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A new physiological method for heart rate correction of the QT interval
1Department of Cardiovascular Medicine, Level 2, John Radcliffe Hospital, Oxford OX3 9DU, UK. patrick.davey@ndm.ox.ac.uk
Aim:
To reassess QT interval rate correction.
Background:
The QT interval is strongly and inversely related to heart rate. To compare QT intervals between different subjects with different heart rates requires the application of a QT interval rate correction formula. To date these formulae have inappropriately assumed a fixed relation between QT interval and heart rate. An alternative method of QT interval rate correction that makes no assumptions about the QT interval-heart rate relation is needed.
Proposal:
A QT heart rate correction method should maintain or accentuate biological QT interval variability, should totally remove the dependence of the rate corrected QT interval on heart rate, and should be applicable over a wide range of conditions with a wide range of differing autonomic states.
Methods:
QT intervals were obtained at rest and during exercise from subjects expected to have different QT intervals and different QT interval-heart rate relations. A linear regression line was obtained from the exercise test data, and the QT interval at a notional heart rate of 60 and 0 beats/min, termed the QT(60) interval, and the QT y intercept obtained by back calculation.
Results:
QT(60) and QT y intercept values were prolonged in heart failure compared with either left ventricular hypertrophy or controls. There was no relation between heart rate and either QT(60) or QT y intercept
Conclusions:
This new physiologically based method of correcting QT interval for heart rate removes the dependence of the corrected QT interval on heart rate, and maintains biological differences.