Klinische Wochenschrift
KlinWochenschr (1990) 68:263-268
9 Springer-Verlag 1990
Doppler Measurement of Cardiac Output Across Prosthetic Mitral Valves H. Dittmann, W. Voelker, K.-R. Karsch, and L. Seipel Medizinische Klinik III, Eberhard.-Karls-Universitfit Tfibingen (Prof. Dr. L. Seipel)
Summary. In 46 patients with a normal functioning mitral valve prosthesis (15 St. Jude, 19 Medtronic Hall, 12 Hancock) cardiac output was measured by pulsed Doppler echocardiography across the valve prosthesis. Simultaneously cardiac output was determined by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract (2.8 1 / m i n - 9.5 l/rain). The prosthetic valve area was calculated using the pressure halftime method. Cardiac output was calculated by multiplying time-velocity integrals with the mitral valve area. Cardiac output measurements across the mitral prosthesis correlated significantly with thermodilution (r = 0.96, SEE = 0.400 l/rain) and pulsed Doppler echocardiography flow measurements in the left ventricular outflow tract (r = 0.82, SEE = 0.679 l/rain). The mean percent error of the Doppler transmitral flow measurement was 10.8 %. Doppler transmitral flow underestimated cardiac output values of more than 6.5 1/min in 6 of 7 patients. Cardiac output measurements across Hancock (SEE=0.473 1/min) and St. Jude prostheses (SEE=0.538 1/min) were more accurate than across Medtronic Hall prostheses (SEE=0.847 1/ min). Cardiac output can be calculated by pulsed Doppler echocardiography across normal functioning mitral prostheses. Due to the different flow dynamics the accuracy of cardiac output measurement depends on the prosthetic valve type. Reliable measurements of cardiac output can be performed across Hancock and St. Jude prostheses only. This method is limited in volume flow measurements across Medtronic Hall prostheses. Abbreviations: MPE = mean percent error; MVP = mitral valve prosthesis; r=correlation coefficient; r95%=95% confidence limit of r; SEE = standard error of the estimate; S E E g 5 % = 95 % confidence limit of SEE
Key words: Flow volume measurement - Prosthetic mitral valve - Doppler echocardiography
Quantitative Doppler echocardiography is increasingly used for the measurement of cardiac output. A variety of methods has been published reporting volume flow measurement in the inflow or outflow tract of the left and right ventricles and in the great arteries [5, 6, 9, 10, 17, 18, 20]. In a previous experimental study using Doppler echocardiography the volume flow was estimated across prosthetic heart valves in vitro [1]. However, flow beyond mechanical and bioprosthetic valves is considerably different. Thus, the purpose of this study was to assess the accuracy of pulsed Doppler echocardiography in the determination of cardiac output across different mechanical and bioprosthetic mitral valve prostheses in vivo.
Method Study Patients The study group consisted of 46 patients with a normal functioning mitral valve prosthesis according to clinical and Doppler echocardiographic examination [3, 4, 22, 24, 28]. Only patients with excellent Doppler signals and high quality echocardiograms were included in the study. Patients with clinical, electrocardiographical, echocardiographical, and Doppler evidence of aortic valve disease, subaortic stenosis, intracardiac shunts, moderate or severe tricuspid regurgitation, left ventricular hypertrophy or myocardial ischemia were excluded from the study [5, 6, 19, 26, 32]. The age of the 32 women and 14 men ranged from 31 to 68 years.
