Beat-to-beat QT interval variability in coronary patients

Effect of Head-Up/-Down Tilt on ECG Segments and Myocardial Temporal Dispersion in Healthy Subjects

The head-up/-down tilt test acutely modifies the autonomic nervous system balance throughout a deactivation of the cardiopulmonary reflexes. The present study examines the influence of head-up/-down tilt on a number of ECG segments. A total of 20 healthy subjects underwent a 5 min ECG and noninvasive hemodynamic bio-impedance recording, during free and controlled breathing, lying at (a) 0°; (b) -45°, tilting up at 45°, and tilting up at 90°. Heart rate variability power spectral analysis was obtained throughout some ECG intervals: P-P (P), P-Q (PQ), P_eQ (from the end of P to Q wave), Q-R peak (QR intervals), Q-R-S (QRS), Q-T peak (QT_p), Q-T end (QT_e), ST_p, ST_e, T peak-T end (T_e), and, eventually, the T_eP segments (from the end of T to the next P waves). Results: In all study conditions, the Low Frequency/High Frequency_PP and LF_{PP normalized units (nu)} were significantly lower than the LF/HF_RR and LF_RRnu, respectively. Conversely, the HF_PP and HF_PPnu were significantly higher in all study conditions. ST_e, QT_p, and QT_e were significantly related to the PP and RR intervals, whereas the T wave amplitude was inversely related to the standard deviations of all the myocardial repolarization variables and to the left ventricular end-systolic volume (LVEDV). The T wave amplitude diminished during head-up tilt and significantly correlated with the LVEDV.

QT variability unrelated to RR variability during stress testing for identification of coronary artery disease

Stress test electrocardiogram (ECG) analysis is widely used for coronary artery disease (CAD) diagnosis despite its limited accuracy. Alterations in autonomic modulation of cardiac electrical activity have been reported in CAD patients during acute ischemia. We hypothesized that those alterations could be reflected in changes in ventricular repolarization dynamics during stress testing that could be measured through QT interval variability (QTV). However, QTV is largely dependent on RR interval variability (RRV), which might hinder intrinsic ventricular repolarization dynamics. In this study, we investigated whether different markers accounting for low-frequency (LF) oscillations of QTV unrelated to RRV during stress testing could be used to separate patients with and without CAD. Power spectral density of QTV unrelated to RRV was obtained based on time-frequency coherence estimation. Instantaneous LF power of QTV and QTV unrelated to RRV were obtained. LF power of QTV unrelated to RRV normalized by LF power of QTV was also studied. Stress test ECG of 100 patients were analysed. Patients referred to coronary angiography were classified into non-CAD or CAD group. LF oscillations in QTV did not show significant differences between CAD and non-CAD groups. However, LF oscillations in QTV unrelated to RRV were significantly higher in the CAD group as compared with the non-CAD group when measured during the first phases of exercise and last phases of recovery. ROC analysis of these indices revealed area under the curve values ranging from 61 to 73%. Binomial logistic regression analysis revealed LF power of QTV unrelated to RRV, both during the first phase of exercise and last phase of recovery, as independent predictors of CAD. In conclusion, this study highlights the importance of removing the influence of RRV when measuring QTV during stress testing for CAD identification and supports the added value of LF oscillations of QTV unrelated to RRV to diagnose CAD from the first minutes of exercise. This article is part of the theme issue 'Advanced computation in cardiovascular physiology: new challenges and opportunities'.

Comparison of QT interval variability of coronary patients without myocardial infarction with that of patients with old myocardial infarction

BACKGROUND

The significant association of myocardial ischemia with elevated QT interval variability (QTV) has been reported in myocardial infarction (MI) patients. However, the influence of the time course of MI on QTV has not been investigated systematically.

METHOD

Short-term QT and RR interval time series were constructed from the 5 min electrocardiograms of 49 coronary patients without MI and 26 patients with old MI (OMI). The QTV, heart rate variability (HRV), and QT-RR coupling of the two groups were analyzed using various time series analysis tools in the time- and frequency-domains, as well as nonlinear dynamics.

RESULTS

Nearly all of the tested QTV indices for coronary patients with OMI were higher than those for patients without MI. However, no significant differences were found between the two groups in any of the variables employed to assess the HRV and QT-RR coupling. All of the markers that showed statistical significances in univariate analyses still possessed the capabilities of distinguishing between the two groups even after adjusting for studied baseline characteristics, including the coronary atherosclerotic burden.

CONCLUSIONS

The results suggested that the QTV increased in coronary patients with OMI compared to those without MI, which might reflect the influence of post-MI remodeling on the beat-to-beat temporal variability of ventricular repolarization. The non-significant differences in the HRV and QT-RR couplings could indicate that there were no differences in the modulation of the autonomic nervous system and interaction of QT with the RR intervals between the two groups.

Short-term QT interval variability in patients with coronary artery disease and congestive heart failure: a comparison with healthy control subjects

This study aimed to test how different QT interval variability (QTV) indices change in patients with coronary artery disease (CAD) and congestive heart failure (CHF). Twenty-nine healthy volunteers, 29 age-matched CAD patients, and 20 age-matched CHF patients were studied. QT time series were derived from 5-min resting lead-II electrocardiogram (ECG). Time domain indices [mean, SD, and QT variability index (QTVI)], frequency-domain indices (LF and HF), and nonlinear indices [sample entropy (SampEn), permutation entropy (PE), and dynamical patterns] were calculated. In order to account for possible influence of heart rate (HR) on QTV, all the calculations except QTVI were repeated on HR-corrected QT time series (QTc) using three correction methods (i.e., Bazett, Fridericia, and Framingham method). Results showed that CHF patients exhibited increased mean, increased SD, increased LF and HF, decreased T-wave amplitude, increased QTVI, and decreased PE, while showed no significant changes in SampEn. Interestingly, CHF patients also showed significantly changed distribution of the dynamical patterns with less monotonously changing patterns while more fluctuated patterns. In CAD group, only QTVI was found significantly increased as compared with healthy controls. Results after HR correction were in common with those before HR correction except for QTc based on Bazett correction. Graphical abstract Fig. The framework of this paper. The arrows show the sequential analysis of the data.

