Auricular Premature Systoles: The Duration of the Electrical Systole

Abstract

In a recent electrocardiographic investigation (Berliner and Lewithin, 1945) the aberration of the ventricular complex of auricular premature systoles (APS)* was studied. Variations in amplitude, duration, direction, and configuration were found and described in detail. In the course of that investigation, a new feature of the APS, shortening of the electrical systole (Q-T interval), was discovered. This subject has since been studied by careful measurements which are reported in the present paper. MATERIAL AND METHODWe used 100 electrocardiograms of different patients in this study, selected from the records of over 250 patients exhibiting APS. The selection was made on the basis of technical qualities of the tracings. We chose only clear records in which the exact end-points of the T waves were easily discernible. Tracings blurred by muscle tremor or technical defects were eliminated; as were such perfect records in which low amplitude of the T waves made accurate measurement of the Q-T interval impossible; and also all those records in which the APS were found to occur at the beginning of a tracing or at its very end (with the exception of Fig. 2A). Records with inverted T waves were purposely included.Of the four leads available in practically all cases, we selected that lead in which the endpoints of the T waves were most distinct, and analyzed one APS of that lead. The degree of prematurity of this APS and the degree of its aberration were determined first, and for this purpose the criteria established in the previous study were again used. Measurements were then made on five successive heart beats, the two beats preceding the APS, the APS itself, and the two beats following it. All measurements were made with the aid of a magnifying glass.The duration of QRS and RS-T t was measured in each of the five beats. The Q-T intervals were then obtained by adding up the values for QRS and RS-T. In the normal beat just preceding the APS, however, RS-T and Q-T could usually not be measured because the P wave of the APS was superimposed on its T wave. That was the reason why the beat preceding it was also mheasured and was chosen as the normal for purposes of comparison. QRS, RS-T, and Q-T of the APS were compared with the respective intervals of the -n6rmal beat and the post-extrasystolic beat. Examples are given in the legend to Fig. 1. RESULTSQRS duration and Q-T interval. In 47 of our 100 APS, the duration of QRS did not differ from that of the normal beats or the difference was too minute for measurement. In 23, QRS duration was shortened; this shortening never exceeded 0-02 second. In 30 the QRS complexes were prolonged. The prolongation was marked (0'02 second or more) in 15 of these. Marked prolongation was usually associated with other features of aberration, viz. * APS will be used as an abbreviation for auricular premature systole(s) throughout this paper. t By RS-T interval we mean the interval beginning at the RS-Tjunction and ending at the end of the T wave.