Heart rate fragmentation as a marker of altered global autonomic nervous system activity: a novel predictor of atrial fibrillation occurrence in the general population

Background

The dysfunction of the autonomic nervous system (ANS) plays an important role in the initiation and maintenance of atrial fibrillation (AF). However, the meaning of high heart rate variability (HRV) in predicting AF is still under debate due to conflicting results in population-based studies. Short-term HRV is conceptually attributed to vagal tone modulation. But recent data suggest that a component of short-term HRV, called heart rate fragmentation, is related to ANS breakdown. On the other hand, parasympathetic activity could be assess by a novel metric, the deceleration capacity (DC).

Objective

To assess predictive capacity of novel HRV-derived metrics, whether fragmentation indices or parameters of vagal tone, regarding the occurrence of AF in general population during long-term follow-up.

Methods

A cohort study was designed to prospectively assess the predictive value of ANS activity level among a healthy retired French population, regarding cardiovascular events and mortality. 1011 subjects aged 65 were enrolled in the study from 2000 to 2002. The enrolled population had no history of AF and a low cardiovascular risk. A median follow-up of 17.8 years (16.0–18.5) was managed. HRV data were acquired by 24-h Holter electrocardiogram (ECG) monitoring at baseline and assessed by frequency domain and time domain methods. Heart rate fragmentation using the percentage of inflection points (PIP), and assessment of specific parasympathetic activity using DC were then calculated. The study outcome was the onset of AF during follow-up, defined as a standard 12-lead ECG or Holter recording with ≥30 s of AF.

Results

AF was diagnosed in 123 patients along the 18-year follow-up, representing a cumulative incidence of 13.4%. Using univariate analysis (Figure 1A), a higher percentage of NN intervals that differ by more than 50 ms from the previous interval (pnn50) and root mean square differences of successive NN intervals (RMSSD) were associated with AF onset (p<0.01). A lower ratio of low-frequency and high-frequency component (LF/HF) was the only frequency-domain parameter found to predict the AF occurrence (p<0.01). The occurrence of AF was predicted by a higher PIP (p<0.01) and lower DC (p<0.01). Through multivariate analysis using clinical parameters that reached statistical significance in univariate analysis (Figure 1B), higher PIP was found as an independent predictor of AF occurrence (HR=2.1, 95% CI: 1.1–3.9, p=0.02), as well as male gender (HR=2.1, 95% CI: 1.1–3.9, p=0.02), and non-sustained supraventricular tachycardia (HR=2.1, 95% CI: 1.1–3.9, p=0.02).

Conclusion

(see Figure 2) Elevated PIP, a marker of heart rate fragmentation secondary to impaired ANS activity, is an independent predictor of the onset of AF in the healthy general population. Therefore, high HRV associated to AF occurrence could be the consequence of general ANS impairment rather than increased parasympathetic activity.

Funding Acknowledgement

Type of funding sources: None.

Sickle cell disease: selected aspects of pathophysiology

Sickle cell disease (SCD), a genetically-determined pathology due to an amino acid substitution (i.e., valine for glutamic acid) on the beta-chain of hemoglobin, is characterized by abnormal blood rheology and periods of painful vascular occlusive crises. Sickle cell trait (SCT) is a typically benign variant in which only one beta chain is affected by the mutation. Although both SCD and SCT have been the subject of numerous studies, information related to neurological function and transfusion therapy is still incomplete: an overview of these areas is presented. An initial section provides pertinent background information on the pathology and clinical significance of these diseases. The roles of three factors in the clinical manifestations of the diseases are then discussed: hypoxia, autonomic nervous system regulation and blood rheology. The possibility of a causal relationship between these three factors and sudden death is also examined. It is concluded that further studies in these specific areas are warranted. It is anticipated that the outcome of such research is likely to provide valuable insights into the pathophysiology of SCD and SCT and will lead to improved clinical management and enhanced quality of life.

Decrease in gait variability while counting backward: a marker of "magnet effect"?

