Principal Factor Waveforms of the Thoracic Qrs Complex.

• Concern has been expressed repeatedly in the electrocardiographic literature as to whether the three leads of a spatial vectorcardiogram contain more or less information than that found in the standard twelve-lead electrocardiogram." Frequently the adequacy of the report of the twelve-lead electrocardiogram has also been questioned and addition of one or more exploratory leads has been recommended." These questions are two aspects of the more fundamental problem: What is the minimum number of leads which can contain all of the electrocardiographic information available on the body surface? A theoretical approach to the answer would be to determine the minimum number of unique building blocks capable of synthesizing any waveform detectable on the body surface. For example, by means of principal factor analysis Scher et al. derived a minimum number of mathematically uncorrelated QRS waveforms found in an assortment of electrocardiographic leads varying from 8 to 32 in number. A practical answer would be to find those body sites especially sensitive to these elemental waveforms so that placement of leads would insure adequate acquisition of information. In the present study we have extended the use of factor analysis to between 150 and 180 exploratory leads systematically spaced over the thoracic surface. This was done in the hope both of deriving a clearer appreciation for the total scope of informa-