Atypical Wenckebach without grouped beating due to dual AV nodal conduction.

A 31-year-old woman reported dizziness in the early postpartum period after receiving dexmedetomidine. The ECG was misinterpreted as complete heart block; however, more careful analysis revealed an atypical Wenckebach pattern with dual AV nodal conduction and termination of nonconducted P waves with junctional escape beats. The patient's rhythm returned to sinus after stopping dexmedetomidine. Atypical Wenckebach patterns account for greater than 50% of patients with Mobitz Type I AV block and can be misinterpreted as high-grade AV block. This case highlights the causes of atypical Wenckebach patterns and how careful analysis of intervals can help clinicians avoid misdiagnosis.

Validation of electrocardiographic criteria for identifying left ventricular dysfunction in patients with previous myocardial infarction.

BACKGROUND: Eleven criteria correlating electrocardiogram (ECG) findings with reduced left ventricular ejection fraction (LVEF) have been previously published. These have not been compared head-to-head in a single study. We studied their value as a screening test to identify patients with reduced LVEF estimated by cardiac magnetic resonance (CMR) imaging. METHODS: ECGs and CMR from 548 patients (age 61 + 11 years, 79% male) with previous myocardial infarction (MI), from the DETERMINE and PRE-DETERMINE studies, were analyzed. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of each criterion for identifying patients with LVEF ≤ 30% and ≤ 40% were studied. A useful screening test should have high sensitivity and NPV. RESULTS: Mean LVEF was 40% (SD = 11%); 264 patients (48.2%) had LVEF ≤ 40%, and 96 patients (17.5%) had LVEF ≤ 30%. Six of 11 criteria were associated with a significant lower LVEF, but had poor sensitivity to identify LVEF ≤ 30% (range 2.1%-55.2%) or LVEF ≤ 40% (1.1%-51.1%); NPVs were good for LVEF ≤ 30% (range 82.8%-85.9%) but not for LVEF ≤ 40% (range 52.1%-60.6%). Goldberger's third criterion (RV4/SV4 < 1) and combinations of maximal QRS duration > 124 ms + either Goldberger's third criterion or Goldberger's first criterion (SV1 or SV2 + RV5 or RV6 ≥ 3.5 mV) had high specificity (95.4%-100%) for LVEF ≤ 40%, although seen in only 48 (8.8%) patients; predictive values were similar on subgroup analysis. CONCLUSIONS: None of the ECG criteria qualified as a good screening test. Three criteria had high specificity for LVEF ≤ 40%, although seen in < 9% of patients. Whether other ECG criteria can better identify LV dysfunction remains to be determined.

PR Prolongation predicts inadequate resynchronization with biventricular pacing in left bundle branch block.

BACKGROUND: PR interval prolongation is associated with poor outcome after cardiac resynchronization therapy (CRT) among patients with left bundle branch block (LBBB) but the mechanisms are unknown. We investigated clinical outcomes, electrocardiogram (ECG), and echocardiogram changes after CRT by PR interval. METHODS: This is a retrospective study of CRT recipients with a baseline ejection fraction ≤35% and ECG showing sinus rhythm and LBBB. Patients were stratified by baseline PR interval quartile and the primary combined endpoint was time to heart transplantation, left ventricular assist device (LVAD) implantation, or death. ECG, echocardiogram, and clinical variables were compared to identify mechanisms for observed differences in outcomes. RESULTS: Of 291 eligible patients, the mean age was 65 years, 60% were male, and 19% had prior atrial fibrillation. Patients with PR prolongation (quartile 4, PR > 200 ms) more frequently had a history of atrial fibrillation, coronary artery bypass graft surgery, prior implantable cardioverter defibrillator implantation, and use of amiodarone than patients in PR quartiles 1-3. A PR > 200ms was associated with an adjusted hazard ratio of 1.7 (95% CI: 1.1-2.5) for the primary endpoint. Patients with PR > 200 ms had less reduction in QRS duration and QRS area after CRT while having more increase in QT and QTc intervals than patients with PR ≤ 200 ms. No major differences were observed in echocardiography by baseline PR interval quartiles. CONCLUSIONS: PR prolongation predicts shorter survival free of heart transplantation or LVAD implantation in patients with LBBB. This may be due to inadequate ventricular resynchronization.

Poor reliability of P-wave terminal force V1 in ischemic stroke.

