QT Variability and Other Electrocardiographic Predictors of Sudden Cardiac Death

This thesis investigates sudden cardiac death, focusing of QT variability, heart-rate variability and other electrocardiographic markers. Topics include: - Normal values for heart-rate variability - Normal values for QT variability - The association of QT variability with sudden cardiac death - The association of QT variability with Heart Failure - The association of thyroid function and Sudden cardiac death - The association of thyroid function with QT variability - The association of COPD with sudden cardiac deat

Increased Short-Term Beat-To-Beat Variability of QT Interval in Patients with Acromegaly.

Cardiovascular diseases, including ventricular arrhythmias are responsible for increased mortality in patients with acromegaly. Acromegaly may cause repolarization abnormalities such as QT prolongation and impairment of repolarization reserve enhancing liability to arrhythmia. The aim of this study was to determine the short-term beat-to-beat QT variability in patients with acromegaly. Thirty acromegalic patients (23 women and 7 men, mean age+/-SD: 55.7+/-10.4 years) were compared with age- and sex-matched volunteers (mean age 51.3+/-7.6 years). Cardiac repolarization parameters including frequency corrected QT interval, PQ and QRS intervals, duration of terminal part of T waves (Tpeak-Tend) and short-term variability of QT interval were evaluated. All acromegalic patients and controls underwent transthoracic echocardiographic examination. Autonomic function was assessed by means of five standard cardiovascular reflex tests. Comparison of the two groups revealed no significant differences in the conventional ECG parameters of repolarization (QT: 401.1+/-30.6 ms vs 389.3+/-16.5 ms, corrected QT interval: 430.1+/-18.6 ms vs 425.6+/-17.3 ms, QT dispersion: 38.2+/-13.2 ms vs 36.6+/-10.2 ms; acromegaly vs control, respectively). However, short-term beat-to-beat QT variability was significantly increased in acromegalic patients (4.23+/-1.03 ms vs 3.02+/-0.80, P<0.0001). There were significant differences between the two groups in the echocardiographic dimensions (left ventricular end diastolic diameter: 52.6+/-5.4 mm vs 48.0+/-3.9 mm, left ventricular end systolic diameter: 32.3+/-5.2 mm vs 29.1+/-4.4 mm, interventricular septum: 11.1+/-2.2 mm vs 8.8+/-0.7 mm, posterior wall of left ventricle: 10.8+/-1.4 mm vs 8.9+/-0.7 mm, P<0.05, respectively). Short-term beat-to-beat QT variability was elevated in patients with acromegaly in spite of unchanged conventional parameters of ventricular repolarization. This enhanced temporal QT variability may be an early indicator of increased liability to arrhythmia

Normal Values of QT Variability in 10-s Electrocardiograms for all Ages

Aims: QT variability is a promising electrocardiographic marker. It has been studied as a screening tool for coronary artery disease and left ventricular hypertrophy, and increased QT variability is a known risk factor for sudden cardiac death. Considering that comprehensive normal values for QT variability were lacking, we set out to establish these in standard 10-s electrocardiograms (ECGs) covering both sexes and all ages. Methods: Ten-second, 12-lead ECGs were provided by five Dutch population studies (Pediatric Normal ECG Study, Leiden University Einthoven Science Project, Prevention of Renal and Vascular End-stage Disease Study, Utrecht Health Project, Rotterdam Study). ECGs were recorded digitally and processed by well-validated analysis software. We selected cardiologically healthy participants, 46% being women. Ages ranged from 11 days to 91 years. After quality control, 13,828 ECGs were available. We assessed three markers: standard deviation of QT intervals (SDqt), short-term QT variability (STVqt), and QT variability index (QTVI). Results: For SDqt and STVqt, the median and the lower limit of normal remained stable with age. The upper limit of normal declined until around age 45, and increased strongly in the elderly, notably so in women. This implies that a subset of the population, small enough not to have appreciable effect on the median, shows a high degree of QT variability with a possible risk of arrhythmias or worse, especially in women. Otherwise, sex differences were negligible in all three measurements. For QTVI, median, and normal limits decreased until age 20, and steadily went up afterwards except for the lower limit of normal, which flattens off after age 65. Conclusion: We report the first set of normal values for QT variability based on 10-s ECGs, for all ages and both sexes

Changes in heart rate variability and QT variability during the first trimester of pregnancy

