Original Article
The Association of Resting Heart Rate and Incident Hypertension: The Henry Ford Hospital Exercise Testing (FIT) Project Amer I. Aladin,1 Mahmoud Al Rifai,1 Shereen H. Rasool,1 Steven J. Keteyian,2 Clinton A. Brawner,2 Erin D. Michos,1 Michael J. Blaha,1 Mouaz H. Al-Mallah,2,3 and John W. McEvoy1 BACKGROUND Given that sympathetic tone is associated with hypertension, we sought to determine whether resting heart rate (RHR), as a surrogate for cardiac autonomic function, was associated with incident hypertension. METHODS We analyzed 21,873 individuals without a history of hypertension who underwent a clinically indicated exercise stress test. Baseline RHR was assessed prior to testing and was categorized as 85 beats-per-minute (bpm). Incident hypertension was defined by subsequent diagnosis codes for new-onset hypertension from three or more encounters. We tested for effect modification by age (85 beats-per-minute (bpm) were at higher risk for
Correspondence: John W. McEvoy (
[email protected]). Initially submitted April 2, 2015; date of first revision May 18, 2015; accepted for publication May 26, 2015; online publication June 25, 2015.
diabetic, and achieve lower metabolic equivalents (METS). Over a median of 4 years follow-up, there were 8,179 cases of incident hypertension. Compared to RHR 85 bpm had increased risk of hypertension after adjustment for CHD risk factors, baseline blood pressure (BP), and METS (hazard ratio = 1.15 (95% confidence interval 1.08–1.23)). Age was an effect modifier (interaction P = 0.02), whereas sex, race, and CHD were not. In age-stratified analyses the relationship remained significant only in those younger than 60 years.
CONCLUSION Elevated RHR is an independent risk factor for incident hypertension, particularly in younger persons. Whether lifestyle modification or other strategies to reduce RHR can prevent incident hypertension in high-risk individuals warrants further study. Keywords: blood pressure; fitness; hypertension; resting heart rate. doi:10.1093/ajh/hpv095
developing hypertension than those with RHR ≤69 bpm.13 However, this study did not account for cardiorespiratory fitness, an important potential confounder. Leveraging data from the Henry Ford Hospital Exercise Testing Project (The FIT Project), we sought to determine whether baseline RHR was associated with incident hypertension, independent of traditional cardiovascular disease risk factors, and cardiorespiratory fitness. METHODS
The details of the FIT Project have been published elsewhere.14 FIT is an investigator-initiated retrospective cohort study of patients who had a clinical exercise stress test. The FIT Project dataset is comprised of the following: (i) directly measured exercise data (e.g., exercise duration and estimated metabolic equivalents (METS) of task); (ii) medical history and medication treatment data taken at the time of the
1Ciccarone Center for the Prevention of Heart Disease, Johns Hopkins School of Medicine, Baltimore, Maryland, USA; 2Division of Cardiovascular Medicine, Henry Ford Hospital, Detroit, Michigan, USA; 3Division of Cardiology and Imaging, King Abdul-Aziz Cardiac Center, Riyadh, Kingdom of Saudi Arabia.
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American Journal of Hypertension 29(2) February 2016 251
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stress test; (iii) supporting clinical data using the electronic medical record and administrative databases; and (iv) epidemiologic follow-up for total mortality and select nonfatal outcomes by way of linkage with the death registry and medical claims files. The study was approved by the Institutional Review Board committee at Henry Ford Hospital. The FIT project study sample consists of 69,885 consecutive patients who underwent physician-referred treadmill stress testing using the standard Bruce protocol15 at Henry Ford Health system-affiliated hospitals and ambulatory care centers in metropolitan Detroit, Michigan, between 1991 and 2009. Patients were excluded from the sample if they were younger than 18 years old at the time of stress testing or if they were evaluated by pharmacological stress testing. The rationale for stress test referral was provided by the referring physician and subsequently categorized into common indications (e.g., chest pain, shortness of breath, preoperative evaluation, and so forth). The treadmill test was symptomlimited in accordance with American Heart Association / American College of Cardiology guidelines.16 We excluded 46,060 persons for prevalent hypertension (defined as previous diagnosis of hypertension, use of antihypertensive medications (including β-blockers or calcium channel blockers), or electronic medical record problem listbased diagnosis of hypertension). Resting blood pressure (BP) measured at the time of the stress test was not used to diagnose prevalent hypertension for the purposes of exclusion. As RHR is altered by conditions or medications affecting the normal electrical conduction system of the heart, we also excluded individuals with a history of atrial fibrillation (n = 216) and those taking digoxin (n = 121). After excluding an additional 1,614 persons for missing covariates, we were left with a final sample size of 21,873 individuals. RHR and BP were taken in the seated position before stress testing by trained clinical personnel. Exercise capacity, expressed in estimated METS, was calculated by the Quinton treadmill controller based on peak speed and elevation, and equations recommended by the American College of Sports Medicine.17 Maximum METS achieved was categorized into 4 groups (