INTRODUCTION: Several ECG markers are postulated to represent underlying atrial remodelling and have been associated with ischemic stroke. P-wave terminal force in lead V1 (PTFV1) is one such marker. We examined the factors that contribute to the reliability of PTFV1 and its association with ischemic stroke. MATERIAL AND METHODS: Four hundred and thirty-five patients that presented with an ischemic stroke or transient ischemic attack (TIA) were identified through a prospectively maintained multi-site institutional stroke database. Control group consisted of age matched patients without prior history of an ischemic stroke or TIA. All patients underwent a 12-lead ECG and 24-hour Holter monitoring during the study period to exclude atrial fibrillation. RESULTS: Morphology consistent with PTFV1 occurred commonly in both the stroke/TIA and control groups. There was no significant difference in the median PTFV1 value between the stroke 3.96 mV ms [Interquartile range (IQR) 2.78-5.58] and control 4.23 mV ms [IQR 2.91-5.57] groups. Measurements of PTFV1 demonstrated excellent intra-observer reliability on assessment of the same P-wave (Intra class correlation (ICC) 0.91, p < 0.001) with narrow limits of agreement 2.21 to -2.95 mV ms. A change in the P wave assessed led to a significant reduction in reliability (ICC 0.79, p < 0.001). Inter-observer, inter P-wave assessment demonstrated further reduction in reliability (ICC 0.68, p < 0.002) with wide limits of agreement 6.17 to -5.78 mV ms, indicating significant under and overestimation of PTFV1. CONCLUSION: The utility of PTFV1 as a clinical marker for ischemic stroke is limited by the reduction in reliability associated with inter-observer and inter P-wave measurements.

Novel electrocardiographic dyssynchrony criteria improve patient selection for cardiac resynchronization therapy.

Aims: We hypothesized that the greater the intra- or interventricular dyssynchrony (intraD, interD), the more effective cardiac resynchronization therapy (CRT) is. We sought to improve patient selection for CRT by using novel ECG dyssynchrony criteria. Methods and results: Left ventricular (LV) intraD was estimated by the absolute time difference between the intrinsicoid deflections (ID) in leads aVL and aVF divided by the QRS duration (QRSd): [aVLID - aVFID]/QRSd (%). InterD was estimated from the formula: [V5ID - V1ID]/QRSd (%). Their >25% value indicated electrical dyssynchrony present (ED+) and ≤25% value electrical dyssynchrony absent (ED-) diagnoses. Using the intraD + interD criteria (intra + interDC) together, if at least one of them indicated ED+ diagnosis, a final ED+ diagnosis, if both indicated ED- diagnosis, a final ED- diagnosis was made. Two authors, blinded to CRT response, retrospectively analysed pre-CRT ECGs of 124 patients with known CRT outcome. CRT response was defined as improvement of ≥ 1 NYHA class, being alive and having no hospitalizations for heart failure during 6 months of follow-up. 35/124 (28%) patients were non-responders (NRs), using the traditional criteria (TC) correct diagnosis was made in the remaining 89/124 (72%) responder (R) cases. The test accuracy (TA) of intra + interDC + TC [100/124 (81%), P < 0.001] was superior to that of TC [89/124 (72%)] due to its superior TA [36/43 (84%) vs. 29/43 (67%), respectively, P = 0.0156] in the non-specific intra-ventricular conduction disturbance (NICD) subgroup [43/124 (35%)]. In the left bundle branch block subgroup [70/124 (56%)] there was no between-criteria difference in TA. Conclusion: The intra + interDC + TC predicts clinical response after CRT more accurately than TC alone, due to greater TA in the NICD subgroup.

Left Ventricular Septal Hypertrophy in Elderly Patients With Aortic Stenosis.