QT interval variability in body surface ECG: measurement, physiological basis, and clinical value: position statement and consensus guidance endorsed by the European Heart Rhythm Association jointly with the ESC Working Group on Cardiac Cellular Electrophysiology

This consensus guideline discusses the electrocardiographic phenomenon of beat-to-beat QT interval variability (QTV) on surface electrocardiograms. The text covers measurement principles, physiological basis, and clinical value of QTV. Technical considerations include QT interval measurement and the relation between QTV and heart rate variability. Research frontiers of QTV include understanding of QTV physiology, systematic evaluation of the link between QTV and direct measures of neural activity, modelling of the QTV dependence on the variability of other physiological variables, distinction between QTV and general T wave shape variability, and assessing of the QTV utility for guiding therapy. Increased QTV appears to be a risk marker of arrhythmic and cardiovascular death. It remains to be established whether it can guide therapy alone or in combination with other risk factors. QT interval variability has a possible role in non-invasive assessment of tonic sympathetic activity.

Etiology of cardiovascular disease in patients with schizophrenia: current perspectives

Cardiovascular morbidity and mortality are important problems among patients with schizophrenia. A wide spectrum of reasons, ranging from genes to the environment, are held responsible for causing the cardiovascular risk factors that may lead to shortening the life expectancy of patients with schizophrenia. Here, we have summarized the etiologic issues related with the cardiovascular risk factors in schizophrenia. First, we focused on heritable factors associated with cardiovascular disease and schizophrenia by mentioning studies about genetics-epigenetics, in the first-episode or drug-naïve patients. In this context, the association and candidate gene studies about metabolic disturbances in schizophrenia are reviewed, and the lack of the effects of epigenetic/posttranscriptional factors such as microRNAs is mentioned. Increased rates of type 2 diabetes mellitus and disrupted metabolic parameters in schizophrenia are forcing clinicians to struggle with metabolic syndrome parameters and related issues, which are also the underlying causes for the risk of having cardiometabolic and cardiovascular etiology. Second, we summarized the findings of metabolic syndrome-related entities and discussed the influence of the illness itself, antipsychotic drug treatment, and the possible disadvantageous lifestyle on the occurrence of metabolic syndrome (MetS) or diabetes mellitus. Third, we emphasized on the risk factors of sudden cardiac death in patients with schizophrenia. We reviewed the findings on the arrhythmias such as QT prolongation, which is a risk factor for Torsade de Pointes and sudden cardiac death or P-wave prolongation that is a risk factor for atrial fibrillation. For example, the use of antipsychotics is an important reason for the prolongation of QT and some other cardiac autonomic dysfunctions. Additionally, we discussed relatively rare issues such as myocarditis and cardiomyopathy, which are important for prognosis in schizophrenia that may have originated from the use of antipsychotic medication. In conclusion, we considered that the studies and awareness about physical needs of patients with schizophrenia are increasing. It seems logical to increase cooperation and shared care between the different health care professionals to screen and treat cardiovascular disease (CVD)-risk factors, MetS, and diabetes in patients with psychiatric disorders, because some risk factors of MetS or CVD are avoidable or at least modifiable to decrease high mortality in schizophrenia. We suggested that future research should focus on conducting an integrated system of studies based on a holistic biopsychosocial evaluation.

The presence of electromechanical mismatch in nonischemic dilated cardiomyopathy is associated with ventricular repolarization instability

BACKGROUND

We analyzed electromechanical mismatch (EMM) and its relationship to ventricular repolarization in patients with nonischemic dilated cardiomyopathy (DCM).

METHODS AND RESULTS

In 39 DCM patients with left ventricular ejection fraction (LVEF) <40% and New York Heart Association functional class ≥III, electroanatomic mapping was used to quantify areas of EMM. High-resolution electrocardiograph was used to measure heart rate variability (HRV) and QT variability index (QTVI). EMM was present in 22 patients (56%, group 1), whereas 17 patients presented no mismatched segments (44%, group 2). The groups did not differ in age (56 ± 10 years in group 1 vs 57 ± 7 years in group 2; P = .82), sex (male: 82% vs 94%; P = .40), LVEF (27 ± 8% vs 25 ± 6%; P = .18), or N-terminal pro-B-type natriuretic peptide (2,350 pg/mL vs 2,831 pg/mL; P = .32). Although heart rate and HRV were similar in both groups (rate: 80 ± 20 beats/min in group 1 vs 74 ± 19 beats/min in group 2 [P = .47]; standard deviation of normal-to normal RR intervals: 106 ± 79 vs 88 ± 115 [P = .61]), we found significantly higher QTVI values in patients from group 1 (-1.15 ± 0.46 vs -1.62 ± 0.51 in group 2; P = .005). In patients with implantable cardioverter-defibrillators, ventricular arrhythmias recorded ≤1 year before enrollment were more frequent in group 1 than in group 2 (58% vs 13%; P = .02).

CONCLUSIONS

EMM is present in a majority of patients with DCM and is associated with ventricular repolarization instability.

Alteration of the QT variability index in end-stage liver disease

Background

A prolonged QT interval can lead to malignant ventricular arrhythmias and sudden cardiac death, and has frequently been found in end-stage liver disease (ESLD). However, myocardial repolarization lability has not yet been fully investigated. We evaluated the QT variability index (QTVI), a marker of temporal inhomogeneity in ventricular repolarization and an abnormality associated with re-entrant malignant ventricular arrhythmias. We determined whether QTVI is affected by the head-up tilt test in ESLD.

