doppler echocardiographic evaluation of patients with porcine mitral valves

Doppler echocardiographic evaluation of patients with porcine mitral valves

The application of Doppler echocardiography to the study of valvular function has recently been extended to include prosthetic valves. We have used Doppler echocardiography to evaluate 40 patients with porcine mitral valves (PMV) implanted 0.5 to 99 months prior to examination. Three parameters of PMV flow were assessed: maximum diastolic left ventricular inflow velocity (V,,,), pressure half-time (P’/?t), and presence or absence of mitral regurgitation (FAR). Normally functioning PMV (n = 29) were characterized by V,,,,= ~180 cm/set and P%t <180 msec. Within this group, P%t was not correlated significantly with the age of the patient nor with prosthesis size. Doppler correctly identified all 10 patients with MR. Among these 10 patients, V,,, was 206 2 53 cm/set, significantly higher than the mean observed in normally functioning prostheses (136 f 24 cm/set, p < 0.001). In eight patients with stenosis of the PMV, mean PHt was 220 f 63 msec, and in seven of eight, it was 2180 msec (p < 0.001 compared to normals). We conclude that: (1) V,,. ~180 cm/set, P%t ~160 msec, and absence of systolic turbulence in the left atrium characterize normally functioning PMV; (2) P’/t 4180 msec identifies patients with stenosis of the PMV; and (3) Doppler echocardiography can detect MR and separate mitral from tricuspid regurgitation. (AM HEART J 111:237, 1986.)

Thomas Ryan, M.D., William F. Armstrong, M.D., James C. Dillon, M.D., and Harvey Feigenbaum, M.D., Indianapolis, Ind.

The stent-mounted, gluteraldehyde-fixed porcine mitral valve (PMV) has gained considerable popu- larity, primarily because of favorable hemodynamic features and a relatively low thromboembolic rate.‘e3 As with all prosthetic valves, infective endocarditis, paravalvular leakage, and thrombus formation are major causes of prosthesis dysfunction.4-6 A problem unique to bioprostheses is the potential for tissue degeneration, which is characterized by leaflet dis- ruption and/or calcium deposition, and may result in hemodynamically significant regurgitation or stenosis,7v8 the risk of which appears to increase significantly 4 to 5 years after valve replacement.3*4

Modern echocardiographic techniques, including Doppler echocardiography, provide valuable information on the function of native valves.s Because of

From the Department of Medicine, Krannert Institute of Cardiology, Indiana University School of Medicine.

This study was supported in part by the Herman C. Krannert Fund,

Indianapolis, Indiana; by Grants HL-06308 and HL-071820, and Clinical Investigator Award HL-01041-02 from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland; by the American Heart Association, Indiana Affiliate, and by a Grant from the Whitaker Foundation, Camp Hill, Pennsylvania. Dr. Armstrong is a recipient of a Clinical Investigator Award from the National Institutes of Health/National Heart, Lung, and Blood Institute.

Received for publication July 1, 1985; accepted Aug. 2, 1985.

Reprint requests: Thomas Ryan, M.D., Indiana University Medical Center, UH N-563, 926 West Michigan St,, Indianapolis, IN 46223.

its ability to directly measure intracardiac blood velocity and direction, Doppler echocardiography provides unique information for patients with valvular pathology. Previous studies suggest that Doppler echocardiography can be applied to the study of patients with prosthetic valves in a fashion similar to its application to native valves.‘O-l5 Although the technique can detect prosthetic valve stenosis and regurgitation, little data exist regarding criteria for normal function, and the reliability and accuracy of Doppler echocardiography in determining prosthesis dysfunction is not firmly established. We have used Doppler echocardiography to evaluate 40 patients with PMV implanted 0.5 to 99 months prior to examination. This report details the results of our study and suggests criteria for defining normal and abnormal function.