OBJECTIVES: Left ventricular (LV) septal hypertrophy in aortic stenosis raises diagnostic and therapeutic questions. However, the etiology and clinical consequences of this finding have not been well studied. The aim of this study was to perform a morphologic evaluation of the LV in aortic stenosis and to investigate the contributing factors and consequences of septal hypertrophy. METHODS: Patients with moderate or severe aortic stenosis were prospectively enrolled. Patients with previous myocardial infarction, wall motion abnormalities, at least moderate valvular regurgitation, known cardiomyopathy, an LV ejection fraction of less than 50%, and age younger than 65 years were excluded. RESULTS: Forty-one patients underwent a final analysis. Septal hypertrophy (LV septal wall thickness ≥15 mm) was confirmed in 21 of 41 patients. The septal hypertrophy group had higher peak aortic valve velocity, a higher diabetes mellitus rate, and a higher rate and longer duration of hypertension than those without septal hypertrophy. The peak aortic valve velocity (odds ratio, 7.1; 95% confidence interval, 1.4-37.1) and diabetes mellitus (odds ratio, 7.4; 95% confidence interval, 1.2-46.2) were the significant factors associated with septal hypertrophy by multivariate analysis. Intraventricular conduction disturbance on electrocardiography was more frequent in the septal hypertrophy group (P = .021). CONCLUSIONS: Left ventricular septal hypertrophy was commonly observed in elderly patients with aortic stenosis, and a higher aortic valve velocity, hypertension, and diabetes mellitus were associated factors. Intraventricular conduction disturbance occurred more often in patients with septal hypertrophy than those without, which implies the pathophysiologic consequence. Further studies are needed to determine the impact of septal hypertrophy and intraventricular conduction disturbance on the prognosis of patients after aortic valve interventions.

Gender equity imbalance in electrocardiology: A call to action.

Despite the increasing number of women entering the medical profession, senior positions and academic productivity in many fields of medicine remain to be men dominated. We explored gender equity in electrocardiology as perceived by recent academic productivity and also active participation (presidencies and board constituents) in both the International Society of Electrocardiology (ISE) and the International Society for Holter and Noninvasive Electrocardiology (ISHNE). Academic productivity was measured by authorship (first and senior) in the Journal of Electrocardiology (JECG) and the Annals of Noninvasive Electrocardiology (ANE) in 2015. The percentage of women ISE and ISHNE Presidents was 5.6% and 0%, respectively. Current women board constituents for each society was 12.1% for ISE, and 9.4% for ISHNE. JECG articles published in 2015 had considerably less women compared to men for both senior (16.3%) and first (25.3%) authorship. ANE articles published in 2015 followed the same trends in gender, having less women compared to men for both senior (9.4%) and first (19.3%) authorship. There is a gender equity imbalance in the field of Electrocardiology. Identifying a gender imbalance is important for understanding reasons behind these trends, and may also help improve gender equity in Electrocardiology.

Heart Rate-Dependent Hysteresis of T-Wave Alternans in Primary Prevention ICD Patients.

BACKGROUND: T-wave alternans (TWA) is usually performed at accelerated heart rates (HR) during exercise, while recovery TWA is typically not analyzed. Consequently, it is still unknown if TWA shows a HR-dependent hysteresis or not. Thus, the aim of the present study was to investigate TWA dependency on HR during both the exercise and recovery phases of an ergometer test, and to evaluate if recovery TWA may contribute to identify subjects at increased risk of arrhythmic events. METHODS: Our HR adaptive match filter was used to identify TWA from electrocardiographic recordings acquired during a bicycle ergometer test in 266 patients with implanted cardio-defibrillator. During the 4-year follow-up, 76 patients developed tachycardia or ventricular fibrillation (ICD_Cases) and 190 did not (ICD_Controls). RESULTS: TWA was statistically lower during exercise than recovery for HRs between 75 and 110 bpm (16-21 µV vs 20-27 µV; P < 0.05), and reverse for HRs between 120 and 130 bpm (41-51 µV vs 28 µV; P < 0.05). ICD_Cases and ICD_Controls showed significantly different TWA at 80 bpm (20 µV vs 15 µV; P < 0.05) and 140 bpm (15 µV vs 22 µV; P < 0.05) during exercise, and at 90 bpm (38 µV vs 21 µV; P < 0.05) and 95 bpm (33-24 µV vs 28 µV; P < 0.05) during recovery. CONCLUSIONS: TWA shows a HR-dependent hysteresis and there is a different behavior of TWA in ICD_Cases and ICD_Controls groups. Consequently, beside exercise TWA also recovery TWA may contribute to identify subjects at increased risk of arrhythmic events.

A wide QRS/T angle in bundle branch blocks is associated with increased risk for coronary heart disease and all-cause mortality in the Atherosclerosis Risk in Communities (ARIC) Study.

