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 Nonnegative1
(n, %)
|
2-Year Arrhythmia-Free Survival, TWA
Nonnegative2
|
2-Year Arrhythmia-Free Survival, TWA
Negative2
|
Sensitivity2
|
Specificity1
|
Normal
(n=150, 81.5%)
|
97 (65%)
|
81%
|
91%
|
78%
|
38%
|
LBBB
(n=34, 18.5%)
|
30 (88%)
|
77%
|
75%
|
88%
|
12%
|
|
1 p<0.01
|
2 p=NS
|
|
|
|
|