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Experimental Physiology Jan 2010Since the first recording of sympathetic nerve activity (SNA) early last century, numerous methods for presentation of the resulting data have developed. In this paper,... (Review)
Review
Since the first recording of sympathetic nerve activity (SNA) early last century, numerous methods for presentation of the resulting data have developed. In this paper, we discuss the common ways of describing SNA and their application to chronic recordings. Suggestions on assessing the quality of SNA are made, including the use of arterial pressure wave-triggered averages and nasopharyngeal stimuli. Calculation of the zero level of the SNA signal from recordings during ganglionic blockade, the average level between bursts and the minimum of arterial pressure wave-triggered averages are compared and shown to be equivalent. The use of normalization between zero and maximal SNA levels to allow comparison between groups is discussed. We recommend that measured microvolt levels of integrated SNA be presented (with the zero/noise level subtracted), along with burst amplitude and frequency information whenever possible. We propose that standardization of the quantifying/reporting of SNA will allow better comparison between disease models and between research groups and ultimately allow data to be more reflective of the human situation.
Topics: Action Potentials; Afferent Pathways; Animals; Blood Pressure; Clinical Laboratory Techniques; Humans; Kidney; Problem Solving; Reference Standards; Sympathetic Nervous System
PubMed: 19700515
DOI: 10.1113/expphysiol.2008.046300 -
German Medical Science : GMS E-journal Oct 2010Electrocardiographic methods still provide the bulk of cardiovascular diagnostics. Cardiac ischemia is associated with typical alterations in cardiac biosignals that... (Review)
Review
BACKGROUND
Electrocardiographic methods still provide the bulk of cardiovascular diagnostics. Cardiac ischemia is associated with typical alterations in cardiac biosignals that have to be measured, analyzed by mathematical algorithms and allegorized for further clinical diagnostics. The fast growing fields of biomedical engineering and applied sciences are intensely focused on generating new approaches to cardiac biosignal analysis for diagnosis and risk stratification in myocardial ischemia.
OBJECTIVES
To present and review the state of the art in and new approaches to electrocardiologic methods for non-invasive detection and risk stratification in coronary artery disease (CAD) and myocardial ischemia; secondarily, to explore the future perspectives of these methods.
METHODS
In follow-up to the Expert Discussion at the 2008 Workshop on "Biosignal Analysis" of the German Society of Biomedical Engineering in Potsdam, Germany, we comprehensively searched the pertinent literature and databases and compiled the results into this review. Then, we categorized the state-of-the-art methods and selected new approaches based on their applications in detection and risk stratification of myocardial ischemia. Finally, we compared the pros and cons of the methods and explored their future potentials for cardiology.
RESULTS
Resting ECG, particularly suited for detecting ST-elevation myocardial infarctions, and exercise ECG, for the diagnosis of stable CAD, are state-of-the-art methods. New exercise-free methods for detecting stable CAD include cardiogoniometry (CGM); methods for detecting acute coronary syndrome without ST elevation are Body Surface Potential Mapping, functional imaging and CGM. Heart rate variability and blood pressure variability analyses, microvolt T-wave alternans and signal-averaged ECG mainly serve in detecting and stratifying the risk for lethal arrythmias in patients with myocardial ischemia or previous myocardial infarctions. Telemedicine and ambient-assisted living support the electrocardiological monitoring of at-risk patients.
CONCLUSIONS
There are many promising methods for the exercise-free, non-invasive detection of CAD and myocardial ischemia in the stable and acute phases. In the coming years, these new methods will help enhance state-of-the-art procedures in routine diagnostics. The future can expect that equally novel methods for risk stratification and telemedicine will transition into clinical routine.