Methods

We assessed 36 ESLD patients and 12 control subjects without overt heart disease before and after the 70-degree head-up tilt test. The electrocardiography signal (lead II) was recorded on a computer with an analog-to-digital converter. The RR interval (RRI) and QT interval were measured after recording 5 min of the digitized electrocardiography. Then, the QT intervals were corrected with Bazett's formula (QTc). QTVI was calculated through the following formula: QTVI = log10 [(QTv/QTm2)/(RRIv/RRIm2)], QTv/RRIv: variance of QTI/RRI, QTm/RRIm: mean of QT interval/RRI.

Results

Cirrhotic patients exhibited an elevated QTVI. In particular, Child class C patients had a significantly increased QTVI compared to Child class A patients and the control subjects in the supine position. However, the head-up tilt test did not cause a significant difference in QTVI in relation to the severity of ESLD.

Conclusions

Myocardial repolarization lability was significantly altered in end-stage liver disease. Our data suggest that the severity of ESLD is associated with the degree of the alteration in the QT variability index.

Beat-to-beat QT interval variability and T-wave amplitude in patients with myocardial infarction

The purpose of this study was to investigate the effects of T-wave amplitude and ECG lead on beat-to-beat QT interval variability (QTV) in patients with myocardial infarction (MI) compared to healthy subjects. Standard resting 12-lead ECGs of 79 MI patients and 69 healthy subjects were investigated. Beat-to-beat QT intervals were measured separately for each lead using a template matching algorithm. In addition, we extracted the beat-to-beat T-wave amplitude in each lead. We computed the standard deviation of beat-to-beat QT intervals as a marker of QTV for both healthy subjects and MI patients. Significant QTV differences were observed between the 12 ECG leads as well as between the groups of healthy subjects and MI patients. Beat-to-beat QTV was significantly higher in MI patients than in healthy subjects for half of the leads. Furthermore, significant T-wave amplitude differences across leads and between groups were observed. A significant inverse relation between beat-to-beat QTV and T-wave amplitude was demonstrated. The group differences in QTV remained significant after co-varying for the T-wave amplitude. In conclusion, the increase in beat-to-beat QTV that has been repeatedly reported in patients with MI is partly due to the lower T-wave amplitudes. However, QTV remains significantly increased in MI patients after covarying for this effect.

Relation between beat-to-beat QT interval variability and T-wave amplitude in healthy subjects

OBJECTIVES

Elevated beat-to-beat QT interval variability (QTV) has been associated with increased cardiovascular morbidity and mortality.The aim of this study was to investigate interlead differences in beat-to-beat QTV of 12-lead ECG and its relationship with the T wave amplitude.

METHODS

Short-term 12-lead ECGs of 72 healthy subjects (17 f, 38 ± 14 years; 55 m, 39 ± 13 years) were studied. Beat-to-beat QT intervals were extracted separately for each lead using a template matching algorithm. We calculated the standard deviation of beat-to-beat QT intervals as a marker of QTV as well as interlead correlation coefficients. In addition, we measured the median T-wave amplitude in each lead.

RESULTS

There was a significant difference in the standard deviation of beat-to-beat QT intervals between leads (minimum: lead V(3) (2.58 ± 1.36 ms), maximum: lead III (7.2 ± 6.4 ms), ANOVA: P < 0.0001). Single measure intraclass correlation coefficients of beat-to-beat QT intervals were 0.27 ± 0.18. Interlead correlation coefficients varied between 0.08 ± 0.33 for lead III and lead V(1) and 0.88 ± 0.09 for lead II and lead aVR. QTV was negatively correlated with the T-wave amplitude (r =-0.62, P < 0.0001). There was no significant affect of mean heart rate, age or gender on QT variability (ANOVA: P > 0.05).

CONCLUSIONS

QTV varies considerably between leads in magnitude as well as temporal patterns. QTV is increased when the T wave is small.

Beat-to-beat vectorcardiographic analysis of ventricular depolarization and repolarization in myocardial infarction

Objectives

Increased beat-to-beat variability in the QT interval has been associated with heart disease and mortality. The purpose of this study was to investigate the beat-to-beat spatial and temporal variations of ventricular depolarization and repolarization in vectorcardiogram (VCG) for characterising myocardial infarction (MI) patients.

Methods

Standard 12-lead ECGs of 84 MI patients (22 f, 63±12 yrs; 62 m, 56±10 yrs) and 69 healthy subjects (17 f, 42±18 yrs; 52 m, 40±13 yrs) were investigated. To extract the beat-to-beat QT intervals, a template-matching algorithm and the singular value decomposition method have been applied to synthesise the ECG data to VCG. Spatial and temporal variations in the QRS complex and T-wave loops were studied by investigating several descriptors (point-to-point distance variability, mean loop length, T-wave morphology dispersion, percentage of loop area, total cosine R-to-T).

Results

Point-to-point distance variability of QRS and T-loops (0.13±0.04 vs. 0.10±0.04, p< 0.0001 and 0.16±0.07 vs. 0.13±0.06, p< 0.05) were significantly larger in the MI group than in the control group. The average T-wave morphology dispersion was significantly higher in the MI group than in the control group (62°±8° vs. 38°±16°, p< 0.0001). Further, its beat-to-beat variability appeared significantly lower in the MI group than in the control group (12°±5° vs. 15°±6°, p< 0.005). Moreover, the average percentage of the T-loop area was found significantly lower in the MI group than the controls (46±17 vs. 55±15, p< 0.001). Finally, the average and beat-to-beat variability of total cosine R-to-T were not found statistically significant between both groups.

Conclusions

Beat-to-beat assessment of VCG parameters may have diagnostic attributes that might help in identifying MI patients.

Advanced electrocardiographic parameters change with severity of mitral regurgitation in Cavalier King Charles Spaniels in sinus rhythm

BACKGROUND

Multiple advanced resting ECG (A-ECG) techniques have improved the diagnostic or prognostic value of ECG in detecting human cardiac diseases even before onset of clinical signs or changes in conventional ECG.

OBJECTIVE

To determine which A-ECG parameters, derived from 12-lead A-ECG recordings, change with severity of mitral regurgitation (MR) caused by myxomatous mitral valve disease (MMVD) in Cavalier King Charles Spaniels (CKCSs) in sinus rhythm.

