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Cardiology Journal 2011Electrolyte disorders can alter cardiac ionic currents kinetics and depending on the changes can promote proarrhythmic or antiarrhythmic effects. The present report... (Review)
Review
Electrolyte disorders can alter cardiac ionic currents kinetics and depending on the changes can promote proarrhythmic or antiarrhythmic effects. The present report reviews the mechanisms, electrophysiolgical (EP), electrocardiographic (ECG), and clinical consequences of electrolyte disorders. Potassium (K⁺) is the most abundent intracellular cation and hypokalemia is the most commont electrolyte abnormality encountered in clinical practice. The most significant ECG manifestation of hypokalemia is a prominent U wave. Several cardiac and non cardiac drugs are known to suppress the HERG K⁺ channel and hence the I(K), and especially in the presence of hypokalemia, can result in prolonged action potential duration and QT interval, QTU alternans, early afterdepolarizations, and torsade de pointes ventricular tachyarrythmia (TdP VT). Hyperkalemia affects up to 8% of hospitalized patients mainly in the setting of compromised renal function. The ECG manifestation of hyperkalemia depends on serum K⁺ level. At 5.5-7.0 mmol/L K⁺, tall peaked, narrow-based T waves are seen. At > 10.0 mmol/L K⁺, sinus arrest, marked intraventricular conduction delay, ventricular techycardia, and ventricular fibrillation can develop. Isolated abnormalities of extracellular calcium (Ca⁺⁺) produce clinically significant EP effects only when they are extreme in either direction. Hypocalcemia, frequently seen in the setting of chronic renal insufficiency, results in prolonged ST segment and QT interval while hypercalcemia, usually seen with hyperparathyroidism, results in shortening of both intervals. Although magnesium is the second most abudent intracellular cation, the significance of magnesium disorders are controversial partly because of the frequent association of other electrolyte abnormalities. However, IV magnesium by blocking the L-type Ca(⁺⁺) current can successfully terminate TdP VT without affecting the prolonged QT interval. Finally, despite the frequency of sodium abnormalities, particularly hyponatremia, its EP effects are rarely clinically significant.
Topics: Arrhythmias, Cardiac; Electrolytes; Humans; Models, Biological; Water-Electrolyte Imbalance
PubMed: 21660912
DOI: No ID Found -
Frontiers in Physiology 2021T-wave alternans (TWA) reflects every-other-beat alterations in the morphology of the electrocardiogram ST segment or T wave in the setting of a constant heart rate,... (Review)
Review
T-wave alternans (TWA) reflects every-other-beat alterations in the morphology of the electrocardiogram ST segment or T wave in the setting of a constant heart rate, hence, in the absence of heart rate variability. It is believed to be associated with the dispersion of repolarization and has been used as a non-invasive marker for predicting the risk of malignant cardiac arrhythmias and sudden cardiac death as numerous studies have shown. This review aims to provide up-to-date review on both experimental and simulation studies in elucidating possible mechanisms underlying the genesis of TWA at the cellular level, as well as the genesis of spatially concordant/discordant alternans at the tissue level, and their transition to cardiac arrhythmia. Recent progress and future perspectives in antiarrhythmic therapies associated with TWA are also discussed.
PubMed: 33746768
DOI: 10.3389/fphys.2021.614946 -
Journal of the American College of... Jan 2006T-wave alternans (TWA) reflects beat-to-beat fluctuations in the electrocardiographic T-wave, and is associated with dispersion of repolarization and the mechanisms for... (Review)
Review
T-wave alternans (TWA) reflects beat-to-beat fluctuations in the electrocardiographic T-wave, and is associated with dispersion of repolarization and the mechanisms for sudden cardiac arrest (SCA). This review examines the bench-to-bedside literature that, over decades, has linked alternans of repolarization in cellular, whole-heart, and human studies with spatial dispersion of repolarization, alternans of cellular action potential, and fluctuations in ionic currents that may lead to ventricular arrhythmias. Collectively, these studies provide a foundation for the clinical use of TWA to reflect susceptibility to ventricular arrhythmias in several disease states. This review then provides a contemporary evidence-based framework for the use of TWA to enhance risk stratification for SCA, identifying populations for whom TWA is best established, those for whom further studies are required, and areas for additional investigation.
Topics: Action Potentials; Bundle-Branch Block; Cardiomyopathy, Hypertrophic; Electrocardiography; Heart Arrest; Heart Conduction System; Heart Rate; Humans; Long QT Syndrome; Risk Assessment; Stroke Volume; Tachycardia, Ventricular; Ventricular Dysfunction, Left; Ventricular Fibrillation
PubMed: 16412847
DOI: 10.1016/j.jacc.2005.08.066 -
Cureus Feb 2023Here, we report a rare case of a three-year-old boy with Jervell and Lange-Nielsen (JLN) syndrome who presented with two episodes of nocturnal agonal gasp provoked by...
