F-wave Amplitude Research Articles

Spatial Variability of the 12-Lead Surface ECG as a Tool for Noninvasive Prediction of Catheter Ablation Outcome in Persistent Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia encountered in clinical practice. Radiofrequency catheter ablation (CA) is increasingly employed to treat this disease, yet the selection of persistent AF patients who will benefit from this treatment remains a challenging task. Several parameters of the surface electrocardiogram (ECG) have been analyzed in previous works to predict AF termination by CA, such as fibrillatory wave (f-wave) amplitude. However, they are usually manually computed and only a subset of electrodes is inspected. In this study, a novel perspective of the role of f-wave amplitude as a potential noninvasive predictor of CA outcome is adopted by exploring ECG interlead spatial variability. An automatic procedure for atrial amplitude computation based on cubic Hermite interpolation is first proposed. To describe the global f-wave peak-to-peak amplitude distribution, signal contributions from multiple leads are then combined by condensing the most representative features of the atrial signal in a reduced-rank approximation based on principal component analysis (PCA). We show that exploiting ECG spatial diversity by means of this PCA-based multilead approach does not only increase the robustness to electrode selection, but also substantially improves the predictive power of the amplitude parameter.

An Echo State Neural Network for QRST Cancellation During Atrial Fibrillation

A novel method for QRST cancellation during atrial fibrillation (AF) is introduced for use in recordings with two or more leads. The method is based on an echo state neural network which estimates the time-varying, nonlinear transfer function between two leads, one lead with atrial activity and another lead without, for the purpose of canceling ventricular activity. The network has different sets of weights that define the input, hidden, and output layers, of which only the output set is adapted for every new sample to be processed. The performance is evaluated on ECG signals, with simulated f-waves added, by determining the root mean square error between the true f-wave signal and the estimated signal, as well as by evaluating the dominant AF frequency. When compared to average beat subtraction (ABS), being the most widely used method for QRST cancellation, the performance is found to be significantly better with an error reduction factor of 0.24-0.43, depending on f-wave amplitude. The estimates of dominant AF frequency are considerably more accurate for all f-wave amplitudes than the AF estimates based on ABS. The novel method is particularly well suited for implementation in mobile health systems where monitoring of AF during extended time periods is of interest.

Opposite Optimal Current Flow Directions for Induction of Neuroplasticity and Excitation Threshold in the Human Motor Cortex

BackgroundDirectional sensitivity is relevant for the excitability threshold of the human primary motor cortex, but its importance for externally induced plasticity is unknown. ObjectiveTo study the influence of current direction on two paradigms inducing neuroplasticity by repetitive transcranial magnetic stimulation (rTMS). MethodsWe studied short-lasting after-effects induced in the human primary motor cortex of 8 healthy subjects, using 5 Hz rTMS applied in six blocks of 200 pulses each, at 90% active motor threshold. We controlled for intensity, frequency, waveform and spinal effects. ResultsOnly biphasic pulses with the effective component delivered in an anterioposterior direction (henceforth posteriorly directed) in the brain yielded an increase of motor-evoked potential (MEP) amplitudes outlasting rTMS. MEP latencies and F-wave amplitudes remained unchanged. Biphasic pulses directed posteroanterior (i.e. anteriorly) were ineffective, as were monophasic pulses from either direction. A 1 Hz study in a group of 12 healthy subjects confirmed facilitation after posteriorly directed biphasic pulses only. ConclusionsThe anisotropy of the human primary motor cortex is relevant for induction of plasticity by subtreshold rTMS, with a current flow opposite to that providing lowest excitability thresholds. This is consistent with the idea of TMS primarily targeting cortical columns of the phylogenetically new M1 in the anterior bank of the central sulcus. For these, anteriorly directed currents are soma-depolarizing, therefore optimal for low thresholds, whereas posteriorly directed currents are soma-hyperpolarizing, likely dendrite-depolarizing and bested suited for induction of plasticity. Our findings should help focus and enhance rTMS effects in experimental and clinical settings.

