THE UPPER LINK OF HUMAN COMMON ATRIAL-FLUTTER CIRCUIT - DEFINITION BYMULTIPLE ENDOCARDIAL RECORDINGS DURING ENTRAINMENT

Common atrial flutter is due to a macroreentry circuit in the right at rium, but the cranial path of the circuit has not been defined. The ob jectives of this article are to determine the cranial fuming point of flutter activation in relation to a hypothetic obstacle, the superior vena cava opening, by examining the changes in activation sequence pro duced by entrainment from different points. In 13 cases of common atri al flutter with typical counter-clockwise right atrial circuits confir med by endocardial mapping the atrium was paced from the high posterio r and mid-septal walls. Entrainment was confirmed by simultaneous reco rdings of 6-7 right atrial electrograms. Changes in sequence of electr ograms from high septum and high anterolateral walls was sought. Elect rogram sequence and morphology did not change with entrainment at the posterior wall with respect to the basal flutter or mid-septal wall en trainment. Pacing ''below'' the superior vena cava did not advance the anterior wall electrogram in relation to the septal electrogram. Thes e findings suppport tile concept that common flutter activation turned around (cranial and anterior to) the superior vena cava opening, and not around the free end of a line of block below the superior vena cav a in the posterior wall. Common atrial flutter activation rotates cran ial (and anterior) to the superior vena cava opening through the ''rig ht atrial roof.'' The line of functional block should span from inferi or to superior vena cava openings.