Peak systolic longitudinal rotation: a new tool for detecting left ventricular systolic function in patients with type 2 diabetes mellitus by two-dimensional speckle tracking echocardiography

Background Type 2 diabetes mellitus (T2DM) is one of the most prevalent cardiac and cerebrovascular risk factors. The study aimed to find a new way to investigate left ventricle (LV) systolic dysfunction in T2DM patients using two-dimensional speckle tracking echocardiography (2D-STE). Methods Fifty-one untreated T2DM patients and 52 normal control subjects were enrolled for the research. Apical four-chamber view was acquired by two-dimensional echocardiography. Segmental and global peak systolic longitudinal rotation (PSLR) degrees were measured by the software of EchoPAC. Results In T2DM patients, global PSLR prominently rotated clockwise, while in normal subjects, global PSLR degrees were so small and almost had no PSLR. HBA1c negatively correlated with apex and global PSLR, that is, T2DM patients with higher HBA1c had a larger clockwise apex and global PSLR. ROC analysis showed that PSLR could detect the accuracy of LV systolic dysfunction. Conclusion Cardiac clockwise global PSLR was found in T2DM patients. The cardiac contractile function in T2DM patients was impaired. The new tool of PSLR can conveniently detect cardiac systolic dysfunction in T2DM patients. HBA1c could predict systolic dysfunction in T2DM patients.


Background
Type 2 diabetes mellitus (T2DM) is one of the most prevalent cardiac and cerebrovascular risk factors [1]. T2DM may alter cardiac structure and function independently of underlying coronary artery disease or hypertension [2]. Left ventricle (LV) remodeling may lead to diabetic cardiomyopathy before LV contractile dysfunction [3]. Initial assessment of LV dysfunction in T2DM patients is vital for the treatment and prognosis.
Two-dimensional speckle tracking echocardiography (2D-STE) has been introduced as a novel method for angle-independent and well reproducibility quantification of LV strain, strain rate and LV twist [4][5][6][7], and by the measurement of these values, LV dysfunction could be assessed. The speckles are the result of constructive and destructive interference of conventional gray scale ultrasound images.
Most of previous studies have measured LV strain, strain rate, twist or torsion by 2D-STE or 3D-STE in T2DM patients for detecting LV systolic and diastole dysfunction, and then demonstrated the impairment of LV function [8][9][10][11][12].
Peak systolic longitudinal rotation (PSLR) as a novel marker means the rotational motion in the long axis of heart. Previous studies have demonstrated that PSLR were small in normal subjects, however, systolic clockwise PSLR motion have been detected in dilated cardiomyopathy, hypertrophic cardiomyopathy, ischemic cardiomyopathy, and arterial hypertension patients [13][14][15], however, the etiology of PSLR is still unknown.
In the research, we want to find a simple method to evaluate the LV contractile dysfunction in T2DM patients. We phased a specific hypothesis that T2DM patients had PSLR in cardiac cycle. The importance and necessity of the study was to determine whether T2DM patients had cardiac PSLR, and evaluated the relationship between PSLR and clinical laboratory indicators, just like fasting plasma glucose and HBA1c. At last, provide a simple and accurate method to detect LV systolic dysfunction in T2DM patients.

Ethical statement
The Human Subjects Committee of the Affiliated Changzhou No.2 People′s Hospital with Nanjing Medical University approved this study. Written informed consent was obtained from each patient enrolled to the research. The reference number for the ethical approval is: [2014]KY010-01.

Study population
Fifthy-seven untreated T2DM patients (37, males) and 52 normal controls (27, males) of similar age and gender were enrolled for this study, however, 4 untreated T2DM patients (2, males) were excluded for the large difference in heart rate, 1 untreated T2DM patients (male) was excluded for fat, and 1 untreated T2DM patients (female) was excluded for COPD. At last, 51 untreated T2DM patients (34, males) were enrolled for the study (Fig. 1). This is a cross-sectional study that was conducted between August 2015 and May 2017, and data was collected prospectively. Subjects with cardiovascular disease, such as coronary artery disease (all of the patients were had coronary artery CT scan to ensure that they had no coronary artery disease), arterial hypertension, myocardial infarction, cardiomyopathy, valvular disease, atrial fibrillation, congenital heart disease, thyroid disease, neoplastic disease, or kidney failure were excluded from the study. In normal control subjects, all of the physical examination tests, the electrocardiogram, and the echocardiography were showed normal. All normal subjects had an absence of diabetes (according to the diagnosis of T2DM, the fasting blood glucose, Two-hour postprandial blood sugar and HbA1c were all showed normal).