Acute effects of Achilles tendon vibration on soleus and tibialis anterior spinal and cortical excitability

Prolonged vibration is known to alter muscle performance. Attenuation of Ia afferent efficacy is the main mechanism suggested. However, changes in motor cortex excitability could also be hypothesized. The purpose of the present study was therefore to analyze the acute and outlasting effects of 1 h of Achilles tendon vibration (frequency, 50 Hz) on the soleus (SOL) and tibialis anterior (TA) neuromuscular excitability. Spinal excitability was investigated by means of H-reflexes and F-waves while cortical excitability was characterized by motor evoked potentials (MEPs) obtained by transcranial magnetic stimulation. Twelve subjects performed the experimental procedures 3 times: at the beginning of the testing session (PRE), immediately after 1 h of Achilles tendon vibration (POST), and 1 h after the end of vibration (POST-1H). Prolonged vibration led to acute reduced H-reflex amplitudes for SOL only (46.9% ± 7.7% vs. 32.8% ± 7%; p = 0.006). Mainly presynaptic inhibition mechanisms were thought to be involved because of unchanged F-wave persistence and amplitude mean values, suggesting unaffected motoneuronal excitability. While no acute effects were reported for SOL and TA cortical excitability, both muscles were characterized by an outlasting increase in their MEP amplitude (0.64 ± 0.2 mV vs. 0.43 ± 0.18 mV and 2.17 ± 0.56 mV vs. 1.26 ± 0.36 mV, respectively; p < 0.05). The high modulation of Ia afferent input by vibration led to changes in motor cortex excitability that could contribute to the enhancement in muscular activation capacities reported after chronic use of tendon vibration.

Writing's Shadow: Corticospinal Activation during Letter Observation

We can recognize handwritten letters despite the variability among writers. One possible strategy is exploiting the motor memory of orthography. By using TMS, we clarified the excitatory and inhibitory neural circuits of the motor corticospinal pathway that might be activated during the observation of handwritten letters. During experiments, participants looked at the handwritten or printed single letter that appeared in a random order. The excitability of the left and right primary motor cortex (M1) was evaluated by motor-evoked potentials elicited by single-pulse TMS. Short interval intracortical inhibition (SICI) of the left M1 was evaluated using paired-pulse TMS. F waves were measured for the right ulnar nerve. We found significant reduction of corticospinal excitability only for the right hand at 300-400 msec after each letter presentation without significant changes in SICI. This suppression is likely to be of supraspinal origin, because of no significant alteration in F-wave amplitudes. These findings suggest that the recognition of handwritten letters may include the implicit knowledge of "writing" in M1. The M1 activation associated with that process, which has been shown in previous neuroimaging studies, is likely to reflect the active suppression of the corticospinal excitability.

Effect of low-frequency rTMS on motor neuron excitability after stroke

The purpose of this study was to test the effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) over the non-lesional hemisphere on motor neuron excitability of the paretic upper limb in post-stroke patients by electrophysiological examination. Thirteen post-stroke patients with spastic upper limb hemiparesis were studied (age, 57.5 ± 11.1 years; time after stroke, 55.2 ± 51.4 months). Low-frequency rTMS of 1 Hz was applied for 20 min to the motor cortex of the non-lesional hemisphere. The M-response amplitude and F-wave parameters were recorded in the abductor pollicis brevis muscle following stimulation of the median nerve in both the affected and unaffected upper limbs. The F-wave frequency, F-max/M ratio (ratio of maximum F-wave amplitude to M-response amplitude), and F-mean/M ratio (the ratio of mean F-wave amplitude to the M-response amplitude) were measured before and after the 20-min rTMS, analyzed for both limbs. Application of low-frequency rTMS did not result in significant changes in the frequency of F-wave and F-max/M ratio in both upper limbs, but significantly decreased F-mean/M ratio in the affected upper limb (P < 0.005), but not in the unaffected limb. Low-frequency rTMS applied to the non-lesional hemisphere might be potentially useful therapeutically for post-stroke patients with spastic upper limb hemiparesis.