264
H. D i t t m a n n et al. : Cardiac O u t p u t Across Prosthetic Mitral Valves
Table 1. Calculated mitral valve areas using the pressure halftime m e t h o d in 46 patients (cm 2) Valve size
Valve type St. Jude
M e d t r o n i c Hall
Hancock
No. 29
2,6-4.0 (n = 6)
2.9-3.6 (n = 2)
No. 31
2.9-3.4 (n = 9)
2.2-3.1 (n = 14)
1.7-2.4 (n=4) 2.2-4.0 (n = 8)
No. 33
--
3.1-3.7
(,,=2) No. 35
-
was 2.4 M H z and the pulse repetition frequency of the Doppler unit was 4 or 6 kHz, depending on the depth of the sampling site. The axial length of the sample volume was 3 mm. The Doppler frequency shifts were processed using a fast Fourier transform spectral analyzer. The M-mode echocardiograms and Doppler frequency spectra were recorded at a paper speed of 100 mm/s on a hard copy unit (Line Scan Recorder 20B, Toshiba).
3.1
(n=0
Ten patients had sinus rhythm and 36 patients had atrial fibrillation. The types of implanted valve prostheses were St. Jude Medical (size 29 and 31) in 15 patients, Medtronic Hall (size 29, 31, 33, 35) in 19 patients, and Hancock bioprostheses (type II, size 29 and 31) in 12 patients (Table 1). Doppler flow calculations at mitral valve prostheses were compared with cardiac output measurements by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract.
Thermodilution Method After routine right heart catheterization in 17 patients a 7 F Swan-Ganz thermodilution catheter was positioned in the pulmonary artery. The thermodilution cardiac output was obtained with an Edward cardiac output instrument model 9520-A by injecting rapidly 10 ml of 0.9% cold sodium chloride solution through the proximal part of the Swan-Ganz thermodilution catheter. Cardiac output was computed as the average of three values with a difference of less than 10%. If the difference between the lowest and highest value of the first three measurements was more than 10%, two additional cardiac output measurements were performed and the extremes were discarded before averaging. In 8 of the 17 patients cardiac output was calculated additionally during symptom limited supine bicycle ergometry on the 25 W or 50 W level.
Echocar diogr ap hy A 90 ~ phased array duplex Doppler echocardiograph (Toshiba SSH-40A with Toshiba SDS-21B) was used for both imaging and determining flow velocity. The ultrasound frequency of the probe
Flow Volume Measurement in the Left Ventricular Outflow Tract In 29 patients volume flow was measured in the center of the aortic valve annulus by Doppler echocardiography. For flow area recording a left parasternal M-mode tracing, controlled by the two-dimensional image, was obtained at the aortic annulus, directly proximal to the insertion of the aortic leaflets [6]. The transducer was then positioned near the apex to obtain the five-chamber view. Flow velocity was recorded in the center of the aortic annulus, just proximal to the aortic valve leaflets. The angle between the assumed blood flow in the outflow tract and the cursor line of the sample volume was kept less than 20 ~.
Flow Volume Measurement Across the Mitral Valve Prosthesis Doppler transmitral flow was simultaneously measured during thermodilution cardiac output calculation or just before or after Doppler flow measurement in the left ventricular outflow tract. The sequence of the Doppler measurements in the left ventricular outflow tract and at the mitral prosthesis was randomized. Cardiac output calculations were performed in the left lateral recumbent position under steady-state conditions with a constant heart rate throughout the measurements. Velocity recordings of the left ventricular inflow were carried out from apical transducer positions. To align the sample volume parallel to the direction of the diastolic inflow, the region just apical of the mitral valve was scanned for maximal diastolic velocities.
Data Analysis All measurements were made with the digitizing pad of an off-line digitizing computer system (Cardio 200, Kontron). The flow area of the aortic annulus was assumed to be circular and calculated from its mid-systolic inner diameter in the M-mode echocardiogram. The diameter measurement was performed in triplicate and averaged [5]. For
H. Dittmann et al. : Cardiac Output Across Prosthetic Mitral Valves
265
10-30 cardiac cycles of medium length and a difference in cycle length of less than 10% Doppler profiles were traced through their darkest portion at their modal velocity. Only those Doppler recordings were chosen that showed maximal flow velocities and a narrow frequency bandwidth representative of undisturbed flow. The area under the curve was the time-velocity integral. The effective mitral valve orifice was then calculated from the transmittal velocity profiles using the pressure half-time method [3, 13, 26, 28]. Cardiac output was calculated as the product of the Doppler time-velocity integral, flow area, and heart rate.
