Heterozygous APOE ε4 carriage associates with improved myocardial efficiency in older age

Background

Carriage of the ancestral APOE ε4 allele confers a risk of developing Alzheimer's and coronary artery disease, but its persistence in human populations also suggests some potential survival advantages. To date it remains unclear whether APOE ε4 carriage independently associates with a better or worse long-term cardiac phenotype.

Purpose

Using data from the 1946 National Survey of Health and Development (NSHD) birth cohort, we investigated whether APOE ε4 carriage associates with adverse or beneficial left ventricular (LV) size and function parameters by echocardiography in older age.

Methods

Based on the presence or absence of APOE ε4, genotypes were divided into: non-APOE ε4 (ε2ε2, ε2ε3, ε3ε3), heterozygous-APOE ε4 (ε2ε4 and ε3ε4) and homozygous-APOE ε4 (ε4ε4). Echocardiographic data at 60–64 years included: left ventricular ejection fraction (LV EF), E/e', systolic and diastolic LV posterior wall and interventricular septal thickness (LVPWTs/d, IVSs/d), and body-surface area indexed LV mass (LVmassi) and myocardial contraction fraction (MCFi). Generalized linear models explored associations between APOE ε4 genotypes as exposures and echocardiographic biomarkers as outcomes. As a combination of gene variants, APOE ε genotype is expected to be an instrumental variable and therefore unconfounded. Thus, Model 1 was unadjusted. To obtain more precise regression estimates, Model 2 was adjusted for factors associated with the outcome, namely sex and socio-economic position (SEP). To explore the mechanistic pathway downstream of APOE ε genotype but upstream of the echocardiographic outcomes, subsequent models were adjusted for mediators as follows: Model 3 for body mass index, Model 4 for the presence of cardiovascular disease (CVD), Model 5 for diabetes, Model 6 for high cholesterol and Model 7 for hypertension.

Results

1464 participants were included. Compared to non-APOE ε4 and homozygous groups, heterozygous-APOE ε4 individuals had similar cardiac phenotypes in terms of EF, E/e', LVPWTs/d, IVSs/d and LVmassi but had a 7% higher MCFi 95% confidence interval [CI]: 1%-13%, p=0.017) which persisted even after adjustment for sex and SEP (95% CI 1%-12%, p=0.026) that was attenuated to 6% after adjustment for CVD (95% CI 0–13% p=0.050) and hypertension (95% CI 1–13% p=0.022).

Conclusion

The heterozygous-APOE ε4 state associates with improved myocardial shortening in older age resulting in greater LV stroke volume generation per 1 mL of myocardium. As we found no association between APOE ε4 carriage and LVPWTs/d, IVSs/d or LVmassi, MCFi enhancement may be mediated by improved myocardial energetics and contractility, with calcium and androgens potentially implicated, rather than through pathological ventricular thickening. Although a dose relationship is normally expected with ε4 carriage, any benefit from increased energetics and contractility is likely to be counterbalances by the higher risk of CVD and cardiovascular risk factors.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): UK Medical Research Council British Heart Foundation

Childhood bradycardia associates with atrioventricular conduction defects in older age: a longitudinal birth cohort study

Background

A high resting heart rate (RHR) has been associated with cardiovascular morbidity and mortality. However, little is known about the long-term effects of childhood bradycardia.

Purpose

This study aimed to explore the association between childhood bradycardia and later-life cardiac phenotype using longitudinal data from the 1946 Medical Research Council National Survey of Health and Development (NSHD) birth cohort.

Methods

RHR was recorded at ages 6 and 7 to provide the bradycardia exposure defined as a childhood RHR<75. Three outcomes were studied: i) echocardiographic data at 60–64 consisting of ejection fraction (EF), left ventricular mass index (LVmassi), myocardial contraction fraction index (MCFi) and E/e'; ii) electrocardiographic (ECG) evidence of atrio-ventricular (AV) conduction defects (Minnesota categories: 6-1, 6-2-1, 6-2-2, 6-2-3, 6-3, 6-8, 8-5-1, 8-5-2, 8-6-1, 8-6-2, 8-6-3 and 8-6-4) or ventricular conduction defects (any Minnesota group 7) by age 60–64; and iii) all-cause and cardiovascular mortality. Generalized linear models (glm) with gamma distribution were used for echocardiographic analyses, glms with binomial distribution for ECG analyses and Cox proportional hazards models for mortality. Adjustment was made for relevant demographic and health-related covariates, and for multiple testing. In order to account for within-subject correlated repeated measures at 6 and 7 years of age, mixed glms (glmms) were used as a sensitivity analysis. To explore any nonlinear relationships, we modeled each outcome as a sum of best fitting fractional polynomials of RHR at 6 and 7 (as continuous variables) and covariates using a “closed test procedure” with backward elimination.

Results

The number of participants included was: 4381 for mortality, 1631 for ECG and 1617 for echocardiography analyses. Childhood bradycardia was associated with male sex (p<0.0001) and higher BMI (p=0.009). In fully adjusted models, childhood bradycardia was associated with 2.91 higher odds of AV conduction defects (95% confidence interval [CI] 1.59–5.31, p=0.0005), even at a false discovery rate of 0.05. Associations persisted in random coefficients glmm models (odds ratio 2.50, 95% CI 1.01–4.31). The fractional polynomials analyses revealed that the log odds of AV conduction defects at 60–64 years of age were linearly associated with RHR at 7 years. There was no association between bradycardia in childhood and ventricular conduction defects, echocardiographic parameters or mortality outcomes.

Conclusions

Longitudinal data indicate that childhood bradycardia trebles the odds of having AV conduction defects, but does not influence mortality or heart size and function in older age. As one in three older adults with AV conduction defects will have been bradycardic in childhood, future research should concentrate on identifying children at risk, the potential mechanisms involved and whether AV blocking drugs accelerate nodal dysfunction.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation (MyoFit46 Special Programme Grant SP/20/2/34841)

The role of the electrocardiographic phenotype in risk stratification for sudden cardiac death in childhood hypertrophic cardiomyopathy

AIMS

The 12-lead electrocardiogram (ECG) is routinely performed in children with hypertrophic cardiomyopathy (HCM). An ECG risk score has been suggested as a useful tool for risk stratification, but this has not been independently validated. This aim of this study was to describe the ECG phenotype of childhood HCM in a large, international, multi-centre cohort and investigate its role in risk prediction for arrhythmic events.

METHODS AND RESULTS

Data from 356 childhood HCM patients with a mean age of 10.1 years (±4.5) were collected from a retrospective, multi-centre international cohort. Three hundred and forty-seven (97.5%) patients had ECG abnormalities at baseline, most commonly repolarization abnormalities (n = 277, 77.8%); left ventricular hypertrophy (n = 240, 67.7%); abnormal QRS axis (n = 126, 35.4%); or QT prolongation (n = 131, 36.8%). Over a median follow-up of 3.9 years (interquartile range 2.0-7.7), 25 (7%) had an arrhythmic event, with an overall annual event rate of 1.38 (95% CI 0.93-2.04). No ECG variables were associated with 5-year arrhythmic event on univariable or multivariable analysis. The ECG risk score threshold of >5 had modest discriminatory ability [C-index 0.60 (95% CI 0.484-0.715)], with corresponding negative and positive predictive values of 96.7% and 6.7.

CONCLUSION

In a large, international, multi-centre cohort of childhood HCM, ECG abnormalities were common and varied. No ECG characteristic, either in isolation or combined in the previously described ECG risk score, was associated with 5-year sudden cardiac death risk. This suggests that the role of baseline ECG phenotype in improving risk stratification in childhood HCM is limited.