Failure in the rate adaptation of the atrial refractory period: its relationship to vulnerability.

We evaluated the relationship of rate-dependent changes in atrial refractoriness to atrial vulnerability in 39 patients. Vulnerability was considered present when sustained atrial tachyarrhythmias, lasting longer than 1 minute, could be provoked with one to three extra stimuli. Adaptation of atrial refractory period duration to rate was defined as: normal: steep rate reduction with a linear correlation slope value of 0.08 or more; non-adaptation: absence of rate reduction, the slope value being 0 to 0.01; poor adaptation: slight reduction with rate, the slope having values of 0.02 to 0.07. Increased vulnerability was demonstrable in 16 of 17 patients with non-adaptation of the effective refractory period (ERP), and in 10 of 10 with a similar defect of the functional refractory period (FRP); in the intermediate category (poor adaptation) the results for ERP and FRP were 7/11 and 5/6. By way of contrast when both measurements showed normal adaptation, vulnerability was elicited in 2/9 patients. The significance between these groups showed P less than 0.005. Of 17 patients with atrial arrhythmia by Holter, 14 showed poor or non-adaptation of the ERP. It is suggested that poor or absent rate adaptation of the atrial refractory period, and a propensity to atrial fibrillation or flutter, constitute a clinical entity not previously described.