Left Bundle Branch Block Reduces the Specificity of T-Wave Alternans Testing

Presentation Time: Tuesday, 1:00 p.m. - 2:00 p.m.

Jennifer D. Cohen, Kenneth M. Stein, Suneet Mittal, Steven M. Markowitz, David J. Slotwiner, Sei Iwai, Mithilesh K. Das, Steven C. Hao, Bruce B. Lerman, Cornell University Medical Center, New York, New York.

Presentation Number: 1186-108

Poster Board Number: 108

Keyword: Beta-adrenergic receptor blockers, Ventricular tachycardia, Electrophysiology

Background: Several noninvasive tests are available to risk stratify pts for sudden cardiac death but are limited by the need for a normal QRS duration for accurate interpretation. T-wave alternans (TWA) has been proposed as a noninvasive test that can be used in pts with left bundle branch block (LBBB). The purpose of this study was to compare and contrast the sensitivity and specificity of TWA in pts with and without LBBB.
Methods: We prospectively evaluated 154 pts (101 men, mean age 62 ± 23 yrs) referred for EPS. All pts underwent EPS using programmed stimulation at two ventricular sites with up to triple extrastimuli with and without isoproterenol or dobutamine. At the time of EPS, all pts underwent TWA testing during rapid atrial pacing with the Cambridge Heart CH2000 or HearTwave system. TWA was interpreted according to standard protocol. Indeterminate tests were excluded from further analysis (31 pts, 20%). Positive EPS was defined as the induction of sustained monomorphic ventricular tachycardia with up to triple ventricular extrastimuli or ventricular fibrillation with up to double ventricular extrastimuli.
Results: 16 pts (13%) had LBBB on ECG and 107 pts (87%) had a normal QRS duration. There was no difference between the two groups with regard to gender, age, indication for EPS, presence of CAD, or use of beta blockers. However, LBBB was associated with a lower LVEF (28% ±8 vs. 40% ±15, p<0.001). 6 pts (38%) with LBBB and 34 pts (32%) with a normal QRS had positive EPS (p=0.78). In comparison, the positivity rate of TWA was 81% in pts with LBBB vs. 43% in pts with a normal QRS (p=0.006). The sensitivity of TWA for predicting inducibility at EPS was 83% in pts with LBBB and 47% in pts without LBBB (p=0.19). However, the specificity was only 20% in the pts with LBBB compared with 59% in the pts with normal QRS (p=0.04).
Conclusions: The presence of a LBBB on ECG was associated with a trend towards increased sensitivity, but also a marked reduction in specificity of TWA for predicting inducibility at EPS. This should be considered when interpreting the results of TWA in pts with LBBB.