The influence of beta-adrenergic agonists and antagonists on T-wave alternans in patients with and without ventricular tachyarrhythmia.

BACKGROUND

T-wave alternans (TWA) is an important noninvasive measurement of ventricular tachyarrhythmia (VT) and is known to be influenced by the sympathetic nervous system. We examined the correlation between TWA measurement and the sympathetic nervous system in patients with and without VT.

METHODS AND RESULTS

Thirty-five patients (28 men, 7 women; mean age, 59 +/- 15 years) with tachyarrhythmia were assigned to two groups: VT group (n = 15) and supraventricular tachyarrhythmia (SVT) group (n = 20). Alternans voltage in lead vector magnitude (eVM) was measured during atrial pacing (90, 110 beats/min (bpm)). After eVM was measured at baseline, propranolol was administered, and eVM was measured again. In a subset of 18 patients (10 with VT and 8 with SVT), isoproterenol was administered prior to propranolol infusion. After propranolol infusion, eVM of both the VT and the SVT groups decreased significantly compared to baseline. The changes in absolute value of eVM at 110 bpm after propranolol infusion were greater in the VT group than in the SVT group (-1.3 +/- 0.8 microV vs -0.5 +/- 0.8 microV, P < 0.05). The eVM values of both the VT and the SVT groups increased after administration of isoproterenol compared to the baseline value. The changes in absolute value and percentile of eVM after isoproterenol infusion were smaller in the VT group than in the SVT group (2.0 +/- 1.8 microV vs 3.9 +/- 3.5 microV, P < 0.05; 21 +/- 18% vs 48 +/- 36%, P < 0.05).

CONCLUSIONS

The sympathetic nervous system has an influence over microvolt-level TWA. Administration of a beta-adrenergic antagonist caused a significant decrease in TWA, particularly in the VT group. This may partially explain the mechanism by which adrenergic antagonists inhibit VTs.