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At least 811 records · Page 45Linked to original sources
PubMed2003

Assessment of cardiovascular autonomic function in myotonic dystrophy type 2 (DM2/PROMM).

BACKGROUND: Proximal myotonic myopathy is an autosomal dominant multisystem disorder with a recently defined CCTG expansion on chromosome 3 in the major subgroup (myotonic dystrophy type 2). Cardiac rhythm disturbances have been described in patients with this disease, but it is not known whether myotonic dystrophy type 2/proximal myotonic myopathy patients suffer from dysautonomia and whether cardiac arrhythmias relate to autonomic dysfunction. OBJECTIVES: To investigate cardiovascular autonomic function in myotonic dystrophy type 2/proximal myotonic myopathy patients with and without cardiac arrhythmias. PATIENTS AND METHODS: Standard autonomic function tests (heart rate responses to Valsalva manoeuvre, deep breathing and active change of posture, and blood pressure responses to active change of posture and sustained handgrip), resting heart rate variability in the time- and frequency-domain, and the corrected QT interval length were determined in 16 patients with genetically defined myotonic dystrophy type 2/proximal myotonic myopathy and compared to the results obtained in 16 age- and sex-matched healthy control subjects. RESULTS: Standard autonomic tests yielded similar results in both groups. Measures of heart rate variability tended to be lower in myotonic dystrophy type 2/proximal myotonic myopathy patients compared to healthy controls, but reached statistical significance only for the number of R-R intervals exceeding 50 ms (p50) and the power spectrum density in the low-frequency range (low-frequency power). Four patients (25%) suffered from mild cardiac rhythm disturbances encompassing paroxysmal tachycardia, sinoatrial block, right bundle branch block, ventricular premature beats and bradycardia. The autonomic responses of these patients were essentially similar compared to those without cardiac arrhythmias, apart from a decreased heart rate response to deep breathing in the patients with cardiac arrhythmias. CONCLUSIONS: We found no major abnormalities of cardiovascular autonomic function in patients with myotonic dystrophy type 2/proximal myotonic myopathy, neither in the whole study group nor in the subgroup of patients with cardiac rhythm abnormalities.

Adult↗
PubMed2003

[Stress, depression and cardiac arrhythmias].

A relationship between behavioural factors and cardiac arrhythmogenesis in humans has been described. Three sets of conditions contribute to the occurrence of arrhythmias: myocardial electrical instability, most often due to coronary artery disease; an acute triggering event, frequently related to mental stress; and a chronic, pervasive, and intense psychological state, often including depression and hopelessness. The autonomic nervous system plays an important role in the occurrence of cardiac arrhythmias and it is well documented that mood alterations as mental stress and depression influence cardiac autonomic balance. There is an increasing body of evidence that patients with the greatest changes in cardiac neural regulation with decreased parasympathetic tone coupled with increased sympathetic activity are at the greatest risk for developing fatal ventricular arrhythmias. These patients have a reduced heart rate variability, increased QT-dispersion and a decreased baroreceptor sensitivity. The influence of stress and depression on the autonomic nervous system and the impact on the occurrence of both atrial and ventricular arrhythmias is being discussed.

Arousal↗
PubMed2002

Interatrial transseptal electrical conduction: comparison of patients with atrial fibrillation and normal controls.

INTRODUCTION: This study analyzed the electrophysiologic properties of interatrial transseptal electrical conduction at Bachmann's bundle and the ostium of the coronary sinus (CS os) in response to pulmonary vein (PV) stimuli, which mimicked spontaneous ectopy. METHODS AND RESULTS: Forty patients with atrial fibrillation (AF) referred for ablation (15 persistent AF and 25 paroxysmal AF) and 15 control patients were enrolled in the study. During decremental extra-stimulus pacing from the PVs, right atrial activation was analyzed using noncontact mapping and multipolar catheters. The refractory periods and conduction times were calculated for Bachmann's bundle, CS os, and left atrium. The dispersion of refractoriness was calculated as the difference between the refractory periods of Bachmann's bundle and the CS os. The refractory period at Bachmann's bundle was 244 msec in the persistent AF group, 213 msec in the paroxysmal AF group, and 199 msec for controls. The refractory period at the CS os was 220 msec in the persistent AF group, 201 msec in the paroxysmal AF group, and 193 msec for controls. The dispersion of refractoriness was 54 msec in the persistent AF group; this was significantly greater than in paroxysmal AF at 32 msec (P < 0.05) and controls at 13 msec (P < 0.01). During decremental pacing, lengthening of conduction times at both Bachmann's bundle and the CS os were significantly greater in the persistent AF group compared with paroxysmal AF or control groups. A higher dispersion of refractoriness was associated with a higher incidence of inducible AF and a lower rate of ablation success. CONCLUSION: There are differences between the left to right interatrial electrical connections between patients with persistent AF, paroxysmal AF and controls.

