Cellular mechanism and arrhythmogenic potential of T-wave alternans in the Brugada syndrome.
BACKGROUND
T-wave alternans (TWA) is characterized by beat to beat alteration in the amplitude, polarity and/or morphology of the electrocardiographic T wave. TWA has been reported in patients with the Brugada syndrome (BS) and is thought to be associated with an increased risk for development of VT/VF. The cellular mechanisms involved are not well-defined and are the subject of this investigation.


METHODS
In an experimental model of BS composed of an arterially perfused canine right ventricular wedge preparation pretreated with verapamil (1-7 microM), an agent with sodium and calcium channel blocking activity, we simultaneously recorded transmembrane action potentials from two epicardial and one endocardial site, together with a pseudo-ECG. At select frequencies, verapamil induced alternans of both the T-wave amplitude and QT interval. The alternans resulted from either loss of the epicardial action potential dome on alternate beats or concealed phase 2 reentry within the epicardium on alternate beats. Loss of the epicardial action potential dome significantly increased transmural dispersion of repolarization (TDR) when compared with control (18.0 +/- 7.8 ms vs. 82.1 +/- 16.8 ms, P < 0.001, n = 8). During alternans, TDR was greater in beats displaying a more negative T wave (55.1 +/- 45.2 ms vs. 89.8 +/- 39.3 ms, P < 0.001, n = 22 data points from 8 preparations).


CONCLUSIONS
Our data indicate that TWA in an experimental model of the Brugada syndrome is due to alternating loss of the epicardial AP dome and/or concealed phase 2 reentry, both serving to increase TDR and create the substrate for the development VT/VF.
Fish
Jeffrey M
JM
Masonic Medical Research Laboratory, Utica, New York 13501-1787, USA. fish@mmrl.edu
Antzelevitch
Charles
C
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000503:physiopathology*; D018780:Body Surface Potential Mapping; D053840:Brugada Syndrome / Q000175:diagnosis / Q000503:physiopathology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004285:Dogs; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D032383:Myocytes, Cardiac