Electrocardiographic abnormalities, and specifically early repolarization (ER) patterns, are increasingly found to be common variants in healthy populations free of heart disease or risk factors. Data are sparse in subjects of African descent, for which no increase in adverse cardiovascular outcomes have been demonstrated. A database of healthy disease-free adult volunteers of sub-Saharan African descent had 12 lead electrocardiograms (ECGs) and transthoracic echocardiograms performed. Statistical tests were then performed on the data to elicit associations; 396 volunteers (63.1% women) with a mean age of 37.4 years met the inclusion and exclusion criteria. An abnormal ECG was identified in 50.5% of volunteers, largely because of underlying ST elevation at the J point (ER), left ventricular hypertrophy (LVH) by voltage criteria, and T-wave inversion. Men were more likely to have abnormal ECGs (odds ratio [OR] 1.75; p <0.001), axes (OR 2.05; p = 0.023), display LVH by Sokolow-Lyon voltage criteria (OR 5.45; p <0.001), and have ER patterns (OR 11.61; p <0.001). Additionally, younger adults were also more likely to display LVH by voltage criteria and ER patterns. Volunteers with LVH by ECG had 5.7% higher LV mass indexes (p = 0.047). An abnormal ECG was not associated with a reduced left ventricular ejection fraction or diastolic dysfunction. ECG abnormalities, especially ER patterns, in black adults of Sub-Saharan descent are common, occurring in half of the normal adults.
Electrocardiograms (ECGs) have long being used as a screening tool for various forms of heart disease in many areas of medical practice. The range of accepted reference ranges on which the definition of normality is based have been obtained by studying cohorts of largely Caucasian European and American healthy adults or smaller samples of black professional athletes. However, defined electrocardiographic abnormalities are found with high frequency in the disease-free state, which is especially common in healthy young black adults of African descent, where up to 50% of such patients may harbor an electrocardiographic anomaly. Many studies have attempted to relate the presence of these abnormalities to an increased risk of death, but few of them have an adequate cohort of black adults of African descent. One such abnormality, termed early repolarization (ER), entails minor degrees of ST elevation with terminal QRS deviations. Although seeming to have sudden cardiac death predictive value in some cohorts of Caucasian adults, ER has never been shown to be detrimental in black cohorts, in which it occurs with increased frequency. Although studies have previously evaluated electrocardiographic abnormalities in healthy nonathletic black cohorts, to the author’s knowledge, none have compared electrocardiographic indexes to echocardiographic data in this population.
Methods
A database of healthy disease-free volunteers from Chris Hani Baragwanath Academic Hospital Advanced Echocardiography unit was subjected to inclusion and exclusion criteria to establish a sample of black volunteers of Sub-Saharan African descent ≥18 years, which by way of history, clinical examination, and echocardiography were deemed heart disease free and without overt risk factors for future heart disease. Ethics clearance for the use of this database for research was obtained from the WITS Human Research Ethics Committee. All patients with a history of hypertension, diabetes, dyslipidemia, HIV, or cardiac and renal conditions were excluded. By definition, all patients had a diagnostic quality 12-lead ECG (0.15 to 150 Hz) and an echocardiograph with adequate views for quantitative assessment.
All ECGs were analyzed using the 2009 AHA/ACCF/HRS recommendations for the standardization and interpreting of the electrocardiogram by manual interpretation by a single reader blinded to the echocardiographic data. In addition, QRS fragmentation and features of ER abnormalities were specifically looked for and recorded. Two-dimensional echocardiography, including tissue Doppler, was performed by a single reader blinded to electrocardiographic data. Patients were excluded if they had either a reduced left ventricular ejection fraction (LVEF) <45% or any overt structural heart disease.
The services of a biomedical statistician were used in the final data analyses. Continuous variables were analyzed by the ANOVA F test, categorical variables by the chi-square, and the Pearson correlation coefficients were determined for selected variables included for multivariate analysis. A p value <0.05 was considered statistically significant.
