Clinical significance of microvolt T-wave alternans

Improved modified moving average analysis of T-wave alternans using least squares-based curve fitting method

T-wave alternans (TWA) in surface electrocardiograph (ECG) signal is considered a marker of abnormal ventricular function which may be associated with ventricular tachycardia. Several methods have been developed in recent years to evaluate the important feature. One such method is known as modified moving average (MMA) analysis, which performs well for different levels of TWA, but it is sensitive to the noise in T-waves. In this paper we propose an improved MMA algorithm, which adds a stage of T-wave curve fitting for the MMA method before intermediate averaging. The curve fitting is performed by means of least square method technique. Our assessment study demonstrates the improved performance.

Microvolt T-wave alternans and the selective use of implantable cardioverter defibrillators for primary prevention: A cost-effectiveness study

Objectives:Implantable cardioverter defibrillators (ICDs) are an effective but expensive treatment for the prevention of sudden cardiac deaths in patients with severe left-ventricular dysfunction. Recent studies suggest that microvolt T-wave alternans (MTWA) predicts mortality and severe arrhythmic events in this population. However, the impact of MTWA on ICD cost-effectiveness is unknown.

Methods:A Markov decision-analysis model evaluated three treatment strategies for primary prevention in patients with severe left-ventricular dysfunction: (i) medical therapy for all; (ii) ICD therapy for all; and (iii) selective ICD therapy based on non-negative (positive or indeterminate) MTWA test results. Incremental cost-effectiveness ratios (ICER) were calculated from the perspective of a third party payer using a 10-year time horizon. Sensitivity analyses examined the robustness of the estimates.

Results:A treatment strategy involving ICD therapy in all patients was associated with an ICER of $121,800/quality-adjusted life-year (QALY) compared with medical therapy, whereas a treatment strategy involving the selective use of ICDs based on MTWA test results was associated with an ICER of $108,900/QALY compared with medical therapy. Sensitivity analyses suggest that, under most scenarios, the selective use of ICDs based on MTWA results does not decrease the ICER to below $100,000/QALY.

Conclusion:MTWA only marginally improves the cost-effectiveness of ICDs for primary prevention in patients with severe left-ventricular dysfunction. There remains a need for improved means to effectively identify which patients will derive the greatest benefit from ICD implantation.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.