T Wave Alternans for Predicting Adverse Effects of Amiodarone in a Patient With Dilated Cardiomyopathy

Microvolt T-wave alternans: a review of techniques, interpretation, utility, clinical studies, and future perspectives

Microvolt T-wave alternans (TWA) testing involves measuring variation in the morphology of the T-wave on an every other beat basis. The magnitude of the variation observed is typically on the order of a few microvolts. Thus in order to detect microvolt TWA, specialized recording and signal processing methods must be employed for reliable measurement. Additionally, microvolt TWA is not generally present at rest even in patients at risk of ventricular tachyarrhythmias and therefore exercise stress, pharmacologic stress, or atrial pacing must be utilized in order to elevate the heart rate. A positive MTWA test is one in which sustained TWA is present with an onset heart rate < or = 110 bpm. With current instrumentation, microvolt TWA represents an inexpensive, convenient non-invasive testing modality. Microvolt TWA has been evaluated prospectively in a variety of patient populations as a means of predicting occurrence of ventricular tachyarrhythmic events and its association with the genesis of ventricular arrhythmias has been demonstrated. Future role of microvolt TWA testing in noninvasive risk stratification is awaiting results of ongoing clinical trials. In this article, we tried to review the techniques, interpretation, indications, clinical studies, and future perspectives of microvolt TWA.

T-wave alternans: marker, mechanism, and methodology for predicting sudden cardiac death

Sudden cardiac death (SCD) is a leading cause of cardiovascular mortality. Therefore, identifying patients at highest risk for SCD is crucial. Conventional noninvasive markers of SCD are inadequate because of low positive predictive value. The presence of visible T-wave alternans (TWA) on electrocardiogram often predicts the occurrence of lethal ventricular arrhythmias. Signal processing methods have made it possible to detect microvolt-level and visually inapparent TWA on electrocardiogram. TWA is caused by underlying regional inhomogeneities of ventricular repolarization, which predispose patients to have ventricular arrhythmias. Microvolt TWA provoked either by atrial pacing, pharmacological stress, or exercise is a promising marker of arrhythmia vulnerability. Several large trials have shown TWA to be comparable or superior to other noninvasive markers and electrophysiologic study in the prediction of SCD. The patient populations in these trials include post myocardial infarction, both ischemic and nonischemic heart failure, and suspected arrhythmias. Prospective trials regarding benefits of implantation of cardioverter-defibrillator therapy based on TWA results are ongoing.

Effect of Long-Term Beta-Blocker Therapy on Microvolt-Level T-Wave Alternans in Association With the Improvement of the Cardiac Sympathetic Nervous System and Systolic Function in Patients With Non-Ischemic Heart Disease

The purpose of this study was to test a hypothesis that T-wave alternans (TWA) is improved in association with an improvement in cardiac sympathetic nervous system and systolic function by oral beta-blocker therapy in patients with non-ischemic heart disease (NIHD). TWA testing, (123)I-metaiodobenzylguanidine (MIBG) imaging and echocardiography were performed at the baseline and 3 months after beta-blocker therapy in 26 patients with NIHD and positive TWA. The alternans voltage (V(alt)), the heart-to mediastinal-ratio on the early (e-H/M) and delayed (d-H/M) images, the washout rate (WR), the left ventricular ejection fraction (LVEF), and the calculated rate of change by beta-blocker therapy in each parameter (ie, deltaV(alt), deltae-H/M, deltad-H/M, deltaWR and deltaLVEF) were measured. After therapy, TWA turned negative in 8 patients (group A) and remained positive in 18 (group B); V(alt) was significantly decreased in group B (p<0.001). In group A, e-H/M, d-H/M and LVEF were significantly increased (e-H/M: p<0.05, d-H/M and LVEF: p<0.01), as were e-H/M and LVEF in group B (p<0.05). There were significant correlations between deltaV(alt) and deltae-H/M (r=-0.61, p<0.01), deltad-H/M (r=-0.82, p<0.0001), deltaWR (r=0.60, p<0.01) and deltaLVEF (r=-0.70, p<0.01). In patients with NIHD, the TWA is improved in association with the improvement in cardiac sympathetic nervous system abnormalities and left ventricular systolic dysfunction by beta-blocker therapy.

Evaluation of heart-rate turbulence as a new prognostic marker in patients with chronic heart failure

The significance of heart-rate turbulence (HRT) in patients with chronic heart failure (CHF) was evaluated to examine whether it is sensitive to the risk of ventricular tachycardia (VT). HRT is reported to predict the prognosis after myocardial infarction (MI), but its prognostic value in patients with CHF remains unknown. HRT was measured in 50 CHF patients (left ventricular ejection fraction <50% and/or left ventricular end-diastolic diameter >55 mm, 34 cardiomyopathy, 16 post-MI) and 21 patients without obvious heart diseases (control). HRT slope and HRT onset were measured by the original definitions using digitized Holter ECG recordings. Cardiac pump function was assessed by echocardiography. The value of the HRT slope was significantly lower in CHF than in control (3.7 +/- 1.7 vs 16.4 +/- 5.3, mean +/- SD, p < 0.01). The value of the HRT onset in patients with CHF was significantly higher than that in control patients (-1.1 +/- 1.9 vs -3.6 +/- 1.7, mean +/- SD, p < 0.05). The HRT slope and onset in CHF patients with VT were nearly identical to those without VT. The HRT slope appears to be a powerful prognostic marker that shows significant differences between CHF subgroups when divided by clinical events; that is, CHF death and CHF hospitalization. However, it has limited value for predicting fatal ventricular arrhythmias.