Abstract 716: Physiologic Relationship Between Left Atrial Size and Function: A Possible Mechanistic Link Between Atrial Volume and Stroke
Introduction: Atrial fibrillation (AF) is associated with a significant increase in stroke risk. Left atrial (LAV) is a powerful predictor of AF, and of stroke even in the absence of AF. Yet, the mechanism underlying the relationship of atrial volume and stroke remains poorly understood.
Methods: Prospectively, outpatients visiting the medical clinics at the Mayo were invited to participate in this study of subclinical risk factors for AF, if they were of age ≥65 years, and had no history or evidence of AF, stroke, valvular and congenital heart disease, or pacemaker implantation. Comprehensive echocardiogram was performed. LA volumetrics for assessment of size and function were measured. LAV was measured using biplane area-length method. Maximal LAV was plotted against active LA emptying volume, which represented the stroke volume associated with atrial contraction (difference between pre-A LAV and minimal LAV).
Results: Of 577 persons (mean age 74±6 years), 65 (11%) developed new AF over a mean follow up of 5±2 years. LA active emptying volume increased with larger maximal LAV only up to a certain level, after which active emptying volume started to plateau and even decreased. In this study, the plateau and decrease occurred when maximal LAV reached ~110 mL (or 55 mL/m2 when indexed to body surface area).
Conclusion: Active LA emptying volume, an index of LA contractile function, appeared to plateau and decrease beyond a certain level of LA stretch. This reduction of mechanical atrial function may lead to stasis and increase in thrombogenicity, providing a potential explanation for the observations of LA size being a robust predictor of AF, and of stroke even in the absence of AF.