Clinical Study On Strain/Strain Rate Imaging For Functional Quantification Of The Left Atrium In Patients With Metabolic Syndrome

Background:The left atrium serves as a distensible reservoir for blood stored during left ventricular systole,a conduit for pulmonary venous flow during early left ventricular diastole,and as a booster pump augmenting left ventricular filling during late diastole.Through the three functions left atrium modulates left ventricular filling and cardiovascular performance.Therefore,it is of great interest to investigat left atrial structure and function.Strain/Strain rate imaging(SRI)enables quantitative measurement of left ventricular(LV)function independent of cardiac translation and tethering effect.However,whether SRI is applicable for detection of left atrial(LA) dysfunction remains unknown.As is known,strain and strain rate represent the magnitude and rate,respectively,of myocardial deformation.Thus,during ventricular systole and lateventricular diastole,atrial strain and strain rates reflect load-independent atrialdistensibility(compliance)and atrial contractile function, respectively.And it has been used to evaluate the atrial function in patients with paroxysmal atrial fibrillation,hypertension,atrial septal defect or cardiac amyloidosis.Large population-based studies have proved that metabolic syndrome(MS),a group of atherogenic risk factors including obesity,hypertension,insulin resistance and dyslipidemia,increases the risk of cardiovascular diseases and all-cause mortality. MS has been reported to be associated with left ventricular hypertrophy,LV diastolic dysfunction and left atrial enlargement in recent reports conducted in hypertensive patients and in general population.MS can increase the incidence of paroxysmal atrial fibrillation and atrial flutter in patients without structural heart diseases. Therefore,of great significance is to investigate the alteration of left atrial structure and function in patients with MS.Objective:The aims of our study were to:(1)explore the impact of metabolic syndrome on left atrial function;(2)detect the main factors attributing to the alterations of left atrial function in MS patients;(3)assess the feasibility of measuring regional longitudinal strain/strain rate profiles in LA wall to quantify LA function.Subjects and methods:A total of 333 consecutive subjects were separated into two groups:(1)The control group consisted of 156 subjects(57 males and 99 females,mean age 52.69±8.69 years old,range 35-85).We excluded subjects with ischemic heart disease,hypertension,congestive heart failure and diabetes mellitus on the basis of previous history(including treatment).(2)Recruited were 177 consecutive subjects with metabolic syndrome(75 males and 102 females,mean age 53.65±8.51 years old,range 26-74),with cardiovascular risk factors(obesity,hypertension,glucose tolerance/diabetes mellitus and dyslipidemia) and no previous history or clinical evidence of heart failure or overt coronary artery disease.According to the ratio of mitral valve annulus mean early and mean late diastolic peak tissue velocity(Ve_global/Va_global)by Doppler tissue velocity imaging (TVI),patients with MS were further divided into MS without left ventricular diastolic abnormality group(Ve_global/Va_global≥1,32 males and 36 females,mean age 53.21±9.68years,range 34-74)and MS with left ventricular diastolic abnormality group(Ve_global/Va_global＜1,43 males and 66 females,mean age 54.17±7.66 years,range 26-66).At inclusion all subjects had a thorough review of their medical history, clinical examination and ECG recording for the detection of clinical events.Informed consent was obtained from all subjects based on a protocol approved by the Ethics Committee of QiLu Hospital,Shandong University.Statistical analyses were performed using SPSS 13.0(SPSS Inc.,Chicago,Ill., USA)software.Data are presented as mean±SD for continuous variables and as proportions for categorical variables.Differences in continuous variables between 2 groups were assessed by independent-samples Student's t tests and comparison among multiple groups was performed by one-way ANOVA.Categorical variables were analyzed by theχ² test.The independent correlation between left atrial function and metabolic factors or left ventricular diastolic function was tested by partial