BACKGROUND: Repolarization abnormality in bundle branch blocks (BBB) is traditionally ignored. This study evaluated the prognostic value of QRS/T angle for mortality in the presence and absence of BBB. METHODS AND RESULTS: Total 15,408 participants (mean age 54 years, 55.2% women, 26.9% blacks, 2.8% with BBB) were from the Arteriosclerosis Risk in Communities Study. Sex stratified Cox regression models were used to compute hazard ratios (HRs) with 95% confidence intervals (CIs) for coronary heart disease (CHD) and all-cause mortality for wide spatial QRS/T angle with and without BBB including right BBB (RBBB), left BBB (LBBB) and indetermined-type ventricular conduction defect (IVCD) and RBBB combined with left anterior fascicular block. During a median 22-year follow-up, 4767 deaths occurred, 728 of them CHD deaths. Using the No-BBB with QRS/T angle below median value as gender-specific reference groups, the mortality risk increase was significant for both women and men with No-BBB and QRS/T angle above the median value. In the pooled ICVD/LBBB group, the risk for CHD death was increased 15.9-fold in women and 6.04 fold in men, and for all-cause deaths 3.01-fold in women and 1.84-fold in men. However, the mortality risk in isolated RBBB group was only significantly increased in women but not in men. CONCLUSION: A wide spatial QRS/T angle in BBB is associated with increased risk for CHD and all-cause mortality over and above the predictive value for BBB alone. The risk for women is as high as or higher than that in men.

An electrocardiographic sign of ischemic preconditioning.

Ischemic preconditioning is a form of intrinsic cardioprotection where an episode of sublethal ischemia protects against subsequent episodes of ischemia. Identifying a clinical biomarker of preconditioning could have important clinical implications, and prior work has focused on the electrocardiographic ST segment. However, the electrophysiology biomarker of preconditioning is increased action potential duration (APD) shortening with subsequent ischemic episodes, and APD shortening should primarily alter the T wave, not the ST segment. We translated findings from simulations to canine to patient models of preconditioning to test the hypothesis that the combination of increased [delta (Δ)] T wave amplitude with decreased ST segment elevation characterizes preconditioning. In simulations, decreased APD caused increased T wave amplitude with minimal ST segment elevation. In contrast, decreased action potential amplitude increased ST segment elevation significantly. In a canine model of preconditioning (9 mongrel dogs undergoing 4 ischemia-reperfusion episodes), ST segment amplitude increased more than T wave amplitude during the first ischemic episode [ΔT/ΔST slope = 0.81, 95% confidence interval (CI) 0.46-1.15]; however, during subsequent ischemic episodes the T wave increased significantly more than the ST segment (ΔT/ΔST slope = 2.43, CI 2.07-2.80) (P < 0.001 for interaction of occlusions 2 vs. 1). A similar result was observed in patients (9 patients undergoing 2 consecutive prolonged occlusions during elective percutaneous coronary intervention), with an increase in slope of ΔT/ΔST of 0.13 (CI -0.15 to 0.42) in the first occlusion to 1.02 (CI 0.31-1.73) in the second occlusion (P = 0.02). This integrated analysis of the T wave and ST segment goes beyond the standard approach to only analyze ST elevation, and detects cellular electrophysiology changes of preconditioning.

Argentina's most important contributions in the field of electrophysiology.

Latin American electrocardiology emerged internationally thanks to the Argentine School of Electrocardiology. All started when the idea of a different anatomy of the conduction system was not only necessary to change the paradigm of a bifascicular system, but also to question diagnostic electrocardiographic criteria adopted by the scientific community without dispute. Almost every scientific contribution coming from the Argentine School of Electrocardiology represented a significant step forward in the understanding of the electrophysiology of the heart and its electrocardiographic counterpart. There is another reason that increases their value: the noticeable simplicity of the technical facilities with which these studies were done from the modest laboratory in Argentina, whose production was purely and genuinely Latin American. In the following lines we summarize what we consider to be the greatest contributions of the Argentine school to world electrophysiology.

True complete left bundle branch block morphology strongly predicts good response to cardiac resynchronization therapy.

