The corrected QT (QTc) interval is a fundamental ECG-derived parameter used in cardiology to assess the electrical stability of the heart. The QT interval itself measures the time between the onset of ventricular depolarization and the completion of repolarization. However, since the QT interval varies inversely with heart rate, correction is essential to standardize interpretation.

Several formulas are used for correction, with Bazett’s (QTc = QT/√RR) being the most widely applied due to its simplicity, though it tends to overestimate QTc at high heart rates and underestimate at low rates. Alternative formulas such as Fridericia’s (QTc = QT/³√RR), Framingham’s (QTc = QT + 0.154[1 – RR]), and Hodges’ provide improved accuracy in certain clinical contexts.

Prolonged QTc has significant clinical implications. It is associated with increased risk of ventricular arrhythmias, including torsades de pointes, sudden cardiac arrest, and drug-induced proarrhythmia. QTc prolongation can be congenital (e.g., Long QT Syndrome) or acquired due to medications (antiarrhythmics, antipsychotics, certain antibiotics), electrolyte imbalances (hypokalemia, hypomagnesemia, hypocalcemia), or structural heart disease. Conversely, abnormally short QTc may suggest conditions like Short QT Syndrome, associated with heightened risk of atrial and ventricular arrhythmias.