Intra-familial aggregation and heritability of aortic versus brachial pulse pressure after imputing pretreatment values in a community of African ancestry

Associations between PHACTR1 gene polymorphisms and pulse pressure in Chinese Han population

A genome-wide association study (GWAS) in Chinese twins was performed to explore associations between genes and pulse pressure (PP) in 2012, and detected a suggestive association in the phosphatase and actin regulator 1 (PHACTR1) gene on chromosome 6p24.1 (rs1223397, P=1.04e⁻⁰⁷). The purpose of the present study was to investigate associations of PHACTR1 gene polymorphisms with PP in a Chinese population. We recruited 347 subjects with PP ≥ 65 mmHg as cases and 359 subjects with 30 ≤ PP ≤ 45 mmHg as controls. Seven single nucleotide polymorphisms (SNPs) in the PHACTR1 gene were genotyped. Logistic regression was performed to explore associations between SNPs and PP in codominant, additive, dominant, recessive and overdominant models. The Pearson’s χ² test was applied to assess the relationships of haplotypes and PP. The A allele of rs9349379 had a positive effect on high PP. Multivariate logistic regression analysis showed that rs9349379 was significantly related to high PP in codominant [AA vs GG, 2.255 (1.132–4.492)], additive [GG vs GA vs AA, 1.368 (1.049–1.783)] and recessive [AA vs GA + GG, 2.062 (1.051–4.045)] models. The positive association between rs499818 and high PP was significant in codominant [AA vs GG, 3.483 (1.044–11.613)] and recessive [AA vs GG + GA, 3.716 (1.119–12.339)] models. No significant association of haplotypes with PP was detected. There was no significant interaction between six SNPs without strong linkage. In conclusion, the present study presents that rs9349379 and rs499818 in the PHACTR1 gene were significantly associated with PP in Chinese population. Future research should be conducted to confirm them.

Aortic Pulse Pressure Amplification Imputed From Simple Clinical Measures Adds to the Ability of Brachial Pressure to Predict Survival

BACKGROUND

Although aortic-to-brachial pulse pressure amplification (PPamp) may offer prognostic information beyond brachial blood pressure (BP), this approach is limited in resource-limited settings. We aimed to derive an equation to impute central aortic PP (PPc) from simple clinical measures and assess whether imputed PPamp adds to the ability of brachial BP to predict mortality.

METHODS

An imputation equation for PPc, incorporating brachial PP, age, mean arterial pressure, and pulse rate, was identified from multivariate modeling of the factors associated with radial applanation tonometry-derived (measured) PPc in 1,179 community participants and validated in a clinical sample of 351 patients. We applied the equation to ambulatory awake BP and pulse rate values in a separate group of 4,796 patients referred for ambulatory monitoring and evaluated the impact on all-cause mortality.

RESULTS

Imputed PPc values closely approximated measured PPc (r (2) = 0.96, mean difference ± (2 × SD) = 1.4±6.2mm Hg). In adjusted Cox proportional models including adjustments for awake brachial PP during 47,111 person-years of follow-up, where 648 patients died, hazards ratio for all-cause mortality per SD of awake PPamp was 0.79 (95% confidence interval (CI): 0.68-0.93, P < 0.005). The hazards ratio for brachial PP with (1.49, CI = 1.36-1.64, P < 0.0001) or without (1.46, CI = 1.35-1.59, P < 0.0001) PPamp in the model was similar. Awake PPamp also predicted survival independent of awake brachial systolic BP (P < 0.0001).

CONCLUSIONS

PPc imputed from simple clinical assessments closely approximates measured PPc. PPamp derived from imputed PPc adds to the ability of brachial BP to predict survival. In resource-limited settings, an imputation equation may be employed to approximate aortic BP and enhance risk prediction.

Intrafamilial aggregation and heritability of tissue Doppler indexes of left ventricular diastolic function in a group of African descent

Although several indexes of left ventricular (LV) diastolic function show heritability, the genetic influence on the tissue Doppler index, E/e' (early transmitral velocity/velocity of myocardial tissue lengthening), an index of LV filling pressures in those of black African descent is currently unknown. Furthermore, whether any genetic influences on E/e' are through an impact of LV remodeling or aortic function is unknown. Intrafamilial aggregation and heritability (SAGE software) of E/e' (echocardiography) were assessed in 129 nuclear families (29 spouse pairs, 216 parent-child pairs, and 113 sibling-sibling pairs) from an urban developing community of black Africans, independent of LV mass index (LVMI), LV relative wall thickness (RWT), central aortic systolic pressure (SBPc), and backward wave pressures (Pb) (applanation tonometry, SphygmoCor software). Independent of confounders including LVMI and RWT, E/e' was correlated in parent-child (r = 0.23; P < .001) and sibling-sibling (r = 0.29; P < .005), but not in spouse (r = 0.13; P = .51) pairs. The relationships between parent-child (r = 0.22; P < .001) and sibling-sibling (r = 0.29; P < .005) pairs persisted with adjustments for SBPc. The relationships between parent-child (r = 0.22; P < .001) and sibling-sibling (r = 0.26; P < .01) pairs also persisted with adjustments for Pb. Independent of confounders including LVMI and RWT, E/e' showed significant heritability (h(2) ± standard error of the mean [SEM] = 0.51 ± 0.11; P < .0001) which similarly persisted with adjustments for SBPc (h(2) ± SEM = 0.50 ± 0.11; P < .0001) and Pb (h(2) ± SEM = 0.49 ± 0.11; P < .0001). In conclusion, in a group of African ancestry, independent of LV remodeling and aortic function, E/e' shows significant intrafamilial aggregation and robust heritability. Hence, genetic factors may play an important role in determining moderate-to-severe LV diastolic dysfunction independent of cardiac remodeling or aortic function in groups of black African ancestry.

Intrafamilial Aggregation and Heritability of Aortic Reflected (Backward) Waves Derived From Wave Separation Analysis

BACKGROUND

Although aortic wave reflection may be inherited, the extent to which indexes of wave reflection derived from wave separation analysis (reflected (backward) wave index (RI) and pressure (Pb)) show intrafamilial aggregation and heritability is uncertain. We therefore aimed to determine the intrafamilial aggregation and heritability of RI and Pb and compare these with indexes of pressure augmentation.

METHODS

Aortic Pb, RI, augmented pressure (Pa), and augmentation index (AIx) were determined using radial applanation tonometry and SphygmoCor software in 1,152 participants of 315 families (111 father-mother, 705 parent-child, and 301 sibling-sibling pairs) from an urban developing community of black Africans. Heritability estimates were determined from Statistical Analysis for Genetic Epidemiology software.

RESULTS

With appropriate adjustments, significant correlations were noted between parent-child pairs for Pb and Pa (P < 0.05 for all), but not for RI (P = 0.50) or AIx (P = 0.90) and between sib-sib pairs for Pb and Pa (P < 0.05), but not for RI (P = 0.54) or AIx (P = 0.14). No correlations for indexes of wave reflection were noted between fathers and mothers (P > 0.57). After adjustments, Pb (h2 = 0.24±0.07) and Pa (h2 = 0.23±0.07) (P < 0.001 for both) but not RI (h2 = 0.04±0.06, P = 0.27) or AIx (h2 = 0.10±0.07, P = 0.07) showed significant heritability.

CONCLUSIONS

Aortic reflected (backward) waves derived from either wave separation (Pb) or pulse wave analysis (Pa) show a similar degree of intrafamilial aggregation and heritability, but the use of RI or AIx may underestimate reflected wave effects.