Endocardial infarct scar recognition by myocardial electrical impedance is not influenced by changes in cardiac activation sequence

Influence of Heart Rate and Change in Wavefront Direction through Pacing on Conduction Velocity and Voltage Amplitude in a Porcine Model: A High-Density Mapping Study

BACKGROUND

Understanding the dynamics of conduction velocity (CV) and voltage amplitude (VA) is crucial in cardiac electrophysiology, particularly for substrate-based catheter ablations targeting slow conduction zones and low voltage areas. This study utilizes ultra-high-density mapping to investigate the impact of heart rate and pacing location on changes in the wavefront direction, CV, and VA of healthy pig hearts.

METHODS

We conducted in vivo electrophysiological studies on four healthy juvenile pigs, involving various pacing locations and heart rates. High-resolution electroanatomic mapping was performed during intrinsic normal sinus rhythm (NSR) and electrical pacing. The study encompassed detailed analyses at three levels: entire heart cavities, subregions, and localized 5-mm-diameter circular areas. Linear mixed-effects models were used to analyze the influence of heart rate and pacing location on CV and VA in different regions.

RESULTS

An increase in heart rate correlated with an increase in conduction velocity and a decrease in voltage amplitude. Pacing influenced conduction velocity and voltage amplitude. Pacing also influenced conduction velocity and voltage amplitude, with varying effects observed based on the pacing location within different heart cavities. Pacing from the right atrium (RA) decreased CV in all heart cavities. The overall CV and VA changes in the whole heart cavities were not uniformly reflected in all subregions and subregional CV and VA changes were not always reflected in the overall analysis. Overall, there was a notable variability in absolute CV and VA changes attributed to pacing.

CONCLUSIONS

Heart rate and pacing location influence CV and VA within healthy juvenile pig hearts. Subregion analysis suggests that specific regions of the heart cavities are more susceptible to pacing. High-resolution mapping aids in detecting regional changes, emphasizing the substantial physiological variations in CV and VA.

Circadian Regulation of Drug Responses: Toward Sex-Specific and Personalized Chronotherapy

Today's challenge for precision medicine involves the integration of the impact of molecular clocks on drug pharmacokinetics, toxicity, and efficacy toward personalized chronotherapy. Meaningful improvements of tolerability and/or efficacy of medications through proper administration timing have been confirmed over the past decade for immunotherapy and chemotherapy against cancer, as well as for commonly used pharmacological agents in cardiovascular, metabolic, inflammatory, and neurological conditions. Experimental and human studies have recently revealed sexually dimorphic circadian drug responses. Dedicated randomized clinical trials should now aim to issue personalized circadian timing recommendations for daily medical practice, integrating innovative technologies for remote longitudinal monitoring of circadian metrics, statistical prediction of molecular clock function from single-timepoint biopsies, and multiscale biorhythmic mathematical modelling. Importantly, chronofit patients with a robust circadian function, who would benefit most from personalized chronotherapy, need to be identified. Conversely, nonchronofit patients could benefit from the emerging pharmacological class of chronobiotics targeting the circadian clock.

Electrophysiological and histological characterization of atrial scarring in a model of isolated atrial myocardial infarction

Background: Characterization of atrial myocardial infarction is hampered by the frequent concurrence of ventricular infarction. Theoretically, atrial infarct scarring could be recognized by multifrequency tissue impedance, like in ventricular infarction, but this remains to be proven. Objective: This study aimed at developing a model of atrial infarction to assess the potential of multifrequency impedance to recognize areas of atrial infarct scar. Methods: Seven anesthetized pigs were submitted to transcatheter occlusion of atrial coronary branches arising from the left coronary circumflex artery. Six weeks later the animals were anesthetized and underwent atrial voltage mapping and multifrequency impedance recordings. The hearts were thereafter extracted for anatomopathological study. Two additional pigs not submitted to atrial branch occlusion were used as controls. Results: Selective occlusion of the atrial branches induced areas of healed infarction in the left atrium in 6 of the 7 cases. Endocardial mapping of the left atrium showed reduced multi-frequency impedance (Phase angle at 307 kHz: from -17.1° ± 5.0° to -8.9° ± 2.6°, p < .01) and low-voltage of bipolar electrograms (.2 ± 0.1 mV vs. 1.9 ± 1.5 mV vs., p < .01) in areas affected by the infarction. Data variability of the impedance phase angle was lower than that of bipolar voltage (coefficient of variability of phase angle at307 kHz vs. bipolar voltage: .30 vs. .77). Histological analysis excluded the presence of ventricular infarction. Conclusion: Selective occlusion of atrial coronary branches permits to set up a model of selective atrial infarction. Atrial multifrequency impedance mapping allowed recognition of atrial infarct scarring with lesser data variability than local bipolar voltage mapping. Our model may have potential applicability on the study of atrial arrhythmia mechanisms.

