Phyllis K. Stein

Heart rate variability: A measure of cardiac autonomic tone

Analysis of HRV based on routine 24-hour Holter recordings provides a sensitive, noninvasive measurement of autonomic input to the heart. HRV can be measured in the time or frequency domain. Each frequency domain variable correlates at least r = 0.85 with a time domain variable. Thus time domain measures can be used as surrogates for frequency domain measures which may simplify future studies. Abnormalities of autonomic input to the heart, which are indicated by decreased indices of HRV, are associated with increased susceptibility to ventricular arrhythmias. Decreased indices of HRV are also associated with CHF, diabetes, and alcoholic cardiomyopathy. Decreased indices of HRV are an independent risk factor for mortality post MI and in patients with advanced CHF. Medications can also affect HRV, and that effect may become an important clinical consideration, especially in high-risk patients.

Association of depression witk reduced heart rate variability in coronary artery disease

Abstract Decreased heart rate (HR) variability is an independent risk factor for mortality in cardiac populations. Clinical depression has also been associated with adverse outcomes in patients with coronary artery disease (CAD). This study tests the hypothesis that depressed patients with CAD have decreased HR variability compared with nondepressed CAD patients. Nineteen patients with angiographically documented CAD and either major or minor depression were compared with a sample of nondepressed CAD patients according to age, sex, and smoking status. All patients underwent 24-hour Holter monitoring, and the standard deviation of all normal-to-normal intervals was used as the primary index of HR variability. HR variability was significantly lower in depressed than nondepressed patients (90 ± 35 vs 117 ± 26 ms; p

RR Variability in Healthy, Middle-Aged Persons Compared With Patients With Chronic Coronary Heart Disease or Recent Acute Myocardial Infarction

BACKGROUND The purpose of this investigation was to establish normal values of RR variability for middle-aged persons and compare them with values found in patients early and late after myocardial infarction. We hypothesized that presence or absence of coronary heart disease, age, and sex (in this order of importance) are all correlated with RR variability. METHODS AND RESULTS To determine normal values for RR variability in middle-aged persons, we recruited a sample of 274 healthy persons 40 to 69 years old. To determine the effect of acute myocardial infarction RR variability, we compared measurements of RR variability made 2 weeks after myocardial infarction (n = 684) with measurements made on age- and sex-matched middle-aged subjects with no history of cardiovascular disease (n = 274). To determine the extent of recovery of RR variability after myocardial infarction, we compared measurements of RR variability made in the group of healthy middle-aged persons with measurements made in 278 patients studied 1 year after myocardial infarction. We performed power spectral analyses on continuous 24-hour ECG recordings to quantify total power, ultralow-frequency (ULF) power, very-low-frequency (VLF) power, low-frequency (LF) power, high-frequency (HF) power, and the ratio of LF to HF (LF/HF) power. Time-domain measures also were calculated. All measures of RR variability were significantly and substantially lower in patients with chronic or subacute coronary heart disease than in healthy subjects. The difference from normal values was much greater 2 weeks after myocardial infarction than 1 year after infarction, but the fractional distribution of total power into its four component bands was similar for the three groups. In healthy subjects, ULF power did not change significantly with age; VLF, LF, and HF power decreased significantly as age increased. Patients with chronic coronary heart disease showed little relation between power spectral measures of RR variability and age. Patients with a recent myocardial infarction showed a strong inverse relation between VLF, LF, and HF power and age and a weak inverse relation between ULF power and age. ULF power best separates the healthy group from either of the two coronary heart disease groups. Differences in RR variability between men and women were small and inconsistent among the three groups. CONCLUSIONS All measures of RR variability were significantly and substantially higher in healthy subjects than in patients with chronic or subacute coronary heart disease. The difference between healthy middle-aged persons and those with coronary heart disease was much greater 2 weeks after myocardial infarction than 1 year after infarction, but the fractional distribution of total power into its four component bands was similar for the healthy group and the two coronary heart disease groups. Values of RR variability previously reported to predict death in patients with known chronic coronary heart disease are rarely (approximately 1%) found in healthy middle-aged individuals. Thus, when measures of RR variability are used to screen groups of middle-aged persons to identify individuals who have substantial risk of coronary deaths or arrhythmic events, misclassification of healthy middle-aged persons should be rare.

