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. 2010 Dec 22:2010:961290.
doi: 10.4061/2010/961290.

QT Measurement and Heart Rate Correction during Hypoglycemia: Is There a Bias?

Toke Folke Christensen  1 , Jette Randløv, Leif Engmann Kristensen, Ebbe Eldrup, Ole Kristian Hejlesen, Johannes Jan Struijk
Affiliations

QT Measurement and Heart Rate Correction during Hypoglycemia: Is There a Bias?

Toke Folke Christensen et al. Cardiol Res Pract. .

Abstract

Introduction. Several studies show that hypoglycemia causes QT interval prolongation. The aim of this study was to investigate the effect of QT measurement methodology, heart rate correction, and insulin types during hypoglycemia. Methods. Ten adult subjects with type 1 diabetes had hypoglycemia induced by intravenous injection of two insulin types in a cross-over design. QT measurements were done using the slope-intersect (SI) and manual annotation (MA) methods. Heart rate correction was done using Bazett's (QTcB) and Fridericia's (QTcF) formulas. Results. The SI method showed significant prolongation at hypoglycemia for QTcB (42(6) ms; P < .001) and QTcF (35(6) ms; P < .001). The MA method showed prolongation at hypoglycemia for QTcB (7(2) ms, P < .05) but not QTcF. No difference in ECG variables between the types of insulin was observed. Discussion. The method for measuring the QT interval has a significant impact on the prolongation of QT during hypoglycemia. Heart rate correction may also influence the QT during hypoglycemia while the type of insulin is insignificant. Prolongation of QTc in this study did not reach pathologic values suggesting that QTc prolongation cannot fully explain the dead-in-bed syndrome.

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Figures

Figure 1
Figure 1
Schematic design of the study. Measurements of ECG (•) are taken three times in a baseline interval prior to insulin injection (t −30, t −10, and t 0), 15 minutes after insulin injection (t 15), at blood glucose nadir (t hypo), and 90 minutes after blood glucose nadir (t post).
Figure 2
Figure 2
Measurements of the T wave offset from ECG lead II using the semiautomatic slope-intersect method (SI) and manual annotation (MA) method. The two ECGs are from t 0 (left side) and at t hypo (right side) at the same episode. At t 0 the SI method underestimates the end of the T wave compared with the MA method. With the flattening of the T wave at t hypo the SI method overestimates the end of the T wave compared with the MA method.
Figure 3
Figure 3
The difference over the course of a hypoglycemia episode in QTc corrected by Fridericia's formula (QTcF) for the manual annotation (MA) and slope-intersect (SI) methods. Data is mean ± SE estimated from the statistical model.
Figure 4
Figure 4
Difference between QTc corrected by Bazett's (QTcB) and Fridericia's (QTcF) formulas. The QT interval is measured using the manual annotation (MA) method. Data is mean ± SE estimated from the statistical model.
See this image and copyright information in PMC

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