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QT Interval Variability (qt + interval_variability)

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Medical Sciences	100%

Selected Abstracts

QT Interval Variability and Adaptation to Heart Rate Changes in Patients with Long QT Syndrome

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1 2009
JAN N, MEC M.D.
Background: Increased QT variability (QTV) has been reported in conditions associated with ventricular arrhythmias. Data on QTV in patients with congenital long QT syndrome (LQTS) are limited. Methods: Ambulatory electrocardiogram recordings were analyzed in 23 genotyped LQTS patients and in 16 healthy subjects (C). Short-term QTV was compared between C and LQTS. The dependence of QT duration on heart rate was evaluated with three different linear models, based either on the RR interval preceding the QT interval (RR0), the RR interval preceding RR0 (RR -1), or the average RR interval in the 60-second period before QT interval (mRR). Results: Short-term QTV was significantly higher in LQTS than in C subjects (14.94 ± 9.33 vs 7.31 ± 1.29 ms; P < 0.001). It was also higher in the non-LQT1 than in LQT1 patients (23.00 ± 9.05 vs 8.74 ± 1.56 ms; P < 0.001) and correlated positively with QTc in LQTS (r = 0.623, P < 0.002). In the C subjects, the linear model based on mRR predicted QT duration significantly better than models based on RR0 and RR -1. It also provided better fit than any nonlinear model based on RR0. This was also true for LQT1 patients. For non-LQT1 patients, all models provided poor prediction of QT interval. Conclusions: QTV is elevated in LQTS patients and is correlated with QTc in LQTS. Significant differences with respect to QTV exist among different genotypes. QT interval duration is strongly affected by noninstantaneous heart rate in both C and LQT1 subjects. These findings could improve formulas for QT interval correction and provide insight on cellular mechanisms of QT adaptation. [source]

Sodium Channel Blockers Enhance the Temporal QT Interval Variability in the Right Precordial Leads in Brugada Syndrome

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2008
Tetsuzou Kanemori M.D.
Background: Temporal QT interval variability is associated with sudden cardiac death. The purpose of this study was to evaluate temporal QT interval variability in Brugada syndrome (BS). Methods: We measured QT and RR intervals in precordial leads (V1,V6) based on 12-beat resting ECG recordings from 16 BS patients (B group) with spontaneous ST elevation in right precordial leads (V1,V2) and from 10 patients with normal hearts (C group). We measured the response in B group before and after administration of pilsicainide (1 mg/kg). The standard deviation (QT-SD, RR-SD) of the time domain and total frequency power (QT-TP, RR-TP) were calculated for all precordial leads, and the latter was to analyze the frequency domain. Results: The right precordial leads in BS exhibited an additional and prominent ST elevation (coved-type) after pilsicainide administration. Both QT-SD and QT-TP values were significantly more increased in B, than in C (5.1 ± 1.2 vs 3.6 ± 0.2 and 23.4 ± 2.9 vs 12.3 ± 1.7 msec2, P < 0.01, respectively) and after pilsicainide administration in B. (5.1 ± 0.4 vs 3.9 ± 0.3, 25.8 ± 3.4 vs 16.3 ± 2.6 msec2, P < 0.01, respectively) However, QT-SD and QT-TP did not significantly change in any of other leads (V3,V6) and RR-SD and RR-TP were similar for both groups, as well as after intravenous pilsicainide administration in B. Conclusions: The temporal QT interval variability was identified in BS. Moreover, sodium channel blocker induced temporal fluctuation in QT interval and it may possibly provide a substrate for ventricular arrhythmia in BS patients. [source]

Left Ventricular Mass Is Associated With Ventricular Repolarization Heterogeneity One Year After Renal Transplantation

