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.

Regular sinus rhythm at about 60 per minute with a wide QRS is noted. The PR interval is 200 msec. The initial Q waves in II, III and aVf suggests an old inferior wall myocardial infarction. The QRS is wide, lasting 160 msec. The slurred S waves in leads I, aVl, V5 and V6 as well as the slurred R waves in V1 suggest right bundle branch block (RBBB). The unusual features about this ECG are the association of RBBB with inferior wall infarction and the QRS width of 160 msec which is rather uncommon in RBBB, though it is more likely in (left bundle branch block) LBBB. RBBB is unlikely to be due to the inferior wall infarction as the coronary territory which supplies the inferior wall is less likely to cause RBBB. Inferior wall infarction is associated with supra Hisean blocks while infra Hisean blocks are the feature of anterior wall infarction. In supra Hisean blocks there is no QRS widening or bundle branch blocks. In inferior wall infarction, if AV block occurs, it is at the level of the AV node as the AV nodal artery arises from the dominant vessel which supplies the inferior wall – either the right coronary artery or the left circumflex coronary artery. Right bundle block in the setting of infarction occurs due to left anterior descending coronary artery involvement. In this case either there is an independant conduction disorder or there is associated involvement of left anterior descending coronary artery along with the right coronary artery / left circumflex lesion which would have caused the inferior wall infarction. This may also explain the relatively wider QRS for an RBBB.

The T wave inversions in inferior leads are part of the manifestations of inferior wall infarction. The ST segment depression and T wave inversion in anterior leads are due to RBBB. The QT interval is also prolonged at 480 msec, which is equal to the corrected QT interval (QTc) because the heart rate is 60 per minute. The wide QRS and QT interval places the person at risk of ventricular tachyarrhythmias. In fact this person presented with syncope, though the tachyarrhythmia was not documented.