Topics: Body Surface Potential Mapping; Coronary Artery Disease; Diagnosis, Computer-Assisted; Electrocardiography; Humans; Myocardial Ischemia; Risk Assessment
PubMed: 21063467
DOI: 10.3205/000116 -
Current Cardiology Reports Sep 2013Microvolt level T-wave alternans (MTWA), a phenomenon of beat-to-beat variability in the repolarization phase of the ventricles, has been closely associated with an... (Review)
Review
Microvolt level T-wave alternans (MTWA), a phenomenon of beat-to-beat variability in the repolarization phase of the ventricles, has been closely associated with an increased risk of ventricular tachyarrhythmic events (VTE) and sudden cardiac death (SCD) during medium- and long-term follow-up. Recent observations also suggest that heightened MTWA magnitude may be closely associated with short-term risk of impending VTE. At the subcellular and cellular level, perturbations in calcium transport processes likely play a primary role in the genesis of alternans, which then secondarily lead to alternans of action potential morphology and duration (APD). As such, MTWA may play a role not only in risk stratification but also more fundamentally in the pathogenesis of VTE. In this paper, we outline recent advances in understanding the pathogenesis of MTWA and also the utility of T-wave alternans testing for clinical risk stratification. We also highlight emerging clinical applications for MTWA.
Topics: Arrhythmias, Cardiac; Death, Sudden, Cardiac; Electrocardiography; Humans; Risk Assessment; Tachycardia, Ventricular
PubMed: 23881581
DOI: 10.1007/s11886-013-0398-7 -
Journal of the American College of... Sep 2011This consensus guideline was prepared on behalf of the International Society for Holter and Noninvasive Electrocardiology and is cosponsored by the Japanese Circulation... (Review)
Review
Microvolt T-wave alternans physiological basis, methods of measurement, and clinical utility--consensus guideline by International Society for Holter and Noninvasive Electrocardiology.
This consensus guideline was prepared on behalf of the International Society for Holter and Noninvasive Electrocardiology and is cosponsored by the Japanese Circulation Society, the Computers in Cardiology Working Group on e-Cardiology of the European Society of Cardiology, and the European Cardiac Arrhythmia Society. It discusses the electrocardiographic phenomenon of T-wave alternans (TWA) (i.e., a beat-to-beat alternation in the morphology and amplitude of the ST-segment or T-wave). This statement focuses on its physiological basis and measurement technologies and its clinical utility in stratifying risk for life-threatening ventricular arrhythmias. Signal processing techniques including the frequency-domain Spectral Method and the time-domain Modified Moving Average method have demonstrated the utility of TWA in arrhythmia risk stratification in prospective studies in >12,000 patients. The majority of exercise-based studies using both methods have reported high relative risks for cardiovascular mortality and for sudden cardiac death in patients with preserved as well as depressed left ventricular ejection fraction. Studies with ambulatory electrocardiogram-based TWA analysis with Modified Moving Average method have yielded significant predictive capacity. However, negative studies with the Spectral Method have also appeared, including 2 interventional studies in patients with implantable defibrillators. Meta-analyses have been performed to gain insights into this issue. Frontiers of TWA research include use in arrhythmia risk stratification of individuals with preserved ejection fraction, improvements in predictivity with quantitative analysis, and utility in guiding medical as well as device-based therapy. Overall, although TWA appears to be a useful marker of risk for arrhythmic and cardiovascular death, there is as yet no definitive evidence that it can guide therapy.
Topics: Animals; Arrhythmias, Cardiac; Cause of Death; Consensus Development Conferences as Topic; Electrocardiography, Ambulatory; Global Health; Humans; Practice Guidelines as Topic; Risk Assessment; Societies, Medical
PubMed: 21920259
DOI: 10.1016/j.jacc.2011.06.029 -
Journal of the American Heart... Sep 2020Background Action potential alternans can induce ventricular tachyarrhythmias and manifest on the surface ECG as T-wave alternans (TWA) and QRS alternans (QRSA). We...