AIMS: To determine whether patients with congestive heart failure and true left bundle branch block (LBBB) morphology have better response to cardiac resynchronization therapy (CRT) than do patients without true LBBB. METHODS AND RESULTS: We defined true LBBB as conventional LBBB plus QRS duration ≥ 130 ms and mid-QRS notching/slurring in at least two of the leads I, aVL, V1, V2, V5, or V6. We prospectively enrolled 58 patients with heart failure and allocated them to three groups: true LBBB (t-LBBB, n = 22); non-true LBBB (nt-LBBB, LBBB with no notch or notches in fewer than two of the leads, n = 17); and non-specific intraventricular conduction delay (IVCD, n = 19). At 6 month follow-up, mean absolute increases in left ventricular ejection fraction were 16.0% ± 11.6% in t-LBBB, 8.1% ± 11.2% in nt-LBBB (P = 0.02), and 3.3% ± 7.8% in IVCD (P < 0.001, t-LBBB vs. IVCD) and changes in mean New York Heart Association class were -1.2 ± 0.6 in t-LBBB, -0.8 ± 0.6 in nt-LBBB (P = 0.071), and -0.5 ± 0.6 in IVCD (P = 0.01, t-LBBB vs. IVCD). All patients with t-LBBB were responders, some were super-responders. Multivariate analysis showed that t-LBBB (odds ratio, OR, 11.680; 95% confidence interval, CI, 1.966-69.390; P = 0.007) and left ventricular end-diastolic dimension (OR, 0.891; 95% CI, 0.797-0.996; P = 0.043) are independent predictors of super-response to CRT. CONCLUSION: In patients with conventional wider LBBB morphology, the presence of mid-QRS notching or slurring is a strong predictor of better response to CRT.

Reference intervals and method sensitivity for electrocardiology, hemodynamics, and body temperature parameters in healthy cynomolgus monkeys.

In nonclinical studies, electrocardiograms (ECG) of cynomolgus monkey are recorded intermittently by external leads in manually restrained animals (snapshot recording) or continuously by jacketed external telemetry (JET) or implanted radiotelemetry transmitter in freely moving animals. With the implanted device, blood pressure and core body temperature can be monitored simultaneously. Despite the frequent use of cynomolgus monkeys in nonclinical safety pharmacology testing, few reference data are available for this species, comparisons of the ECG recording methods are limited, and power analyses are seldom conducted. In this study, pretreatment data were recorded from 406, 663, and 131 healthy experimentally naïve monkeys using the snapshot, JET, and implantable method, respectively, from 2019 to 2021. Reference intervals were determined for ECG, blood pressure, and body temperature parameters. Diurnal effects were observed in these parameters, with the exception of QRS and pulse pressure. The QRS, QT, and heart rate-corrected QTc intervals, as well as blood pressure, had a weak positive relationship with age and/or body weight. There were no sex differences in these parameters, and the country of origin only had minimal influences. Compared to telemetry, snapshot ECG data had shorter RR, PR, and QT intervals and longer QRS interval. The JET and implanted telemetry ECG data were comparable. Effect size analysis was conducted to estimate the method sensitivity for each parameter in common non-clinical study design scenarios. Snapshot recording, JET, and implanted telemetry were sensitive to detect 7-15 milliseconds of changes in QTc intervals in standard study designs, indicating these are powerful methods for assessment of QT prolongation in vivo.

Cardiovascular waveforms - can we extract more from routine signals?

Cardiovascular waveforms such as blood pressure, ECG and photoplethysmography (PPG), are routinely acquired by specialised monitoring devices. Such devices include bedside monitors, wearables and radiotelemetry which sample at very high fidelity, yet most of this numerical data is disregarded and focus tends to reside on single point averages such as the maxima, minima, amplitude, rate and intervals. Whilst, these measures are undoubtedly of value, we may be missing important information by simplifying the complex waveform signal in this way. This Special Collection showcases recent advances in the appraisal of routine signals. Ultimately, such approaches and technologies may assist in improving the accuracy and sensitivity of detecting physiological change. This, in turn, may assist with identifying efficacy or safety signals for investigational new drugs or aidpatient diagnosis and management, supporting scientific and clinical decision making.

The History of Atrial Flutter Electrophysiology, from Entrainment to Ablation: A 100-Year Experience in the Precision Electrocardiology.

Atrial flutter (AFL) is a regular supraventricular reentrant tachycardia generating a continuous fluttering of the baseline electrocardiography (ECG) at a rate of 250 to 300 beats per minute. AFL is classified based on the involvement of the cavo-tricuspid isthmus in the circuit. The "isthmic" (or type 1) AFL develops entirely in the right atrium; this circuit is commonly activated in a counter-clockwise direction, generating the common sawtooth ECG morphology in the inferior leads (slow descendent-fast ascendent). AFL can be nonisthmus dependent (type 2), often presenting with faster atrial rate and most commonly a left atrial location.

2021 ISHNE/HRS/EHRA/APHRS Collaborative Statement on mHealth in Arrhythmia Management: Digital Medical Tools for Heart Rhythm Professionals: From the International Society for Holter and Noninvasive Electrocardiology/Heart Rhythm Society/European Heart Rhythm Association/Asia Pacific Heart Rhythm Society.

