CIRCADIAN VARIATION OF THE QT INTERVAL IN PATIENTS WITH SUDDEN CARDIAC DEATH AFTER MYOCARDIAL-INFARCTION

To evaluate the potential prognostic value of the circadian variation of QT intervals in predicting sudden cardiac death (SCD) in patients a fter myocardial infarction (MI), 15 pairs of post-MI patients (15 died suddenly within 1 year after MI [SCD victims] and 15 remained event-f ree [MI survivors]) were studied (mean age 60 +/- 8 years; 24 men and 6 women). The pairs were matched for age, gender, infarct site, presen ce of Q wave, left ventricular ejection fraction, thrombolytic and bet a-blocker therapy. Fourteen normal subjects served as controls (mean a ge 55 +/- 9 years; 12 men). A 24-hour Halter electrocardiographic (ECG ) recording was obtained from each subject. All recordings were analyz ed using a Halter ECG analyser. QT, RR, and heart rate-corrected QT in tervals (QTc) were automatically calculated by the analyzer, and hourl y and 24-hour mean values of each measurement were derived from each r ecording. There was a pronounced circadian variation in the QT interva l in parallel with the trend in the RR interval in normal subjects and in MI survivors. Circadian variation in both indexes was blunted in S CD victims. The QT interval was significantly longer at night than dur ing the day in normal subjects (388 +/- 28 vs 355 +/- 21 ms, p = 0.001 ) and in MI survivors (358 +/- 25 vs 346 +/- 15 ms, p = 0.008), but no t in SCD victims (357 +/- 32 vs 350 +/- 31 ms, p = 0.6). The 24-hour m ean value of the QT interval in SCD victims did not differ significant ly from that in normal subjects or MI survivors. The QT interval at ni ght was significantly shorter in SCD victims than in normal subjects ( 357 +/- 32 vs 388 +/- 28 ms, p = 0.02), but daytime values were simila r. The QT interval in SCD victims did not differ significantly from th at of MI survivors at any time. The QTc interval exhibited a small cir cadian variation in normal subjects. This variation was abolished in S CD victims and MI survivors. The 24-hour mean value of QTc was signifi cantly longer in SCD victims than in normal subjects (424 +/- 25 vs 40 2 +/- 21 ms, p = 0.02), and in MI survivors (424 +/- 25 vs 404 +/- 32 ms, p <0.05). The QTc interval of SCD victims differed from that of no rmal subjects during both the day (421 +/- 25 vs 400 +/- 17 ms, p = 0. 02) and night (424 +/- 26 vs 403 +/- 23 ms, p = 0.03). Thus, blunted c ircadian variation in QT intervals, abolished circadian variation in Q Tc intervals, and prolonged QTc intervals may suggest an increased ris k of SCD in patients after MI. (C) 1998 by Excerpta Medica, Inc.