Estimates of repolarization dispersion from electrocardiographic measurements

Time-Warping Analysis of the T-Wave Peak-to-End Interval to Quantify Ventricular Repolarization Dispersion During Ischemia

Variations in the dispersion of ventricular repolarization can be quantified by T-wave time-warping based index, dw. However, the early phase of the T-wave can be affected by ST-segment changes during ischemia. We hypothesized that restricting dw to the T-wave peak-to-end ( Tpe) would circumvent this limitation while still quantifying variations in repolarization dispersion. A total of 101 ECG recordings from patients undergoing coronary occlusion, together with their control recordings, were analyzed. A series of dw values was calculated by quantifying the Tpe morphological variations between the T-waves at different occlusion stages and a baseline T-wave. We introduced a normalized version of dw, Rd, reflecting variations of dw during occlusion relative to control recordings ( Rd = 1 corresponds to the same level of variation). The dw series followed a gradually increasing trend with occlusion time, reaching median [range] Rd values of 9.44 [1.01, 80.74] at the occlusion end. Rd at occlusion end was significantly higher than threshold values of 1, 2, 5, and 10 in 94.1%, 85.11%, 64.4% and 48.5% of patients, respectively. The spatial lead-wise analysis of dw showed distinct distributions depending on the occluded artery, suggesting a relation with the ischemia location. The relative variation R with ischemia of index dw (9.4) is greater than that of the T-wave amplitude (7.7), Tpe interval (2.7) and T-wave width (3.0). In conclusion, dw tracks ischemic-induced variations in repolarization dispersion in a more robust manner than classical indexes, avoiding the impact of ST segment elevation/depression or early T-wave distortions, thus warranting further clinical studies.

Tipping the scales of understanding: An engineering approach to design and implement whole-body cardiac electrophysiology experimental models

The study of cardiac electrophysiology is built on experimental models that span all scales, from ion channels to whole-body preparations. Novel discoveries made at each scale have contributed to our fundamental understanding of human cardiac electrophysiology, which informs clinicians as they detect, diagnose, and treat complex cardiac pathologies. This expert review describes an engineering approach to developing experimental models that is applicable across scales. The review also outlines how we applied the approach to create a set of multiscale whole-body experimental models of cardiac electrophysiology, models that are driving new insights into the response of the myocardium to acute ischemia. Specifically, we propose that researchers must address three critical requirements to develop an effective experimental model: 1) how the experimental model replicates and maintains human physiological conditions, 2) how the interventions possible with the experimental model capture human pathophysiology, and 3) what signals need to be measured, at which levels of resolution and fidelity, and what are the resulting requirements of the measurement system and the access to the organs of interest. We will discuss these requirements in the context of two examples of whole-body experimental models, a closed chest in situ model of cardiac ischemia and an isolated-heart, torso-tank preparation, both of which we have developed over decades and used to gather valuable insights from hundreds of experiments.

Weighted Time Warping Improves T-wave Morphology Markers Clinical Significance

Background: T-wave (TW) morphology indices based on time-warping (d_w) have shown significant cardiovascular risk stratification value. However, errors in the location of TW boundaries may impact their prognostic power. Our aim was to test the hypothesis that a weighted time-warping function (WF) would reduce the sensitivity of d_w to these errors and improve their clinical significance. Methods: The WFs were proportional to (i) the reference TW (T), and (ii) the absolute value of its derivative (D). The index d_w was recalculated using these WFs, and its performance was compared to the unweighted control case (C) in four different scenarios: 1) robustness against simulated TW boundaries location errors; 2) ability to retain physiological information in an electrophysiological cardiac model; 3) ability to monitor blood potassium concentration changes ([K⁺]) in 29 hemodialysis (HD) patients; 4) and the sudden cardiac death (SCD) risk stratification value of the TW morphology restitution (TMR) index, derived from d_w, in 651 chronic heart failure (CHF) patients. Results and Discussion: The WFs led to a reduced sensitivity (R) of d_w to TW boundary location errors as compared to C (median R=0.19 and 0.22 and 0.35 for T, D and C, respectively). They also preserved the physiological relationship between d_w and repolarization dispersion changes at ventricular level. No improvements in [K⁺] tracking were observed for the HD patients (Pearsons median correlation [r] between [K⁺] and d_w was 0.86r0.90 for T, D and C). In CHF patients, the SCD risk stratification value of TMR was improved by applying T (hazard ratio, HAR, of 2.80), followed by D (HAR=2.32) and C (HAR=2.23). Conclusions and Significance: The proposed WFs, with T showing the best performance, increased the robustness of time-warping based markers against TW location errors preserving their physiological information content and boosting their SCD risk stratification value. Results from this work support the use of T when deriving d_w for future clinical applications.

Spectrum of clinical applications of interlead ECG heterogeneity assessment: From myocardial ischemia detection to sudden cardiac death risk stratification

Heterogeneity in depolarization and repolarization among regions of cardiac cells has long been recognized as a major factor in cardiac arrhythmogenesis. This fundamental principle has motivated development of noninvasive techniques for quantification of heterogeneity using the surface electrocardiogram (ECG). The initial approaches focused on interval analysis such as interlead QT dispersion and T_peak -T_end difference. However, because of inherent difficulties in measuring the termination point of the T wave and commonly encountered irregularities in the apex of the T wave, additional techniques have been pursued. The newer methods incorporate assessment of the entire morphology of the T wave and in some cases of the R wave as well. This goal has been accomplished using a number of promising vectorial approaches with the resting 12-lead ECG. An important limitation of vectorcardiographic analyses is that they require exquisite stability of the recordings and are not inherently suitable for use in exercise tolerance testing (ETT) and/or ambulatory ECG monitoring for provocative stress testing or evaluation of the influence of daily activities on cardiac electrical instability. The objectives of the present review are to describe a technique that has been under clinical evaluation for nearly a decade, termed "interlead ECG heterogeneity." Preclinical testing data will be briefly reviewed. We will discuss the main clinical findings with regard to sudden cardiac death risk stratification, heart failure evaluation, and myocardial ischemia detection using standard recording platforms including resting 12-lead ECG, ambulatory ECG monitoring, ETT, and pharmacologic stress testing in conjunction with single-photon emission computed tomography myocardial perfusion imaging.

Breathing rate and heart rate as confounding factors in measuring T wave alternans and morphological variability in ECG

OBJECTIVE

High morphological variability magnitude (MVM) and microvolt T wave alternans (TWA) within an electrocardiogram (ECG) signifies increased electrical instability and risk of sudden cardiac death. However, the influence of breathing rate (BR), heart rate (HR), and signal-to-noise ratio (SNR) is unknown and may inflate measured values.

APPROACH

We synthesize ECGs with morphologies derived from the Physikalisch-Technische Bundesanstalt Database. We calculate MVM and TWA at varying BRs, HRs and SNRs. We compare the MVM and TWA of signal with versus without breathing at varying HRs and SNRs. We then quantify the percentage of MVM and TWA estimates affected by BR and HR in a healthy population and assess the effect of removing these affected estimates on a method for classifying individuals with and without post-traumatic stress disorder (PTSD).