METHODS

Patient population. Between May, 1983, and Novem- ber, 1984, 40 patients (28 women) with porcine valves in the mitral position (Hancock or Carpentier-Edwards) were examined with Doppler echocardiography. The patients ranged in age from 28 to 83 (mean 58) years. Indications for mitral valve replacement were rheumatic disease in 35 patients, infective endocarditis in three, and severe mitral regurgitation secondary to ischemic heart disease in two. Six patients also had prosthetic aortic valves, one patient had a porcine tricuspid valve, and two

237

238 Ryan et al. February, 1986

American Heart Journal

Table I. Normally functioning porcine mitral valves

Patient no.

Age br)

Lloppler data Duration of Size of

implantation prosthesis 2DE V,, P’zt (no) (mm) Rhythm Clinical data data (cmlseci (msec) MK

1 63

2 59

3 76

4 65

5 66

6 59

7 83

8 61

9 51

10 56

11 50

12 41

13 56

14 54

15 53

16 81

17 48

18 56

19 71

20 56

21 73

22 60

23 61

24 54

25 53

26 65

27 63

28 74

29 40

Mean 61 I 10

12

44

58

39

61

13

25

81

45

60

3

0.5

40

48

33

97

89

5'

48

60

72

60

60

44

84

77

99

90

50 2 28

AF AF AF SR AF AF AF AF AF SR AF SR

AF AF AF AF AF AF AF AF AF AF SK SR AF AF AF AF SR

TR

Porcine AV & TV with TS Porcine AV; TVA with TR

-

Porcine AV; TS; TR TR

Porcine AV AR; TR

Porcine AV; TR

TR Porcine AV; TR

TR LV dys

TR TR; LV dys

TVA with TR LV dys; TR

AR -

-

N N

TL N N N N N N

N N N N N N

N N N N N N N N N N

N

110 100

180 140

160 160

125 130

170 150

100 140

110 130

170 110

160 130

130 140

130 120

120 130

170 130

130 130

125 110

100 110

175 150

120 160

110 150

160 100

140 130

130 160

130 150

125 150

120 140

110 140

140 160

160 160

150 140

136 & 24 136 + 18

No No NO No No No No No No No No No No NO No NO Yes No No No No No NO No No No No No No

AF = atria1 fibrillation; SR = sinus rhythm; V.,,, = maximum left ventricular inflow velocity; P’p~t = pressure half-time; MR = mitral regurgitation; TR = tricuspid regurgitation; AV = aortic valve; TV = tricuspid valve; TVA = tricuspid annuloplasty; TS = tricuspid stenosis; AR = aortic regurgitation; LV dys = left ventricular dysfunction; N = no abnormalities noted; TL = thickened leaflets; 2DE = two-dimensional echocardiography.

had undergone tricuspid annuloplasty. Thirteen patients were in sinus rhythm and 27 were in atria1 fibrillation at the time of examination. The patients were studied 18 days to 99 months (mean 55.5 months) after valve replacement. Ten patients underwent cardiac catheterization for suspected prosthesis malfunction.

Doppler echocardiography. Doppler echocardiographic examinations were performed using commercially available instruments (Ultra Imager, Electronics for Medicine, Honeywell, or Irex Exemplar). For pulsed Doppler studies, either a 2.25 MHz single-element mechanical transducer or a phased-array system which samples at 2.0 MHz was used. Maximum nonambiguously detectable velocity was t- 225 cmlsec to a depth to 6 cm, and f 135 cm/set from 6 to 10 cm. By shifting the zero line, velocities of 450 and 270 cm/set, respectively, could be detected. In continuous mode, velocities as high as 6 m/set could be measured. Doppler frequency shift spectral analysis was recorded on hard copy at a paper speed of 50 or 100 mm/set which was used for all data analysis and measurements.

PMV flow was recorded from the apical window with the sample volume positioned to obtain an optimal signal, as parallel as possible to the assumed direction of flow. The left atrium (LA) was interrogated from the apical and parasternal windows for the presence of systolic regurgitant flow. Aortic, pulmonary, and tricuspid flow patterns were also sampled and recorded in each patient. All Doppler echocardiographic examinations were of ade- quate technical quality to allow analysis.