ANIMALS

Seventy-six privately owned CKCSs.

METHODS

Dogs were prospectively divided into 5 groups according to the degree of MR (estimated by color Doppler mapping as the percentage of the left atrial area affected by the MR jet) and presence of clinical signs. High fidelity approximately 5-minute 12-lead ECG recordings were evaluated using custom software to calculate multiple conventional and A-ECG parameters.

RESULTS

Nineteen of 76 ECG parameters were significantly different (P < .05) across the 5 dog groups. A 4-parameter model that incorporated results from 1 parameter of heart rate variability, 2 parameters of QT variability, and 1 parameter of QRS amplitude was identified that explained 82.4% of the variance with a correlation coefficient (R) of 0.60 (P < .01). When age or murmur grade was included in the statistical model the prediction value further increased the R to 0.74 and 0.85 (P < .01), respectively.

CONCLUSION

In CKCSs with sinus rhythm, 4 selected A-ECG parameters further improve prediction of MR jet severity beyond age and murmur grade, although the predictive increment in this study probably is not sufficient to warrant utilization in clinical veterinary practice.

New approach for T-wave end detection on electrocardiogram: performance in noisy conditions

Background

The detection of T-wave end points on electrocardiogram (ECG) is a basic procedure for ECG processing and analysis. Several methods have been proposed and tested, featuring high accuracy and percentages of correct detection. Nevertheless, their performance in noisy conditions remains an open problem.

Methods

A new approach and algorithm for T-wave end location based on the computation of Trapezium's areas is proposed and validated (in terms of accuracy and repeatability), using signals from the Physionet QT Database. The performance of the proposed algorithm in noisy conditions has been tested and compared with one of the most used approaches for estimating the T-wave end point: the method based on the threshold on the first derivative.

Results

The results indicated that the proposed approach based on Trapezium's areas outperformed the baseline method with respect to accuracy and repeatability. Also, the proposed method is more robust to wideband noise.

Conclusions

The trapezium-based approach has a good performance in noisy conditions and does not rely on any empirical threshold. It is very adequate for use in scenarios where the levels of broadband noise are significant.

Increased QT variability in patients with anorexia nervosa--an indicator for increased cardiac mortality?

OBJECTIVE

Increased mortality in anorexia nervosa is associated with autonomic dysfunction and prolongation of the QT interval. In this study, we examined the relative importance of repolarization abnormalities and vagal modulation of heart rate. In particular, we hypothesized that patients with anorexia nervosa show increased QT interval variability, particularly since this measure has been shown to correlate with serious cardiac arrhythmias.

METHOD

We assessed linear and nonlinear heart rate variability (HRV) parameters as well as measures of QT variability in 20 female patients with anorexia nervosa and 20 controls. In patients, parameters were correlated with serum electrolytes.

RESULTS

QT variability was significantly increased in the patient group and correlated negatively with serum potassium concentrations. HRV measures showed a shift of autonomic balance towards vagal predominance.

DISCUSSION

The increase in QT variability might at least in part account for the higher risk of cardiac arrhythmias in patients with anorexia nervosa. Once validated in a prospective study design, parameters of QT variability might serve as surrogate markers for arrhythmia risk stratification in anorexia nervosa. Supplementation with potassium might normalize QT variability abnormalities.

Heart rate variability, QT variability, and electrodermal activity during exercise

PURPOSE

Various measures of autonomic function have been developed, and their applicability and significance during exercise are controversial.

METHODS

Physiological data were therefore obtained from 23 sport students before, during, and after exercise. Measures of R-R interval variability, QT variability index (QTvi), and electrodermal activity (EDA) were calculated. We applied an incremental protocol applying 70%, 85%, 100%, and 110% of the individual anaerobic threshold for standardized comparison.

RESULTS

Although HR increased stepwise, parasympathetic parameters such as the root mean square of successive differences were not different during exercise and do not mirror autonomic function satisfactorily. Similar results were observed with the approximate entropy of R-R intervals (ApEnRR). In contrast, the increase in sympathetic activity was well reflected in the EDA, QTvi, and ApEn of the QT interval (ApEnQT)/ApEnRR ratio.

CONCLUSION

We suggest that linear and nonlinear parameters of R-R variability do not adequately reflect vagal modulation. Sympathetic function can be assessed by EDA, QTvi, or ApEnQT/ApEnRR ratio.

Beat-to-beat heart rate and QT interval variability in first episode neuroleptic-naive psychosis

INTRODUCTION

Though increased risk of sudden death in patients with schizophrenia is well-documented, the mechanisms remain unclear. Recent studies report two known risk factors for sudden cardiac death and other arrhythmias in schizophrenia, i.e., decreased RR interval variability (RRV) and increased QT interval variability (QTV). However, these studies did not control for the effects of medication. Herein, we report the results of our study comparing RRV and QTV in first episode neuroleptic-naive psychosis patients with healthy matched controls.

METHODS

24 patients with first episode neuroleptic naïve psychosis were matched with 26 healthy controls on age and gender. After an overnight fast, all participants underwent an electrocardiogram recording in the morning.

RESULTS

In comparison with matched controls, patients with first episode neuroleptic-naïve psychosis had significantly increased QTV corrected for RRV, and decreased RRV.

CONCLUSIONS

The observed alterations in RRV and QTV may reflect impaired cardiac autonomic function that could underlie risk for abnormal ventricular repolarization and thereby increase the risk of sudden death and other arrhythmias. Our data suggest that RRV and QTV alterations may be independent of medication effects in first episode psychosis patients.

Beat-to-beat QT interval variability is primarily affected by the autonomic nervous system

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 ms(2), 4.2 +/- 1.4 and 4.2 +/- 1.2 vs 8.4 +/- 4.9 ms(2), 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.

Left ventricular mass is associated with ventricular repolarization heterogeneity one year after renal transplantation

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 m(2) compared with 40 patients with eGFR > or =60 mL/min/1.73 m(2) (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, R(2)= 0.23; p < 0.001), rMSSD-QT (R = 0.27; R(2)= 0.10; p = 0.034), and QTRR (R = 0.55; R(2)= 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.

