Effects of respiration on the vectorcardiogram obtained with the Frank lead system.

Vectorcardiograms were recorded with the Frank lead system using electrodes positioned at the level of the 5 th intercostal space with the subject in the supine position. Deep inspiration produced the following significant changes compared with deep expiration: (1) the maximum leftward forces of the P, QRS, and T vectors decreased, whereas the maximum anterior and posterior forces of the QRS and T vectors increased; (2) the maximum spatial QRS vector decreased in magnitude; (3) the maximum spatial P, QRS, and T vectors shifted vertically, posteriorly and vertically, and anteriorly, respectively; and (4) the spatial QRS-T angle increased remarkably. The spatial instantaneous QRS vectors were analyzed at 5 msec intervals in 35 of the 61 subjects. With inspiration, the 35- through 50-msec vectors shifted posteriorly with markedly reduced leftward forces and increased posterior forces. It was suggested that the respiration-related vectorcardiographic changes reflected cardiac anatomic positional change, distortion of lead-field potential by lung gases, and other mechanisms. Since the respiratory effect is potentially important for vectorcardiographic interpretation, vectorcardiograms should be recorded under identical respiratory status.