A lot of studies analysing repolarisation changes and the occurrence of ventricular arrhythmias used QTc interval even in patients with bundle branch block. Do you know why JTc interval has not been more often used in this population? I notice that also a calculation of JTc interval is different among studies: from JTc=QTc−QRS to JTc = JT/ √RR. Which calculation do you recommend? For me JTc = JT/ √RR is more acceptable, as in this calculation JT interval is corrected to RR interval and not only to QT interval as in the first calculation.
I can see the logic of using JTc, as it takes into account the width of the QRS, but I don’t know if we have much information on the association between JTc and risk of adverse events. All the big studies, as far as I know, have used QTc. I think the best JT correction formula can only be worked out by doing a study.
Remember that repolarisation begins as soon as depolarisation, that is, at the onset of the QRS. It's just that we cannot see it because it is obscured by depolarisation (QRS). To exclude the QRS would be physiologically arbitrary. The JTc in fact EXCLUDES the QRS by definition. If parts of the heart are depolarised later they will repolarise later. The onset of the QRS is a fiducial point much more easily identifiable than the so called J point.
Also the so called Bazett formula was never used by Bazett. His formula - which involved a constant "k", was modified by Taran and Szilagyi (American Heart Journal 1947, 33, 14-26). The applicability of heart rate correction and assessment of risk of eg, SCD is continuously debated. The number of papers on a topic is inversely proportional to our understanding of it! I am not convinced about heart rate correction.
Study question is like this. Is JTc is better than QTc? OK try to understand that
1. depolarization of cell is phase 0 and is of
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