Mean Voltage Amplitude Research Articles

Abstract 14823: Atrial Electrical Substrates Associated With Atrial Fibrillation Drivers Analyzed With Real-Time Phase Mapping “ExTRa Mapping” in Patients With Persistent Atrial Fibrillation

Introduction: Elucidation of the mechanism of atrial fibrillation (AF) will lead to improved catheter ablation outcomes. However, the electrical substrates on which AF drivers such as meandering rotors and multiple wavelets are likely to appear are still unclear. Methods: Twenty-nine patients (age 68±10 years, eight females) with persistent AF were included in this study. Real-time phase mapping (ExTRa mapping) was performed in the left atrium during AF. After that, electroanatomical mapping such as voltage and activation mapping with HD-grid catheter was performed after conversion to sinus rhythm with cardioversion. According to the nonpassively activated ratio (%NP: the ratio of the form of rotors and/or multiple wavelets to the recording time), the recorded three highest %NP (Active-area) and three lowest %NP areas (Passive-area) were collected in each subject. Electrical property and overlapping with the low-voltage zone (LVZ, voltage amplitude <0.5mV) or mid-voltage zone (MVZ, 0.5-1.0mV) within these areas were assessed and compared between the Active- and the Passive-areas. Results: We analyzed a total of 87 Active- and 84 Passive-areas and the mean %NP were 61±8% and 13±8%, respectively. Signals with ≥4 fractionated components (fractionated electrograms) were seen significantly more in the Active-areas than in the Passive-areas (53% vs. 26%, respectively; p<0.001, Figure A ). However, there was no difference in the conduction velocity (0.70±0.34m/s vs. 0.73±0.30m/s; p=0.577), mean voltage amplitude (1.78±1.54mV vs. 1.71±1.53mV; p=0.794) and coinciding with LVA/MVA (43% vs. 41%; p=0.785) between the Active- and the Passive-areas ( Figure B-D ). Conclusion: AF drivers tended to appear in the area with fractionated electrograms. High %NP areas partly overlapped, but not always coincided with LVA/MVA, as much as low %NP areas.

Predictors of low voltage areas in persistent atrial fibrillation: is it really a matter of time?

Time has been postulated as an important factor for electrical remodeling of the left atrium (LA) in persistent atrial fibrillation (AF) ('AF begets AF'). However, it is still a matter of debate if structural changes are the cause or consequence of AF. We sought to determine the clinical and invasive parameters, which correlate with LA scar as determined by voltage mapping, in patients with persistent AF. Seventy consecutive patients undergoing ablation of persistent (49%) or long-standing persistent AF (51%), between January 2013 and February 2014, were enrolled in the study. Besides clinical parameters, 2D echocardiographic assessment of LA size and LA pressure (LAP) after transseptal puncture was also considered. Bipolar endocardial signals with a mean voltage amplitude < 0.1mV during AF were defined as LA scar. In the univariable analysis, LA scar was associated with age, gender, coronary artery disease (CAD), glomerular filtration rate (GFR), LA size and LAP. Arrhythmia duration, mild to moderate mitral regurgitation (MR), left ventricular dysfunction and left ventricular hypertrophy showed no significant correlation with atrial scar (all p > 0.05). In a multivariable regression model, LA scar area was independently associated with age, female gender and LA area. AF duration was not associated with LA scar. In this study, older age, greater LA area and female gender predicted the degree of LA scar, while other variables tested did not. In particular, we found no significant association between AF duration and LA scar.

Function of masticatory muscles during the initial phase of activator treatment.

The function of masticatory muscles and the development of the bite force were studied in 15 children before and during the first six months of the treatment of distal occlusion with an activator. Electromyographic recordings of the activity of the anterior and posterior portions of the temporal muscle, the masseter muscle and the anterior belly of the digastric muscle were made bilaterally in the rest position of the mandible and with the activator inserted. Recordings were also made during chewing and swallowing of apple and peanuts and during chewing of chewing gum as well as during maximal bite in the intercuspal position and on the activator. The mean voltage amplitude, the duration and the coordination of the activity were analysed. The maximum bite force was measured at the first molars and at the incisors. In most of the children, the clinical improvement was rapid as evident from a decrease in overjet and in the ANB angle as well as a change in the molar relation. The bite force measured at the incisors increased during the period of treatment. The muscle activity in the rest position was low and was the same with or without the activator. Thus, insertion of the activator did not increase the muscle activity. The activity of the posterior portion of the temporal muscle in the rest position was comparatively high at the start of treatment but decreased during the period of observation. The activity of the masseter and temporal muscles during maximal bite and chewing was influenced by the occlusal instability created during the course of treatment. The decrease of the postural activity of the posterior temporal muscle may reflect an adaptation to a new mandibular position.

