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QRS Duration Index: Explanation and Clinical Context The QRS Duration Index (QRSd Index) is a heart rate–corrected measure of ventricular depolarization duration, initially described by Brodie et al. in 1982. It is calculated by dividing the QRS duration (in milliseconds) by the square root of the RR interval (in seconds). This index accounts for heart rate variability when assessing intraventricular conduction and c
QRS-T Angle Index: Explanation and Clinical Context The QRS-T angle represents the spatial difference between the depolarization (QRS) and repolarization (T wave) vectors of the heart on a 12-lead ECG. A wider QRS-T angle is associated with abnormal ventricular repolarization and is a strong predictor of adverse cardiovascular events, including sudden cardiac death and all-cause mortality. Normal values are usually <
QRSD Ratio (Bundle Branch Differentiation): Explanation and Clinical Context The QRSD Ratio is a metric used to differentiate types of bundle branch conduction delays on ECG, especially in borderline QRS prolongation cases. It is calculated by dividing the QRS duration (ms) by the square root of the RR interval (ms), providing heart rate–corrected QRS assessment. A QRSD ratio <1.15 is typically considered normal, ind
QTc Bazett Formula: Explanation and Clinical Context The QT interval represents the time from the start of ventricular depolarization to the end of ventricular repolarization on an electrocardiogram (ECG). QT interval duration varies with heart rate, and QTc (corrected QT) is calculated to standardize QT for heart rate. Bazett's formula is the most widely used correction: QTc = QT / √RR, where QT is in milliseconds a
Comprehensive explanation and clinical context The QT interval measures ventricular depolarisation and repolarisation on the electrocardiogram. Correcting the QT interval for heart rate yields QTc. Several correction formulae exist. Bazett's formula divides QT by the square root of the RR interval in seconds. Fridericia's formula divides QT by the cube root of the RR interval. Framingham's formula adjusts QT by addin
QTc Fridericia Correction: Explanation and Clinical Context The Fridericia formula is used to correct the QT interval for heart rate: QTcF = QT / (RR^1/3), where RR is the interval between heartbeats in seconds. It provides a more accurate correction than Bazett's formula, especially at extreme heart rates. QTc prolongation is associated with increased risk of ventricular arrhythmias, including Torsades de Pointes, a