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.
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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.
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