Influence of basic atrial rhythm on intraatrial conduction of extrastimuli

Atrial arrhythmias appear to be related to the genesis of intraatrial conduction delays by extrastimuli. To clarify the effects of the basic atrial cycle on intraatrial conduction of extrastimuli, atrial conduction delays and conduction delay zones were measured in 22 patients with and without atrial arrhythmias. Basic cycles were (A) sinus rhythm; (B) paced at the right atrial (RA) appendage with maximum cycle length possible; (C) paced at the RA appendage with cycle length of 600 ms; and (D) paced at the proximal coronary sinus at the same cycle length as B. Extrastimuli were always delivered at the RA appendage. Conduction delays and conduction delay zones were 5- to 7-fold longer when driving stimuli and extrastimuli were delivered through the same electrodes than when the basic cycle was sinus or driven at a distance from the extrastimuli (p less than 0.001). This effect must be considered when groups of patients or the results of interventions are compared.