Relation Between Heart Rate and Cognition in the Women’s Health and Aging Study

Background

    Bradycardia is a common finding among older adults and is likely related to medications as well as acquired cardiac conduction abnormalities.^{1, 2}   Although there is little data regarding the significance of bradycardia on function or quality of life in older adults, most cases of asymptomatic bradycardia are considered benign and not in need of intervention.^{3, 4}   Interestingly, small studies have shown that older adults with bradycardia and indications for pacemaker have improved cerebral blood flow and cognitive function following pacemaker implantation.^{5, 6}   It is possible that less severe but equally persistent bradycardia in older adults may also be associated with deficits in cognitive function potentially responsive to intervention. Therefore, we plan to explore the relation between varying levels of bradycardia and cognitive function in a cohort of community-dwelling older adults.

Hypothesis

    Bradycardia is associated with decreased cognitive function in older adults.

Methods

    The cohort to be studied includes 436 female patients, aged 70 to 80 years, enrolled in the Women’s Health and Aging Study (WHAS) II.  In this cohort, we plan to compare the relationship between baseline heart rate (HR) and performance in a wide range of cognitive function tasks.  Dependent variables will include measures of cognitive function as assessed in WHAS II (e.g. mini mental status examination, prospective memory testing, brief test of attention, pattern comparison, digit span, clock drawing, word fluency, and trail making).  Measures of ability to perform certain instrumental activities of daily living also may be included in this analysis (e.g. telephone use, correct change, meal preparation, and medication scheduling).  Techniques for analysis will include chi-square tests to evaluate bivariate associations between dependent variables and ranges of baseline HR (e.g. mild bradycardia as HR=50-59, moderate bradycardia as HR=40-49, severe bradycardia as HR<40).  To complement the resting heart rate recorded on the baseline electrocardiogram (ECG), a number of additional heart rate variables will be constructed using 6-hour holter monitoring data collected for each patient (e.g. average HR, percent of total time with low HR, longest time period [in minutes] spent with low HR, range between highest and lowest recorded HR).

    To assess the independent association between heart rate and levels of cognitive performance, multivariate analyses will be performed.  Variables to be considered in multivariate analyses will include taking medications known to affect cognitive function (e.g. anticholinergic medications) and having a medical condition known to directly affect cognitive function (e.g. cerebrovascular disease).  Analyses will also adjust for factors known to influence heart rate (e.g. medications, known cardiac conduction abnormalities, and medical conditions such as anemia, thyroid disease, hypokalemia, and clinically significant atherosclerosis).  The presence of clinically significant atherosclerosis will be characterized by values taken from measures of the arm-brachial index (ABI) and by analysis of ECGs for signs of previous ischemic heart events (e.g. presence of Q waves, particularly in the inferior leads).

Summary

    We expect to find that bradycardia is associated with decreased levels of cognitive ability among older women living in the community. 

References

1. Manolio TA, Furberg CD, Rautaharju PM, et al. Cardiac arrhythmias on 24-h ambulatory electrocardiography in older women and men: the Cardiovascular Health Study. J Am Coll Cardiol. Mar 15 1994;23(4):916-925.

2. Abdon NJ. Frequency and distribution of long-term ECG-recorded cardiac arrhythmias in an elderly population. With special reference to neurological symptoms. Acta Med Scand. 1981;209(3):175-183.

3. Gregoratos G, Abrams J, Epstein AE, et al. ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices: summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker Guidelines). Circulation. Oct 15 2002;106(16):2145-2161.

4. Gann D, Tolentino A, Samet P. Electrophysiologic evaluation of elderly patients with sinus bradycardia: a long-term follow-up study. Ann Intern Med. Jan 1979;90(1):24-29.

5. Barbe C, Puisieux F, Jansen I, et al. Improvement of cognitive function after pacemaker implantation in very old persons with bradycardia. J Am Geriatr Soc. Apr 2002;50(4):778-780.

6. Koide H, Kobayashi S, Kitani M, Tsunematsu T, Nakazawa Y. Improvement of cerebral blood flow and cognitive function following pacemaker implantation in patients with bradycardia. Gerontology. 1994;40(5):279-285.