The QT Variability Index (QTVI) is a non-invasive measure of repolarization lability that has been applied to a wide variety of subjects with cardiovascular disease. It is a ratio of normalized QT variability to normalized heart rate variability, and therefore includes an assessment of autonomic nervous system tone. The approach assesses beat-to-beat variability in the duration of the QT and U wave in conventional surface electrocardiographic recordings, as well as determines the heart rate variability (HRV) from the same recording. As opposed to T wave alternans, QTVI assesses variance in repolarization at all frequencies. Nineteen studies have published data on QTVI in healthy individuals, while 20 have evaluated its performance in cohorts with cardiovascular disease. Six studies have assessed the utility of QTVI in predicting VT/VF, cardiac arrest, or cardiovascular death. A prospective study utilizing QTVI to determine therapy allocation has not been performed, and therefore the final determination of the value of the metric awaits definitive exploration.
Keywords: APD; CV; Cardiovascular mortality; HF; HRV; Heart failure; ICD; LVEF; NYHA; New York Heart Association classification; QT; QT variability; QT variability index; QTVI; QTVN; Repolarization; SCD; T wave alternans; TWA; U wave; action potential duration; cardiovascular; heart failure; heart rate variance; implantable cardioverter defibrillator; left ventricular ejection fraction; normalized QT variability; sudden cardiac death.
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