CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 5, November/December 2023 AFRICA 293 Sample size was calculated according to: total sample size (n) = [(Zα + Zβ)/C]2 + 3 where the standard normal deviation for α = Zα = 1.960, the standard normal deviation for β = Zβ = 0.842 and the expected correlation coefficient = 0.408.11 This yielded a sample size of 41 patients. However, we included 81 patients in this study. The included patients underwent detailed history taking through an interview using a predesigned anonymous questionnaire. The questionnaire required data concerning demographic characteristics, history of RHD and previous interventional surgery, and history of AF and other arrhythmias. Patients also underwent a general examination, including measurement of height and weight, and pulse rate. From height and weight, the body surface area (BSA) was estimated using Mosteller’s formula:12 BSA (m2) = √ _____________________ height (cm) × weight (kg) ____________________ 3 600 The BSA was used as an index for the annular dimensions of the cardiac valves.13 A standard 12-lead ECG was done to determine whether the patient was in sinus rhythm or AF, to detect any other arrhythmia, to assess ECG signs of chamber enlargement, such as p pulmonale, RV strain or right bundle branch block, and to identify A-V conduction abnormalities. The echocardiography examination and image acquisition were performed using the Acuson X300™ ultrasound system (Siemens, Germany). Images were interpreted and measures were taken using the Horos Mac 10.5.8 social advice image viewer system. The MVA was assessed in each patient. Assessment of MVA by planimetry, assessment of transmitral diastolic pressure gradient, pressure half-time (PHT) and systolic pulmonary artery pressure (SPAP) were performed according to Cherry et al.14 An inferior vena cava (IVC) diameter of ≤ 2.1 cm that collapsed more than 50% with a sniff suggested a normal right atrial (RA) pressure of 3 mmHg (range 0–5 mmHg), while an IVC diameter of > 2.1 cm that collapsed less than 50% with a sniff suggested a high RA pressure of 15 mmHg (range 10–20 mmHg). An intermediate value of 8 mmHg (range 5–10 mmHg) was used in indeterminate cases in which the IVC diameter and collapse did not fit this paradigm.15 MS severity was graded using the MVA, which was considered normal if it measured 4–5 cm2. An MVA of > 1.5, 1.5–1 and < 1 cm2 were interpreted as mild, moderate and severe grades of stenosis, respectively.14 Severity of mitral regurgitation (MR) was assessed using the vena contracta (the area where blood goes through the valve leaflets). Because the breadth of the vena contracta correlates with the diameter of the regurgitant orifice area, it is a reliable indicator of the severity of MR. Less than 3 mm of vena contracta width was considered mild MR, while a width of 3–6.9 mm was considered moderate MR and ≥ 7 mm was considered severe MR.16 The LA anteroposterior diameter was determined in the parasternal long-axis view perpendicular to the posterior wall long axis, leading edge to leading edge (M-mode) or inner edge to inner edge (2DE), and measured at the level of the aortic sinuses.17 LA volume was assessed by the biplane area–length method, which is better at assessing the true LA area in cases of MS. This is because in MS there is a tented area below the mitral valve due to the deformation and doming of the leaflets. Other methods of calculating the LA area draw a straight line between the annulus and may miss this tented area. The biplane area–length approach was used at the end of systole to gather measurements from the frame immediately preceding themitral valve opening. Apical four- and two-chamber (A4CH, A2CH) views were adjusted to be of good quality with no foreshortening. The endocardial border was enabled to be visualised and the maximal area was measured with a planimeter, excluding the area under the MVA, pulmonary veins and LA appendage. The length between the mid-line of the plane of the mitral annulus and the opposite superior aspect of the LA was measured.17 The LA volume was computed in this study using the formula: LA volume = 0.85 (A4CH–A2CH)/L, where L is the average of the two lengths. As a qualitycontrol measure, we frequently examined for LA shortening and confirmed that the two lengths did not differ by more than 5 mm. A discrepancy of > 5 mm between the two lengths indicates that the LA may have foreshortened the lengths from one view; the lengths were then re-measured to guarantee accuracy. Moreover, LA volume index (LAVI) was calculated according to this formula: LAVI = LA volume/BSA.18 To calculate LA function, the following formulae were used: LA total emptying volume = LAVmax – LAVmin, LA total emptying fraction = (LAVmax – LAVmin)/LAVmax. To obtain the LA maximum volume (LAVmax), the LA volume was measured at end-systole, just before the opening of the mitral valve (at the end of the T wave on the ECG), while for minimum LA volume (LAVmin), at end-diastole, the LA volume was measured just before mitral valve closure (at the beginning of the QRS complex on the ECG).17 The ranges and severity cut-off values for LA area and volume were interpreted in accordance with the American Society of Echocardiography and European Association of Cardiovascular Imaging Standards for quantifying cardiac chambers in adults using echocardiography.17 The primary outcome of the studywas the potential correlation between MVA and LA function, whereas the secondary outcome was the differences in echocardiographic parameters of LA function between patients in sinus rhythm and AF. Statistical analysis The data were analysed by the statistical package for the social sciences (version 25.0; SPSS Inc, Chicago, Illinois, USA) software for Windows. Continuous variables are expressed as mean ± standard deviation (SD) and categorical variables are expressed as absolute numbers and percentage. The Spearman correlation test was used to measure the correlation between quantitative variables. Comparisons of continuous variables were performed using the unpaired Student’s t-test and comparisons of categorical variables were performed using the chi-squared test. A p-value < 0.05 was considered statistically significant.
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