Doppler echocardiographic evaluation of normal and thrombosed Björk-Shiley mitral prosthetic valves

International Elsevier

Journal of Cardiology,

20 (1988) 387-393

387

IJC 00727

Doppler echocardiographic evaluation of normal and thrombosed Bjiirk-Shiley mitral prosthetic valves S. Radhakrishnan, Departmeni

V.K. Behl, Rajiv Bajaj, M.L. Bhatia and S. Shrivastava

of Cardiology and Cardiothoracic Surgev, All India Institute Ansarl Nagar, New Delhi, India (Received

28 August

1987; revision

accepted

Radhakrishnan S, Behl VK, Bajaj R, Bhatia ML, cardiographic evaluation of normal and thrombosed valves. Int J Cardiol 1988;20:387-393.

21 February

of Medical Sciences,

1988)

Shrivastava Bjijrk-Shiley

S. Doppler echomitral prosthetic

Doppler echocardiographic characteristics of 75 normally functioning Bjiirk-Shiley mitral prostheses were studied in patients whose valvar function was considered normal by clinical and fluoroscopic evaluation. The mean Doppler peak and end-diastolic gradients were 9.01 f 3.23 mm Hg, and 2.36 f 1.0 mm Hg, respectively. The mean area of the mitral valve calculated by the half-time method was 2.58 f 0.38 cm*. No significant difference between the various Doppler parameters was found for the two different valve sizes (25 and 27 mm) studied. Trivial mitral regurgitation was detected in 21 (28%) cases. Doppler echocardiography was performed in six patients with suspected malfunction of the Bjiirk-Shiley mitral prosthesis subsequently confirmed at operation. The end-diastolic gradients in the six patients were 16, 20, 10, 14, 16, and 24 mm Hg, respectively. The calculated areas of the mitral valve were 1.57, 1.37, 1.3, 1.5, 1.46, and 1.3 cm*, respectively. The values of the gradient and calculated areas in malfunctioning valves were very different from those found in normally functioning Bjiirk-Shiley mitral prostheses. It is concluded that Doppler echocardiography is a very useful noninvasive technique for the study of the function of the Bjiirk-Shiley mitral prosthesis and provides quantitative information regarding pressure gradients and valvar area. Key words: malfunction

Bjiirk-Shiley

prosthesis;

Doppler

echocardiography;

Correspondence to: S. Shrivastava, M.D.. Dept. of Cardiology, Ansari Nagar, New Delhi-110029, India.

0167-5273/88/$03.50

0 1988 Elsevier

Science Publishers

All India Institute

B.V. (Biomedical

Division)

Prosthetic

of Medical

valve

Sciences,

388

Introduction Doppler echocardiography has been found to be a reliable method for detecting and assessing the severity of native mitral valvar stenosis [l]. Recent reports show that Doppler echocardiography is also useful in detecting malfunction of prosthetic valves [2,3]. In this study we evaluated Doppler flow characteristics across normally functioning Bjiirk-Shiley mitral prostheses in a large number of patients, so as to determine the normal values for various Doppler parameters in order to facilitate detection of valvar malfunction. In addition, we also report the Doppler echocardiographic findings in six patients who presented with symptoms related to malfunction of their Bjbrk-Shiley mitral prostheses and were subsequently proved at operation to have thrombosis of the valve. Materials

and Methods

During the past four months, 75 patients with a normally functioning Bjork-Shiley mitral prosthesis were referred for routine echocardiographic examination. All these patients were asymptomatic and had normal physical examination. The fluoroscopic evaluation was normal in all cases. The echocardiographic examination was performed between 7 days to 12 years (mean 21 months) of the surgical procedure. Their ages ranged between 15-50 years (mean 30.2 + 9.55 years). There were 28 males and 47 females. Two valve sizes studied were 25 mm (n = 26) and 27 mm (n = 49). The plano-convex model was studied in two patients (27 mm size). The other models were the convexo-concave (n = 20 of the 25-mm size, and n = 36 of the 27-mm size) and the modified convexo-concave (monostrut) (n = 6 of the 25-mm size, and n = 11 of the 27-n-m size) models. In addition, during this period six patients with clinical and fluoroscopic evidence of valvar malfunction were studied. All these patients underwent surgical thrombectomy within 24 hours of the procedure. Doppler echocardiographic examination was performed with an ATL Ultramark 8 machine which is equipped with both a pulsed and continuous wave Doppler system. Echocardiographic examination was first performed to determine chamber size and left ventricular function and the disc motion was seen on the M-mode tracing. Subsequently Doppler velocity profile across the prosthetic valve was obtained by placing the transducer in the apical position and the records were taken on video tape in all patients and if necessary also on strip chart recorder at 100 mm/second paper speed. To interrogate for the presence of mitral regurgitation the sample volume was placed in the left atrium, using apical and left parasternal windows. The diastolic flow velocity profile was first evaluated by the pulsed Doppler by placing the sample volume in the left ventricle in the apical position. Subsequent measurements, in all patients, were made by the signal obtained by continuous wave Doppler examination from the apical view. A good signal showing the maximum peak velocity and a complete envelope was a prerequisite for calculation in all cases. Peak diastolic and end-diastolic velocities were measured in meters per second. The peak and end-diastolic gradients were calculated using the

