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Author
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Pawel
Ptaszynski, Thomas
Klingenheben, Stefan H. Hohnloser, J.W. Goethe University Frankfurt,
Frankfurt, Germany
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Background: Microvolt level T-wave alternans
(MTWA) is increasingly used for arrhythmia risk stratification in patients
prone to malignant ventricular tachyarrhythmias and sudden cardiac death.
Antiadrenergic therapy by means of beta blocker (BB) administration may
influence MTWA assessment using exercise testing, mainly because patients may
not achieve a sufficient increase in heart rate. However the effects of BB on
MTWA assessment have not been prospectively studied.
Methods. Consecutive patients scheduled for ICD implantation underwent
noninvasive MTWA assessment using bicycle exercise testing (spectral method;
CH2000, Cambridge Heart Inc) on and off BB treatment in random order.
Antiadrenergic therapy was withheld for at least 5 half lifes prior to the
test off BB. Results of MTWA tests were compared using Fisher’s exact test.
Separate analysis was performed in a subgroup of patients who were on chronic
amiodarone treatment.
Results: Sixty-six patients were included in the protocol. Of these, 17
were treated with amiodarone. Patients on BB had a resting heart rate of 71+10
bpm compared to 79+10 bpm of BB (p<0.05). The maximal exercise
heart rate averaged 102+13 bpm to 107+13 bpm of BB (p<0.05).
Whereas 13 pts (27%) tested MTWA positive on BB, the positivity rate was 47%
(23 pts) off the drug (p=0.05).The prevalence of an indeterminate test result
decreased from 41% to 24% (p=0.09). In the subgroup of patients with
amiodarone, no patient tested MTWA positive, irrespective of the status of BB
therapy. The proportion of indeterminate tests was 88% on and 82% off BB
therapy exclusively due to chronotropic incompetence during testing.
Conclusion: MTWA assessment is facilitated by withholding BB prior to
testing by reducing the prevalence of indeterminate tests as a consequence of
insufficient heart rate increase. Chronic amiodarone therapy results in
chronotropic incompetence in almost all patients which precludes
exercise-based MTWA assessment.
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