Double atrial tachycardia with functional atrial dissociation.

A 57-year-old man with hypertensive and coronary heart disease and bradycardia-tachycardia syndrome suffered from paroxysmal palpitations, during which ECG showed a low atrial tachycardia at a rate of 150-200 beats/min with Wenckebach A-V block. During electrophysiological study an episode of atrial tachycardia appeared, characterized by: - atrial potentials in the high atrial electrocardiogram with regular cycle length (500-530 msec); - atrial potentials in the His bundle electrocardiogram with cycle length (570-580 msec), interrupted by premature atrial beats with coupling interval of 420-480 msec and with an atriogram of identical morphology. A-V conduction showed Wenckebach A-V block. After the cycles of 570-580 msec the low atrial potentials were simultaneous or preceded or followed the high atrial potentials by 10-20 msec. After the cycles of 420-480 msec the low atrial potentials preceded the high ones by 40-70 msec. Then, high atrial tachycardia abruptly stopped and the low atrial tachycardia only persisted with the same cycle length (570-580 msec); the high atrium was captured by the low atrial impulses with a low atrium - high atrium interval of 70 msec. These findings suggest that during the first part of tachycardia a conduction neither from high to low atrium, nor from low to high atrium can be possible. It is therefore a particular case of double atrial tachycardia - to our knowledge never before described in literature - sustained a few seconds because of functional atrial dissociation, induced by refractoriness related to the impulses delivered by the two tachycardia foci. The double atrial tachycardia was not diagnosed in the surface ECG leads. The two foci both appear to be localized at atrial level. The electrophysiological mechanism and the differential diagnosis with tachycardias at different sites are discussed.