Impaired crossed facilitation of the corticospinal pathway after cervical spinal cord injury

In uninjured humans, it is well established that voluntary contraction of muscles on one side of the body can facilitate transmission in the contralateral corticospinal pathway. This crossed facilitatory effect may favor interlimb coordination and motor performance. Whether this aspect of corticospinal function is preserved after chronic spinal cord injury (SCI) is unknown. Here, using transcranial magnetic stimulation, we show in patients with chronic cervical SCI (C(5)-C(8)) that the size of motor evoked potentials (MEPs) in a resting intrinsic hand muscle remained unchanged during increasing levels of voluntary contraction with a contralateral distal or proximal arm muscle. In contrast, MEP size in a resting hand muscle was increased during the same motor tasks in healthy control subjects. The magnitude of voluntary electromyography was negatively correlated with MEP size after chronic cervical SCI and positively correlated in healthy control subjects. To examine the mechanisms contributing to MEP crossed facilitation we examined short-interval intracortical inhibition (SICI), interhemispheric inhibition (IHI), and motoneuronal behavior by testing F waves and cervicomedullary MEPs (CMEPs). During strong voluntary contractions SICI was unchanged after cervical SCI and decreased in healthy control subjects compared with rest. F-wave amplitude and persistence and CMEP size remained unchanged after cervical SCI and increased in healthy control subjects compared with rest. In addition, during strong voluntary contractions IHI was unchanged in cervical SCI compared with rest. Our results indicate that GABAergic intracortical circuits, interhemispheric glutamatergic projections between motor cortices, and excitability of index finger motoneurons are neural mechanisms underlying, at least in part, the lack of crossed corticospinal facilitation observed after SCI. Our data point to the spinal motoneurons as a critical site for modulating corticospinal transmission after chronic cervical SCI.

Anti-spastic effects of the direct application of vibratory stimuli to the spastic muscles of hemiplegic limbs in post-stroke patients: A proof-of-principle study

To investigate whether the direct application of vibratory stimuli inhibits spasticity in the hemiplegic upper limbs of post-stroke patients. A randomized controlled study. Thirty-six post-stroke patients. Patients were randomly allocated to the "Rest group", "Stretch group", or "Direct application of vibratory stimuli group". After relaxing in a supine posture for 30 min, subjects received the interventions for 5 min. The Modified Ashworth Scale scores and F-wave parameters were recorded before, immediately after and 30 min after each intervention. The Rest group showed no significant changes in F-wave parameters and Modified Ashworth Scale scores. The Stretch group showed a tendency to decrease in F-wave amplitude and F/M ratio immediately after the intervention, but not 30 min later. The Direct application of vibratory stimuli group showed significant improvements in F-wave parameters and Modified Ashworth Scale scores immediately after the intervention, which remained 30 minutes later. The changes in F-wave parameters and Modified Ashworth Scale scores observed in the Direct application of vibratory stimuli group significantly differed from those in the Rest group and the Stretch group. The direct application of vibratory stimuli has anti-spastic effects in the hemiplegic upper limbs of post-stroke patients.

Area 5 Influences Excitability within the Primary Motor Cortex in Humans

In non-human primates, Brodmann's area 5 (BA 5) has direct connectivity with primary motor cortex (M1), is largely dedicated to the representation of the hand and may have evolved with the ability to perform skilled hand movement. Less is known about human BA 5 and its interaction with M1 neural circuits related to hand control. The present study examines the influence of BA 5 on excitatory and inhibitory neural circuitry within M1 bilaterally before and after continuous (cTBS), intermittent (iTBS), and sham theta-burst stimulation (sham TBS) over left hemisphere BA 5. Using single and paired-pulse TMS, measurements of motor evoked potentials (MEPs), short interval intracortical inhibition (SICI), and intracortical facilitation (ICF) were quantified for the representation of the first dorsal interosseous muscle. Results indicate that cTBS over BA 5 influences M1 excitability such that MEP amplitudes are increased bilaterally for up to one hour. ITBS over BA 5 results in an increase in MEP amplitude contralateral to stimulation with a delayed onset that persists up to one hour. SICI and ICF were unaltered following TBS over BA 5. Similarly, F-wave amplitude and latency were unaltered following cTBS over BA 5. The data suggest that BA 5 alters M1 output directed to the hand by influencing corticospinal neurons and not interneurons that mediate SICI or ICF circuitry. Targeting BA 5 via cTBS and iTBS is a novel mechanism to powerfully modulate activity within M1 and may provide an avenue for investigating hand control in healthy populations and modifying impaired hand function in clinical populations.

