Methods

The HCHS/SOL is a population-based cohort study designed to examine risk and protective factors for chronic diseases and quantify morbidity and mortality prospectively. Details of the sampling methods and design have been published. Briefly, from March 2008 to June 2011, 16,415 self-identified Hispanic/Latino subjects from diverse background (Cubans, Dominicans, Mexicans, Puerto Ricans, Central Americans, and South Americans) aged 18 to 74 years were examined. Participants were recruited from randomly selected households in 4 United States communities (Bronx, New York; Chicago, Illinois; Miami, Florida; and San Diego, California). Households were selected using a stratified 2-stage area probability sample design. Census block groups were randomly selected in the defined community areas of each field center, and households were randomly selected in each sampled block group. Households were screened for eligibility, and Hispanic/Latino subjects aged 18 to 74 years were selected in each household agreeing to participate. Oversampling occurred at each stage, with block groups in areas of Hispanic/Latino concentration, households associated with a Hispanic/Latino surname, and subjects aged 45 to 74 years selected at higher rates than their counterparts. Sampling weights were generated to reflect the probabilities of selection at each stage. The study was approved by the institutional review board at each participating institution; written informed consent was obtained from all participants.

The study design, protocol, and implementation have been previously published in detail. The baseline examination included medical history, medication use, family history, tobacco use, anthropometry, blood pressure, phlebotomy for laboratory studies, and an electrocardiography. Major CVD risk factors were defined based on current national guidelines.

Hypercholesterolemia and dyslipidemia were defined as a total cholesterol level of ≥240 mg/dl, low-density lipoprotein cholesterol level of ≥160 mg/dl, or high-density lipoprotein cholesterol level of <40 mg/dl (for subjects with and without diabetes) or receiving cholesterol-lowering medication. Hypertension was defined as systolic blood pressure ≥140 mm Hg and diastolic blood pressure ≥90 mm Hg or receiving antihypertensive medication. Diabetes mellitus was defined as a fasting plasma glucose level of ≥126 mg/dl, a 2-hour postload plasma glucose level of ≥200 mg/dl, a hemoglobin A1c level of ≥6.5%, or the use of antihyperglycemic medications. Blood pressure and heart rate were measured by standard epidemiology procedures (5-minute rest, 3 measurements), using an automated blood pressure device (Omron model HEM-907 XL; Omron Healthcare Inc, Bannockburn, Illinois) in a seated position. Smoking status was categorized as current smoker, past smoker, and never smoked. A positive family history of CVD was defined as answering yes to the question of having a first-degree relative who had a heart attack at age <55 years. The presence of previous CVD was ascertained by answering yes to the questions of having had previous heart attack, coronary revascularization (coronary artery bypass grafting, percutaneous transluminal coronary angioplasty, or stent), rheumatic heart disease, heart failure, or stroke or transient ischemic attack. Electrocardiograms were obtained after an overnight fast and at least 2 hours after glucose load administration.

Standard, 10-second, simultaneous, 12-lead electrocardiogram at rest was digitally acquired using a GE MAC 1200 electrocardiograph (GE, Milwaukee, Wisconsin) at 10 mm/mV calibration and a speed of 25 mm/s. ECG reading was performed centrally at the Epidemiological Cardiology Research Center, Wake Forest School of Medicine, Winston Salem, North Carolina. All electrocardiograms were initially inspected visually for technical errors and inadequate quality before being automatically processed using GE 12-SL Marquette Version 2001 (GE, Milwaukee, Wisconsin). ECG abnormalities were classified and coded using the Minnesota ECG Classification. In addition to the individual ECG abnormalities, ECG tracings were classified as having a major or minor abnormality. Participants with only minor ECG abnormalities were classified as having “any minor abnormalities”, and participants with major ECG abnormalities with or without coexisting minor ECG abnormalities were classified as having “any major ECG abnormalities”. Major ECG abnormalities included major ventricular conduction defect; definite myocardial infarction (defined as the presence of major Q-wave abnormalities); possible myocardial infarction (defined as the presence of minor Q-QS wave plus major ST-T abnormalities); major isolated ST-T abnormalities; left ventricular hypertrophy plus major ST-T abnormalities; major atrioventricular conduction abnormalities; and major QT prolongation (QT interval ≥116% or JTI if QRS interval ≥120 ms), pacemaker, and other major arrhythmias. Minor ECG abnormalities included minor isolated Q-QS waves, minor isolated ST-T abnormalities, high R waves, ST segment elevation, incomplete right bundle branch block, minor QT prolongation (QT interval ≥112% or JTI if QRS interval ≥120 ms), short PR interval, left-axis deviation, right-axis deviation, frequent ventricular premature beats, and other minor abnormalities.

In addition to the Minnesota code–defined ECG abnormalities, the automatically calculated global measurements of QT, PR, and QRS intervals were also obtained. To calculate corrected QT (QTc) interval from the raw QT and heart rate, recommendation of using linear models for adjustment for QTc from the American Heart Association, American College of Cardiology, and Heart Rhythm Society for the Standardization and Interpretation of the Electrocardiogram was followed. Therefore, the Framingham linear regression formula {QTc = QT + 0.154 [1 − (60/heart rate)]} was used. QTc values of ≥460 ms in women and ≥450 ms in men were considered abnormal (i.e., prolonged QTc).