Sympathetic skin nerve discharges in relation to amplitude of skin resistance responses.

ABSTRACTSympathetic skin nerve action potentials were recorded in the median nerve of 5 healthy college students. A linear and significant correlation was found between the mean voltage amplitude of the sympathetic bursts and the amplitude of skin resistance responses (SRRs). Thus amplitude of skin resistance responses seems to be an index of sympathetic activity.

A quantitative study of muscle nerve sympathetic activity in resting normotensive and hypertensive subjects.

Recordings of multi-unit sympathetic activity were made from muscle branches of the peroneal or median nerves in 33 healthy and 12 hypertensive subjects resting in the recumbent position. Simultaneous recordings of intra-arterial blood pressure were made on 17 normotensive and all hypertensive subjects. The neural activity, quantified by counting the number of sympathetic pulse-synchronous impulse bursts in the mean voltage neurogram (burst incidence) was plotted against the age and the arterial blood pressure level of the subjects. Between different subjects there were marked differences in mean burst incidence, from less than 10 to more than 90 bursts/100 heart beats and there was a tendency for increasing values with increasing age. Taking the age differences into account there was no significant correlation between the amount of activity and the blood pressure level. The effect of spontaneous temporary blood pressure fluctuations was studied by correlation different pressure parameters of individual heart beats to the probability of occurrence of a sympathetic burst and to the mean voltage amplitude of the occurring burst. Irrespective of the mean burst incidence, the occurrence of the bursts and their mean voltage amplitudes were determined mainly by fluctuations of the diastolic blood pressure. The diastolic pressure threshold for sympathetic outflow was found to be reset to higher blood pressure values in the hypertensive subjects and the variability of their thresholds was also greater than for the normotensive controls. At a given diastolic blood pressure, more sympathetic activity occurred if diastolic blood pressure was falling than if it was rising, and this directional dependence was more pronounced in the hypertensive subjects. We suggest that the increased directional dependence accounts for the greater variability of the blood pressure threshold for sympathetic outflow in the hypertensive subjects. The differences can be expalined on the basis of findings in animals with experimental hypertension, and it appears that they are secondary to the hypertension.

Effect of lower body negative pressure on human muscle nerve sympathetic activity.

1. Recordings of multi-unit sympathetic activity were made from muscle branches of the median nerve in five healthy subjects during application of lower body negative pressure (l.b.n.p.). Simultaneous recordings of arterial blood pressure were made in four subjects. The strength of the neural activity was quantitated by counting the number of pulse synchronous sympathetic bursts and their amplitudes in the mean voltage neurogram.2. The general appearance of the sympathetic activity in pulse synchronous bursts was similar during control periods and during l.b.n.p., but during l.b.n.p. there was always an increase in the number of sympathetic bursts and usually also in the mean voltage amplitude of the bursts.3. The probability of occurrence of a burst was correlated to different blood pressure parameters of individual heart beats and both during control periods and during l.b.n.p. there was regularly a close negative correlation to diastolic, a low correlation to systolic, an intermediate negative correlation to mean and a positive correlation to pulse pressures.4. The changes in arterial blood pressure during l.b.n.p. were small and in most cases statistically insignificant. The observed increases in the number of sympathetic bursts during l.b.n.p. were significantly greater than what could be expected on the basis of the blood pressure changes.5. The findings suggest that the reflex control from the arterial baroreceptors is maintained during l.b.n.p. but, since the increase of sympathetic activity during l.b.n.p. could not be explained by a change in stimulation of the arterial baroreceptors, influence from other receptor groups (presumably intrathoracic volume receptors) must also have occurred.

Human muscle nerve sympathetic activity at rest. Relationship to blood pressure and age.

