An-Echocardiographic-Study of Net Atrioventricular Compliance in Juvenile and Adult Mitral Stenosis

N Sudhayakumar, G Rajesh, N Anilkumar, S Abdul Khader, 
Cicy Bastian, VL Jayaprakash, K Jayaprakash

Department of Cardiology, Medical College, Kottayam

Background: Left atrial compliance is an important determinant of symptoms in mitral stenosis. About onethird of patients with mitral stenosis have reduced left ventricular compliance. We measured the net atrioventricular compliance in rheumatic mitral stenosis patients noninvasively and analyzed if there were any clinical, electrocardiographic, roentgenographic or echocardiographic correlates of net atrioventricular compliance.

Methods and Results: Seventy-six patients with mitral stenosis were analyzed and as many normal subjects taken as control group. Patients were divided into two groups—those 20 years and below were grouped as juvenile mitral stenosis and those above 20 years as adult mitral stenosis patients. The net atrioventricular compliance in patients with mitral stenosis was significantly impaired compared to normal population. Mean compliance in juvenile group was 4.66±2.18 ml/mmHg (range 2.17-9.6) and in adult group it was 4.79±1.99 ml/mmHg (range 2.04-8.9) (p = ns). There was no difference in net atrioventricular compliance between the juvenile and adult patients with mitral stenosis. Mitral valve area showed an independent positive correlation with net atrioventricular compliance. 

Conclusions: The net atrioventricular compliance was significantly reduced in patients with rheumatic mitral stenosis; however, there was essentially no difference in the net atrioventricular compliance between the juvenile and adult patients with mitral stenosis. The net atrioventricular compliance may not be responsible for the more severe symptoms observed in juvenile mitral stenosis. (Indian Heart J 2004; 56: 32–36)

Key Words: Echocardiography, Atrioventricular compliance, Mitral stenosis

At any given severity of mitral stenosis (MS), levels of cardiac output and pulmonary vascular resistance (PVR) set the clinical picture. Left atrial (LA) compliance is one of the important determinants of PVR. Pressure decay across the mitral valve depends on mitral valve area (MVA), net atrioventricular (AV) compliance (Cn) and transmitral gradient (TMG).1–3 Net AV compliance implies compliance characteristics of both the chambers, atrium and ventricle, as a single unit. When the compliance of either of these chambers is normal, any abnormality of Cn reflects abnormal compliance of the other chamber. In a case of pure MS we expect the left ventricular (LV) compliance to be normal. Therefore, an abnormal Cn reflects abnormality in atrial compliance. Usually the LV diastolic pressure is normal in patients with isolated MS. About one-third of patients with MS have reduced LV compliance. Conditions like coexisting mitral regurgitation(MR), aortic valve disease, ischemic heart disease and systemic hypertension may elevate LV diastolic pressure. 

Methods

The net AV compliance can be assessed noninvasively.Flachskampf et al.4 in 1992 derived the echo Doppler formula for calculating the net AV compliance. The net AV compliance can also be calculated by invasive hemodynamic methods. Both the methods have been compared in a subsequent study by Schwammenthal et al.5 who found that there was no difference in the calculated compliance using either method.  

Rheumatic heart disease patients with pure mitral stenosis were included in the study. Based on the age, patients were grouped as juvenile MS (< 20 years) and adult MS (>20 years). Patients were included irrespective of the duration of the disease. Those with LV hypertrophy, hypertension, coronary artery disease, Lutembacher syndrome, other valvular heart diseases, atrial fibrillation, pericardial disease and patients with isovolumic relaxation time (IVRT) of the left ventricle more than 100 ms were excluded from the study. Age- and sex-matched normal individuals were taken as controls. All patients were clinically evaluated. Chest X-ray and a 12-lead electrocardiogram were obtained for each patient.  

A complete standard echocardiographic examination was performed using the GE RT 6800 color Doppler echocardiography machine. The examination was performed under basal condition in quiet surroundings. Left atrial area in apical four-chamber view, mean and peak gradients across mitral valve, LV systolic function parameters, dv/dt of mitral valve Doppler-E downslope, and tricuspid regurgitation (TR) jet velocity were measured, in addition to other routine data. Pulmonary artery systolic pressure (PASP) was calculated from the TR jet gradient. Since the patients included in the study did not have any mitral or aortic regurgitation, the continuity equation was used to calculate the MVA. In order to determine the MVA by continuity equation the left ventricular outflow tract (LVOT) diameter (D) from a zoomed systolic freeze frame in parasternal long axis view and mitral and aortic time velocity integral (TVI) were measured. MVA was then calculated as follows:

Using the above information Cn was calculated by the Flachskampf et al.4 formula (see Appendix).  

Isovolumic relaxation time (IVRT) and ejection fraction (EF) were measured to assess LV function. An IVRT exceeding 100 ms and EF <50% were considered abnormal.