ONCE SUBTRACTED DISPERSION RELATIONS IN DESCRIPTION OF THE ππ D- AND F-WAVE AMPLITUDES

Once subtracted dispersion relations with imposed crossing symmetry condition are applied in description of the ππ D- and F-wave amplitudes. We show that these equations impose strong constraints on experimental data and model amplitudes.

The effect of local corticosteroid injection on F-wave conduction velocity and sympathetic skin response in carpal tunnel syndrome.

The aim of this study was to evaluate the efficacy of steroid injection for the treatment of the carpal tunnel syndrome (CTS), with F-wave parameters and sympathetic skin response (SSR). Seventeen hands of 10 women patients were treated with local steroid injection with 2-month follow-up. All patients underwent single injection into the carpal tunnel. Response to injection was measured nerve conduction studies (NCSs), median nerve F waves, and SSR before and after treatment. To determine the normal values, 42 hands of 21 healthy women were also studied. There was a significant improvement of sensory and motor nerve conduction values when compared to baseline values (P < 0.01). At the end of follow-up period, the median sensory distal latency and the sensory latency differences between the median and the ulnar nerve were improved 35 and 65%, respectively. The maximum, mean F-wave amplitudes and chronodispersion showed a slight improvement with respect to baseline values and controls, but statistical significance was not achieved after treatment. Although no statistically significant improvements were observed in SSR parameters, slightly decreased amplitudes and increased habituation of SSR were noted at the end of the treatment. The present study shows that the local steroid injection results in improvement in NCSs values, but the F-wave parameters were not effectual in short-term outcome of CTS treatment. These findings suggest that the sensory latency differences between the median and the ulnar wrist-to-digit 4 are better parameters in the median nerve recovery after treatment than the median sensory distal latency. Furthermore, the SSR does not seem to be a sensitive method in follow-up of CTS treatment.

The Effect of Electrical Passive Cycling on Spasticity in War Veterans with Spinal Cord Injury

Introduction: Muscle atrophy, spasticity, and deformity are among long term complication of spinal cord injury (SCI) veterans. There are numerous studies evaluating effect of functional electrical stimulation on muscle properties of SCI people, but less research has focused on the benefits of passive cycling in the management of spasticity and improving ROM of lower limbs in individuals with SCI. Aims: To evaluate the effect of electrical passive cycling on passive range of movement spasticity and electrodiagnostic parameters in SCI veterans. Methods: Sixty-four SCI veterans referred to two clinical and research center in Tehran were recruited in this prospective clinical trial. The subjects were divided into two groups according to electrical passive cycling usage: (1) patients who did not use pedal exercise (control group), (2) patients used Electrical passive cycling up to optimal level (intervention group). Main outcome measures included hip, knee, and ankle range of motion, spasticity scale, and electrodiagnostic parameters including F-Wave Consistency, F-Wave Amplitude, H/M Ratio, F/M Ratio, H-Reflex Onset Latency, and H-Reflex Amplitude. Data were recorded at the time of receiving and 1 year after pedal exercise usage. Results: Sixty-four SCI patients including 95.3% male, 4.7% female with mean age 43 years old were included in this study. All patients except one suffered from complete SCI. The involved spinal levels were cervical (17.2%), upper thoracic (34.4%), lower thoracic (45.3%), and lumbar (3.1%). Spasticity scale decreased significantly after passive cycling in group 2. Also hip, knee, and ankle ROM in group 2 were significantly improved after pedal exercise. There was a significant difference in H max/M max (RT<) and F/M ratio after versus before electric passive cycling system in group 2. Conclusion: These findings suggest that passive rhythmic leg exercise can lead to decrease in spasticity, increase in passive ROM of lower limbs and improvement in electrodiagnostic parameters of spasticity in patients with SCI.

Diagnostic Value of the Analysisof F-wave Parameters in Inflammatory Diseases of the Spine

Objective. To analyze the most significant criteria for early detection of radiculopathy in patients with inflammatory diseases of the spine basing on the analysis of F-wave parameters obtained by stimulation electroneuromyography of lower extremities. Material and Methods. Primary F-wave parameters were studied in two groups of patients with inflammatory diseases of the spine: with diagnosed radiculopathy (n = 12), and without radiculopathy (n = 14). Results. The most diagnostically significant parameters of electroneuromyography were F-wave amplitude, minimal velocity, and tacheodispersion. They allow for detection of neurological pathology at early stages of its development when marked clinical symptoms of radiculopathy are not manifested. Conclusion. Diagnostically significant parameters of the wave may be used in preclinical diagnosis of radiculopathy in patients with inflammatory diseases of the spine both for the assessment of initial neurological status and indications for surgical treatment, and for estimation of postoperative dynamics.