n=46 9- r:0.8/+ -~ 8- y=0.%x+1.28 ~ SEE=0.665 [/rnin 7- HPE=10.B•
Reproducibility
Fig. 1. Flow volume measurement by Doppler across the mitral valve prosthesis (MVP) compared with Doppler flow measurement in the left ventricular outflow tract and cardiac output by thermodilution at rest. Line of identity is drawn. MPE= mean percent error
6-
o
= / == DS 9 D~e
9
/ /
9 9 9
3
2
/
9 St.Jude Hedtr.HoL[ =Hancock
9
1 /
&ardiac Output (titers/min)
In ten randomly chosen patients the reproducibility of the mitral valve area calculation and timevelocity integral measurement for one observer and between two observers was determined.
Statistics Linear regression analysis and paired t test were used to evaluate data. The 95% confidence limits for the correlation coefficients (r) and SEE were calculated. Mean percent error (MPE) of the Doppler transmitral flow measurement was calculated as an average of absolute percent errors. A probability (p) value of < 0.05 was considered statistically significant [23].
Results
Mitral Valve Area The calculated valve area in all prosthetic mitral valves ranged from 1.7 cm 2 to 4 . 0 c m 2 (mean 2.9-t-0.5 c m 2, Table 1). The area for 15 St. Jude Medical valves ranged from 2.6 c m 2 t o 4 . 0 c m 2 (mean 3.2_+0.3 cm2), which was higher than the orifice area in 19 Medtronic Hall prostheses (range 2.2 c m 2 t o 3.7 c m 2, m e a n 2.9 + 0.4 c m 2 ; p < 0.05) and in 12 Hancock bioprostheses (range, 1 . 7 4 . 0 cm2; mean, 2.6-I-0.6 c m 2 ; p
KlinWochenschr (1990) 68:263-268
9 Springer-Verlag 1990
Doppler Measurement of Cardiac Output Across Prosthetic Mitral Valves H. Dittmann, W. Voelker, K.-R. Karsch, and L. Seipel Medizinische Klinik III, Eberhard.-Karls-Universitfit Tfibingen (Prof. Dr. L. Seipel)
Summary. In 46 patients with a normal functioning mitral valve prosthesis (15 St. Jude, 19 Medtronic Hall, 12 Hancock) cardiac output was measured by pulsed Doppler echocardiography across the valve prosthesis. Simultaneously cardiac output was determined by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract (2.8 1 / m i n - 9.5 l/rain). The prosthetic valve area was calculated using the pressure halftime method. Cardiac output was calculated by multiplying time-velocity integrals with the mitral valve area. Cardiac output measurements across the mitral prosthesis correlated significantly with thermodilution (r = 0.96, SEE = 0.400 l/rain) and pulsed Doppler echocardiography flow measurements in the left ventricular outflow tract (r = 0.82, SEE = 0.679 l/rain). The mean percent error of the Doppler transmitral flow measurement was 10.8 %. Doppler transmitral flow underestimated cardiac output values of more than 6.5 1/min in 6 of 7 patients. Cardiac output measurements across Hancock (SEE=0.473 1/min) and St. Jude prostheses (SEE=0.538 1/min) were more accurate than across Medtronic Hall prostheses (SEE=0.847 1/ min). Cardiac output can be calculated by pulsed Doppler echocardiography across normal functioning mitral prostheses. Due to the different flow dynamics the accuracy of cardiac output measurement depends on the prosthetic valve type. Reliable measurements of cardiac output can be performed across Hancock and St. Jude prostheses only. This method is limited in volume flow measurements across Medtronic Hall prostheses. Abbreviations: MPE = mean percent error; MVP = mitral valve prosthesis; r=correlation coefficient; r95%=95% confidence limit of r; SEE = standard error of the estimate; S E E g 5 % = 95 % confidence limit of SEE
Key words: Flow volume measurement - Prosthetic mitral valve - Doppler echocardiography
Quantitative Doppler echocardiography is increasingly used for the measurement of cardiac output. A variety of methods has been published reporting volume flow measurement in the inflow or outflow tract of the left and right ventricles and in the great arteries [5, 6, 9, 10, 17, 18, 20]. In a previous experimental study using Doppler echocardiography the volume flow was estimated across prosthetic heart valves in vitro [1]. However, flow beyond mechanical and bioprosthetic valves is considerably different. Thus, the purpose of this study was to assess the accuracy of pulsed Doppler echocardiography in the determination of cardiac output across different mechanical and bioprosthetic mitral valve prostheses in vivo.