Biochemistry
In T2DM patients and normal subjects, fasting plasma glucose, two-hour postprandial blood sugar and glycated hemoglobin (HBA1c) were measured.

Conventional 2D Doppler echocardiography
All enrolled subjects underwent conventional 2D Doppler echocardiography (Vivid E9, GE healthcare). Echocardiography examination was done before beginning drugs in T2DM patients. Left atrial diameter (LAD), interventricular septum thickness and LV posterior wall thickness in end-diastole (IVSD and LVPWD) were measured in the parasternal long-axis view of LV by M-mode. LV enddiastole volume (LVEDV), LV end-systole volume (LVESV) and LV ejection fraction (LVEF) were measured by modified biplane Simpson′s method. Peak early and late diastolic velocities of mitral valve (E and A, respectively) were measured by pulsed-wave Doppler, and the ratio of E/A was then calculated. Peak early (e′) and late (a′) diastolic annular velocities were obtained by averaging the values at septum and lateral positions using pulse wave Tissue Doppler Imaging (TDI), and E/e′ was calculated.
ECG leads were connected to each patient. Standard high frame rate (> 60 /s) of the apical four-, three-and two-chamber views of three consecutive cycles while patients held their breath were stored for offline analysis.

Analysis of LV systolic function
The apical four-, three-and two-chamber views were analyzed using 2D-STE software (2D-Strain, EchoPAC PC 113, GE Healthcare, Horten, Norway) by two experienced cardiologist. First, we defined cardiac PSLR as the rotation of the LV cross section. Segmental and global PSLR degrees were measured. Using the SAX-MV option of EchoPAC software displayed on the apical four-chamber view. The LV walls were divided into six segments: base-septal, middle-septal, apex, middle-lateral, and base-lateral, and one segment containing mitral valve, respectively. The segment containing mitral valve was excluded for the analysis. Then segmental and global PSLR of LV walls were measured via the software (Fig. 2).
Second, we used LAX, A4C and A2C options for the analysis of LV longitudinal strain and strain rate by the software, "LAX" means apical three chamber view. LV longitudinal strain (including LS-endo, LS-mid, and LSepi, which represented LV endomycardial, middle myocardial and epimycardial walls, respectively) and LV longitudinal strain rate (LSr) were calculated and recorded.

Statistical analysis
All data analyses were performed using SPSS 21.0 software (SPSS, Chicago, IL, USA). Data was presented as the mean ± standard deviation (SD). p-value < 0.05 was

Reproducibility and repeatability
Intraobserver and interobserver variability for global PSLR were determined by repeating measurements in all enrolled T2DM patients and normal subjects. For the second intraobserver measurements, the observer was "blinded" to results of the initial measurements.

Basic information in T2DM patients and normal subjects
There were significant differences in body weight, BSA (body surface area), BMI (body mass index), HR, SBP, DBP, LVEDV, Indexed LVEDV, indexed LVESV, LVEF, e′, a′ and E/E′. LVEDV, indexed LVEDV, indexed LVESV, LVEF and e′ in T2DM patients were significantly lower than normal subject, while a′ and E/e′ were significantly larger than normal subjects. (Table 1).

Segmental and global PSLR
In T2DM and normal subjects, segmental PSLR of lateral wall rotated counter-clockwise, while septum rotated clockwise. In normal subjects, global PSLR degrees were so small and almost had no PSLR. In T2DM patients, global PSLR prominently rotated clockwise. A smaller PSLR of base-lateral, middle-lateral walls, while a larger apex and global PSLR in T2DM patients were observed when compared with normal subjects. There were no significant differences in base-septum and middle septum between the two groups. (Table 2, Fig. 3).  (Table 3, Fig. 4).  Fig. 5).

Reproducibility and repeatability
The results for the intraobserver and interobserver variability for the global PSLR upon repeated measurements in all study patients were shown in Table 5. We compared the interobserver and intraobserver variability with the first time, and found there were no differences among the three time. There were significant differences between T2DM patients and normal subjects in interobserver and intraobserver analysis. What′s more, the results demonstrated that the analysis of the software had the well repeatability and reliability of the study.

