Date of Award

5-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Nursing

Research Advisor

Patricia A. Cowan, Ph.D.

Committee

Donna S. Husch, Ph.D. Zoila V. Sanchez, Ph.D. Glenn T. Wetzel, Ph. D. Mona N. Wicks, Ph.D.

Keywords

adolescents, heart rate variability, impaired glucose tolerance, left ventricular hypertrophy, obesity, QT

Abstract

The prevalence of childhood obesity has increased remarkably within the past ten years with black youth disproportionately affected. Childhood obesity is linked to cardiovascular risk. Purposes of this study were to explore relationships between cardiac autonomic risk factors of heart rate variability (HRV), QT corrected (QTc) Interval duration, and Cornell voltage measures for left ventricular hypertrophy (LVH) to body mass index (BMI), relative body mass index (RBMI), and blood pressure (BP) measures, and to examine the effects of impaired glucose tolerance (IGT), hypertension, and race on these cardiac autonomic risk factors in overweight-obese adolescents.

Methods: Overweight and obese adolescents (N = 128), ages 11-18 years, (60.2% black, 63.3% female) were included in this secondary data analysis. During the original study BMI, resting BP, 12-lead electrocardiogram (ECG), and 24-hour Holter measures were obtained. Overweight was defined as BMI ≥ 85th percentile on age-gender specific growth charts and obesity as ³ 95th percentile. Systolic or diastolic BP > 90th percentile for age, height, and sex was considered elevated BP. An oral glucose tolerance test (1g of dextrose/kg with a maximum of 75 g) or mixed meal tolerance test [(Sustacal/Boost) (6 kcal/kg, body weight, max 360 kcal)] was conducted with IGT defined as either a fasting blood glucose ³ 100 and < 126 mg/dl or 2-hr post-load glucose ³ 140 and < 200 mg/dl based on the American Diabetes Association criteria. Holter data were analyzed for HRV time and frequency domain measures of circadian fluctuation (SDNN) and parasympathetic function (high frequency; HF) using Multi-parameter Arrhythmia Review Station (MARS) PC Analysis and Editing system. QTc and Cornell voltage (Sv3 + RaVL) measurements for LVH were obtained from a 12-lead ECG.

Results: In the total sample, 28% had IGT, 34% had prolonged QTc, 51% met criteria for elevated BP, and none met Cornell criteria for LVH. BMI and RBMI did not correlate with HRV measures, QTc, or Cornell voltage. Systolic BP was modestly correlated to Cornell voltage (r = 0.231, p = 0.009). No significant difference was noted between glucose tolerance groups for HRV (HF, p = 0.25; SDNN, p = 0.108), QTc (p = 0.59), or Cornell voltage (p = 0.33). However, the IGT group tended to have a higher frequency of elevated BP (64% vs. 47%, χ = 3.047, p = 0.08). There was no significant difference in HF (p = 0.31), SDNN (p = 0.80), and QTc (p = 0.92) between BP groups. However, overweight-obese adolescents with elevated BP displayed significantly higher measures of Cornell voltage (0.95 mV vs. 0.76 mV, p = 0.004) than non-hypertensive peers. No significant difference was identified between blacks vs. whites for HF (p = 0.106), QTc (p = 0.599), or Cornell voltage (p = 0.965) measures, however black youth displayed significantly lower SDNN (p < 0.001). The prevalence of IGT was similar between racial groups (28.57% vs. 27.45%, χ = 0.01, p = 0.890).

Conclusion: Obesity alone is an independent factor for cardiovascular risk. Screening for QTc and LVH using Cornell voltage measurements for LVH using 12-lead ECG is recommended in all overweight-obese youth. Further studies examining a more diverse weight group should be considered.

DOI

10.21007/etd.cghs.2009.0176

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