Doppler echocardiographic measurements. After visual inspection of all recorded complexes, those contain- ing the highest velocities with the narrowest spectral envelope were used for analysis. Three or four such complexes were measured and averaged in each case. The following parameters of transmitral flow were assessed in each patient: (1) Maximum diastolic inflow velocity (V,,,) was identified and defined as the highest velocity of the early diastolic left ventricular inflow jet. The velocity of the late diastolic inflow wave, corresponding to left atria1 systole, was ignored in determining this value. (2) Pres- sure half-time (P% t) was calculated according to the

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Number 2 Doppler evaluation of porcine mitral valves 239

1624060 -98 cm/e

Clf~6tllllIlfii,llltlllll(lll(tllltttllllltlll

Fig. 1. Normally functioning PMV flow in a patient in sinus rhythm. Arrowheads indicate location of the sample volume, Highest flow velocity occurs in early (E) and late (A) diastole, coinciding with the rapid left ventricular filling phase and atria1 systole, respectively. Values for maxium left ventricular inflow velocity (VJ and pressure half-time (PIAt) are shown. LA = left atrium: LV = left ventricle.

method of Hatle et a1.16 (3) Mitral regurgitation (MR) was considered present if broad spectrum high velocity flow was detected in the LA during systole.

Two-dimensional echocardiography. Two-dimensional echocardiography @DE) was performed in 37 patients using commercially available instruments with either a 2.25,3.0, or 3.5 MHz mechanical transducer. Studies were obtained either in conjunction with or, in the case of some patients with normally functioning prostheses, up to 7 weeks prior to Doppler examination. Echocardiograms were interpreted in light of the clinical setting, but without knowledge of the Doppler results.

Cardiac catheterization. Cardiac catheterization was performed within 48 hours of Doppler examination in 10 patients. Routine left- and right-heart catheterization was performed using standard hemodynamic and angiographic meth0ds.l’ Pressures were measured using a calibrated fluid-filled catheter system. Cardiac output was measured by the Fick method. Mitral regurgitation was graded in severity from 0 to 4+.

Statistics. The relationships of mitral stenosis (MS), MR, or both to V,,, and P ‘/z t were assessed using two-way analysis of variance. T tests were used to evaluate a priori contrasts.‘* Sensitivity was defined as number of true positive detections divided by total number of positives in the group. Specificity was defined as number of true negative detections divided by the total number of nega- tives in the group. Predictive value was defined as the percent of patients with a positive result who were true positive. Values were expressed as mean 2 standard devi- ation.

RESULTS

Normal porcine mitral valves. Twenty-nine patients comprised the cohort with normally functioning prostheses (Table I). For the purpose of this study, normal prosthesis function was defined as absence of symptoms attributable to infective endocarditis and absence of clinical evidence of MS and/or MR. 2DE was performed in 26 of these patients. Twenty- five of 26 studies (96 % ) were interpreted as showing no evidence of prosthesis dysfunction. One patient (No. 3, Table I) had thickened leaflets by ZDE, but was without signs or symptoms suggestive of either MS or endocarditis. Among these patients, PMV were implanted 0.5 to 99 (mean 50.2) months prior to study. Because of their satisfactory clinical course, no patient in this group underwent cardiac catheterization.

A normal PMV flow pattern is illustrated in Fig. 1. It is characterized by an M-shaped pattern reflecting both early and late diastolic left ventricular inflow. In most cases, the spectral band was relatively narrow, indicating laminar flow. Qualita- tively, the pattern of PMV flow was similar to that seen in normal native mitral valves. Systole was characterized by absence of transmit& flow. Patients in atrial fibrillation had a similar early diastolic flow pattern, but lacked a late diastolic component.



