Multisize Electrode Field-of-View: Validation by High Resolution Gadolinium-Enhanced Cardiac Magnetic Resonance.

BACKGROUND: Voltage mapping to detect ventricular scar is important for guiding catheter ablation, but the field-of-view of unipolar, bipolar, conventional, and microelectrodes as it relates to the extent of viable myocardium (VM) is not well defined. OBJECTIVES: The purpose of this study was to evaluate electroanatomic voltage-mapping (EAVM) with different-size electrodes for identifying VM, validated against high-resolution ex-vivo cardiac magnetic resonance (HR-LGE-CMR). METHODS: A total of 9 swine with early-reperfusion myocardial infarction were mapped with the QDOT microcatheter. HR-LGE-CMR (0.3-mm slices) were merged with EAVM. At each EAVM point, the underlying VM in multisize transmural cylinders and spheres was quantified from ex vivo CMR and related to unipolar and bipolar voltages recorded from conventional and microelectrodes. RESULTS: In each swine, 220 mapping points (Q1, Q3: 216, 260 mapping points) were collected. Infarcts were heterogeneous and nontransmural. Unipolar and bipolar voltage increased with VM volumes from >175 mm3 up to >525 mm3 (equivalent to a 5-mm radius cylinder with height >6.69 mm). VM volumes in subendocardial cylinders with 1- or 3-mm depth correlated poorly with all voltages. Unipolar voltages recorded with conventional and microelectrodes were similar (difference 0.17 ± 2.66 mV) and correlated best to VM within a sphere of radius 10 and 8 mm, respectively. Distance-weighting did not improve the correlation. CONCLUSIONS: Voltage increases with transmural volume of VM but correlates poorly with small amounts of VM, which limits EAVM in defining heterogeneous scar. Microelectrodes cannot distinguish thin from thick areas of subendocardial VM. The field-of-view for unipolar recordings for microelectrodes and conventional electrodes appears to be 8 to 10 mm, respectively, and unexpectedly similar.

Quantification of Large Transmural Biopsies Reveals Heterogeneity in Innervation Patterns in Chronic Myocardial Infarction.

BACKGROUND: Abnormal cardiac innervation plays an important role in arrhythmogenicity after myocardial infarction (MI). Data regarding reperfusion models and innervation abnormalities in the medium to long term after MI are sparse. Histologic quantification of the small-sized cardiac nerves is challenging, and transmural analysis has not been performed. OBJECTIVES: This study sought to assess cardiac innervation patterns in transmural biopsy sections in a porcine reperfusion model of MI (MI-R) using a novel method for nerve quantification. METHODS: Transmural biopsy sections from 4 swine (n = 83) at 3 months after MI-R and 3 controls (n = 38) were stained with picrosirius red (fibrosis) and beta-III-tubulin (autonomic nerves). Biopsy sections were classified as infarct core, border zone, or remote zone. Each biopsy section was analyzed with a custom software pipeline, allowing calculation of nerve density and classification into innervation types at the 1 × 1-mm resolution level. Relocation of the classified squares to the original biopsy position enabled transmural quantification and innervation heterogeneity assessment. RESULTS: Coexisting hyperinnervation, hypoinnervation, and denervation were present in all transmural MI-R biopsy sections. The innervation heterogeneity was greatest in the infarct core (median: 0.14; IQR: 0.12-0.15), followed by the border zone (median: 0.05; IQR: 0.04-0.07; P = 0.02) and remote zone (median: 0.02; IQR: 0.02-0.03; P < 0.0001). Only in the border zone was a positive linear relation between fibrosis and innervation heterogeneity observed (R = 0.79; P < 0.0001). CONCLUSIONS: This novel method allows quantification of nerve density and heterogeneity in large transmural biopsy sections. In the chronic phase after MI-R, alternating innervation patterns were identified within the same biopsy section. Persistent innervation heterogeneity, in particular in the border zone biopsy sections, may contribute to late arrhythmogenicity.

The West Jutland Tele-Electrocardiogram Registry (WEJU-tECG): content, data quality, and research potential.