Background Action potential alternans can induce ventricular tachyarrhythmias and manifest on the surface ECG as T-wave alternans (TWA) and QRS alternans (QRSA). We sought to evaluate microvolt QRSA in cardiomyopathy patients in relation to TWA and ventricular tachyarrhythmia outcomes. Methods and Results Prospectively enrolled cardiomyopathy patients (n=100) with prophylactic defibrillators had 12-lead ECGs recorded during ventricular pacing from 100 to 120 beats/min. QRSA and TWA were quantified in moving 128-beat segments using the spectral method. Segments were categorized as QRSA positive (QRSA+) and/or TWA positive (TWA+) based on ≥2 precordial leads having alternans magnitude >0 and signal:noise >3. Patients were similarly categorized based on having ≥3 consecutive segments with alternans. TWA+ and QRSA+ occurred together in 31% of patients and alone in 18% and 14% of patients, respectively. Although TWA magnitude (1.4±0.4 versus 4.7±1.0 µV, <0.01) and proportion of TWA+ studies (16% versus 46%, <0.01) increased with rate, QRSA did not change. QRS duration was longer in QRSA+ than QRSA-negative patients (138±23 versus 113±26 ms, <0.01). At 3.5 years follow-up, appropriate defibrillator therapy or sustained ventricular tachyarrhythmia was greater in QRSA+ than QRSA-negative patients (30% versus 8%, =0.02) but similar in TWA+ and TWA-negative patients. Among QRSA+ patients, the event rate was greater in those without TWA (62% versus 21%, =0.02). Multivariable Cox analysis revealed QRSA+ (hazard ratio [HR], 4.6; 95% CI, 1.5-14; =0.009) and QRS duration >120 ms (HR, 4.1; 95% CI, 1.3-12; =0.014) to predict events. Conclusions Microvolt QRSA is novel phenomenon in cardiomyopathy patients that can exist without TWA and is associated with QRS prolongation. QRSA increases the risk of ventricular tachyarrhythmia 4-fold, which merits further study as a risk stratifier.
Topics: Aged; Algorithms; Arrhythmias, Cardiac; Canada; Cardiomyopathies; Case-Control Studies; Defibrillators, Implantable; Electrocardiography; Female; Heart Ventricles; Humans; Male; Middle Aged; Noise; Prospective Studies; Risk Factors; Tachycardia, Ventricular
PubMed: 32806990
DOI: 10.1161/JAHA.119.016461 -
American Journal of Physiology. Heart... Feb 2014Electrocardiographic alternans, a phenomenon of beat-to-beat alternation in cardiac electrical waveforms, has been implicated in the pathogenesis of ventricular... (Review)
Review
Electrocardiographic alternans, a phenomenon of beat-to-beat alternation in cardiac electrical waveforms, has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death (SCD). In the clinical setting, a positive microvolt T-wave alternans test has been associated with a heightened risk of arrhythmic mortality and SCD during medium- and long-term follow-up. However, rather than merely being associated with an increased risk for SCD, several lines of preclinical and clinical evidence suggest that cardiac alternans may play a causative role in generating the acute electrophysiological substrate necessary for the onset of ventricular arrhythmias. Deficiencies in Ca(2+) transport processes have been implicated in the genesis of alternans at the subcellular and cellular level and are hypothesized to contribute to the conditions necessary for dispersion of refractoriness, wave break, reentry, and onset of arrhythmia. As such, detecting acute surges in alternans may provide a mechanism for predicting the impending onset of arrhythmia and opens the door to delivering upstream antiarrhythmic therapies. In this review, we discuss the preclinical and clinical evidence to support a causative association between alternans and acute arrhythmogenesis and outline the potential clinical implications of such an association.
