QT variability during rest and exercise in patients with implantable cardioverter defibrillators and healthy controls

Psychological factors and cardiac repolarization instability during anger in implantable cardioverter defibrillator patients

Background

Evidence indicates that emotions such as anger are associated with increased incidence of sudden cardiac death, but the biological mechanisms remain unclear. We tested the hypothesis that, in patients with sudden death vulnerability, anger would be associated with arrhythmic vulnerability, indexed by cardiac repolarization instability.

Methods

Patients with coronary artery disease (CAD) and an implantable cardioverter defibrillator (ICD; n = 41) and healthy controls (n = 26) gave an anger‐inducing speech (anger recall), rated their current (state) anger, and completed measures of trait (chronic) levels of Anger and Hostility. Repolarization instability was measured using QT Variability Index (QTVI) at resting baseline and during anger recall using continuous ECG.

Results

ICD patients had significantly higher QTVI at baseline and during anger recall compared with controls, indicating greater arrhythmic vulnerability overall. QTVI increased from baseline to anger recall to a similar extent in both groups. In ICD patients but not controls, during anger recall, self‐rated anger was related to QTVI (r = .44, p = .007). Trait (chronic) Anger Expression (r = .26, p = .04), Anger Control (r = −.26, p = .04), and Hostility (r = .25, p = .05) were each associated with the change in QTVI from baseline to anger recall (ΔQTVI). Moderation analyses evaluated whether psychological trait associations with ΔQTVI were specific to the ICD group. Results indicated that Hostility scores predicted ΔQTVI from baseline to anger recall in ICD patients (β = 0.07, p = .01), but not in controls.

Conclusions

Anger increases repolarization lability, but in patients with CAD and arrhythmic vulnerability, chronic and acute anger interact to trigger cardiac repolarization lability associated with susceptibility to malignant arrhythmias.

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.

Entropy of cardiac repolarization predicts ventricular arrhythmias and mortality in patients receiving an implantable cardioverter-defibrillator for primary prevention of sudden death

AIMS

The need for a readily available, inexpensive, non-invasive method for improved risk stratification of heart failure (HF) patients is paramount. Prior studies have proposed that distinct fluctuation patterns underlying the variability of physiological signals have unique prognostic value. We tested this hypothesis in an extensively phenotyped cohort of HF patients using EntropyX_QT, a novel non-linear measure of cardiac repolarization dynamics.

METHODS AND RESULTS

In a prospective, multicentre, observational study of 852 patients in sinus rhythm undergoing clinically indicated primary prevention implantable cardioverter-defibrillator (ICD) implantation (2003-10), exposures included demographics, history, physical examination, medications, laboratory results, serum biomarkers, ejection fraction, conventional electrocardiographic (ECG) analyses of heart rate and QT variability, and EntropyX_QT. The primary outcome was first 'appropriate' ICD shock for ventricular arrhythmias. The secondary outcome was composite events (appropriate ICD shock and all-cause mortality). After exclusions, the cohort (n = 816) had a mean age of 60 ± 13 years, 28% women, 36% African Americans, 56% ischaemic cardiomyopathy, and 29 ± 16% Seattle HF risk score (SHFS) 5-year predicted mortality. Over 45 ± 24 months, there were 134 appropriate shocks and 166 deaths. After adjusting for 30 exposures, the hazard ratios (comparing the 5th to 1st quintile of EntropyX_QT) for primary and secondary outcomes were 3.29 (95% CI 1.74-6.21) and 2.28 (1.53-3.41), respectively. Addition of EntropyX_QT to a model comprised of the exposures or SHFS significantly increased net reclassification and the ROC curve area.

CONCLUSIONS

EntropyX_QT measured during ICD implantation strongly and independently predicts appropriate shock and all-cause mortality over follow-up. EntropyX_QT complements conventional risk predictors and has the potential for broad clinical application.

QT Variability Index

The QT Variability Index (QTVI) is a non-invasive measure of repolarization lability that has been applied to a wide variety of subjects with cardiovascular disease. It is a ratio of normalized QT variability to normalized heart rate variability, and therefore includes an assessment of autonomic nervous system tone. The approach assesses beat-to-beat variability in the duration of the QT and U wave in conventional surface electrocardiographic recordings, as well as determines the heart rate variability (HRV) from the same recording. As opposed to T wave alternans, QTVI assesses variance in repolarization at all frequencies. Nineteen studies have published data on QTVI in healthy individuals, while 20 have evaluated its performance in cohorts with cardiovascular disease. Six studies have assessed the utility of QTVI in predicting VT/VF, cardiac arrest, or cardiovascular death. A prospective study utilizing QTVI to determine therapy allocation has not been performed, and therefore the final determination of the value of the metric awaits definitive exploration.

