December 1997, Volume 47, Issue 12

Original Article

Assessment of Minimal Mitral Regurgitation: Comparative Study with Doppler Echocardiography and Ventriculography

Hasan Fehmi  ( Department of Cardiology, Gulhane Military Medical Academy, Ankara, Turkey. )
Cemal Sag  ( Department of Cardiology, Gulhane Military Medical Academy, Ankara, Turkey. )
Ata Kirilmaz  ( Department of Cardiology, Gulhane Military Medical Academy, Ankara, Turkey. )
Tuncay Altun  ( Department of Cardiology, Gulhane Military Medical Academy, Ankara, Turkey. )
Deniz Demirkan  ( Department of Cardiology, Gulhane Military Medical Academy, Ankara, Turkey. )

Abstract

This study was designed to assess color Doppler echocardiographic parameters in subjects with minimal mitral regurgitation (MR) in an otherwise normal heart. Study cases were selected during a five month period from 2500 young males with an echocardiographic indication on the basis of subjects’ complaints and physical examination. Left ventriculography was per-fomred and subjects were dichotomized into group-1 (n=30) if there was angiographically MR and into group -2 (11:30) if they were intact. Patients in group-1 were described as to have ‘true MR’ and MR flow in group-2 was named ‘physiological’. Doppler echocandiographic variablm of true and physiological MR are compared to each other. The following echocardiographic variables were significantly different between group-1 and group-2: 1) the ratio of the max. duration of MR/mean systolic interval in parastemal long axis (0.710:0.244 vs 0.430:_0.268, respec- tively, p<0.001), 2) the ratio of the maximum duration of MR/mean systolic interval in apical four  hamber view (0.550_t0.361 vs 031710.272 respectively, p=0.007), 3) thepeak velocity of the regurgitant flow in parastemal log axis (180177 vs 120169, respectively, p=0.003), 4) the regurgitant jet area in parastemal long axis (0.813¢0.651 vs 0.411i0.431, respectively, p=0.007). The maximal duration of MR/mean systolic time interval _>_0.6, regurgitant jet area 20.4 cm2, and regurgitant peak velocity 3130 cm/sec. in parasternal long axis dichotomize the cases into true with a predictive value of 76%, 67% and 63%, respectively (JPMA 47: 92, 1997).

Subjects and Methods

The subjects were selected during a five-month period among 2500 young male admittants, who were recniited for the army. All subjects with minimal MR and otherwise, structurally nomral heart by Doppler echocardiographic evaluation and who signed the informed consent underwent cardiac catheterization and left ventriculography for confirmation of MR. Echocardiography was indicated on the basis of subjects’ complaints and upon physical examination. Subjects with poor acoustic window, multiple premature ventricular contractions and/or catlreter—induced MR at the time of ventriculography making the quantification of MR impossible and with concomitant valvular heart disease were excluded from the study. Patients with any systemic disease including hypertension and mitral valve prolapse fulfilling Perloff’s criteria6 or with systolic displacement into the left atrium in the parasternal views were also excluded, Thus, the study consisted of 60 subjects; Group-1 comprised 30 patients who had angiographically confirmed MR and represented the patients with hemodynamically important and true MR. There was no evidence of MR by ventriculography in the remaining 30 patients. All subjects were men, ranging in age from 19 to 34 years (mean 221-2.5).

Introduction

Many investigators have argued that Doppler is too sensitive in nritral regurgitation (MR), frequently detecting small amounts of insufficiency, in otherwise normal hearts.  Reported prevalence of MR in normal subjects varies considerably1-5. Differences in Doppler techniques, definitions of regurgitation, age and racial body habitus may partly explain this discrepancy. The hemodynamic significance, if any, of this minimal or trace mitral regurgitation remains uncertain. To what extent the Doppler examination of this How patterns reflect the ‘true rnitral regurgitation’ is also an unknown issue. To assess hemodynarrric uncertainty and the role of Doppler echocardiography in the evaluation of minimal MR, we performed left ventriculography in subjects found to have minimal MR by Doppler echocardiography.

