Electrical behavior of T-wave polarity alternans in patients with congenital long QT syndrome

OBJECTIVES This study tvas designed to evaluate the incidence and character istics of onset of T-wave polarity alternans (TWPA) in patients with long Q T syndrome. BACKGROUND The T-wave alternans is a phenomenon that consists of brat-to-be at variability in the amplitude, morphology, and sometimes polarity of the T-wave, and it may trigger life-threatening arrhythmias. METHODSThe 24-h Holter recordings of 11 patients with congenital long QT sy ndrome were studied. Episodes of TWPA with 10 or more consecutive cycles we re selected and analyzed as Follows: 1) mean cycle length (MCL) and QTc int erval duration (QTcI) of the episodes of TWPA and the 10 cycles preceding a nd succeeding the TWPA; 2) MCL and QTcI of the third, second, and first min ute before onset (Mn_(3), Mn_(2), Mn_(1)); 3) MCL and QTcI from the tenth t o the first cycle immediately preceding the onset of TWPA (R_(10) to R_(1)) ; 4) MCL and QTcI from the first to the fourteenth cycle during alternans ( R-0 to R-14); 5) MCL and QTcI from the first to the tenth cycle immediately succeeding TWPA (R+1 to R+10); 6) linear correlation (Lnc) between QT inte rval and cycle length (CL) (LncQT/CL) during alternans and for the 10 prece ding cycles; 7) Lnc between the first three alternans cycles and episode du ration (Lnc 3CL/EpD); and 8) difference between the longest and shortest QT c interval. We also selected episodes consisting of four or more consecutiv e cycles in order to analyze daily rhythms of the phenomenon. RESULTS The TWPA was observed in 5 (45%) out of the 11 patients studied. Th e alternans process is initiated by a sudden shortening of the first altern ans cycle without previous heart rate changes and ends at the moment when p rolongation of the cycle tends to occur. LncQT/CL-alternans: r = 0.38 +/- 0 .2 (p = 0.20); without alternans: r = 0.81 +/- 0.06 (p = 0.01). Lnc 3CL/EpD : r = 0.002 (p = 0.992). The QTc difference during alternans: 312.0 +/- 52. 1 ms; without alternans: 86.0 +/- 36.4 ms (p = 0.001). Daily rhythm: 71% of the episodes occurred between 8 AM and 8 PM, with higher incidence during the morning. CONCLUSIONS The TWPA was dependent on the cardiac CL; there was loss of the LncQT/CL and an increase in the QT interval variability. Like other biolog ical variables, T-wave polarity alternans has a higher density during the m orning. (C) 2000 by the American College of Cardiology.