Relationship between beat-to-beat variability of RT-peak and RT-end intervals in normal controls, patients with anxiety, and patients with cardiovascular disease

BACKGROUND

Some studies suggest that it is important to take the end of "T" wave to quantify QT-interval variability, which signifies cardiac repolarization lability, as there is substantial and important information beyond the peak of the T wave on the surface electrocardiogram.

METHODS

In this study, we examined the relationship between the variability of beat-to-beat RTe (beginning of R-peak to T-end) and the variability of RTp (R-peak to T-peak) in the following groups: normal controls (n = 26), patients with anxiety (n = 26), and patients with cardiovascular disease with or without diabetes (n = 63). We obtained ECG sampled at 1024 Hz in lead II configuration in supine posture to obtain beat-to-beat interbeat interval (R-R) and RT-interval variability for 256 seconds.

RESULTS

We found significant positive correlations (r = 0.8; P < 0.00001) in normal controls and patients with anxiety between the variability of RTeVI and RTpVI (RTe and RTp variability indices, respectively, corrected for the mean of RTe and RTp and the mean and the variance of R-R). These correlations were also statistically significant in the medically ill group but the r values were much smaller (r = 0.45 in various groups). The slopes were also significantly different between the two groups (P < 0.001). Bland-Altman plots also showed better agreement between the two measures in the controls and patients with anxiety compared to the group with cardiovascular disease.

CONCLUSIONS

These findings have methodological implications for studies comparing people with and without overt cardiovascular illness. While RTe or RTp variability index may be used interchangeably in normal controls and some patients with no overt cardiovascular problems, it may be more prudent to use both RTe and RTp variability indices in patients with cardiovascular illness. These indices, especially RTeVI, may provide different information about cardiac repolarization lability. Future studies should address the importance of the relative usefulness of these two measures especially in cardiac patients before and after successful treatment.

Acute psychosis leads to increased QT variability in patients suffering from schizophrenia

Patients with schizophrenia have been reported to experience sudden cardiac death 3 times more likely than individuals from the general population. One important factor related to an increased risk of cardiac arrhythmias and sudden death is the prolongation of the QTc interval. This study examined whether acute psychosis might influence the beat-to-beat variability of the QT interval, which reflects effectively cardiac repolarization lability. High resolution electrocardiographic recordings were performed in 25 unmedicated patients suffering from acute schizophrenia and matched controls. From these, parameters of beat-to-beat heart rate and QT variability measures such as approximate entropy and QT variability index (QTvi) were calculated. Measures were correlated with the scale for the assessment of positive symptoms (SAPS) and negative symptoms (SANS). QTvi was significantly higher in patients with schizophrenia compared to controls. While QTvi correlated with the degree of delusions and hallucinations, no correlation with electrolyte concentrations was found. Approximate entropy of heart rate was decreased indicating reduced complexity and decreased vagal tone. In conclusion, increased QT variability in patients with schizophrenia indicates abnormal cardiac repolarization lability, which can result in serious cardiac arrhythmias. The correlation of positive symptoms with QT variability might indicate high sympathetic cardiac activity in these patients, which might be associated with increased cardiovascular mortality.

Real-time multichannel system for beat-to-beat QT interval variability

The measurement of beat-to-beat QT interval variability (QTV) shows clinical promise for identifying several types of cardiac pathology. However, until now, there has been no device capable of displaying, in real time on a beat-to-beat basis, changes in QTV in all 12 conventional leads in a continuously monitored patient. Although several software programs have been designed to analyze QTV, heretofore, such programs have all involved only a few channels (at most) and/or have required laborious user interaction or offline calculations and postprocessing, limiting their clinical utility. This article describes a PC-based electrocardiogram software program recently codeveloped by our laboratories that, in real time, acquires, analyzes, and displays QTV in each of the 8 independent channels that constitute the 12-lead conventional electrocardiogram. The system also analyzes and displays the QTV from QT-interval signals that are derived from multiple channels and from singular value decomposition such that the effect of noise and other artifacts on the QTV results are substantially reduced compared with existing single-channel methods.

Increased pulse-wave velocity in patients with anxiety: implications for autonomic dysfunction

Decreased vagal function is associated with vascular dysfunction. In this study, we compared vascular indices and correlated heart rate and QT variability measures with vascular indices in patients with anxiety disorders and normal controls. We compared age- and sex-matched controls (n=23) and patients with anxiety (n=25) using the Vascular Profiler (VP-1000; Colin Medical Instruments, Japan), approved by the US Food and Drug Administration. Using this machine, we obtained ankle and brachial blood pressure (BP) in both arms (brachial), both legs (ankle), and carotid artery, and lead I electrocardiogram (ECG) and phonocardiogram. Using these signals, pulse-wave velocity (PWV), and arterial stiffness index % and preejection period can be calculated. We also obtained ECG sampled at 1000 Hz in lead II configuration in supine posture to obtain beat-to-beat interbeat interval (R-R) and QT interval variability for 256 s. Patients with anxiety had significantly higher carotid mean arterial pressure (MAP) %, brachial-ankle PWV (BAPWV), arterial stiffness index %, MAP, and diastolic BP of the extremities compared to controls. We found significant negative correlations (r values from .4 to .65; P<.05 to .007) between R-R interval high-frequency (0.15-0.5 Hz) power (which is an indicator of cardiac vagal function), and increased BAPWV and systolic BP of the extremities only in patients. We were unable to find such correlations in controls. We also found significant positive correlations between QT variability index (a probable indicator of cardiac sympathetic function) and MAP of the extremities and BAPWV only in the patient group. These findings suggest an important association between decreased vagal and increased sympathetic function, and decreased arterial compliance and possible atherosclerotic changes and increased BP in patients with anxiety.