Echocardiography

Doppler examinations were performed with commercially available system, Hewlett Packard Sonos 2500 equipped with 2.5 MHz transducer. All echocardio graphic measurements were perforrnedinasingle session. The median interval between angiography and Dopplerexanrination was 3 days (range 0 to 8 days).
Color Doppler Echocardiography
Color image mode was set in velocity mode. Flow direction towards and away from the transducer was coded red and blue, respectively. Maximum velocity of colorbar display was adjusted until good qualitative color images were obtained. Doppler color gain was first turned down completely and then increased very gradually until the static background noise barely appeared. The size of the color sampling and black and white display were reduced as much as possible to enhance the frame rate and thus the color image quality. The wall filter was set to 400 Hz. Parastemal long axis and apical four- chamber views were used to trace the jet of MR. Jet area >2.l cm2 was considered exclusion criteria arbitrarily.
Pulsed and continuous Doppler study:
Systolic time was measured as the interval between the closing and the opening of the mitral leaflets. Duration of regurgitant flow was calculated just above the level of 90 crn/second. Measurements were repeated atleast three times in both views and the mean and the maximal value of the duration of regurgitant flow were used in the analysis. To minimize the effect of differentRR intervals, the mean systolic time interval was used as a denominator and the ratio of the mean duration of MR/mean systolic time interval (mean lvIRd/MSTI) and the ratio of the maximal duration of MR/mean systolic time interval (max. MRd/MSTI) were used as variables in both views. Mitral valve regurgitation was defined as minimal or mild when regurgitant spectral signals were confined to just below the mitral valve or inthe proximal one-fourth of the left atrial chamber. Cases exceeding this grade were not included in this study. In addition to pulsed Doppler operation, examination by continuous-wave Doppler technique and a non-irnaging transducer were used where blood flow velocities exceeded the Nyquist limit of the pulsed Doppler system. Maximum velocity of the regurgitant flow in both views was another variable.
Cardiac catheterization and left ventriculography:
Left sided heart catheterization was perfonned by the femoral approach with maximal 40 ml of iohexol (Omnipaque 350 mg/ml) injected at a rate of 15 rnl/sec. adjusted to the weight and intraventriculardiameters both ina 30—degree right anterior oblique (RAO) and a 45 to 60 degree left anterior oblique (LAQ) view. Pressures were obtained with a micromanometer-tipped catheter and recorded to determine pressure difference after ventriculography. Mitral regurgitation was graded between 1+~and 4+ as described by Grossman7.‘ Regurgitation that is 1+ essentially clears with each beat and never opacifies the entire left atrium. When regurgitation is 2+, it does not clear with one beat and does opacify the entire left atrium after several beats; however, opacification does not equal to that of the left ventricle. Two cardiologists graded the degree of mitral regurgitation independently. Decision of a third experienced cardiologist was accepted in the presence of conflict. No patient presented MR above grade 2+.

Results

This study is unique for its feature of comparing transthorasic echocardiographic minimal MR with catheterization findings. Ventriculography was performed to dichotomize the cases into true and physiologic MR groups.
Among the echocardiographic parameters compared between group-1 (n=30) and group-2 (n=30), the most significant differences were found in the followingpararneters; l) the meanMRd/MSTI and the max.MRd/MSTI in parastemal long axis view (p<0.000l and p<0.0001 , respectively);,2) the mean MRd/MSTI and the max. MRd/MSTI in apical four chamber view (p=0.027 and p=0.007, respectively); 3) regurgitant jet area in parastemal long axis (p=0.007); 4) the peak velocity of the re gurgitant flow in parastemal long axis (p=0.003) (values in number are depicted in Table 1).

One patient in group 1 and 5 cases in group 2 revealed no regurgitant flow in parastemal long axis. The patient in group 1 had a peak velocity of 154 crn/sec, but no regurgitant area in parastemal long axis. In apical four- chamber, this patient revealed relatively small jet area (0.084 cm2), but the ratio of max.MRd/MSTI was 0.938 with a peak velocity of 155 cm/sec. Two of the 5 cases with no pulsed—Doppler regurgitation in parastemal long axis in group 2 revealed only minute amount of jet area (0.087 and 0.037 cm2 in parastemal long axis, 0.223 and 0.197 cm2 in apical four-chamber) otherwise, normal pulsed and continuous Doppler evaluation. In other words, regurgitant jet areas measured were the only inclusion criteria for these cases. In the remaining 3 cases, parastemal long axis revealed jet area within range of 0.007 to 0.344 cmz. In apical four chamber view of these three cases, peak velocities were 96, 100 and 120 crn/sec.,jet areas were 0.414, 0.595 and 0.540 cm2 and max. MRd/MSTI were 0.257, 0.231 and 0.571, respectively. Apical four-chamber view revealed no pulsed or continuous Doppler spectrum in 6 patients in group 1. Four of these patients revealed jet areas between 0.125 and 0.274 cm2), while the other 2 patients revealed no regurgitant color Dopplerin apical four- chamber. Parastemal long axis view in these 6 patients was highly suggestive of true MR and the jet area was between 0.228 and 1.42 cm2 (mean 0.562 cmz), peak velocity between 125 and 232 cm/sec. (mean 158 cm/sec.) and max.MRd/MSTI between 0.421 and 0.877 (mean0.633). Pulsed and continuous Doppler in apical four- charnberview was not suggestive in 10 cases of group-2. Regurgitant jet area in this echocardiographic view was betwen 0 and 0.459 cm2 (mean 0.230_~J:0. 129 cm2). Echocardiographic variables in parastemal long axis were highly suggestive of physiologic regurgitation Jet area was 0.260,-_l:0. 167 cm2, max.MRd/MSTI 0.283_-r0. 157. The regurgitant jet area in apical four-chamber view was not significantly different between group-1 andgroup-2 (p>0.05). The regurgitant jet was not detected in 4 patients in apical four chamber and in 2 patients in parastemal long axis in group-1. According to the logistic regression analysis of the data, the max.MRd/MSTI in parastemal long axis 20.6 has a predictive value of 73% in dichotornizing the casgs into true and physiologic MR. Re gurgitant jet area 20.4 cm in parastemal long axis has a predictive value of 67% in diagnosing true MR and 63% in physiologic MR. Inparastemal long axis, regurgitant peak velocity
The regurgitant area was not indicative of the degree of MR in group- 1.

