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Prolonged Ventricular Repolarization in Hypertension: Is It Heart Rate?—Reply

Prolonged Ventricular Repolarization in Hypertension: Is It Heart Rate?—Reply In reply We thank Funck-Brentano and Charbit for their comments on our study,1 in which we found that prolonged QTc is a risk factor for coronary events and cardiovascular mortality in uncomplicated hypertensive subjects. Given that the Bazett correction formula tends to overcorrect QT interval,1 Funck-Brentano and Charbit propose that heart rate, rather than QTc, might be associated with cardiovascular outcome in our study. This is an interesting and potentially important hypothesis. However, we had previously reported in the same population with a shorter follow-up that heart rate had no significant association with cardiovascular morbidity and mortality over the next few years.2 We rechecked this hypothesis in the present database by including heart rate as an additional explanatory variable for coronary events, and again we found that it did not predict coronary events (P = .36 in the Cox model). We also tested the prognostic value of alternative formulas for correcting QT interval, including the loglinear Fridericia equation (QTc = QT/RR1/3),3 the Framingham equation (QTc = QT + 154 [1 − RR]),4 and the equation (QTindex = QT × [heart rate + 100)/656]) proposed by Rautaharju et al.5 The prognostic power of the different QT correction formulas was compared by adding the variables, one at a time, to a basic model of prognostic variables that included heart rate and major cardiovascular risk factors. All of the correction formulas were independent predictors of subsequent coronary events. Coronary heart disease risk increased by 33% for each 1-SD increase in Bazett-corrected QTc (95% confidence interval [CI], +8% to +64%; P<.01), by 28% for Fridericia QTc (95% CI, +4% to +58%; P = .03), by 27% for Framingham QTc (95% CI, +4% to +54%; P = .03), and by 30% for Rautaharju QTindex (95% CI, +6% to +59%; P = .02). In Cox analysis, QT interval duration yielded similar predictive powers for coronary events using the Bazett formula (−2 log likelihood, 1101) and the alternative formulas (−2 log likelihood, 1103, 1103, and 1102 for the Fridericia, Framingham, and Rautaharju et al formulas, respectively). As reported in our article, the Bazett correction results in a significant residual correlation between QTc and heart rate,1 and different corrections may have a better ability to correct for the effect of heart rate. However, in this1 and in other populations,6 the Bazett correction formula was found to be at least as good as other correction formulas as a tool for estimating cardiovascular risk. Correspondence: Dr Schillaci, Unit of Internal Medicine, Angiology and Arteriosclerosis, Department of Clinical and Experimental Medicine, University of Perugia Medical School, Hospital “Santa Maria della Misericordia,” Piazzale Menghini, 1, 06132 Perugia, Italy (skill@unipg.it). References 1. Schillaci GPirro MRonti T et al. Prognostic impact of prolonged ventricular repolarization in hypertension. Arch Intern Med 2006;166909- 913PubMedGoogle ScholarCrossref 2. Verdecchia PSchillaci GBorgioni C et al. Adverse prognostic value of a blunted circadian rhythm of heart rate in essential hypertension. J Hypertens 1998;161335- 1343PubMedGoogle ScholarCrossref 3. Fridericia LS Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand 1920;53469- 486Google ScholarCrossref 4. Sagie ALarson MGGoldberg RJBengtson JRLevy D An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol 1992;70797- 801PubMedGoogle ScholarCrossref 5. Rautaharju PMManolio TAPsaty BMBorhani NOFurberg CDCardiovascular Health Study Collaborative Research Group, Correlates of QT prolongation in older adults (the Cardiovascular Health study). Am J Cardiol 1994;73999- 1002PubMedGoogle ScholarCrossref 6. Dekker JMCrow RSHannan PJSchouten EGFolsom AR Heart rate-corrected QT interval prolongation predicts risk of coronary heart disease in black and white middle-aged men and women: the ARIC study. J Am Coll Cardiol 2004;43565- 571PubMedGoogle ScholarCrossref http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Internal Medicine American Medical Association