Results
A total of 396 volunteers (63.1% women) with a mean age of 37.4 years met the inclusion and exclusion criteria. Men had a lower mean body mass index (25.1 vs 27.9 kg/m 2 , p <0.001) but a higher mean body surface area (1.8 vs 1.7 m 2 , p <0.001) than women. The mean cohort blood pressure was 123/77 mm Hg. Electrocardiographic data of the entire cohort is listed in Table 1 and electrocardiographic abnormalities stratified by gender and age in Table 2 . An abnormal ECG was identified in more than half of volunteers, largely because of underlying ST elevation at the J point (ER), left ventricular hypertrophy (LVH) by voltage criteria, and T-wave inversion. Younger men were more likely to have abnormal ECGs, display LVH by Sokolow-Lyon voltage criteria, and have ER patterns. Volunteers with LVH by voltage criteria were more likely to display T-wave inversion in the lateral leads (odds ratio 4.42; p <0.001), although this only occurred in 38.5% of cases.
| Parameter | Female (N = 250) | Male (N = 146) | Total (N = 396) | p Value |
|---|---|---|---|---|
| Abnormal ECG | 99 (39.6%) | 101 (69.2%) | 200 (50.5%) | <0.001 |
| Heart rate (beats/min) | 74.8 (12.2) | 69.1 (12.6) | 72.7 (12.6) | <0.001 |
| Intervals | ||||
| PR duration (ms) | 154.9 (21.1) | 160.4 (22.8) | 156.9 (21.9) | 0.016 |
| QTc duration (ms) | 417.9 (25.4) | 398.0 (25.0) | 410.6 (27.0) | <0.001 |
| Rhythm | ||||
| Normal sinus | 237 (94.8%) | 134 (91.8%) | 371 (93.7%) | NS |
| Sinus bradycardia | 2 (0.8%) | 4 (2.7%) | 6 (1.5%) | |
| Sinus tachycardia | 6 (2.4%) | 1 (0.7%) | 7 (1.8%) | |
| Sinus with 1 st degree AV block | 4 (1.6%) | 6 (4.1%) | 10 (2.5%) | |
| Ectopic atrial | 0 (0.0%) | 1 (0.7%) | 1 (0.3%) | |
| Junctional | 1 (0.4%) | 0 (0.0%) | 1 (0.3%) | |
| Axis | 0.023 | |||
| Normal | 235 (94.0%) | 128 (87.7%) | 363 (91.7%) | |
| Left | 8 (3.2%) | 15 (10.3%) | 23 (5.8%) | |
| Right | 5 (2.0%) | 3 (2.1%) | 8 (2.0%) | |
| P wave morphology | NS | |||
| Normal | 232 (92.8%) | 139 (95.2%) | 371 (93.7%) | |
| Right atrial enlargement (RAE) | 11 (4.4%) | 4 (2.7%) | 15 (3.8%) | |
| Left atrial enlargement (LAE) | 6 (2.4%) | 3 (2.1%) | 9 (2.3%) | |
| Biatrial enlargement | 1 (0.4%) | 0 (0.0%) | 1 (0.3%) | |
| QRS abnormalities | ||||
| Pathological q waves | 2 (0.8%) | 3 (2.1%) | 5 (1.4%) | NS |
| QRS duration >90ms | 1 (0.4%) | 4 (2.8%) | 5 (1.3%) | NS |
| LVH Sokolow-Lyon voltage | 11 (4.4%) | 35 (24.0%) | 46 (11.6%) | <0.001 |
| LVH Cornell voltage | 3 (1.2%) | 3 (2.1%) | 6 (1.5%) | NS |
| RVH (R>S V 1 + prom S V 6 ) | 1 (0.4%) | 2 (1.4%) | 3 (0.8%) | NS |
| Poor R progression/ small complexes | 23 (9.2%) | 4 (2.7%) | 27 (6.8%) | 0.014 |