QT variability index on 24-hour Holter independently predicts mortality in patients with heart failure: analysis of Gruppo Italiano per lo Studio della Sopravvivenza nell'Insufficienza Cardiaca (GISSI-HF) trial

BACKGROUND

Increased temporal variability of repolarization, as reflected by QT interval variability measured over 10-15 minutes, predicted spontaneous ventricular arrhythmias and death in implantable cardioverter-defibrillator patients in mild to moderate heart failure (HF).

OBJECTIVE

The purpose of this study was to test our hypothesis that increased mean QT variability over 24 hours would be associated with increased cardiovascular (CV) mortality in a heterogeneous HF population.

METHODS

The Gruppo Italiano per lo Studio della Sopravvivenza nell'Insufficienza Cardiaca-Heart Failure trial prospectively enrolled subjects with HF of any cause. Twenty-four-hour Holter recordings from 268 subjects were analyzed using a template-matching, semiautomatic algorithm to measure QT and heart rate time series in sequential 5-minute epochs over 24 hours. The QT variability index (QTVI) was expressed as the log ratio of the normalized QT variance over normalized heart rate variance. Total and CV mortality were assessed as a function of continuous and dichotomous QTVI (>-0.84) in univariate and multivariable Cox proportional hazards models, adjusting for significant clinical predictors.

RESULTS

After a median of 47 months, there were 53 deaths, of which 44 were from CV causes. A significant association with the outcome was found for QTVI both as continuous and dichotomous variables after adjustment for clinical covariates (age >70, New York Heart Association class III-IV, left ventricular ejection fraction, nonsustained ventricular tachycardia, creatinine): QTVI hazard ratio (HR) 4.0 (confidence interval [CI] 1.8-88; P = .008) for total and 4.4 (CI 1.9-10.1; P = .0006) for CV mortality; QTVI >-0.84 HR 2.0 (CI 1.1-3.6; P = .02) for total and 2.1 (CI 1.1-3.8; P = .02) for CV mortality.

CONCLUSION

Increased repolarization lability, as reflected in QTVI measured over 24 hours, is associated with increased risk for total and CV mortality in a heterogeneous population with chronic HF.

Exercise-induced repolarization changes in patients with stable coronary artery disease

Exercise is a classic trigger of ventricular arrhythmias in the setting of coronary artery disease (CAD). The aim of this study was to examine the changes of novel indexes of repolarization in patients with stable CAD who underwent exercise stress testing. Sixty-seven consecutive patients (mean age 62 ± 9 years, 60 men) who underwent treadmill exercise stress testing according to the Bruce protocol and completed the test without evidence of ischemia were enrolled. Baseline clinical and demographic characteristics were recorded, and indexes of repolarization such as corrected QT (QTc) interval, T peak-to-end (Tpe) interval, and Tpe/QT ratio were assessed at baseline and at peak exercise. A similar group of control subjects without CAD (n = 68, mean age 60 ± 11 years, 52 men) were also studied. All participants successfully completed the test. In the patient group, the QTc interval significantly increased from baseline to peak exercise (median 385 ms [25th percentile 357 ms, 75th percentile 407 ms] vs 418 ms [381 ms, 447 ms], p <0.001). The Tpe interval and the Tpe/QT ratio were also significantly increased at peak exercise (42 ms [36 ms, 60 ms] vs 78 ms [60 ms, 84 ms], p <0.001; and 0.17 [0.14, 0.22] vs 0.21 [0.16, 0.25], p = 0.015). In the control group, the QTc interval did not change significantly, the Tpe interval decreased at peak exercise (62 ms [41 ms, 80 ms] vs 48 ms [40 ms, 78 ms], p = 0.05), and the Tpe/QT ratio did not show a significant change (0.18 [0.12, 0.22] vs 0.16 [1.14, 0.21], p = 0.39). In patients with stable CAD and normal treadmill exercise stress test results, the QTc interval, the Tpe interval, and the Tpe/QT ratio increased during exercise. In conclusion, it is reasonable to assume that despite the absence of inducible ischemia, the spatial dispersion of repolarization is increased during exercise, exposing these patients to increased arrhythmic risk.

Cardiac regulation and electrocardiographic factors contributing to the measurement of repolarization variability

Cellular and macroelectrical instability within the heart ventricles during repolarization is described as a potential triggering mechanism of life-threatening arrhythmias. Although this phenomenon was observed in animal and in vitro studies, significant efforts have been put into the design of computerized technologies to quantify very subtle variations of the repolarization signal from the surface electrocardiograms. These technologies aim at capturing repolarization instability of ventricular repolarization while controlling for the normal variability. Currently, the methods have focused on the autonomic regulation of the heart rate as a primary confounding factor (such as in the QT variability index). However, there are other factors that can influence the measurements of beat-to beat variability of the repolarization segment. Among them, the amplitude of the repolarization signal, the selected lead, and the heart vector orientation are very important and too often neglected in clinical investigations. We will discuss these factors and provocatively describe why they should be cautiously considered to avoid erroneous measurements of repolarization instability.