T-Wave Alternans Has Lower Specificity in Left Bundle Branch Block

Category:  09 Signal Average ECG/T-Wave Alternans

Presentation Time: Thursday, 2:00 p.m. - 2:15 p.m.

Daniel P. Morin, MD, MPH, Eran S. Zacks, MD, Andreas C. Mauer, MD, Daniel Cantillon, MD, Steven M. Markowitz, MD, Suneet Mittal, MD, Sei Iwai, MD, Bindi K. Shah, MD, Bruce B. Lerman, MD and Kenneth M. Stein, MD. Cornell University Medical Center, New York, NY

Presentation Number: AB14-3

Keyword: T-wave alternans, Bundle branch block

Background: T wave alternans (TWA) has been proposed as a means of risk stratification for sudden cardiac death. It is unknown whether bundle branch block influences TWA.
Methods: We prospectively evaluated 265 consecutive pts with CAD, NSVT and LVEF < 40% who were followed for at least two years after TWA study. TWA was determined during exercise or by atrial pacing (CL=550 ms) at the time of electrophysiologic testing and was interpreted using standard criteria. Based on prior investigations, positive and indeterminate TWA were grouped together as ‘nonnegative’. A physician blinded to the results of TWA examined each pt’s ECG for evidence of conduction delay. Follow-up was conducted through chart review, device interrogation, and query of the Social Security Death Index.
Results: There were 150 pts (57%) with normal conduction and 34 pts (13%) with LBBB (QRS duration 97±12 ms vs. 147±18 ms, p<0.001). Pts with other QRS morphologies (n=81, 31%) were excluded. Pts with LBBB were significantly older than normals (70±10 vs 64±11 years, p<0.01) and had lower LVEF (25±8% vs 30±8%, p<0.01). 65% of pts with LBBB received an ICD, compared with 45% of normals (p=0.02). More pts with LBBB than normals had nonnegative TWA (88% vs 65%, p=0.007). There was no difference in the TWA indeterminacy rate between the groups (32% vs 27%, p=0.54). There was a nonsignificant trend toward a higher 2-year event rate in pts with LBBB vs normals (24% vs 15%, p=0.23). The sensitivity of TWA testing for the combined endpoint of VT, VF, or death within two years was comparable between LBBB and normals (88% vs 78%, p=0.50). However, there was a significantly lower specificity among LBBB pts than among normals (12% vs 38%, p=0.006).
Conclusions: TWA is more often nonnegative in pts with LBBB than in normals. In the presence of LBBB, TWA testing has similar sensitivity but diminished specificity for the combined endpoint of VT, VF, or death within two years.

	TWA Nonnegative^1 (n, %)	2-Year Arrhythmia-Free Survival, TWA Nonnegative^2	2-Year Arrhythmia-Free Survival, TWA Negative^2	Sensitivity^2	Specificity^1
Normal (n=150, 81.5%)	97 (65%)	81%	91%	78%	38%
LBBB (n=34, 18.5%)	30 (88%)	77%	75%	88%	12%
	^1p<0.01	^2 p=NS