Discussion
The main findings of the research were: ①Global PSLR motion prominently rotated clockwise in T2DM patients. ②Higher HBA1c had larger apex and global PSLR in T2DM patients. ③Apex and global PSLR could reflect LV contractile dysfunction in T2DM patients. No significant difference was found between the two results. LVEF is always used for detecting contractile function in normal subjects and cardiac disease patients. However, in the study, LVEF was similar in T2DM patients and normal subjects. It cannot reflect early systolic dysfunction in T2DM patients. Previous reports used 2D-STE or 3D-STE to measure strain, strain rate or LV torsion for assessment of cardiac systolic and diastolic dysfunction. Ernande L et al. [16] used 2D-STE to measure longitudinal and radial systolic strain in T2DM patients, and found that longitudinal and radial systolic function were impaired in asymptomatic patients with T2DM. Enomoto M et al. [17] found global longitudinal and circumferential strain were lower in patients with T2DM than in the controls by using 3D-STE, and concluded that diabetic microangiopathy and its accumulated effects significantly related to subclinical LV dysfunction were characterized by impaired longitudinal shortening. In the research, we introduced a new way to detect systolic dysfunction which was defined as PSLR. PSLR was first reported by Popović ZB in 2007, and the researcher found that in dilated cardiomyopathy and ischemic cardiomyopathy patients, the cardiac had LR [13]. The orientation of the LR is unclear at present. In T2DM patients, prominently clockwise PSLR was detected. A smaller PSLR of base-lateral, middle-lateral walls, while a larger apex and global PSLR in T2DM patients was observed when compared with normal subjects, and there was no significant difference in septum wall. The pathogenesis of T2DM cardiomyopathy is likely to be multifactorial, including micro vascular disease, altered myocardial metabolism, and structural changes in the myocardium with increased fibrosis [18]. We considered the orientation of PSLR may be linked to myocardium fibrosis. According to the theory of "myocardial band" [19], and a normal myocardium consists of subendocardial, middle, and subepicardial fibers. When the normal myocardium became fibrosis, we thought the primary balance among the myocardium was disappeared, as a result, PSLR was detected. Further researches of our group want to verify the hypothesis between PSLR and myocardium fibrosis in T2DM animal model.
From the results, we found that there were no differences in LS-endo, LS-middle, LS-epi and LSr between T2DM patients and normal subjects, however, global, apex and lateral PSLR had the significant difference between the two groups, so we concluded that PSLR was an accurate and simple method.
HBA1c negatively correlated with apex and global PSLR, respectively. No correlations were discovered among fasting plasma glucose, LVEF with segmental and global PSLR. Therefore, higher HBA1c of T2DM patients had larger apex and global PSLR. ROC analysis showed that the area under ROC curve values of apex and global PSLR was: 0.693 and 0.641. Comparison of ROC analysis curves between apex and global LR had no significant difference. From the results, we concluded that apex and global PSLR could reflect the contractile dysfunction in T2DM patients. HBA1c could predict systolic dysfunction in T2DM patients.

Conclusions
In the study, we found contractile function was impaired in T2DM patients. Cardiac clockwise PSLR was found in T2DM patients. The new tool PSLR can be flexible and conveniently to detect cardiac systolic dysfunction in T2DM patients. HBA1c could also predict systolic dysfunction in T2DM patients.

Limitations
First, the number of T2DM patients and normal subjects in this study was small. Second, the technique of Echo-PAC in the analysis of two-dimensional images has the shortcoming of out-of plane motion, if the speckles move out of plane during contraction, the software cannot be tracked successfully. In the research, we just told the patients hold their breath to prevent the condition. Third, large differences in heart rate, fat patients and patients with COPD were insufficient and excluded for the analysis. TDI: Tissue Doppler imaging HJ, YZN and FL designed the study and carried out the study, data collection and analysis, HJ wrote and revised the manuscript. HHL revised the manuscript after the first revision and did some statistical analysis for supplement. FL and RYF designed part of the experiments, and collected the T2DM patients. SD and LJ performed the statistical analysis. All authors have read and approved the manuscript, and ensure that this is the case.
Funding none.

Availability of data and materials
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Ethics approval and consent to participate
The study complied with the Declaration of Helsinki and was reviewed and approved by the Human Subjects Committee of Changzhou No. 2 People's Hospital approved this study. Written informed consent was obtained from each couple enrolled in the study.

Consent for publication
This manuscript does not include any individual person's data.