Prolonged Ventricular Repolarization in Hypertension: Is It Heart Rate?—Reply

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Publisher
American Medical Association
Copyright
Copyright © 2006 American Medical Association. All Rights Reserved.
ISSN
0003-9926
eISSN
1538-3679
DOI
10.1001/archinte.166.19.2157-b
Publisher site
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Abstract

In reply We thank Funck-Brentano and Charbit for their comments on our study,1 in which we found that prolonged QTc is a risk factor for coronary events and cardiovascular mortality in uncomplicated hypertensive subjects. Given that the Bazett correction formula tends to overcorrect QT interval,1 Funck-Brentano and Charbit propose that heart rate, rather than QTc, might be associated with cardiovascular outcome in our study. This is an interesting and potentially important hypothesis. However, we had previously reported in the same population with a shorter follow-up that heart rate had no significant association with cardiovascular morbidity and mortality over the next few years.2 We rechecked this hypothesis in the present database by including heart rate as an additional explanatory variable for coronary events, and again we found that it did not predict coronary events (P = .36 in the Cox model). We also tested the prognostic value of alternative formulas for correcting QT interval, including the loglinear Fridericia equation (QTc = QT/RR1/3),3 the Framingham equation (QTc = QT + 154 [1 − RR]),4 and the equation (QTindex = QT × [heart rate + 100)/656]) proposed by Rautaharju et al.5 The prognostic power of the different QT correction formulas was compared by adding the variables, one at a time, to a basic model of prognostic variables that included heart rate and major cardiovascular risk factors. All of the correction formulas were independent predictors of subsequent coronary events. Coronary heart disease risk increased by 33% for each 1-SD increase in Bazett-corrected QTc (95% confidence interval [CI], +8% to +64%; P<.01), by 28% for Fridericia QTc (95% CI, +4% to +58%; P = .03), by 27% for Framingham QTc (95% CI, +4% to +54%; P = .03), and by 30% for Rautaharju QTindex (95% CI, +6% to +59%; P = .02). In Cox analysis, QT interval duration yielded similar predictive powers for coronary events using the Bazett formula (−2 log likelihood, 1101) and the alternative formulas (−2 log likelihood, 1103, 1103, and 1102 for the Fridericia, Framingham, and Rautaharju et al formulas, respectively). As reported in our article, the Bazett correction results in a significant residual correlation between QTc and heart rate,1 and different corrections may have a better ability to correct for the effect of heart rate. However, in this1 and in other populations,6 the Bazett correction formula was found to be at least as good as other correction formulas as a tool for estimating cardiovascular risk. Correspondence: Dr Schillaci, Unit of Internal Medicine, Angiology and Arteriosclerosis, Department of Clinical and Experimental Medicine, University of Perugia Medical School, Hospital “Santa Maria della Misericordia,” Piazzale Menghini, 1, 06132 Perugia, Italy (skill@unipg.it). References 1. Schillaci GPirro MRonti T et al. Prognostic impact of prolonged ventricular repolarization in hypertension. Arch Intern Med 2006;166909- 913PubMedGoogle ScholarCrossref 2. Verdecchia PSchillaci GBorgioni C et al. Adverse prognostic value of a blunted circadian rhythm of heart rate in essential hypertension. J Hypertens 1998;161335- 1343PubMedGoogle ScholarCrossref 3. Fridericia LS Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand 1920;53469- 486Google ScholarCrossref 4. Sagie ALarson MGGoldberg RJBengtson JRLevy D An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol 1992;70797- 801PubMedGoogle ScholarCrossref 5. Rautaharju PMManolio TAPsaty BMBorhani NOFurberg CDCardiovascular Health Study Collaborative Research Group, Correlates of QT prolongation in older adults (the Cardiovascular Health study). Am J Cardiol 1994;73999- 1002PubMedGoogle ScholarCrossref 6. Dekker JMCrow RSHannan PJSchouten EGFolsom AR Heart rate-corrected QT interval prolongation predicts risk of coronary heart disease in black and white middle-aged men and women: the ARIC study. J Am Coll Cardiol 2004;43565- 571PubMedGoogle ScholarCrossref

Journal

Archives of Internal MedicineAmerican Medical Association

Published: Oct 23, 2006

Keywords: hypertension,heart rate,ventricular repolarization

References