Power spectrum analysis and cardiovascular morbidity in anxiety disorders

Spectral analysis of heart rate variability (HRV) and related measures has been shown to be a reliable noninvasive technique enabling quantitative assessment of cardiovascular autonomic regulatory responses to autonomic regulatory mechanisms; it provides a dynamic probe of sympathetic and parasympathetic tone, reflecting the interactions between the two. Over 20 studies reported abnormalities of HRV in anxiety, and patients with heart disease and anxiety are at increased risk for morbidity and mortality. Psychiatric drugs partly correct abnormalities of HRV and, recently, autonomic drugs (beta-blockers) have been studied in anxiety disorders. The authors call for further studies, especially in patients with co-existing anxiety disorders and heart disease, incorporating assessment of HRV.

Coronary artery disease alters ventricular repolarization dynamics in type 2 diabetes

Ventricular repolarization dynamics (VRD) is an important predictor of outcome in diabetes. We examined the potential impact of coronary artery disease (CAD) on VRD in type 2 diabetic patients. We recorded 5-minute high-resolution resting electrocardiograms in 38 diabetic patients undergoing elective coronary angiography, and in 38 age- and gender-matched apparently healthy subjects (controls). Using leads-I and -II, time-domain indices of VRD were calculated. Coronary angiography was regarded as positive if >/= 50% stenosis was found. Angiography was positive in 21 diabetic patients (55%). Patients with CAD had a significantly higher degree of VRD than controls (SDNN(QT): 15.81 +/- 7.22 ms versus 8.94 +/- 6.04 ms; P < 0.001, rMSSD(QT): 21.02 +/- 7.07 ms versus 11.18 +/- 7.45 ms; P < 0.001). Ventricular repolarization dynamics in diabetic patients with negative angiograms did not differ from VRD in controls (SDNN(QT): 8.94 +/- 6.04 ms versus 7.44 +/- 5.72 ms; P = 0.67, rMSSD(QT): 11.18 +/- 7.45 ms versus 10.22 +/- 5.35 ms; P = 0.82). CAD increases VRD in patients with type 2 diabetes. Therefore, changes in ventricular repolarization in diabetic patients may be due to silent CAD rather than due to diabetes per se.

Depression, the autonomic nervous system, and coronary heart disease

Depression is a risk factor for medical morbidity and mortality in patients with coronary heart disease (CHD). Dysregulation of the autonomic nervous system (ANS) may explain why depressed patients are at increased risk. Studies of medically well, depressed psychiatric patients have found elevated levels of plasma catecholamines and other markers of altered ANS function compared with controls. Studies of depressed patients with CHD have also uncovered evidence of ANS dysfunction, including elevated heart rate, low heart rate variability, exaggerated heart rate responses to physical stressors, high variability in ventricular repolarization, and low baroreceptor sensitivity. All of these indicators of ANS dysfunction have been associated with increased risks of mortality and cardiac morbidity in patients with CHD. Further research is needed to determine whether ANS dysfunction mediates the effects of depression on the course and outcome of CHD, and to develop clinical interventions that improve cardiovascular autonomic regulation while relieving depression in patients with CHD.

Beat-to-beat heart rate and QT variability in patients with congestive cardiac failure: blunted response to orthostatic challenge

BACKGROUND

Congestive cardiac failure is associated with increased sympathetic activity and impaired baroreflex function. We sought to test the hypothesis that these patients also have blunted response of beat-to-beat QT interval variability during orthostatic challenge.

METHODS

We compared beat-to-beat heart rate and QT interval data in 17 patients with congestive cardiac failure and 17 age-matched normal controls in supine normal breathing, supine controlled breathing, and standing controlled breathing conditions. The ECG data were acquired in lead II configuration at a sampling rate of 1000 Hz.

RESULTS

Supine controlled breathing was associated with an increase in spectral HF power (0.15-0.5 Hz) of HR and QT interval time series compared to spontaneous breathing condition only in controls. While there were significant changes in HR, HR LF power, HR LF/HF ratios, and QT variability measures in standing posture in controls, there were no such changes in patients.

CONCLUSIONS

This impairment of postural changes of HR variability is most likely due to an impaired baroreceptor function in patients with congestive heart failure. The etiology of this is likely due to an increased cardiac sympathetic and a decreased vagal function. However, the relationship of postural changes in beat-to-beat QT interval variability and baroreflex need further investigation.

Effect of age on diurnal changes of 24-hour QT interval variability

QT interval on the surface electrocardiogram (ECG) reflects the time for repolarization of myocardium and prolongation of QTc is strongly associated with sudden cardiac death. Studies using novel techniques on beat-to-beat QT interval variability (QTV) have shown that it is influenced by the autonomic nervous system and is a predictor of sudden cardiac death. In this study, we examined the awake and sleep changes in QTV in 39 normal adults (mean age, 35 years) and 10 children (mean age, 11 years) using 24-hour ECG records. We obtained eight 5-minute segments of ECG sampled at 1000 Hz from the 24-hour records. Our results show that there is a diurnal variation of QTvm, detrended QT interval variance corrected for mean QT, and QTvi, an index of QTvm divided by heart rate variability corrected for mean heart rate. There was a significant increase in mean QT during sleep, whereas there was a significant decrease in QTvm and QTvi. QTvi significantly increased during the early morning hours. There were significant but modest correlations between the average 24-hour and awake QTvi and age (p < 0.01). There were also decreased low-frequency and high-frequency powers of QT during sleep. Coherence between heart rate and QT interval fluctuations in the range of 0-0.5 Hz, and especially in the high-frequency range (0.15-0.5 Hz), was significantly lower in adults than in children (p < 0.0002). These findings demonstrate diurnal fluctuations in ventricular repolarization lability. We speculate that these effects may relate to changes in cardiac autonomic function and may contribute to the well-known diurnal variation in the incidence of ventricular arrhythmias.

