QT interval variability explained

QT interval variability (QTV) refers to the physiological phenomenon of beat-to-beat fluctuations in QT interval of electrocardiograms. Increased QTV appears to be a marker of arrhythmic and cardiovascular death; it may also play a role for noninvasive assessment of sympathetic nervous system activity.^[1]

Other terms used include: "QT variability", "beat-to-beat variability of ventricular repolarization (BRV)"

QT interval measurement

Under normal resting conditions, beat-to-beat changes in QT interval are very small with a standard deviation typically below 5 ms. Digital high resolution ECG sampled at 300 Hz or higher and dedicated computer algorithms are required for QTV assessment.^[2] Template-based algorithms that use parts of, or the entire ECG waveform usually deliver good results;^[3] template stretching or warping techniques^[4] perform comparably well in the presence of noise.

QTV Analysis

A number of metrics have been proposed for QTV quantification. The QT variability index (QTVi) has been most frequently reported in the literature:

QTVi =log (SDQT ^{2 /(QT} _{mean} ) ^{2})/(SDHR ^{2 /(HR} _{mean} ) ^{2}) , where SDQT , SDHR , QT _{mean} , and HR _{mean} denote standard deviation and mean of QT interval and heart rate time series, respectively.^[5]

More advanced approaches that take into account the relationship between QTV and heart rate variability include vector autoregressive process models^[6] and information domain approaches.^[7]

Notes and References

1. Baumert. Mathias. Porta. Alberto. Vos. Marc A.. Malik. Marek. Couderc. Jean-Philippe. Laguna. Pablo. Piccirillo. Gianfranco. Smith. Godfrey L.. Tereshchenko. Larisa G.. Volders. Paul G.A.. QT interval variability in body surface ECG: measurement, physiological basis, and clinical value: position statement and consensus guidance endorsed by the European Heart Rhythm Association jointly with the ESC Working Group on Cardiac Cellular Electrophysiology. Europace. June 2016. 18. 6. 925–944. 10.1093/europace/euv405. 26823389. 4905605.
2. Baumert. Mathias. Schmidt. Martin. Zaunseder. Sebastian. Porta. Alberto. 2016-03-01. Effects of ECG sampling rate on QT interval variability measurement. Biomedical Signal Processing and Control. 25. 159–164. 10.1016/j.bspc.2015.11.011. 1746-8094.
3. Baumert. Mathias. Starc. Vito. Porta. Alberto. 2012-07-30. Conventional QT Variability Measurement vs. Template Matching Techniques: Comparison of Performance Using Simulated and Real ECG. PLOS ONE. 7. 7. e41920. 10.1371/journal.pone.0041920. 22860030. 3408402. 1932-6203. free.
4. Web site: 2DSW – Two-Dimensional Signal Warping (2DSW). 2dsw.com. 2017-12-01.
5. Berger. Ronald D.. Kasper. Edward K.. Baughman. Kenneth L.. Marban. Eduardo. Calkins. Hugh. Tomaselli. Gordon F.. 1997-09-02. Beat-to-Beat QT Interval Variability: Novel Evidence for Repolarization Lability in Ischemic and Nonischemic Dilated Cardiomyopathy. Circulation. en. 96. 5. 1557–1565. 10.1161/01.cir.96.5.1557. 0009-7322. 9315547.
6. Porta. A.. Baselli. G.. Caiani. E.. Malliani. A.. Lombardi. F.. Cerutti. S.. 1998-01-01. Quantifying electrocardiogram RT-RR variability interactions. Medical and Biological Engineering and Computing. en. 36. 1. 27–34. 10.1007/bf02522854. 9614745. 26095975. 0140-0118.
7. Porta. Alberto. Bari. Vlasta. Maria. Beatrice De. Baumert. Mathias. A network physiology approach to the assessment of the link between sinoatrial and ventricular cardiac controls. Physiological Measurement. 38. 7. 1472–1489. 10.1088/1361-6579/aa6e95. 28430108. 2017. 3435105 .