Dynamic QT interval analysis in uraemic patients receiving chronic haemodialysis Simonetta Genovesi a , Rodolfo Rivera b , Paolo Fabbrini a , Chiara Dossi a , Giuseppe Bonforte b , Luca Mircoli d , Alberto U. Ferrari a , Andrea Stella a and Marco Stramba-Badiale c Objective To analyse the duration of the QT interval and its relationship with heart rate changes in patients with uraemia, before and during haemodialysis. Methods QT and RR intervals were measured automatically using a dedicated algorithm with 24-h Holter recordings in 29 patients (15 women) receiving chronic haemodialysis. QT corrected for heart rate (QTc) and the slope of QT/RR linear regression were calculated. Arterial blood pressure (ABP) was measured before and during haemodialysis. Plasma concentrations of K , Mg 2 and Ca 2 were assessed before and after haemodialysis. Results ABP decreased significantly from baseline (102.7 6 11.0 mmHg) during the first (100.6 6 8.8 mmHg, P < 0.05), second (95.6 6 10.6 mmHg, P < 0.05), and third (94.9 6 10.3 mmHg, P < 0.05) hours of haemodialysis. QTc was longer during haemodialysis than during a 4-h period of no dialysis (447 6 28 ms compared with 429 6 22 ms, P < 0.001), and increased progressively during haemodialysis, with the greatest value during the last hour of haemodialysis (454 6 32 ms compared with 426 6 22 ms, P < 0.001). QT/RR slopes and correlation coefficients were lower during haemodialysis than during the period of no dialysis (0.13 6 0.08 compared with 0.20 6 0.07, P < 0.001 and 0.48 6 0.30 compared with 0.81 6 0.20, respectively; P < 0.001), suggesting a reduced ability to adapt the QT interval in response to changes in heart rate. The effects of haemodialysis on QT interval and the QT/RR relationship were greater in women than in men. QTc variations during dialysis were not correlated with changes in ABP, but were inversely related to changes in Ca 2 concentration (r 2 0.35; P 0.001). Conclusions In patients with uraemia, the haemodialysis session induces a progressive increase in QT interval and modifies its relationship with heart rate. These effects may predispose some individuals to ventricular arrhythmias at the end of and immediately after the haemodialysis session. J Hypertens 21:1921–1926 & 2003 Lippincott Williams & Wilkins. Journal of Hypertension 2003, 21:1921–1926 Keywords: 24-h Holter monitoring, sex, haemodialysis, QT interval, QT/RR relationship, ventricular arrhythmias a DIMEP Universita ` degli Studi di Milano Bicocca, Monza, b Ospedale di Desio, Desio, c IRCCS Istituto Auxologico Italiano and d IRCCS Ospedale Maggiore, Milan, Italy. Correspondence and requests for reprints to Dr Simonetta Genovesi, University of Milano-Bicocca, Dipartimento di Medicina Clinica Prevenzione e Biotecnologie Sanitarie, Via Cadore 48 20052 Monza, Italy. Tel: +39 039 2332375; fax: +39 039 2332376; e-mail: simonetta.genovesi@unimib.it Received 30 April 2003 Revised 1 July 2003 Accepted 4 July 2003 Introduction Patients with end-stage renal disease requiring main- tenance haemodialysis have a high mortality rate that is primarily attributable to cardiovascular diseases, includ- ing ventricular arrhythmias and sudden death [1]. The incidence of arrhythmias increases during and immedi- ately after the haemodialysis session [2,3]. Previous studies have shown that haemodialysis induces altera- tions in the electrocardiogram (prolongation of the QT interval) and increases spatial QT dispersion [4–7]. These abnormalities of ventricular repolarization may favour ventricular arrhythmias. Prolongation of the QT interval is associated with an increased risk of sudden death in the long QT syndromes [8], in patients with myocardial infarction [9] and even in healthy adult individuals [10] or during infancy [11]. Furthermore, increased QT dispersion is associated with greater risk of malignant arrhythmias after myocardial infarction [12] and in congestive heart failure [13]. Data on haemodialysis-related alterations in the ECG have been obtained by measuring QT interval and spatial QT dispersion from the standard 12-lead ECG before and after the haemodialysis session. However, the QT interval measured from a short ECG tracing may not reflect the dynamic changes in duration of repolarization and its relationship with heart rate. Bazett’s formula is currently used to correct QT inter- val for heart rate in resting conditions, but its use for the long-term analysis of ventricular repolarization is questionable. New developments in the computerized analysis of Holter recording have made possible the Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Original article 1921 0263-6352 & 2003 Lippincott Williams & Wilkins DOI: 10.1097/01.hjh.0000084770.37215.c0