Fig. 2. This patient, who had undergone PMV placement and tricuspid annuloplasty 5 years prior to examination, presented with a systolic murmur at the lower left sternal border. Panel A demonstrates normal PMV flow. V,,, is not elevated. Panel B demonstrates the absence of systolic turbulent flow in the left atrium. Panel C demonstrates high-velocity, turbulent systolic flow in the right atrium (RA), indicating tricuspid regurgitation (TR). SYS = systole.

Table II. Dysfunctioning porcine mitral valves

Patient Age (yr)

Duration of implantation

(mo)

C’atheteri- Doppler data ration Data

Size of prosthesis 2DE V ,n31 PJ bt MVg

(mm) Rhythm data (cm/see) (msec) MR (mm Hg) MR

30 56 72 31 37 72 32 59 94 33 42 96 34 42 66 35 54 96 36 66 7 37 55 94 38 62 29 39 28 52 40 61 39

Mean 51 k 12 65 _t 30

27 3 1 27 29 31 33 29 33 33 31 33 -

SR SR AF AF SR AF SR SR SR SR AF

TL TL,P

TL TL P N N

TL,P TL,P

P P

220 190 Yes 18 200 260 Yes 24 160 180 Yes 12 210 350 No 18

290 200 Yes 15 210 140 Yes 0 200 150 Yes 15 200 160 Yes 5 170 190 Yes 16 290 240 Yes 18 120 160 Yes

206 + 50 202 + 61

2+ 4+ 4+ 0 4+ 4+ 2+ 4+ 3+ 4+

MR estimated on a scale of 0 (none) to 4f (severe) using right anterior oblique angiogram. MVg = mean mitral valve gradient; N = no abnormalities noted; P = prolapsed leaflet; TL = thickened leaflets; other abbreviations as in Table 1.

Mean V,,, within this group was 136 +- 24 cm/set and, in all cases, was ~180 cm/set. This is higher than the range seen in normal adult subjects, in whom the upper limit of normal is approximately 130 cm/sec.‘s

P% t was also prolonged compared to normal native valves.16* lg The range among 29 patients was 100 to 160 msec, with a mean of 136 + 18 msec. P% t did not correlate significantly with the age of the patient nor with the prosthesis size.

Regurgitant systolic LA flow was not detected by Doppler echocardiography in 28 of 29 patients without clinical evidence of valve dysfunction (97% specificity). In one patient (No. 17, Table I), however, Doppler interrogation of the LA revealed the presence of systolic turbulence despite a lack of clinical evidence supporting regurgitation This patient, whose prosthesis was implanted 97 months prior to study, had a relatively high V,, (175 cm/set). Whether this represents a true false posi-

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tive finding or whether MR was present but clinical- ly inapparent is unknown. Seven patients with apical systolic murmur had no other findings suggestive of prosthesis malfunction. In each, systolic turbulence was detected in the right, but not the LA, thus demonstrating the presence of tricuspid regurgitation. Fig. 2 depicts a normal pattern of transmitral flow in a patient with atria1 fibrillation who underwent tricuspid annuloplasty 5 years prior to study (No. 21, Table I). While the LA was free of systolic turbulent flow, interrogation of the right atrium showed significant tricuspid regurgitation.

Abnormally functioning porcine mitral valves. Eleven patients undergoing Doppler examination had PMV dysfunction (Table II). Of these, 10 patients had cardiac catheterization as part of their evaluation. These patients were younger than those with normally functioning prostheses (51 -+ 12 years vs 61 ? 10 years, p < 0.05), but did not differ with respect to size of prosthesis nor duration of implantation.

All patients in this group had 2DE as part of their evaluation. Valve leaflet structure and motion were felt to be normal in two patients. In six, leaflets were judged as abnormally thickened with reduced excursion. In six, the leaflets prolapsed beyond the plane of the sewing ring during systole.