Male human motor cortex stimulus-response characteristics are not altered by aging

Evidence suggests that there are aging-related changes in corticospinal stimulus-response curve characteristics in later life. However, there is also limited evidence that these changes may only be evident in postmenopausal women and not in men. This study compared corticospinal stimulus-response curves from a group of young men [19.8 ± 1.6 yr (range 17-23 yr)] and a group of old men [n = 18, aged 64.1 ± 5.0 yr (range 55-73 yr)]. Transcranial magnetic stimulation (TMS) over the contralateral motor cortex was used to evoke motor potentials at a range of stimulus intensities in the first dorsal interosseous muscle of each hand separately. There was no effect of age group or hemisphere (i.e., left vs. right motor cortex) on motor evoked potential (MEP) amplitude or any other stimulus-response characteristic. MEP variability was strongly modulated by resting motor threshold but not by age. M-wave (but not F-wave) amplitude was reduced in old men, but expressing MEP amplitude as a ratio of M-wave amplitude did not reveal any age-related differences in cortically evoked stimulus-response characteristics. We conclude that male corticospinal stimulus-response characteristics are not altered by advancing age and that previously reported age-related changes in motor cortical excitability assessed with TMS are likely due to changes inherent in the female participants only. Future studies are warranted to fully elucidate the relationship between, and functional significance of, changes in circulating neuroactive sex hormones and motor function in later life.

Crossing symmetry implemented in ππ D- and F-wave amplitudes

Once subtracted dispersion relations with imposed crossing symmetry condition are applied in description of the ππ D and F wave amplitudes. Equations similar to those with one subtraction (so called GKPY equations) and to those with two subtractions (the Roy's equations) for the S and P waves are derived. We show that they impose strong constraints on experimental data and model amplitudes. Therefore, together with already known GKPY equations these relations can be efficiently used to test the ππ amplitudes in the S , P and D wave.

Effect of motor imagery and voluntary muscle contraction on the F wave

We tested the validity of instructing patients to minimally contract the muscle to facilitate F-wave recording in clinical practice. In 12 healthy subjects, F waves were recorded from the first dorsal interosseous muscle at rest, during motor imagery, and at up to 30% of the maximal voluntary contraction (MVC). F-wave persistence increased significantly from 32.5 +/- 11.9% (mean +/- SD) at rest to 58.3 +/- 15.2% during motor imagery and 90.0 +/- 8.7% during 3% MVC. It then remained the same during stepwise changes to and from 30% MVC before decreasing significantly from 80.8 +/- 18.5% during 3% MVC to 48.7 +/- 23.8% during motor imagery and 27.0 +/- 16.0% at rest. The trial average of F-wave amplitude showed a similar pattern of facilitation. Motor imagery enhances F-wave persistence and amplitude, which further increase with a slight muscle contraction and show no additional change with a stronger effort.

5. F-wave by different methods of motor imagery with isometric opponens pollicis activity

Our aim of this study was to investigate how transcranial magnetic stimulations (TMS) affect the spinal motoneuron excitability as measured by the amplitude of F-waves in the first dorsal interosseous muscle. Seven healthy subjects took part in the study. The effects of TMS were examined using a conditioning-test paradigm. Conditioning pulses of magnetic stimulation were delivered over motor cortex, prefrontal cortex, parietal cortex or cervical root, at various inter-stimulus intervals (ISIs, 5–300 ms) with the subjects at rest; Test electrical stimuli were delivered to the ulnar nerve to evoke an F-wave. The conditioning stimuli over motor cortex significantly increased the peak amplitude of F-wave with either 5–20 or 165–220 ms ISI. The conditioning stimuli over prefrontal cortex significantly increased the F-wave amplitude with either 85–120 or 225–240 ms ISI. The conditioning stimuli over parietal cortex produced little effect on the F-wave. The conditioning stimuli over cervical root increased the F-wave amplitude with 125–300 ms ISI. The facilitation of F-wave by the motor cortex stimulation might result from the activation of corticospinal output or the afferent feedback due to muscle twitch. The facilitation of F-wave by the prefrontal stimulation might have a non-corticospinal origin.

