Download African Americans have a markedly increased prevalence of left

Additional details of Methods
Dallas Heart Study
Details of the design and methods of the Dallas Heart Study have been reported
elsewhere.1 We conducted a multistep probability sample of the estimated 1.43 million
civilian, non-institutionalized English- or Spanish- speaking Dallas County residents
based on the U. S. Postal Service 2000 Delivery Sequence File. African Americans were
oversampled to ensure that they represented 50% of the final cohort. Eligible subjects
were invited to participate in three stages of the project: an initial home visit during
which a household survey was administered (ages 18 – 65, n=6101), a second home visit
(ages 30 – 65, n= 3398) during which blood and urine specimens were obtained, and a
third visit at the University of Texas at Southwestern Medical Center (n=2971, ages 3067). Of the latter subjects, 2707 (91%) underwent cardiac MRI and 264 subjects did not
(n=164 African American, n=65 white, n=32 Hispanic, n=3 other). The most common
reason that a cardiac MRI was not performed was claustrophobia (n=182, 6% of eligible
cohort) or the participant had a contra-indication to MRI (usually metal in the body,
n=48, 1.6%). In comparing subjects who did or did not have a cardiac MRI, those with a
MRI had a lower systolic blood pressure, BMI, and age than those who did not have a
MRI, both for African Americans (systolic blood pressure: 131 ± 18 vs. 134 ±16 mm Hg,
p=0.09; BMI: 31 ± 8 vs. 36 ± 11 kg/m2, p<0.001; age: 46 ± 9 vs. 47 ± 9 years, p=0.05,
respectively) and for whites (systolic blood pressure: 123 ± 13 vs. 128 ± 15 mm Hg,
p=0.01; BMI: 29 ± 6 vs. 34 ± 9 kg/m2, p<0.001; age: 46 ± 9 vs. 49 ± 9 years, p=0.02,
respectively).
1
Survey Instrument
A 60 minute computer-assisted interview was conducted at the first home visit by trained
field interviewers. Detailed information regarding socioeconomic status was gathered
including level of completed education, income, and indices of self-reported financial
strain.
Cardiac MRI
MRI was performed using two comparable 1.5 Tesla MRI systems (Philips Medical
Systems). Briefly, short-axis breath-hold, electrocardiographic-gated cine MR images
were obtained from the apex to the base of the left ventricle using the following
parameters: 6mm slice, 4mm gap, field of view of 36-40, acquired pixel size at 36cm
field of view 1.29 x 2.58, and temporal resolution of 40 msec. Data were analyzed using
the MASS software (Medis medical imaging systems, Leiden, The Netherlands).
Endocardial and epicardial borders were traced manually to measure LV cavity and wall
volume in each slice. Measurements from each slice were summed using the method of
disks. Myocardial mass was estimated by multiplying the myocardial wall volume at
end-diastole by the specific gravity of muscle (1.05 gm/ml). The papillary muscles were
included in the myocardial mass. LVEF was calculated in the standard fashion from the
endocardial volumes: ejection fraction = 100*(end-diastolic volume – end-systolic
volume)/end-diastolic volume. To determine inter-scan variability, patients were scanned
once, taken off the scanner briefly, and then rescanned. Interobserver difference for LV
mass was 9.2 ±5 grams (5.8 ± 3.5%, n=15), intraobserver was 10.5 ± 8.6 grams (7.1 ±
6.0 %, n=8), and interscan variability was 4.9 ± 10.9 grams (2.9 ± 7.5%, n=8).
2
Defining left ventricular hypertrophy
We identified a subpopulation (n=380) of the Dallas Heart Study who were free of
hypertension (systolic blood pressure < 140 mm Hg and diastolic blood pressure < 90
mm Hg at each visit and no self-reported hypertensive therapy), were normal weight
(BMI 18.5 through 25 kg/m2), were not diabetic or vigorous athletes (e.g., rowers,
weightlifters, or bicyclists), had no history of myocardial infarction, and had LVEF 
0.55. The ethnic composition of the subpopulation was 140 African American, 166 white,
59 Hispanic, and 15 Other. The mean systolic blood pressure was 114 ± 9 mm Hg and
mean BMI 22 ± 1.6 kg/m2. We dichotomized by gender (n=213 women; n=167 men) and
defined gender-specific values of LVH as the 97.5% percentile of this reference
population: LV mass/body surface area (BSA) 89 g/m2 (women) and 112 g/m2 (men), LV
mass/height2.7 39 g/m2.7 (women) and 48 g/m2.7 (men), LV mass/fat-free mass 3.7 g/kg
(men and women).
3
References for online supplement
1.
Victor RG, Haley RW, Willett DL, Peshock RM, Vaeth PC, Leonard D, Basit M,
Cooper RS, Iannacchione VG, Visscher WA, Staab JM, Hobbs HH. The Dallas
Heart Study: a population-based probability sample for the multidisciplinary
study of ethnic differences in cardiovascular health. Am J Cardiol. 2004;93:14731480.
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