Differentiation using minimally-invasive bioimpedance measurements of healthy and pathological lung tissue through bronchoscopy

Purpose

To use minimally-invasive transcatheter electrical impedance spectroscopy measurements for tissue differentiation among healthy lung tissue and pathologic lung tissue from patients with different respiratory diseases (neoplasm, fibrosis, pneumonia and emphysema) to complement the diagnosis at real time during bronchoscopic procedures.

Methods

Multi-frequency bioimpedance measurements were performed in 102 patients. The two most discriminative frequencies for impedance modulus (|Z|), phase angle (PA), resistance (R) and reactance (Xc) were selected based on the maximum mean pair-wise Euclidean distances between paired groups. One-way ANOVA for parametric variables and Kruskal-Wallis for non-parametric data tests have been performed with post-hoc tests. Discriminant analysis has also been performed to find a linear combination of features to separate among tissue groups.

Results

We found statistically significant differences for all the parameters between: neoplasm and pneumonia (p < 0.05); neoplasm and healthy lung tissue (p < 0.001); neoplasm and emphysema (p < 0.001); fibrosis and healthy lung tissue (p ≤ 0.001) and pneumonia and healthy lung tissue (p < 0.01). For fibrosis and emphysema (p < 0.05) only in |Z|, R and Xc; and between pneumonia and emphysema (p < 0.05) only in |Z| and R. No statistically significant differences (p > 0.05) are found between neoplasm and fibrosis; fibrosis and pneumonia; and between healthy lung tissue and emphysema.

Conclusion

The application of minimally-invasive electrical impedance spectroscopy measurements in lung tissue have proven to be useful for tissue differentiation between those pathologies that leads increased tissue and inflammatory cells and those ones that contain more air and destruction of alveolar septa, which could help clinicians to improve diagnosis.

Biophysical Tissue Characterization of Ventricular Tachycardia Substrate With Local Impedance Mapping to Predict Critical Sites

BACKGROUND

New tools are needed to improve ventricular tachycardia (VT) substrate characterization and optimize outcomes. LI provides biophysical tissue characterization.

OBJECTIVES

The purpose of this study was to test local impedance (LI)-based mapping to predict critical ventricular tachycardia components after myocardial infarction (MI).

METHODS

One month after a nonreperfused anterior MI, endo-epicardial high-density electroanatomic mapping and endocardial LI mapping were performed in 23 Landrace Large X White pigs. LI thresholds were set using the blood pool value to define a 10 Ω range: low (<blood pool -1Ω), intermediate (≥blood pool -1Ω and ≤blood pool +9Ω), and high (normal) tissue resistance (>blood pool +9Ω).

RESULTS

Low LI was detected in low-voltage areas in 100% of cases, but intermediate LI was found in both core (87%) and border zone (12.5%) voltage areas. A total of 17 VTs were induced (VT isthmus identified in 9 animals). VT inducibility was associated with the size of intermediate LI area (OR: 1.19 [95% CI: 1.0-1.4]; P = 0.039) and the presence of specific LI patterns: LI corridor (OR: 15.0 [95% CI: 1.3-169.9]; P = 0.029); LI gradient (OR: 30.0 [95% CI: 2.1-421.1]; P = 0.012), high LI heterogeneity (OR: 21.7 [95% CI: 1.8-260.6]; P = 0.015), and presence of ≥2 low LI regions (OR: 11.3 [95% CI: 1.0-130.2]; P = 0.053). Potential VT isthmuses were in areas of intermediate LI and colocalized to LI patterns associated with VT inducibility in all cases (LI corridors or LI gradient). Low LI regions did not actively participate in the VT circuit (0%).