Eight patients had stenosis of the PMV with a transprosthesis gradient of 12 to 24 (mean 17) mm Hg. Seven of eight had a P ‘/z t 3 180 msec (mean 220 f 66 msec) (Fig. 3). One patient (No. 36, Table II) had moderate MR at catheterization, with a transmitral gradient of 15 mm Hg and a Pi/z t of 150 msec. Fig. 4 illustrates prolongation of the P*/z t in a symptomatic patient with an 18 mm Hg mitral gradient. Patients with MS also had significant elevation of V,,, (mean 218 f 49 cm/see) compared to patients with normally functioning prostheses (p < 0.001).

Ten patients had evidence of MR (Fig. 5). In nine, the diagnosis was confirmed by contrast left ventric- ulography. All had at least 2+ MR. In one patient (No. 40, Table II), cardiac catheterization was not performed. Clinical findings, however, strongly sug- gested significant regurgitation, which was confirmed at autopsy by detection of a disrupted leaflet. Thus, Doppler correctly identified all 10 patients with MR. In patients with MR, V,,, was 206 * 53 cmhec, significantly higher than the mean observed in normally functioning prostheses (136 2 24 cm/ set, p < 0.001).

Two-dimensional echocardiography. Among 26 patients with normally functioning prostheses who underwent 2DE examination, 25 were without evidence of dysfunction. One patient (No. 3, Table I),

301

‘; s E

100

.

i

. . . . . . .

. . . . . .

. . . . . . . .

..-

. . “..

. .

300

200

00

NORMAL and PURELY

REGURGITANT PMV

(n=36]

STENOTIC PMV

(n=8)

*p<o. 001

Fig. 3. P’/z t in patients with normal or purely regurgitant PMV (left) vs stenotic PMV (right).

had abnormally thickened leaflets. In 11 patients with prosthesis dysfunction, 2DE failed to detect any abnormality in two. Thus, 2DE had an overall sensitivity of 82%, a specificity of 96%) and a predictive value of 90 % , for detection of prosthesis dysfunction. Abnormal 2DE findings, however, pro- vided limited information regarding the specific type of abnormality. Whereas a prolapsed leaflet was specific for the presence of MR, sensitivity was only 60%. Abnormally thickened leaflets were noted in five of eight patients with MS and in 5 of 10 with MR.

DISCUSSION

We report here our experience using Doppler echocardiography in patients with porcine prostheses in the mitral position. Three parameters of transmitral flow were employed to establish guidelines for identifying normal and abnormal function.

Maximum left ventricular inflow velocity. V,,, is dependent on orifice size and volumetric flow. In our series, mean V,, in patients with normal prostheses was slightly higher than has been reported in those with normal native va1ves.l’ This is not surprising, and most likely reflects the reduced effective orifice



Fig. 4. PMV flow pattern in a patient (No. 39, Table II) with a transprosthesis gradient of 18 mm Hg. Maximum left ventricular inflow velocity was 290 cm/set and Pli? t was 240 msec. Paper speed was 100 mm/set.

4 Chamber

Fig. 5. The presence of MR can be detected from both the parasternal long-axis (left) and apical four-chamber (right) views. High-velocity, turbulent flow is recorded in the left atrium (LA) during systole (SYS)

of most porcine mitral vB1ves.l An increased V,, isolated lesion. Poor left ventricular function can (2180 cm/set) was often found in patients with offset this increase and result in a reduced V,,,. In stenotic or regurgitant valves, but was neither sensi- one patient (No. 32, Table II) with severe MR and a tive nor specific for either lesion. V,,, is increased in 12 mm Hg transmitral gradient, V,,, was only 160 patients with MS because of the restriction to flow cm/set. This apparent discrepancy may be ex- across the prosthesis and in patients with MR plained partly by relatively poor left ventricular because of high flow. In patients with combined MS compliance, resulting in reduction of the rate of left and MR, V,,,,, was elevated more than in either ventricular filling. This patient had a cardiac index

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of 2.0 L/min/m” and a left ventricular end-diastolic pressure of 20 mm Hg.

