Lead field of ECG leads calculated by a computer thorax model-an application of reciprocity

The authors have applied the principle of reciprocity to a computer model of the thorax to calculate the properties of ECG-leads in the defection of myocardial sources. The method developed gives the sensitivity distribution, i.e. the lead field, of an ECG-lead in the whole area of the heart in one run of the modeling program. With the used finite difference element model with 78,571 nodes the sensitivity, i.e. lead vectors, of ECG-leads can be calculated at 2,968 locations. These lead vectors form an almost continuous lead field, which provides the sensitivity information in different sections of the heart. Also the sensitivity in endocardial and epicardial regions can be separately analyzed. Here the sensitivity properties of lead III are examined. The Brody effect was observed to increase the endocardial sensitivity. The endocardium is about 80% more sensitive than the epicardium. The left atrium section has the highest sensitivity as could be expected from the lead geometry this section being closest to the measuring electrode