CONCLUSIONS

LI mapping is feasible and may add useful characterization of the VT substrate. Specific LI patterns (ie, corridors, gradients) were associated with VT inducibility and colocalized with the VT isthmus, thus representing a potential new target for ablation in substrate-based procedures.

Lipomatous Metaplasia Enables Ventricular Tachycardia by Reducing Current Loss Within the Protected Corridor

BACKGROUND

Post-myocardial infarction ventricular tachycardia (VT) is due to re-entry through surviving conductive myocardial corridors across infarcted tissue. However, not all conductive corridors participate in re-entry.

OBJECTIVES

This study sought to test the hypothesis that critical VT corridors are more likely to traverse near lipomatous metaplasia (LM) and that current loss is reduced during impulse propagation through such corridors.

METHODS

Among 30 patients in the Prospective 2-center INFINITY (Intra-Myocardial Fat Deposition and Ventricular Tachycardia in Cardiomyopathy) study, potential VT-viable corridors within myocardial scar or LM were computed from late gadolinium enhancement cardiac magnetic resonance images. Because late gadolinium enhancement highlights both scar and LM, LM was distinguished from scar by using computed tomography. The SD of the current along each corridor was measured.

RESULTS

Scar exhibited lower impedance than LM (median Z-score -0.22 [IQR: -0.84 to 0.35] vs -0.07 [IQR: -0.67 to 0.54]; P < 0.001). Among all 381 corridors, 84 were proven to participate in VT re-entry circuits, 83 (99%) of which traversed or were adjacent to LM. In comparison, only 13 (4%) non-VT corridors were adjacent to LM. Critical corridors adjacent to LM displayed lower SD of current compared with noncritical corridors through scar but distant from LM (2.0 [IQR: 1.0 to 3.4] μA vs 8.4 [IQR: 5.5 to 12.8] μA; P < 0.001).

CONCLUSIONS

Corridors critical to VT circuitry traverse infarcted tissue through or near LM. This association is likely mediated by increased regional resistance and reduced current loss as impulses traverse corridors adjacent to LM.

Requirement of larger local impedance reduction for successful lesion formation at carinal area during pulmonary vein isolation

PURPOSE

Local impedance (LI) measurement from an ablation catheter is useful in predicting lesion size and acute success of pulmonary vein isolation (PVI). The LI variation can be described by absolute LI drop (ΔLID) or ΔLID/initial LI (%LID). We evaluated the utility of these parameters in predicting acute lesion durability during PVI using a novel catheter capable of measuring both LI and contact force (CF).

METHODS

PVI with a targeted CF, power, and duration was performed in 23 consecutive patients with paroxysmal atrial fibrillation. LI was blinded to operators during ablation. Parameters for each RF application were collected and compared for acute successful lesions and gaps.

RESULTS

A total of 1633 RF applications including 97 (5.9%) gap lesions were analyzed. Successful lesions were more frequently observed at non-carinal sites and those with higher contact force, FTI, initial LI, and larger variation of LI and generator impedance (GI). Multivariate analysis demonstrated that absolute GI drop (ΔGID) [OR 1.09 (1.04-1.15), p < 0.001], ΔLID [1.12 (1.09-1.16), p < 0.001], ΔGID/initial GI (%GID) [OR 1.04 (1.01-1.07), p = 0.01], and %LID [OR 1.15 (1.12-1.28), p < 0.001] were significantly associated with successful lesions, and carinal site [OR 0.15(0.09-0.24), p < 0.001] was significantly related to gaps. Both ΔLID and %LID equally predicted the acute durability of lesions during PVI. ΔLID ≥ 24Ω and %LID ≥ 15% at the carina, and ΔLID ≥ 21Ω and %LID ≥ 14% at non-carinal sites significantly predicted acute successful lesions with negative predictive values of 93-99%.

