A two-sample Mendelian randomization analysis of heart rate variability and cerebral small vessel disease

Causal relationships involving brain imaging-derived phenotypes based on UKB imaging cohort: a review of Mendelian randomization studies

The UK Biobank (UKB) has the largest adult brain imaging dataset, which encompasses over 40,000 participants. A significant number of Mendelian randomization (MR) studies based on UKB neuroimaging data have been published to validate potential causal relationships identified in observational studies. Relevant articles published before December 2023 were identified following the PRISMA protocol. Included studies (n = 34) revealed that there were causal relationships between various lifestyles, diseases, biomarkers, and brain image-derived phenotypes (BIDPs). In terms of lifestyle habits and environmental factors, there were causal relationships between alcohol consumption, tea intake, coffee consumption, smoking, educational attainment, and certain BIDPs. Additionally, some BIDPs could serve as mediators between leisure/physical inactivity and major depressive disorder. Regarding diseases, BIDPs have been found to have causal relationships not only with Alzheimer's disease, stroke, psychiatric disorders, and migraine, but also with cardiovascular diseases, diabetes, poor oral health, osteoporosis, and ankle sprain. In addition, there were causal relationships between certain biological markers and BIDPs, such as blood pressure, LDL-C, IL-6, telomere length, and more.

Analysis of the Relationship between Recent Small Subcortical Infarcts and Autonomic Nervous Dysfunction

OBJECTIVE

Autonomic Nervous System (ANS) dysfunction may be involved in the pathogenesis of Cerebral Small Vessel Disease (CSVD). The study aimed to explore the relationship between Recent Small Subcortical Infarct (RSSI) and Blood Pressure Variability (BPV), and Heart Rate Variability (HRV).

METHODS

A total of 588 patients from the CSVD registration research database of Henan Province were included in this study, and were divided into two groups according to the presence of RSSI. Clinical data, including demographic characteristics, disease history, laboratory indexes, 24-hour ambulatory blood pressure and electrocardiogram indicators, and imaging markers of CSVD, were collected. Univariate and binary logistic regression analyses were used to study the relationship between RSSI and indicators of laboratory, HRV and BPV in the CSVD population.

RESULTS

Multivariate analysis showed that higher 24-hour mean Diastolic Blood Pressure (DBP)[Odds Ratios (OR)=1.083,95% Confidence Intervals (CI)=(1.038,1.129), p < 0.001], Standard Deviation (SD) of 24-hour DBP [OR=1.059,95%CI=(1.000,1.121), p = 0.049], nocturnal mean Systolic Blood Pressure (SBP) [OR=1.020,95%CI=(1.004,1.035), p = 0.012], nocturnal mean DBP [OR=1.025,95%CI=(1.009,1.040), p = 0.002] were independent risk factors for RSSI. In contrast, the decrease of the standard deviation of N-N intervals (SDNN) [OR=0.994,95%CI=(0.989,1.000), p = 0.035] was beneficial to the occurrence of RSSI. In addition, neutrophil counts [OR=1.138,95%CI=(1.030,1.258), p = 0.011], total cholesterol (TC) [OR=1.203,95%CI=(1.008,1.437), p = 0.041] and High-Density Lipoprotein (HDL) [OR=0.391, 95%CI=(0.195,0.786), p = 0.008] were also independently associated with the occurrence of RSSI. After adjusting for confounding factors, except for TC, the other factors remained associated with the occurrence of RSSI.

CONCLUSION

Increased 24-hour mean DBP, nocturnal mean SBP and DBP, SD of 24-hour DBP and decreased SDNN were independently correlated with RSSI occurrence, suggesting that sympathetic overactivity plays a role in the pathogenesis of RSSI.

Heart rate response and recovery during exercise predict future delirium risk-A prospective cohort study in middle- to older-aged adults

BACKGROUND

Delirium is a neurocognitive disorder characterized by an abrupt decline in attention, awareness, and cognition after surgical/illness-induced stressors on the brain. There is now an increasing focus on how cardiovascular health interacts with neurocognitive disorders given their overlapping risk factors and links to subsequent dementia and mortality. One common indicator for cardiovascular health is the heart rate response/recovery (HRR) to exercise, but how this relates to future delirium is unknown.

