RT Book, Section A1 Prystowsky, Eric N. A2 Prystowsky, Eric N. A2 Klein, George J. A2 Daubert, James P. SR Print(0) ID 1176522068 T1 Apparent Paradoxical Conduction T2 Cardiac Arrhythmias: Interpretation, Diagnosis, and Treatment, 2e YR 2020 FD 2020 PB McGraw Hill PP New York, NY SN 9781260118209 LK accesscardiology.mhmedical.com/content.aspx?aid=1176522068 RD 2023/12/07 AB Conduction of premature atrial complexes (PACs) is usually predictable in a patient with a relatively constant heart rate. A late (i.e., long atrial coupling interval) PAC will conduct to the ventricle and a relatively early (i.e., short atrial coupling interval) PAC often blocks in the atrioventricular (AV) conduction system. In some instances, however, apparent paradoxical conduction can occur in the AV conduction system. This happens when a late PAC conducts to the ventricle, an earlier PAC blocks, but—unexpectedly—a PAC with even a shorter coupling interval again conducts to the ventricle. Various electrophysiologic phenomena can explain these conduction patterns, but they are often very difficult to diagnose by surface electrocardiography only. Resumption of conduction may occur because of supernormal excitability and conduction, which is probably relatively rare, but more commonly can be explained by other mechanisms, especially the gap phenomenon. Specific issues related to the bundle branch conduction system are presented in detail in Chapter 3.