Topics: Arrhythmias, Cardiac; Brugada Syndrome; Cardiac Conduction System Disease; Death, Sudden, Cardiac; Electrocardiography; Heart Conduction System; Heart Rate; Humans; Risk Assessment; Ventricular Fibrillation
PubMed: 24322612
DOI: 10.1152/ajpheart.00639.2013 -
International Journal of Molecular... May 2021Non-ischemic dilated cardiomyopathy encompasses a wide spectrum of myocardial disorders, characterized by left ventricular dilatation with systolic impairment and... (Review)
Review
Non-ischemic dilated cardiomyopathy encompasses a wide spectrum of myocardial disorders, characterized by left ventricular dilatation with systolic impairment and increased risk of sudden cardiac death. In spite of all the therapeutic progress that has been made in recent years, dilated cardiomyopathy continues to be an important cause of cardiac transplant, being associated with an enormous cost burden for health care systems worldwide. Predicting the prognosis of patients with dilated cardiomyopathy is essential to individualize treatment. Late gadolinium enhancement-cardiac magnetic resonance imaging, microvolt T-wave alternans, and genetic testing have emerged as powerful tools in predicting sudden cardiac death occurrence and maximizing patient's selection. Despite all these new diagnostic modalities, additional tests to complement or replace current tools are required for better risk stratification. Therefore, biomarkers are an easy and important tool that can help to detect patients at risk of adverse cardiovascular events. Additionally, identifying potential biomarkers involved in dilated cardiomyopathy can provide us important information regarding the diagnostic, prognostic, risk stratification, and response to treatment for these patients. Many potential biomarkers have been studied in patients with dilated cardiomyopathy, but only a few have been adopted in current practice. Therefore, the aim of our review is to provide the clinicians with an update on the well-known and novel biomarkers that can be useful for risk stratification of patients with non-ischemic dilated cardiomyopathy.
Topics: Biomarkers; Cardiomyopathy, Dilated; Contrast Media; Gadolinium; Humans; Magnetic Resonance Imaging; Risk Assessment
PubMed: 34073616
DOI: 10.3390/ijms22115688 -
Turkish Neurosurgery 2017Intraoperative neurophysiological monitoring (IONM) monitors the functional integrity of critical neural structures by electrophysiological methods during surgery....
AIM
Intraoperative neurophysiological monitoring (IONM) monitors the functional integrity of critical neural structures by electrophysiological methods during surgery. Multimodality combines different neurophysiological methods to maximize diagnostic efficacy and provide a safety margin to improve the outcomes of spinal surgery. Our aim was to share our intraoperative monitoring experiences with patients who underwent surgery because of spinal cord pathologies between September 2013 and January 2015.
MATERIAL AND METHODS
We had twenty-six cases. Location of the lesions, surgery, neurological findings, and electrophysiological findings intraoperatively and postoperatively were documented.
RESULTS
The combination of motor evoked potential (MEP), somatosensorial evoked potential (SSEP), free-run and trigger electromyography (EMG) were performed according to lesion localization. MEPs plus SSEPs were run in 23 patients and MEPs with triggered EMG were performed in 4 patients. In only one patient, optimal recording could not be elicited because of technical problems. MEP and SSEP changes were recorded in 12 and 3 patients respectively. Postoperative neurological deficits were observed in 2 patients. Deficits were transient in one case and permanent in the other. While baseline MEP responses were either absent or low amplitude ( < 50 microvolt) in 7 patients, following resection they were either visible or increased in amplitude. Surgery was ended in one patient with C7-T2 intramedullary tumour after the right distal MEP response disappeared.
CONCLUSION
Multimodal IONM is an important method to monitor the neural structures under risk in spine surgery and to keep the surgery within safety limits, especially for intramedullary spinal cord lesion surgery.