CONCLUSIONS

Both ΔLID and %LID were equally useful in predicting acute successful lesions during PVI. Larger cut-off values should be applied to carinal sites.

Nanoengineered Sprayable Therapy for Treating Myocardial Infarction

We report the development, as well as the in vitro and in vivo testing, of a sprayable nanotherapeutic that uses surface engineered custom-designed multiarmed peptide grafted nanogold for on-the-spot coating of an infarcted myocardial surface. When applied to mouse hearts, 1 week after infarction, the spray-on treatment resulted in an increase in cardiac function (2.4-fold), muscle contractility, and myocardial electrical conductivity. The applied nanogold remained at the treatment site 28 days postapplication with no off-target organ infiltration. Further, the infarct size in the mice that received treatment was found to be <10% of the total left ventricle area, while the number of blood vessels, prohealing macrophages, and cardiomyocytes increased to levels comparable to that of a healthy animal. Our cumulative data suggest that the therapeutic action of our spray-on nanotherapeutic is highly effective, and in practice, its application is simpler than other regenerative approaches for treating an infarcted heart.

Local Electrical Impedance Mapping of the Atria: Conclusions on Substrate Properties and Confounding Factors

The treatment of atrial fibrillation and other cardiac arrhythmias as a major cause of cardiovascular hospitalization has remained a challenge predominantly for patients with severely remodeled substrate. Individualized ablation strategies are extremely important both for pulmonary vein isolation and subsequent ablations. Current approaches to identifying arrhythmogenic regions rely on electrogram-based features such as activation time and voltage. Novel technologies now enable clinical assessment of the local impedance as tissue property. Previous studies demonstrated its use for ablation monitoring and indicated its potential to differentiate healthy substrate, scar, and pathological tissue. This study investigates the potential of local electrical impedance-based substrate mapping of the atria for human in-vivo data. The presented pipeline for impedance mapping particularly contains options for dealing with undesirable effects originating from cardiac motion, catheter motion, or proximity to other intracardiac devices. Bloodpool impedance was automatically determined as a patient-specific reference. Full-chamber, left atrial impedance maps were drawn up from interpolating the measured impedances to the atrial endocardium. Finally, the origin and magnitude of oscillations of the raw impedance recording were probed into. The most dominant reason for exclusion of impedance samples was the loss of endocardial contact. With median elevations above the bloodpool impedance between 29 and 46 Ω, the impedance within the pulmonary veins significantly exceeded the remaining atrial walls presenting median elevations above the bloodpool impedance between 16 and 20 Ω. Previous ablation lesions were distinguished from their surroundings by a significant drop in local impedance while the corresponding regions did not differ for the control group. The raw impedance was found to oscillate with median amplitudes between 6 and 17 Ω depending on the patient. Oscillations were traced back to an interplay of atrial, ventricular, and respiratory motion. In summary, local impedance measurements demonstrated their capability to distinguish pathological atrial tissue from physiological substrate. Methods to limit the influence of confounding factors that still hinder impedance mapping were presented. Measurements at different frequencies or the combination of multiple electrodes could lead to further improvement. The presented examples indicate that electrogram- and impedance-based substrate mapping have the potential to complement each other toward better patient outcomes in future.

A Novel High-Resolution Surface Electrocardiographic Method to Identify and Characterize Myocardial Scar: A Proof-of-Concept Study

Background

The placement of the left ventricular (LV) lead in an area free of myocardial scar is an important determinant of cardiac resynchronization therapy response. We sought to develop and validate a simple, practical, and novel electrocardiographic (ECG)-based approach to intraoperatively identify the presence of LV scar. We hypothesized that there would be a reduction in the measured amplitude of the LV pacing stimulus on the skin surface using a high-resolution (HR) ECG when pacing from LV regions with scar compared with regions without scar. We term this the ECG Amplitude Signal Evaluation (EASE) method.

Methods

Consecutive patients with ischemic LV systolic dysfunction and standard criteria for de novo cardiac resynchronization therapy implantation were prospectively enrolled. All underwent a preimplant contrast-enhanced cardiac magnetic resonance study to assess for scar. The average amplitude of the LV pacing impulse was sampled on HR surface ECG intraprocedurally and then compared with the cardiac magnetic resonance results.