Beat-to-beat repolarisation variability in body surface electrocardiograms

The repolarisation variability in body surface electrocardiograms has been evaluated by beat-to-beat QT interval variability. Interpolated R-peak time and template T-wave matching algorithms were used to determine the characteristic time points of the R-wave and T-wave, respectively. The T-wave time can be determined accurately and robustly by searching for the best match between a template T-wave and measured T-waves. The authors studied 5 min multichannel ECG recordings (35 channels) measured in 20 healthy subjects. A QT variability of 2.24 +/- 0.79 ms was obtained (1.15 +/- 0.30 ms, if linear detrend was used), which is significantly lower than that reported in several other studies. To explore this discrepancy, the sensitivity of the template matching algorithm to periodic and random noise on the ECG was estimated by a simulation study. The results showed that the repolarisation variability depended on selection of the appropriate lead, the signal-to-noise ratio and the effectiveness of baseline correction. Lead II of a standard 12-lead ECG is a reasonable choice for QT variability analysis; however, precordial leads V3-V6 could be better with regard to the amplitude of the T-wave. Poor signal-to-noise ratios can lead to unrealistic values for repolarisation variability.

Heart rate and QT interval variability: abnormal alpha-2 adrenergic function in patients with panic disorder

Anxiety disorders are associated with an increase in cardiovascular mortality. Studies using heart rate (HR) and QT interval variability measures suggest a decreased cardiac vagal function and a relatively increased sympathetic function in anxiety. This is important, as increased sympathovagal balance is associated with life-threatening arrhythmias. Several studies have shown that panic disorder is associated with an increased sensitivity to yohimbine and a blunted growth hormone response to clonidine, which are alpha-2 adrenoceptor antagonist and agonist, respectively. This study investigated the changes in QTvi (QT variance corrected for mean QT interval squared/HR variance corrected for mean HR squared) during placebo, oral clonidine (150 mg) and oral yohimbine (20 mg) in a double-blind design in 12 normal controls and 19 patients with panic disorder. HR and QT variability measures, especially QTvi, were obtained before and after the administration of these drugs to patients in supine and standing postures. As expected, patients with panic disorder became more anxious after yohimbine. In addition, the patients had a significant increase in QTvi after yohimbine and a significant decrease in QTvi after clonidine, which was not seen in the control group. The decreased anxiety after placebo was associated with decreased QTvi in patients. This study supports the previous reports of an abnormal sensitivity of alpha-2 adrenergic receptors in patients with panic disorder compared to controls and partly explains the association of increased cardiovascular mortality with conditions of anxiety. QTvi, a non-invasive indicator of cardiac repolarization lability, appears to be a useful tool to study cardiac sympathetic function.

Effect of nortriptyline and paroxetine on measures of chaos of heart rate time series in patients with panic disorder

Tricyclic antidepressants have notable cardiac side effects, and this issue has become important due to the recent reports of increased cardiovascular mortality in patients with depression and anxiety. Several previous studies indicate that serotonin reuptake inhibitors (SRIs) do not appear to have such adverse effects. Apart from the effects of these drugs on routine 12-lead ECG, the effects on beat-to-beat heart rate (HR) and QT interval time series provide more information on the side effects related to cardiac autonomic function. In this study, we evaluated the effects of two antidepressants, nortriptyline (n=13), a tricyclic, and paroxetine (n=16), an SRI inhibitor, on HR variability in patients with panic disorder, using a measure of chaos, the largest Lyapunov exponent (LLE) using pre- and posttreatment HR time series. Our results show that nortriptyline is associated with a decrease in LLE of high frequency (HF: 0.15-0.5 Hz) filtered series, which is most likely due to its anticholinergic effect, while paroxetine had no such effect. Paroxetine significantly decreased sympathovagal ratios as measured by a decrease in LLE of LF/HF. These results suggest that paroxetine appears to be safer in regards to cardiovascular effects compared to nortriptyline in this group of patients.

Atrioventricular conduction variability in coronary patients

Variability in atrioventricular (AV) conduction has been described in healthy subjects, whereas data for coronary patients are lacking. This study was designed to evaluate AV conduction variability in patients with stable coronary artery disease. Beat-to-beat PR interval variability with 5-minute resting high-resolution electrocardiogram recordings was measured in 30 men (mean age 50.9 years) with effort angina pectoris and 30 age-matched men without clinically evident coronary artery disease (controls). To evaluate the degree of coronary artery disease in coronary patients, coronary angiography was performed. Coronary patients displayed significantly lower values of PR interval variability compared with control subjects (P <.001). Relative PR variability (PRPP) index, calculated as the ratio of normalized PR variability to cycle length variability, was significantly higher in coronary patients (P =.001) and did depend on the degree of coronary artery disease. We concluded that coronary artery disease is associated with decreased beat-to-beat fluctuations in AV conduction. Increased relative PR variability index suggests inhomogeneous AV conduction in stable coronary atherosclerosis.

Effect of fluoxetine, pemoline and placebo on heart period and QT variability in normal humans

OBJECTIVE

To measure the effects of fluoxetine and pemoline on heart period and QT variability.

METHODS

Healthy volunteers were randomly assigned treatment with 20 mg daily of fluoxetine (n=7), 56.25 mg of pemoline (n=7) or placebo (n=9). Twenty-four-hour Holter ECGs were obtained before and after approximately 8 weeks of double-blind treatment.

RESULTS

There were no significant changes in the fluoxetine group. Pemoline was associated with a significant decrease in the high frequency (HF) power (0.15-0.5 Hz, P=.02) and fractal dimension of RR time series (P=.03). QTvi, a measure of QT interval variability, increased in the pemoline group (P=.05).

CONCLUSION

Pemoline, but not fluoxetine, decreases heart period variability (HPV) in the HF power, suggesting a vagolytic effect on cardiac autonomic function. Pemoline is also associated with an increase in QT interval variability, a measure that is sensitive to adrenergic agonists.