389

modified Bernoulli equation P = 4 X V2, where P = pressure gradient, and V = maximum velocity in meters per second, the gradient being expressed in millimeters of mercury (mm Hg). The mitral valve area was calculated by the pressure half-time method described for native mitral valve [4]. The valve area was expressed in square centimeters. All calculations were an average of three cardiac cycles for patients in sinus rhythm and five cardiac cycles in patients with atria1 fibrillation. The presence of mitral regurgitation was diagnosed by a holosystolic signal in the left atria1 cavity. It was considered trivial or mild if the signal was detected only at or within two centimeters of the prosthetic valve and significant if detected beyond this in the left atria1 cavity. Statistical comparison of peak velocity and gradients, and end-diastolic velocity and gradients, and mitral valve area was done between the patients having 27-mm and 25-mm Bjiirk-Shiley mitral prostheses using the Student t-test.

Results Fig. 1 shows a flow velocity envelope across the mitral valve obtained with pulsed Doppler by placing the sample volume in the left ventricle, in an apical view, in a patient with a normally functioning Bjork-Shiley mitral prosthesis. The flow pattern resembles that of a normal native mitral valve. An early peak occurs in the beginning of diastole followed by a rapid fall. A second peak corresponding to atria1 systole occurs in patients in normal sinus rhythm.

Fig. 1. Pulsed Doppler echocardiography in a patient with normally functioning Bj&k-Shiley prosthesis. Inset shows Doppler sample volume in the left ventricle, in the apical 4-chamber view, beneath the prosthetic valve.

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Fig. 2. Continuous wave Doppler tracing of Case III with prosthetic valve thrombosis. The peak velocity was increased to 2.5 meters/second. The end-diastolic velocity and gradient were 1.6 meters/second and 10 mm Hg, respectively. The calculated mitral valve area was 1.3 cm’.

Normally Functioning Prosthetic Valves Echocardiographic Findings. The left ventricular function and opening and closing angles of the Bjbrk-Shiley mitral prosthesis disc as seen in the M-mode echocardiography was normal in all the cases. Doppler Findings. The peak and end-diastolic velocity and gradients are shown in Table 1. When patients with the two valve sizes were compared, no significant differences were found for the various parameters assessed. 95% confidence limit values for the end-diastolic gradients and mitral valve area were determined. 95%

TABLE Doppler valves. Size 25(N26) 27(N49)

1 velocities,

gradients and valve area for normally

functioning

Bjiirk-Shiley

PV

PG

EDV

EDG

(m/W

(mm Hg)

(m/set)

(-

1.1-2.2 (1.53zbO.25) 1.1-2.3 (1.49+0.24)

4.8-19.2 (9.58 f 3.26) 4.8-20.8 (8.85 + 3.20)

0.4-1.3 (0.76 + 0.28) o-1.4 (0.66 f 0.37)

0.64-6.4 (2.45 + 1.80) O-7.8 (2.27 + 2)

mitral prosthetic

MVA Hg)

(cm* ) 1.9-3.1 (2.61 k 0.38) 2-3.2 (2.56 + 0.28)

PV = peak velocity; PG = peak gradient; EDV = end-diastolic velocity; EDG = end-diastolic gradient; MVA = mitral valve area; m/set = meters per second. Numbers in parentheses indicate mean and standard deviation.

391 TABLE

2

Clinical, echocardiographic. prosthetic valve malfunction. Case

I II III IV V VI

Clinical

fluoroscopic

and

data

Doppler

findings

M-mode

echo

in patients

with

Bjiirk-Shiley

Doppler

mitral

echo

Symptoms

Valve sounds

MR

Valve opening and closing

Fluoroscopy

EDV

EDG

MVA

Dyspnea NYHA Dyspnea NYHA Dyspnea NYHA Dyspnea NYHA Dyspnea NYHA Dyspnea NYHA

Decreased

Nil

Blunted

Normal

2.23

20

1.37

Decreased

Nil

Blunted

Normal

2.0

16

1.57

Decreased

Nil

Blunted

Diminished

1.6

10

1.3

Decreased

Nil

Blunted

Normal

2.0

16

1.46

Decreased

Nil

Normal

Diminished

2.4

24

1.3

Decreased

Nil

Normal

Normal

1.87

14

1.57

Class III Class III Class II Class III Class III Class III

MR = mitral regurgitation; EDV = end-diastolic (mm Hg); MVA = mitral valve area (cm*).

velocity

(meters/set);

EDG = end-diastolic

gradient

confidence limits for the end-diastolic gradient were 1.72-3.17 and 1.69-2.8 for the 25mm and 27-mm size, respectively. 95% confidence limits for the mitral valve area were 1.8-3.3 cm* and 2.4-2.6 cm2 for the 25-mm and 27-mm sizes, respectively. Mitral regurgitation was present in 21 (28%) cases. It was present in 8 (30.8%) patients with a 25-mm valve and 13 (26.5%) patients with a 27-mm valve (P = NS). Nine (52.2%) of the 17 patients with the newer, monostrut variety of the valve had mitral regurgitation. In all the patients the regurgitation jet was minimal, never extending more than 2 cm into the left atria1 cavity and was also very localized.

