QT interval

The time from the start of the QRS complex to the end of the T wave on an electrocardiogram, spanning ventricular depolarization and repolarization.

QRS complex: The electrocardiographic waveform marking rapid ventricular depolarization. Its onset marks the QT interval’s starting point.
Long QT syndrome: A group of inherited or acquired conditions associated with delayed ventricular repolarization and prolonged QT intervals. It is the principal clinical syndrome defined by abnormal QT prolongation.
QTc: A QT interval adjusted mathematically for heart rate. Unlike raw QT, QTc attempts to account for rate-dependent duration changes.
T-wave end measurement: The process of identifying where the T wave returns to the ECG baseline. Uncertain endpoint placement changes the measured QT duration.
T wave: The electrocardiographic waveform that primarily represents ventricular repolarization. Its end marks the QT interval’s endpoint.
Torsades de pointes: A polymorphic ventricular tachycardia associated with a prolonged QT interval. QT prolongation can create conditions that permit this dangerous rhythm.
Bazett formula: A formula that divides QT duration by the square root of the RR interval to estimate QTc. It is widely used but can overcorrect at high heart rates.
QT correction formula: A mathematical method for adjusting QT duration for heart rate. No single correction method performs equally well across all rates and patients.
Ventricular action potential: The sequence of voltage changes across a ventricular heart cell during activation and recovery. Its depolarization and repolarization phases underlie the interval’s duration.
Drug-induced long QT syndrome: QT prolongation caused by medications that alter cardiac repolarization. Medication effects are a major preventable cause of prolonged QT.

Linked from 28 pages