Adult↗
PubMed2000

Elevated plasma fatty acid concentrations stimulate the cardiac autonomic nervous system in healthy subjects.

BACKGROUND: Fatty acids have been shown to stimulate the sympathetic nervous system in rats. Power spectral analysis of heart rate variability (HRV) is a safe and useful tool with which to evaluate cardiac autonomic nervous system (ANS) activity. Whether changes in plasma fatty acid concentrations affect the sympathetic nervous system or HRV in humans is unknown. OBJECTIVE: We investigated the possible changes in HRV after a significant increase in plasma fatty acid concentration. DESIGN: Subjects were randomly assigned to receive an infusion of lipid emulsion (10% triacylglycerol emulsion for 180 min) + heparin (a bolus of 200 U followed by 0.2 U*min(-)(1)*kg body wt(-)(1); n = 20) or 0.9% NaCl (for 180 min; n = 10). RESULTS: Lipid emulsion + heparin infusion was associated with a rise in plasma epinephrine and norepinephrine concentrations. The rise in plasma fatty acid concentration was associated with a significant decline in the RR interval (P: < 0.03) and in total power (P: < 0.03). Analysis of the different components of HRV showed that lipid emulsion + heparin infusion stimulated low- frequency (LF) components (P: < 0.03 at the second hour and P: < 0. 01 at the third hour) and inhibited high-frequency (HF) components (P: < 0.03 at the second and third hours). Consequently, the LF-HF ratio was significantly stimulated (P: < 0.03 at the second hour and P: < 0.01 at the third hour). Such results persisted, although attenuated, when the study was repeated in association with a propranolol infusion (n = 8). CONCLUSION: Elevated plasma fatty acid concentrations may stimulate cardiac autonomic nervous system activity.

Adult↗
PubMed1999

Cardiac autonomic adjustments to normal human pregnancy: insight from spectral analysis of R-R interval and systolic arterial pressure variability.

OBJECTIVE: To assess the adaptation in autonomic control mechanisms that accompanies the marked haemodynamic changes, such as increases in cardiac size and output, that occur in the course of normal human pregnancy. DESIGN: We studied 14 healthy pregnant women (aged 30+/-1 years) before the 6th week (early stage) and within weeks 32-34 (late stage) of pregnancy, while they were at rest or in a state of active orthostatism (standing), which enhances sympathetic activity. METHODS: We used echocardiography to assess cardiac volumes and mass, and spectral analysis of the R-R interval and systolic arterial pressure variability to obtain indices of autonomic regulation of the circulation. This non-invasive methodology, recently validated with direct recordings of muscle sympathetic nerve activity, furnishes quantitative markers of sympathetic modulation of the sino-atrial node (low frequency component, LF in normalized units, nu), vagal modulation (high frequency component, HF in normalized units, nu) and the overall arterial pressure-heart rate baroreflex gain (alpha index). RESULTS: Late pregnancy was characterized by an increase in cardiac size and volumes and by a reduction of R-R interval, R-R interval variance and the alpha index, together with an increase in the LF/HF ratio (from 1.4+/-0.4 to 5.6+/-1.9). Changes in markers of autonomic modulation of the sino-atrial node normally induced by the standing position were blunted. CONCLUSIONS: The late stage of normal human pregnancy appears to be characterized by alterations in the autonomic control of the circulation and by attenuated responsiveness to active standing, possibly as a consequence of the accompanying increase in cardiac size.

Adult↗
PubMed1996

A new method for analysis of atrial activation during chronic atrial fibrillation in man.