MAIN RESULTS

For signals with high SNR (>15 dB), MVM is significantly increased when BRs are > 9 respirations/minute (rpm) and HRs are < 100 beats/minute (bpm). Increased TWAs are detected for HR/BR pairs of 60/15, 60/30 and 120/30 bpm/rpm. For 18 healthy participants, 8.33% of TWA windows and 66.76% of MVM windows are affected by BR and HR. On average, the number of windows with TWA elevations > 47 μV decreases by 23% after excluding regions with significant BR and HR effect. Adding HR and BR to a morphological variability feature increases the classification performance by 6% for individuals with and without PTSD.

SIGNIFICANCE

Physiological BR and HR significantly increase MVM and TWA , indicating that BR and HR should be considered separately as confounders. The code for this work has been released as part of an open-source toolbox.

Dispersion of ventricular repolarization: Temporal and spatial

Repolarization heterogeneity (RH) is an intrinsic property of ventricular myocardium and the reason for T-wave formation on electrocardiogram (ECG). Exceeding the physiologically based RH level is associated with appearance of life-threatening ventricular arrhythmias and sudden cardiac death. In this regard, an accurate and comprehensive evaluation of the degree of RH parameters is of importance for assessment of heart state and arrhythmic risk. This review is devoted to comprehensive consideration of RH phenomena in terms of electrophysiological processes underlying RH, cardiac electric field formation during ventricular repolarization, as well as clinical significance of RH and its reflection on ECG parameters. The formation of transmural, apicobasal, left-to-right and anterior-posterior gradients of action potential durations and end of repolarization times resulting from the heterogenous distribution of repolarizing ion currents and action potential morphology throughout the heart ventricles, and the different sensitivity of myocardial cells in different ventricular regions to the action of pharmacological agents, temperature, frequency of stimulation, etc., are being discussed. The review is focused on the fact that RH has different aspects – temporal and spatial, global and local; ECG reflection of various RH aspects and their clinical significance are being discussed. Strategies for comprehensive assessment of ventricular RH using different ECG indices reflecting various RH aspects are presented.

Body Surface Mapping of Ventricular Repolarization Heterogeneity: An Ex-vivo Multiparameter Study

Background

Increased heterogeneity of ventricular repolarization is associated with life-threatening arrhythmia and sudden cardiac death (SCD). T-wave analysis through body surface potential mapping (BSPM) is a promising tool for risk stratification, but the clinical effectiveness of current electrocardiographic indices is still unclear, with limited experimental validation. This study aims to investigate performance of non-invasive state-of-the-art and novel T-wave markers for repolarization dispersion in an ex vivo model.

Methods

Langendorff-perfused pig hearts (N = 7) were suspended in a human-shaped 256-electrode torso tank. Tank potentials were recorded during sinus rhythm before and after introducing repolarization inhomogeneities through local perfusion with dofetilide and/or pinacidil. Drug-induced repolarization gradients were investigated from BSPMs at different experiment phases. Dispersion of electrical recovery was quantified by duration parameters, i.e., the time interval between the peak and the offset of T-wave (T_PEAK-T_END) and QT interval, and variability over time and electrodes was also assessed. The degree of T-wave symmetry to the peak was quantified by the ratio between the terminal and initial portions of T-wave area (Asy). Morphological variability between left and right BSPM electrodes was measured by dynamic time warping (DTW). Finally, T-wave organization was assessed by the complexity of repolarization index (CR), i.e., the amount of energy non-preserved by the dominant eigenvector computed by principal component analysis (PCA), and the error between each multilead T-wave and its 3D PCA approximation (NMSE). Body surface indices were compared with global measures of epicardial dispersion of repolarization, and with local gradients between adjacent ventricular sites.

Results

After drug intervention, both regional and global repolarization heterogeneity were significantly enhanced. On the body surface, T_PEAK-T_END was significantly prolonged and less stable in time in all experiments, while QT interval showed higher variability across the interventions in terms of duration and spatial dispersion. The rising slope of the repolarization profile was steeper, and T-waves were more asymmetric than at baseline. Interventricular shape dissimilarity was enhanced by repolarization gradients according to DTW. Organized T-wave patterns were associated with abnormal repolarization, and they were properly described by the first principal components.

Conclusion

Repolarization heterogeneity significantly affects T-wave properties, and can be non-invasively captured by BSPM-based metrics.

Magnetic Resonance Imaging of Contracting Ultrathin Cardiac Tissue

OBJECTIVE

Integrating cardiac-tissue patches into the beating heart and evaluating the long-term effects of such integration on cardiac contractility are two challenges in an emerging field of regenerative medicine. This pilot study presents tools for the imaging of contracting multicellular cardiac tissue constructs (MTCs) in vitro and demonstrates the feasibility of tracking the early development of strand geometry and contractions in ultrathin strands and layers of cardiac tissue using CINE MRI.

APPROACH

Cultured, ultrathin (~50-100-micron) MTCs of rat neonatal cardiomyocytes were plated in rectangular cell chambers (4.5 × 2.0 cm) with and without ultrathin, carbon EP electrodes embedded in the floor of the cell chamber. Two-dimensional, steady-state free precession (SSFP) CINE MRI, cell microscopy, and tissue photography were performed on Days 5-9 of cell development. Potential confounders and MRI artifacts were evaluated using non-contracting cardiac tissues and cell-free chambers filled with the cell-culture medium.

MAIN RESULTS

Synchronized contractions formed by Day 7; individual contracting tissue strands became identifiable by Day 9. The global patterns and details of the strand geometry and movement patterns in the SSFP images were in excellent agreement with microscopic and photographic images. No synchronized movement was identifiable by either microscopy or CINE MRI in the non-contracting MTCs or the cell-free medium. The EP recordings revealed well-defined depolarization and repolarization waveforms; the imaging artifacts generated by the carbon electrodes were small.

SIGNIFICANCE

This pilot study demonstrates the feasibility of imaging cardiac-strand patterns and contractile activity in ultrathin, two-dimensional cardiac tissue in commonly used clinical scanners.

Tracking interlead heterogeneity of R- and T-wave morphology to disclose latent risk for sudden cardiac death

Sudden cardiac death (SCD) due primarily to ventricular fibrillation claims 1.5 million lives worldwide each year. In 45%-50% of cases, it is the first manifestation of underlying heart disease. Traditional risk factors including smoking, hypertension, age, sex, as well as depressed left ventricular ejection fraction lack sufficient sensitivity and specificity to forewarn of impending life-threatening arrhythmias. There has been a decades-long search for electrocardiographic (ECG) markers of SCD risk. Several interval-based indices such as QT dispersion and T_peak-T_end interval held initial promise but ultimately yielded mixed results. Recently, the focus has been on interlead heterogeneity of R- and T-wave morphology. The new approaches have involved advanced analytical tools including vectorcardiographic techniques and second central moment analysis of QRS-aligned templates to quantify heterogeneity of depolarization and repolarization waveforms. The results of current studies appear to be robust and worthy of further exploration. This review examines the electrophysiological underpinnings of heterogeneity-based risk assessment and provides an update of clinical techniques. We also discuss future directions whereby tracking heterogeneity may help to disclose latent risk for SCD not only in ECG recordings made at rest but also during ambulatory ECG monitoring and exercise tolerance testing.

