Electrocardiographic characteristics of pacing from the right atrial appendage during atrioventricular sequential pacing.

In the interpretation of electrocardiograms recorded during atrioventricular sequential pacing, uncertainty frequently arises in the assessment for evidence of atrial capture. In the present study, electrocardiographic characterization of pacing from the right atrial appendage as a component of atrioventricular pacing was performed on tracings obtained from 16 patients with bipolar dual chamber pacing units, and from 18 patients with unipolar dual chamber pacing units in which large overshoot potentials occurred following the atrial pacing spike. Atrial complexes resulting from bipolar pacing of the right atrial appendage were found to be uniformly prolonged and of diminished amplitude compared to those in sinus rhythm; they were also noted to contain sequential inferoposterior and leftward-posterior component vectors. The exponential overshoot-decay complex associated with unipolar atrial pacing appeared as a vector directed along the axis from the pulse generator to the pacing lead; the degree to which this deflection interfered with identification of atrial capture in various leads was thus largely dependent on pulse generator location. It was concluded that careful systematic inspection of multiple electrocardiographic leads will generally permit the characteristic features of pacing the right atrial appendage to be recognized, thus facilitating correct interpretation of atrial capture during atrioventricular sequential pacing.