How to do exercise-induced T-wave alternans testing using the spectral method

The present review summarizes current aspects on how to perform noninvasive microvolt T-wave alternans (mTWA) testing in clinical practice. The focus is on methodologic issues such as patient-related, or technical aspects, and interpretation of the results. Special attention is given to the different sources of noise that may interfere with mTWA assessment. The role of beta-blocker therapy and its potential effect on mTWA is discussed as well. In the first clinical studies of mTWA, a high rate of indeterminate test results was observed. In this respect, patient-related indeterminacy has been demonstrated to be associated with an increased mortality and such tests are thus regarded as “abnormal” whereas technically inadequate tests are classified as indeterminate. Since mTWA evolves over time in patients with structural heart disease, the “optimal timing” for mTWA assessment is rather in the chronic phase than in the acute setting of heart disease. (Cardiol J 2008; 15: 288-292

Ocena mikrowoltowej zmienności załamka T podczas wysiłku fizycznego za pomocą metody spektralnej

W niniejszym artykule podsumowano najnowsze aspekty nieinwazyjnej oceny mikrowoltowej zmienności (naprzemienności) załamka T (mTWA) w praktyce klinicznej. Skoncentrowano się na kwestiach metodologicznych, w tym czynnikach związanych z pacjentem oraz aspektach technicznych, a także na interpretacji wyników. Szczególną uwagę zwrócono na różne źródła szumu, które mogą utrudniać ocenę mTWA. Omówiono również rolę terapii lekami beta-adrenolitycznymi i jej potencjalny wpływ na mTWA. W pierwszych próbach klinicznych dotyczących mTWA zaobserwowano duży odsetek nieokreślonych wyników tych ocen. Wykazano jednak, że rezultaty nieokreślone z przyczyn zależnych od pacjenta wiążą się ze zwiększoną śmiertelnością i takie wyniki obecnie uważa się za nieprawidłowe, a jako nieokreślone klasyfikuje się te, które są nieodpowiednie pod względem technicznym. Ponieważ u pacjentów ze strukturalną chorobą serca mTWA zmienia się w czasie, optymalnym momentem jej oceny jest raczej przewlekła niż ostra faza choroby serca

Effect of metoprolol and d,l-sotalol on microvolt-level T-wave alternans Results of a prospective, double-blind, randomized study

AbstractOBJECTIVESThe study evaluated the effects of metoprolol, a pure beta-blocker, and d,l-sotalol, a beta-blocker with additional class III antiarrhythmic effects, on microvolt-level T-wave alternans (TWA).BACKGROUNDAssessment of TWA is increasingly used for purposes of risk stratification in patients prone to sudden death. There are only sparse data regarding the effects of beta-blockers and antiarrhythmic drugs on TWA.METHODSPatients with a history of documented or suspected malignant ventricular tachyarrhythmias were eligible. All patients underwent invasive electrophysiologic (EP) testing including programmed ventricular stimulation and determination of TWA at increasing heart rates using atrial pacing. Reproducibility of TWA at two consecutive drug-free baseline measurements was tested in a random patient subset. Following baseline measurements, all patients were randomized either to double-blind intravenous infusion of sotalol (1.0 mg/kg) or metoprolol (0.1 mg/kg). Results of TWA assessment at baseline and after drug exposure were compared.RESULTSFifty-four consecutive patients were studied. In 12 patients, repetitive baseline measurement of TWA revealed stable alternans voltage (Valt) values (9.1 ± 5.8 μV vs. 8.5 ± 5.7 μV, p = NS). After drug administration, Valtdecreased by 35% with metoprolol (7.9 ± 6.0 μV to 4.9 ± 4.2 μV; p < 0.001) and by 38% with sotalol (8.6 ± 6.8 μV to 4.4 ± 2.3 μV; p = 0.001). In eight patients with positive TWA at baseline, repeated measurement revealed negative test results.CONCLUSIONSIn patients prone to sudden cardiac death, there is a reduction in TWA amplitude following the administration of antiadrenergic drugs. This result indicates that TWA is responsive to the pharmacologic milieu and suggests that, to assess a patient’s risk of spontaneous ventricular arrhythmia, the patient should be tested while maintaining the pharmacologic regimen under which the risk of arrhythmia is being assessed. This applies particularly for beta-blocker therapy

Do Beta-Blockers Impact Microvolt T-Wave Alternans Testing in Patients at Risk for Ventricular Arrhythmias? A Meta-Analysis