Time Domain Measurements of Heart Rate Variability

Assessment of HRV through time domain variables is a simple and practical method of assessing autonomic function. In this capacity its utility has been demonstrated in normal subjects and in diverse cardiac and noncardiac pathologic states. It can be used to assess the effects of drugs and other interventions, including exercise and psychological and physical stress on cardiac autonomic tone. Importantly, decreased HRV is almost uniformly associated with adverse outcome. The prognostic information appears to incorporate both alterations in autonomic tone and longer term components and is best assessed using ambulatory ECG recordings. Defining the clinical applicability and physiologic mechanisms of changes in HRV remain active areas of research.

Change in heart rate and heart rate variability during treatment for depression in patients with coronary heart disease

Objective Major depression is a common problem in patients with coronary heart disease (CHD) and is associated with an increased risk for cardiac morbidity and mortality. It is not known whether treating depression will improve medical prognosis in patients with CHD. Depression is also associated with elevated heart rate and reduced heart rate variability (HRV), which are known risk factors for cardiac morbidity and mortality that may explain the increased risk associated with depression. The purpose of this study was to determine whether treatment for depression with cognitive behavior therapy (CBT) is associated with decreased heart rate or increased HRV. Methods Thirty depressed patients with stable CHD, classified as either mildly or moderately to severely depressed, received up to 16 sessions of CBT. The 24-hour heart rate and HRV were measured in these patients and in 22 medically comparable nondepressed controls before and after treatment of the depressed patients. Results Average heart rate and daytime rMSSD (reflecting mostly parasympathetic activity) improved significantly in the severely depressed patients, but remained unchanged in the mildly depressed and the control patients. However, only rMSSD improved to a level comparable to the control patients. None of the remaining indices of HRV showed improvement. Conclusions The results suggest that treating depression with CBT may reduce heart rate and increase short-term HRV. Thus, CBT may have a beneficial effect on a risk factor for mortality in depressed patients with coronary heart disease. A randomized, controlled study is needed to confirm these findings.

Severe depression is associated with markedly reduced heart rate variability in patients with stable coronary heart disease

OBJECTIVE The purpose of this study was to investigate the relationship between depression and heart rate variability in cardiac patients. METHODS Heart rate variability was measured during 24-hour ambulatory electrocardiographic (ECG) monitoring in 40 medically stable out-patients with documented coronary heart disease meeting current diagnostic criteria for major depression, and 32 nondepressed, but otherwise comparable, patients. Patients discontinued beta-blockers and antidepressant medications at the time of study. Depressed patients were classified as mildly (n = 21) or moderately-to-severely depressed (n = 19) on the basis of Beck Depression Inventory scores. RESULTS There were no significant differences among the groups in age, gender, blood pressure, history of myocardial infarction, diabetes, or smoking. Heart rates were higher and nearly all indices of heart rate variability were significantly reduced in the moderately-to-severely versus the nondepressed group. Heart rates were also higher and mean values for heart rate variability lower in the mildly depressed group compared with the nondepressed group, but these differences did not attain statistical significance. CONCLUSION The association of moderate to severe depression with reduced heart rate variability in patients with stable coronary heart disease may reflect altered cardiac autonomic modulation and may explain their increased risk for mortality.

TRADITIONAL AND NONLINEAR HEART RATE VARIABILITY ARE EACH INDEPENDENTLY ASSOCIATED WITH MORTALITY AFTER MYOCARDIAL INFARCTION

Introduction: Decreased heart rate variability (HRV) and abnormal nonlinear HRV shortly after myocardial infarction (MI) are risk factors for mortality. Traditional HRV predicts mortality in patients with a range of times post‐MI, but the association of nonlinear HRV and outcome in this population is unknown.

RR Interval Dynamics Before Atrial Fibrillation in Patients After Coronary Artery Bypass Graft Surgery

