Evaluation of baseline ECG in patients undergoing Oral Flecainide Challenge test for suspected Brugada Syndrome: An analysis of lead II

Abstract

Background and ObjectivesWe analyzed Lead II in patients undergoing an Oral Flecainide Challenge test (FCT), to identify any pointers that could predict a positive FCT and thereby help in recognition of latent BS.MethodsThe following parameters in lead II were retrospectively analyzed from the pre-test ECG in 62 patients undergoing FCT for suspected BS: The presence or absence of S waves, S wave amplitude, duration and upslope duration; J point parameters- Early repolarization, QRS notch, and QRS Slur; ST segment parameters-lack of isoelectric ST segment, ST duration and QT interval.Results48 had positive FCT (Group-1) while 14 were negative for FCT(Group-2). Lack of an isoelectric ST segment (50% vs 14.29%, p = 0.018) and slurring of QRS (33.33% vs 0%, p = 0.014) was more common in Group-1 than Group-2. Group-1 had shorter ST segment duration (median 81.5 (IQR 64–103.5) vs 110 (IQR 90–132), p = 0.002) and shorter ST: QT ratio (median 0.28 (IQR 0.22–0.35) vs 0.23 (0.18–0.27), p = 0.007). QRS notch/depressed J point (87.5%), QRS slur (100%), and lack of isoelectric ST segment (92.31%) had high sensitivity for predicting an inducible Type 1 Brugada pattern. Combining two parameters- ST: QT ratio<0.24 and lack of isoelectric ST segment-considerably improved the specificity (73.3%), and the positive predictive value of the test to 76%. The results remained accurate when validated in a small prospective cohort.ConclusionShortened ST segment in Lead II, lack of isoelectric ST segment, slurred QRS and ST/QT ratio <0.24 are predictive of underlying Brugada pattern in baseline ECG.

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“…QRS notching/depressed J-point conveyed a sensitivity of 87.5%, QRS lowering conveyed 100% sensitivity and lack of isoelectric ST segment, when all 3 are combined they had a high sensitivity in predicting inducible type 1 Brugada syndrome. When combining all of these together with the ST to QT ratio less than 0.24 and lack of isoelectric ST segment increased the specificity to 73.3% and a positive predictive value of 76% [ 7 ]. Individuals with SCN5A mutations only have a 20% to 30% chance of having a positive ECG.…”

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“…In this issue of IPEJ, Rai et al. [16] presents an interesting observation based on changes in limb lead II in patients undergoing Flecainide challenge. Features suggesting a shortened phase 2 and 3 of repolarization in lead II evidenced as shortened ST segment, shortened ST/QT ratio and lack of an isoelectric segment along with a slurred QRS complex predicted a positivity of flecainide challenge quite accurately, in their retrospective analysis which was tested prospectively and they were successful in duplicating the results with 100% sensitivity and a 100% negative predictive value.…”