A Theoretical Analysis of Electrogastrography (EGG) Signatures Associated With Gastric Dysrhythmias

Routine screening and accurate diagnosis of chronic gastrointestinal motility disorders represent a significant problem in current clinical practice. The electrogastrography (EGG) provides a noninvasive option for assessing gastric slow waves, as a means of diagnosing gastric dysrhythmias, but its uptake in motility practice has been limited partly due to an incomplete sensitivity and specificity. This paper presents the development of a human whole-organ gastric model to enable virtual (in silico) testing of gastric electrophysiological dispersion in order to improve the diagnostic accuracy of EGG. The model was developed to simulate normal gastric slow wave conduction as well as three types of dysrhythmias identified in recent high-resolution gastric mapping studies: conduction block, re-entry, and ectopic pacemaking. The stomach simulations were then applied in a torso model to identify predicted EGG signatures of normal and dysrhythmic slow wave profiles. The resulting EGG data were compared using percentage differences and correlation coefficients. Virtual EGG channels that demonstrated a percentage difference over 100% and a correlation coefficient less than ±0.2 (threshold relaxed to ±0.5 for the ectopic pacemaker case) were further investigated for their specific distinguishing features. In particular, anatomical locations from the epigastric region and specific channel configurations were identified that could be used to clinically diagnose the three classes of human gastric dysrhythmia. These locations and channels predicted by simulations present a promising methodology for improving the clinical reliability and applications of EGG.

Automatic Identification of the Repolarization Endpoint by Computing the Dominant T-wave on a Reduced Number of Leads

Electrocardiographic (ECG) T-wave endpoint (T_end) identification suffers lack of reliability due to the presence of noise and variability among leads. T_end identification can be improved by using global repolarization waveforms obtained by combining several leads. The dominant T-wave (DTW) is a global repolarization waveform that proved to improve T_end identification when computed using the 15 (I to III, aVr, aVl, aVf, V1 to V6, X, Y, Z) leads usually available in clinics, of which only 8 (I, II, V1 to V6) are independent. The aim of the present study was to evaluate if the 8 independent leads are sufficient to obtain a DTW which allows a reliable T_end identification. To this aim T_end measures automatically identified from 15-dependent-lead DTWs of 46 control healthy subjects (CHS) and 103 acute myocardial infarction patients (AMIP) were compared with those obtained from 8-independent-lead DTWs. Results indicate that T_end distributions have not statistically different median values (CHS: 340 ms vs. 340 ms, respectively; AMIP: 325 ms vs. 320 ms, respectively), besides being strongly correlated (CHS: ρ=0.97, AMIP: 0.88; P<10^-27). Thus, measuring T_end from the 15-dependent-lead DTWs is statistically equivalent to measuring T_end from the 8-independent-lead DTWs. In conclusion, for the clinical purpose of automatic T_end identification from DTW, the 8 independent leads can be used without a statistically significant loss of accuracy but with a significant decrement of computational effort. The lead dependence of 7 out of 15 leads does not introduce a significant bias in the T_end determination from 15 dependent lead DTWs.

Functional and pharmacological analysis of cardiomyocytes differentiated from human peripheral blood mononuclear-derived pluripotent stem cells

Advances in induced pluripotent stem cell (iPSC) technology have set the stage for routine derivation of patient- and disease-specific human iPSC-cardiomyocyte (CM) models for preclinical drug screening and personalized medicine approaches. Peripheral blood mononuclear cells (PBMCs) are an advantageous source of somatic cells because they are easily obtained and readily amenable to transduction. Here, we report that the electrophysiological properties and pharmacological responses of PBMC-derived iPSC CM are generally similar to those of iPSC CM derived from other somatic cells, using patch-clamp, calcium transient, and multielectrode array (MEA) analyses. Distinct iPSC lines derived from a single patient display similar electrophysiological features and pharmacological responses. Finally, we demonstrate that human iPSC CMs undergo acute changes in calcium-handling properties and gene expression in response to rapid electrical stimulation, laying the foundation for an in-vitro-tachypacing model system for the study of human tachyarrhythmias.

Evaluation of ventricular repolarization dispersion during acute myocardial ischemia: spatial and temporal ECG indices

In this work, we studied the evolution of different electrocardiogram (ECG) indices of ventricular repolarization dispersion (VRD) during acute transmural myocardial ischemia in 95 patients undergoing percutaneous coronary intervention (PCI). We studied both temporal indices of VRD (T-VRD), based on the time intervals of the ECG wave, and spatial indices of VRD (S-VRD), based on the eigenvalues of the spatial correlation matrix of the ECG. The T-wave peak-to-end interval I(TPE) index showed statistically significant differences during left anterior descending artery and right coronary artery (RCA) occlusion for almost the complete time course of the PCI procedure with respect to the control recording. Regarding S-VRD indices, we observed statistically significant increases in the ratio of second to the first eigenvalue I(T21), the ratio of the third to the first eigenvalue I(T31) and the T-wave residuum I(TWR) during RCA occlusions. We also found a statistically significant increase in the I(T31) during left circumflex artery occlusions. To evaluate the evolution of VRD indices during acute ischemia, we calculated the relative change parameter R(I) for each index I. Maximal relative changes (R(I)) during acute ischemia were found for the S-VRD indices I(T21), the first eigenvalue I(λ1) and the second eigenvalue I(λ2), with changes 64, 57 and 52 times their baseline range of variation during the control recording, respectively. Also, we found that relative changes with respect to the baseline were higher in patients with T-wave alternans (TWA) than in those without TWA. In conclusion, results suggest that I(TPE) as well as I(T21), I(T31) and I(TWR) are very responsive to dispersion changes induced by ischemia, but with a behavior which very much depends on the occluded artery.

The application of root mean square electrocardiography (RMS ECG) for the detection of acquired and congenital long QT syndrome

BACKGROUND

Precise measurement of the QT interval is often hampered by difficulty determining the end of the low amplitude T wave. Root mean square electrocardiography (RMS ECG) provides a novel alternative measure of ventricular repolarization. Experimental data have shown that the interval between the RMS ECG QRS and T wave peaks (RTPK) closely reflects the mean ventricular action potential duration while the RMS T wave width (TW) tracks the dispersion of repolarization timing. Here, we tested the precision of RMS ECG to assess ventricular repolarization in humans in the setting of drug-induced and congenital Long QT Syndrome (LQTS).

METHODS

RMS ECG signals were derived from high-resolution 24 hour Holter monitor recordings from 68 subjects after receiving placebo and moxifloxacin and from standard 12 lead ECGs obtained in 97 subjects with LQTS and 97 age- and sex-matched controls. RTPK, QTRMS and RMS TW intervals were automatically measured using custom software and compared to traditional QT measures using lead II.

