Myocardial connections between left atrial myocardium and coronary sinus musculature in man

Introduction: Anatomic studies have shown that muscle morphologically ident ical to that of the atrial myocardium consistently surrounds the coronary s inus (CS). The CS musculature is connected to the left atrial (LA) myocardi um in a variable fashion, with fewer connections in its distal portion. The aim of this study was to document the presence of connections between the LA myocardium and the CS musculature, using pacing maneuvers in man, and to study their potential association with natural atrial arrhythmia occurrenc e. Methods and Results: Thirty patients (19 men; mean age 50.5 years) underwen t electrophysiologic study, during which a decapolar catheter with 2-mm int erelectrode spacing every 10 mm was inserted into the CS, with the proximal electrode pair positioned at the ostium. Associated atrial arrhythmias wer e paroxysmal atrial fibrillation in 5, typical atrial flutter in 13, LA flu tter in 1, and other in 11. Baseline S1 and a single extrastimulus were del ivered during distal and proximal CS pacing, while recordings were obtained from the four remaining bipoles. During distal CS pacing, double potential s with increasing interpotential interval from proximal to distal CS as a f unction of extrastimulus prematurity were detected in nine patients, sugges ting block in a discrete local pathway distally connecting the CS to the LA and leading to reversion of low LA activation. Local delay in this pathway without complete CS-LA block resulting in LA activation fusion was observe d in eight patients. A single nonfractionated potential at the distal CS, e ven at the shortest attainable S1-S2 coupling interval, which was interpret ed as no block within distal CS-LA connection(s), was observed in the outer 13 patients. History of atrial fibrillation or atypical atrial flutter was found in 8 of 9 patients with block at the distal CS-LA connection but in only 3 of 13 patients with no CS-LA connection block (P=0.004). Conclusion: The ability to dissociate the LA from the distal CS suggests th e presence of discrete connections between these structures in man. This ob servation appears to be associated with the clinical occurrence of atrial a rrhythmias.