Local Conduction Velocity Mapping for Electrocardiographic Imaging

International audienceSlow conduction is a well-known pro-arrhythmic feature for tachycardia and fibrillation. Cardiac conduction velocity (CV) mapping can be extremely helpful for investigating unusual activation patterns. Although methods have been developed to estimate velocity vector field, from ex-vivo preparations (e.g. from optical mapping recordings), the estimation from in-vivo electrograms (EGMs) remains challenging. This paper presents a new method specifically designed for EGMs reconstructed non-invasively from body surface potentials using electrocardiographic imaging (ECGi). The algorithm is based on cardiac activation maps and assumes either a linear or quadratic wavefront shape. The proposed methodology was performed on computed and experimental data for epicardial pacing on healthy tissue. The results were compared with reference velocity vector fields and evaluated by analyzing the errors of direction and speed. The outcomes indicate that a linear wavefront is the most suited for cardiac propagation in healthy tissue

Arrhythmias After Tetralogy of Fallot Repair

Tetralogy of Fallot is the most common cyanotic congenital heart disease, with a good outcome after total surgical correction. In spite of a low perioperative mortality and a good quality of life, late sudden death remains a significant clinical problem, mainly related to episodes of sustained ventricular tachycardia and ventricular fibrillation. Fibro-fatty substitution around infundibular resection, intraventricular septal scar, and patchy myocardial fibrosis, may provide anatomical substrates of abnormal depolarization and repolarization causing reentrant ventricular arrhythmias. Several non-invasive indices based on classical examination such as ECG, signal-averaging ECG, and echocardiography have been proposed to identify patients at high risk of sudden death, with hopeful results. In the last years other more sophisticated invasive and non-invasive tools, such as heart rate variability, electroanatomic mapping and cardiac magnetic resonance added a relevant contribution to risk stratification. Even if each method per se is affected by some limitations, a comprehensive multifactorial clinical and investigative examination can provide an accurate risk evaluation for every patien

Comparing Non-invasive Inverse Electrocardiography With Invasive Endocardial and Epicardial Electroanatomical Mapping During Sinus Rhythm

This study presents a novel non-invasive equivalent dipole layer (EDL) based inverse electrocardiography (iECG) technique which estimates both endocardial and epicardial ventricular activation sequences. We aimed to quantitatively compare our iECG approach with invasive electro-anatomical mapping (EAM) during sinus rhythm with the objective of enabling functional substrate imaging and sudden cardiac death risk stratification in patients with cardiomyopathy. Thirteen patients (77% males, 48 ± 20 years old) referred for endocardial and epicardial EAM underwent 67-electrode body surface potential mapping and CT imaging. The EDL-based iECG approach was improved by mimicking the effects of the His-Purkinje system on ventricular activation. EAM local activation timing (LAT) maps were compared with iECG-LAT maps using absolute differences and Pearson’s correlation coefficient, reported as mean ± standard deviation [95% confidence interval]. The correlation coefficient between iECG-LAT maps and EAM was 0.54 ± 0.19 [0.49–0.59] for epicardial activation, 0.50 ± 0.27 [0.41–0.58] for right ventricular endocardial activation and 0.44 ± 0.29 [0.32–0.56] for left ventricular endocardial activation. The absolute difference in timing between iECG maps and EAM was 17.4 ± 7.2 ms for epicardial maps, 19.5 ± 7.7 ms for right ventricular endocardial maps, 27.9 ± 8.7 ms for left ventricular endocardial maps. The absolute distance between right ventricular endocardial breakthrough sites was 30 ± 16 mm and 31 ± 17 mm for the left ventricle. The absolute distance for latest epicardial activation was median 12.8 [IQR: 2.9–29.3] mm. This first in-human quantitative comparison of iECG and invasive LAT-maps on both the endocardial and epicardial surface during sinus rhythm showed improved agreement, although with considerable absolute difference and moderate correlation coefficient. Non-invasive iECG requires further refinements to facilitate clinical implementation and risk stratification

Electrocardiographic imaging demonstrates electrical synchrony improvement by dynamic atrioventricular delays in patients with left bundle branch block and preserved atrioventricular conduction

