T-WAVE HUMPS AS A POTENTIAL ELECTROCARDIOGRAPHIC MARKER OF THE LONG QT SYNDROME

Objectives. This study attempted to determine the prevalence and elect rocardiographic (ECG) lead distribution of T wave ''humps'' (T2, after an initial T wave peak, T1) among families with long QT syndrome and control subjects. Background. T wave abnormalities have been suggested as another facet of familiar long QT syndrome, in addition to prolong ation of the rate-corrected QT interval (QTc), that might aid in the d iagnosis of affected subjects. Methods. The ECGs from 254 members of 1 3 families with long QT syndrome (each with two to four generations of affected members) and from 2,948 healthy control subjects (age greate r than or equal to 16 years, QTc interval 0.39 to 0.46 s) were collect ed and analyzed. Tracings from families with long QT syndrome were rea d without knowledge of QTc interval or family member status (210 blood relatives and 44 spouses). Results. We found that T2 was present in 5 3%, 27% and 5% of blood relatives with a ''prolonged'' (greater than o r equal to 0.47 s), ''borderline'' (0.42 to 0.46 s) and ''normal'' (le ss than or equal to 0.41 s) QTc interval, respectively (p < 0.0001), b ut in only 5% and 0% of spouses with a borderline and normal QTc inter val, respectively (p = 0.06 vs. blood relatives). Among blood relative s with T2, the mean [+/-SD] maximal T1T2 interval was 0.10 +/- 0.03 s and correlated with the QTc interval (p < 0.01); a completely distinct U wave was seen in 23%. T2 was confined to leads V-2 and V-3 in 10%, whereas V-4, V-5, V-6 or a limb lead was involved in 90% of blood rela tives with T2. Among blood relatives with a borderline QTc interval, 5 0% of those with versus 20% of those without major symptoms manifested T2 in at least one left precordial or limb lead (p = 0.05). A T2 ampl itude >1 mm (grade III) was observed, respectively, in 19%, 6% and 0% of blood relatives with a prolonged, borderline and normal QTc interva l with T2 in at least one left precordial or limb lead. Among the 2,94 8 control subjects, 0.6% exhibited T2 confined to leads V-2 and V-3, a nd 0.9% had T2 involving one or more left precordial lend (but none of the limb leads). Among 37 asymptomatic adult blood relatives with QTc intervals 0.42 to 0.46 s, T2 was found in left precordial or limb lea ds in 9 (24%; 5 with limb lead involvement) versus only 1.9% of contro l subjects with a borderline QTc interval (p < 0.0001). Conclusions. T hese findings are consistent with the hypothesis that in families with long QT syndrome, T wave humps involving left precordial or (especial ly) limb leads, even among asymptomatic blood relatives with a borderl ine QTc interval, suggest the presence of the long QT syndrome trait.