Atrial Fibrillation: Disease of the? Left Atrial Chamber Only

Objectives: Atrial fibrillation (AF) is associated with reduced quality of life, higher morbidity, higher mortality and is frequently associated with heart failure. However, little is known about the impact of AF on left and right atrial contractility, especially on atrial myofilament function. To validate the impact of chronic AF on atrial contractility we evaluate calcium induced force myofilament contractility of left and right atrial skinned fibers in atrial tissue obtained during elective on pump CABG.

Methods: The study was approved by the local ethical committee. After written informed consent 120 patients were included, right (RAA) and left auricle (LAA) tissue was collected during CABG and was prepared for skinned fiber measurements. Patients were divided into two groups: Group SR: 96 patients with preoperative sinus rhythm and Group AF: 24 patients with preoperative AF. Skinned fibers were exposed to increasing calcium concentrations (physiological range: pCa 5.0–pCa 5.2) and force values (mN) recorded. Demographic and echocardiographic data were logged.

Results: There were no significant differences in demographic data. We observed significant reduced force values in LAA and RAA fibers in AF patients at physiological pCa steps (p < 0.05). In general RAA force values were reduced compared with LAA force values. Differences in force values between RAA and LAA were significantly smaller in AF patients. AF patients revealed larger LA diameter (6.2 ± 1.5 vs. 5.2 ± 1.1 cm, p 0.03), higher LA area (25 ± 4.5 vs. 10± 3.1 cm², p 0.01), LA volume (81 ± 15 vs. 54 ± 3 ml, p 0.01), RA area (19 ± 3.2 vs. 14 ± 1.7 cm², p 0.04). RV and LV dimensions and LVEF were comparable ([Table 1]).

Table 1 Force values of LAA and RAA with and without AF

	Force value (mN) pCa 4.5	Force value (mN) pCa 5.0	Force value (mN) pCa 5.2
LAA Group SR	1.11 ± 0.3 mN	0.86 ± 0.3 mN	0.71 ± 0.09 mN
LAA Group AF	0.81 ± 0.1 mN	0.70 ± 0.1 mN	0.60 ± 1.1 mN
RAA Group SR	0.76 ± 0.07 mN	0.67 ± 0.07 mN	0.60 ± 0.05 mN
RAA Group AF	0.59 ± 0.09 mN	0.51 ± 0.09 mN	0.49 ± 0.03 mN

Conclusion: These preliminary results of this study show that myofilament function is compromised in both atria in AF patients. Furthermore, AF had a significantly higher impact on left atrial compared with right atrial contractility. These data show that the left atrium is more affected by AF what might contribute to earlier deterioration of left ventricular function and subsequent heart failure in AF.