Counting backward (CB) and walking are both rhythmic tasks. An improvement of CB performance has been reported while walking, and has been interpreted as a "magnet effect" which is the tendency of biological oscillators to attract each other. The objective of this study was to compare the coefficient of variation (CoV) of stride time (ST) and the number of enumerated figures while single- and dual-tasking between older adults who increased and decreased their CoV of ST while CB. The number of enumerated figures and the CoV of ST under single-task (i.e., CB while sitting or walking alone) and dual-task (i.e., CB while walking) were measured among 100 community-dwelling older subjects (mean, 69.8 ± 0.07 years). Subjects were separated into two groups according to the dual-task-related changes in CoV of ST (i.e., either above or below the mean value of CoV of ST under single-task). Seventeen participants decreased their CoV of ST while CB compared to usual walking (2.6 ± 1.6% vs. 2.0 ± 1.3%, P < 0.001), while 83 increased their CoV of ST (1.7 ± 0.6% vs 3.4 ± 2.3%, P < 0.001). The subjects who decreased their CoV of ST had a tendency to enumerate more figures while walking compared to sitting (20.9 ± 6.3 vs 19.4 ± 4.7, P = 0.046) unlike those who increased their CoV of ST (20.3 ± 5.0 vs 21.8 ± 6.0 while sitting, P = 0.001). We found that most of subjects had worse gait and CB performance while dual-tasking. Conversely, a limited number of subjects improved significantly their gait performance and simultaneously had a tendency to improve their CB performance while walking compared to sitting. This behavior was observed only among subjects with the highest gait variability and could be interpreted as an implicit strategy based on the "magnet effect".

Birth prematurity determines prolonged autonomic nervous system immaturity

Because of its multiple involvement in physiological processes, autonomic nervous system (ANS) activity, a key regulator of homeostatic control, demonstrates a progressive increase during pregnancy. The profile of its maturation, mainly in the parasympathetic arm, in premature or full term infants, may help us to better understand its pathophysiological role. We prospectively evaluated ANS maturity in a group of 23 premature (PREM) infants at their theoretical term age and in 8 full term (FT) newborns. All recordings were registered close to the theoretical full term period (from 38 to 41 weeks) for the PREM group and during the first week of life for the FT newborns. Polygraphic recordings, EEG monitoring associated with visual clinical control, and Holter ECG, were performed simultaneously. ANS indices were then calculated during quiet sleep periods, using Wavelet transform of RR (beat to beat) intervals. High frequency components were found to be significantly lower in the PREM than in the FT group (p<0.05). Furthermore, at theoretical full term age, the greater the prematurity, the lower was parasympathetic activity. Because it is easy, monitoring of parasympathetic activity may help us to understand autonomic maturation and its clinical prognostic implications.

Influence of exercise training on cardiac baroreflex sensitivity in patients with COPD

Decreased spontaneous cardiac baroreflex sensitivity (BRS), which could lead to the onset of cardiovascular events, has been demonstrated in chronic obstructive pulmonary disease patients. This study evaluates the effects of an exercise training programme on BRS. Twenty-one chronic obstructive pulmonary disease patients (mean+/-SD age 62+/-9 yrs; forced expiratory volume in one second 43.6+/-18.1% of the predicted value) with mild hypoxaemia (arterial oxygen tension 8.96+/-1.18 kPa) were compared to 18 healthy age-matched subjects. BRS was calculated as the slope of the baroreflex sequences between spontaneous changes in systolic blood pressure and subsequent consecutive relative risk deviation length, and was measured in the supine position and following head-up tilt for sympathetic stimulation. Pulmonary function test results and blood gas levels, measured only in patients, did not change after the training programme. Exercise training increased the maximal sustained workload (16.5%) and peak oxygen consumption (20.5%). Before training, BRS was lower in patients than in controls (2.7+/-1.5 versus 7.8+/-4.9 ms x mmHg(-1)) and tilting induced a smaller reduction in BRS (13 versus 34%). After training, BRS increased to 3.4+/-2.6 ms x mmHg(-1) in patients but remained lower than in controls. The response to the tilt test remained unchanged after training. It is concluded that, in chronic obstructive pulmonary disease patients, exercise training is associated with a gain in spontaneous baroreflex sensitivity, reflecting cardiovascular benefits.

[Activity of the autonomous nervous system measured based on the variability of heart rate in female urinary incontinence]

OBJECTIVES

To compare the ANS activity, measured by heart rate variability (HRV) in various types of female urinary incontinence (UI).

MATERIALS AND METHODS

25 patients were included in this prospective study: 11 presented stress UI without sphincter incompetence, 9 presented mixed UI and 5 presented urge UI. UI without idiopathic detrusor instability (IDI) (n = 11) was compared to UI with IDI (N = 14.). No statistically significant difference was observed for mean age of the patients in the two groups. A 24-hour Holter ECG, under the conditions of the patient's everyday life, provided time and frequency indices (Fourier transform) of HRV, reflecting the sympathetic, parasympathetic and global ANS activity.

RESULTS

The global ANS activity of the patients with either mixed UI, urge UI or UI with IDI, was statistically significantly lower (p < 0.05) than that of patients with stress UI. The sympathetic-vagal balance, heart rate, blood pressure, and Ditrovie score were not significantly different between the groups.