RESULTS

All measures of repolarization were prolonged during moxifloxacin administration and in LQTS subjects, but the variance of RMS intervals was significantly smaller than traditional lead II measurements. TW was prolonged during moxifloxacin and in subjects with LQT-2, but not LQT-1 or LQT-3.

CONCLUSION

These data validate the application of RMS ECG for the detection of drug-induced and congenital LQTS. RMS ECG measurements are more precise than the current standard of care lead II measurements.

Use of the dominant T wave to enhance reliability of T-wave offset identification

T-wave offset (Toff) identification may be jeopardized by the presence of a significant inter-method (IMV) and inter-lead (ILV) Toff variability. Thus, the aim of the present study was to investigate if the dominant T wave (DTW) may be used to enhance Toff-identification reliability. DTWs and 15-lead ECG T waves of 46 control healthy subjects (CHS) and 103 acute myocardial infarction patients (AMIP) were analyzed for Toff identification using Zhang et al.'s (M1) and Daskalov and Christov's (M2) methods. Results indicate that IMV is significantly reduced when identifying Toff from the DTW rather than from single ECG leads in both populations (CHS: 5ms vs. 5-15ms; AMIP: 10ms vs. 10-20ms). Moreover, when analyzing ILV, Toff was found to be equivalent (correlation=0.71-0.98; P<10(-14)) to the median Toff among leads, but required only one identification instead of 15. Thus, the DTW can be used to enhance Toff-identification reliability.

A working heart-brainstem preparation of the rat for the study of reflex mediated autonomic influences on atrial arrhythmia development

Vagal nerve activity has been shown to play a role in the formation and maintenance of atrial fibrillation (AF). Nerves on the atria are now increasingly being targeted using ablation-based therapies for the treatment of paroxysmal AF. In vivo, changes in vagal activity are part of an integrated autonomic profile that invariably involves accompanying modulations in sympathetic activity. To date, it has not been possible to replicate endogenous profiles of autonomic activity with the experimental set-ups used to study the effects of vagal stimulation on AF development. In this paper, we describe an experimental set-up using an in situ preparation that addresses these challenges for the first time. A high resolution surface electrode array has been used to make recordings of atrial electrograms during baroreflex activation from a preparation with intact innervation from brainstem to heart. This provides a novel framework for relating reflex-mediated autonomic activity to altered regional impulse propagation and electrical rhythm in the atria.

Increased dispersion of ventricular repolarization in Emery Dreifuss muscular dystrophy patients

Background

Sudden cardiac death (SCD) is common in patients with Emery-Dreifuss muscular dystrophy (EDMD) and is attributed to the development of life-threatening arrhythmias that occur in the presence of normal left ventricular systolic function. Heterogeneity of ventricular repolarization is considered to provide an electrophysiological substrate for malignant arrhythmias. QTc dispersion (QTc-D) and JTc dispersion (JTc-D) are electrocardiographic parameters indicative of heterogeneity of ventricular repolarization. The aim of our study was to evaluate the heterogeneity of ventricular repolarization in patients with Emery-Dreifuss muscular dystrophy with preserved systolic and diastolic cardiac function

Material/Methods

The study involved 36 EDMD patients (age 20±12, 26 M) and 36 healthy subjects used as controls, matched for age and sex. Heart rate, QRS duration, maximum and minimum QT and JT interval, QTc-D and JTc-D measurements were performed.

Results

Compared to the healthy control group, the EDMD group presented increased values of QTc-D (82.7±44.2 vs. 53.1±13.7; P=0,003) and JTc-D (73.6±32.3 vs. 60.4±11.1 ms; P=0.001). No correlation between QTc dispersion and ejection fraction (R=0.2, P=0.3) was found.

Conclusions

Our study showed a significant increase of QTc-D and JTc-D in Emery-Dreifuss muscular dystrophy patients with preserved systolic and diastolic cardiac function.

Heterogeneity of ventricular repolarization in newborns with severe aortic coarctation

Sudden death is a possible occurrence for newborns younger than 1 year with severe aortic coarctation (CoA) before surgical correction. Basic research and animal experiments have shown electrophysiologic changes during mechanical ventricular pressure overload. The current study aimed to evaluate the effect of severe CoA on the heterogeneity of ventricular repolarization by examining corrected QT and JT interval dispersion (respectively, QTc-D and JTc-D) and electrocardiographic parameters of spatial heterogeneity of ventricular repolarization in newborns with no associated congenital cardiac malformations. The study enrolled 30 isolated severe CoA neonates (age, 45 ± 15 days; 17 males) with normal size and wall thickness of the left ventricle before surgical correction and 30 age- and sex-matched healthy newborns used as control subjects. Heart rate, QRS duration, maximum and minimum QT and JT intervals, and QTc-D and JTc-D measurements were performed. The healthy control group did not significantly differ from the CoA group in terms of heart rate, weight, height, and echocardiographic parameters. Compared with the healthy control group, the CoA group presented significantly increased values of QTc-D (109.7 ± 43.4 vs. 23 ± 15 ms; P = 0.03) and JTc-D (99.1 ± 43.3 vs. 65.8 ± 24.1 ms; P = 0.04). A statistically significant correlation was found between the Doppler peak pressure gradient across the coarctation site and the values of QTc-D (r = 0.48; P = 0.03) and JTc-D (r = 0.42; P = 0.04). Our study showed significantly increased QTc-D and JTc-D in isolated CoA newborns with normal left ventricular geometry.

Repolarization heterogeneity and rate dependency in a canine rapid pacing model of heart failure

BACKGROUND

Repolarization heterogeneity and rate dependency have long been established as factors contributing to arrhythmogenic risk. However, there are conflicting observations regarding the nature and extent of ventricular repolarization heterogeneity that complicate understanding of arrhythmogenic mechanisms. To explore these disparate findings, we studied ventricular repolarization heterogeneity and rate dependency in a canine, rapid pacing model of heart failure.

METHODS AND RESULTS

We studied ventricular repolarization heterogeneity and rate dependency in 10 canine hearts (5 normal and 5 after 1 month of rapid pacing at 240 beats per minute) by analyzing 64 body surface electrocardiograms, 64 epicardial, and 190 intramural plunge electrograms. We estimated mean ventricular depolarization and repolarization times from R- and T-wave peaks of the root-mean-square electrocardiogram (body surface) and local depolarization and repolarization times using activation-recovery interval (ARI) methods from recordings obtained during a range of fixed rate pacing. In addition, we estimated local epicardial and transmural gradients of ARIs to assess cardiac locations of greatest spatial repolarization heterogeneity. We compared changes in repolarization at different rates between normal and heart failure hearts. Findings documented prolongation of repolarization, repolarization rate dependency, and increased repolarization gradients in the heart failure hearts compared with control as observed from body surface, epicardial, and transmural measurements. Maximum local epicardial and intramural ARI gradients were comparable both in heart failure and control hearts. Intramural ARI distributions tended to be more irregular in the heart failure hearts compared with the systematic epicardium to endocardium ARI increase observed in control animals.

