EP tracings in sinus rhythm demonstrating the basic intervals

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Upper six tracings (white) show the surface electrocardiogram. The green channel shows right atrial tracings: HRAd: distal pair of high right atrial electrodes; HRAp: proximal pair of high right atrial electrodes. The yellow channel represents His bundle recordings: HISd: distal pair of His bundle electrodes; HISp: proximal pair of His bundle electrodes. CS12: distal pair of coronary sinus electrodes. STIM: channel marking pacing stimuli if present (not present in this recording). The interval between the red (earliest onset of P wave in surface electrocardiogram) and green (onset of atrial activity in the His bundle electrodes) vertical lines represents the PA interval, denoting the conduction time from the sinus node to the low right atrium where the His bundle electrode is situated. The interval from the vertical green line to the triphasic His bundle tracing (H) in the HISd tracing represents the AH interval. The interval between H and the ventricular activation (V) represents the HV interval. AH is prolonged in supra Hisean blocks and HV is prolonged in infra Hisean blocks. A split His with H-H prolongation will be seen in intra Hisean blocks. The complexes corresponding to the V seen in the surface electrocardiogram are the QRS complexes. The slow speed recordings in the right panel represents the continuous Holter recording of surface ECG during the EP study.