Ventricular And Atrial Synchronicity In The Patients With Metabolic Syndrome

BackgroundMetabolic syndrome(MS),which was first described by Reaven,consisted of obesity,hypertension,impaired glucose tolerance,hyperinsulinemia and dyslipidemia characterized by elevated triglyceride,and low HDL concentration.The National Cholesterol Education Program(NCEP)has showed that the prevalence of the MS currently exceeds 20%of individuals who are at least 20 years of age,and 40%of the population＞40 years of age.Furthermore,in China,the prevalence of MS is 16.5%, including 10.0%in males and 23.3%in females.MS has been one of the major health care issues currently affecting many countries.Obesity,hypertension,hyperglycemia,dyslipidemia,elevated triglyceride and low HDL in MS are all important risk factors to cause left ventricular hypertrophy. Recently,Tan et al demonstrated impaired left ventricular synchronicity in hypertensive patients with left ventricular hypertrophy.Kosmala et al found left ventricular asynchrony common in patients with diabetes and left ventricular synchronicity.Meanwhile,the incidences of heart failure in MS are significantly high. Heart failure can lead to electrical and structural remodeling of the ventricle and atria. Ghio et al have found that inter- and intraventricular asynchrony existed in the patients with heart failure.Correcting the asynchrony by biventricular pacing can improve ventricular function in patients with congestive heart failure.Furthermore, heart failure can also cause atrial remodeling.The morbility of atrial fibrillation is increased in the patients with heart failure.Katarina et al have demonstrated that patients with heart failure indeed had interatrial and right atrial asynchrony.Since the patients with MS not only have left ventricular hypertrophy but also can develop into heart failure,we considered that it would be interesting to study interventricular, inter- and intraatrial synchronicity in patients with MS.Tissue Doppler imaging(TDI),is a new echocardiographic technique that uses high amplitude,low frequency ultrasound signals reflected from the myocardium.TDI allows the simultaneous examination of several regional cardiac structure movements with an excellent time resolution of approximately 10 ms,and has been used to evaluate ventricular synchronicity in both healthy and diseased hearts.ObjectivesIn our study we will use TDI to detect the left ventricular(LV),interventricular, inter- and intraatrial synchronicity in patients with MS who have still not developed into heart failure,compare with those in normal subjects and find the differences between them,then discuss the factors impacting on the differences.Methods1.Study Population:The study consisted of 260 subjects who visited our hospital from October 2006 to July 2007.All the subjects were divided into two groups:the Control group and the MS group.The subjects in the control group were all healthy people with normal heart rate,blood pressure,ECG and echocardiogram, without any cardiovascular diseases such as coronary heart diseases(CHD)or heart failure.Meanwhile,they were normal in the examinations of fasting glucose and insulin,fasting plasma lipids.The MS group was diagnosed according to the International Diabetes Federation(IDF)definition of MS in individuals.2.Measurements:(1)LV synchronicity:TDI was performed to assess the long-axis function of the LV using the apical four-chamber,two-chamber,and long-axis view.A 12-segment model was used to assess regional LV function.This included the anterior, anteroseptal,septum,inferior,posterior and lateral segments at the basal level and mid-level of the ventricle,respectively.Myocardial velocity curves were reconstituted off-line using the 6 basal and 6 mid-segmental models.The basal segments were sampled just above the mitral annulus level,and the middle segments were sampled at the mid-level of the LV.The time to peak myocardial systolic velocity during the ejection phase(Ts)and the time to peak myocardial early diastolic velocity(Te)were measured with referenced to QRS complex.Then,Ts and Te were corrected by heart rate and changed to Tsc and Tec.For the assessment of synchronicity,the maximal difference in Tsc and Tec between any two of the LV segments(Ts-diff,Te-diff)and the standard deviation of Tsc(Ts-SD)and Tec(Te-SD)were calculated.(2)Interventricular synchronicity:Myocardial velocity curves were reconstituted off-line using the LV lateral wall and RA free wall basal segmental models.The basal segments were sampled just above the mitral annulus and tricuspid annulus level. The time to peak myocardial systolic velocity during the ejection phase(Ts)and the time to peak myocardial early diastolic velocity(Te)were measured with referenced to QRS complex.Then,Ts and Te were corrected by heart rate and changed to Tsc and Tec.So using this method,Tlsc and Tlec from LV lateral wall,Trsc and Trec from RV free wall were all obtained.The difference between Tlsc and Trsc(Tlv_rv_s)and difference between Tlec and Trec(Tlv_rv_e)were calculated as the systolic and diastolic interventricualr asynchrony.