Aims: Cardiac resynchronization therapy programmed to dynamically fuse pacing with intrinsic conduction using atrioventricular (AV) timing algorithms (e.g. SyncAV) has shown promise; however, mechanistic data are lacking. This study assessed the impact of SyncAV on electrical dyssynchrony across various pacing modalities using non-invasive epicardial electrocardiographic imaging (ECGi). Methods and results: Twenty-five patients with left bundle-branch block (median QRS duration (QRSd) 162.7 ms) and intact AV conduction (PR interval 174.0 ms) were prospectively enrolled. ECGi was performed acutely during biventricular pacing with fixed nominal AV delays (BiV) and using SyncAV (optimized for the narrowest QRSd) during: BiV + SyncAV, LV-only single-site (LVSS + SyncAV), MultiPoint pacing (MPP + SyncAV), and LV-only MPP (LVMPP + SyncAV). Dyssynchrony was quantified via ECGi (LV activation time, LVAT; RV activation time, RVAT; LV electrical dispersion index, LVEDi; ventricular electrical uncoupling index, VEU; and biventricular total activation time, VVtat). Intrinsic conduction LVAT (124 ms) was significantly reduced by BiV pacing (109 ms) (P = 0.001) and further reduced by LVSS + SyncAV (103 ms), BiV + SyncAV (103 ms), LVMPP + SyncAV (95 ms), and MPP + SyncAV (90 ms). Intrinsic RVAT (93 ms), VVtat (130 ms), LVEDi (36 ms), VEU (50 ms), and QRSd (163 ms) were reduced by SyncAV across all pacing modes. More patients exhibited minimal LVAT, VVtat, LVEDi, and QRSd with MPP + SyncAV than any other modality. Conclusion: Dynamic AV delay programming targeting fusion with intrinsic conduction significantly reduced dyssynchrony, as quantified by ECGi and QRSd for all evaluated pacing modes. MPP + SyncAV achieved the greatest synchrony overall but not for all patients, highlighting the value of pacing mode individualization during fusion optimization

Personalized Modeling of Atrial Activation and P-waves: a Comparison Between Invasive and Non-Invasive Cardiac Mapping

Biatrial personalized models incorporating functional and anatomical features are becoming a promising tool for planning therapy for patients with atrial fibrillation (AF). Conduction velocity (CV) is one of the main features to be matched during the process of functional personalization, as it can identify electrical abnormalities in the cardiac tissue. The spatial distribution of CV can be estimated from local activation times (LAT) maps from non-invasive electrocardiographic imaging (ECGI) or invasive electroanatomical mapping systems (EAMS). We investigated the effect of using either invasive LAT maps from EAMS or non-invasive LAT maps from ECGI to personalize two biatrial models by comparing the virtual P-waves obtained from these LAT maps with the measured P-waves from the surface electrocardiogram (ECG). For both modalities – ECGI and EAMS – we found a qualitative match between simulated and measured P-waves but observed quantitative differences. The root-mean-square error (RMSE) between measured and simulated signals for patient A was 0.26±0.11 mV and 0.38±0.31 mV, while for patient B it was 0.21±0.09 mV and 0.14±0.05 mV for EAMS and ECGI, respectively. The correlation between measured and simulated signals from ECGI and EAMS was 0.69±0.34 and 0.71±0.26 for patient A and 0.71±0.18 and 0.72±0.18 for patient B. Our results suggest that LAT maps from ECGI and EAMS show differences, which are also reflected in the computed P-wave on the body surface

A novel simplified approach to radiofrequency catheter ablation of idiopathic ventricular outflow tract premature ventricular contractions : from substrate analysis to results

