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.