(3)Inter- and Intra-atrial synchronicity:As to assess the synchronicity of atria, myocardial velocity curves were reconstituted off-line using the RA free wall,the interatrial septum,the LA free wall.The time difference from the onset of the P wave to the onset of the A wave at the right atrium(P-RA),the IAS(P-IAS),and the left atrium(P-LA)was measured.Intra-atrial asynchrony was defined as the differences between P-IAS and P-RA(RA asynchrony)and between P-LA and P-IAS (LA asynchrony).Interatrial asynchrony was defined as the difference between P-LA and P-RA.3.Statistical Analysis:Data were analyzed using a statistical software program (SPSS for Windows,version 13.0,SPSS Inc.).Data were expressed as the mean±SD. Student's two tailed t-test,chi-square test were used where appropriate.Pearson correlation coefficients were used to test correlations between the parameters of synchronicity and age,blood pressure,waist to hip ratio,body mass index(BMI),TG, TC,LDL-C,HDL-C,fasting blood glucose and LVMI.The stepwise multiple variable regression models were also used to determine the variables most predictive of synchronicity.Variable entry into the stepwise regression models required a P-value＜0.10.A P-value＜0.05 was considered statistically significant.Results1.LV synchronicity:Diastolic synchronicity was impaired in MS group which was measured by Te-SD and Te-diff.The Te-SD and Te-diff was significantly prolonged in MS group when compared with the control group(Te-SD:20.98±11.40 ms vs.16.27±5.37 ms;Te-diff:67.52±41.31 ms vs.45.43±17.07 ms;all P＜0.001). Systolic synchronicity,as measured by Ts-SD and Ts-diff,was also abnormal in MS group.The Ts-SD and Ts-diff was significantly prolonged in MS group when compared with the control group(Ts-SD:24.66±15.47 ms vs.17.33±5.64 ms;Ts-diff: 71.91±48.30 ms vs.47.31±17.20 ms;all P＜0.001).2.Interventricular synchronicity:Systolic and diastolic synchronicities of LV lateral wall were impaired in MS group which were measure by Tlsc and Tlec.Tlsc was significantly prolonged in MS group when it was compared with the control group(161.91±32.77 ms vs.141.46±28.00 ms;P＜0.001).Similarly,Tlec was also prolonged in MS group(572.78±43.22 ms vs.543.23±37.05 ms;P＜0.001).However, Trsc and Trec were not significant in MS group compared with the controls.Therefore, the interventricular synchronicity measured by Tlv_rv_s and Tlv_rv_e were significantly different(Tlv_rv_s:-4.24±36.30 ms vs.-22.71±26.39 ms;Tlv_rv_e: 22.07±39.03 ms vs.2.16±33.57 ms;all P＜0.001).3.Inter- and Intra-atrial synchronicity:P-LA and P-IAS were significantly prolonged in MS group when it was compared with the control group(P-LA: 64.18±13.91 ms vs.55.39±12.58 ms,P=0.002;P-IAS:36.31±12.35 ms vs. 31.54±11.50 ms,P＜0.001).However,P-RA was not significantly prolonged (22.96±8.10 ms vs.22.48±8.12 ms,P＞0.05).So the RA,interatrial and LA synchronicity in MS group,compared with the controls,were all obviously significant, which reveals that inter- and intra-atrial asynchronies indeed exist in the patients with MS.4.Stepwise multiple variable analysis:(1)LV synchronicity:We revealed that waist-to-hip ratio,fasting blood glucose, age and LVMI were independent predictors of impaired LV diastolic synchronicity in MS,whereas age and LVMI were independent predictors of impaired LV systolic synchronicity in MS.(2)Interventricular synchronicity:Stepwise multiple variable analyses showed that age and LVMI were independent predictors of Tlv_rv_s and Tlv_rv_e.(3)Inter- and Intra-atrial synchronicity:Stepwise multiple variable analyses found that LVMI were independent predictors of RA,interatrial and LA asynchrony.Conclusion1.The patients with MS is associated with abnormal LV diastolic and systolic functions.2.Compared with the normal subjects,systolic and diastolic synchronicity was impaired in the patient with MS,but has still not developed into the level of heart failure.3.Our study revealed that waist-to-hip ratio,fasting blood glucose,age and LVMI were independent predictors of impaired LV diastolic synchronicity in MS, whereas age and LVMI were independent predictors of impaired LV systolic synchronicity in MS.4.We also observed the significant interventricualr,interatrial and intraatrial asynchronies in patients with MS.LVMI is the independent predictor of the interventricualr asynchrony,whereas the inter- and intra-atrial asynchronies have linear correlations with LVMI and LA,and LVMI is the independent predictor of these asychronies.