Temporal variation in T wave
alternans positivity post-MI: Implications for risk assessment.
Derek V Exner
Authors: Ryan Mitchell; Henry Duff; Wayne Tymchak; Jamie McMeekin; Katherine
Kavanagh; For the REFINE Investigators; Derek V Exner; George Veenhuyzen;
Satish Raj; Sandeep Aggarwal
8:00 - 6:00
Prophylactic implantable
cardioverter defibrillator (ICD) therapy reduces mortality in patients with
LV dysfunction post-MI. However, widespread ICD use is limited by cost. Identifying
post-MI patients most & least likely to benefit from an ICD is important
for maximizing cost-effectiveness. Assessment of beat-to-beat changes in
cardiac repolarization (T-wave alternans; TWA) is a non-invasive technique
that may be useful in determining the risk of serious arrhythmias post-MI. Test
results are characterized as positive (significant TWA at heart rate (HR)
<110 bpm), negative (no TWA at this HR), or indeterminate. Prior studies
indicate that TWA positivity early (<1 month) post-MI does not predict the
development of serious arrhythmias, while positivity late (6-12 months)
post-MI does. The optimal timing of TWA evaluation is unclear, but is vital
for accurate risk assessment. The aim of this analysis was to describe
temporal patterns of TWA in patients with LV dysfunction post-MI. Results.
The average age of the 60 patients was 58 years, 84% were male, 64% had
suffered an anterior MI & the mean baseline LV ejection fraction was 0.38
(0.09). Appropriate medical therapy (94% ASA, 87% ACE inhibitor, 87%
beta-blocker, 74% statin) was used. Few (3%)patients received amiodarone. TWA
treadmill assessments were performed serially (4, 8, & 16 weeks) post-MI
using commercial equipment (Cambridge Heart). Most (98%) patients had at
least 2 of the 3 assessments. At week 4, 44% of the patients were TWA
positive, 47% negative & 9% indeterminate. At week 8, 71% of patients
were persistently TWA positive, negative or indeterminate. Most remaining
patients changed from TWA negative to positive (14%) or from positive to
negative (12%). At week 16, 78% of patients were persistently TWA positive,
negative or indeterminate vs week 8. Remaining patients largely changed from
negative to positive (10%) or from positive to negative (5%). Conclusion.
Significant individual variation in TWA results are observed over the initial
16 weeks post-MI. Future studies are needed to determine the optimum timing
of TWA assessment in this population & the prognostic significance of
temporal changes in TWA. |