tag:blogger.com,1999:blog-549949223388475481.post5052072532530270720..comments2024-03-28T14:02:08.119-05:00Comments on Dr. Smith's ECG Blog: H/o MI and stents with brief angina has this ED ECG. And what is Fractional Flow Reserve?Unknownnoreply@blogger.comBlogger2125tag:blogger.com,1999:blog-549949223388475481.post-55766355522366103402020-02-02T14:54:09.964-06:002020-02-02T14:54:09.964-06:00THANKS for your comment Jerry. I respectfully am h...THANKS for your comment Jerry. I respectfully am happy to agree to DISAGREE with you on this one. I always use “area under the curve” when calculating axis in non-RBBB tracings. But with RBBB — there is terminal delay, as manifest by wide terminal S waves in lateral leads (especially in leads I and V6) — whereas I was taught that when looking for a hemiblock (in addition to RBBB) — we are looking for THAT portion of the QRS in lead I that occurs BEFORE that wide terminal S wave (ie, before the RBBB component … ) — and by the criteria I have always used, the straight part of the QRS is isoelectric, and not predominantly negative in lead I ==> therefore, not a LPHB in my opinion. <br /><br />Looking closer, I’d add 2 more points: i) With LPHB — activation of the LV begins through the intact LAH (left anterior hemifascicle). Since the LAH is oriented to the left and superiorly (relatively speaking) — a small initial upright deflection ( = an r wave) is initially inscribed in lead I, at the same time as a negative initial deflection ( = a q wave) is inscribed in lead III. Terminal forces with LPHB are oriented to the right and inferiorly (in the direction of the blocked LPH = left posterior hemifascicle) — thus, the QRS complex in lead III manifests a large positive deflection ( = a tall R wave). Because the terminal forces with LPHB are oriented to the right and inferiorly — a deep S wave should be produced in lead I BEFORE the terminal delay from the RBBB is seen.<br /><br />ii) If all that was used was “area under the curve” for the S in lead I — then one would diagnose MANY more LPHBs — because many patients with simple RBBB have very wide terminal S waves.<br /><br />THANKS again for your comment Jerry — I think it’s good to sometimes disagree on a few things — :)ECG Interpretationhttps://www.blogger.com/profile/02309020028961384995noreply@blogger.comtag:blogger.com,1999:blog-549949223388475481.post-76640825696952843972020-02-02T08:31:55.187-06:002020-02-02T08:31:55.187-06:00Thanks, Steve, for an excellent teaching case and ...Thanks, Steve, for an excellent teaching case and thanks, Ken, for your terrific insights.<br /><br />Ken... Steve appears to be leaning IN FAVOR OF a diagnosis of LPFB; however, he is obviously aware of your thoughts which lean AWAY FROM LPFB.<br /><br />Though I am no official impasse-breaker, I would have to agree a bit more with Steve, and here's why...<br /><br />I, too, immediately noted the parity of R wave height and S wave depth in Lead I. But using height and depth to determine net voltage is really just a "quick and dirty" method of assessing net voltage of a deflection. Granted, it's one that we all use - MYSELF INCLUDED - because it is fast and it is "usually" correct.<br /><br />However, when the situation arises - as in this Lead I - where there IS parity of height and depth between the R wave and the S wave, there is one more characteristic that needs to be assessed and that is the relative WIDTHS of the two deflections. What we are actually doing here is determining the MAGNITUDE of two different vectors (R vector and S vector) which are represented on the tracing as an R wave and an S wave. It is the MAGNITUDE that determines the net voltage and AMPLITUDE is just PART of that calculation. Granted, it IS a MAJOR part of the calculation and that is why it is the characteristic we most often use.<br /><br />Bear in mind that the "QRS complex" is NOT a single deflection representing depolarization. It is a "complex" of different deflections traveling in different directions DURING depolarization. As a matter of fact, though we call it a "QRS complex," it's official name is "QRS interval." So there are times that we must consider each deflection individually - and this is one of those times.<br /><br />While we commonly reduce this determination to the AMPLITUDE (height or depth) of the deflections, that is just, as I said earlier, a poor substitute for the actual magnitude. One doesn't need to be a whiz in integral calculus here to see that the S wave - though it has the same amplitude as the R wave - is visibly wider than the R wave. There is much more area under the curve (AUC), or in this case, area WITHIN the curve, which is the true representation of magnitude.<br /><br />Therefore, I respectfully submit that the MAGNITUDE of the QRS interval in Lead I is net negative and thus consistent with LPFB.Jerry W. Jones, MD FACEP FAAEMhttps://www.blogger.com/profile/10333187745825224414noreply@blogger.com