METHODS

Study design and population

A cross-sectional study was conducted during a 9-month period (from January 2019 to September 2019). Patients were recruited at National Obesity Centre and the Centre for treatment of Diabetes and Hypertension of the Yaoundé Central Hospital. We included in the study, T2DM adults aged 18 and above, no matter the duration of diabetes follow up, with no history of a proven cardiac disease caused by a condition other than hypertension (HTN) or T2DM such as coronary artery disease, significant valvular heart disease, obstructive hypertrophic cardiomyopathy, atrial fibrillation or flutter.

Data collection

A thorough clinical examination was carried out at inclusion. The variables assessed at this point of the study included, the age and gender of participants, diabetes characteristics, cardiovascular risk factors, clinical, anthropometric and haemodynamic parameters. The clinical examination was followed by a resting electrocardiographic recording.

Echocardiography

Transthoracic echocardiography was performed in all patients using a machine equipped with a 5 MHz X5-1 probe (Plilips iE33) and the QLAB Ultrasound cardiac analysis software for strain measurement. Standard echocardiographic parameters were obtained, these included LV ejection fraction through Simpson’s Biplane method, LV mass index and LV diastolic function through Tissue Doppler imaging derived E and E’ peak velocities at the lateral mitral annulus. The biplane Simpson’s method was used for calculation of LA volumes. Left atrial volume was planimetered in the four-chamber and two-chamber views by tracing the endocardial border (pulmonary vein confluence and LA appendage were excluded)9.
Maximum LA volume (LA max) was obtained at left ventricular (LV) end-systole, from the 2D frame, just before the mitral valve opened. Pre-atrial volume (Vpre-A) was obtained from the diastolic frame, just before the mitral valve reopened as the result of atrial contraction. Left atrial minimum volume (LA min) was assessed at LV end-diastole, from the smallest volume seen after LA contraction.
Left atrial phasic function assessment was done using the following formulas 10:
Reservoir function: LA emptying fraction total = ((LA max – LA min)/LA max) × 100%; expansion index = ((LA max – LA min)/LA min) × 100%
Conduit function: Passive emptying volume = LA max - Vpre-A; passive LA emptying fraction = ((LA max - Vpre-A)/LA max) × 100%;
Contractile function: LA active emptying fraction = ((LA pre-A – LA min)/LA pre-A) × 100%; LA active emptying volume = V pre-A – LA min.
The echocardiographic evaluation was concluded by peak atrial longitudinal strain (PALS) measurement by 2D speckle tracking echocardiography. Apical four- and two-chamber views were obtained using 2D greyscale echocardiography for speckle-tracking analysis. This was performed during end-expiratory breath-hold and stable ECG recording. An adequate greyscale image that allowed separation of myocardial tissue and surrounding structures was obtained. Three consecutive cardiac cycles were recorded and averaged. The QLAB software allowed offline semi-automated analysis of speckle-based strain. The endocardial surface of the LA was traced manually in both four- and two-chamber views by a three-point-and-click approach. The system then automatically generates an epicardial surface tracing (Figure 1). The region of interest was thus created, and this was then manually adjusted as needed to allow for adequate speckle tracking 11. A PALS value less than 32% was considered abnormal.

Statistical analysis

Statistical analysis was performed with SPSS version 25.0 software. Continuous variables were expressed as mean ± standard deviation (SD), while categorical variables were described with number of subjects (percentages). Means and proportions were respectively compared with the Student t test and Chi square or Fisher exact test. Multivariate linear regression analysis was used to identify possible independent determinants of abnormal PALS. Independent variables with a p-value less than 0.05 on bivariate analysis were included in the multivariate model. A p value < 0.05 was considered statistically significant.