CONCLUSIONS

This study documented prolongation of repolarization, increase in both epicardial and transmural repolarization gradients, and irregularity of transmural distribution in a rapid pacing canine model of heart failure compared with control animals. The findings support previously published results of increased repolarization heterogeneity and repolarization prolongation observed in rapid pacing models of heart failure. New findings are the irregularity of transmural heterogeneity and the ability of noninvasive root-mean-square electrocardiogram R-T intervals to estimate mean ventricular repolarization duration in the setting of rapid pacing models of heart failure. These findings suggest increased arrhythmogenic risk in this model and potentially in patients with heart failure.

Growth factor-induced mobilization of cardiac progenitor cells reduces the risk of arrhythmias, in a rat model of chronic myocardial infarction

Heart repair by stem cell treatment may involve life-threatening arrhythmias. Cardiac progenitor cells (CPCs) appear best suited for reconstituting lost myocardium without posing arrhythmic risks, being commissioned towards cardiac phenotype. In this study we tested the hypothesis that mobilization of CPCs through locally delivered Hepatocyte Growth Factor and Insulin-Like Growth Factor-1 to heal chronic myocardial infarction (MI), lowers the proneness to arrhythmias. We used 133 adult male Wistar rats either with one-month old MI and treated with growth factors (GFs, n = 60) or vehicle (V, n = 55), or sham operated (n = 18). In selected groups of animals, prior to and two weeks after GF/V delivery, we evaluated stress-induced ventricular arrhythmias by telemetry-ECG, cardiac mechanics by echocardiography, and ventricular excitability, conduction velocity and refractoriness by epicardial multiple-lead recording. Invasive hemodynamic measurements were performed before sacrifice and eventually the hearts were subjected to anatomical, morphometric, immunohistochemical, and molecular biology analyses. When compared with untreated MI, GFs decreased stress-induced arrhythmias and concurrently prolonged the effective refractory period (ERP) without affecting neither the duration of ventricular repolarization, as suggested by measurements of QTc interval and mRNA levels for K-channel α-subunits Kv4.2 and Kv4.3, nor the dispersion of refractoriness. Further, markers of cardiomyocyte reactive hypertrophy, including mRNA levels for K-channel α-subunit Kv1.4 and β-subunit KChIP2, interstitial fibrosis and negative structural remodeling were significantly reduced in peri-infarcted/remote ventricular myocardium. Finally, analyses of BrdU incorporation and distribution of connexin43 and N-cadherin indicated that cytokines generated new vessels and electromechanically-connected myocytes and abolished the correlation of infarct size with deterioration of mechanical function. In conclusion, local injection of GFs ameliorates electromechanical competence in chronic MI. Reduced arrhythmogenesis is attributable to prolongation of ERP resulting from improved intercellular coupling via increased expression of connexin43, and attenuation of unfavorable remodeling.

Reverse electrical remodeling of the ventricles following successful restoration of sinus rhythm in patients with persistent atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) has been shown to be associated with reduced survival and increased ventricular arrhythmogenesis. The purpose of this study was to assess the effects of AF with adequate rate control on the electrophysiologic properties of the ventricles. We hypothesized that AF results in increased ventricular arrhythmogenic risk and that reverse remodeling occurs post-successful cardioversion.

METHODS

In nine patients with persistent AF, we recorded 12-lead electrocardiograms (ECGs) and 1-hour high-resolution Holter ECGs (H12+, Mortara Instrument, Inc. Milwaukee, WI, USA; recorders [1000 sps] immediately following cardioversion (Day 1) and after 30 days of maintaining sinus rhythm (Day 30). We measured QTc, QT dispersion, and calculated estimates of mean ventricular action potential duration (RT), diastolic interval (DI), T-wave width (TW), T-wave peak-to-end, and their respective scatter on Day 1 and Day 30. Maintenance of normal sinus rhythm was confirmed with a weekly trans-telephonic ECG transmission.

RESULTS

The average QTc interval decreased from 449 ± 28 ms on Day 1 to 422 ± 36 ms on Day 30 (P = 0.04). There was no significant difference in the average QT dispersion. A significant decrease was also noted in DI and TW scatter at Day 30 when compared with Day 1 (P = 0.03 and 0.04, respectively). A decrease in RT scatter was also noted albeit not statistically significant (P = 0.07).

CONCLUSION

Our results suggest a greater propensity to ventricular arrhythmogenesis in the immediate period following restoration of sinus rhythm and reverse electrical remodeling of the ventricles during the first month after successful maintenance of sinus rhythm. (PACE 2010; 33:1198-1202).

Increased heterogenity of ventricular repolarization in obese nonhypertensive children

OBJECTIVE

Obese children, without arterial hypertension, may be a unique clinical opportunity to evaluate the effect of obesity, per se, on ventricular repolarization, excluding the influence of possible comorbidities. The QTc dispersion (QTc-d), JTc dispersion (JTc-d), and transmural dispersion of repolarization (TDR) have been suggested to be electrocardiographic indexes reflecting the physiological variability of regional ventricular repolarization. The aim of our study is to define the effects of obesity on the ventricular repolarization in obese children who have no other clinically appreciable cause of heart disease.

METHODS

The study involved 70 subjects (48 male, 22 female), with a mean age (± standard deviation) of 13 ± 2 years. A total of 35 individuals were obese (Group A: 24 male, 11 female, mean body mass index [BMI] of 38.2 ± 5.8 kg/m(2) ), and 35 participants were healthy lean children (Group C: 24 male, 11 female, mean BMI of 22.3 ± 0.3 kg/m(2) ). Heart rate; QRS duration; maximum and minimum QT interval; and QTc-d, JTc-d, and TDR measurement were performed.

RESULTS

Compared with the healthy control group, obese children presented increased values of the QTc-d, JTc-d, and TDR (31.1 ± 10.6 vs 46.2 ± 15.3 ms, P < 0.003; 29.8 ± 8.5 vs 40.1 ± 10.3 ms, P < 0.04; 83.2 ± 13.5 vs 100.7 ± 16.3 ms, P < 0.05). A statistically significant correlation was found between the values of QTc-d, insulin serum concentration (r = 0.46, P = 0.04), and homeostasis model assessment of insulin resistance (r = 0.34, P = 0.03).

CONCLUSIONS

Our data suggest that obese nonhypertensive children have an increased ventricular repolarization heterogeneity in relation to controls.

Beat-to-beat three-dimensional ECG variability predicts ventricular arrhythmia in ICD recipients

BACKGROUND

Methodological difficulties associated with QT measurements prompt the search for new electrocardiographic markers of repolarization heterogeneity.

OBJECTIVE

We hypothesized that beat-to-beat 3-dimensional vectorcardiogram variability predicts ventricular arrhythmia (VA) in patients with structural heart disease, left ventricular systolic dysfunction, and implanted implantable cardioverter-defibrillators (ICDs).