correlation coefficient.Variables with a P value less than 0.10 in univariate analysis were entered into the multivariate model with a stepwise regression analysis. Receiver operating characteristic(ROC)curve were used to assess the diagnostic efficacy of strain and strain rate.We considered results significant when the P value was＜0.05.Results:(1)There was no difference between the normal and MS groups in age and gender.As expected,the MS was associated with significantly higher waist circumference and body mass index;higher systolic,diastolic,and pulse pressures; higher TG and LDL-C;lower HDL-C;lower ISI;and higher fasting glucose,insulin levels and HOMO-IRI.(2)Compared with the controls,participants with the MS had significantly greater septal and posterior wall thicknesses,larger LA and LV end diastolic dimension,greater LV mass and LV mass index and greater peak velocity of A wave, smaller E/A ratio,early diastolic tissue velocity and Ve_global/Va_globalratio.LA index of MS with left ventricular diastolic abnormality group was also greater than control. There were no differences in LVEF and peak velocity of mitral E wave.(2)Compared with control group,mean S,mean SSR and mean ESR were significantly lower in MS patients,while mean ASR showed no difference.Compared with MS patients without LV diastolic abnormality,mean S and mean ESR were significantly decreased in MS patients with LV diastolic abnormality,while mean SSR and mean ASR showed no difference.(3)Partial correlation was used to detect the independent relationship between left atrial function and metabolic factors after controlling for variables standing for left ventricular diastolic function.Mean S was significantly correlated with systolic BP,diastolic BP,pulse pressure,waist circumference,Waist-to-hip ratio,cholesterol, triglyceride and LDL-C level,FBG and FINS level ISI and HOMO-IN.Mean SSR was significantly correlated with age,systolic BP,diastolic BP,pulse pressure,waist circumference,Waist-to-hip ratio,cholesterol,triglyceride,HDL-C and LDL-C level, FBG and FINS level,ISI and HOMO-IRI.Mean ESR was significantly correlated with age,systolic BP,diastolic BP,pulse pressure,waist circumference,Waist-to-hip ratio,cholesterol,triglyceride,HDL-C and LDL-C level,FBG and FINS level,ISI and HOMO-IRI.(4)Partial correlation was used to detect the independent relationship between left atrial function and left ventricular diastolic function after controlling for metabolic variables.Mean S was significantly correlated with Ve_global,and mean ESR was significantly correlated with Ve_globaland Ve_global/Va_globalratio.(5)It is suggested that systolic BP,Ve_global,insulin sensitivity index,cholesterol level and waist-to-hip ratio were significant determinants of mean S,and that mean SSR was significant correlated with systolic BP,cholesterol level,Ve_lobal,insulin sensitivity index,age and HDL-C.Ve_global,systolic BP,cholesterol level,age and waist circumference were significant determinants of mean ESR in the multivariate model.(6)The ability of Strain/Strain rate to detect subjects with metabolic syndrome was assessed by using ROC curves.The area under the ROC curve of mean S was 0.897.A S value of 21.5%had 76%sensitivity and 89%specificity for detecting subjects with metabolic syndrome.A SSR value of 1.27S^-1had 73%sensitivity and 87%specificity for detecting subjects with metabolic syndrome.The area under the ROC curve of ESR was 0.893.A ESR value of -1.225 s^-1had 89%sensitivity and 82%specificity for detecting subjects with metabolic syndrome.The area under the ROC curve of SSR was 0.857 Conclusion:(1)This study was the first to evaluate the left atrial function in MS patients by strain and SR imaging.The LA reservoir and conduit functions were impaired in patients with MS.(2)The impairment of left atrial function was influenced by both metabolic disturbance and left ventricular diastolic function,and the impairment was significant before the manifestation of left ventricular diastolic abnormality.(3)Central obesity,hypertension,dyslipidemia and decreased insulin sensitivity index which were the main components of MS were significantly independent factors responsible for impaired LA function.(4)Strain and SR imaging enabled detection of LA dysfunction in subjects with metabolic syndrome,with high sensitivity and specificity.