The HCHS/SOL cohort was recruited with the use of a stratified 2-stage area probability sampling design in which participant’s households were sampled from augmented residential mailing lists from preselected census block groups within each of the 4 regional field centers. The target population was the noninstitutionalized Hispanic/Latino population aged 18 to 74 years residing in the defined community areas. Trimmed normalized sampling weights adjusted for nonresponse for enumerated but nonenrolled household members were derived and later calibrated to the 2010 US Census. Complete details of the sampling design have been reported in a technical report prepared by the study coordinating center. To account for the complex sampling design, all reported means and proportions are weighted. Model-based means, proportions, odds ratios, and p values were obtained by fitting linear and logistic regression models for complex survey data. Standard errors were computed using Taylor linearization method. All analyses were performed using SAS 9.3 survey specific procedures (SAS Institute, Cary, North Carolina). Participants with missing ECG readings (n = 203) and missing data on CVD risk factors (n = 284), which includes 9 participants >74 years old, and 152, 49, 18, 71, 144, and 13 missing ≥1 of serum cholesterol, BMI, blood pressure, smoking, family history of CVD, or diabetes status, respectively, and CVD status variables (n = 116) were excluded from all analyses, leaving 15,812 participants in the analysis sample. To preserve the study design and ensure that the standard errors are computed correctly, the exclusions were made using the DOMAIN statement in SAS survey procedures. Weighted prevalence percentages have been age standardized to the year 2000 Census to make them more comparable to National Health and Nutrition Examination Survey data.

Results

Baseline characteristics of the study group are listed in Table 1 . At baseline examination, men had greater prevalence of a history of hypercholesterolemia, being current smokers, having a history of heart attack and coronary revascularization; they had higher systolic and diastolic blood pressures. Women were older, more obese, and had faster heart rates.

The prevalent age-adjusted major and minor ECG abnormalities comparing men and women are listed in Table 2 . Major ECG abnormalities were more frequent in men. The 3 more common major ECG abnormalities in men were major Q waves (Minnesota code [MC] 1.1 and 1.2), ventricular conduction defects (MC 7.1, 7.2, 7.4, and 7.8), and major isolated ST-T abnormalities (MC 4.1, 4.2, 5.1, or 5.2). In women, these ECG abnormalities had also the highest prevalence, but compared with men, the prevalence of major Q waves (MC 1.1 and 1.2) and ventricular conduction defects (MC 7.1, 7.2, 7.4, and 7.8) were significantly less and major isolated ST-T abnormalities (MC 4.1, 4.2, 5.1, or 5.2) were greater. There were significant differences in the prevalence of certain minor ECG abnormalities. Men had a greater prevalence of minor isolated Q waves (MC 1.3), tall R waves (MC 3.1, 3.3, and 3.4), ST elevation (MC 9.2), incomplete right bundle branch block (MC 7.3), left-axis deviation (MC 2.1), frequent ventricular premature beats (MC 8.1.2 and 8.1.3), and sinus bradycardia (MC 8.8). Women had a greater prevalence of minor isolated ST-T abnormalities (MC 4.3, 4.4, 5.3, and 5.4), low QRS voltage (MC 9.1), and minor QT prolongation index.

The comparison of the prevalent ECG findings and major and minor ECG abnormalities by CVD risk status or disease in men and women is listed in Tables 3 and 4 . There was a significant trend, in both men and women, for increasing heart rate, QRS and QTc duration, and QT prolongation index as the number of CVD risk factors increased or in the presence of prevalent CVD, compared with those with no CVD risk factors. Examining major ECG abnormalities in men, there was a significant trend for increasing prevalence of major Q waves (MC 1.1 and 1.2), major isolated ST-T abnormalities (MC 4.1, 4.2, 5.1, or 5.2), left ventricular hypertrophy plus major ST-T abnormality (MC 3.1 + [4.1, 4.2, 5.1, or 5.2]), and ventricular conduction defects (MC 7.1, 7.2, 7.4, and 7.8) with the number of CVD risk factors and prevalent CVD. The prevalence of any major ECG abnormality was 6.22% in men without CVD risk factors or disease and 28.44% in those with prevalent CVD. In women, the prevalence of any major ECG abnormality was 5.40% in those without CVD risk factors or disease and 16.71% in those with prevalent CVD. In women, significant trends were observed for the presence of major Q waves (MC 1.1 and 1.2), major isolated ST-T abnormalities (MC 4.1, 4.2, 5.1, or 5.2), left ventricular hypertrophy plus major ST-T abnormality (MC 3.1 + [4.1, 4.2, 5.1, or 5.2]), and major QT prolongation index (QT interval ≥116%) with the number of CVD risk factors and prevalent CVD. Examining minor ECG abnormalities in men, there was a significant trend for greater prevalence of minor isolated ST-T abnormalities (MC 4.3, 4.4, 5.3, and 5.4) with greater risk factor burden. An inverse trend for ST elevation (MC 9.2) and sinus bradycardia was present with greater risk factor burden. ST elevation (MC 9.2) was observed in 15.24% of men without CVD risk factors or disease; these were most commonly seen in the inferior leads. In women, significant trends were observed for the presence of minor isolated Q waves (MC 1.3), minor isolated ST-T abnormalities (MC 4.3, 4.4, 5.3, and 5.4), and tall R waves (MC 3.1, 3.3, and 3.4) across the risk factor burden groups. ST elevation in women showed no reverse trend, and the prevalence was less (0.78%) in those without CVD risk factors or disease.

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