The effect of atrial rhythm on the thoracic impedance cardiogram.

We have observed that the thoracic impedance waveform is altered when there is a change in atrial rhythm. In order to investigate this, we selected for review impedance cardiograms of patients with various atrial rhythms. The study showed that the thoracic impedance waveform displays characteristic deflections that are specifically associated with different atrial rhythms and are analogous to those seen on the electrocardiogram. The finding that the waveform was sensitive even to the small atrial movements discernible during the rhythm of coarse atrial fibrillation was consistent with the possibility that blood flow within the vena cave-right atrial and/or the pulmonary venous-left atrial systems may be important in the genesis of the cardiac thoracic impedance waveform.