Assessment Of Mitral Valve Structure And Function Using Real-time Three-dimensional Transesophageal Echocardiography In Patients With Non-valvular Atrial Fibrillation

Background and objectiveAtrial fibrillation is the most common clinically significant cardiac arrhythmia. The rules of orderly atrial electrical activity lost, instead of fast disorderly fibrillation which is one of the most severe atrial electrical activity. The induction of structural remodeling by atrial fibrosis and the induction of electrical remodelling by shortening of the atrial effective refractory period and of the action potential duration may lead to the genesis of atrial fibrillation. The incidence of atrial fibrillation increases with age. Many previous studies have shown that the incidence of atrial fibrillation in the aged raised significantly. The morbidity of atrial fibrillation can reach 5% to 8% in 70-year-olds people and 10% in the people over the age 80. According to the latest figures, the rate of prevalence of atrial fibrillation is around 0.77% in 2004 in our country. Among all the atrial fibrillation cases, non-valvular atrial fibrillation(NVAF), valvular atrial fibrillation, and lone atrial fibrillation were 12.9%, 65.2%, 21.9% respectively.Due to population aging, coronary heart disease, hypertension, diabetes, hyperthyroidism,heart failure patients shows high morbidity and mortality rate with increased risk of atrial fibrillation. Atrial fibrillation is associated with high morbidity of thromboembolism, myocardial infarction, stroke, cardiac arrest which increase patient mortality. The burden of atrial fibrillation related severe complications are expected to increase in parallel with the aging of the population. Recent clinical trial reported that atrial fibrillation was an independent factor to predict mortality, so the treatment of atrial fibrillation became a major subject for clinical. The routine therapy to reduce the morbidity of atrial fibrillation is divided into controlling ventricular rate, maintaining sinus rhythm and antithrombotic. In addtion, we also need to prevent and treat the possible cause of atrial fibrillation. Pathogenesis of atrial fibrillation is complicated and causes change with times. Although there are so many methods for the treatment of atrial fibrillation, the incidence of atrial fibrillation is still increasing. Therefore, to clarify the mechanism of the pathogenesis of atrial fibrillation is important to prevent and treat atrial fibrillation. Multiple factors are contributed to the left atrium diameter(LAD) in patients with NVAF, especially the duration of atrial fibrillation. With the occurrence and development of atrial fibrillation, LAD will change. Mitral regurgitation(MR) was significantly correlated with the LAD in patients with NVAF. The increase of LAD may lead to mitral apparatus abnormal. Annulus dilation and leaflet configuration are the main reason for MR, which influence the balance of closing force and lead to incompetence of leaflet closure.Conventional M-mode echocardiography and two-dimensional transthoracic echocardiography(2D-TTE) are the most important tools for doctor to diagnosis the mitral valve disease, and thereby lay a foundation for studying anatomical structure and pathological structure. Compare with other technologies, 2D-TTE is more facility, cheap, non-invasive, no radiation damage and high reproducibility. Although color Doppler flow imaging is beneficial to evaluate the complex MR. It also has shortages they can’t display the anatomy and adjacent relationship of mitral valve. Real-time three-dimensional transthoracic echocardiography(RT-3D-TTE) have made it easier to demonstrated the geometries of non-visualized mitral valve structures through three-dimensional reconstruction and automatic measurements. But its also has some limitations such as to be easily influenced by the position of patients, obesity, the gas in thoracic cavity and other factors. With the rapid development of ultrasound and software technology, the real-time three-dimensional transoesophageal echocardiography has evolved fast. This technique is useful in diagnosising and analysising specific geometries and pathology in mitral valve disease, and can display an excellent image with a high resolution. Using the real-time three-dimensional transoesophageal echocardiography(RT-3D-TEE), the mitral valve 3D image is oriented and presented an “en face” view from the left atrium as the surgeon’s orientation. The additional application of the Qlab mitral valve quantification(MVQ) software offers a detailed mitral valve anatomic structure, providing online or offline quantitative measurements of the annulus and leaflet.There was a large number of previous studies to show that RT-3D-TEE can quantitatively analysis the parameters of mitral valve leaflets in patients with atrial fibrillation, but RT-3D-TEE analysis the parameters of mitral valve annulus in patients with atrial fibrillation were rarely reported. Hence, the aim of this study is to quantitatively evaluate the structure and function of mitral valve using RT-3D-TEE in patients with non-valvular atrial fibrillation(NVAF). We explore the mechanism of MR in patients with NVAF, which can provide a reliable basis for clinical diagnosis, treatment, efficacy and prognosis. Materials and Methods1. Study populationWe selected 54 cases of hospitalized patients, whom were given radiofrequency ablation therapies during July 2014 to February 2015 in Zhengzhou University People’s Hospital. The subjects were examined by 2D-TTE and RT-3D-TEE. According to the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation, we divided patients with atrial fibrillation into 2 groups, which included: 39 patients(20 males, 19 females) as the paroxysmal atrial fibrillation(Pa AF) group, the mean age was 56.79±9.11; 15 patients(10 males, 5 females) as the persistent atrial fibrillation(Pe AF) group, the mean age was 60.13±6.13. 