Understanding the Pathophysiology of Atrial Fibrillation from Clinical Observations

Atrial fibrosis in heart surgery patients

In chronic atrial fibrillation, increased expression of angiotensinconverting enzyme (ACE) promotes upregulation of profibrotic proteins. Atrial fibrillation early after cardiac surgery (poAF) is common but unpredictable, and is regarded as a different entity. Therefore, the present study tested whether atrial expression of ACE, osteopontin (OPN), and collagen is elevated in patients with no history of AF but who develop poAF. Thus, 19 patients (66 +/- 9 years) with postoperative sinus rhythm (poSR) were compared to 14 patients (68 +/- 10) who experienced poAF. mRNA and protein expression were determined by RT-PCR and Western blotting. Picrosirius red was used to stain collagen. The medians for ACE, OPN, type I collagen (Col I), and type III collagen (Col III) mRNA and protein expression did not significantly differ between poSR and poAF (U-test). However, the Col III/I protein ratio was significantly lower in patients with poAF (2.62 vs. 1.09; poSR vs. poAF; p < 0.05). Our data suggest that the occurrence of poAF is not dependent on increased ACE and OPN expression, rendering the determination of preoperative OPN plasma levels inadequate to estimate the risk for the occurrence of poAF. Contrarily, a shift in atrial collagen expression levels in favor of Col I is linked to the occurrence of poAF.