Left atrial myocardial extension onto pulmonary veins in humans: Anatomic observations relevant for atrial arrhythmias

Introduction: Electrophysiologic studies have shown that spontaneous initia tion of atrial fibrillation (AF) by ectopic beats may originate from within pulmonary veins. The extensions of left atrial myocardium are considered t o play a role, but there is little detailed anatomic information available, particularly in humans. Methods and Results: Thirty-nine human autopsy hearts were studied; 22 with AF and 17 without atrial arrhythmias. The muscle fiber arrangement of the left atrial wall and pulmonary veins was dissected. In 18 hearts, myocardia l sleeves were studied microscopically; in five hearts, three-dimensional r econstruction of the fiber arrangement in the myocardial sleeves was perfor med. Of 99 pulmonary veins examined, 96 contained a myocardial sleeve. The length of the sleeves was largest in the superior pulmonary veins (P < 0.01 ). There mere no statistically significant differences between uniform and nonuniform muscle fiber arrangements. Microscopic evaluation revealed myoca rdial sleeves positioned on the adventitial side of the pulmonary vein, sep arated from the muscular media by a fibrofatty tissue plane. The most dista l zone of the myocardial sleeves showed increasing fibrosis with encapsulat ion of small groups of myocardial cells and eventually with total disappear ance of atrophic cells within fibrous tissue. Node-like structures were not encountered. There was no relationship with presence or absence of AF. Conclusion: The observation that the peripheral zones of myocardial sleeves are associated with increasing connective tissue deposition between myocar dial muscle groups suggests a degenerative change that, from the histologic viewpoint, fits with progressive ischemia, These changes could provide a b asis for microreentry and, hence, for atrial arrhythmias.