Pressure half-time. P%t has been correlated with the severity of MS, and can be readily obtained from Doppler recordings. It has the advantage of being relatively flow-independent. In normal subjects, P ‘/z t is usually less than 60 msec and, in the setting of native MS, ranges from 100 to 400 msec.16z lg P l/z t has been correlated with mitral valve area derived from cardiac catheterization data.16v20 Among patients with normally functioning prostheses, P ‘/z t was longer than in normal native valves. We feel this increase in P% t reflects the reduced effective orifice size and small gradient which is commonly found across the PMV. In contrast, Weinstein et a1.21 found no difference in P ‘/z t between normally functioning St. Jude Medical mitral prostheses and native valves in healthy subjects. 21 As they speculated, this may reflect a lack of sensitivity of P% t to quantitate relatively insignificant gradients across large ori- fices. Instead, this disparity may point out a hemodynamic difference between tissue valves and cen- tral flow mechanical prostheses. In our study, P% t was prolonged in patients with MS, but not with MR, confirming that the parameter behaves relatively independently of flow volume.

P% t did not correlate significantly with the size of the PMV. There are several potential reasons for this finding. P ‘/z t is affected by the presence of MS and potentially by the duration of implantation. In addition, left ventricular compliance might further affect the transmitral flow rate. Thus a small influ- ence on PI/z t by prosthesis size could be effectively masked by other variables. Finally, despite the fact that overall range of prosthesis size was considerable (25 to 35 mm), 25 of 28 prostheses fell within the narrow range of 31 to 35 mm. This would likely prevent the determination of a statistically significant correlation.

Mitral regurgitation. The third parameter of prosthesis function addressed in this study was the presence or absence of LA systolic turbulence indic- ative of MR. Doppler echocardiography is a sensitive technique for detecting MR, particularly when it is due to rheumatic heart disease.22 In our series, Doppler echocardiography correctly identified all 10 patients with MR. The sensitivity and specificity for detecting MR was 100% and 97 % , respectively. In one patient, presumably without MR, systolic turbulence was detected in the LA by Doppler echocardiography. Four patients with MR also dem- onstrated tricuspid regurgitation on Doppler echocardiographic examination, as did 13 patients with normally functioning prostheses. Thus, Doppler

echocardiography was helpful, not only in detecting MR but also in distinguishing mitral from tricuspid regurgitation. This is particularly important in situ- ations where auscultatory findings may be ambigu- ous.23, 24

2DE has proven utility in the noninvasive study of patients with bioprosthetic valves. The information gained is largely anatomic and includes an assessment of sewing ring stability, leaflet structure and mobility, and left ventricular function. Previous studies have shown that 2DE is useful in document- ing normal function.6 Despite the observation that certain echocardiographic findings are specific for dysfunction, overall sensitivity is lacking.25s 26 This may be due in part to the relatively subjective nature by which leaflet thickness and excursion are estimated. Our findings are in support of these results. Doppler and 2DE, which are ideally performed as parts of a comprehensive examination, provide complementary sets of data, one hemodynamic and the other anatomic. When used in conjunction, they should increase the yield of ultrasound in the diagnosis of bioprosthesis dysfunction.

In summary, Doppler echocardiography offers potential for the evaluation of patients with PMV. Criteria for establishing normal function are presented as well as guidelines for defining and quantitating severity of dysfunction. Doppler echocardiography is a sensitive and specific means of identifying both stenotic and regurgitant prostheses. It is useful, when physical findings may be confus- ing, in differentiating murmurs due to prosthesis malfunction from those originating elsewhere. Final- ly, because it offers sensitive and quantitative assessment of flow, Doppler echocardiography may be helpful in the serial evaluation of patients.

The authors wish to thank MS Nancy Naan for secretarial support, Naomi Fineberg, Ph.D, for providing valuable assistance with the statistics, and Bruce Wailer, M.D., for interpretation of autopsy findings.

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doppler echocardiographic evaluation of patients with porcine mitral valves

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