Summary: Premature ventricular contractions (PVCs) are a common finding in the general population. The most common site of PVCs, in patients without structural heart disease, is the right ventricular outflow tract (RVOT) and the left ventricular outflow tract (LVOT). The prognosis associated with frequent PVCs depends on the presence of structural heart disease, so that idiopathic PVCs have been considered benign. Recently however, evidence has emerged that a small percentage of those patients may present with polymorphic ventricular tachycardia or ventricular fibrillation or evolve to left ventricular dysfunction. Catheter ablation is indicated for frequent symptomatic PVCs refractory to medical therapy or in case of patient’s preference. Currently, catheter ablation is based on activation mapping, confirmed by pace mapping match of at least 11/12 ECG leads between the paced beat and the PVC morphology. The acute success rate ranges from 78% to 100% according to the series, and to the location of the PVCs. Remote magnetic navigation presents as a good option for PVC ablation offering a high success rate with better safety profile. Intraprocedural low PVC burden occurs in up to 30% to 48% of cases, resulting in either, cancelation of the ablation procedure in up to 11% of patients, or reduction of the success rate from 85% to 56% when ablation is attempted with pace mapping only. Recently non-invasive mapping systems based on the electrocardiogram analysis (ECGI) have been developed. These systems are capable of mapping an arrhythmia with just one beat, instead of the usual point by point acquisition, being especially useful in the case of rare arrhythmias. EGGI also constitutes a valuable noninvasive tool for studying the mechanisms of arrhythmias. With this system we were able to demonstrate the presence of an electrophysiological substrate in the RVOT of patients with PVCs and apparently normal hearts. It has been accepted for many years that in patients with idiopathic PVCs from the outflow tracts, the RVOT displays normal electroanatomical mapping features and electrophysiological properties. However, we have demonstrated that there is a substrate for idiopathic PVCs in the form of low voltage areas (LVAs) that are not detected by usual image methods including cardiac magnetic resonance (CMR). We described for the first time, the association between the presence of ST-segment elevation in V1-V2 at the 2nd intercostal space (ICS) with LVAs across the RVOT and have proposed it as a non-invasive electrocardiographic marker of LVAs. We also identified the presence of abnormal potentials in intracardiac electrograms at the ablation site during diastole, after the T wave of the surface ECG that became presystolic during the PVC and were called diastolic potentials (DPs). In Chapter V we describe in detail the study that validated those findings and evaluated the feasibility and efficacy of a proposed simplified substrate approach, for catheter ablation in patients with low intraprocedural PVC burden, defined as less than 2 PVCs/min in the first 5 minutes of the procedure. It consists of fast mapping of the RVOT in sinus rhythm looking for LVAs and DPs, identifying the area, and finally performing a restricted activation map of the PVCs at that area. Briefly, it was a prospective single-arm clinical trial at two centers and three groups were studied: a) patients with low intraprocedural PVC burden that underwent ablation with the novel simplified approach method (study group); b) patients with low intraprocedural PVC burden that underwent ablation using the standard activation mapping method between 2016 and 2018 (historical group); and c) patients without PVCs, subjected to catheter ablation of supraventricular tachycardias that agreed to have a voltage map of the RVOT in sinus rhythm performed (validation group). The calculated sample size was 38 patients in each group. The exclusion criteria were as follows: known structural heart disease, history of sustained ventricular arrhythmias, inability to perform CMR, previous ablation and standard 12-Lead ECG with evidence of conduction or electrical disease or abnormal QRS morphology were excluded. Patients in the study and validation groups, had an ECG performed at the 2nd ICS and the RVOT mapped in sinus rhythm to assess the presence of ST-segment elevation, and LVAS and DPs, respectively. The results were compared between both groups. The study group and the historical group were compared regarding the efficacy of the new simplified ablation method in terms of abolishment of the PVCs and improvement of procedure speed and success rate. When available, ECGI was performed in the study group to evaluate the accuracy of the method to identify the site of origin of the PVCs. The ECGI was performed with two systems, the Amycard (EP Solutions SA, Switzerland) and the VIVO (Catheter Precision, NJ USA). The prevalence of LVAs and DPs was significantly higher in the study group in comparison with the validation group, respectively, 71% vs 11%, p<0.0001 and 87% vs 8%, p<0.0001. The ST-segment elevation was a good predictor of LVAS with a sensitivity of 87%, specificity of 96%, positive predictor value of 93% and negative predictor value of 91%. The novel simplified approach abolished the PVCs in 90% of the patients as opposed to 47% of patients in the historical group, p<0.0001. Only 74% patients underwent ablation in the historical group versus 100% in the study group. In patients that underwent ablation, the procedure time was significantly lower in the study group when comparing to the historical group, 130 (100-164) vs 183 (160-203) min, p<0.0001 and the success rate was significantly higher, 90% vs 64%, p=0.013. The recurrence rate in patients with a successful ablation after a median follow-up time of 1060 (574-1807) days, was not significantly different between both groups, Log-Rank=0.125 ECGI before ablation was performed in 17 patients in the study group. In 6 patients the ECGI was performed just with the Amycard system, in two just with the VIVO system and in 9 patients both systems were used. We found a good agreement between the ECGI and the invasive mapping, with the predicted site of origin being in the same or contiguous segment of the ablation site in 14/15 patients (93%) with the Amycard system and in 100% of patients with the VIVO system. When both systems were used simultaneously, the agreement between them was 8/9 (90%). So, in conclusion, the proposed approach partially based on substrate mapping including searching for LVAs and DPs, proved to be feasible, faster, and more efficient than the previous approach based exclusively on activation mapping. ST-segment elevation at the 2nd ICS proved to be a good predictor of LVAs. ECGI was a valuable tool to noninvasively predict the site of origin the arrhythmia