Method Study Patients The study group consisted of 46 patients with a normal functioning mitral valve prosthesis according to clinical and Doppler echocardiographic examination [3, 4, 22, 24, 28]. Only patients with excellent Doppler signals and high quality echocardiograms were included in the study. Patients with clinical, electrocardiographical, echocardiographical, and Doppler evidence of aortic valve disease, subaortic stenosis, intracardiac shunts, moderate or severe tricuspid regurgitation, left ventricular hypertrophy or myocardial ischemia were excluded from the study [5, 6, 19, 26, 32]. The age of the 32 women and 14 men ranged from 31 to 68 years.
264
H. D i t t m a n n et al. : Cardiac O u t p u t Across Prosthetic Mitral Valves
Table 1. Calculated mitral valve areas using the pressure halftime m e t h o d in 46 patients (cm 2) Valve size
Valve type St. Jude
M e d t r o n i c Hall
Hancock
No. 29
2,6-4.0 (n = 6)
2.9-3.6 (n = 2)
No. 31
2.9-3.4 (n = 9)
2.2-3.1 (n = 14)
1.7-2.4 (n=4) 2.2-4.0 (n = 8)
No. 33
--
3.1-3.7
(,,=2) No. 35
-
was 2.4 M H z and the pulse repetition frequency of the Doppler unit was 4 or 6 kHz, depending on the depth of the sampling site. The axial length of the sample volume was 3 mm. The Doppler frequency shifts were processed using a fast Fourier transform spectral analyzer. The M-mode echocardiograms and Doppler frequency spectra were recorded at a paper speed of 100 mm/s on a hard copy unit (Line Scan Recorder 20B, Toshiba).
3.1
(n=0
Ten patients had sinus rhythm and 36 patients had atrial fibrillation. The types of implanted valve prostheses were St. Jude Medical (size 29 and 31) in 15 patients, Medtronic Hall (size 29, 31, 33, 35) in 19 patients, and Hancock bioprostheses (type II, size 29 and 31) in 12 patients (Table 1). Doppler flow calculations at mitral valve prostheses were compared with cardiac output measurements by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract.
Thermodilution Method After routine right heart catheterization in 17 patients a 7 F Swan-Ganz thermodilution catheter was positioned in the pulmonary artery. The thermodilution cardiac output was obtained with an Edward cardiac output instrument model 9520-A by injecting rapidly 10 ml of 0.9% cold sodium chloride solution through the proximal part of the Swan-Ganz thermodilution catheter. Cardiac output was computed as the average of three values with a difference of less than 10%. If the difference between the lowest and highest value of the first three measurements was more than 10%, two additional cardiac output measurements were performed and the extremes were discarded before averaging. In 8 of the 17 patients cardiac output was calculated additionally during symptom limited supine bicycle ergometry on the 25 W or 50 W level.
