. SUMMARY n conclusion, Doppler echocardiographic assessment of CPHV s in the mitral position has shown good hemodynamic performance with low peak and mean transmitral gradients and satisfactory effective mitral orifice areas that compare favorably with that of another bileaflet valve that has been used extensively, the SJM valve. REFERENCES l. Hugel W. Heart valve replacement with the St. Jude medical valve prosthesis (pp 10-15). Lillehei CW. The St. Jude cardiac valvular prosthesis: a clinical appraisal at two years (pp ). Sezai Y. St. Jude medical valvular prosthesis: comparison among various kinds of prosthetic valves. n: St. Jude Medical nc nternational Valve Symposium, Scottsdale, Ariwna, March 5-8, Lillehei CW. Worldwide experience with the St. Jude Medical valve prosthesis: clinical and hemodynamis: results. Contemporary Surgery 1982;20: Chaux A, Gray RJ, MadoffJM, Feldman H, Sustaita H. An appreciation of the new St. Jude valvular prosthesis. J Thorac Cardiovasc Surg 1981;81: Hade L, Angelsen B. Pulsed and continuous wave Doppler in diagnosis and assessment of various heart lesions. n: Hade L, ed. Doppler ultrasound in cardiology. Philadelphia: Lea & Feiberger, 1985:200-l. 5. Helmcke F, Nanda NC, Hsiung MC, et al. Color Doppler assessment of mitral regurgitation with orthogonal planes. Circulation 1987;75: Gabbay S, McQueen DM, Yellin EL, Frater RWM. n vitro hydrodynamic comparison of mitral valve bioprostheses. Circulation 1979;60(suppl ): Reisner S, Meltzer R. Normal values of prosthetic valve Doppler echocardiographic parameters: a review. JAM Soc ECHOCARDOGR 1988;1: Chambers J, Cross J, Deverall P, Sowton E. Echocardiographic description of the Carbomedics bileaflet prosthetic heart valve. JAm Coli Cardiol1993;21: Burstow P, Nishimura R, Bailey K, et al. Continuous wave Doppler echocardiographic measurement of prosthetic valve gradients-a simultaneous Doppler-catheter correlative study. Circulation 1989;80: Panidis P, Ross J, Mintz GS. Normal and abnormal prosthetic valve function as assessed by Doppler echocardiograhy. JAm Coli Cardiol1986;8: Alam M, Rosmanm HS, Lakier JB, et al. Doppler and echocardiographic features of normal and dysfunctioning bioprosthetic valves. JAm Coli Cardiol1987;10: Williams GA, Labovitz AJ. Doppler hemodynamic evaluation of Starr-Edwards, Bjork-Shiley, Hancock and Carpentier-Edwards cardiac valves. Am J Cardiol1985;56: Dumesnil J, Honos G, Lemieux M, et al. Validation and applications of mitral prosthetic valvular areas calculated by Doppler echocardiography. Am J Cardiol1990;65: Cooper D, Stewart W, Schiavone W, et al. Evaluation of normal prosthetic valve function by Doppler echocardiography. Am Heart J 1987;114: