Stress testing in coronary artery disease by Magnetic Field Imaging: a 3D current distribution model.

OBJECTIVE: Magnetic field imaging (MFI) combines depolarization and repolarization registration of the cardiac electromagnetic field with a 3D current distribution model. An interesting application for MFI is the possibility to detect myocardial ischemia under stress. METHODS: Using a new reconstruction technique, it is possible to generate a pseudo-current distribution on the epicardial surface: the comparison of the time evolution of such current distributions at rest and under stress shows difference in coronary artery disease (CAD). The model works with a realistic epicardial surface generate on the basis of computerised tomography or magnetic resonance tomography data or with a standardized ellipsoidal model. To take into account the vectorial character of the epicardial current distribution, the current flow in the epicardial surface element is represented in the graphic display by a cone. Thus indicating the direction of current flow the height of the cone represents the current intensity. RESULTS: As an example of the method, data of pharmacological stress MFI on a CAD patient will be presented. The newly developed algorithm operates in different segments of the electromagnetic heart beat. The indicated myocardial area strongly correlated to invasive coronary angiography results. In such a situation the advantage provided by the "friendly" ellipsoidal surface on the numerical solution of the inverse problem seems to overcome the advantage of a realistic heart model. CONCLUSION: We conclude MFI is a promising procedure for a non-invasive stress testing as well as screening method as for localization of myocardial ischemia.

Musicians versus nonmusicians. A neurophysiological approach.

The ability to perceive sounds and correctly categorize them within a scale is the result of the interaction between inherited capabilities and acquired rules. If a subject listens to a melody, occasional and unexpected endings of the melody typically evoke characteristic auditory evoked responses in the latency range of 300-400 ms (P300). Also, earlier stages of auditory information processing have been exhaustively investigated by means of mismatch negativity (MMN), a deflection that occurs in the auditory evoked response at a latency of about 200 ms, whenever a deviance is randomly inserted in a series of otherwise equal stimuli. Conceivably, perceptual deviations could also be detected against expectancies that are based on abstract rules; introspective experience suggests that such deviations may also elicit fast intuitive responses that typically initiate processes of analytical reasoning for confirmation. In music, the physical features of the stimulus are, in fact, always changing, because the melodic contour consists of a series of notes with different pitch characteristics. In such a condition, a typical mismatch negativity would not be evoked on the basis of physical deviance, but rather of criteria involving the musical contour of the stimulus. In this study, 20 healthy subjects (10 nonmusicians and 10 musicians) underwent auditory stimulation (tone, chord, chord sequence, Mozart and Bach melodies) and both electrical and magnetic recordings. Clear N1 was recorded for all paradigms, in all subjects; MMN and P300 were also recorded, and their amplitudes and latencies were significantly correlated with the musicality score and with the paradigm's difficulty.