Cardiovascular risk factors and autonomic indices in relation to fatal and non-fatal coronary events

Importance of resting heart rate

Resting heart rate is a determinant of cardiac output and physiological homeostasis. Although a simple, but critical, parameter, this vital sign predicts adverse outcomes, including mortality, and development of diseases in otherwise normal and healthy individuals. Temporal changes in heart rate can have valuable predictive capabilities. Heart rate can reflect disease severity in patients with various medical conditions. While heart rate represents a compilation of physiological inputs, including sympathetic and parasympathetic tone, aside from the underlying intrinsic sinus rate, how resting heart rate affects outcomes is uncertain. Mechanisms relating resting heart rate to outcomes may be disease-dependent but why resting heart rate in otherwise healthy, normal individuals affects outcomes remains obscure. For specific conditions, physiologically appropriate heart rate reductions may improve outcomes. However, to date, in the normal population, evidence that interventions aimed at reducing heart rate improves outcomes remains undefined. Emerging data suggest that reduction in heart rate via vagal activation and/or sympathetic inhibition is propitious.

The relationships between the plasma metabolome and orthostatic blood pressure responses

Whereas autonomic dysfunction and the metabolic syndrome are clinically associated, the relationships with the plasma metabolome is unknown. We explored the association between orthostatic blood pressure responses and 818 plasma metabolites in middle-aged subjects from the general population. We included 3803 out of 6251 subjects (mean age, 57 years; 52% women) from the Malmö sub-cohort of The Swedish CardioPulmonary bioImage Study with information on smoking habits, diabetes, antihypertensive drug treatment, anthropometrics, hemodynamic measurements and 818 plasma metabolites (mass-spectrometry). The associations between each metabolite and orthostatic systolic blood pressure responses were determined using multivariable linear regression analysis and p values were corrected using the Bonferroni method. Six amino acids, five vitamins, co-factors and carbohydrates, nine lipids and two xenobiotics were associated with orthostatic blood pressure after adjusting for age, gender and systolic blood pressure. After additional adjustments for BMI, diabetes, smoking and antihypertensive treatment, the association remained significant for six lipids, four amino acids and one xenobiotic. Twenty-two out of 818 plasma metabolites were associated with orthostatic blood pressure responses. Eleven metabolites, including lipids in the dihydrosphingomyelin and sphingosine pathways, were independently associated with orthostatic systolic blood pressure responses after additional adjustment for markers of cardio-metabolic disease.

Subclinical atherosclerosis and risk factors in relation to autonomic indices in the general population

OBJECTIVE

Orthostatic hypotension and resting heart rate (RHR) are associated with cardiovascular disease (CVD). However, it is unknown how these factors relate to subclinical CVD. We examined the relationship between orthostatic blood pressure (BP) response, RHR and cardiovascular risk factors, including coronary artery calcification score (CACS) and arterial stiffness, in the general population.

METHODS

We included 5493 individuals (age 50-64 years; 46.6% men) from The Swedish CArdioPulmonary-bio-Image Study (SCAPIS). Anthropometric and haemodynamic data, biochemistry, CACS and carotid-femoral pulse wave velocity (PWV) were retrieved. Individuals were categorized into binary variables that manifest orthostatic hypotension and in quartiles of orthostatic BP responses and RHR, respectively. Differences across the various characteristics were tested using χ 2 for categorical variables and analysis of variance and Kruskal-Wallis test for continuous variables.

RESULTS

The mean (SD) SBP and DBP decrease upon standing was -3.8 (10.2) and -9.5 (6.4) mmHg, respectively. Manifest orthostatic hypotension (1.7% of the population) associated with age ( P  = 0.021), systolic, diastolic and pulse pressure ( P  < 0.001), CACS (<0.001), PWV ( P  = 0.004), HbA1c ( P  < 0.001) and glucose levels ( P  = 0.035). Age ( P  < 0.001), CACS ( P  = 0.045) and PWV ( P  < 0.001) differed according to systolic orthostatic BP, with the highest values seen in those with highest and lowest systolic orthostatic BP-responses. RHR was associated with PWV ( P  < 0.001), SBP and DBP ( P  < 0.001) as well as anthropometric parameters ( P  < 0.001) but not CACS ( P  = 0.137).

CONCLUSION

Subclinical abnormalities in cardiovascular autonomic function, such as impaired and exaggerated orthostatic BP response and increased resting heart rate, are associated with markers of increased cardiovascular risk in the general population.