This collaborative statement from the International Society for Holter and Noninvasive Electrocardiology/Heart Rhythm Society/European Heart Rhythm Association/Asia Pacific Heart Rhythm Society describes the current status of mobile health ("mHealth") technologies in arrhythmia management. The range of digital medical tools and heart rhythm disorders that they may be applied to and clinical decisions that may be enabled are discussed. The facilitation of comorbidity and lifestyle management (increasingly recognized to play a role in heart rhythm disorders) and patient self-management are novel aspects of mHealth. The promises of predictive analytics but also operational challenges in embedding mHealth into routine clinical care are explored.

Comparison between smartphone electrocardiography and standard three-lead base apex electrocardiography in healthy horses.

BACKGROUND: Cardiac arrhythmias are commonly auscultated during routine physical examinations in horses and determining the underlying electrical abnormality using an ECG is important. The most commonly used device is a three-lead base apex system (Televet), however few practitioners carry this for routine visits. With recognition of the utility of smartphone-based ECGs in humans, dogs and ruminants, the AliveCor single-lead bipolar smartphone-based ECG has gained popularity. The objective of this study was to determine if AliveCor and Televet ECG measurements were comparable in healthy horses using multiple observers. METHODS: ECGs were performed on 15 healthy horses simultaneously using the AliveCor and Televet. RESULTS: There was very good to perfect interdevice and interobserver agreement for heart rate and RR interval measurement, and moderate-to-good interdevice and interobserver agreement for detection of non-pathological arrhythmias. Interdevice agreement for measurement of P-wave and QRS duration, QT, PR and T-peak to T-end interval was poor to fair. Interestingly, interobserver agreement for P-wave and QRS duration, QT, PR, and T-peak to T-end interval measurements was fair to good. CONCLUSION: Overall, the AliveCor is comparable to the Televet for heart rate and RR measurement, and for the detection of non-pathogenic arrhythmias with acceptable agreement between observers.

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 (TPEAK-TEND) 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, TPEAK-TEND 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.

Insights Into the Spatiotemporal Patterns of Complexity of Ventricular Fibrillation by Multilead Analysis of Body Surface Potential Maps.

BACKGROUND: Ventricular fibrillation (VF) is the main cause of sudden cardiac death, but its mechanisms are still unclear. We propose a noninvasive approach to describe the progression of VF complexity from body surface potential maps (BSPMs). METHODS: We mapped 252 VF episodes (16 ± 10 s) with a 252-electrode vest in 110 patients (89 male, 47 ± 18 years): 50 terminated spontaneously, otherwise by electrical cardioversion (DCC). Changes in complexity were assessed between the onset ("VF start") and the end ("VF end") of VF by the nondipolar component index (N D I B S P M ), measuring the fraction of energy nonpreserved by an equivalent 3D dipole from BSPMs. Higher NDI reflected lower VF organization. We also examined other standard body surface markers of VF dynamics, including fibrillatory wave amplitude (A BSPM ), surface cycle length (BsCL BSPM ) and Shannon entropy (S h E n B S P M ). Differences between patients with and without structural heart diseases (SHD, 32 vs. NSHD, 78) were also tested at those stages. Electrocardiographic features were validated with simultaneous endocardium cycle length (CL) in a subset of 30 patients. RESULTS: All BSPM markers measure an increase in electrical complexity during VF (p < 0.0001), and more significantly in NSHD patients. Complexity is significantly higher at the end of sustained VF episodes requiring DCC. Intraepisode intracardiac CL shortening (VF start 197 ± 24 vs. VF end 169 ± 20 ms; p < 0.0001) correlates with an increase in NDI, and decline in surface CL, f-wave amplitude, and entropy (p < 0.0001). In SHD patients VF is initially more complex than in NSHD patients (N D I B S P M , p = 0.0007; S h E n B S P M , p < 0.0001), with moderately slower (BsCL BSPM , p = 0.06), low-amplitude f-waves (A BSPM , p < 0.0001). In this population, lower NDI (p = 0.004) and slower surface CL (p = 0.008) at early stage of VF predict self-termination. In the NSHD group, a more abrupt increase in VF complexity is quantified by all BSPM parameters during sustained VF (p < 0.0001), whereas arrhythmia evolution is stable during self-terminating episodes, hinting at additional mechanisms driving VF dynamics. CONCLUSION: Multilead BSPM analysis underlines distinct degrees of VF complexity based on substrate characteristics.