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.

Atrial pacing with 2 :1 AV block

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Tracings from an electrophysiological study (EPS) with intracardiac and surface electrocardiograms showing 2:1 AV conduction during atrial pacing. The upper six channels in white colour are surface electrocadiograms (leads I, II, III, AVF, V1 and V6). The pacing spikes are sharp deflections of very short duration. The P waves and QRS complexes are marked in lead II. The width of P waves and QRS complexes are more than the usual because the recording speed is much higher for an EP study, usually at 100 or 200 mm/sec rather than the 25 mm/sec for usual ECG tracings. Higher recording speeds are used to delineate short intracardiac signal intervals well. Only half the paced P waves have an associated QRS complex while half do not have (blocked P). This is because the atrial pacing rate is above the Wenckebach threshold of the AV node. Please note that 2:1 AV block is the highest grade of Wenckebach type of block possible (2:1 conduction can also occur in Mobitz type II AV block).

The polarization artefact seen in HRAd (High Right Atrium, distal) channel. This suggests that the pacing stimulus is being delivered from this electrode pair. HRAp (HRA proximal) channel does not show this artefact, nor does any other channel. The polarisation artefact is a seen as a broader signal with an amplitude lesser than that of the pacing stimulus, in the channel from which the pacing stimulus is being delivered. This artifact helps us to find the site of pacing when an EP tracing is given.

HISd (distal His bundle electrode pair) shows a good triphasic His bundle potential (H) and ventricular signal which is of lower amplitude than in the CS12 (distal pair of coronary sinus electrodes). The CS12 channel in this case shows a small pacing signal and a high amplitude ventricular signal. The electrodes in the coronary sinus are usually numbered from distal proximal (CS12 to CS9-10 in case of decapolar electrode). The STIM channel just depicts the intervals at which the pacing stimuli are delivered, without recording any intra cardiac signals. There is also a marker at the level of the pacing stimulus.

The various intervals (PA, AH, HV, RR, PP etc) can be measured with online calipers. Some of the channels have been hidden in this image (CS34 – CS9-10) to prevent cluttering of screen. This helps the operator to concentrate on the tracing important for this particular study. In case of need, they can always be made available on the screen. It is possible to change the recording speed of the display in online as well as offline mode. This helps in evaluating the rhythm better.

Please note that the conducted P waves have a corresponding A wave, followed by H and V in the HISd channel, while the blocked P waves have only an A and no H or V. This indicates that the A is blocked above the His bundle, presumably at the AV node. The A wave in the HRAp channel precedes that in the HIS channels indicating supero-inferior conduction.

The intervals in the lowermost green bar is cumulative time interval from 0 to 2000 msec.