Measures Of Heart Period Variability Research Articles

Comparison of baroreflex sensitivity and heart period variability after myocardial infarction

In animals, baroreflex sensitivity is inversely related to the likelihood of ventricular fibrillation during myocardial ischemia. After myocardial infarction in human patients, reduced baroreflex sensitivity is associated with increased mortality. A reduced standard deviation of normal RR intervals over a 24 h period is also associated with reduced survival after myocardial infarction. Therefore, 32 normotensive men who had survived their first myocardial infarction were studied to define the relation between baroreflex sensitivity assessed with phenylephrine injection and three Hotter electrocardiographic measures of tonic vagal activity: the percent of successive normal RR intervals >50 ms, the root mean square successive difference of normal RR intervals and the power in the high frequency energy of the normal RR interval power spectrum.Correlations among the Holter measures of heart period variability were ≥0.94, indicating that these measures are so strongly correlated that any one of them can be used to represent the others. Baroreflex sensitivity showed weaker correlations with the three Holter variables (0.57 to 0.63), indicating that the Holter measures did not accurately predict baroreflex sensitivity. Baroreflex sensitivity showed a stronger correlation with the three Hotter variables during the night than during the day. Baroreflex sensitivity and tonic vagal activity reflected by Holter variables were reduced more in patients with inferior myocardial infarction than in those with anterior infarction. The relative utility of baroreflex sensitivity and Holter measures of tonic vagal activity in predicting sudden cardiac death after myocardial infarction needs to be evaluated in a large prospective study.

Comparison of time- and frequency domain-based measures of cardiac parasympathetic activity in Holter recordings after myocardial infarction

The standard deviation of normal RR intervals predicts mortality after acute myocardial infarction independently of left ventricular function and ventricular arrhythmias. 1 Myers et al 2 suggested that this measure of heart period variability is a broad-band measure composed of high and low frequency components, and suggested that patients with malignant arrhythmias have reduced power in the high frequency band of the heart period or heart rate power spectrum. The high frequency band of the heart rate power spectrum reflects vagally mediated respiratory sinus arrhythmia. 3–5 Also, 2 time domain measures—the percent of absolute differences between successive normal RR intervals that exceed 50 ms (pNN50) and the root mean square successive difference (r-MSSD)—have been used as measures of tonic vagal activity. 6 The objective of this study was to determine the strength of association among 3 measures of tonic vagal activity: the high frequency band (0.15 to 0.50 Hz) in the heart period power spectrum, pNN50 and r-MSSD. We expected strong correlations among these 3 variables, and hoped that the correlations would be strong enough to permit their interchangeable use for assessing tonic vagal activity in long duration electrocardiographic recordings. We expected weaker correlations of these 3 measures with measures of total heart rate or heart period variability, such as the standard deviation of normal RR intervals or the total power in the heart period power spectrum.

The Relation between Neonatal Heart Period Patterns and Developmental Outcome

Developmental psychophysiologists have long been interested in a means for evaluating infants at risk for cognitive disabilities. The current research addressed the utility of a noninvasive measure of cardiac vagal tone in predicting developmental outcome. At 40 weeks conceptional age, 3 min of resting EKG were recorded from 80 infants. Four groups of infants were evaluated: prematures who had no medical complications in the postnatal period; prematures who experienced respiratory distress syndrome during the postnatal period; term infants who experienced birth asphyxia during labor and/or postdelivery; and healthy term infants. The mental scale of the Bayley Scales of Mental Development was administered at 8 and 12 months conceptional age. Heart period data were analyzed to derive mean heart period, heart period variability, and estimates of vagal tone for each subject. Analyses of the relationship between the heart period variables and 8- and 12-month outcome (i.e., Bayley Scales) indicated that infants with high vagal tone at 40 weeks conceptional age always had positive developmental outcome at both eight and 12 months of age. Infants with low vagal tone had varied outcomes. Measures of medical complications and other measures of heart period variability were not related to developmental outcome. The results suggest that measurement of cardiac vagal tone may provide an important means for assessing risk in birth stressed populations.