Application Of Echocardiography To Evaluate Myocardial Energy Expenditure In Primary Hypertension Patients

BackgroundPrimary hypertension is one of the most common cardiovascular disease and is a major public health problem worldwide. According to epidemiological studies hypertension is an independent risk factor for stroke and coronary heart disease. There are about 50 million people suffering from hypertension in the United States and in Japan about 60% of the people over the age of 60 have high blood pressure. In China, the incidence of hypertension among 35 to 74-year-old Chinese adults is 27. 2%. However, the pathogenesis of primary hypertension is not clear, and there is limited research on myocardial energy metabolism in hypertensive patients. The commonly used methods for evaluating myocardial energy metabolism include cardiac magnetic resonance spectroscopy (31P-MRS), metabolomics and noninvasive echocardiography. Cardiac magnetic resonance spectroscopy method was first used in vivo in 1976 and has since become the primary method to determine myocardial energy metabolism in vivo. However,31P-MRS assessment of myocardial energy metabolism has its limitations:the myocardium is in constant motion thus interference with signal acquisition is common; location of regions of interest is difficult due to low noise ratio; quantitative data analysis is difficult; technical operations are difficult and it is relatively expensive. Metabolomics, first proposed in 1999 by Professor Nicholson, is the use of nuclear magnetic resonance, high performance liquid chromatography, gas chromatography and mass spectrometry to analyse the pathophysiological and genetic modification in endogenous metabolites to determine the energy metabolism of tissues。However, as the heart neither produces nor stores energy, it receives energy through nutrients in blood. Therefore, serum markers are necessary to determine cardiac energy metabolism. However, due to low sensitivity and specificity of serum markers, signal overlapping, and high cost, metabolomics is rarely used. In clinical practice, we prefer simple, safe, cheap, stable and reproducible methods to determine myocardial energy expenditure (MEE). In 2003 Vittorio Palmieri used echocardiography to determine myocardial energy expenditure from the formula:myocardial energy expenditure (MEE)=end-systolic stress×ejection time×stroke volume, and concluded that:①in a large sample of hypertensive patients (excluding diabetes, coronary heart disease, valvular stenosis), MEE is proportional to pressure overload as well as the degree of valvular regurgitation,②In a large sample of mobile patients with left ventricular systolic dysfunction, the decrease in cardiac ejection fraction was independently related to myocardial energy expenditure, lower body fat content and higher fibrinogen level. However, except for left ventricular ejection fraction and other relative variances, higher MEE and lower body fat content are independent factors of cardiac death. Shen et al used echocardiography to investigate the value of myocardial energy expenditure for assessing left ventricular systolic function and remodeling in primary hypertension patients. They found that, in four remodeling groups, the hypertensive patients had significantly higher cESS and MEE than controls except left ventricular concentric remodeling group. Left ventricular concentric hypertrophy group had the highest cESS and MEE in hypertensive patients. MEE showed significant correlations with indicators of left ventricular systolic function and remodeling in bivariate correlation analysis (all P<0.01). In conclusion, MEE obtained noninvasively from echocardiographic measures could reflect different myocardial energy expenditure of different left ventricular patterns, both MEE and cESS might be effective indicators for assessing left ventricular systolic function in primary hypertension. Nevertheless, there is fewer study about the relationship between changes of myocardial energy expenditure and left ventricular diastolic function in patients with primary hypertension, and limited research on the clinical significance of changes of myocardial energy expenditure in the primary hypertensive patients before and after standard treatment. Thus, we have studied its characteristics and clinical significance in our research.Part one The relation between changes of myocardial energy expenditure and left ventricular diastolic function in patients with primary hypertensionObjective To investigate and compare the clinical significance and difference of myocardial energy expenditure in patients with primary hypertension with or without left ventricular diastolic dysfunction.Method 128 patients with primary hypertension were recruited. The pulsed Doppler was used to measure the diastolic early maximal velocity (E) and late maximal velocity (A) of mitral flow. The structural and systolic functional parameters were measured simultaneously, and the circumferential end-systolic wall stress (cESS), myocardial energy expenditure (MEE) and left ventricular mass index (LVMI) calculated by the corresponding formulas. Tissue Doppler imaging (TDI) was used to obtain the movement spectrum of mitral annulus, early(E') and late(A') diastolic maximal velocities were measured. The patients were divided into six groups according to the ratio of mitral flow velocity and mitral annulus movement spectrum:G1(E'/A≥1), G2(E'/A'<1), G3(E/A>1), G4(E/A<1), G5(E/E'≥8) and G6(E/E'<8), respectively.Results G2 group had significantly higher LA, LV, IVS, PWTd, LVMI, cESS and MEE compared to G1. Compared to G6, G5 had higher BMI, FS, LVEF and lower LA, left ventricular stroke volume and ejection time, heart rate, cESS and MEE. Although G3 and G4 had no significant difference in cESS, MEE, LVEF and structural parameters, E'/A' and E/E' showed significant correlation with cESS, MEE and LVMI, whereas E/A with age.Conclusion The myocardial energy expenditure level in hypertensive patients with left ventricular diastolic dysfunction is higher than those with normal diastolic function. Tissue Doppler imaging is superior to the pulsed Doppler in assessing left ventricular diastolic function.Part two The significance of changes of myocardial energy expenditure in the primary hypertension patients before and after standard treatmentObjective To investigate and compare the significance and difference of myocardial energy expenditure in patients with primary hypertension before and after 3 months standard treatment.Method 53 patients with primary hypertension were recruited and they were given 3 months of standard treatment to control their blood pressure under 140/90 mmHg. We recruited 52 volunteers with normal blood pressure as control group. The Doppler imaging was used to measure the internal diameter of aortic annulus (AD), the blood flow velocity and ejection time of aortic valve and their integration. The structural and systolic functional parameters were measured simultaneously, and the circumferential end-systolic wall stress (cESS) and myocardial energy expenditure (MEE) calculated by the corresponding formulas.Results After treatment, the blood pressure, cESS and MEE were all significantly decreased, although no significant difference in AD, VT, PWTs, LVIDs and HR were noted. Compare to normal control group, the patients with 3 months treatment had higher SBP, LVET, VT, IVS, PWTs, LA and lower RA. There was significant difference in MEE between the two group rather than cESS.Conclusion After 3 months of standard treatment, the MEE in patients with primary hypertension was significantly decreased. It was significantly correlated with the changes in blood pressure, rather than other parameters. Short-time blood pressure control could get lower MEE instead of normal MEE.