Results

A total of 38 LV pacing sites were assessed among 13 recipients. The median voltage measured on the surface HR ECG in regions with scar was reduced by 41% (interquartile range, 17% to 63%), whereas there was no measurable change in voltage (interquartile range, 0 to 0%) in regions without scar compared with the maximal amplitude (Wilcoxon P < 0.0001).

Conclusion

The EASE method appears to be of potential value as a novel intraoperative tool to guide LV lead placement to regions free of scar. Future work is required to validate the utility of this method in a larger patient cohort.

How to get the optimal defibrillation lead parameters using myocardial perfusion scintigraphy in patients with coronary artery disease

The conventional criteria for a defibrillation lead (DL) implantation don't take into account presence of scar or deep ischemia in the myocardium. This may impair a proper functioning of the DL. We sought to optimize the DL implantation placement using rest myocardial perfusion scintigraphy (MPS), which allow detecting areas of myocardial hypoperfusion (MH). To study the influence of MH and scarring, detected by MPS, on the DL parameters in patients with coronary artery disease (CAD). 69 patients (male-65, age 64.8 ± 7.7 years) with CAD and indications for ICD implantation were enrolled. Two days before ICD implantation all patients underwent MPS at rest. Then patients were divided in 2 groups. In the 1st group DL was implanted considering MPS results: to the septal position, if the most significant MH were detected in the apical segments, and to the apical position, if MH were in the septal segments. In the 2nd group DL was implanted using the conventional approach without considering MPS results. Clinical 12 months follow-up was performed with ICD interrogation. Patients of both groups were comparable by clinical and scintigraphic parameters. In the same time, in the 1st group pacing threshold was lower (p < 0.0001) and ventricle signal amplitude was higher (p < 0.0001) comparing with the 2nd group at all control points. The presence of MH detected by MPS in the area of the DL placement worsens its parameters. The results of MPS in patients with CAD can be useful for optimization of DL placement.

Atrial signal amplitude predicts atrial high-rate episodes in implantable cardioverter defibrillator patients: Insights from a large database of remote monitoring transmissions

BACKGROUND

Parameters measured during implantable cardioverter defibrillator (ICD) implant also depend on bioelectrical properties of the myocardium. We aimed to explore their potential association with clinical outcomes in patients with single/dual-chamber ICD and cardiac resynchronization therapy defibrillator (CRT-D).

METHODS

In the framework of the Home Monitoring Expert Alliance, baseline electrical parameters for all implanted leads were compared by the occurrence of all-cause mortality, adjudicated ventricular arrhythmia (VA), and atrial high-rate episode lasting ≥24 hours (24 h AHRE).

RESULTS

In a cohort of 2976 patients (58.1% ICD) with a median follow-up of 25 months, event rates were 3.1/100 patient-years for all-cause mortality, 18.1/100 patient-years for VA, and 9.3/100 patient-years for 24 h AHRE. At univariate analysis, baseline shock impedance was consistently lower in groups with events than without, with a 40 Ω cutoff that better identified high-risk patients. However, at multivariable analysis, the adjusted-hazard ratios (HRs) lost statistical significance for any endpoint. Baseline atrial sensing amplitude during sinus rhythm was lower in patients with 24 h AHRE than in those without (2.45 [IQR: 1.65-3.85] vs 3.51 [IQR: 2.37-4.67] mV, P < .01). The adjusted HR for 24 h AHRE in patients with atrial sensing >1.5 mV vs those with values ≤1.5 mV was 0.52 (95% CI: 0.33-0.83), P = .006.

CONCLUSIONS

Although lower baseline shock impedance was observed in patients with events, the association lost statistical significance at multivariable analysis. Conversely, low sinus rhythm atrial sensing (≤1.5 mV) measured with standard transvenous leads could identify subjects at high risk of atrial arrhythmia.

Local impedance guides catheter ablation in patients with ventricular tachycardia

AIMS

Catheter contact and local tissue characteristics are relevant information for successful radiofrequency current (RFC)-ablation. Local impedance (LI) has been shown to reflect tissue characteristics and lesion formation during RFC-ablation. Using a novel ablation catheter incorporating three mini-electrodes, we investigated LI in relation to generator impedance (GI) in patients with ventricular tachycardia (VT) and its applicability as an indicator of effective RFC-ablation.