Topics: Adolescent; Adult; Aged; Child; Child, Preschool; Electromyography; Evoked Potentials, Motor; Evoked Potentials, Somatosensory; Female; Humans; Intraoperative Neurophysiological Monitoring; Male; Middle Aged; Neurosurgical Procedures; Postoperative Period; Spinal Cord Diseases; Young Adult
PubMed: 27593793
DOI: 10.5137/1019-5149.JTN.16414-15.1 -
Heart Rhythm Mar 2009Detection of microvolt levels of T-wave alternans (TWA) has been shown to be useful in identifying individuals at heightened risk for sudden cardiac death. The... (Review)
Review
Detection of microvolt levels of T-wave alternans (TWA) has been shown to be useful in identifying individuals at heightened risk for sudden cardiac death. The mechanistic bases for TWA are complex, at the cellular level involving multiple mechanisms, particularly instabilities in membrane voltage (i.e., steep action potential duration restitution slope) and disruptions in intracellular calcium cycling dynamics. The integrative factors influencing TWA at the systemic level are also multifold. We focus on three main variables: heart rate, autonomic nervous system activity, and myocardial ischemia. Clinically, there is growing interest in extending TWA testing to include ambulatory ECG monitoring as well as exercise. The former modality permits assessment of the influence of diverse provocative stimuli of daily life, including physical activity, circadian factors, mental stress, and sleep-state related disturbances in respiratory and cardiovascular function. Two major emerging concepts in clinical TWA testing are discussed: quantitative analysis of TWA level to complement the current binary classification scheme, and risk stratification of patients with preserved left ventricular function, the population with the largest absolute number of sudden cardiac deaths.
Topics: Animals; Autonomic Nervous System; Death, Sudden, Cardiac; Electrocardiography; Electrocardiography, Ambulatory; Electrophysiologic Techniques, Cardiac; Exercise Test; Heart Rate; Humans; Risk Assessment; Stroke Volume
PubMed: 19251221
DOI: 10.1016/j.hrthm.2008.11.019 -
Annals of Noninvasive Electrocardiology... Oct 2011Microvolt T-wave alternans (MTWA) has been proposed as a predictor of the risk of ventricular tachyarrhythmias (VT) and sudden cardiac death (SCD). Aim of this study was... (Meta-Analysis)
Meta-Analysis Review
Predictive value of microvolt T-wave alternans for cardiac death or ventricular tachyarrhythmic events in ischemic and nonischemic cardiomyopathy patients: a meta-analysis.
BACKGROUND
Microvolt T-wave alternans (MTWA) has been proposed as a predictor of the risk of ventricular tachyarrhythmias (VT) and sudden cardiac death (SCD). Aim of this study was to perform a systematic review of the literature and a meta-analysis of MTWA in primary prevention patients with ischemic and nonischemic cardiomyopathy.
METHODS
The positive predictive value (PPV), negative predictive value (NPV), and relative risk (RR) of MTWA in predicting death, cardiac death, and SCD during follow-up were reported.
RESULTS
Fifteen studies involving 5681 patients (mean age 62 years, mean ejection fraction 32%) were included. The summary PPV during the average 26-month follow-up was 14% (95% CI: 13-15); NPV was 95% (95% CI: 94-96), and the univariate RR was 2.35 (95% CI: 1.68-3.28). The predictive value of MTWA was similar in patients with ischemic and nonischemic cardiomyopathy. The average RR for SCD or VT events of an abnormal MTWA was 2.40, similar to that for cardiac death. When we grouped the studies together depending upon whether beta-blockers were withheld prior to MTWA screening, the beta-blockers group showed an RR of 5.88. By contrast, the group in which beta-blocker therapy was withheld had an RR of 1.63.
CONCLUSION
A positive MTWA determined an approximately 2.5-fold higher risk of cardiac death and life-threatening arrhythmia and showed a very high NPV both in ischemic and nonischemic patients. An abnormal MTWA test was associated with a 5-fold increased risk for cardiac mortality in the low-indeterminate group and about a 6-fold increased risk in beta-blockers group.
Topics: Adrenergic beta-Antagonists; Cardiomyopathies; Death, Sudden, Cardiac; Defibrillators, Implantable; Electrocardiography; Electrophysiologic Techniques, Cardiac; Female; Humans; Male; Middle Aged; Predictive Value of Tests; Primary Prevention; Prognosis; Risk Assessment; Tachycardia, Ventricular
PubMed: 22008495
DOI: 10.1111/j.1542-474X.2011.00467.x