To further clarify the mechanisms maintaining chronic atrial fibrillation (CAF), a method identifying preferable activation patterns of the atria during fibrillation, by time averaging of multiple discrete excitation vectors, was developed. Repeated recordings, each of 56 atrial bipolar electrograms simultaneously acquired during 8 s, were made at multiple sites in the right atrial free wall and the left atrial appendage in 16 patients with CAF using a 2.17 x 3.54 cm electrode array. The local activation times (LAT's) in each recording were estimated as the median activation time at the respective measurement point. By calculating the time difference between the LAT's at adjacent measurement points in two spatial dimensions, a direction vector was created for each activation wave passing each set of measurement points, a total of 42 sets. By time averaging of the individual direction vectors (typically n = 55) at each set of measurement points, preferable activation patterns were determined. Three types of activation patterns were found: 1) inconsistent activation (n = 5), 2) consistent activation with preferential propagation directions (n = 7) and 3) consistent activation with impulses originating from a localizable site within the recording area (n = 4). All activation patterns were reproducible and the two latter patterns were proven significant using statistical tests. We conclude that this new method is useful in further clarification of the mechanisms involved in the maintenance of atrial fibrillation.

Aged↗
PubMed1988

Atrioventricular nodal conduction and refractoriness following abrupt changes in cycle length.

The properties of the atrioventricular (AV) nodal conduction and effective refractory period in man are generally evaluated at a constant basic cycle length (CL) and, in most cases, they demonstrate an inverse relationship to the drive cycle. The response of AV node to abrupt change in CL is less defined. We therefore studied the effects of abrupt changes in CL on AV nodal conduction time and refractoriness in 18 patients. AV nodal conduction time, and effective and functional refractory periods were measured during: (1) a constant long CL, (2) a constant short CL, and (3) after an abrupt increase in CL just prior to the introduction of extrastimuli. In 10 of the 18 patients a constant long CL of 600 ms, a constant short CL of 400 ms and a sudden short-to-long change in CL (400 to 600 ms) were tested. AV nodal conduction times (A2H2) were measured at the shortest and longest comparable A1A2 intervals. The mean value of the shortest A2H2 intervals for constant CL of 600 ms was 144 +/- 18 ms; for a constant CL of 400 ms it was 162 +/- 17 ms; after a sudden short-to-long change in CL (400 to 600 ms) it was 142 +/- 14 ms. The mean value of the longest A2H2 intervals at a constant CL of 600 ms was 185 +/- 18 ms; at a constant CL of 400 ms it was 236 +/- 26 ms (p less than 0.01) and after a short-to-long change in CL (400 to 600 ms) 199 +/- 21 ms. AV nodal effective refractory periods measured at the same three CLs had mean values of 279 +/- 13 ms; 300 +/- 15 ms and 294 +/- 13 ms, respectively. Similar results were obtained when other CLs such as 700 to 900, 500 to 900, and 400 to 700 ms were tested. The data suggest that after abrupt short-to-long changes in CL, AV nodal function curves shift from long constant CL toward short constant CL as the coupling intervals decrease, indicating a cumulative pattern. Although the return to baseline conduction time after the fast basic rate is known to be slow, the limitation of this effect to the very early premature beat in the human has not been reported previously.

Adult↗
PubMed1996

Heart rate variability in isolated rabbit hearts.

The presence of heart rate variability (HRV) in patients with cardiac denervation after heart transplantation raised our interest in HRV of isolated, denervated hearts. Hearts from seven adult white ELCO rabbits were transferred to a perfusion apparatus. All hearts were perfused in the working mode and in the Langendorff mode for 20 minutes each. HRV was analyzed in the frequency domain. A computer simulated test ECG at a constant rate of 2 Hz was used for error estimation of the system. In the isolated, denervated heart, HRV was of random, broadband fluctuations, different from the well-characterized oscillations at specific frequencies in intact animals. Mean NN was 423 +/- 51 ms in the Langendorff mode, 406 +/- 33 ms in the working heart mode, and 500 ms in the test ECG. Total power was 663 +/- 207 ms2, 817 +/- 318 ms2, and 3.7 ms2, respectively. There was no significant difference in any measure of HRV between Langendorff and working heart modes. The data provide evidence for the presence of HRV in isolated, denervated rabbit hearts. Left atrial and ventricular filling, i.e., the working heart mode, did not alter HRV, indicating that left atrial or ventricular stretch did not influence the sinus nodal discharge rate.