Discussion

Valvular regurgitation occurs not uncommonly in patients with structurally normal hearts referred for echocardiographic examination. Mitral regurgitation is the most common and in the majority of cases, the severity of regurgitation evaluated semiquantitatively by Doppler echocardiography is n1inimal3. Choong et al3 reported the prevalence of mitral regurgitation as 19% by Doppler examination among 867 subjects with no structural abnormality on 2D echocardiograms. In nearly all records (98%) with MR, there was only either trace or grade 1+ regurgitation As pointed out in the study by Yoshida and colleagues5. MR could be detected in 43% of individuals within third decade. Regurgitant area in healthy subjects (in group-2) in our study ranged from 0.0 to 2.1cm2, rather high in comparison with those of Yoshida. This canbe attributed to the selection of our patients, as they might present echocardiographic, electrocardiographic and/or physical variabilities. Table I shows that parasternal long axis is more sensitive than apical four chamber in detecting true MR. This can be partly attributed to more distance between probe and pulsed sample volume in apical four chamber.
Regurgitant jet area has notbeen conelated well with the angiographic severity of MR8. Area of regurgitant jet in our groups was also unconfrnnative to dichotomize the cases into one of the groups (except of parasternal long axis) or to grade the severity of MR in group-l. With Doppler echocardiography, regurgitant signals were not detected in 5 patients in group-l and 9 subjects in group-2 (six in apical four chamber and 5 in parastemal long axis), although color Doppler cchocardiography revealed regurgitant color. This may be due to very localized small jets and failure to position the sample volume in the jet as well as the time consumed. A previous study states that the total regurgitant area including‘ the surrounding swirling llow in transthoracic studies gives the best correlations with left ventrieulography in MR9. However, the central aliased core of the regurgitant j et with the mosaic pattern was traced as the regurgitant area in this study. But our cases present minimal regurgitant jet area and represent a different group, namely minimal regurgitantjet, in comparison with those of the above mentioned study. In conclusion. in parasternal long axis the max. MRd/MSTI 20.6, regurgitant jet area 20.4 cmz, regurgitant peak velocity 2130 crn/sec. dichotomize the cases into true. Otherwise physiologic MR. We think long term follow-up of these patients is essential in the evaluation of this pathology. Different eclrocardio graphic systems and perspectives should be used10.
Limitations: Excessively low gain would result in underestimation of MR because of elimination of lower velocity signals. An excessively high gain would clutter the image with static ‘noise’, making it difileult to visualize the outline of MR. Therefore, it is important to optimize the gain settings when perfomring the color Doppler examination. Small changes in transducer angulation and motion may produce marked variations in the size of the regurgitant jet. This made it mandatory forthe examiner to move and angle the transducer slightly in various directions when examining the flow patterns in each of the two standard planes. But the angle between the septal plane and Doppler line was not over 20 degrees. Dimensions and size of the regurgitant jet signals as well as peak velocity are related not only to the size of the defect in the valve but also to the pressure gradient across the valve. But velocities obtained for MR were in the range of one or two meters per second in our study. This may partly be explained by the small amount of regurgitant volume and difficulty to keep the sample volume on jet flow. Our subjects were also free of any disease which could cause increment in intraventricular pressure. Possible misleading grouping of cases because of true MR missed in left ventriculography was prevented to most extent by excluding the patients with eccentric MR jets which was the most common reason responsible for the discrepancy between Doppler techniques and ventriculography.

References

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