Electrophysiologic characteristics of the sinus venosa in patients with typical atrial flutter

BACKGROUND: The sinus venosa is a posterior barrier of typical atrial flutter. However, its electrophysiology has not been studied. METHODS AND RESULTS: The study population included 20 patients with typical atrial flutter (Group 1) and 20 patients with paroxysmal supraventricular tachycardia (Group 2). The noncontact mapping system was used to evaluate the electrophysiology of the sinus venosa (SV) during coronary sinus (CS) and low right atrial (LRA) pacing and atrial activation during typical atrial flutter. The results showed 12 of Group 1 patients (60%) had two lines of block, one in the CT and the other in the SV. The virtual electrograms in the CT and SV showed double potentials. Eight patients (40%) had only one line of block in the CT. During atrial pacing at the cycle length of 500 ms, nine of Group 1 patients had a line of block on the SV. None of the Group 2 patients had a line of block. During atrial pacing at the CL of 300 ms, 12 of Group 1 patients had a line of block on the SV. Eight of Group 1 patients had transverse conduction through the SV during atrial pacing. None of the Group 2 had a line of block. CONCLUSIONS: This study showed that the SV formed the posterior line of block in 60% of the patients with typical atrial flutter. Fixed conduction block and rate-dependent conduction block in the SV may be involved in the pathogenesis of typical AFL.