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 2 2008
M. Arnol
Ventricular repolarization heterogeneity (VRH) is associated with the risk of arrhythmia and cardiac death. This study investigated the association between VRH and left ventricular mass (LVM) in renal transplant recipients 1 year after transplantation. Echocardiography and 5-min 12-lead electrocardiogram were recorded and GFR was estimated (eGFR) in 68 nondiabetic patients. Beat-to-beat QT interval variability algorithm was used to calculate SDNN-QT and rMSSD-QT indices of VRH. To quantify QT interval variability relative to heart rate fluctuations, QTRR index was calculated. Left ventricular hypertrophy (LVH) was present in 44 patients (65%). LVM and incidence of LVH were increased in 28 patients with eGFR <60 mL/min/1.73 m2 compared with 40 patients with eGFR ,60 mL/min/1.73 m2 (248 ± 61 g and 86% vs. 210 ± 46 g and 50%, respectively; p < 0.01). A direct correlation was found between LVM and SDNN-QT (R = 0.47, R2= 0.23; p < 0.001), rMSSD-QT (R = 0.27; R2= 0.10; p = 0.034), and QTRR (R = 0.55; R2= 0.31; p < 0.001) indices. In conclusion, greater LVM is associated with increased VRH in renal transplant recipients, providing a link with the high risk of arrhythmia and cardiac death, specifically in patients with decreased graft function. [source]

Influence of Age on Linear and Nonlinear Measures of Autonomic Cardiovascular Modulation

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2010
Michael K. Boettger M.D.
Background: Age has been identified as an independent risk factor for cardiovascular diseases. In addition, autonomic imbalance toward sympathetic preponderance has been shown to facilitate the occurrence of heart disease. Here, we aimed to assess autonomic modulation of cardiovascular parameters during normal ageing applying well-established linear and novel nonlinear parameters. Methods: Linear and nonlinear measures of heart rate variability and complexity as well as measures of QT interval variability and baroreflex sensitivity were obtained from a total of 131 healthy, medication-free participants from a continuous age range between 20 and 90 years, who were allocated to three different age groups. Results: Heart rate variability and complexity significantly decreased with age, while regularity of heart rate time series increased. In addition, QT interval variability linearly increased with age, while baroreflex sensitivity showed a pronounced decrease. Overall, concerning effects of ageing, linear and nonlinear parameters showed equal differentiation between groups. Conclusion: These data indicate a shift of autonomic balance toward sympathetic predominance in higher age groups, limiting the reactiveness of the cardiovascular system to adjust to different demands and increasing the risk for developing tachyarrhythmias. Ann Noninvasive Electrocardiol 2010;15(2):165,174 [source]

Beat-to-Beat QT Interval Variability Is Primarily Affected by the Autonomic Nervous System

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2008
Ph.D., Takanao Mine M.D.
Background: Beat-to-beat QT interval variability is associated with life-threatening arrhythmias and sudden death, however, its precious mechanism and the autonomic modulation on it remains unclear. The purpose of this study was to determine the effect of drugs that modulate the autonomic nervous system on beat-to-beat QT interval. Method: RR and QT intervals were determined for 512 consecutive beats during fixed atrial pacing with and without propranolol and automatic blockade (propranolol plus atropine) in 11 patients without structural heart disease. Studied parameters included: RR, QTpeak (QRS onset to the peak of T wave), QTend (QRS onset to the end of T wave) interval, standard deviation (SD) of the RR, QTpeak, and QTend (RR-SD, QTpeak-SD, and QTend-SD), coefficients of variation (RR- CV, QTpeak-CV, and QTend-CV) from time domain analysis, total power (TP; RR-TP, QTpeak-TP, and QTend-TP), and power spectral density of the low-frequency band (LF; RR-LF, QTpeak-LF, and QTend-LF) and the high-frequency band (HF; RR-HF, QTpeak-HF and QTend-HF). Results: Administration of propranolol and infusion of atropine resulted in the reduction of SD, CV, TP, and HF of the QTend interval when compared to controlled atrial pacing (3.7 ± 0.6 and 3.5 ± 0.5 vs 4.8 ± 1.4 ms, 0.9 ± 0.1 and 0.9 ± 0.1 vs 1.2 ± 0.3%, 7.0 ± 2.2 and 7.0 ± 2.2 vs 13.4 ± 8.1 ms2, 4.2 ± 1.4 and 4.2 ± 1.2 vs 8.4 ± 4.9 ms2, respectively). Administration of propranolol and atropine did not affect RR interval or QTpeak interval indices during controlled atrial pacing. Conclusions: Beat-to-beat QT interval variability is affected by drugs that modulate the autonomic nervous system. [source]