The effect of body position on P-wave axis

Changes in body position are known to change the electrical axis of the heart, resulting in changes in QRS amplitude, ST segment shifts, and T-wave inversions. We investigated the effect of body position changes on the frontal plane P-wave axis of ten healthy volunteers. Subjects were monitored using three accelerometers recorded with two channels of ECG. Ten subjects followed a protocol of standing, sitting, walking, lying supine, and lying on the right and left sides for five minutes each. Median P-wave and QRS vectors in the frontal plane were computed. With standing, sitting, right and left positions, P axis had mean shifts (10 +- 11 deg, 7 +- 12 deg, 2 +- 11 deg), and 12 +- 6 deg respectively when compared to the supine position. When compared to QRS shifts, P-wave shifts were larger with more variability and poorly correlated with QRS axis shifts.