Introduction: The presence of changes in the resting electrocardiogram (ECG) is an independent factor for the onset of coronary artery disease and is associated with an increased mortality rate and increased risk for cardiovascular disease. The importance of identifying electrocardiographic changes and their relationship with cardiovascular disease has been extensively studied in the Caucasian, Latino and African American population. Despite this, there is no information on the parameters of normality, as well as on electrocardiographic abnormalities and their relationship with cardiovascular risk factors in Angolans; although there are some data from studies in some African populations, local studies are necessary, given the variation of environmental and behavioral conditions of different population groups. Objectives: To evaluate the ECG in a population of the Bengo province, North of Angola, in its baseline, regarding the parameters of normality, and the presence of electrocardiographic alterations and their association with cardiovascular risk factors. Methods: The data analyzed in this work come from the database of a population-based study called CardioBengo, carried out at the Health Research Center of Angola. This is a cross-sectional community-based study conducted from September 2013 to March 2014. Data were analyzed considering stratification by gender. Continuous variables were expressed as mean±SD and categorical variables were expressed as number and proportions. The normal limits of the ECG parameters were taken as the 2nd and 98th percentiles of the distribution by age group and sex, the Mann-Whitney and Kruskal-Wallis tests were used to compare the medians. Differences between groups were assessed by Student's t test and the difference between two independent population proportions assessed by Chi-square test. Multivariate logistic regression analysis was performed to estimate the association between any minor or major electrocardiographic change with age and the sum of cardiovascular risk factors by sex. Adjusted odds ratios (ORs) were presented with a 95% confidence interval. Student's t-test and Chi-square, one-way ANOVA and Kruskal-Wallis non-parametric tests were used for comparison between the pregnant and non-pregnant groups, as appropriate. Statistical analysis was performed using the IBM SPSS version 26 software and the R software (version 4.0.5). Results: The study involved 2 379 participants (880 men and 1449 women), aged between 15 and 84 years, 63% female. The mean age was 35.0±14.4 years. The normal limits of measurements were different between men and women: HR 49 to 100 bpm vs. 55 to 108 bpm, P wave duration 81 to 130 ms vs. 84 to 130 ms, PR interval 119 to 210 ms vs. 120 to 202 ms, QRS duration 74 to 110 ms vs. 70 to 104 ms, QT interval 324 to 441 ms vs. 314 to 438 ms, P wave axis -290 to 850 vs. -180 to 810, QRS axis -130 to 850 vs. -180 to 820, T wave axis 00 to 720 vs. -80 to 730, Sokolow-Lyon index 2.13 to 6.21 mV vs. 1.60 to 4.87 mV, Cornell index 0.17 to 6.24 mV vs. 0.14 mV to 4.35 mV. It was found that 4.58% of the participants had major electrocardiographic alterations, especially in women, and 22.3% had minor electrocardiographic alterations, which were more frequent in men. The most common major electrocardiographic abnormalities were left ventricular hypertrophy with major ST-T abnormalities, ventricular conduction defect and major Q wave abnormalities. The most common minor electrocardiographic abnormalities were abnormal T wave inversion, isolated minor ST abnormalities and premature beats. The study identified two individuals with atrial fibrillation, which represents an estimated prevalence of 0.084% (0.11% in males and 0.067% in females). High blood pressure, diabetes mellitus, hypercholesterolemia, alcohol consumption and smoking were significantly associated with major and minor electrocardiographic changes. Comparing pregnant vs non-pregnant women, we found the following mean values: Heart rate (83 bpm vs. 74 bpm, p<0.001), PR interval (146 ms vs. 151 ms, p=0.034), QT interval (360 ms vs. 378 ms, p<0.001), QTIc Fridericia (398 ms vs. 403, p=0.017), QTIc Framingham (399 ms vs. 404 ms, p=0.013) and T wave axis (340 vs. 410, p=0.001). The main changes found were: sinus tachycardia (4.4% vs. 2.5%), T wave inversion (14.9% vs. 1.7%) and left ventricular hypertrophy (11.4% vs. 11.7 %, p=0.726). Conclusion: Our results suggest that the normal ranges of most ECG parameters vary according to age and sex, and ECG diagnostic criteria should therefore be specific for these demographic measures. Most participants had minor electrocardiographic abnormalities. Major abnormalities were more prevalent in women and minor electrocardiographic abnormalities were more prevalent in men. Electrocardiographic changes had significant associations with major cardiovascular risk factors. Pregnant women had significantly higher values of heart rate, and significantly lower values of systolic and diastolic blood pressure, PR interval, QT interval, QT interval corrected by Fridericia and Framingham's formula and T wave axis. The duration of the P wave was reduced as the pregnancy progressed from the first to the third trimester. Sinus tachycardia, T wave inversion, ST-segment alteration and left ventricular hypertrophy were the main alterations found. The values described for the analyzed electrocardiographic measurements can be used as a reference for Angolan adults without established heart disease. The ECG, being a safe test, with good accuracy, inexpensive and wide availability, can be used in cardiovascular epidemiology to predict cardiovascular risk and the implementation of preventative strategies in Angolans.
Key-words: Normal ECG, Electrocardiographic changes, Cardiovascular Risk factors, Angola