Cardiac Conduction
In order to objectively define cardiac conduction in a cohort, we identified 181 patients who had invasive electrophysiologic measure of the His-Purkinje system (i.e. H-V interval measurement in ms) as well as a surface EKG measuring QRS duration (in ms). Repolarization via the surface EKG was also measured (maximum QT interval in ms). HV was measured via standard electrophysiologic lab practices12. During electrophysiologic study, patients were classified as having dual atrioventricular (AV) node physiology or not having dual AV node physiology from the presence or absence ofdiscontinuous antegrade AV nodal conduction  in response to atrial programmed electrical premature stimulation using an abrupt increase in AV nodal conduction time of ≥50 ms in response to a decrement of 10 ms as the definition of dual AV nodal pathway physiology.