According to our results, ionic imbalance and dialysis itself may cause changes in P duration and dispersion simultaneously.

Background: QT interval (QT) and QT dispersion (QTd) are electrocardiograph (ECG) parameters for the evaluation of myocardial repolarization. The inhomogeneity of ventricular repolarization is associated with ventricular arrhythmias. An increased QT, QTd, and increased incidence of nocturnal cardiac rhythm disturbances have been described in patients with obstructive sleep apnea (OSA), while other investigators did not find a relationship between ventricular arrhythmias and OSA. Hypothesis: The aim of this study was to examine the occurrence of ventricular arrhythmias and to measure QT parameters in patients with untreated OSA using an ambulatory Holter-ECG. Methods: A total of 25 patients with untreated OSA were studied. After routine biochemical investigation and 2-dimensional, M-mode echocardiography, a 24-hour Holter-ECG was recorded to detect cardiac arrhythmias and QT parameters. QT parameters were measured by the QT Guard system. Results: Only the QT interval increased significantly during the nighttime period (nocturnal QT interval: 423.1 ± 34.6 ms, daytime QT interval: 381.6 ± 33.8 ms, 24-hour QT interval: 394.7 ± 31.1 ms). However, during the nighttime QT interval (422.8 ± 14.9 ms), QTd (31.2 ± 11.0 ms) and QT dispersion (30.5 ± 10.2 ms) did not show any change compared to 24-hour (QTc interval: 423.7 ± 14.2 ms, QTd: 28.8 ± 9.4 ms, QTcd: 30.5 ± 9.43 ms) and daytime levels (QTc interval: 423.9 ± 14.3 ms, QTd: 27.3 ± 10.7 ms, QTcd: 29.9 ± 11.1 ms). None of the patients had ventricular arrhythmias. Conclusions: QTd and QTcd did not increase during the nighttime period. Our study did not show an increased risk of ventricular arrhythmias in this population during the monitoring period.

Frequent premature ventricular complexes (PVCs) have been demonstrated to cause tachycardiomyopathy in some individuals with a structurally normal heart. We report a patient with severe congestive cardiomyopathy which did not respond to cardiac resynchronization therapy (CRT). Ambulatory monitoring and interrogation of the device memory revealed frequent monomorphic PVCs that were considered a potential cause of the failure of CRT. Radiofrequency ablation of the focus at the postero-inferior left ventricle eliminated the arrhythmia, with a resultant rapid improvement in the clinical status and echo parameters. As PVCs are often associated with severe heart failure, the presence of frequent extrasystoles may be an underrecognized cause of a non-response to resynchronization therapy.

Abstract. Interlead variability of the QT interval in surface electrocardiogram (ECG), i.e., QT dispersion, reflects regional differences in ventricular recovery time, and it has been linked to the occurrence of malignant arrhythmias in different cardiac diseases. The purpose of the study was to assess the effect of hemodialysis on QT and corrected QT (QTc) interval and dispersion in chronic hemodialyzed patients. Data of 34 nondiabetic patients (male/female = 21/13; mean age, 54 ± 15 yr) on chronic hemodialysis were studied. Polysulfone capillaries and bicarbonate dialysate containing (in mEq/L) 135 Na+, 2.0 K+, 1.5 Ca2+, and 1.0 Mg2+ were used. Simultaneous 12-lead ECG were recorded before and after hemodialysis in a standard setting. The QT intervals for each lead were measured manually on enlarged (×3) ECG by one observer using calipers. Each QT interval was corrected for patient heart rate: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{QTc}=\mathrm{QT}/\sqrt{RR}\) \end{document} (in milliseconds [ms]). The average cycle intervals were 853 ± 152 ms predialysis and 830 ± 173 ms postdialysis; the difference was not significant. The maximal QT interval changed significantly from 449 ± 43 to 469 ± 41 ms (P < 0.01). The corrected maximal QT interval increased significantly from 482 ± 42 to 519 ± 33 ms (P < 0.01). The QT dispersion changed from 56 ± 15 to 85 ± 12 ms (P < 0.001) and the corrected QT interval dispersion from 62 ± 18 to 95 ± 17 ms (P < 0.001). During hemodialysis, the serum potassium and phosphate levels decreased from 5.5 ± 0.8 to 3.9 ± 0.5 (mM) and from 2.3 ± 0.5 to 1.6 ± 0.4 (mM), respectively, whereas calcium increased from 2.2 ± 0.23 to 2.5 ± 0.22 (mM). It is concluded that hemodialysis increases the QT and QTc interval and QT and QTc dispersion in patients with end-stage renal failure. Thus, it may be stated that the nonhomogeneity of regional ventricular repolarization increases during hemodialysis. Measurement of QT and QTc dispersion is a simple bedside method that can be used for analyzing ventricular repolarization during hemodialysis.