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Paul,
Thank you very much for this! This could be very important, indeed. I could not find any information about this in ACLS, Chou, or even Braunwald. This started bothering me about a month ago when the Marquette algorithm measured a QTc > 500 on a LBBB. I had a feeling that a different set of rules might apply (just as a different set of rules applies for diagnosing AMI). It's interesting that they call it the JT and JTI instead of JT and JTc. Regardless, why couldn't the Marquette algorithm calculate it for you? Seems like that would be a big help. Why bother calculating a QTc in the presence of IVCD if it needs qualification? Very cool information.
Best,
Tom B.
In a message dated 10/8/2006 12:14:59 PM Eastern Daylight Time, PMATERAMD@... writes:
hi Tom, this is always a important issue when dealing with IVCD, BBB, paced beats etc when trying to determine if the QTc is abnormal or not when trying to determine if there is pathological QT due to toxins, meds(anti-arrhythmic, psych, GI, allergy, etc), electrolytes, generally because some of the QT changes are fictitiously prolonged in IVCD, BBB, paced beats so there is a fairly straight forward formula to correct for IVCD to determine "QTc" start with the formula to get JT which is the correction formula for IVCD patients ... JT = QT - QRSd ... then to calculate JTI = JT x (HR+100) / 518 with an abnormal JTI being > 112 ... it is important to understand this formula is only for IVCD and that we are trying to determine true repolarization interval , if you try this formula in NSR you will find the JT is not much different than in IVCD therefore this formula corrects for the IVCD and gives us a better indication of actual prolongation of the "QT" due to repolarization abnormality, I use this formula occasionally because as part of my job I do clearance physicals (and ECG consults for the rest of the staff) for DCPD, DCFD, US Park Police and US Secret Service and many patients have "unusual" ECGs that they were obviously born with including RBBB, LBBB, IVCD etcgood luck,stay safe,PaulPaul A. Matera, MD, D-EM, D-IM, EMTP
Public Safety Medicine, EMS
Director Emeritus - Critical Care / EM, Providence Hospital, DC
Associate Clinical Professor, GWU
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