QT interval dispersion in healthy subject and survivors at sudden cardiac death: Circadian variation in a twenty-four-hour assessment

Twenty-four-hour acquisition of QT dispersion (QTd) from the Halter and the circadian variation of QTd were evaluated in 20 survivors of sudden cardiac death (SCD), in 20 healthy subjects, and in 14 control patients without a history of cardiac arrest who were age, sex, diagnosis and therapy matched to 14 SCD patients. Computer-assisted QT measurements were performed on 24-hour Holter recordings; each recording was divided into 288 5-minute segments and templates representing the average QRST were generated. QTd was calculated as the difference between QT intervals in leads V-1 and V-5 for each template on Halter. The 24-hour mean QTd was significantly greater in SCD patients (40 +/- 28 ms) than in healthy subjects (20 +/- 10 ms) and control patients (15 +/- 5 ms) (p <0.05). There was a circadian variation in QTd with greater values at night (0 to 6 A.M.) than at daytime (10 A.M. to 4 P.M.) in healthy subjects (25 +/- 13 vs 15 +/- 8 ms, p <0.001) and control patients (18 +/- 10 vs 12 +/- 4 ms p <0.05), whereas in SCD patients there was no significant difference between night and day values (45 +/- 31 vs 37 +/- 28 ms, p = NS). It is concluded that QTd measured by Halter was greater in SCD patients than in healthy subjects and matched control patients during the entire day. QTd has a clear circadian variation in normal subjects, whereas this variation is blunted in SCD patients. QTd measured on Halter differentiates survivors of cardiac arrest and may be a useful tool for risk stratification. (C) 1997 by Excerpta Medica, Inc.