CONCLUSIONS

This preliminary study shows that IDI is associated with a global reduction of ANS activity compared to that of patients without IDI. Modifications of sympathetic, parasympathetic and global ANS activity were also observed between the various types of female UI.

A drug interaction study between ticlopidine and cyclosporin in heart transplant recipients

OBJECTIVES

Previous uncontrolled studies have suggested an interaction between ticlopidine, a major antiplatelet agent, and cyclosporin in heart- and kidney-transplant recipients. The aims of this study were to examine in a randomised, double-blind fashion, the possible interaction between cyclosporin A and ticlopidine (250 mg per day) and the tolerability of this combination in heart-transplant recipients.

METHODS

Twenty heart-transplant recipients were randomised into either a treated or a placebo group. Blood samples were drawn for time-course evaluation of cyclosporin blood levels over a period of 12 h, following the morning intake of cyclosporin and, for platelet aggregation studies, before and after 14 days of ticlopidine administration. Twenty four-hour urine samples were collected for 6-beta-hydroxycortisol measurements, before and after 14 days of ticlopidine.

RESULTS

Although given at half the recommended daily dosage, ticlopidine significantly reduced platelet aggregation. Pharmacokinetic parameters indicate that the bioavailability of cyclosporin A was not significantly modified by ticlopidine. However, one patient in the ticlopidine group was withdrawn because of a major fall in cyclosporin blood level within 3 days of treatment. Urinary excretion of 6-beta-hydroxycortisol was augmented after treatment in the ticlopidine group compared with the placebo group, suggesting that induction of drug metabolism might have occurred. Data also show quite a large intra-individual variability in cyclosporin bioavailability in the placebo group, suggesting that poor absorption of the drug formulation and/or poor compliance might have contributed to the decreased cyclosporin blood levels in the patient withdrawn from this study and in previous uncontrolled studies.

CONCLUSION

Cyclosporin bioavailability was not clearly modified by a half dosage of ticlopidine in this study. We, however, recommend closely monitoring cyclosporin blood levels when prescribing ticlopidine. Further studies will be needed with new formulations of cyclosporin or when using the full dosage of ticlopidine.

Control of bias in dietary trial to prevent coronary recurrences: The Lyon Diet Heart Study

BACKGROUND AND OBJECTIVES

A major limitation of dietary trials is that double blind design is not feasible. These trials are therefore prone to biases. The Lyon diet heart study is a single-blind secondary prevention trial to test the hypothesis that a Mediterranean-type of diet may prevent recurrences after a first myocardial infarction. A surprising 73% reduction of the risk of new major cardiac events was observed in the experimental group. For this reason, it is important to describe the methods used in the trial. We now report our techniques to randomize the patients, to change their diet and to control for possible bias, in particular any investigator or attending physician bias.

DESIGN

In this dietary trial, a specific design was used to recruit and randomize the patients without informing them and their physicians that they were participating in a comparative trial. The attending physician bias was evaluated by studying drug usage and the investigator bias by constructing a questionnaire from which specific scores were used to evaluate (1) how the patients appreciated their participation in the study and (2) whether this participation resulted in significant changes in their way of living.

SUBJECTS

605 survivors of a first myocardial infarction were randomized into either a control or a Mediterranean group.

RESULTS

The two randomized groups were similar for all the variables of prognosis. Drug usage was not significantly different between groups, suggesting that there was no major attending physician bias. Analyses of the appreciation scores and of the change score did not detect any significant investigator bias.

CONCLUSIONS

Although the study cannot be completely shielded from minor biases, the data presented here provide evidence that the dietary modifications per se were protective, not other (including psychosocial) changes resulting from the participation to the trial.

Effect of a 6-week endurance training programme and branched-chain amino acid supplementation on histomorphometric characteristics of aged human muscle

The effects of a 6-week endurance training programme and a branched-chain amino acid (BCAA) supplementation were investigated on skeletal muscle histomorphometric characteristics of elderly men. Seventeen elderly men, age (63 +/- 5 years), height (173 +/- 5 cm) and weight (75 +/- 8 kg) were included in the study. One group (n = 9) received an oral BCAA supplementation for 6 weeks (16, 2 and 2 g per day of leucine, isoleucine and valine, respectively), while another group (n = 8) received a placebo. During these 6 weeks, subjects trained on a Monark cycle ergometer at 75 +/- 9% of their maximal heart rate for 1 h/day, 4 days/week. Muscle biopsy samples taken at rest before and after endurance training were analyzed for capillarization, fibre type distribution and fibre area. As a result of endurance training, maximal oxygen uptake was significantly increased by about 5% in control and BCAA supplemented groups (P < 0.01). The number of capillaries per fibre and in contact with type I fibres was significantly increased (P < 0.05), this effect being similar in control and BCAA supplemented groups. The percentage distribution and area of type I, type IIa and type IIb fibres did not differ between the two groups and remained unchanged with endurance training. It is concluded that skeletal muscle of elderly men can adapt to a 6-week endurance training programme and that a BCAA supplementation does not further enhance the induced histomorphometric changes.