Clinical Application of Electrocardiographic Imaging in Patients with Ischemic Cardiomyopathy, Early Repolarization Syndrome and Brugada Syndrome

Electrocardiographic Imaging (ECGI) is a noninvasive modality for human application in both research and clinical settings. It is an important tool for investigation of abnormal electrophysiological (EP) substrates and arrhythmias in patients. Multi-channel body surface potential recordings and the patient-specific heart-torso geometry from ECG gated computed tomography are processed by ECGI algorithms to reconstruct epicardial potentials, electrograms and patterns of activation and repolarization. ECGI is able to continuously generate high-resolution, panoramic EP maps of the entire heart on a beat-by-beat basis, which cannot be achieved with invasive catheter mapping. ECGI was applied in ischemic cardiomyopathy patients to characterize the abnormal EP substrate associated with myocardial infarction. In patients who developed ventricular tachycardia during the study, the arrhythmia activation pattern and site of origin were correlated with the EP substrate to identify components of the reentry circuit. The study subjects included patients with and without a history of clinical ventricular arrhythmias. The properties of scar EP substrate were compared between the two groups to determine whether substantial differences exist. This differentiating capability of ECGI was examined as a potential tool for arrhythmic risk stratification in this population. In a separate clinical study, ECGI was applied in a group of patients with early repolarization syndrome, which has been recently shown to be associated with an increased risk of ventricular fibrillation. The ventricular activation and repolarization patterns during sinus rhythm were characterized and compared with data from normal controls. This study aimed to provide insights into the mechanisms of the early repolarization ECG pattern and the related arrhythmogenesis. ECGI was also applied in patients with Brugada syndrome to image the EP substrate and to study the underlying mechanisms of the Brugada ECG pattern and abnormal epicardial electrograms. Heart rate change protocol in selected patients helped unmask the coexistence of abnormal conduction and abnormal repolarization in the EP substrate. Brugada syndrome patients were also compared with patients with right bundle branch block (generally considered benign) to determine whether the substrate was specific to Brugada syndrome, and whether ECGI can differentiate between these two pathologies with similar ECG patterns. The above studies demonstrated the feasibility and clinical importance of ECGI for noninvasive diagnosis, pre-procedural guidance and arrhythmic risk stratification in human subjects

Acidosis slows electrical conduction through the atrio-ventricular node

Acidosis affects the mechanical and electrical activity of mammalian hearts but comparatively little is known about its effects on the function of the atrio-ventricular node (AVN). In this study, the electrical activity of the epicardial surface of the left ventricle of isolated Langendorff-perfused rabbit hearts was examined using optical methods. Perfusion with hypercapnic Tyrode's solution (20% CO2, pH 6.7) increased the time of earliest activation (Tact) from 100.5 ± 7.9 to 166.1 ± 7.2 ms (n = 8) at a pacing cycle length (PCL) of 300 ms (37°C). Tact increased at shorter PCL, and the hypercapnic solution prolonged Tact further: at 150 ms PCL, Tact was prolonged from 131.0 ± 5.2 to 174.9 ± 16.3 ms. 2:1 AVN block was common at shorter cycle lengths. Atrial and ventricular conduction times were not significantly affected by the hypercapnic solution suggesting that the increased delay originated in the AVN. Isolated right atrial preparations were superfused with Tyrode's solutions at pH 7.4 (control), 6.8 and 6.3. Low pH prolonged the atrial-Hisian (AH) interval, the AVN effective and functional refractory periods and Wenckebach cycle length significantly. Complete AVN block occurred in 6 out of 9 preparations. Optical imaging of conduction at the AV junction revealed increased conduction delay in the region of the AVN, with less marked effects in atrial and ventricular tissue. Thus acidosis can dramatically prolong the AVN delay, and in combination with short cycle lengths, this can cause partial or complete AVN block and is therefore implicated in the development of brady-arrhythmias in conditions of local or systemic acidosis