Correspondence to: James J. Purcell, MD, 31 Woodland St, Hartford, CT 06105
To the Editor:
Although it has been many years since the article by Drs. Wanchun and Zhnorui1 appeared in CHEST, I feel one of their conclusions—ie, that the narrow P waves (NPs) such as P5 and P6 of strip 2B; P2, P3, and P10 of strip 2C (Fig 1
); and P5 and P10 of strip V1 (Fig 2
) are due to the fact that during sinus rhythm (SR) the left atrium did not depolarize—is incorrect and should be challenged for two reasons. Both reasons show that the NP focus is not the sinoatrial node (SAN), as the authors contend, but rather a different focus.
The first reason is that the rate of the NPs, which is nearly constant, is definitely faster than the rate of the wide P waves (WPs) [ie, those SAN P waves with a block or delay in Bachmann bundle (BB)], as can be seen from the fact that the P5–P6 interval of strip 2B and the P2–P3 interval strip of 2C is less than the P5–P7 or P7–P9 intervals of strip 2C.
The second reason is that the NPs occur only after a retrograde P wave fails to appear immediately after a junctional beat and not with an intermittent randomness as implied by the authors. This indicates that the NP focus lacks entrance block protection from the retrograde P waves, whereas the SAN has entrance block protection. The latter can be seen by the fact that, in strip 2C, the length of the WP SAN cycles ended by P7 and P9 are the same length, despite the fact that the times from their immediately preceding retrograde P waves are different.
As the NP focus is not the SAN, the possibility is also ruled out that the NPs are the result of SR with a complete recovery in BB(2) with almost simultaneous activation of both atria.
Because there was a retrograde block in the SAN junction of the interpolated retrograde P waves, the retrograde limb of a SAN reentry in the SAN junction probably would also have been blocked. Therefore, it’s highly unlikely the NPs occur as a result of SAN reentry with a failure to depolarize the left atrium.
However, the NPs may represent right atrial depolarizations in left atrial P waves originating near the left atrial termination of BB (Fig 82–) where the left atrial part of the P wave is not discernible.3
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