| Right bundle branch block (RBBB) | 1 (0.4%) | 1 (0.7%) | 2 (0.5%) | NS |
| Repolarization abnormalities | ||||
| ST elevation at J point (V 2/3 2mm, else 1mm) | 9 (3.6%) | 61 (41.8%) | 70 (17.7%) | <0.001 |
| Inferior: II, III, aVF | 3 (1.2%) | 24 (16.4%) | 27 (6.8%) | <0.001 |
| Anteroseptal: V 2 to V 4 | 5 (2.0%) | 49 (33.8%) | 54 (13.6%) | <0.001 |
| Lateral: V 5 to V 6 , aVL, I | 5 (2.0%) | 43 (29.7%) | 48 (12.1%) | <0.001 |
| Right: aVR, V 1 (none Brugada T1 pattern) | 3 (1.2%) | 9 (6.2%) | 12 (3.0%) | 0.005 |
| ST depression >0.5mm | 1 (0.4%) | 0 (0.0%) | 1 (0.3%) | NS |
| Abnormal T wave inversion | 26 (10.4%) | 11 (7.5%) | 37 (9.3%) | NS |
| Inferior: II, III, aVF | 11 (4.7%) | 8 (5.6%) | 19 (4.8%) | NS |
| Anteroseptal: V 2 to V 4 | 21 (8.4%) | 6 (4.1%) | 27 (6.8%) | NS |
| Lateral: V 5 to V 6 , aVL, I | 8 (3.2%) | 5 (3.4%) | 13 (3.3 | NS |
| Other abnormality | <0.001 | |||
| Delta wave | 1 (0.4%) | 1 (0.7%) | 2 (0.5%) | |
| Epsilon wave | 2 (0.8%) | 26 (17.8%) | 28 (7.1%) | |
| Fragmented QRS | 4 (1.6%) | 7 (4.8%) | 11 (2.8%) | |
| PVCs >10% | 1 (0.4%) | 0 (0.0%) | 1 (0.3%) | |
| Abnormality | Males (N = 146) | Females (N = 250) | OR | p Value |
|---|---|---|---|---|
| 146 (100%) | 250 (100) | |||
| Abnormal ECG | 101 (69.2%) | 99 (39.6) | 1.75 | <0.001 |
| Abnormal axis | 18 (12.3%) | 15 (6.0%) | 2.05 | 0.023 |
| LVH (Sokolow-Lyon voltage) | 35 (24.0%) | 11 (4.4%) | 5.45 | <0.001 |
| LVH (Cornell voltage) | 3 (2.1%) | 3 (1.2%) | 1.71 | NS |
| Poor R progression/ small complexes | 4 (2.7%) | 23 (9.2%) | 0.30 | 0.014 |
| Epsilon wave | 26 (17.8%) | 2 (0.8%) | 22.26 | <0.001 |
| ST elevation at J point (V 2/3 2mm, else 1mm) | 61 (41.8%) | 9 (3.6%) | 11.61 | <0.001 |
| Inferior: II, III, aVF | 24 (16.4%) | 3 (1.2%) | 13.70 | <0.001 |
| Anteroseptal: V 2 to V 4 | 49 (33.8%) | 5 (2.0%) | 16.90 | <0.001 |
| Lateral: V 5 to V 6 , aVL, I | 43 (29.7%) | 5 (2.0%) | 14.83 | <0.001 |
| Right: aVR, V 1 (none Brugada TI pattern) | 9 (6.2%) | 3 (1.2%) | 5.14 | 0.005 |
| ST segment slope in leads with ST elevation | 61 (100%) | 9 (100%) | ||
| Ascending | 33 (54.1%) | 3 (33.3%) | 1.62 | NS |
| Descending | 1 (1.6%) | 0 (0.0%) | NS | |
| Horizontal | 15 (24.6%) | 2 (22.2%) | 1.11 | NS |
| ST depression >0.5mm | 0 (0.0%) | 1 (0.4%) | NS | |
| Abnormal T wave inversion | 11 (7.5%) | 26 (10.4%) | 0.72 | NS |
| Inferior: II, III, aVF | 8 (5.6%) | 11 (4.7%) | 1.20 | NS |
| Anteroseptal: V 2 to V 4 | 6 (4.1%) | 21 (8.4%) | 0.45 | NS |
| Lateral: V 5 to V 6 , aVL, I | 5 (3.4%) | 8 (3.2%) | 1.04 | NS |
| Abnormality | Age >36 (N = 193) | Age ≤36 (N = 205) | OR | P Value |
|---|---|---|---|---|