METHODS AND RESULTS

Baseline impedance, Δimpedance during ablation and drop rate (Δimpedance/time) were analyzed for 625 RFC-applications in 28 patients with recurrent VT undergoing RFC-ablation. LI was lower in scarred (87.0 Ω [79.0-95.0]) compared to healthy myocardium (97.5 Ω ([82.75-111.50]; P = .03) while GI did not differ between scarred and healthy myocardium. ΔLI was higher (18 Ω [9.4-26.0]) for VT-terminating as compared to non-terminating RFC-ablation (ΔLI 13 Ω [8.85-18.0]; P = .03), but did not differ for ΔGI between terminating vs nonterminating RFC-ablation. Correspondingly, LI drop rate was higher for RFC-ablation terminating the VT compared with RFC-ablation not terminating the VT (0.63 Ω/s [0.52-0.76] vs 0.32 Ω [0.20-0.58]; P = .008) while there was no difference for GI drop rate. ΔLI was higher in patients with nonischemic cardiomyopathy vs patients with ischemic cardiomyopathy (16 Ω [11.0-20.0] vs 11.0 Ω [7.85-17.00]; P = .003).

CONCLUSION

Our findings suggest that LI is a sensitive parameter to guide RFC-ablation in patients with VT. LI indicates differences in tissue characteristics and generally is higher in patients with nonischemic cardiomyopathy. Hence, the etiology of the underlying cardiomyopathy needs to be considered when adopting LI for monitoring catheter ablation of VT.

Mapping of ventricular tachycardia in patients with ischemic cardiomyopathy: Current approaches and future perspectives

Despite the technical improvements made in recent years, the overall long-term success rate of ventricular tachycardia (VT) ablation in patients with ischemic cardiomyopathy remains disappointing. This unsatisfactory situation has persisted even though several approaches to VT substrate ablation allow mapping and ablation of noninducible/nontolerated arrhythmias. The current substrate mapping methods present some shortcomings regarding the accurate definition of the true scar, the modality of detection in sinus rhythm of abnormal electrograms that identify sites of critical channels during VT and the possibility to determine the boundaries of functional re-entrant circuits during sinus or paced rhythms. In this review, we focus on current and proposed ablation strategies for VT to provide an overview of the potential/real application (and results) of several ablation approaches and future perspectives.

Histopathological Characterization of Radiofrequency Ablation in Ventricular Scar Tissue

OBJECTIVES

This study sought to characterize the histopathological features of radiofrequency ablation (RFA) in heterogeneous ventricular scar in comparison to those in healthy myocardium.

BACKGROUND

The histopathological features of RFA have been studied largely in normal myocardium. However, its effect on clinically relevant heterogeneous scar is not well understood.

METHODS

Five swine with chronic infarction underwent RFA using 35-W, 45-s, 10-20 g (Biosense Webster, Irwindale, California) in heterogenous scar tissue (voltage ≤1.5 mV) and healthy myocardium (≥3.0 mV). The location of each application was marked using the electroanatomical mapping system. Histological sections at intervals of 0.5 mm with hematoxylin and eosin and Masson's trichrome stained intervals were created. A pathologist blinded to the myocardium type characterized the extent of RF injury in cellular, extracellular, and vascular structures.

RESULTS

In healthy myocardium, 23 of 23 lesions (100%) were well demarcated and could be precisely measured (width: 11.3 ± 3.3 mm; depth: 7.3 ± 2.0 mm). In scar tissue, only 3 of 30 lesions (10%) were identified, and none could be measured due to a lack of defined borders. Lesions in healthy myocardium had a distinctive architecture showing a coagulative necrosis core surrounded by an outer rim of contraction band necrosis. Lesions in scar had ill-defined tissue injury without a distinct architecture. In all ablated regions, viable myocytes remained interspersed between necrotic myocytes exhibiting characteristics of both coagulative and contraction band necrosis. Connective tissue was more resistant to thermal injury in comparison to cardiomyocytes.

