Introduction
Abnormalities in left ventricular function are well described in vertically infected HIV-positive children [1–4]. Although antiretroviral therapy (ART) is effective in preventing the vertical transmission of HIV during pregnancy and parturition, HIV-negative children exposed to ART in utero may have depressed left ventricular contractility, lower left ventricular mass and resting tachycardia [4–6]. Subclinical left ventricular dysfunction in HIV-negative children born to HIV-positive women and exposed to ART may be clinically relevant given the relationship in adults between subclinical left ventricular dysfunction and the progression to overt heart failure [7,8]. Earlier studies [4,5,9] have shown left ventricular morphologic and systolic abnormalities are present in HIV-negative infants exposed to HIV and ART in utero that persists throughout preschool age. However, it is currently unclear if left ventricular dysfunction in these children persists, worsens, or resolves in preadolescence. It is also unknown if diastolic function is altered in HIV-negative children exposed to ART but may be important due to the prognostic value of diastolic function in predicting clinical outcomes in children with known cardiac disease [10]. Therefore, the objective of this study was to characterize left ventricular systolic and diastolic function in HIV-negative preadolescent children exposed to ART in utero and compare them with healthy unexposed children. We hypothesized that abnormalities in left ventricular morphology and left ventricular function would be present in HIV-negative preadolescent ART-exposed children compared with unexposed children.
Participants
Thirty preadolescent HIV-negative children (8–12 years) born to HIV-positive women and exposed to ART in utero [ART(+)] and 30 HIV-negative age, sex, and race matched HIV-negative children (8–12 years) born to HIV-negative women [ART(−)] were compared. ART-exposed children were recruited from a convenience sample of women attending the AIDS Clinical Trials Unit at Washington University School of Medicine (WUSM) and all were enrolled in routine pediatric care. Children born to HIV-negative women were recruited through WUSM volunteers for health. ART(+) children received prophylactic ART for at least 6 weeks postpartum. None of the children had been diagnosed with growth restriction or cardiovascular/metabolic disease and were not taking medications that would affect left ventricular function. HIV-positive women received ART during pregnancy according to standard-of-care (10% monotherapy with zidovudine and 90% combination ART) and all but one had intravenous zidovudine during parturition. None of the women had a diagnosis of prepregnancy or gestational diabetes. The study was approved by the WUSM Human Research Protection Office and all children/parents provided written assent/consent prior to participation.
Procedures
Echocardiography
A complete two-dimensional Doppler and tissue-Doppler echocardiographic examination was conducted (General Electric, Milwaukee, Wisconsin, USA). Left ventricular end-diastolic and end-systolic volumes and left ventricular mass were determined according to recommendations of the American Society of Echocardiography [11]. Pulsed-wave Doppler mitral inflow velocities of early left ventricular filling (E) and atrial filling (A) were obtained at the mitral leaflet tips in the apical four-chamber view. Tissue-Doppler imaging (TDI) was performed in the apical four-chamber view to determine the peak systolic shortening velocity (S′) and early diastolic myocardial relaxation velocity (E′) for regional assessment of systolic and diastolic function, respectively [12]. E′ and S′ were calculated by averaging the velocities of the lateral and septal base as recommended [13]. The ratio of mitral E-wave to E′ velocity was derived as an estimate of left ventricular filling pressure. Color TDI-derived longitudinal strain imaging was performed at the lateral and septal base to derive peak systolic strain. All echocardiograms were performed and analyzed by one of the authors, unaware of the maternal or child history.
Statistical analysis
Sample size was based on anticipated differences in neonatal systolic function (fractional shortening, strain) between groups and was based on data from Lipshultz et al. [4] and a previous study from our institution [14]. Comparisons of outcome parameters were performed by independent t-tests, Mann–Whitney U-test, or linear regression, as appropriate. Regression models were then run with group as the primary predictor of interest, adjusting for sports participation and hours of daily television viewing, as these variables tended to differ between groups. Within HIV-positive women, backward elimination linear regression was used to examine the relationship between HIV-related and specific left ventricular function variables, whereas also considering child and maternal demographics, maternal smoking/cocaine use, and maternal pregnancy characteristics. Variables remaining in the model were those with P-value less than 10. Beta coefficients, standard errors, P-values, and the overall R2 of the final models are reported. Statistical significance was determined at P-value less than 0.05.
Results
Demographics
Age, sex, race, anthropometric, and birth characteristics were similar between groups (Table 1). Seventy-three percentage of HIV-positive women used lamivudine/zidovudine (among others) and 43% of HIV-positive women took a protease inhibitor during pregnancy. A greater percentage of HIV-positive women had lower third trimester blood pressure than HIV-negative women (Table 1). Other maternal characteristics during pregnancy were similar between HIV-positive and HIV-negative women (Table 1).
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Table 1: Maternal and child demographics.
Left ventricular function
Results with and without statistically controlling for organized sport participation and TV viewing were similar, therefore, data are presented without statistical controlling for these variables. There was no difference in resting heart rate between groups. Left ventricular mass index was significantly lower in ART(+) than ART(−) children (Table 2). Other variables of left ventricular structure and function including TDI-derived peak systolic strain did not differ between groups. The diastolic mitral early (E) to late (A) mitral inflow velocity ratio (E/A) tended to be lower in ART(+) children compared with ART(−) children. Early diastolic annular velocity (E′) was significantly lower in ART(+) children compared with ART(−) children (Table 2).
Table 2: Echocardiographic parameters of children.
