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Atrial and Ventricular Volume and Function In Atrial Fibrillation - A Magnetic Resonance Imaging Study

Susette Krohn Therkelsen 

Summary

Atrial fibrillation (AF) is the most common cardiac arrhythmia and the prevalence
increases in older age-groups. For persons above the age of 40 years the lifetime risk of developing AF is 25%. Cardiac dimensions and function have only been evaluated with Magnetic Resonance Imaging (MRI) in few studies in patients with AF, and never before and after cardioversion in patients with persistent AF.

Our aims were:
1) To evaluate the reproducibility of MRI in assessing atrial volumes and ejection fraction (EF) in healthy volunteers and atrial and ventricular volumes and EF in patients with AF.
2) To describe atrial and ventricular volume and EF evaluated with MRI as well as plasma atrial (ANP) and B-type natriuretic peptide (BNP) in patients with permanent AF and persistent AF, and evaluate the changes in persistent AF before and after cardioversion.
3) To evaluate the association between plasma ANP and BNP and cardiac volume and EF measured with MRI in patients with AF.
4) To evaluate if any of the measured variables were predictive of recurrent AF in persistent AF.

Nineteen healthy volunteers, 19 patients with permanent AF and 60 consecutive patients with persistent AF scheduled for elective cardioversion were examined. All patients with persistent AF had a baseline examination the day before cardioversion, and follow up examinations 1, 30 and 180 days after cardioversion, if still in sinus rhythm.
MRI is a highly reproducible method for measurement of atrial dimensions in healthy volunteers and atrial and ventricular dimensions in patients with atrial fibrillation.Patients with AF had significantly larger atrial volumes, higher levels of plasma ANP and BNP and lower atrial EF than healthy volunteers. Plasma levels of ANP and BNP, atrial volumes and EF and right ventricular volumes and EF were similar in patients with persistent and permanent AF. Patients with persistent AF had dilated left ventricles and lower EF compared to patients with permanent AF. All atrial and ventricular volumes, LV mass and plasma levels of ANP and BNP decreased significantly after cardioversion of patients with persistent AF and EF increased.
Right atrial volumes were normalised after 180 days of sinus rhythm; however, left atrial volume and plasma ANP and BNP were still significantly increased compared to healthy volunteers. The ventricular dilatation is decreasing following cardioversion,but far from normalised after 180 days of sinus rhythm. The ventricular dilatation in persistent AF is reduced by approximately 50 % after 180 days of sinus rhythm following cardioversion.Duration of AF and hypertension were the only variables predictive of recurrent AF following CV.Left and right atrial volumes in patients with AF were positively associated with plasma ANP and BNP, and left ventricular EF was negatively associated to plasma ANP. There were no associations to atrial or right ventricular function and ventricular volumes. ΔLA volume (Δ = value at baseline – value at 180 days) were predictive of Δplasma ANP and Δplasma BNP following CV. There were no associations between Δplasma ANP or delta ΔBNP and Δright atrial volumes, Δventricular volumes, Δatrial EF or Δventricular EF.

Cardioversion of patients with persistent AF seems to induce a substantial improvement of atrial and ventricular dimensions and systolic function in favour of sinus rhythm. The continuous increase of plasma ANP, plasma BNP, left atrial volumes and ventricular volume and the continuous decrease of EF even after 180 days of sinus rhythm might be suggestive of longstanding or even permanent changes. Atrial volume – especially LA volume seems to be an important determinant of plasma ANP and BNP in AF. This supports the hypothesis that BNP is mainly produced in the atria in AF, suggesting that increased plasma BNP in AF is due to other mechanisms than in heart failure.