METHODS

Baseline orthogonal electrocardiograms were recorded in 414 patients with structural heart disease (mean age 59.4 ± 12.0; 280 white [68%] and 134 black [32%]) at rest before implantation of ICD for primary prevention of sudden cardiac death. R and T peaks of 30 consecutive sinus beats were plotted in 3 dimensions to form an R peaks cloud and a T peaks cloud. The volume of the peaks cloud was calculated as the volume within the convex hull. Patients were followed up for at least 6 months; sustained VA with appropriate ICD therapies served as an end point.

RESULTS

During a mean follow-up time of 18.4 ± 12.5 months, 61 of the 414 patients (14.73% or 9.6% per person-year of follow-up) experienced sustained VA with appropriate ICD therapies: 41 of them were white and 20 were black. In the multivariate Cox model that included inducibility of VA and use of beta-blockers, the highest tertile of T/R peaks cloud volume ratio significantly predicted VA (hazard ratio 1.68, 95% confidence interval 1.01 to 2.80; P = .046) in all patients. T peaks cloud volume and T/R peaks cloud volume ratio were significantly smaller in black subjects (median 0.09 [interquartile range 0.04 to 0.15] vs. median 0.11 [interquartile range 0.06 to 0.22], P = .002).

CONCLUSION

A relatively large T peaks cloud volume is associated with increased risk of VA in patients with structural heart disease and systolic dysfunction.

Robust QT interval estimation--from algorithm to validation

BACKGROUND

This article presents an effort of measuring QT interval with automatic computerized algorithms. The aims of the algorithms are consistency as well as accuracy. Multilead and multibeat information from a given segment of ECG are used for more consistent QT interval measurement.

METHODS

A representative beat is generated from selected segment of each lead, and then a composite beat is formed by the representative beats of all independent leads. The end result of the QT measure is so-called global QT measurement, which usually correlates with the longest QT interval in multiple leads. Individual lead QT interval was estimated by using the global measurement as a starting point, and then adapted to the signal of the particular lead and beat. In general, beat-by-beat QT measurement is more prone to noise, therefore less reliable than the global estimation. It is usually difficult to know if difference of beat-by-beat QT interval is due to true physiological change or noise fluctuation.

RESULTS

The algorithm was tested independently by a clinical database. It is also tested against action potential duration (APD) generated by a Cell-to-ECG forward-modeling based simulation signals. The modeling approach provided an objective test for the QT estimation. The modeling approach allowed us to evaluate the QT measurement versus APD. The mean error between the algorithm and cardiologist QT intervals is 3.95 +/- 5.5 ms, based on the large clinical trial database consisting of 15,910 ECGs. The mean error between QT intervals and maximum APD is 17 +/- 2.4, and the correlation coefficient is 0.99.

CONCLUSIONS

The global QT interval measurement method presented in this study shows very satisfactory results against the CSE database and a large clinical trial database. The modeling test approach used in this study provides an alternative "gold standard" for QT interval measurement.

A reliability analysis of cardiac repolarization time markers

Only a limited number of studies have addressed the reliability of extracellular markers of cardiac repolarization time, such as the classical marker RT(eg) defined as the time of maximum upslope of the electrogram T wave. This work presents an extensive three-dimensional simulation study of cardiac repolarization time, extending the previous one-dimensional simulation study of a myocardial strand by Steinhaus [B.M. Steinhaus, Estimating cardiac transmembrane activation and recovery times from unipolar and bipolar extracellular electrograms: a simulation study, Circ. Res. 64 (3) (1989) 449]. The simulations are based on the bidomain - Luo-Rudy phase I system with rotational fiber anisotropy and homogeneous or heterogeneous transmural intrinsic membrane properties. The classical extracellular marker RT(eg) is compared with the gold standard of fastest repolarization time RT(tap), defined as the time of minimum derivative during the downstroke of the transmembrane action potential (TAP). Additionally, a new extracellular marker RT90(eg) is compared with the gold standard of late repolarization time RT90(tap), defined as the time when the TAP reaches 90% of its resting value. The results show a good global match between the extracellular and transmembrane repolarization markers, with small relative mean discrepancy (<or=1.6%) and high correlation coefficients (>or=0.92), ensuring a reasonably good global match between the associated repolarization sequences. However, large local discrepancies of the extracellular versus transmembrane markers may ensue in regions where the curvature of the repolarization front changes abruptly (e.g. near front collisions) or is negligible (e.g. where repolarization proceeds almost uniformly across fiber). As a consequence, the spatial distribution of activation-recovery intervals (ARI) may provide an inaccurate estimate of (and weakly correlated with) the spatial distribution of action potential durations (APD).

Experimental measures of ventricular activation and synchrony

BACKGROUND

A widened QRS complex as a primary indication for cardiac resynchronization therapy (CRT) for heart failure patients has been reported to be an inconsistent indicator for dyssynchronous ventricular activation. The purpose of this study was to conduct a detailed experimental investigation of total ventricular activation time (TVAT), determine how to measure it accurately, and compare it to the commonly used measure of QRS width. In addition, we investigated a measure of electrical synchrony and determined its relationship to the duration of ventricular activation.

METHODS

Unipolar electrograms (EGs) were recorded from the myocardial volume using plunge needle electrodes, from the epicardial surface using "sock" electrode arrays, and from the surface of an electrolytic torso-shaped tank. EGs were analyzed to determine a root mean square (RMS)-based measure of ventricular activation and electrical ventricular synchrony.

RESULTS

The RMS-based technique provided an accurate means of measuring TVAT from unipolar EGs recorded from the heart, the entire tank surface, or the precordial leads. In normal canine hearts, a quantification of ventricular electrical synchrony (VES) for normal ventricular activation showed that the ventricles activate, on average, within 3 ms of each other with the left typically activating first.

CONCLUSION

Conclusions from this study are: (1) ventricular activation was reflected accurately by the RMS width obtained from direct cardiac measurements and from precordial leads on the tank surface and (2) VES was not strongly correlated with TVAT.

Cardiac repolarization analysis using the surface electrocardiogram

Sudden cardiac death (SCD) is a challenging health problem in the western world. Analysis of cardiac repolarization from the electrocardiogram (ECG) provides valuable information for stratifying patients according to their risk of suffering from arrhythmic events that could end in SCD, as well as for assessing efficacy of antiarrhythmic therapies. In this paper, we start by exploring the cellular basis of ECG repolarization waveforms under both normal and pathological conditions. We then describe basic preprocessing steps that need to be accomplished on the ECG signal before extracting repolarization indices. A comprehensive review of techniques aimed to characterize spatial or temporal repolarization dispersion is provided, together with a summary of their usefulness for clinical risk stratification. Techniques that describe spatial dispersion of repolarization are based on either differences in repolarization duration or T-wave loop morphology. Techniques that evaluate temporal dispersion of repolarization include the analysis of QT interval adaptation to heart rate changes, QT interval and T-wave variability, and T-wave alternans.