Regression analysis
Multivariate analysis revealed that older maternal age (β = −1.2, P < 0.06) and lower maternal third trimester CD4 count (β = 0.04, P < 0.01) were independently associated with lower E′ (R2 = 0.37). Maternal cocaine use during pregnancy was associated with significantly lower left ventricular mass index (β = −12.95, P < 0.001). Males (β = 7.34, P < 0.001) and older children (β = 1.63, P < 0.001) had higher left ventricular mass index (model = R2 = 0.66) as expected. No HIV-related variables were significantly associated with left ventricular mass index. Smoking during pregnancy (β = −2.87, P < 0.03), maternal prior hypertension (β = −4.17, P < 0.04), or preeclampsia (β = −3.67, P < 0.02), and increasing gestational age (β = −0.57, P < 0.001) were independently associated with lower peak systolic strain (R2 = 0.66).
Discussion
The results of this study demonstrate the identification of reduced (but within normal limits) left ventricular diastolic function in HIV-negative preadolescent children exposed to ART in utero and postpartum. To our knowledge, this is the first study to characterize left ventricular diastolic function, in addition to systolic function and left ventricular structure, in HIV-negative children exposed to ART in utero and suggest that exposure to ART has residual effects on left ventricular diastolic function through preadolescence. These data also are consistent with the CHAART-1 and P2C2 HIV studies [1,3,5,9] demonstrating that morphologic alterations persist but indicate that systolic function abnormalities in ART-exposed infants and preschool age children may resolve by preadolescence; however, this needs to be confirmed by large, longitudinal studies.
Our finding that myocardial relaxation based on TDI-derived E’ was lower in HIV-negative children exposed to ART is novel. Previous studies in ART-exposed children have demonstrated reduced end diastolic volumes [4,5], however, the authors did not report TDI-derived myocardial velocities or Doppler-derived inflow velocities during diastole as in the current study. TDI is an alternative method to measure diastolic function that complements traditional two-dimensional and Doppler analyses to detect diastolic abnormalities [13] and may be more sensitive as it is relatively loaded independent [15]. Impaired diastolic function has been reported in adults with HIV [16–19] and has been associated with HIV infection [18,20,21], depressed immune function [22], and advanced disease [23]. Altered diastolic function in those with HIV has also been associated with impaired whole-body and myocardial glucose metabolism [24]. These findings may be consistent with the fetal origins hypothesis wherein an abnormal metabolic environment in utero is reported to be associated with future cardiovascular disease [25]. Prior studies have reported that ART may contribute to impaired diastolic function in adults [26]; however, this is unclear in children [27]. Animal studies suggest that nucleoside reverse transcriptase inhibitors may result in cardiomyopathic effects when administered in high doses [28] including mitochondrial ultrastructural abnormalities [29] and mtDNA depletion and mutations [30] through the inhibition of DNA polymerase gamma [31]. It is possible that exposure to ART in utero may impair energy-dependent myocardial relaxation secondary to altered mitochondrial function in children born to HIV-positive women.
The clinical implications of lower diastolic function in children exposed to ART are unclear. Impaired myocardial relaxation in HIV-negative adults with heart disease has important clinical implications as diastolic dysfunction frequently precedes left ventricular systolic dysfunction [7,8,32]. In children with dilated cardiomyopathy, lower E’ is associated with increased rates of adverse clinical outcomes and hospitalizations [10]. It is possible that in ART-exposed children during adolescence and early adulthood, lower diastolic function coupled with accumulating cardiovascular risk factors (e.g., obesity, inactivity, insulin resistance) could lead to worsening diastolic function and future systolic dysfunction [7,8]. This is speculative, but overall, our results are consistent with Lipshultz et al.[3] and agree that monitoring of left ventricular function in ART-exposed children should be considered through adolescence and likely into adulthood.
Our study extended the previous findings of lower left ventricular mass in HIV-negative infants and preschool age children exposed to ART [4,5] showing that this left ventricular structural difference persists into preadolescence. The mechanism for lower left ventricular mass in ART-exposed children is unknown but may be due to abnormal myocyte development as previously demonstrated in rodents who were exposed to ART in utero[33,34]. Cardiac growth as assessed by left ventricular mass is positively associated with higher myocardial relaxation velocities in healthy children [12], thus, lower left ventricular mass in ART-exposed children may have contributed to the differences in diastolic function between groups in the current study. Interestingly, whole-body growth was shown to be stunted in uninfected children exposed to ART [35] suggesting ART exposure may impede both antenatal and postnatal growth.
Limitations: the study design was cross-sectional and measurements of left ventricular function were not obtained in participants at birth, during infancy or preschool age and as such longitudinal changes in left ventricular function were not determined. Due to the small sample size, it is possible that the echo-Doppler variables may be different if conducted in a larger population. It was not possible to determine whether the differences in left ventricular function were attributable to maternal illicit drug use, maternal blood pressure, or more sedentary lifestyles of the HIV-positive cohort and because all participants took prophylactic ART for at least 6 weeks, we cannot discern whether the effect was due to exposure to ART in utero, during the postpartum period, or both.
Conclusion
HIV-negative preadolescent children exposed to ART in utero and postpartum have lower values of left ventricular diastolic function and left ventricular mass compared with their peers but the clinical implications remain unclear. Differences in left ventricular systolic function previously reported in infancy were not present in preadolescence. Additional data are required to determine whether echocardiographic evaluations are needed for children exposed to ART throughout adolescence and adulthood.
Acknowledgements
Funding: NIH Clinical Trials #NCT01107834. This project was supported by the HiiV HIV Collaborative Investigator Research Award Program and by National Institutes of Health AIDS Clinical Trials Unit (AI-069495), National Center for Research Resources (NCRR, RR024992) and NIH Roadmap for Medical Research.
Conflicts of interest
There are no conflicts of interest.
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