Pseudo-cross-stimulation due to first degree AV block.

During routine interrogation of a dual chamber pacemaker, atrial pacing stimulus outputs were found to coincide with surface electrogram QRS complexes raising concern for cross-stimulation. Scrutiny of the native rhythm, however, confirmed this to be "pseudo-cross-stimulation" where marked first degree AV block resulted in alignment of atrial stimulus outputs with preceding QRS complexes. Although cross-stimulation is rare, familiarity with cross-stimulation and pseudo-cross-stimulation is important because its recognition will avoid erroneous diagnoses of lead dislodgment or device malfunction.