CONCLUSIONS

RFA in scarred myocardium results in irregular tissue injury and unpredictable effect on surviving cardiomyocytes. This may be related to biophysical differences between healthy and scarred myocardium.

Ablation Lesion Characterization in Scarred Substrate Assessed Using Cardiac Magnetic Resonance

OBJECTIVES

This study examined radiofrequency catheter ablation (RFCA) lesions within and around scar by cardiac magnetic resonance (CMR) imaging and histology.

BACKGROUND

Substrate modification by RFCA is the cornerstone therapy for ventricular arrhythmias. RFCA in scarred myocardium, however, is not well understood.

METHODS

We performed electroanatomic mapping and RFCA in the left ventricles of 8 swine with myocardial infarction. Non-contrast-enhanced T₁-weighted (T1w) and contrast-enhanced CMR after RFCA were compared with gross pathology and histology.

RESULTS

Of 59 lesions, 17 were in normal myocardium (voltage >1.5 mV), 21 in border zone (0.5 to 1.5 mV), and 21 in scar (<0.5 mV). All RFCA lesions were enhanced in T1w CMR, whereas scar was hypointense, allowing discrimination among normal myocardium, scar, and RFCA lesions. With contrast-enhancement, lesions and scar were similarly enhanced and not distinguishable. Lesion width and depth in T1w CMR correlated with necrosis in pathology (both; r² = 0.94, p < 0.001). CMR lesion volume was significantly different in normal myocardium, border zone, and scar (median: 397 [interquartile range (IQR): 301 to 474] mm³, 121 [IQR: 87 to 201] mm³, 66 [IQR: 33 to 123] mm³, respectively). RFCA force-time integral, impedance, and voltage changes did not correlate with lesion volume in border zone or scar. Histology showed that ablation necrosis extended into fibrotic tissue in 26 lesions and beyond in 14 lesions. In 7 lesions, necrosis expansion was blocked and redirected by fat.

CONCLUSIONS

T1w CMR can selectively enhance necrotic tissue in and around scar and may allow determination of the completeness of ablation intra- and post-procedure. Lesion formation in scar is affected by tissue characteristics, with fibrosis and fat acting as thermal insulators.

First clinical use of novel ablation catheter incorporating local impedance data

INTRODUCTION

Successful catheter ablation is limited by both poor spatial resolution of abnormal local signals and inability to deliver an effective lesion due to poor tissue contact. We report first worldwide use of the Intellanav MiFi OI catheter (Boston Scientific), providing ultra-high density mapping and incorporating a "DirectSense" algorithm to measure local tissue impedance (LI).

METHODS AND RESULTS

31 patients (65±6 years, 20 male) underwent ablation. LI from the catheter, generator impedance (GI) and maximum electrogram amplitude were recorded in the blood pool, and in regions from healthy to dense scar before, during and after ablation. The catheter demonstrated clear nearfield signal where standard bipolar recordings included farfield signal. LI was lower in dense scar than either healthy tissue or blood pool, and demonstrated an exponential relationship with maximum electrogram amplitude. Maximum LI drop on ablation linearly correlated with initial LI. The median LI drop for successful lesions, resulting in lack of local tissue capture, was 16.0Ω (12.1-19.8 Ω) for LV and 14.6 Ω (10.0-18.3 Ω) for LA, which was larger than for unsuccessful lesions (LV: 9.4 Ω [5.4-15.6 Ω] P = 0.001; LA: 6.8 Ω [4.7-13.0 Ω], P = 0.049). LI percentage drop was also significantly larger for successful than unsuccessful lesions (LV: 17.1 Ω [14.0-19.6 Ω] vs. 10.6 Ω (7.1-16.5 Ω) P = 0.002; LA: 14.2 Ω [10.8-19.5 Ω] vs. 7.5Ω [5.1-11.0 Ω], P = 0.005).

CONCLUSION

This novel catheter gives reproducible recordings of local impedance, which are dependent on scar level. Absolute LI drop, and also percentage drop, on ablation may give an indication of tissue contact and subsequent effective lesion formation.