Statistical analysis: Statistical analysis was done using the ANOVA method. In situations where ANOVA could not be applied, KRUSKAL-WALLIS H method was applied. Multiple regression analysis was also performed to determine the independent correlation of certain variables with AV compliance.

Results

Baseline data: A total of 118 patients with rheumatic MS were examined. Patients with atrial fibrillation (36), systemic hypertension (4), Lutembacher syndrome (1) and coronary artery disease (1) were excluded. Of the remaining 76 patients studied, 20 belonged to the juvenile MS group and 56 to the adult group. Seventy-six age- and sex-matched normal individuals were taken as the control group. Baseline data of the patients is shown in Table 1. Mean age of the control was 33.3±12.03 years; in the juvenile group it was 16.4±2.5 years and in the adult group, 42.64±10.5 years. On chest X-ray, 35% of the juvenile and 59% of the adult patients had LA enlargement. The electrocardiogram showed right ventricular hypertrophy in 65% and 45% of juvenile and adult patients, respectively. The mean MVA of the study population was 1.06±0.38 cm2. The mean LA area was 24.71±7.8 cm2 in the study group as a whole; in adult MS it was 26.36±12.6 cm2 and in juvenile MS it was 20.34±5.96 cm2 (p = 0.04). Mean mitral gradient (MG) was significantly more in juvenile MS (14.23±7.33 mmHg) compared to the adult MS group (10.89±4.33 mmHg) (p = 0.016). MG in the study group as a whole was 11.75±5.44 mmHg. Peak gradient (PG) was similar in both groups:20.96±8.46 mmHg in juvenile v. 20.1±6.65 mmHg in adult MS. PG in the study group as a whole was 20.34±7.13 mmHg. PA systolic pressure was significantly greater in juvenile MS (68±14.9 mmHg) compared to adult MS (57.4±16.5 mmHg) (p = 0.03) (Table 1).

According to MVA, mitral stenosis patients were divided into mild (>1.5 cm2), moderate (1-1.5 cm2) and severe (<1 cm2) group. Fifty percent of the juvenile and 51.8% of the adult patients had severe MS; 30% of juvenile and 35.7% of adult patients had moderate MS. Mild MS was seen in 20% of juvenile and 12.5% of adult patients. Most of the juvenile (75%) and adult (68%) patients were symptomatic. The juvenile patients had greater symptoms—75% were in functional class II-IV of which 25% were in class III-IV, compared to 68% and 21% of adult patients, respectively. However, this difference did not reach statistical significance. 

Net AV compliance: Compliance was divided into three groups —low, moderate and good as shown in Table 2. Forty percent of the Juveniles and 39.3% of adults belonged to the low compliance category; 50% of juveniles and 44.7% of adults belonged to moderate compliance category. Good compliance category accounted for 10% of juvenile MS and 16% of adult MS patients. Majority of the patients belonged to low or moderate compliance categories. The mean compliance in the control group was 12.77±4.11 ml/ mmHg (range 10.2–21.4). The mean compliance in the juvenile group was 4.66±2.18 ml/mmHg (range 2.17–9.6) and in the adult group, 4.79±1.99 ml/mmHg (range 2.04– 8.9). There was no difference in the compliance between juvenile MS and adult MS patients (p = ns).

Correlates of compliance: Patients with a highly compliant LA were less symptomatic. Only 5% of juvenile and less than 2% of adult patients in the good compliance group had class II-IV symptoms; 70% of the juvenile and 68% of adult patients in low and moderate compliance group had class II-IV symptoms as shown in Table 3. As the compliance decreased, the symptoms worsened. In the juvenile patients, left atrial area (LAA) was 23.7 cm2, 18.3 cm2 and 17 cm2 in the low, moderate and good compliance groups respectively. In the adult patients, the corresponding values were 32.1 cm2, 25.1 cm2 and 23.2 cm2 respectively. In both adult and juvenile patients compliance decreased as the LAA increased. MVA was 0.72 cm2, 1.26 cm2 and 1.27 cm2 in juvenile patients in the low, moderate and good compliance groups, respectively. Corresponding values in the adult patients were 0.8 cm2, 1.15 cm2 and 1.5 cm2 respectively. Fig. 1 shows the relationship between the MVA and compliance. A decrease in the MVA was associated with a decrease in the compliance.

The mean PASP in the juvenile MS patients was 77.25 mmHg, 58.75 mmHg and 25 mmHg among the low, moderate and good compliance groups, respectively. The corresponding values in the adults were 64.1 mmHg, 53.88 mmHg and 26.5 mmHg, respectively. The mean TMG in juvenile MS patients was 19.3 mmHg, 11.3 mmHg and 8.1 mmHg in the low, moderate and good compliance groups respectively. In the adults the respective values were 13.7 mmHg, 11.9 mmHg and 6.9 mmHg. This data suggests that as the LA compliance decreased there was an increase in the mitral gradient and pulmonary artery systolic pressure i.e. PASP and MG showed an inverse relation with compliance, in adults as well as in juvenile patients (Table 4 and Fig. 2). Multiple regression analysis revealed that only MVA had a significant independent positive correlation with compliance (Table 5). 

