Microvolt T - Wave Alternans During Atrial and Ventricular Pacing
Category: 09 Signal Average ECG/T-Wave
Alternans
Presentation Time: Friday, 9:30 a.m. - 10:30 a.m.
Alaa Shalaby, MD, Andrew Voigt, MD, Aiman Elsaed, MD, PhD,
Presentation Number: P4-32
Keyword: T-wave alternans, Diagnostic techniques
Introduction: Microvolt T - wave alternans (MTWA) has
demonstrated value in assessing risk for sudden death. To evaluate MTWA,
exercise testing or atrial pacing (AP) are used. We hypothesized that despite
altered repolarization due to ventricular pacing (VP), VP could be utilized to
assess MTWA. We compared results of MTWA obtained by AP and VP.
Methods: Patients (pts) underwent AP and VP in random order. Medications
were continued at time of testing. Pacing was at a fixed rate of 550msec in
both chambers. Spectral analysis of MTWA was completed by commercially
available tools (Cambridge Heart, USA). Results were assessed as negative (N)
or nonnegative (NN) which included positive and indeterminate results. Maximum
amplitude of MTWA (Mv) in concordant positive results, as well as noise levels
in all, were compared in both pacing modes.
Results: Forty two consecutive pts were evaluated, of whom 31 completed
both tests. AP was not possible in 10 pts (24%) due to atrioventricular block
(7) or atrial fibrillation (3).VP was not possible in 2 (5%) with frequent
ectopy. All pts were male, aged 66.7±10.8 years. Ejection fraction was 32.8 +/-
12.6 with coronary artery disease in 76%. Pts were on betablockers (76%), ACE-I
(79%), digoxin (23%) and amiodarone (12%) at time of testing. AP was N in 17
pts (53%) and NN in 15 (47%), while VP was N in 16 (40%) and NN in 24 (60%). Twenty
five (80%) of 31 paired tests were concordant indicating good agreement between
both tests (k=0.62, p<0.001). VP had a better negative than positive
predictive value (NPV 92% vs PPV 72%) and was more sensitive (93%) than
specific (71%) when referenced to AP. There were no differences in clinical
variables between pts with concordant or noncordant tests other than amiodarone
use which was more likely in nonconcordants (p=0.02). Mv from both tests had
significant positive correlation (r=0.63, p=0.05) with a trend toward higher
values of Mv by VP (10.7±5.3 vs 7.8±3.9, p=0.058). VP noise was significantly
higher (1.4±0.8 vs 1±0.8, p <0.01).
Conclusion: Despite overall agreement between results of VP and AP, VP
appears to generate higher levels of Mv and noise with higher percentage of NN
results. New cutoffs for positive VP may need to be established.