The risk of new-onset arrhythmia during pregnancy is high, presumably relating to changes in both haemodynamic and cardiac autonomic function. The ability to non-invasively assess an individual's risk of developing arrhythmia during pregnancy would therefore be clinically significant. We aimed to quantify electrocardiographic temporal characteristics during the first trimester of pregnancy and to compare these with non-pregnant controls.Ninety-nine pregnant women and sixty-three non-pregnant women underwent non-invasive cardiovascular and haemodynamic assessment during a protocol consisting of various physiological states (postural manoeurvres, light exercise and metronomic breathing). Variables measured included stroke volume, cardiac output, heart rate, heart rate variability, QT and QT variability and QTVI (a measure of the variability of QT relative to that of RR).Heart rate (p &#60; 0.0005, p &#60; 0.0005, p &#60; 0.0005) and cardiac output (p = 0.043, p &#60; 0.0005, p &#60; 0.0005) were greater in pregnant women in all physiological states (respectively for the supine position, light exercise and metronomic breathing state), whilst stroke volume was lower in pregnancy only during the supine position (p &#60; 0.0005). QTe (Q wave onset to T wave end) and QTa (T wave apex) were significantly shortened (p &#60; 0.05) and QTeVI and QTaVI were increased in pregnancy in all physiological states (p &#60; 0.0005). QT variability (p &#60; 0.002) was greater in pregnant women during the supine position, whilst heart rate variability was reduced in pregnancy in all states (p &#60; 0.0005).Early pregnancy is associated with substantial changes in heart rate variability, reflecting a reduction in parasympathetic tone and an increase in sympathetic activity. QTVI shifted to a less favourable value, reflecting a greater than normal amount of QT variability. QTVI appears to be a useful method for quantifying changes in QT variability relative to RR (or heart rate) variability, being sensitive not only to physiological state but also to gestational age. We support the use of non-invasive markers of cardiac electrical variability to evaluate the risk of arrhythmic events in pregnancy, and we recommend the use of multiple physiological states during the assessment protocol

Stability analysis of RR and QT variability for cosmonauts data

Stability analysis of cardiovascular oscillations together with nonlinear nalysis gives important and complements information about their autonomic regulations. New nonlinear tools like M-indexes gives possibility to analyze stability of the most pure dynamic process that is observed with the help of RR and QT intervals variability

Transcranial direct current stimulation improves the QT variability index and autonomic cardiac control in healthy subjects older than 60 years

Background: Noninvasive brain stimulation technique is an interesting tool to investigate the causal relation between cortical functioning and autonomic nervous system (ANS) responses. Objective: The objective of this report is to evaluate whether anodal transcranial direct current stimulation (tDCS) over the temporal cortex influences short-period temporal ventricular repolarization dispersion and cardiovascular ANS control in elderly subjects. Subjects and methods: In 50 healthy subjects (29 subjects younger than 60 years and 21 subjects older than 60 years) matched for gender, short-period RR and systolic blood pressure spectral variability, QT variability index (QTVI), and noninvasive hemodynamic data were obtained during anodal tDCS or sham stimulation. Results: In the older group, the QTVI, low-frequency (LF) power expressed in normalized units, the ratio between LF and high-frequency (HF) power, and systemic peripheral resistances decreased, whereas HF power expressed in normalized units and α HF power increased during the active compared to the sham condition (P,0.05). Conclusion: In healthy subjects older than 60 years, tDCS elicits cardiovascular and autonomic changes. Particularly, it improves temporal ventricular repolarization dispersion, reduces sinus sympathetic activity and systemic peripheral resistance, and increases vagal sinus activity and baroreflex sensitivity

SB-QTVW: An alternate index to differentiate between healthy and acute ischemic/infarcted patients using vector magnitude derived QT variability

Myocardial ischemia alters ventricular repolarization through a variety of mechanisms. Studies show that QTVI, an index of QT variability, is elevated during acute ischemia and cardiomyopathy. This indicates an increased QT variability in ischemic patients. Preliminary studies from our laboratory showed that the length of vector magnitude derived QT interval varies by less than 16 ms in healthy controls, and frequently varies more than 16 ms in ischemic patients. With this study, we introduced an alternative index - QT Variability Window (QTVW), and tested the hypothesis that ischemia causes the length of resting QT intervals in vector magnitude to vary more than a QTVW of 16 ms. Results from our study support our hypothesis. Furthermore, in certain cases, our algorithm was able to differentiate between the healthy controls and acute ischemic patients using as few as 20 consecutive beats. These findings provide an alternative index, QTVW, to assess ventricular repolarization following ischemia

Nonlinear analysis of RR and QT variability for cosmonauts data

Nonlinear analysis of cardiovascular oscillations gives important information about their autonomic regulations. New nonlinear tools like Mindexes gives possibility to analyze the most pure dynamic process that are observed by RR and QT intervals variability. Time series classification that is based on Mindexes allows using stationary methods of oscillation variability like Fourier analysis for sure