Animals↗
PubMed1997

Heart rate variability in patients with familial amyloid polyneuropathy.

The purpose of this study was to evaluate heart rate variability (HRV) in patients with familial amyloid polyneuropathy (FAP) using the time- and frequency-domain analysis. The study population consisted of 19 patients with FAP, and 19 age and sex matched normal volunteers. The 24-hour Holter recordings of all subjects in sinus rhythm and off medication were analyzed. Five time-domain indices of HRV were computed. The frequency component of HRV was calculated by fast Fourier transform analysis of the RR intervals. The power spectrum of the low frequency (LF) between 0.04-0.15 Hz and high frequency (HF) between 0.15-0.40 Hz and the LF/HF ratio was calculated. Global measures of HRV including the standard deviation of the mean of RR intervals (SDNN) and the standard deviation of 5-minute mean RR intervals (SDANN) were decreased in patients with FAP. Specific vagal influences on HRV including the proportion of RR intervals more than 50 milliseconds different (pNN50) and the HF power on spectral analysis were less in patients with FAP. LF power and LF/HF ratio were more decreased in patients with FAP at the advanced stage than at the early stage. In conclusion, HRV was significantly decreased in patients with FAP at the early stage, and sympathetic activity was more decreased in patients at the advanced stage. These findings suggest that the decrease of the HRV is an indicator of this disease and the power spectral analysis of the HRV is beneficial in assessing the severity of the autonomic dysfunction.

Adult↗
PubMed2002

Cirrhotic cardiomyopathy: a pathophysiological review of circulatory dysfunction in liver disease.

The systemic circulation in patients with cirrhosis is hyperdynamic with an increased cardiac output and heart rate and a reduced systemic vascular resistance as the most pronounced alterations. The concomitant cardiac dysfunction has recently been termed "cirrhotic cardiomyopathy", which is an entity different from that seen in alcoholic heart muscle disease. Clinically, these patients present with sodium fluid retention and strain often unmasks the presence of latent heart failure. No specific treatment can yet be recommended but caution should be used with respect to procedures that may stress the heart such as shunt implantation and liver transplantation.

Autonomic Nervous System Diseases↗
PubMed1998

Reliability of noninvasive methods to measure cardiac autonomic function.

Cardiac autonomic modulation was examined in 10 healthy subjects (mean age = 27.8 +/- 1.7) at rest (paced breathing at 12 and 16 breaths/min) and during a submaximal cycle ergometer exercise test. Heart rate variability (HRV) spectral parameters and spontaneous baroreflex (SBR) function variables showed no significant differences between mean values for any of the testing conditions. Spectral parameters and SBR function did not differ significantly between the resting conditions. Significant reliability coefficients (r = 0.59-0.73) were observed for all spectral parameters except low frequency power (r = 0.22) during 12 breaths/min, with moderately lower values during 16 breaths/min (r = 0.10-0.75) and exercise (r = 0.20-0.89). Significant reliability coefficients were observed for baroreflex sensitivity at 12 (r = 0.83) and 16 (r = 0.92) breaths/min. It was concluded that at rest, HRV spectral and SBR analyses are reliable methods for studying cardiac autonomic balance.

Adult↗
PubMed1999

Real-time measurement of cardiac vagal tone in conscious dogs.

Rapid changes in heart rate are caused by changes in parasympathetic tone. The NeuroScope is an electronic device designed to offer an objective real-time measure of instantaneous cardiac vagal tone by phase demodulation of a high-resolution time domain of R-R wave intervals. Data are displayed against an arbitrary but linear scale, the cardiac index of parasympathetic activity (CIPA). To validate this method, 10 conscious healthy dogs were each given six incremental doses of atropine (0.01 mg/kg) to a total dose of 0.06 mg/kg or equal volumes of saline. A dose-response curve was constructed. At the maximum dose of atropine, CIPA values fell to 1. 3 +/- 0.7% (SD) of baseline, whereas R-R intervals fell to 51.5 +/- 11.5% of baseline, and standard deviation of the R-R wave interval fell to 10.6 +/- 6.5% of baseline. These findings show that the NeuroScope can provide a specific real-time index of cardiac vagal tone in dogs without need for recourse to atropine.