Repolarization changes induced by mental stress in normal subjects and patients with coronary artery disease: effect of nitroglycerine

OBJECTIVES

Mental stress can significantly affect ventricular repolarization, which could potentially trigger arrhythmias. We compared the effect of mental stress on repolarization indexed by the amplitude and area of the T wave in patients with coronary artery disease (CAD) and healthy subjects.

METHODS

Fourteen healthy controls (11 M, mean age 42 years) and 14 patients with stable CAD (12 M, mean age 64) underwent a mental stress protocol consisting of mental arithmetic followed by a speech (5 minutes each), which was performed on two occasions following either nitroglycerine (NTG) or placebo. Multiple 12-lead electrocardiograms were acquired and repolarization was analyzed using automatically measured T wave amplitude (T(amp)) and area (T(area)).

RESULTS

When preceded by placebo the overall effect of mental stress, whether induced by arithmetic or speech, was significantly different in CAD patients compared with controls, with a decrease in T(amp) and T(area) in controls and an increase in patients; e.g., change in T(amp) during arithmetic -20 +/- 3 microV in controls versus 4 +/- 2 microV in patients, p < .001, and during speech -9 +/- 3 microV in controls versus 7 +/- 1 microV in patients, p < .001. Following NTG, the effect of stress on repolarization was similar in the 2 groups, with a reversed effect, i.e., decrease instead of increase in T(amp) and T(area) in CAD patients.

CONCLUSIONS

The effect of mental stress on ventricular repolarization is significantly different in CAD patients compared with healthy controls. These differences are considerably reduced by NTG.

Ventricular repolarization pattern under heart cooling in the rabbit

AIM

Prolongation of ventricular repolarization is characteristic of myocardial cooling. In the present study, we investigated whether this prolongation is uniform or not throughout ventricular epicardium and how these hypothermia-induced changes express in the body surface potential distribution.

METHODS

Epicardial and body surface potential mapping from 64 unipolar leads was carried out in 18 anaesthetized adult rabbits. Mild hypothermia documented by lowering the mediastinal and rectal temperature from 38 to 32 degrees C was elicited by perfusion of the mediastinum with cooled saline. Activation times, repolarization times and activation-recovery intervals were determined in each epicardial lead.

RESULTS

Baseline activation-recovery intervals distributed non-uniformly on the ventricular epicardium, increasing progressively from the apex to the base and from the left ventricular (LV) sites to the right ventricular (RV) sites (P < 0.05), governing the repolarization sequence of ventricular epicardium. Heart cooling from 38 to 32 degrees C produced the heterogeneous prolongation of activation-recovery intervals which was more pronounced at the apex than at the base, and in the LV areas compared to the RV areas (P < 0.05). These nonuniform changes in local repolarization durations resulted in the development of base-to-apex repolarization sequence and inversion of the body surface potential distribution during the T wave.

CONCLUSION

Thus, under cooling the rabbit heart from 38 to 32 degrees C, the nonuniform prolongation of local repolarization durations resulted in the reversal of ventricular epicardial repolarization sequence which, in turn, was responsible for the inversion in the body surface potential distribution during the T wave.

Methods for accurate measures of total ventricular activation time

The purpose of this study was to determine improved measures of total ventricular activation time for the diagnosis and treatment of patients undergoing cardiac resynchronization therapy (CRT). This work investigates the accuracy of a root mean square (RMS) based QRS width computed from unipolar electrograms (EGs) measured in heart for representing true total ventricular activation time (TVAT). The study also investigated the use subsets of EGs obtained from the endocardial and epicardial surfaces as indicators of TVAT. Transmural needle electrodes (96) were used to obtain 960 EGs from six normal isolated canine hearts. RMS-based QRS-widths from the endocardial and epicardial surfaces and volume were compared to the TVAT measured from all 960 EGs. No statistically significant differences were found in RMS-based QRS-widths obtained from all three sets of electrograms when compared with true TVAT. Activation times obtained from endocardial and epicardial surfaces were found to be poor indicators of true TVAT. The results support the use of RMS techniques for providing more accurate measures of TVAT.

A semi-automatic feature detection algorithm for hemodynamic signals using curvature-based feature extraction

Specific features of hemodynamic signals are invaluable for elucidating ventricular and vascular function. A semi-automatic algorithm is presented that enables accurate detection of any feature in any hemodynamic signal, using feature extraction from local maxima and minima in signal curvature. A particular feature is selected manually in the first beat and then detected automatically in subsequent beats.

Scatter in repolarization timing predicts clinical events in post-myocardial infarction patients

BACKGROUND

Increased spatial and temporal dispersion of repolarization contributes to ventricular arrhythmogenesis. Beat-to-beat fluctuations in T-wave timing are thought to represent such dispersion and may predict clinical events.

OBJECTIVE

The purpose of this study was to assess whether a novel noninvasive measure of beat-to-beat instability in T-wave timing would provide additive prognostic information in post-myocardial infarction patients.

METHODS

We studied 678 patients from 12 hospitals with 32-lead 5-minute electrocardiogram recordings 6-8 weeks after myocardial infarction. Custom software identified R wave-to-T wave intervals (RTIs) and diastolic intervals (DIs). Repolarization scatter (RTI:DI(StdErr)) was then calculated as the standard error about the RTI:DI regression line. In addition, left ventricular ejection fraction (LVEF), short-term heart rate variability (HRV) parameters, and QT variability index were measured. Patients were followed for the composite endpoint of death or life-threatening ventricular arrhythmia.

RESULTS

After a mean follow-up of 63 months, 134 patients met the composite endpoint. An RTI:DI(StdErr) >5.50 ms was associated with a 210% increase in arrhythmias or deaths (P <.001). After adjusting for LVEF, RTI:DI(StdErr) remained an independent predictor (P <.001). RTI:DI(StdErr) was also independent of short-term HRV parameters and the QT variability index.

CONCLUSIONS

Increased repolarization scatter, a measure of high-frequency, cycle-length-dependent repolarization instability, predicts poor outcomes in patients after myocardial infarction.

Diurnal variation and dispersion in QT interval in cirrhosis: relation to haemodynamic changes

BACKGROUND/AIMS

A long QT(C) interval has been described in a substantial fraction of patients with cirrhosis, but information on QT variation and dispersion is sparse. The aim was to determine QT variation with time and QT dispersion (QT(disp)).

METHODS

The study population comprised 23 patients with cirrhosis, undergoing a haemodynamic investigation. 24-h 12 lead Holter monitoring provided information on QT and heart rate variability.

RESULTS

Mean QT(C) was above upper normal limit (440 ms(1/2)) in eleven patients (47%) and significantly higher than in controls (441 vs 400 ms(1/2), p<0.01). The minimum value of QT(C) (but not the maximum value) showed a significant diurnal variation both in cirrhosis and controls. QT(disp) in cirrhosis and controls was similar (33 vs 36 ms, ns), but related to indicators of liver dysfunction, central circulation time, and arterial blood pressure (r=0.44-0.58, p=0.03-0.001). No diurnal variation of QT(disp) was found in cirrhosis. Heart rate variability was reduced with a significant relation to central hypovolaemia (r=0.55, p=0.01).

