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QT interval variability

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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.

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

QT interval measurement
Beat-to-beat measurement of QT interval using two-dimensional signal warping (2DSW).

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. Template-based algorithms that use parts of, or the entire ECG waveform usually deliver good results; template stretching or warping techniques 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: Q T V i = log ⁡ S D Q T 2 / ( Q T m e a n ) 2 S D H R 2 / ( H R m e a n ) 2 {\displaystyle QTVi=\log {\frac {SDQT^{2}/(QT_{mean})^{2}}{SDHR^{2}/(HR_{mean})^{2}}}} , where S D Q T {\displaystyle SDQT} , S D H R {\displaystyle SDHR} , Q T m e a n {\displaystyle QT_{mean}} , and H R m e a n {\displaystyle HR_{mean}} denote standard deviation and mean of QT interval and heart rate time series, respectively.

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

Examples of heart rate and QT interval variability.
Example traces of heart rate and QT interval variability in a normal heart and after myocardial infarction.

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. (June 2016). "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. 18 (6): 925–944. doi:10.1093/europace/euv405. PMC 4905605. PMID 26823389.
  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. doi:10.1016/j.bspc.2015.11.011. ISSN 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. doi:10.1371/journal.pone.0041920. ISSN 1932-6203. PMC 3408402. PMID 22860030.
  4. "2DSW – Two-Dimensional Signal Warping (2DSW)". 2dsw.com. Retrieved 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. 96 (5): 1557–1565. doi:10.1161/01.cir.96.5.1557. ISSN 0009-7322. PMID 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. 36 (1): 27–34. doi:10.1007/bf02522854. ISSN 0140-0118. PMID 9614745. S2CID 26095975.
  7. Porta, Alberto; Bari, Vlasta; Maria, Beatrice De; Baumert, Mathias (2017). "A network physiology approach to the assessment of the link between sinoatrial and ventricular cardiac controls". Physiological Measurement. 38 (7): 1472–1489. doi:10.1088/1361-6579/aa6e95. PMID 28430108. S2CID 3435105.
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