M Masselli

Atrial and Ventricular Tachycardias : Invasive Validation and Reproducibility of Magnetocardiographic Imaging

Magnetic localization of the site of onset of cardiac arrhythmias both of atrial and ventricular origin was first reported in 1986 (Fenici et al, 1987–89). However the accuracy of such localization procedures had not been validated so far. In this paper the reproducibility of such measurements is reported in several patients. Moreover the validation of magnetic localisation of ventricular tachycardia with conventional invasive endocardial mapping is described in one patient with previous myocardial infarction (MI).

Magnetocardiographic localization of a pacing catheter

Magnetocardiographic mapping during cardiac endocardia1 pacing was initially attempted by us, in patients undergoing invasive electrophysiological study for clinical reasons, in order to ascertain the reliability of the biomagnetic method in localizing a dipolar source placed in the human heart (Fenici et a1 1985,1986a,b,c). Subsequently similar results have been reported, with measurements carried out in two patients with permanently implanted pacemakers (Schmitz 1988) and in animals (Costa Monteiro et a1 1987). Here we report present results of an ongoing systematic research, carried out in our catheterization laboratory to quantify the accuracy of MCG localization of a catheter pacing different sites of the heart.

Magnetocardiographic localization of Kent bundles

First MCG recording in one patient with WPW was reported by Erne’ and Fenici (1984). Since then several preliminary measurements have been published (Fenici et al 1985–88; Katila et al 1988; Novak el al 1988; Oeff et al 1989), demonstrating the accuracy of MCG to localize Kent type accessory pathways. Here we report present results of our ongoing perspective study carried out to interprete the MCG patterns and to compare the respective localization power of electrocardiographic and magnetocardiographic criteria.

Clinical value of magnetocardiography

Magnetocardiography, that is to say the recording of the magnetic field generated by the electrical activity of the heart, was born in 1963 when Baule and McFee, using an induction coil, measured for the first time magnetic signals produced by a human heart [2]. Since then, the evolution from a pioneering experimental observation to the present state of art has passed through fundamental technological progress. First, in 1970, the introduction of superconducting instrumentation in the MIT shielded room demonstrated that magnetocardiograms of quality comparable with that of standard electrocardiograms could be recorded [6, 8, 36]. The next important step was the adoption of gradiometric detection coils which allowed MCG recording in unshielded laboratories [1, 3, 33,44, 47] and opened the way to pioneering clinical measurements [4, 16, 18]. During the same years MCG were also recorded without a superconducting instrumentation [9]. Since the beginning the question arose whether or not magnetic measurements could increase the diagnostic capability of cardiologists in respect to more conventional methods. Several different approaches were used to quantify the information [5, 8, 33, 39] and, although some authors still favour analysis of MCG signal in the time domain both at standard [7, 28, 49] as well as at high resolution [38] isofield contour maps are nowadays preferred to give images of the magnetic field distribution during depolarization and repolarization [10, 11, 13, 21, 22, 27, 29].