Calcium Channel Blockers Influence the Sensitivity of T-Wave Alternans Testing in Patients with Ischemic Cardiomyopathy
Jennifer D Cohen
Authors: Bruce B Lerman; Steven C Hao; Mithilesh K Das; Sei Iwai; David J Slotwiner; Steven M Markowitz; Suneet Mittal; Kenneth M Stein; Jennifer D Cohen
8:00 - 6:00

Background: Recent studies suggest that a steep action potential duration restitution curve is a key determinant of T wave alternans (TWA) and the propensity for VF and that calcium channel blockade (CCB) reduces this slope. The purpose of this study was to evaluate the effect of CCB on TWA testing in humans.

Methods: We prospectively evaluated 151 pts with CAD and LVEF ?40% (125 M, 66 ? 10 yrs) referred for EPS due to NSVT. All pts underwent EPS using programmed stimulation at 2 ventricular sites with up to triple extrastimuli. At the time of EPS, all pts underwent TWA testing during rapid atrial pacing (550 msec) with the Cambridge Heart CH2000 system or HearTwave system. TWA was interpreted according to standard criteria. Positive EPS was defined as the induction of sustained monomorphic VT with up to triple ventricular extrastimuli or VF with up to double ventricular extrastimuli.

Results: 26 (17%) pts were on oral CCB at the time of EPS. There were no significant differences between pts on and off CCB with regard to age, gender, or LVEF. Of the pts on CCB, 5 (19%) had positive, 14 (54%) had negative, and 7 (27%) had indeterminate TWA. In contrast, there was a significantly higher rate of TWA positivity in the pts not on CCB of whom 59 (47%) had positive, 36 (29%) had negative, and 30 (24%) had indeterminate TWA (p=0.02). In a multivariate model, the only independent predictors of TWA were EF (p=0.009) and lack of CCB use (odds ratio 4.0, p=0.02). Excluding indeterminates, the sensitivity of TWA for predicting a positive EPS was significantly greater in the CCB (-) than in the CCB (+) group (64% vs. 17%, p=0.004). The specificity of TWA for predicting a positive EPS was 40% in the CCB (-) group and 57% in the CCB (+) group (p=NS).

Conclusions: Oral CCB use has a significant influence on the yield of TWA testing and on the sensitivity of TWA for predicting inducibility during EPS. This influence is independent of CCB effects on heart rate since all pts tested underwent a standardized pacing protocol. These results highlight the importance of considering CCB status when interpreting TWA results.