METHODS

Electrocardiogram data were examined in 38,740 middle- to older-aged UK Biobank participants (mean age = 58.1 years, range: 40-72 years; 47.3% males) who completed a standardized submaximal exercise stress test (15-s baseline, 6-min exercise, and 1-min recovery) and required hospitalization during follow-up. An HRR index was derived as the product of the heart rate (HR) responses during exercise (peak/resting HRs) and recovery (peak/recovery HRs) and categorized into low/average/high groups as the bottom quartile/middle 2 quartiles/top quartile, respectively. Associations between 3 HRR groups and new-onset delirium were investigated using Cox proportional hazards models and a 2-year landmark analysis to minimize reverse causation. Sociodemographic factors, lifestyle factors/physical activity, cardiovascular risk, comorbidities, cognition, and maximal workload achieved were included as covariates.

RESULTS

During a median follow-up period of 11 years, 348 participants (9/1000) newly developed delirium. Compared with the high HRR group (16/1000), the risk for delirium was almost doubled in those with low HRR (hazard ratio = 1.90, 95% confidence interval (95%CI): 1.30-2.79, p = 0.001) and average HRR (hazard ratio = 1.54, 95%CI: 1.07-2.22, p = 0.020)). Low HRR was equivalent to being 6 years older, a current smoker, or ≥3 additional cardiovascular disease risks. Results were robust in sensitivity analysis, but the risk appeared larger in those with better cognition and when only postoperative delirium was considered (n = 147; hazard ratio = 2.66, 95%CI: 1.46-4.85, p = 0.001).

CONCLUSION

HRR during submaximal exercise is associated with future risk for delirium. Given that HRR is potentially modifiable, it may prove useful for neurological risk stratification alongside traditional cardiovascular risk factors.

Implication of heart rate variability on cerebral small vessel disease: A potential therapeutic target

OBJECTIVE

This study aimed to investigate the relationships of heart rate variability (HRV) with the presence, severity, and individual neuroimaging markers of cerebral small vessel disease (CSVD).

METHOD

A total of 4676 participants from the Third China National Stroke Registry (CNSR-III) study were included in this cross-sectional analysis. CSVD and its markers, including white matter hyperintensity (WMH), lacunes, enlarged perivascular spaces (EPVS), cerebral microbleeds (CMBs), and brain atrophy (BA), were evaluated. Two common HRV parameters, including the square root of the mean of the sum of the squares of differences between adjacent N-N intervals (RMSSD) and the standard deviation of all N-N intervals (SDNN), were used to evaluate the function of the autonomic nervous system (ANS). Binary or ordinal logistic regression analyses were performed to investigate the association between HRV and CSVD. In addition, two-sample mendelian randomization (MR) analyses were performed to investigate the causality of HRV with CSVD.

RESULTS

RMSSD was significantly associated with total burden of CSVD (Wardlaw's scale, common odds ratio [cOR] 0.80, 95% confidence interval [CI] 0.67-0.96, p = 0.02; Rothwell's scale, cOR 0.75, 95% CI 0.60-0.93, p = 0.008) and the presence of CSVD (Rothwell, OR 0.75, 95% CI 0.60-0.93, p = 0.008). However, no significant associations between SDNN and the presence or total burden of CSVD were observed. Moreover, RMSSD was related to WMH burden (OR 0.80, 95% CI 0.66-0.96, p = 0.02), modified WMH burden (cOR 0.82, 95% CI 0.69-0.97, p = 0.02), and Deep-WMH (OR 0.75, 95% CI 0.62-0.91, p = 0.003), while SDNN was related to Deep-WMH (OR 0.80, 95% CI 0.66-0.96, p = 0.02) and BA (cOR 0.80, 95% CI 0.68-0.95, p = 0.009). Furthermore, adding HRV to the conventional model based on vascualr risk factors enhanced the predictive performance for CSVD, as validated by the integrated discrimination index (p < 0.05). In addition, no causality between HRV and CSVD was observed in two-sample MR analyses.