Thrombosed Values. The clinical, echocardiographic, fluoroscopic and Doppler findings of the six patients with thrombosis of the Bjiirk-Shiley mitral prosthesis are shown in Table 2. All the patients had presented with dyspnea of recent onset (varying between NYHA Class II and III). The prosthetic valve sounds were reported to be decreased in every patient. M-mode echocardiography showed that prosthetic angles were blunted in four patients. Fluoroscopy showed a reduced opening angle in only two patients. The Doppler end-diastolic gradient in these patients varied from 10 mm Hg to 24 mm Hg and the mitral valve area varied from 1.3 cm2 to 1.57 cm2. These values were significantly different from the values obtained in patients with normally functioning Bjbrk-Shiley mitral prostheses. Abnormal mitral regurgitation was not detected in any patient. All patients underwent surgical exploration of the mitral valve and an underlying thrombus was removed.

392

Discussion Non-invasive determination of pressure gradients across obstructed native mitral valves by Doppler echocardiography using the modified Bernoulli equation (pressure gradient = 4 x V2) has been found to be very reliable [l]. The technique has also been utilized to predict accurately the area of native atrioventricular valves using the half-time method [4]. Recently, the use of Doppler echocardiography has been further extended to determine non-invasively the pressure gradient across and area of prosthetic valves [5]. In our study, we found values for end-diastolic velocities and gradients and the mitral valve area to be within a very close range, findings previously reported by Sagar et al. [2]. Other authors [5-71 have, however, found a much wider range for the orificial area of various mitral valve prostheses. The area for the Bjbrk-Shiley mitral prosthesis varied between 1.8 and 3.7 cm’ in one study by the Doppler method [5]. The wide variations in the orificial area have been attributed to different orientations of the valve in relation to the interventricular septum and the posterior wall of the left ventricle [7]. Our results are in very close agreement with those found in in vitro hemodynamic and catheterization studies [7,8]. In our study, the normal values for peak velocities and gradients and valve area as determined by Doppler echocardiography are similar to those obtained by others in much smaller numbers of cases studied [2-51. Comparison of the two valve sizes showed no significant difference for the various Doppler parameters and confirms the results seen by others [5]. No difference in Doppler velocities or valve area could be seen for the newer models of Bjork-Shiley valves (which have a greater opening angle and have been shown to provide more favorable hemodynamics in in vitro studies [9]). The number of such valves studied, however, is too small to give any definite conclusion. Minimal regurgitation across normally functioning Bjiirk-Shiley mitral prostheses has been demonstrated by angiographic studies [lo]. We found trivial mitral regurgitation in 28% of our cases, in keeping with the observation of Panidis et al. [3] who found mitral regurgitation in 38% of cases by Doppler. Interestingly, 9/17 (52%) patients with the newer models of the valve showed mitral regurgitation. This is also substantiated by in vitro studies where the incidence of valve regurgitation was greater with the newer models due to greater opening angles [9]. Doppler assessment of mitral regurgitation may be fallacious because of the difficulty in positioning the sample volume relative to the mechanical prosthesis [ll]. This may account for the variability in detecting mitral regurgitation [2-51 and also for the lower incidence of mitral regurgitation as compared to in vitro studies. In patients with malfunction of a Bjiirk-Shiley prosthesis, the M-mode echocardiographic examination was normal in two of the six cases. Fluoroscopic evaluation was also normal in four of the six patients. Our study, like others [12], thus shows that Doppler echocardiography may be superior to M-mode or fluoroscopic techniques in the identification of valvar thrombosis. In conclusion, we submit that Doppler echocardiography is an additional useful non-invasive tool in the evaluation of Bjbrk-Shiley mitral prostheses and provides quantitative information regarding pressure gradients and valve areas. A baseline postoperative Doppler study would allow comparison at a later date when valve malfunction is suspected.

393

Acknowledgements We wish to acknowledge our surgical colleagues, Professor P. Venugopal, Drs. Sampath Kumar, A. Balram, K.S. Iyer, B. Das and Dr. Anita Saxena from the Department of Cardiology for helping us in evaluation of these cases. We are also thankful to the technical staff of Echocardiography Laboratory in assisting us in completing this study.

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