Treatment of depression in patients with heart disease

There is a growing body of evidence that depression significantly and adversely affects cardiovascular health. Perhaps the most prominent finding is the documented increase in mortality rate in patients with depression after myocardial infarction. The critical questions of interest to both the clinician and researcher are whether there are safe and effective treatments for depression in patients with heart disease and whether treatment of depression reduces the increased risk of cardiac morbidity and mortality. Though the data are limited and are primarily from open or comparator trials, the tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and specific psychotherapies appear to be effective for treatment of depression in patients with ischemic heart disease (IHD), and response rates are comparable to those reported in depressed patients without heart disease; however, there has been only one placebo-controlled trial to date, and therefore it is premature to come to definitive conclusions regarding the efficacy of antidepressant therapies in this patient population. With respect to safety, the TCAs are associated with documented adverse cardiovascular effects, including increases in heart rate, orthostatic hypotension, and conduction delays. Use of TCAs in patients with IHD carries a proven increased risk of cardiac morbidity and perhaps of mortality as well. The SSRIs appear to be relatively safe and effective treatment for depression in patients with comorbid IHD.

Beat-to-beat QT interval variability before and after cardiac surgery

Non-uniform recovery of excitability may be essential in triggering malignant ventricular tachycardia after cardiac surgery. Thirty-five channels ECG was recorded for 6 min in 27 patients before and after heart surgery and in 20 control subjects. Off-line analysis was performed. RR interval duration, RR SD, QT SD and power spectra of RR variability were computed from 256 s stable RR and QT interval series. When compared to controls, patients had decreased RR SD and increased QT SD before surgery (p<0.002 and p<0.0005, respectively); RR SD further decreased and QT SD increased after the surgery (p<0.0001 and p<0.0002, respectively). Increase of QT variability and decrease of RR variability after cardiac surgery may reflect disrupted electrophysiological stability of the myocardium and thus electrophysiological substrate for triggering malignant arrhythmia.

Beat-to-beat assessment of QT/RR interval ratio in severe heart failure and overt myocardial ischemia: a measure of electrical integrity in diseased hearts

The study was designed to assess the beat-to-beat variation of ventricular repolarization in patients with myocardial ischemia, hear failure, and in normal subjects. Autonomic tone may alter the dynamic QT/RR interval relation and thus may be involved in ventricular arrhythmia development, especially in the diseased heart. The study included 145 patients (age 16-86 years) with CHF (LVEF < or = 0.30) or unstable angina pectoris (LVEF > 0.60). The control group consisted of healthy volunteers giving physiological baseline measures for the evaluated parameters: cycle length, QT interval, and QT/RR interval ratio during three time periods. In patients with myocardial ischemia (LVEF > 0.60) and healthy subjects the QT/RR interval ratio did not reveal significant differences between both groups (QT/RR(CAD) = 0.36 +/- 0.77 vs QT/RR(controls) = 0.28 +/- 0.83; NS). In sharp contrast, in patients with severe heart failure, RR dependent instantaneous variation of the QT interval was almost missing and regression line analysis disclosed a QT/RR interval slope substantially enhanced by 196% (compared to normal subjects) and 131% (compared to CAD patients; P < 0.05) with a complete loss of circadian modulation (QT/RR(CHF) = 0.83 +/- 0.71 vs QT/RR(CAD) = 0.36 +/- 0.77 vs QT/RR(controls) = 0.28 +/- 0.83; P < 0.05). Beat-to-beat QT interval assessment provides a dynamic parameter of physiological and altered repolarization in defined study groups. Compared to other groups (preserved LVEF), patients with left ventricular impairment exhibited a significantly increased sensitivity of repolarization to cycle length (enhanced QT/RR interval ratio) and a blunted circadian modulation of the QT interval. This is consistent with concept that increased repolarization disparity may be deleterious being a potential pathophysiological basis for enhanced arrhythmic risk.

Effects of depression on QT interval variability after myocardial infarction

OBJECTIVES

Clinical depression is a risk factor for cardiac mortality in patients with coronary heart disease. High QT interval variability is a risk factor for arrhythmic events, including sudden cardiac death. The purpose of this study was to determine whether depression is associated with increased QT variability in patients recovering from myocardial infarction.

METHODS

Twenty patients with major depression recovering from a recent myocardial infarction were matched with 20 nondepressed post-myocardial infarction patients on age and sex, and all underwent 24-hour Holter monitoring.

RESULTS

There were no differences between groups on average heart rate, heart rate variability, or other electrocardiographic measures. However, the QT interval showed significantly greater variability in the depressed than in the nondepressed group, especially at midnight and at 6:00 AM.

CONCLUSIONS

Depressed post-myocardial infarction patients may be at greater risk for sudden cardiac death as a result of abnormalities in ventricular repolarization. More work is needed to determine the clinical and prognostic significance of QT variability in these patients.

Significant difference in beat-to-beat QT interval variability among different leads

QT interval on the surface electrocardiogram (ECG) reflects the time for repolarization of myocardium, and QTc prolongation is strongly associated with sudden cardiac death. Findings of studies that have examined the dispersion of QT interval in 12-lead ECGs strongly suggest that an increased QT dispersion between different leads is associated with an increased risk of cardiac mortality. Recent studies using novel techniques on beat-to-beat QT interval variability have also shown that the interval is both influenced by the autonomic nervous system and a predictor of sudden cardiac death. However, in these studies the variability of QT was quantified in a single lead, and thus is different from QT dispersion. The present study examined whether there was a significant difference between QT variability (detrended QT variance [QTv]) and Qtvi (index of QT interval variability corrected for mean QT squared divided by heart rate variability corrected for mean heart rate squared) in 17 data sets of continuous ECGs recorded in three channels (leads V(5), V(1), and V(3)) during ambulatory monitoring of ECG digitized at 1,000 Hz. The results showed a highly significant difference between QT variability measures (QTv and QTvi) (P < 0.0001) in two of three lead configurations that were used (V(5) and V(1) versus V(3)). This finding underscores the importance of using the same lead while recording ECG for the calculation of QT variability, though further investigations are clearly warranted before any definitive conclusion can be made. These findings should be evaluated in relation to the issue of local versus global cardiac repolarization of ventricular myocardium.