Normal variations in multiple precordial leads

1. 1. Wilson precordial leads have been correlated with autopsy findings in a group of 1,000 cases. In this communication, an analysis is presented of the precordial electrocardiograms of fifty-two patients whose hearts were considered normal by gross and microscopic examination. 2. 2. The P wave was consistently upright in Leads V 4, V 5, and V 6 and varied from erect to diphasic in Leads V 1, V 2, and V 3, depending upon the position of the electrode in reference to the right atrium. 3. 3. The total QRS interval and the duration of each component phase were determined in Leads V 1, V 2, V 5, and V 6 with aid of a Cambridge measuring device. The average QRS interval was 0.078 second and the upper limit in this series was 0.098 second. There was a trend toward slight lengthening of QRS duration with increasing cardiac weight. 4. 4. A QRS complex was found in both Leads V 1 and V 2 in two cases, but was not present in leads further to the left. An initial Q with succeeding R was not found in leads over the right ventricle, but was present in at least one lead over the left ventricle in approximately two-thirds of the cases. This Q wave was brief in duration, reaching its nadir within 0.02 second, and was small in magnitude, amounting to less than 25 per cent of the amplitude of the succeeding R wave. 5. 5. The interval elapsing from the onset of the R wave to its peak was taken as an index of the time required for the impulse to pass through the segment of ventricular wall beneath the exploring electrode. The time interval from onset to peak of R was invariably minimal in Lead V 1 and increased progressively in leads further to the left to reach a maximum in Leads V 5 or V 6. The significantly longer duration of the R wave in leads over the left than in leads over the right ventricle was in keeping with the normal difference in thickness of their respective walls. There was a trend toward a slightly greater duration of the R wave in Lead V 6 with increasing ventricular weight. As the electrode was moved from positions over the right to positions over the left ventricle, a progressive increase in the amplitude of the R wave and a reciprocal decrease in the S wave was found in every case. Low voltage R waves that were less than 7 mm. in height in all six precordial leads were found in four normal subjects in this series. Normal variations in the position of the transitional zone and form of QRS complexes recorded in this zone are illustrated and discussed. 6.