CONCLUSIONS

Twenty-four hours QT(C) is prolonged in a substantial fraction of patients with cirrhosis, but with normal diurnal variation. The combination of long QT(C) and normal QT(disp) suggests delayed myocyte repolarisation on the cellular level, rather than temporal and spatial heterogeneity in the myocardial wall.

Effect of Weight Loss following Bariatric Surgery on Myocardial Dispersion of Repolarization in Morbidly Obese Patients

BACKGROUND

Weight-stable obese subjects have an increased risk of arrhythmias and sudden death, even in the absence of cardiac dysfunction, and the risk of sudden cardiac death (SCD) with increasing weight is seen in both genders. The mechanism of unexplained deaths in obese patients is still unclear and may be related to ventricular repolarization abnormalities. The aim of this study is to determine the effect of severe obesity on spatial and transmural ventricular repolarization and to clarify the influence of bariatric surgery with a consequent substantial weight loss on arrhythmogenic substrate in the morbidly obese population.

METHODS

For the study, we enrolled 100 severely obese patients; 50 age-matched non-obese healthy subjects were also recruited as controls. All subjects underwent conventional 12-lead electrocardiography for analysis of spatial and transmural ventricular repolarization assessed by corrected QT dispersion (QTc-d), corrected JT dispersion (JTc-d) and transmural dispersion of repolarization, (TDR). All subjects underwent bariatric surgery and were resubmitted to electrocardiographic, biochemical and anthropometric examination 12 months postoperatively.

RESULTS

Severely obese patients had greater values in QTc-d, JTc-d and TDR than the normal-weight controls. Bariatric surgery reduced significantly the QTc-d value, JTc-d value and TDR value. There was a significant correlation between decrease of heterogeneity of repolarization indexes (QTd, JTd and TDR) and bariatric surgery-induced weight loss.

CONCLUSIONS

In severely obese patients, surgically-induced weight loss is associated with significant decrease in the heterogeneity of ventricular repolarization. The reduction of spatial (QTc-d, JTc-d) and transmural dispersion of repolarization (TDR) may be of clinical significance, by reducing the risk of potentially fatal arrhythmias in morbidly obese subjects.

Biventricular pacing and heterogeneity of ventricular repolarization in heart failure patients

OBJECTIVE

The aim of our study was to evaluate the effect of cardiac resyncronization therapy (CRT) on QT dispersion (QTd), JT dispersion (JTd) and transmural dispersion of re-polarization (TDR), markers of heterogeneity of ventricular repolarization in a study population with severe heart failure.

METHODS AND RESULTS

Fifty patients (43 male, 7 female, aged 60.2 ± 3.1 years) suffering from congestive heart failure (N = 39 NYHA class III; N = 11 NYHA class IV) as a result of coronary artery disease (N = 19) or of dilated cardiomyopathy (N = 31), sinus rhythm, QRS duration >130 ms (mean QRS duration >156 ± 21 ms), an ejection fraction < 35%, left ventricular end-diastolic diameter >55 mm, underwent permanent biventricular DDDR pacemaker implantation. A 12-lead standard electrocardiogram was performed at baseline, during right-, left-, and biventricular pacing and QTd, JTd and TDR were assessed. Biventricular pacing significantly reduced QTd (73.93 ± 19.4 ms during BiVP vs 91 ± 6.7 ms at sinus rhythm, p = 0.004), JTd (73.18 ± 17.16 ms during BiVP vs 100.72 ± 39.04 at baseline p = 0.003), TDR (93.16 ± 15.60 vs 101.55 ± 19.08 at baseline; p<0.004), as compared to sinus rhythm. Right ventricular endocardial pacing and left ventricular epicardial pacing both enhanced QTd (RVendoP 94 ± 51 ms, p<0.03; LVepiP 116 ±71 ms, p<0.02) and TDR (RVendoP 108.13 ± 19.94 ms; p<0.002; LVepiP 114.71 ± 26.1; p<0.05).There was no effect on JTd during right and left ventricular stimulation.

CONCLUSIONS

Biventricular pacing causes a statistically significant reduction of ventricular heterogeneity of ripolarization and has an electrophysiological antiarrhythmic influence on arrhythmogenic substrate of dilatative cardiomiopathy.

Effects of Cardiac Resynchronization Therapy on Ventricular Repolarization in Patients with Congestive Heart Failure

INTRODUCTION

Biventricular pacing has been shown to improve the clinical status of patients with congestive heart failure, but little is known about its influence on ventricular repolarization. The aim of our study was to evaluate the effect of biventricular pacing on ECG markers of ventricular repolarization in patients with congestive heart failure.

METHODS AND RESULTS

Twenty-five patients with congestive heart failure, sinus rhythm (SR), and complete LBBB (6 females; age 61 +/- 8 years; NYHA class II-III; echocardiographic ejection fraction 21 +/- 5%; QRS > or = 130 ms) underwent permanent biventricular DDDR pacemaker implantation. A high-resolution 65-lead body-surface ECG recording was performed at baseline and during right-, left-, and biventricular pacing, and the total 65-lead root mean square curve of the QRST complex and the interlead QT dispersion were assessed. The QRS duration was increased during right (RV)- and left ventricular (LV) pacing (127 +/- 26% and 117 +/- 40%; P < 0.05), as compared to SR (100%) and biventricular pacing (93 +/- 16%; ns). The QTc interval was increased during RV and LV pacing (112 +/- 12% and 114 +/- 14%; P < 0.05) as compared to SR (100%) or biventricular pacing (99 +/- 12%). There was no effect on JT interval during all pacing modes. The T(peak-end) interval was increased during right (120 +/- 34%; P < 0.01) and LV pacing (113 +/- 29%; P < 0.05) but decreased during biventricular pacing (81 +/- 19%; P < 0.01). A similar effect was found for the T(peak-end) integral and the T(peak) amplitude. QT dispersion was increased during right ventricular (129 +/- 16 ms; P < 0.05) and decreased during biventricular pacing (90 +/- 12 ms; P < 0.01), as compared to SR (114 +/- 22 ms).

CONCLUSIONS

Using a high-resolution surface ECG, biventricular pacing resulted in a significant reduction of ECG markers of ventricular dispersion of repolarization.

Heart rate influences on repolarization duration and morphology in symptomatic versus asymptomatic KCNQ1 mutation carriers

QT and Tp/Te intervals were longer in patients with LQT1 (n = 67) than in nonaffected subjects (n = 52) but did not differentiate symptomatic (n = 21) from asymptomatic patients (n = 46). At fast heart rate, the time to accumulate the last part of total T-wave area (the t50-97 interval) was longer in symptomatic carriers compared with asymptomatic patients (119 +/- 19 vs 106 +/- 15 ms, p <0.01). The latter group had significantly longer t50-97 intervals than nonaffected subjects (96 +/- 14 ms, p <0.01).