Significant mitral valve disease leads to LA structural remodeling due to left atrial dilatation, myocyte necrosis, interstitial fibrosis, and disorganization of atrial muscle bundles. This LA remodeling causes progressive impairment of left atrium mechanical function.13,14
Conventional Echocardiographic parameters for atrial function assessment is being done by atrial volume assessment which is load and operator dependent and does not accurately evaluate atrial reservoir function. Two-dimensional transthoracic speckle tracking echocardiography (2D STE) allows the assessment of global left atrium mechanic with the advantage that it is a load-independent parameter which depicts myocardial function.15,16,17 As of now, strain related algorithms are not validated for the evaluation of left atrial function. Left atrial strain calculation is currently done utilizing the strain software for left ventricle with adjustments to the width of the “region of interest”.
Left atrial function has three phases namely- Reservoir function, Conduit function and Booster pump function. Reservoir phase is characterized by Filling and stretching of the left atrium which causes positive atrial strain reaching its peak in systole. In the next phase, Conduit function is characterized by passive left atrial emptying with the opening of the mitral valve resulting in decreased atrial strain up to a plateau period. A second positive deflection in the strain curve is then observed corresponding to atrial Systole, that is the Booster pump function. Two positive strain values are generally measured for LA strain assessment, namely Peak atrial longitudinal strain (PALS) being measured at the end of the reservoir phase and Peak atrial contraction strain (PACS) being measured following the P wave and represents active atrial contraction.18
Many studies have been conducted for assessing the impact of balloon mitral valvotomy on atrial volumes, atrial pumping function, and atrial reservoir functions.19,20,21. However there are very few studies for assessing the effect of valvotomy on global left atrial strain. In one of such studies, Rohani et al. studied the acute effect of balloon mitral valvotomy and mitral valve replacement in patients with mitral stenosis and found that the peak atrial longitudinal strain (PALS) was impaired in patients with severe symptomatic mitral stenosis and improved acutely after treatment with a Pre BMV PALS of 5.1 ± 11.6 and immediate Post BMV of 6.5 ± 17.7 (P < 0.0001). A similar result was also demonstrated by Sravan K Reddy et al (2019).1,22
There is a significant change in LA area post BMV in our study which is consistent with Vijay et al Pre BMV LA area of 3713.00 ± 847.15 mm2 and immediate Post BMV of 3232.83 ± 806.72 (P 0.004) and LA area at 1 month of BMV was 2955.03 ± 550.55 mm2 (p = 0.0001).23 Whereas Rohani et al demonstrated an insignificant change in LA area in BMV intervention with Pre BMV LA area of 6.5 ± 31.7 cm2 and immediate Post BMV of 6.6 ± 31.5 (0.401).22 We found that a successful BMV procedure associated with a decreased Transmitral gradient and increase in MVA and this was correlated with a decrease in LA pressure (mean PCWP). This is in concordance with the result of Bitigen A et al.19
A successful BMV procedure is characterized by battery of Hemodynamic changes i.e decrease in left atrium afterload which is reflected by an increase in mitral valve area, decrease in diastolic transmitral gradients, and decrease in systolic pulmonary artery pressure. In our study, there was also a significant reduction in the left atrial strain post-balloon mitral valvotomy which also persisted till 3 months of follow up. Improvement of MVA or decrease of PAP is a good indicator of successful BMV, and improvement of PALS could be a new confirmatory tool.
Right ventricular systolic function in patients with mitral stenosis-
Our study showed that the RV systolic function is impaired in patients with severe MS as assessed by both global and segmental RV longitudinal strain. It goes in concordance with earlier hemodynamic and clinical studies, which showed impaired RV function in MS patients24. The increased RV afterload in severe MS patients are attributed to chronic pulmonary venous congestion, which ultimately leads to PH with a resultant either incipient or overt RV systolic dysfunction. There is also a second school of thought to this RV systolic dysfunction, i.e the direct rheumatic involvement of the RV with resultant myocyte necrosis, replacement fibrosis and calcification is the explanation of such depressed RV systolic function.25 Quantitative assessment of RV function is not an easy task owing to the complex RV anatomy. Hence RV dysfunction is usually overlooked before the emergence of clinical signs of systemic venous congestion.26 Research is at its healm for an optimal tool for RV function assessment, with the latest in this is 2D strain, which has been developed for the quantitative assessment of global and segmental myocardial function.27 The major studies reflecting the effect of BMV intervention on RV strain is by Kumar et al.28 (2014) and Ozdemir et al29 (2010). Both of these studies had demonstrated a reduced RV GLS in patients with MS. There was difference in regional RV longitudinal strain, as seen in significant decrease in the RV strain values of the septal segments. This is in agreement with the data obtained by Ozdemir et al29. and Kumar et al.28 This disproportionate decrease in septal RV strain is attributed to two factors, 1st for extensive rheumatic endocarditis and scarring extend from the mitral annulus to the surrounding LV segments in severe MS, thus reflecting changes that actually affect LV septum with indirect affection to the RV side28. The second assumption for this regional difference in strain values was presented by Kumar et al.28 who demonstrated that the septum is affected by even with moderate degrees of pulmonary hypertension and RV free wall gets affected by severe degrees of pulmonary hypertension.
In our study, Immediately after BMV, there was significant improvement of the RV GLS compared with the RV GLS before BMV (post three months − 17.33 ± 6.6 vs. post 24 hrs − 13.83 ± 6.6 vs. baseline − 10.09 ± 5.7, P = 0.0001). Kumar et al28 also demonstrated significant improvement in RV GLS after BMV compared with the baseline measurements before BMV (− 11.24 ± 4.24 vs. −9.07 ± 4.7, P = 0.02). This improvement could be attributed secondary to the relief of LV inflow obstruction, leading to improvement in the RV afterload. Also we do presume that this improvement is directly related to a significant reduction in both RV volumes as well as RV systolic pressure post‑BMV.
Thus the present study demonstrated that both LA and RV functions assessed by 2D echocardiography and Speckle Tracking Echocardiography are impaired in patient with severe MS. There is improvement in these indices after successful BMV with further improvement after 3 months. The major contributing factors attributable are the cascade of hemodynamic changes that incur post BMV are increase in mitral valve area, reduction in Left Atrial (LA) area, fall in LA pressure with reduction in peak and mean mitral valve gradient as well as fall in PASP and degree of TR. It is yet to ascertain whether the left atrial strain further reduces during mid- and long-term follow-up and also if this correlates with the reduction in atrial fibrillation and thrombus formation.
Limitation
This study was done in a relatively small group of patients with a single centre experience and thus need to be confirmed in larger population. The smaller sample size is primarily attributable to Covid19 pandemic. Due to lack of long‑term follow‑up, we cannot judge about the prognostic effect of Speckle tracking Echocardiography. There is no information about the LA active emptying fraction for patients with MS before and after therapeutic intervention, only PALS was taken into consideration in the present study. Also, there is no control arm taken for the present study.