ABSTRACT
It has become apparent that some drugs adversely prolong the QT interval on an electrocardiogram (ECG) (1). Regulatory authorities are also becoming increasingly sensitive to this potential safety issue as evidenced by recent interactions between pharmaceutical companies and the Food and Drug Administration. The difficulty in assessing QT interval prolongation is that QT intervals have large intrasubject and between-subject variability and are affected by heart rate (2, 3), sex (4, 5), food (6), chest lead placement (7), and diurnal variation (8), to name a few. Since QT intervals are dependent on heart rate, raw QT intervals are rarely analyzed. Instead, corrected QT intervals (QTc), which control for heart rate, are used. Bazett’s correction (QTcB) is the most commonly used and is defined as
QTcB QT√RR QT
√60/HR (1)
where QT is the QT interval in msec, RR is the RR interval in msec, and HR is heart rate in bpm (9).
