The relation of respiratory changes in the horizontal QRS and T-wave axes to movement of the thoracic electrodes.

Summary Changes in the horizontal QRS and T-wave axes with respiration have been observed by a number of authors. Similar changes were found in this study with the 12-lead ECG. However, the changes in the electrical axes were primarily a function of respiratory displacement of the precordial electrodes. Prevention of this displacement essentially eliminated the shift of the horizontal axes. Previously described horizontal QRS and T-wave axis shifts of several vectorcardiographic leads were re-analyzed relative to the electrode movement found in this study. These changes also were in agreement with the electrode movement predicted from inspiration. The electrode movement attendant to respiration will distort the vector analysis of the heart's electrical potentials. Respiratory displacement would have its greatest effect upon electrical axes recorded during work, exercise stress tests, or in ECG's purposely recorded during deep inspiration.