| 193 (100%) | 205 (100%) | |||
| Abnormal ECG | 93 (48.2%) | 109 (53.2%) | 0.91 | NS |
| LVH (Sokolow-Lyon voltage) | 12 (6.2%) | 34 (16.6%) | 0.37 | 0.001 |
| LVH (Cornell) | 4 (2.1%) | 2 (1.0%) | 2.12 | NS |
| Poor R progression/ clockwise rotation | 21 (10.9%) | 6 (2.9%) | 3.72 | 0.002 |
| Epsilon wave | 9 (4.7%) | 20 (9.8%) | 0.48 | NS |
| ST elevation at J point (V 2/3 2mm, else 1mm) | 26 (13.5%) | 46 (22.4%) | 0.60 | NS |
| Inferior II, III, aVF | 5 (2.6%) | 24 (11.7%) | 0.22 | 0.001 |
| Anteroseptal V 2 to V 4 | 20 (10.4%) | 35 (17.1%) | 0.61 | NS |
| Lateral V 5 to V 6 , aVL, I | 18 (9.3%) | 32 (15.7%) | 0.59 | NS |
| Right aVR, V 1 (none Brugada TI pattern) | 6 (3.1%) | 6 (2.9%) | 1.06 | NS |
| Abnormal T wave inversion | 22 (11.4%) | 15 (7.3%) | 1.56 | NS |
ER was most commonly found in anterior and lateral electrocardiographic leads, with a lower contribution from inferior leads and more rarely in the right precordial leads. Of importance, none of the patients with right precordial ST J-point elevation met criteria for type 1 Brugada pattern. Although an associated epsilon wave was commonly seen in ER ECGs, it was present in <50% of cases. The ST-segment slope in ER cases was ascending in most cases, with a horizontal ST segment seen less frequently. A descending ST segment was exceedingly rare.
The associations of electrocardiographic data with echocardiographic measures, including electrocardiographic data of the 6 volunteers found to have LVH confirmed on echocardiography, are listed in Table 3 . Although neither LVH by voltage criteria or any repolarization abnormality in this cohort was not predictive for LVH on echocardiography, volunteers with LVH by ECG had 5.7% higher mean LV mass indexes (p = 0.047). P-wave abnormalities were not correlated with atrial enlargement in our cohort, although the numbers were small. Importantly, an abnormal ECG was not associated with a reduced LVEF or any echocardiographic measures of diastolic dysfunction.
| Echo parameter | − ECG abnormality | + ECG abnormality | p Value |
|---|---|---|---|
| Normal ECG | Abnormal ECG | ||
| Left ventricular ejection fraction (LVEF) | 62.8 (6.6) | 62.4 (6.2) | NS |
| Normal axis | Abnormal axis | ||
| Left ventricular mass index (LVMI) | 66.9 (16.8) | 75.9 (15.6) | 0.017 |
| No LVH by voltage | LVH by voltage | ||
| Left ventricular mass index (LVMI) | 66.7 (16.4) | 72.4 (18.9) | 0.047 |
| Parameter | Correlated ECG Parameter | r | p Value |
|---|---|---|---|
| Left atrial volume index | QTc interval | -0.1392 | 0.0062 |
| Age | QTc interval | 0.2150 | <0.0001 |
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