Effect of cardiac exposure by median sternotomy on atrial fibrillation cycle length

Epicardial mapping is a powerful tool that has enabled us to gain insight into the electrical phenomena perpetuating atrial fibrillation and has guided the design of surgical and catheter-based therapeutic strategies. However, epicardial data are acquired during abnormal physiological conditions; the patients are anaesthetized, their chests opened, dislocating the heart and exposing it to air of room temperature, and the autonomic tone is modulated due to the surgery. The effect of intra-operative conditions on atrial electrophysiological properties have not been investigated before. Thus in the present study we assessed the atrial cycle length, shown to be an index of atrial refractoriness, and the ventricular rate before and during open-heart surgery in 10 patients with chronic atrial fibrillation and an underlying heart disease.

Using a newly introduced and validated ECG method known as frequency analysis of fibrillatory ECG (FAF-ECG), the atrial cycle length and the ventricular rate were determined just before surgery. After anaesthesia and median sternotomy, epicardial mapping of the entire right atrial free wall was performed. The mean ventricular rate as well as the dominant atrial fibrillation cycle length consistently increased, the former from 71 to 92 beats x min(-1) (mean of all patients, P<0.05) and the latter from 156 to 172 ms (P<0.05).

Atrial fibrillation cycle length, an index of atrial refractoriness, is increased as an effect of anaesthesia and heart exposure during open-heart surgery in patients with chronic atrial fibrillation, implying that atrial activation might be altered, which must be considered when interpreting data from epicardial conduction analysis.