Magnetocardiographic QT dispersion during cardiovascular autonomic function tests

QT dispersion is considered to reflect nonhomogeneity of ventricular repola rization. The autonomic nervous system modulates QT interval duration, but the effect may not be spatially homogenous. Magnetocardiography (MCG) regis ters the weak magnetic fields generated by myocardial electric currents wit h high localizing accuracy. We studied the effects of rapid cardiovascular autonomic nervous adjustment on QT dispersion in MCG. Ten healthy male volu nteers were monitored during deep breathing, the Valsalva maneuver, sustain ed handgrip, hyperventilation, the cold presser test and mental stress. 67 MCG channels and 12 ECG leads were recorded simultaneously. A computer algo rithm was used for QT interval measurements. QT dispersion was defined as m aximum - minimum or standard deviation of the QT(peak) and QT(end) interval s. In MCG the QT(end) dispersion increased during deep inspiration compared with deep expiration (96 +/- 19 ms v 73 +/- 27 ms, p = 0.05). Magnetic QT dispersion tended to increase during the bradycardia phase of the Valsalva maneuver, but the change was obvious only for QT(end) (55 +/- 26 ms v 76 +/ - 29 ms, p < 0.05). Other tests had no significant effect on QT dispersion, not even the cold presser test, although it causes strong sympathetic acti vation. Magnetic and electric QT(peak) and QT(end) intervals correlated clo sely (r = 0.93 and 0.91), whereas the QT dispersion measures showed no corr elation. In conclusion, magnetic QT dispersion is not modified by rapid cha nges in autonomic tone, but maneuvers involving deep respiratory efforts an d changes in ventricular loading affect QT dispersion measurements.