Discussion

In some patients with MS, while estimating MVA by pressure half-time method, there was at times a mismatch between the MVA obtained and the gradient measured – a large MVA was found to be inappropriately associated with a high TMG.6–8 Impaired LA compliance could be responsible for a steep mitral E downslope, thereby overestimating the MVA. The MVA of these patients should be measured by other methods like planimetry or continuity equation.9,10 Atrial compliance is known to be rapidly changing during the initial days after a procedure (balloon or surgical valvotomy) on the mitral valve.11 It would be interesting to note the changes in compliance during this period (24–72 hrs after a procedure on the MV). During this period the MVA estimated by the pressure half-time is found to be inaccurate because of the change in compliance, as this is one of the determinants of pressure decay across the mitral valve.1,5 Pre- and postoperative measurement of net AV compliance would be worthwhile in the follow-up of these patients.12,13 A poorly compliant LA tolerates MR badly. Patients with a poor LA compliance can be identified who may have a stormy postoperative period if they develop MR during the procedure.  

Juvenile MS patients are known to have a more severe disease symptomatically, hemodynamically and pathologically. It has been postulated that impaired LA compliance or adverse response of the pulmonary vasculature may be responsible for this. In the present study it has been shown that the compliance was significantly impaired in MS patients compared to controls. It was also noted that the juvenile patients had more severe symptoms and smaller MVA compared to adults. Among the MS patients compliance was similar in juvenile and adult patients. Therefore, difference in LA compliance as the sole mechanism was not responsible for the more severe symptoms in juvenile MS patients.

We expect patients with a lower LA compliance to be more symptomatic. Analyzing the symptoms in various compliance groups, it was apparent that the both juvenile and adult patients with low and moderate compliance were more symptomatic. Majority of the patients with good compliance were in class I compared to patients with low and moderate compliance, who were in class II-IV. Comparing the MVA and compliance it was found that any change in MVA was directly reflected in the compliance. When the MVA decreased, the compliance decreased. This effect was seen in both juvenile and adult patients. The relation between PASP and compliance was inverse. As the net AV compliance decreased, the PASP increased. Similarly the mean gradient was also found to be inversely related to net AV compliance. As the compliance decreased the gradient increased. Multiple regression analysis showed that only MVA had an independent positive correlation with net AV compliance. However, it is possible that there may be other determinants of LA compliance like physical properties of atrial myocardium and restraining effect of surrounding structures. However, the present study was not designed to address these issues.

Limitations of the study: The relative small size of the study group (especially the juvenile group) was a definite limitation. Another limitation was that the duration of the disease was not taken into consideration. Therefore the effect of duration of the disease on compliance could not be looked into.

Conclusions: The net AV compliance in patients with MS was significantly impaired compared to the normal population. Symptoms, PASP, LAA and mean TMG were inversely related to the compliance. Mitral valve area had an independent positive correlation with compliance. Between the two groups—juvenile and adult MS patients, there was essentially no difference in the net AV compliance. Our data suggests that a difference in net AV compliance may not be responsible for the more severe symptoms and more severe pulmonary artery hypertension observed in juvenile MS patients compared to adults. In mitral stenosis net atrioventricular compliance is dependent only on the mitral valve area and does not differ in the juvenile and adult patients.

Appendix

According of Flachskampf et al4 the net AV compliance can be calculated as follows.

The equation is derived as follows:  

The atrium and ventricle can be regarded as 2 capacitors in series  

Cn = (1/Ca + 1/Cv)-1  

Net compliance is also the change in volume shift between atrium and ventricle during diastole divided by the change in transmitral pressure difference.  

Cn = dv/dDp 

With respect to time this would be  

Cn = (dv/dt)/(dDp/dt)  

dv/dt is flow rate (Q), through the mitral valve i.e., effective mitral valve area × mitral velocity (v). For restrictive orifices Bernoulli equation applies, dDp/dt can be substituted by rv (dv/dt)  

Cn = (dv/dt)/(dDp/dt)  

= Q/(dDp/dt) = (MVA × v)/rv(dv/dt) = MVA/r (dv/dt)  

where Cn is measured in cm3/(dynes/cm2), r is density of blood (1.05 g/cm3) and dv/dt in cm/s2 is the deceleration of mitral E-wave downslope. To express Cn in cm3/mmHg the right side of the equation is multiplied by 1333 (dynes/ cm2)/mmHg, and incorporating r yields the simple equation:  

Cn = 1270 (MVA/E-wave downslope).

Correspondence:
Dr N Sudhayakumar, 
Professor and Head of Cardiology, 
Medical College, Gandhinagar, 
Kottayam 686008.
e-mail : ktm_sudhay@sancharnet.in

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