F-Wave Characteristics as Surrogate Markers of Spasticity in Patients With Secondary Progressive Multiple Sclerosis

We sought to identify significant ulnar nerve conduction abnormalities and also to detect ulnar F-wave variable changes in patients with secondary progressive multiple sclerosis (MS). Conventional conduction study was performed unilaterally to ulnar nerves of eight men and 12 women with secondary progressive MS (mean age, 47.5 +/- 6.6 years), having spastic hemiparesis and hand spasticity. A series of 40 electrical stimuli were also delivered to their ulnar nerves unilaterally so as to obtain F waves. The side of examination was ipsilateral to the side of spastic paresis. The following F-wave variables were estimated: F-wave persistence, latency, amplitude, duration, and F chronodispersion. Ten patients with remitting-relapsing MS without any evidence of hand spasticity and 20 age- and gender-matched healthy volunteers served as controls. Motor and sensory conduction study was normal in all participants. The F-wave persistence, latency, and duration parameters and also the F chronodispersion were comparable between groups. The mean and maximum F-wave amplitude values (P = 0.005) and the F mean/M (P = 0.001) and F maximal/M (P = 0.001) ratios were significantly higher than those of controls. Finally, the F-wave amplitude parameters in patients with secondary progressive MS significantly correlated with the degree of spasticity and the duration of disease. Significant amplitude F-wave abnormalities occurred in patients with secondary progressive MS and hand spasticity, emphasizing the contribution of upper motor neurons damage in the genesis of F waves.

Beneficial effects of footbaths in controlling spasticity after stroke

Footbaths are considered to provide beneficial thermal therapy for post-stroke patients with spasticity, but their anti-spastic effects have not been investigated comprehensively. The present study aimed to evaluate alterations in motor-neuron excitability using F-wave parameters in post-stroke patients with spastic hemiplegia. Subjects' legs below the knee joint were immersed in water at 41 degrees C and F-wave recordings were made over the abductor hallucis muscle before, immediately after, and 30 min after thermal treatment. Antidromic stimulation was performed on the tibial nerve at the ankle. Measurements included F-wave amplitude, F-wave/M-response ratio, changes in modified Ashworth scale (MAS), body temperature and surface-skin temperature. The mean values of both F-wave parameters were higher on the affected side before footbath treatment. In post-stroke patients, the mean values of F-wave parameters were significantly reduced after footbath treatment (P < 0.01). The anti-spastic effects of footbath treatment were indicated by decreased F-wave parameters, in parallel with decreases in MAS. Body temperature was significantly increased both immediately after, and 30 min following footbath treatment in both groups, which appeared to play an important role in decreased spasticity. Surface-skin temperature increased immediately after footbath treatment in both groups and returned to baseline 30 min later. These findings demonstrate that the use of footbaths is an effective nonpharmacological anti-spastic treatment that might facilitate stroke rehabilitation.

Clinical value of fibrillatory wave amplitude on surface ECG in patients with persistent atrial fibrillation

We postulated that amplitude of fibrillatory (F)-wave in patients with persistent AF would correlate with clinical characteristics and outcome in patients undergoing catheter ablation for AF. Maximal and mean amplitude of F-waves were measured in V1 and lead II in 90 patients prior to ablation for persistent AF. F-wave amplitudes were correlated to clinical, echocardiographic variables, and outcome. F-wave > or = 0.1 mV in lead II and V1 was correlated with younger age and shorter AF history, and in lead II only was correlated with a smaller left atrium. Higher F-wave amplitude at baseline predicted AF termination during ablation. Maximal amplitude of > or = 0.07 mV predicted AF termination by ablation with 82%/79% sensitivity and 68%/73% specificity in V1/lead II respectively. An association between F-wave amplitude and AF recurrence was observed. Forty-three percent of patients with mean f wave amplitude <0.05 in lead V1 had AF recurrence compared to 12% of those with F-wave > or = 0.05 (p = 0.004). Longer AF duration, older age and larger LA size are associated with fine AF amplitude. High F-wave amplitude predicts procedural termination of arrhyhmia in patients with persistent AF and freedom from AF upon follow-up.