Spotlight: How to Measure QTc Interval?

The 12-lead ECG continues to be one of the most important noninvasive diagnostic tools in daily clinical practice, since it offers high level of clinincal information at low costs. However, accurate interpretation of the ECG remains a challenge for many physicians. Correct assessment of the different time intervals may be time-consuming even in a normal ECG, particularly since automated ECG softwares have proven to be rather unprecise. Measuring ECG intervals needs even more diligence in the presence of arrhythmias (e.g. atrial fibrillation) where accurate determination of the QT interval has to be based on averaging several measurements. Interpretation of the QT interval may be further hampered by the presence of tachycardia or severe bradycardia. Thus, the influence of heart rate as well as of bundle branch blocks on repolarization measures need to be corrected (QTc). For this purpose, several correction formulas have been developed and validated for use in clinical practice. Considering these aspects is the base for correct measurement and interpretation of cardiac repolarization.