Beta-Blockers and Microvolt T-Wave Alternans.  Introduction: Results of microvolt T-wave alternans (MTWA) studies vary and may be influenced by whether beta-blocker therapy was withheld prior to MTWA assessment. We conducted a meta-analysis of the predictive value of MTWA screening for ventricular arrhythmic events in primary prevention patients with left ventricular dysfunction and examined whether results differed depending upon whether beta-blocker use was withheld prior to MTWA testing. Methods and Results: Prospective studies that evaluated whether MTWA predicted ventricular arrhythmic events published between January 1980 and September 2008 were identified. Summary estimates for the predictive value of MTWA were derived with random-effects models. Nine studies involving 3,939 patients were identified. Overall, an abnormal MTWA (positive and indeterminate) test was associated with an almost 2-fold increased risk for arrhythmic events (pooled RR = 1.95, 95% CI: 1.29–2.96; P = 0.002). However, significant heterogeneity across studies was observed (P = 0.024). In the 4 studies in which beta-blocker therapy was not withheld prior to MTWA assessment, an abnormal MTWA test was associated with a 5-fold increased risk for arrhythmic events (pooled RR = 5.39, 95% CI: 2.68–10.84; P < 0.001) and was robust to sensitivity analyses. In contrast, the association was much weaker in those studies where the use of beta-blocker therapy was withheld prior to MTWA testing (pooled RR = 1.40, 95% CI: 1.06–1.84; P = 0.02). Conclusions: In primary prevention patients with left ventricular dysfunction, the predictive power of MTWA varied widely, based on whether beta-blocker therapy was withheld prior to its assessment. This observation may explain the inconsistent results of MTWA studies in this population. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1009-1014, September 2010)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79161/1/j.1540-8167.2010.01757.x.pd

Evidence regarding clinical use of microvolt T-wave alternans

Background: Microvolt T-wave alternans (MTWA) testing in many studies has proven to be a highly accurate predictor of ventricular tachyarrhythmic events (VTEs) in patients with risk factors for sudden cardiac death (SCD) but without a prior history of sustained VTEs (primary prevention patients). In some recent studies involving primary prevention patients with prophylactically implanted cardioverter-defibrillators (ICDs), MTWA has not performed as well. Objective: This study examined the hypothesis that MTWA is an accurate predictor of VTEs in primary prevention patients without implanted ICDs, but not of appropriate ICD therapy in such patients with implanted ICDs. Methods: This study identified prospective clinical trials evaluating MTWA measured using the spectral analytic method in primary prevention populations and analyzed studies in which: (1) few patients had implanted ICDs and as a result none or a small fraction (≤15%) of the reported end point VTEs were appropriate ICD therapies (low ICD group), or (2) many of the patients had implanted ICDs and the majority of the reported end point VTEs were appropriate ICD therapies (high ICD group). Results: In the low ICD group comprising 3,682 patients, the hazard ratio associated with a nonnegative versus negative MTWA test was 13.6 (95% confidence interval [CI] 8.5 to 30.4) and the annual event rate among the MTWA-negative patients was 0.3% (95% CI: 0.1% to 0.5%). In contrast, in the high ICD group comprising 2,234 patients, the hazard ratio was only 1.6 (95% CI: 1.2 to 2.1) and the annual event rate among the MTWA-negative patients was elevated to 5.4% (95% CI: 4.1% to 6.7%). In support of these findings, we analyzed published data from the Multicenter Automatic Defibrillator Trial II (MADIT II) and Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) trials and determined that in those trials only 32% of patients who received appropriate ICD therapy averted an SCD. Conclusion: This study found that MTWA testing using the spectral analytic method provides an accurate means of predicting VTEs in primary prevention patients without implanted ICDs; in particular, the event rate is very low among such patients with a negative MTWA test. In prospective trials of ICD therapy, the number of patients receiving appropriate ICD therapy greatly exceeds the number of patients who avert SCD as a result of ICD therapy. In trials involving patients with implanted ICDs, these excess appropriate ICD therapies seem to distribute randomly between MTWA-negative and MTWA-nonnegative patients, obscuring the predictive accuracy of MTWA for SCD. Appropriate ICD therapy is an unreliable surrogate end point for SCD

Microvolt T-wave alternans as a predictor of mortality and severe arrhythmias in patients with left-ventricular dysfunction: a systematic review and meta-analysis

<p>Abstract</p> <p>Background</p> <p>Studies have demonstrated that the use of implantable cardioverter defibrillators (ICDs) is effective for the primary prevention of arrhythmic events but due to imposing costs, there remains a need to identify which patients will derive the greatest benefit. Microvolt T-wave alternans (MTWA) has been proposed to assist in this stratification.</p> <p>Methods</p> <p>We systematically searched the literature using MEDLINE, EMBASE, Current Contents, the Cochrane Library, INAHTA, and the Web of Science to identify all primary prevention randomized controlled trials and prospective cohort studies with at least 12 months of follow-up examining MTWA as a predictor of mortality and severe arrhythmic events in patients with severe left-ventricular dysfunction. The search was limited to full-text English publications between January 1990 and May 2007. The primary outcome was a composite of mortality and severe arrhythmias. Data were synthesized using Bayesian hierarchical models.</p> <p>Results</p> <p>We identified no trials and 8 published cohort studies involving a total of 1,946 patients, including 332 positive, 656 negative, 84 indeterminate, and 874 non-negative (which includes both positive and indeterminate tests) MTWA test results. The risk of mortality or severe arrhythmic events was higher in patients with a positive MTWA compared to a negative test (RR = 2.7, 95% credible interval (CrI) = 1.4, 6.1). Similar results were obtained when comparing non-negative MTWA to a negative test.</p> <p>Conclusion</p> <p>A positive MTWA test predicts mortality or severe arrhythmic events in a population of individuals with severe left ventricular dysfunction. However, the wide credible interval suggests the clinical utility of this test remains incompletely defined, ranging from very modest to substantial. Additional high quality studies are required to better refine the role of MTWA in the decision making process for ICD implantation.</p

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

Language endangerment and language documentation in Africa

Non peer reviewe