20 cases(9 males, 11 females) as the sinus rhythm group, the mean age was 55.13±7.68.All patients with atrial fibrillation after admission must be diagnosed as Pa AF or Pe AF after the examination of ECG, holter monitoring. The above objects of study have been informed consent. Exclusive criteria: heart valve disease, congenital heart disease, prosthetic heart valves, esophageal varices, esophageal neoplasms, acute or chronic infective disease, etc.2. Echocardiography examinationEchocardiography was performed with the Philips i E33 ultrasound system equipped with X5-1 transducer(1-3 MHz), X7-2t transducer(2-7 MHz) and the additional application of the QLab with MVQ software. Using 2D-TTE technique to measure LAD in the parasternal left ventricular long axis view. Using color Doppler flow imaging technique to obtain three consecutive cardiac cycles of apical four-chamber view and apical two-chamber view and to measure MR. All three-dimension echocardiographic data were offline analyzed using MVQ software. To measure mitral annulus parameters: anterolateral to posteromedial diameter(DAl Pm), anterior-to-posterior diameter(DAP), height(H), three dimensional circumference(C3D), two dimensional area(A2D), nonplanarity angle(NPA); mitral valve leaflets parameters: mitral leaflets surface area in early-diastolic phase, mitral leaflets surface area in late-systole phase, mitral valve coaptation area, the index of mitral valve coaptation.3. Statistical analysisAll statistical analyses were performed using SPSS 18.0 software. Continuous data were expressed as mean ± SD. Differences in quantitative data were compared with t test. Mean comparison in three groups was conducted with single factor variance analysis, and the pairwise comparison was performed with LSD method. Pearson’s correlation was used to analyze the correlation between mitral valve parameters and LAD. The enumeration data were compared with the 2c test. Inter-observer and intra-observer variability was described using Bland-Altman statistics. The difference had statistical significance(P<0.05). Results1. Comparing of the general data in different cardiac rhythm groupsIn comparison of the general data in different cardiac rhythm groups, the sex, body mass index, hypertension, coronary heart disease, diabetes, stroke, thyroid diseases, smoking history, drinking history does not show significantly differences(P>0.05). There is significant difference in age among the three groups(P<0.05).2. Comparing of mitral valve parameters and LAD in different cardiac rhythm groupsThere were significant differences in DAl Pm, C3 D, A2 D, mitral leaflets surface area in late-systole phase, the index of mitral valve coaptation and LAD among the different cardiac rhythm groups(P<0.05). Compared with the sinus rhythm group, the parameters of DAl Pm, C3 D, A2 D, mitral leaflets surface area in late-systole phase and LAD were larger in Pa AF group(P<0.05); The DAl Pm, DAP, C3 D, A2 D, mitral leaflets surface area in late-systole phase and LAD were larger, but the index of mitral valve coaptation was smaller in the patients with Pe AF group(P<0.05). There was no significant statistical difference in mitral valve parameters and LAD between Pa AF group and Pe AF group(P>0.05).3. Comparing of mitral valve parameters and LAD in different degree of MRThe patients were divided into two groups according to the degree of MR: mild MR group(n=51) and moderate or severe MR group(n=23). Compared with mild MR group, the DAl Pm, DAP, C3 D, A2 D, NPA and LAD were larger, while the index of mitral valve coaptation was smaller in moderate or severe MR group(P<0.05). There was no significant statistical difference in mitral valve coaptation area between the two groups(P>0.05).4. Correlation between LAD and mitral valve parametersCorrelative analysis showed that there was a significant positive correlation between LAD and DAl Pm, DAP, C3 D, A2D(r=0.718, P=0.000; r=0.347, P=0.004; r=0.602, P=0.000; r=0.548, P=0.000, respectively). There was a significant negative correlation between LAD and the index of mitral valve coaptation(r=-0.319, P=0.008).5. Distribution of patients with LAD enlargment and moderate or severe MR in different cardiac rhythmThe patients with LAD enlargment in Pa AF group and Pe AF group are obviously more than in sinus rhythm group, and significant difference(P<0.05). The patients with moderate or severe MR in Pa AF group and Pe AF group are also obviously more than in sinus rhythm group, and significant difference(P<0.05).6. Distribution of patients with LAD enlargment in different degree of MRThe patients with LAD enlargment in moderate or severe MR group are obviously more than in mild MR group, and significant difference(P<0.05).7. Inter-and intra-observer variabilityInter-observer and intra-observer agreement of assessment with Bland-Altman analysis of DAl Pm, DAP, H, C3 D, A2 D, NPA, mitral valve coaptation area and the index of mitral valve coaptation with RT-3D-TEE showed small differences and fair limits of agreement. Conclusion1. The number of NVAF cases increased with the increasing of age.2. There is an interaction between NVAF and LAD. The longer of atrial fibrillation last, the larger LAD become. When the left atrial enlargement, Pa AF is readily transformed into Pe AF, which is the one of pathogenesis for the development and maintainance of NVAF.3. The duration of atrial fibrillation and LAD can change the mitral valve structural and function and lead to MR, especially in Pe AF patients.4. The abnormal of mitral annulus and mitral valve leaflets is a critical mechanism for MR in patients with NVAF. The saddle of mitral annulus become enlargement, and the index of mitral valve coaptation become small in the patients with moderate or severe MR.5. There was a significant positive correlation between LAD and DAl Pm, DAP, C3 D, A2 D, and significant negative correlation between LAD and the index of mitral valve coaptation.6. RT-3D-TEE can be used as a quantitative, reproducible method to assess the structure and function of mitral valve in patients with NVAF, which can help us to understand the mechanism of MR.