Echocar diogr ap hy A 90 ~ phased array duplex Doppler echocardiograph (Toshiba SSH-40A with Toshiba SDS-21B) was used for both imaging and determining flow velocity. The ultrasound frequency of the probe
Flow Volume Measurement in the Left Ventricular Outflow Tract In 29 patients volume flow was measured in the center of the aortic valve annulus by Doppler echocardiography. For flow area recording a left parasternal M-mode tracing, controlled by the two-dimensional image, was obtained at the aortic annulus, directly proximal to the insertion of the aortic leaflets [6]. The transducer was then positioned near the apex to obtain the five-chamber view. Flow velocity was recorded in the center of the aortic annulus, just proximal to the aortic valve leaflets. The angle between the assumed blood flow in the outflow tract and the cursor line of the sample volume was kept less than 20 ~.
Flow Volume Measurement Across the Mitral Valve Prosthesis Doppler transmitral flow was simultaneously measured during thermodilution cardiac output calculation or just before or after Doppler flow measurement in the left ventricular outflow tract. The sequence of the Doppler measurements in the left ventricular outflow tract and at the mitral prosthesis was randomized. Cardiac output calculations were performed in the left lateral recumbent position under steady-state conditions with a constant heart rate throughout the measurements. Velocity recordings of the left ventricular inflow were carried out from apical transducer positions. To align the sample volume parallel to the direction of the diastolic inflow, the region just apical of the mitral valve was scanned for maximal diastolic velocities.
Data Analysis All measurements were made with the digitizing pad of an off-line digitizing computer system (Cardio 200, Kontron). The flow area of the aortic annulus was assumed to be circular and calculated from its mid-systolic inner diameter in the M-mode echocardiogram. The diameter measurement was performed in triplicate and averaged [5]. For
H. Dittmann et al. : Cardiac Output Across Prosthetic Mitral Valves
265
10-30 cardiac cycles of medium length and a difference in cycle length of less than 10% Doppler profiles were traced through their darkest portion at their modal velocity. Only those Doppler recordings were chosen that showed maximal flow velocities and a narrow frequency bandwidth representative of undisturbed flow. The area under the curve was the time-velocity integral. The effective mitral valve orifice was then calculated from the transmittal velocity profiles using the pressure half-time method [3, 13, 26, 28]. Cardiac output was calculated as the product of the Doppler time-velocity integral, flow area, and heart rate.
n=46 9- r:0.8/+ -~ 8- y=0.%x+1.28 ~ SEE=0.665 [/rnin 7- HPE=10.B•
Reproducibility
Fig. 1. Flow volume measurement by Doppler across the mitral valve prosthesis (MVP) compared with Doppler flow measurement in the left ventricular outflow tract and cardiac output by thermodilution at rest. Line of identity is drawn. MPE= mean percent error
6-
o
= / == DS 9 D~e
9
/ /
9 9 9
3
2
/
9 St.Jude Hedtr.HoL[ =Hancock
9
1 /
&ardiac Output (titers/min)
In ten randomly chosen patients the reproducibility of the mitral valve area calculation and timevelocity integral measurement for one observer and between two observers was determined.
Statistics Linear regression analysis and paired t test were used to evaluate data. The 95% confidence limits for the correlation coefficients (r) and SEE were calculated. Mean percent error (MPE) of the Doppler transmitral flow measurement was calculated as an average of absolute percent errors. A probability (p) value of < 0.05 was considered statistically significant [23].
Results
Mitral Valve Area The calculated valve area in all prosthetic mitral valves ranged from 1.7 cm 2 to 4 . 0 c m 2 (mean 2.9-t-0.5 c m 2, Table 1). The area for 15 St. Jude Medical valves ranged from 2.6 c m 2 t o 4 . 0 c m 2 (mean 3.2_+0.3 cm2), which was higher than the orifice area in 19 Medtronic Hall prostheses (range 2.2 c m 2 t o 3.7 c m 2, m e a n 2.9 + 0.4 c m 2 ; p < 0.05) and in 12 Hancock bioprostheses (range, 1 . 7 4 . 0 cm2; mean, 2.6-I-0.6 c m 2 ; p
