Discussion
Although some mild forms of MR can be present in healthy individuals, severe forms can result in serious problems (13). MR in a moderate to severe form is the most frequent valvular disease in the USA (1) and the second most surgery-required valvular complication in Europe (14).
MR can occur due to various causes and mechanisms. The etiologies are classified either as ischemic -a consequence of coronary disease- or otherwise non-ischemic. Mechanisms are divided into two groups: organic (primary) with an intrinsic valvular lesion which contains degenerative mitral valve disease as the most frequent mechanism of MR (60–70%) and functional (secondary) with a structurally normal but deformed mitral valve as a result of left ventricular remodeling (13). The primary mechanism is subclassified based on the leaflet movement, as a normal movement represents class I, and excessive or restricted movement is classified as class II and III, respectively (15).
After suspicion is raised about the MR through clinical presentations and physical examinations like a displaced apical impulse, systolic murmur, third heart sound, early diastolic rumble, and atrial fibrillation, clinical and paraclinical studies to investigate the MR should be pursued. Signs and symptoms of heart failure (HF) and severe MR should be looked for in the clinical assessment, although they are not specific to MR (16). TTE is usually the first paraclinical modality to assess regurgitation. Gathering data on causes, mechanisms, severity, and the impact of regurgitation must be followed (8, 13).
Chronic volume overload of the left ventricle can happen as a consequence of a neglected MR. this can lead to increased left atrial pressure, increased pulmonary venous pressure, pulmonary edema, and subsequently, right-sided HF. Severe MR is associated with a 5-year mortality of 50%. Facing outcomes of the MR, like HF, will be inevitable for the survivors, as it happens for approximately 90% of them (17). MR independently increases the burden of other cardiac conditions, as it increases the mortality in patients with severe systolic HF (18).
According to the management guidelines, surgery is introduced as the only definite treatment (19). The severity of the MR increases the necessity of the surgery, even in the presence of advanced HF or ventricular dysfunction (20). This shows the importance of precise quantification of the severity. Paraclinical imaging methods, along with criteria, are developing to achieve an optimal introduction of patients to surgery (8). Other factors, like the cause and mechanism of the MR, affect the decision for surgical correction as well (15).
Different features should be gathered through echocardiography to determine the regurgitation severity, which can be divided into four groups. To begin with, the structure of the valve, leaflets, and mechanical findings should be described. It can range from normal leaflets to severely damaged valves with lesions like large perforations or flail leaflets. The size of the left atrium and ventricle should also be measured. Secondly, a qualitative Doppler assessment of color flow jet area, flow convergence, and Continuous Wave Doppler (CWD) jet is required.
Further, semi-quantitative data like VCW, pulmonary vein flow, and mitral inflow must be gathered. Last but not least, quantitative measures are reported to clarify MR severity. These factors include the EROA, a basic measure representing the regurgitation severity, and RVol, which can help estimate the overload burden and the RF. Values of EROA and RVol are the strongest predictors of the outcome. While data from these four groups should be assessed together, some features can individually specify the lesion severity (8).
Three methods are available to calculate the quantitative measures of MR severity: The flow convergence method (PISA method), the Quantitative volumetric method, and the Quantitative pulsed Doppler method. All these methods have some common components (Rvol, RF, and EROA). RVol is determined as the blood volume which regurgitates in one beat. RF is defined as RVol divided by the stroke volume through the regurgitant valve, and the EROA is calculated as the RVol divided by the VTI of the regurgitation jet. These quantitative methods have some complexities. An expert operator is required to assess the primary measures. Because, for example, in some methods assessing the mitral annulus diameter is required, which is hard to obtain, or unless an exact radius value is prepared in the PISA method, the EROA would be largely miscalculated (8).
In cases where TTE reports suboptimal results, TEE can be helpful (8). In TEE, the proximity of the probe to the mitral valve with a higher spatial resolution can help to recognize the MR severity more accurately (3). It also can give a better perspective on the exact location of the deficit, which can facilitate further interventions and surgeries (9, 18). TEE is useful when more exact quantification of the measures is required, for instance, jet color characteristics like VCW, VCA, and PISA radius. TEE can also more accurately evaluate the pulmonary veins and potential reverse flow (18). However, TEE is a semi-invasive method that relies on geometric assumptions and is not generally available, making TTE the suitable method for preliminary and serial studies of MR (9). TEE demonstrates the color jets larger than TTE, and as it is done under sedation, because of the altered hemodynamic status and particularly decreased blood pressure, the MR severity might be underestimated (18).
Accurate evaluation and quantification of MR severity are crucial to assessing the valve status to decide on required interventions. This led to the introduction of new instruments and modalities. Three-dimensional (3D) techniques have improved the measurements, for instance, on Rvol and the ventricle diameters (21, 22). Also, new methods like multi-slice CT scan and CMR are introduced, which improve the assessments, and are growingly used to substitute the previous echocardiographic suboptimal results or as alternatives (9, 23).
In the current study, the MR severity of 93 patients was determined using conventional semi-quantitative (VCW) and quantitative (RVOl, RF, EROA) measures. Due to technical difficulties in obtaining these quantitative measures, along with the non-feasibility of TEE as a routine option for further investigations (as a result of limited availability, aggressiveness, and dependence on sedation), we made an effort to identify new parameters which are easier to obtain by TTE and do not rely on operators’ expertise. This study introduces new hemodynamic burden indices (MVVTI/LVOTVTI; MVAVTI-i; MVAVTI/LVOTDVTI; E velocity-LA area-i) for this purpose and examines their correlation and diagnostic value to express the severity of the MR. These indices show an excellent diagnostic value in recognizing patients with severe MR. While there are uncertainties about the effect of normalization of the conventional measures on BSA on its diagnostic value (8), we used two indices (MVAVTI-i; MVAVTI/LVOTDVTI) which BSA is contained in them.
To our notice, this is the first time that these indices have been used in this manner. Consequently, similar data was not available for further comparison of the results. Similar studies with larger sample sizes should be conducted to further validate these indices and introduce them to the diagnostic criteria.