Here, we report a rare case of a three-year-old boy with Jervell and Lange-Nielsen (JLN) syndrome who presented with two episodes of nocturnal agonal gasp provoked by fever mimicking syncope in the last six months with a history of sudden cardiac death in one elderly sibling. Interestingly, an electrocardiogram (EKG) revealed macro T-wave alternans (TWA) indicative of a high risk of malignant ventricular arrhythmia in the form of ventricular fibrillation and sudden cardiac death. TWA in JLN syndrome has not been described in the global literature so far. Our case is unique and the first to describe macro TWA in JLN syndrome and is a teaching point to young cardiologists to always look for macro TWA in the EKG of long QT syndrome for risk stratification, management, and, most importantly, avoiding the risk of sudden cardiac death.
PubMed: 36909039
DOI: 10.7759/cureus.34762 -
Annals of Noninvasive Electrocardiology... Jul 2020Sudden infant death syndrome is more frequent in preterm infants (PTI) than term infants and may be due to cardiac repolarization instability, which may manifest as...
BACKGROUND
Sudden infant death syndrome is more frequent in preterm infants (PTI) than term infants and may be due to cardiac repolarization instability, which may manifest as T-wave alternans (TWA) on the electrocardiogram (ECG). Therefore, the aim of the present work was to analyze TWA in nonpathological PTI and to open an issue on its physiological interpretation.
METHODS
Clinical population consisted of ten nonpathological PTI (gestational age ranging from 29 to 34 weeks; birth weight ranging from 0.84 to 2.10 kg) from whom ECG recordings were obtained ("Preterm infant cardio-respiratory signals database" by Physionet). TWA was identified through the heart-rate adapting match filter method and characterized in terms of mean amplitude values (TWAA). TWA correlation with several other clinical and ECG features, among which gestational age-birth weight ratio, RR interval, heart-rate variability, and QT interval, was also performed.
RESULTS
TWA was variable among infants (TWAA = 26 ± 11 µV). Significant correlations were found between TWAA versus birth weight (ρ = -0.72, p = .02), TWAA versus gestational age-birth weight ratio (ρ = 0.76, p = .02) and TWAA versus heart-rate variability (ρ = -0.71, p = .02).
CONCLUSIONS
Our preliminary retrospective study suggests that nonpathological PTI show TWA of few tens of µV, the interpretation of which is still an open issue but could indicate a condition of cardiac risk possibly related to the low development status of the infant. Further investigations are needed to solve this issue.
Topics: Arrhythmias, Cardiac; Electrocardiography; Female; Humans; Infant, Newborn; Infant, Premature; Male; Retrospective Studies
PubMed: 31986237
DOI: 10.1111/anec.12745 -
Arquivos Brasileiros de Cardiologia Mar 2011Accurate recognition of individuals at higher immediate risk of sudden cardiac death (SCD) is still an open question. The fortuitous nature of acute cardiovascular... (Review)
Review
Accurate recognition of individuals at higher immediate risk of sudden cardiac death (SCD) is still an open question. The fortuitous nature of acute cardiovascular events just does not seem to fit the well-known model of ventricular tachycardia/fibrillation induction in a static arrhythmogenic substrate by a synchronous trigger. On the mechanism of SCD, a dynamical electrical instability would better explain the rarity of the simultaneous association of a correct trigger and an appropriate cardiac substrate. Several studies have been conducted trying to measure this cardiac electrical instability (or any valid surrogate) in an ECG beat stream. Among the current possible candidates we can number QT prolongation, QT dispersion, late potentials, T-wave alternans (TWA), and heart rate turbulence. This article reviews the particular role of TWA in the current cardiac risk stratification scenario. TWA findings are still heterogeneous, ranging from very good to nearly null prognostic performance depending on the clinical population observed and clinical protocol in use. To fill the current gaps in the TWA base of knowledge, practitioners, and researchers should better explore the technical features of the several technologies available for TWA evaluation and pay greater attention to the fact that TWA values are responsive to several factors other than medications. Information about the cellular and subcellular mechanisms of TWA is outside the scope of this article, but the reader is referred to some of the good papers available on this topic whenever this extra information could help the understanding of the concepts and facts covered herein.
Topics: Death, Sudden, Cardiac; Electrocardiography; Heart Diseases; Heart Rate; Humans; Predictive Value of Tests; Prognosis; Risk Assessment; Risk Factors
PubMed: 21359487
DOI: No ID Found -
Arquivos Brasileiros de Cardiologia May 2018Sudden cardiac death is the most frequent death mechanism in Chagas disease, responsible for 55% to 65% of the deaths of patients with chronic Chagas cardiomyopathy... (Observational Study)
Observational Study
BACKGROUND
Sudden cardiac death is the most frequent death mechanism in Chagas disease, responsible for 55% to 65% of the deaths of patients with chronic Chagas cardiomyopathy (CCC). The most often involved electrophysiological mechanisms are ventricular tachycardia and ventricular fibrillation. The implantable cardioverter defibrillator (ICD) has a beneficial role in preventing sudden death due to malignant ventricular arrhythmias, and, thus the correct identification of patients at risk is required. The association of microvolt T-wave alternans (MTWA) with the appearance of ventricular arrhythmias has been assessed in different heart diseases. The role of MTWA is mostly unknown in patients with CCC.
