Do Beta-blockers impact microvolt T-wave alternans testing in patients at risk for ventricular arrhythmias? A meta-analysis.

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.