24-Hour Heart Rate May Signal CV Risk in Young Adults Without Hypertension

Marlene Busko

February 18, 2016

PHILADELPHIA, PA — Mean 24-hour ambulatory heart rate (HR) was independently linked with mean 24-hour systolic and diastolic blood pressure (BP), C-reactive protein (CRP), and insulin resistance, in a small study of young adults without hypertension, diabetes, or prior MI or stroke[1].

These findings suggest that "24-hour HR is associated with known risk factors for atherosclerosis prior to the development of diabetes or sustained hypertension," Drs Cynthia Cheng and Constantine Daskalakis (Thomas Jefferson University, Philadelphia, PA) write in an article published February 12, 2016 in Open Heart.

However, based on office measurements, as opposed to 24-hour measurements, heart rate was no longer significantly associated with blood pressure in these 186 outpatients, with a mean age of 27.

The message to clinicians is that 24-hour ambulatory heart rate and blood-pressure monitoring can help determine whether a particular younger, at-risk patient has constantly elevated blood pressure (even if it is borderline), blood pressure that is elevated only in the office, or a persistently elevated heart rate—"all markers that you should pay more attention to, to prevent [potential hypertension, heart attack, or stroke] down the line," Cheng told heartwire from Medscape. "Either way, you're going to try to get these people to exercise more, eat less salt, [and eat a healthy diet]."

Systolic Nondipping BP, Masked Prehypertension Common

Studies have shown that resting heart rate predicts CV morbidity and mortality in older adults with and without CV disease. However, the role of heart rate in the early pathogenesis of atherosclerosis in younger adults is not clear, Cheng and Daskalakis observe.

They aimed to examine the link between 24-hour ambulatory heart rate and blood pressure, after controlling for endothelial dysfunction, insulin resistance, inflammatory markers, and adiposity in young adults without hypertension. Their secondary objective was to evaluate how heart rate was affected by adiposity, inflammation, and insulin resistance.

They enrolled 115 women (62%) and 71 men (38%) aged 18 to 45, who underwent 24-hour ambulatory blood-pressure and heart-rate monitoring and plethysmography to determine forearm blood flow and had blood tests.

The 24-hour BP readings were based on an average of 42 readings while awake and eight readings while asleep.

Although none of the participants had hypertension, 24% had prehypertension: 10% had white-coat prehypertension (office readings only); 10% had masked prehypertension (24-hour readings only); and 4% had prehypertension from both office readings and 24-hour readings.

Prehypertension was defined as office systolic BP of 120 to 139 mm Hg or diastolic BP of 80 to 89 mm Hg or 24-hour systolic BP of 130 to 134 mm Hg or diastolic BP of 80 to 84 mm Hg.

Another 35% of the patients had nondipping systolic BP (their mean systolic BP dropped less than 10% when they slept vs when they were awake).

Thus a "sizable proportion" of participants had systolic nondipping BP or masked prehypertension, possibly suggesting that they already had early stages of cardiovascular disease, the researchers note.

The patients had a mean heart rate of 69 beats per minute (bpm) based on office measurements and a mean heart rate of 75 bpm based on 24-hour measurements (77 bpm while awake and 64 bpm while asleep).

They had mean blood pressures of 108/65 mm Hg based on office measurements and 117/72 mm Hg based on 24-hour measurements.

In multivariable analysis, heart rate, forearm blood flow, and plasminogen activator inhibitor-1 (PAI-1) were all associated with blood pressure. A 10-bpm increase in 24-hour heart rate was associated with a 1.3-mm-Hg increase in 24-hour systolic BP (P=0.042) and a 1.7-mm-Hg increase in 24-hour diastolic BP ( P=0.001). A 300% increase in forearm blood flow was associated with a 1.4-mm-Hg decrease in systolic BP (P=0.013) only. PAI-1 levels were linked with both systolic BP (P=0.041) and diastolic BP (P=0.015).

On the other hand, insulin resistance and CRP, but not body-mass index (BMI), predicted heart rate. A doubling in CRP was associated with a 1.3-bpm higher 24-hour heart rate (P=0.007), and insulin resistance was inversely related to heart rate.

The importance of resting heart rate as a prognostic target and potential therapeutic target is not yet generally accepted, Cheng and Daskalakis note. Thus, longer, larger studies are needed. "Prospective longitudinal studies are needed to further elucidate the causal pathways that link adiposity, inflammation, insulin resistance, endothelial function, and HR and the degree to which HR measured in early life can predict the incidence of atherosclerosis and cardiovascular disease," they write.

The authors have no relevant financial relationships.

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