Initial combined cryotherapy and irradiation for unresectable non-small cell lung cancer. Preliminary results

In unresectable non-small cell lung cancer (NSCLC) with a patent mainstem bronchus, some studies of obstructive tumors, showed (1) a poor role for irradiation in obtaining efficient debulking and (2) an interest in preliminary laser treatment in these patients. Cryotherapy is another method to obtain debulking. Moreover, several studies showed that cryotherapy would increase the radiosensitivity of a tumor. We performed a preliminary protocol combining successively initial cryotherapy followed by irradiation in inoperable NSCLC (either for local or functional contraindications). Thirty-eight patients were included and treated first by cryotherapy performed under general anesthesia and then with external irradiation in a curative intent. The efficiency of cryotherapy assessed on bronchoscopy was found to be volume-efficient (VE) in 26 of the 38 patients and non-volume-efficient (NVE) in the other 12 patients. After irradiation in the VE group, 17 of the 26 patients had no bronchial residual tumor (NRT). In contrast, all of the patients in the NVE group had a bronchial residual tumor (RT). Survival in the VE group (median, 397 days) was significantly higher than the survival of the NVE group (median, 144 days). Survival was found to be independent of the surgical contraindication (local or functional). The best survival was associated both with the efficiency of the initial debulking (VE) by cryotherapy and with the local control (NRT) induced by the irradiation (median, 560 days). Local control was obtained in 65 percent (17/26) of the cases in the VE group and was never observed in the NVE group. In our study the VE group's local control is better than the 35 percent usually reported after irradiation alone. These results argue for the efficient potentiation of irradiation by cryotherapy.

Quantification of valvular regurgitation by cardiac blood pool scintigraphy: correlation with catheterization

The diagnosis of valvular regurgitation (R) is usually based on clinical signs. Quantification conventionally requires catheterization (C). We have quantified R with cardiac blood pool scintigraphy (CBPS) and compared the results with those obtained by C. Regurgitant fraction (RF) determined by C was calculated with the technique of Dodge. Forward output was measured by thermodilution or cardiogreen dilution. The RF at CBPS was obtained by the stroke index ratio (SIR) minus 1.2 divided by SIR, where SIR is the ratio of the stroke counts of left ventricle over those of the right ventricle. Stroke counts are calculated directly from the time-activity curves. Each time-activity curve was obtained by drawing one region of interest around each diastolic image. The correction factor (1.2) was calculated from a large normal population. 22 patients had aortic R, 7 mitral R, 12 both, 8 patients had no evidence of regurgitation. RF of the patients with R varied from 27 to 71% (x = 42%) at C and from 26 to 74% (y = 41%) at CBPS. Linear regression shows a good correlation coefficient (r = 0.82). The regression equation is y = 0.93x + 1.8. No correlation was found between RF (CBPS or C) and the severity of R assessed visually from angiography.

IN CONCLUSION

CBPS, a non-invasive method, allows easy and repeatable determination of RF and correlates well with data obtained at catheterization.

Lactate determination with the lactate analyser LA 640: a critical study

Using the new method of sample preparation developed by the manufacturer in 1979, the lactate analyser LA 640 now provides reliable measurements of blood lactic acid from blood micro-samples of 20 microliters within 2 min. Reproducibility is comparable to that obtained by spectrophotometric assay with +/- 0.2 mmol . l-1 for 95% confidence limits. High accuracy was also obtained with 95% linked confidence limits within +/- 0.19 mmol . l-1 and +/- 0.46 mmol . l-1 for blood lactate concentrations of from 2-4 and 7-9 mmol . l-1 respectively. Due to a lactate concentration increase of 0.5 mmol . l-1 . h-1 in whole blood kept at 20 degrees C, the blood must be immediately diluted in the buffer haemolysing solution after withdrawal. This diluted sample can then be stored at room temperature without alteration, provided the concentration in the dilution is lower than 0.8 mmol . l-1. For serial successive measurements, a new sample can be tested before the electrode current reaches its background value.