Animals↗
PubMed1991

Ontogeny of canine intrathoracic cardiac nervous system.

The functional cardiac innervation of 61 puppies from nine different litters (2-8 littermates), ranging in age from 1 day to 7 wk, was investigated. The efferent sympathetic nervous system exerted minimal effects on the heart of 1-day-old puppies, gradually influencing the heart more thereafter such that by 7 wk of life it was functionally mature. In contrast, efferent parasympathetic cardiac innervation was well developed at birth, maturing thereafter such that by 4-7 wk of age its capacity to modulate the heart was similar to that found in adults. The right- and left-sided efferent sympathetic and parasympathetic intrathoracic nervous systems induced similar cardiac modulation throughout this period of development. Cardiac myocyte beta-adrenergic receptors were partially functional at birth, as determined by responses elicited by supramaximal doses of the beta-agonist isoproterenol. Responses elicited by isoproterenol became greater over the following 7 wk of life, when they were found to be similar to those elicited in adults. By 1 wk of age, synaptic mechanisms in intrathoracic sympathetic ganglia involved in cardiac regulation were relatively well developed, with cardiopulmonary-cardiac reflexes present but not functionally mature at that age. It is concluded that maturation of the efferent sympathetic nervous system modulating the canine heart depends to a large extent on the ontogeny of cardiac beta-adrenergic receptors rather than the ontogeny of synapses in intrathoracic ganglia. Furthermore, even though functional cardiac efferent parasympathetic innervation is present before efferent sympathetic innervation, both reach maturity at about the same age.

Animals↗
PubMed1999

Noninvasive exploration of cardiac autonomic neuropathy. Four reliable methods for diabetes?

OBJECTIVE: The purpose of this work was to assess relevant information that could be provided by various mathematical analyses of spontaneous blood pressure (BP) and heart rate (HR) variabilities in diabetic cardiovascular neuropathy. RESEARCH DESIGN AND METHODS: There were 10 healthy volunteers and 11 diabetic subjects included in the study. Diabetic patients were selected for nonsymptomatic orthostatic hypotension in an assessment of their cardiovascular autonomic impairment. Cardiac autonomic function was scored according to Ewing's methodology adapted to the use of a Finapres device. The spontaneous beat-to-beat BP and HR variabilities were then analyzed on a 1-h recording in supine subjects. The global variabilities were assessed by standard deviation, fractal dimension, and spectral power. The cardiac baroreflex function was estimated by cross-spectral sequences and Z analyses. RESULTS: In diabetic patients, Ewing's scores ranged from 1 to 4.5, confirming cardiovascular autonomic dysfunction. In these diabetic patients, global indices of variabilities were consistently lower than in healthy subjects. Furthermore, some of them (standard deviation and fractal dimension of HR, spectral power of systolic blood pressure and HR) were significantly correlated with the Ewing's scores. The Z methods and the spectral analysis found that the cardiac baroreflex was less effective in diabetic subjects. However, the baroreflex sensitivity could not be reliably assessed in all the patients. The sequence method pointed out a decreased number of baroreflex sequences in diabetic subjects that was correlated to the Ewing's score. CONCLUSIONS: Indices of HR spontaneous beat-to-beat variability are consistently related to the degree of cardiac autonomic dysfunction, according to Ewing's methodology. The Z method and spectral analysis confirmed that the cardiac baroreflex was impaired in diabetic patients. These methods might be clinically relevant for use in detecting incipient neuropathy in diabetic patients.

Adult↗
PubMed1992

Physiology of rate-responsive pacing.

The search for a pacemaker that accurately and easily mimics normal physiology is a continuing effort. There have been many achievements in the past, including sensing of the pacing chamber and programming of the pacing rate, sensitivity, and output. Present pacing developments include atrioventricular synchrony and rate adaptiveness. Results of studies on activation sequence and circadian variations will impact future pacing. The usefulness, cost effectiveness, and clinical value of some of the new pacing features remain unclear. Further clinical trials are necessary to clarify the value of new pacing techniques.

Adams-Stokes Syndrome↗