T Wave Alternans (TWA) is a cardiac risk indicator which measures the functional cardioelectric instability substrate. Recognized as a powerful potential risk marker and despite its clinical interest, it is not commonly used in today practice. Traditional estimation of TWA has been made on the surface ECG, hence providing the researcher with an anatomically non-specific marker. We addressed the assessment of TWA in ECG Imaging (ECGI) recordings to characterize the test with regionalization and spatial specificity, hence identifying those cardiac regions with functional cardiac instability according to this marker.
ECGI potentials were obtained from 7 patients with Long QT syndrome by recording signals in the patient torso during about 60 seconds. Epicardium registers were estimated through inverse problem algorithms and the whole set of signals were analyzed by means of the Temporal Method to find the alternans amplitude and waveform.
TWA amplitudes were in general spatially scattered in the torso, whereas high amplitude regions trended to be spatially grouped in the epicardium. In addition, the M-mode representation of the TWA waveforms along sets of consecutively chosen points in the torso mesh yielded loosely structured spatio-temporal distribution of the TWA waveform, whereas in the epicardium they were structured both in time and space. Our results point out that TWA could be spatially grouped in the epicardial signals, and that ECGI could yield a clinically useful representation on TWA spatio-temporal distribution.