CONCLUSION

Decreased HRV may be a potential risk factor of CSVD, implying the possible role of the ANS in the pathogenesis of CSVD.

Relationship between heart rate variability and cognitive function in patients with enlarged perivascular space

Objective

To explore the relationship between heart rate variability (HRV), the brain distribution of enlarged perivascular space (EPVS), and cognitive impairment in patients with EPVS.

Materials and methods

The clinical and imaging data of 199 patients with EPVS were retrospectively analyzed. EPVS load in the basal ganglia (BG) and centrum semiovale (CS) regions were assessed using the Potter’s method. Cognitive function was evaluated using the Montreal Cognitive Assessment Scale. A logistic regression model was used to analyze the relationship between HRV, the brain distribution of EPVS and cognitive function in patients with EPVS. A receiver operating characteristic curve was used to assess the predictive value of HRV for cognitive function in patients with EPVS.

Results

Of the 199 patients, 27 and 42 presented with severe BG-EPVS and cognitive impairment, respectively. Significant differences were observed in the root mean square of successive differences of normal-normal (NN) intervals for period of interest (rMSSD), the percentage of adjacent NN intervals greater than 50 ms (PNN50), and the ratio of low-frequency power (LF) to high-frequency power (HF) between the mild and severe BG-EPVS groups (P &lt; 0.05). Patients who presented with and without cognitive impairment differed significantly in the standard deviation of NN intervals (SDNN), rMSSD, PNN50, total power, LF, and LF/HF (P &lt; 0.05). rMSSD (odds ratio [OR] 0.871, 95% confidence interval [CI] 0.768–0.988) and LF/HF (OR 3.854, 95% CI 1.196–12.419) were independent influencing factors of BG-EPVS, and rMSSD (OR 0.936, 95% CI 0.898–0.976) was an independent influencing factor of cognitive impairment in patients with EPVS. The optimal cut-off point was 0.312, with an area under the curve of 0.795 (95% CI 0.719–0.872) for predicting cognitive impairment in patients with EPVS by rMSSD.

Conclusion

Reduced HRV is involved in the pathophysiological mechanisms of the formation and development of BG-EPVS and is associated with cognitive impairment in patients with EPVS, independent of CS-EPVS. For patients with HRV changes but without autonomic nervous system symptoms, positive intervention may slow the occurrence or progression of EPVS and cognitive impairment in patients with EPVS.

Decreased nighttime heart rate variability and progression of white matter hyperintensities of presumed vascular origin. A prospective study in community-dwelling older adults

OBJECTIVES

Evidence on the role of autonomic dysfunction on white matter hyperintensities (WMH) progression is limited. This study aims to assess the impact of a low nighttime heart rate variability (HRV) on WMH progression in community-dwelling older adults.

MATERIALS AND METHODS

Following a prospective longitudinal study design, all individuals aged ≥60 years enrolled in the Atahualpa Project Cohort from 2012 to 2019 were invited to receive baseline HRV determinations through 24-h Holter monitoring, together with clinical interviews and brain MRIs. These individuals were periodically followed by means of annual door-to-door surveys, and those who also received brain MRIs at the end of the study (May 2021) were included in the analysis. Poisson regression models, adjusted for relevant confounders, were fitted to assess the incidence rate ratio (IRR) of WMH progression according to nighttime standard deviation of normal-to-normal R-R intervals (SDNN).

RESULTS

This study included 254 individuals aged ≥60 years (mean age: 65.4 ± 5.9 years; 55% women). The mean nighttime SDNN was 116.8 ± 36.3 ms. Follow-up MRIs showed WMH progression in 103 (41%) individuals after a median follow-up of 6.5 years. In unadjusted analyses, nighttime SDNN was lower among participants who developed WMH progression than in those who did not (p < 0.001). A Poisson regression model, adjusted for relevant covariates, disclosed a significantly inverse association between nighttime SDNN and WMH progression (IRR: 0.99; 95% C.I.: 0.98-0.99; p = 0.014).

CONCLUSIONS

Study results show an inverse association between decreased nighttime SDNN and WMH progression, and provide support for the role of sympathetic overactivity in this relationship.