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Abstract
Several formulas have been proposed to adjust the QT interval for heart rate, the
most commonly used being the QT correction formula (![Math Eq]()
) proposed in 1920 by Bazett. The QTC formula was derived from observations in only 39 young subjects. Recently, the adequacy
of Bazett's formula has been questioned. To evaluate the heart rate QT association,
the QT interval was measured on the initial baseline electrocardiogram of 5,018 subjects
(2,239 men and 2,779 women) from the Framingham Heart Study with a mean age of 44
years (range 28 to 62). Persons with coronary artery disease were excluded. A linear
regression model was developed for correcting QT according to RR cycle length. The
large sample allowed for subdivision of the population into sex-specific deciles of
RR intervals and for comparison of QT, Bazett's QTC and linear corrected QT (QTLC). The mean RR interval was 0.81 second (range 0.5 to 1.47) heart rate 74 beats/min
(range 41 to 120), and mean QT was 0.35 second (range 0.24 to 0.49) in men and 0.36
second (range 0.26 to 0.48) In women. The linear regression model yielded a correction
formula (for a reference RR interval of 1 second): QTLC = QT + 0.154 (1 − RR) that applies for men and women. This equation corrects QT more
reliably than the Bazett's formula, which overcorrects the QT interval at fast heart
rates and undercorrects it at low heart rates. Lower and upper limits of normal QT
values in relation to RR were generated. A simple linear equation was developed that
is more accurate than Bazett's correction at different cycle lengths and more convenient
for clinical practice. This formula alleviates the need to apply secondary corrections
to Bazett's formula. Additional investigation is warranted to determined whether QTLC improves the identification of subjects at high risk for malignant arrhythmias or
sudden death.
) proposed in 1920 by Bazett. The QTC formula was derived from observations in only 39 young subjects. Recently, the adequacy
of Bazett's formula has been questioned. To evaluate the heart rate QT association,
the QT interval was measured on the initial baseline electrocardiogram of 5,018 subjects
(2,239 men and 2,779 women) from the Framingham Heart Study with a mean age of 44
years (range 28 to 62). Persons with coronary artery disease were excluded. A linear
regression model was developed for correcting QT according to RR cycle length. The
large sample allowed for subdivision of the population into sex-specific deciles of
RR intervals and for comparison of QT, Bazett's QTC and linear corrected QT (QTLC). The mean RR interval was 0.81 second (range 0.5 to 1.47) heart rate 74 beats/min
(range 41 to 120), and mean QT was 0.35 second (range 0.24 to 0.49) in men and 0.36
second (range 0.26 to 0.48) In women. The linear regression model yielded a correction
formula (for a reference RR interval of 1 second): QTLC = QT + 0.154 (1 − RR) that applies for men and women. This equation corrects QT more
reliably than the Bazett's formula, which overcorrects the QT interval at fast heart
rates and undercorrects it at low heart rates. Lower and upper limits of normal QT
values in relation to RR were generated. A simple linear equation was developed that
is more accurate than Bazett's correction at different cycle lengths and more convenient
for clinical practice. This formula alleviates the need to apply secondary corrections
to Bazett's formula. Additional investigation is warranted to determined whether QTLC improves the identification of subjects at high risk for malignant arrhythmias or
sudden death.To read this article in full you will need to make a payment
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References
- Prolonged QT interval syndromes.JAMA. 1986; 256: 2985-2987
- Long QT: good, bad or indifferent?.J Am Coll Cardiol. 1984; 4: 398-413
- The long QT syndrome.Mod Concepts Cardiovasc Dis. 1985; 54: 45-50
- The relation between QT interval and ventricular arrhythmias in acute myocardial infarction.Acta Med Scand. 1978; 20 4: 17-19
- QT interval and primary ventricular fibrillation in acute myocardial infarction.Am Heart J. 1981; 101: 118-119
- Prognostic importance of Qtc interval at discharge after acute myocardial infarction: a multicenter study of 865 patients.Am Heart J. 1984; 108: 395-400
- Repolarization abnormalities in survivors of out of hospital ventricular fibrillation.Circulation. 1978; 57: 654-658
- Prediction of sudden death from QTc interval prolongation in patients with chronic ischemic heart disease.J Electrocardiol. 1986; 19: 203-212
- Usefulness of QTc interval on the discharge electrocardiogram for predicting survival after myocardial infarction.Am J Cardiol. 1986; 57: 1066-1068
- QT interval prolongation as predictor of sudden death in patient with myocardial infarction.Circulation. 1978; 57: 1074-1077
- Corrected QT interval during one year follow-up after an acute myocardial infarction.Eur Heart J. 1986; 7: 299-304
- Prognostic value of predischarge 12 lead electrocardiogram after myocardial infarction compare with other routine clinical variable.Br Heart J. 1987; 57: 306-312
- An analysis of the time-relations of electrocardiogram.Heart. 1920; 7: 353-370
- An exponential formula for heart rate dependence of QT interval during cardiac pacing in humans: reevaluation of Bazett's formula.Am J Cardiol. 1984; 54: 103-108
- The duration of the QT interval as a function of heart rate: a derivation based on physical principles and a comparison to measured values.Am Heart J. 1985; 110: 872-878
- Correction of the QT interval for heart rate: review of different formulas and the use of Bazett's formula in myocardial infarction.Am Heart J. 1985; 109: 568-574
- Evaluation of 10 QT prediction formulas in 881 middle-aged men from the seven countries study: emphasis on the cubic root Fridericia's equation.J Electrocardiol. 1988; 21: 219-229
- An improved method to correct the QT interval of the electrocardiogram for changes in heart rate.J Pharmacol Methods. 1989; 22: 207-217
- Applicability of the correcting QT interval for heart rate (letter).Am Heart J. 1980; 99: 678
- Die systlendauer in elektrokardiogramm bei normalen menchen und bei Herzkranken.Acta Med Scand. 1920; 53: 469-486
- Normal duration of QT interval.Am Heart J. 1942; 23: 522-553
- The normal duration of the electrocardiographic ventricular complex.J Clin Invest. 1936; 15: 335-642
- Applied regression analysis and other multivariable methods.in: 2nd ed. PWS Kent Publishing, Boston1988: 109-110
- The REG procedure.in: 4th ed. SAS/STAT User's Guide, Version 6. vol 2. SAS Institute, Inc, Cary, NC1989: 1351-1456
- Influence of the autonomic nervous system on the QT interval in man.Am J Cardiol. 1982; 50: 1099-1103
- Contribution of heart rate to QT interval shortening during exercise.Eur Heart J. 1983; 4: 265-271
- The QT interval and cycle length: the influence of atropine, hyoscine and exercise.Br J Clin Pharmacol. 1983; 16: 615-621
- The QT interval during reflex cardiovascular adaptation.Circulation. 1984; 69: 22-25
- Duration of the QT interval and total cardiovascular mortality in healthy persons (The Framingham Study experience).Am J Cardiol. 1991; 67: 55-58
- QTc prolongation measured by standard 12 lead electrocardiography is an independent risk factor for sudden death due to cardiac arrest.Circulation. 1991; 83: 1888-1894
- QT interval prolongation predicts cardiovascular mortality in an apparently healthy population.Circulation. 1991; 84: 1516-1523
Article info
Publication history
Accepted:
May 21,
1992
Received:
May 1,
1992
Identification
Copyright
© 1992 Published by Elsevier Inc.
