Peter P. Domitrovich

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.

Effect of exercise training on heart rate variability in healthy older adults

OBJECTIVE To determine the effect of exercise training on cardiac autonomic modulation in normal older adults by using analysis of heart rate variability. SUBJECTS The exercise group consisted of 7 men and 9 women aged 66 +/- 4 years. The comparison group consisted of 7 men and 9 women also aged 66 +/- 4 years. METHOD Heart rate variability was determined from 24-hour Holter recordings before and after 12 months of supervised exercise, which consisted of 3 months of stretching and 9 months of 5 hours/week aerobic exercise at approximately 70% of maximal oxygen uptake. Heart rate variability was measured at baseline and 12 months later in the comparison group, who had not changed their usual activity level. RESULTS In the exercise group maximal oxygen consumption increased from 1.8 +/- 0.5 L/min to 2.2 +/- 0.7 L/min (P <.05). The standard deviation of normal interbeat intervals increased from 126 +/- 21 ms to 142 +/- 25 ms. Mean nighttime heart rate decreased from 67 +/- 6 beats/min to 63 +/- 5 beats/min. Increased fitness level had little effect on indexes of heart rate variability, which reflect parasympathetic or mixed sympathetic/parasympathetic modulation of heart rate. There was no change in heart rate or heart rate variability in the comparison group. CONCLUSIONS Exercise training increases total heart rate variability in normal older adults. The most marked alterations are in nocturnal heart rate. Heart rate variability is stable over a 1-year period in older adults who do not alter their activity level.

Sometimes Higher Heart Rate Variability Is Not Better Heart Rate Variability: Results of Graphical and Nonlinear Analyses

Objective: To determine the prevalence and effect on traditional heart rate variability (HRV) indices of abnormal HRV patterns in the elderly.

Ambulatory ECG-Based T-Wave Alternans Predicts Sudden Cardiac Death in High-Risk Post-MI Patients with Left Ventricular Dysfunction in the EPHESUS Study

Background: Exercise microvolt T‐wave alternans (TWA) identifies sudden cardiac death (SCD) risk. TWA can be measured from ambulatory ECGs (AECGs) using modified moving average (MMA) method. Whether MMA TWA from AECGs predicts SCD in post‐MI patients with left ventricular dysfunction (LVD) is unknown.

The relationship of heart rate and heart rate variability to non-diabetic fasting glucose levels and the metabolic syndrome: The Cardiovascular Health Study

Background  Increased heart rate (HR) and diminished heart rate variability (HRV) are signs of early cardiovascular autonomic neuropathy. We tested the hypotheses that increased HR and diminished HRV are present in people: (i) with increased fasting glucose (FG) levels not in the range of diabetes mellitus (DM), and (ii) in people with the metabolic syndrome (MetS) independent of elevated FG levels.

A Simple Method to Identify Sleep Apnea Using Holter Recordings

Introduction: Despite its severe cardiovascular and other consequences, sleep apnea syndrome frequently is undiagnosed. Because apneas result in repeated autonomic arousals associated with cyclic variations in heart rate (CVHR), we hypothesized that sleep apnea syndrome could be identified from simple HR tachograms (graphs of HR vs time) derived from ECG monitoring.

Heart rate variability and its changes over 5 years in older adults

PURPOSE to characterise the association between age, ageing and heart rate variability (HRV) in older individuals, 585 adults age >65 years with two 24-h Holter recordings in the Cardiovascular Health Study were studied. METHODS heart rate (HR), ventricular premature contractions (VPCs), atrial premature contractions (APCs), frequency-domain, ratio-based and non-linear HRV and heart rate turbulence (HRT) were examined cross-sectionally by 5-year age groups and prospectively over 5 years. Analyses adjusted for gender, lower versus elevated cardiovascular (CV) risk and for the change in CV risk. RESULTS HR declined, and VPCs and APCs increased per 5-year increase in age. Frequency-domain HRV decreased more at 65-69, less at 70-74 and minimally at > or =75 years, independent of CVD risk or change in CVD risk. Ratio and non-linear HRV continued to decline to > or =75 years old. Ratio HRV and HRT slope were more strongly related to CVD risk than frequency-domain HRV. CONCLUSIONS cardiac autonomic function, assessed by frequency-domain HRV, declines most at 65-70 and levels off at age >75. The decline is independent of CVD risk or change in CVD risk. Ratio-based and non-linear HRV and HRT slope continued to change with increasing age and were more closely related to CVD risk than frequency-domain HRV.

Novel Measures of Heart Rate Variability Predict Cardiovascular Mortality in Older Adults Independent of Traditional Cardiovascular Risk Factors: The Cardiovascular Health Study (CHS)

Background: It is unknown whether abnormal heart rate turbulence (HRT) and abnormal fractal properties of heart rate variability identify older adults at increased risk of cardiovascular death (CVdth).

Autonomic nervous system responses during sedative infusions of dexmedetomidine

BACKGROUND The purpose of this study was to determine the effects of dexmedetomidine on systemic and cardiac autonomic reflex responses during rest and during thermal stress. METHODS Volunteers received either placebo or low- or high-dose dexmedetomidine (target plasma concentrations 0.3 or 0.6 ng/ml, respectively) infusions in a prospectively randomized, double-blinded crossover study design. After 1 h, baroreflex sensitivity was assessed, and then core body temperature was raised to the sweating threshold and then lowered to the shivering threshold. Plasma catecholamines and blood pressure were measured, and cardiac autonomic responses were assessed by analysis of heart rate variability. RESULTS Compared with placebo, plasma norepinephrine concentrations, blood pressure, heart rate, and some heart rate variability measures were lower after 1-h infusion of dexmedetomidine, but baroreflex responses did not differ significantly. Dexmedetomidine blunted the systemic and cardiac sympathetic effects of sweating observed during placebo infusion but had no effect on parasympathetic measures. Increases in blood pressure, and systemic catecholamines due to shivering were observed during placebo and dexmedetomidine, but these responses were less with dexmedetomidine. During shivering, dexmedetomidine infusion was associated with higher low-frequency and high-frequency heart rate variability power but lower heart rate compared with the sweating threshold and with the control period, suggesting nonreciprocal cardiac autonomic responses. CONCLUSIONS Infusion of dexmedetomidine results in compensated reductions in systemic sympathetic tone without changes in baroreflex sensitivity. Dexmedetomidine blunts heart rate and the systemic sympathetic activation due to sweating, but it is less effective in blunting cardiac sympathetic responses to shivering. During dexmedetomidine infusion, cardiac sympathetic and parasympathetic tone may have nonreciprocal changes during shivering.