Diaphragmatic origin of false atrial dissociation evidenced through intra-vascular recordings

In a patient suffering from respiratory insufficiency, an atrial dissociation pattern was found in the surface ECG recording, having the appearance of ectopic P waves, independent from sinus P waves and followed by microfibrillation waves of 450 ms duration. No electrical activity corresponding to the presumed ectopic P waves could be recorded from left and right atria. Conversely, such activity was recorded from the inferior vena cava (IVC) 1.5 cm below its junction with the right atrium, with a maximum amplitude; the occurrence and duration of these recordings appeared to be exactly synchronized with surface ectopic P waves/microfibrillation aspects and the inspiratory phase of respiration. Intravascular recording can be considered as a useful procedure to differentiate false and actual atrial dissociation.