BACKGROUND Atrial fibrillation/flutter (AF) is a frequent complication of coronary artery bypass graft surgery (CABG) that leads to increased costs and morbidity. We hypothesized that heart rate variability (HRV), an indicator of cardiac sympathovagal balance, is altered before the onset of postoperative AF. Because nonlinear methods of HRV analysis provide information about heart rate dynamics not evident from usual HRV measures, we also hypothesized that approximate entropy (ApEn), a nonlinear measure of HRV, might have predictive value. METHODS AND RESULTS Analysis of HRV was performed in 3 sequential 20-minute intervals preceding the onset of postoperative AF (24 episodes in 18 patients). These data were compared with corresponding intervals in 18 sex- and age-matched postoperative control subjects who did not develop AF. Patients had left ventricular ejection fractions >45% before surgery and were not receiving beta-blockers during ambulatory ECG monitoring after surgery. Logistic regression demonstrated that on the basis of averaged values for the three 20-minute intervals, increased heart rate and decreased ApEn were independently associated with AF. Heart rate dynamics before AF was associated with either lower (n= 19) or higher (n=5) RR interval variation by traditional measures of HRV or quantitative Poincaré analysis, suggesting the possibility of divergent autonomic conditions before AF onset. CONCLUSIONS In the hour before AF after CABG surgery, higher heart rate and lower heart rate complexity compared with values in control patients were independent predictors of AF. Decreased ApEn occurs in patients with either increased or decreased HRV by traditional measures and may provide a useful tool for risk stratification or investigation of mechanisms.

Differing Effects of Age on Heart Rate Variability in Men and Women

Gender and age are both known to affect heart rate variability (HRV). Their interaction is not known. HRV, determined from 24-hour Holter recordings, was compared between gender-matched older (15 men and 15 women, aged 67 +/- 3 years, range 64 to 76) and younger (15 men and 15 women, aged 33 +/- 4 years, range 26 to 42) subjects selected for an age difference of approximately 35 years. HRV for older and younger subjects was compared separately by gender. HRV was also compared by gender within groups. Heart rates were significantly higher, and all time and frequency domain indexes of HRV were significantly lower among the older than among the younger men. Among the women only the shorter term indexes of HRV were significantly lower in the older group. When HRV was compared by gender within age groups, there were no significant differences between men and women in the older group. In the younger group, men had lower heart rates, and all 24-hour time domain indexes of HRV, except those that reflect vagal modulation of heart rate, were significantly higher than those in women. We conclude that HRV is comparable in older men and women. However, HRV is differently affected by age. In men, for whom initial levels of HRV are significantly higher, older age is associated with a global reduction in HRV, reflecting reductions in both sympathetic and parasympathetic modulation and a loss of circadian variability. In women, older age is associated mainly with a decline in shorter term indexes of HRV without significant changes in circadian variability.

Dietary Fish and ω-3 Fatty Acid Consumption and Heart Rate Variability in US Adults

Background— Fish and &ohgr;-3 fatty acid consumption reduce risk of cardiac death, but mechanisms are not well established. Heart rate variability (HRV) predicts cardiac death and reflects specific electrophysiological pathways and influences. We hypothesized that habitual consumption of fish and marine &ohgr;-3 fatty acids would be associated with more favorable HRV, elucidating electrophysiological influences and supporting effects on clinical risk. Methods and Results— In a population-based cohort of older US adults, we evaluated cross-sectional associations of usual dietary fish and &ohgr;-3 consumption during the prior year and ECG-derived (n=4263) and 24-hour Holter monitor–derived (n=1152) HRV. After multivariable adjustment, consumption of tuna or other broiled/baked fish was associated with specific HRV components, including indices suggesting greater vagal predominance and moderated baroreceptor responses (eg, higher root mean square successive differences of normal-to-normal intervals [P=0.001]; higher normalized high-frequency power [P=0.008]; and lower low-frequency/high-frequency ratio [P=0.03]) and less erratic sinoatrial node firing (eg, lower Poincaré ratio [P=0.02] and higher short-term fractal scaling exponent [P=0.005]) but not measures of circadian fluctuations (eg, 24-hour standard deviation of normal-to-normal intervals). Findings were similar for estimated dietary consumption of marine &ohgr;-3 fatty acids. For magnitudes of observed differences in HRV comparing the highest to lowest category of fish intake, differences in relative risk of cardiac death during 10.8 years of follow-up ranged from 1.1% (for difference in standard deviation of normal-to-normal intervals) to 5.9% and 8.4% (for differences in Poincaré ratio and short-term fractal scaling exponent) lower risk. Conclusions— Habitual tuna/other fish and marine &ohgr;-3 consumption are associated with specific HRV components in older adults, particularly indices of vagal activity, baroreceptor responses, and sinoatrial node function. Cellular mechanisms and implications for clinical risk deserve further investigation.