1. Recordings of multi-unit sympathetic activity were made from median or peroneal muscle nerve fascicles in thirty-three healthy subjects, resting in recumbent position. Simultaneous recordings of intra-arterial blood pressure were made in seventeen subjects. The neural activity, quantified by counting the number of pulse synchronous sympathetic bursts in the mean voltage neurogram (burst incidence), was plotted against the arterial blood pressure level and the age of the subjects. The effects of spontaneous temporary blood pressure fluctuations were studied by correlating different pressure parameters of individual heart beats to the probability of occurrence of a sympathetic burst and to the amplitude of the occurring burst.2. Between different subjects there were marked differences in burst incidence, from less than 10 to more than 90 bursts/100 heart beats. No correlation was found to interindividual differences in the arterial blood pressure level but there was a slight tendency for increasing burst incidence with increasing age.3. Irrespective of the magnitude of the burst incidence, the bursts always occurred more frequently during spontaneous transient blood pressure reductions than during transient increases in blood pressure. When, for each heart cycle, the occurrence of a sympathetic burst was correlated with different blood pressure parameters there was regularly a close negative correlation to diastolic pressure, a low correlation to systolic and an intermediary negative correlation to mean blood pressure. There was a positive correlation to pulse pressure and to pulse interval.4. When measured for individual heart beats, not only the occurrence but also the mean voltage amplitude of the sympathetic bursts tended to increase with decreasing diastolic pressure.5. In a given subject when comparing heart beats with the same diastolic pressure, the occurrence as well as the amplitude of the sympathetic bursts was higher for heart beats occurring during falling than for heart beats occurring during rising blood pressure. For a given change in diastolic blood pressure, sympathetic activity changed more if pressure was falling than if it was rising.6. The findings suggest that the sympathetic outflow is modulated by arterial baroreflex mechanisms and that transient variations in the strength of the activity are, to a large extent, determined by diastolic blood pressure fluctuations. The intimate correlation with ;dynamic' variations in blood pressure and the absence of correlation to the ;static' blood pressure level suggests that the sympathetic outflow to skeletal muscles is of importance for buffering acute blood pressure changes but has little influence on the long term blood pressure level. The difference in reflex sensitivity between falling and rising pressure indicates that acute blood pressure decreases may be buffered more efficiently than acute blood pressure increases.7. In twenty-seven subjects baroreflex latency was calculated from the QRS-complexes in the e.c.g. to the appropriate systolic inhibition in the sympathetic activity. When recording in the peroneal nerve, the latency ranged between 1.16 and 1.49 sec and there was a positive correlation with the height of the subjects. It is suggested that such latency measurements may be used clinically to evaluate conduction in sympathetic fibres.

Relation between facial morphology and activity of the masticatory muscles.

SummaryThe relation between muscle activity and facial morphology was studied in twenty‐five boys and twenty‐seven girls, aged 9–11 years. The activity in the anterior and posterior parts of the temporal muscle, the masseter muscle and the upper lip was recorded bilaterally with the mandible in postural position and during chewing, swallowing and maximal bite. The electromyograms were analysed in respect of maximal mean voltage amplitude and the duration of muscle activity. Facial morphology was studied with the aid of profile roentgenograms and model analysis. The activity in postural position was found to be greater in the posterior than in the anterior part of the temporal muscle. The average mean voltage amplitude in the temporal and masseter muscles was greatest during maximal bite, smaller during chewing and smallest during swallowing. In the orbicularis oris muscle the activity was greater during the opening phase of the chewing cycle than during the closing phase.In postural position the activity in the anterior and posterior parts of the temporal muscle were positively correlated. The amplitudes in the anterior and posterior parts of the temporal muscle and in the masseter muscle were positively correlated during chewing, swallowing and maximal bite. The amplitudes in these muscles during chewing were positively correlated with those in the same muscles during maximal bite. During swallowing the amplitude in the upper lip was negatively correlated with that in the anterior part of the temporal muscle.The clearest correlations between muscle activity and facial morphology were found during chewing and maximal bite. During these functions the amplitudes in the temporal and masseter muscles were large in cases with a tendency to parallelism between the jaws bases and between the mandibular occlusal line and the mandibular line. These cases with considerable muscle activity are characterized by rectangular shape of the face in profile and small lower face height.