OBJECTIVES
To evaluate the association between MTWA and the occurrence of malignant ventricular arrhythmias in patients with CCC.
METHOD
This is a case-control study including patients with CCC and ICD, with history of malignant ventricular arrhythmias (case group), and patients with CCC and no history of those arrhythmias (control group). The MTWA test results were classified as negative and non-negative (positive and indeterminate). The significance level adopted was a = 0.05.
RESULTS
We recruited 96 patients, 45 cases (46.8%) and 51 controls (53.1%). The MTWA test was non-negative in 36/45 cases (80%) and 15/51 controls (29.4%) [OR = 9.60 (95%CI: 3.41 - 27.93)]. After adjustment for known confounding factors in a logistic regression model, the non-negative result continued to be associated with malignant ventricular arrhythmias [OR = 5.17 (95%CI: 1.05 - 25.51)].
CONCLUSION
Patients with CCC and history of malignant ventricular arrhythmias more often have a non-negative MTWA test as compared to patients with no history of arrhythmia.
Topics: Arrhythmias, Cardiac; Case-Control Studies; Chagas Disease; Death, Sudden, Cardiac; Defibrillators, Implantable; Electrocardiography; Female; Humans; Male; Middle Aged; Risk Factors; Survival Analysis; Tachycardia, Ventricular
PubMed: 29641645
DOI: 10.5935/abc.20180056 -
Frontiers in Physiology 2021Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular...
Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular tachy-arrhythmias, while vagus nerve stimulation has shown promising anti-arrhythmic effects in and animal studies. We aimed to examine the effect of non-invasive, acute low-level tragus stimulation (LLTS) on TWA in patients with ischemic cardiomyopathy and heart failure. 26 patients with ischemic cardiomyopathy (left ventricular ejection fraction <35%) and chronic stable heart failure, previously implanted with an automatic implantable cardioverter defibrillator (ICD) device with an atrial lead (dual chamber ICD or cardiac resynchronization therapy defibrillator), were enrolled in the study. Each patient sequentially received, (1) Sham LLTS (electrode on tragus, but no stimulation delivered) for 5 min; (2) Active LLTS at two different frequencies (5 and 20 Hz, 15 min each); and (3) Active LLTS, during concomitant atrial pacing at 100 bpm at two different frequencies (5 and 20 Hz, 15 min each). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 5/20 Hz, amplitude 1 mA lower than the discomfort threshold). TWA burden was assessed using continuous ECG monitoring during sham and active LLTS in sinus rhythm, as well as during atrial pacing. Right atrial pacing at 100 bpm led to significantly heightened TWA burden compared to sinus rhythm, with or without LLTS. Acute LLTS at both 5 and 20 Hz, during sinus rhythm led to a significant rise in TWA burden in the precordial leads ( < 0.05). Acute LLTS results in a heart-rate dependent increase in TWA burden.
PubMed: 34366894
DOI: 10.3389/fphys.2021.707724 -
IEEE Journal of Biomedical and Health... Nov 2022T-wave alternans (TWA) manifests as beat-to-beat fluctuations of T-wave morphology on the electrocardiogram (ECG), with physiological bases not fully understood. Using a...
OBJECTIVE
T-wave alternans (TWA) manifests as beat-to-beat fluctuations of T-wave morphology on the electrocardiogram (ECG), with physiological bases not fully understood. Using a biophysical model of the ECG, we demonstrate and give explicit relations that TWA depends on the i) spatial covariance between myocytes' repolarization time and alternans; and ii) global alternans (common to every myocyte).
METHODS
We quantified the spatial covariance and global alternans by means of two new metrics, R index and δ, respectively. They were validated on both synthetic and real signals. Computerized simulations were generated using a biophysical model linking the action potentials with the surface ECG. Then, the metrics were computed in STAFF-III dataset, containing ECGs from patients who underwent coronary angioplasty with prolonged balloon inflations, and the time courses of the metrics were analyzed together with TWA measured on the surface ECG.
RESULTS
The metrics properly estimated the spatial covariance and global alternans in the synthetic data. In the STAFF-III dataset, the R index progressively increased from baseline to the fourth minute of inflation (median ∆R=0.81 ms; p 0.05), whereas δ was mostly unaltered during the intervention ( δ=0 ms).
CONCLUSION
We reported, for the first time, that TWA is significantly driven by the myocyte's spatial covariance between their repolarization times and alternans, and not by global alternans, when TWA is generated by regional ischemia.
SIGNIFICANCE
The metrics may reveal new complementary insights into the mechanisms underlying TWA.
Topics: Humans; Electrocardiography; Arrhythmias, Cardiac; Action Potentials; Muscle Cells
PubMed: 35905062
DOI: 10.1109/JBHI.2022.3195060 -
Anesthesiology Sep 2017
Topics: Child, Preschool; Electrocardiography; Humans; Long QT Syndrome; Male
PubMed: 28346324
DOI: 10.1097/ALN.0000000000001618