Practically speaking, distinction between a junctional vs low atrial rhythm is largely academic, since clinical significance of these 2 entities is similar.( Figure reproduced from Grauer K: ECG-2014-ePub ). N OTE : Whether a negative P wave is seen before, after, or is hidden within the QRS is determined not only by location of origin of the AV nodal impulse, but by the relative speed of conduction back to the atria compared to down the ventricles. Clinically - Situation C is most common, whereas it is rare to see a P wave after the QRS ( situation D ). As a result - the P wave in lead II may be negative appearing either before ( Panel B ) or after ( Panel D ) the QRS - or - no P wave at all may be seen ( Panel C ). It then travels back ( retrograde ) to the atria, and down to the ventricles. N OTE : With junctional beats ( or junctional rhythm ) - the impulse originates from the AV Node. The impulse originates in the SA Node - travels through the atria - slows down a bit as it passes through the AV Node - and is then transmitted down through the conduction system to the ventricles. Panel A illustrates the normal forward conduction of sinus rhythm. įigure-3: Laddergram of the 3 possibilities for P wave appearance in lead II with junctional beats or junctional rhythm. B OTTOM L INE : The rhythm in Figure-1 is either Low Atrial or Junctional at a rate of ~100/minute. That said, I fully acknowledge my confusion about how to interpret P wave morphology in leads V1 and V2, as highlighted by the thin, vertical blue line in Figure-1 ( which I drew corresponding to what I perceived as the end of the P wave in simultaneously-obtained lead II ). P wave morphology in lead V1 is often helpful in further clarification of impulse origin.What can be said - is the large size of the negative P waves in the inferior leads suggests the impulse is arising from a considerable distance away (ie, from either low in the atria or from the AV node ).The ECG picture in Figure-1, in which inferior lead P waves are negative and P waves are positive in leads aVR and aVL ( BLUE arrows ) is consistent with either a Junctional or Low Atrial Rhythm. Suffice it to say that assessment of P wave morphology ( positive, negative, biphasic, or null deflection ) in multiple leads of the 12-lead tracing assists in location prediction. Precise localization of the site of an ectopic atrial impulse is beyond the scope of this ECG Blog, and rests in the domain of the cardiology electrophysiologist.
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