AIM: To present the content, data quality, and research potential of the West Jutland Tele-Electrocardiogram Registry (WEJU-tECG). METHODS: Danish patients reporting symptoms indicating heart disease in the prehospital setting are subjected to a 12-lead tele-electrocardiogram (ECG) in the ambulance, which is digitally sent to a local tele-centre. WEJU-tECG is a newly established Danish registry containing information from the individual tele-ECGs received at the Regional Hospital West Jutland tele-centre. RESULTS: WEJU-tECG holds extracted information from all tele-ECGs with a valid Civil Personal Register number between 2011 and 2020. WEJU-tECG contains information on patient characteristics, tele-ECG data (including a computerised tele-ECG interpretation), vital signs, and time information. A unique Civil Personal Register number allows individual-level linkage between WEJU-tECG and other Danish registries and enables complete follow-up. WEJU-tECG contains 43,696 tele-ECGs from 29,489 different patient contacts among 20,280 different patients. WEJU-tECG contains 5566 patients with ST-segment deviations. The median age is 67 years and 45% are women. Completeness is highest for time information (100% for all variables), tele-ECG data (99% for heart rate, the specific intervals and axes, and QRS duration, and 86% for J-point deviation), and patient characteristics (100% for all variables). Completeness is lowest for vital signs (13% for systolic, diastolic, and mean arterial blood pressure, and 12% for blood oxygen saturation). The computerised tele-ECG interpretation had a negative predictive value of 80% for ST-segment elevation myocardial infarction and 94% for non-ST-segment elevation myocardial infarction and a positive predictive value of 45% for ST-segment elevation myocardial infarction and 32% for non-ST-segment elevation myocardial infarction. CONCLUSIONS: WEJU-tECG is a novel population-based tele-ECG registry with high research potential.

Multielectrode Unipolar Voltage Mapping and Electrogram Morphology to Identify Post-Infarct Scar Geometry: Validation by Histology.

OBJECTIVES: This study sought to evaluate the ability of uni- and bipolar electrograms collected with a multielectrode catheter with smaller electrodes to: 1) delineate scar; and 2) determine local scar complexity. BACKGROUND: Early reperfusion results in variable endocardial scar, often overlaid with surviving viable myocardium. Although bipolar voltage (BV) mapping is considered the pillar of substrate-based ablation, the role of unipolar voltage (UV) mapping has not been sufficiently explored. It has been suggested that bipolar electrograms collected with small electrode catheters can better identify complex scar geometries. METHODS: Twelve swine with early reperfusion infarctions were mapped with the 48-electrode OctaRay catheter and a conventional catheter during sinus rhythm. BV electrograms with double components were identified. Transmural (n = 933) biopsy specimens corresponding to mapping points were obtained, histologically assessed, and classified by scar geometry. RESULTS: OctaRay UV (UVOcta) and BV (BVOcta) amplitude were associated with the amount of viable myocardium at a given location, with a stronger association for UVOcta (R2 = 0.767 vs 0.473). Cutoff values of 3.7 mV and 1.0 mV could delineate scar (area under the curve: 0.803 and 0.728 for UVOcta and BVOcta, respectively). The morphology of bipolar electrograms collected with the OctaRay catheter more frequently identified areas with 2 layers of surviving myocardium than electrograms collected with the conventional catheter (84% vs 71%). CONCLUSIONS: UV mapping can generate a map to delineate the area of interest when using a multielectrode catheter. Within this area of interest, the morphology of bipolar electrograms can identify areas in which a surviving epicardial layer may overlay a poorly coupled, potentially arrhythmogenic, endocardium.

Mini-, Micro-, and Conventional Electrodes: An in Vivo Electrophysiology and Ex Vivo Histology Head-to-Head Comparison.

OBJECTIVES: This study sought to assess the relative effect of catheter, tissue, and catheter-tissue parameters, on the ability to determine the amount of viable myocardium in vivo. BACKGROUND: Although multiple variables impact bipolar voltages (BVs), electrode size, interelectrode spacing, and directional dependency are of particular interest with the development of catheters incorporating mini and microelectrodes. METHODS: Nine swine with early reperfusion myocardial infarctions were mapped using the QDot catheter and then remapped using a Pentaray catheter. All QDot points were matched with Pentaray points within 5 mm. The swine were sacrificed, and mapping data projected onto the heart. Transmural biopsies corresponding to mapping points were obtained, allowing a comparison of electrograms recorded by mini, micro-, and conventional electrodes with histology. RESULTS: The conventional BV of 2,322 QDot points was 1.9 ± 1.3 mV. The largest of the 3 microelectrode BVs (BVµMax) average 4.8 ± 3.1 mV. The difference between the largest (BVµMax) and smallest (BVµMin) at a given location was 53.7 ± 18.1%. The relationships between both BVµMax and BVµMin and between the conventional BV and BVµMax were positively related but with a significant spread in data, which was more pronounced for the latter. Pentaray points positively related to the BVµMax with poor fit. On histology, increasing viable myocardium increased voltage, but both the slope coefficient and fit were best for BVµMax. CONCLUSIONS: Using histology, we could demonstrate that BVµMax is superior to identify viable myocardium compared with BVC and BV using the Pentaray catheter. The ability to simultaneously record 3 BVµs with different orientations, for the same beat, with controllable contact and selecting BVµMax for local BV may partially compensate for wave front direction.

Repeat pulmonary vein isolation in patients with atrial fibrillation: low ablation index is associated with increased risk of recurrent arrhythmia.

OBJECTIVES: We aimed to investigate the predictors of recurrent arrhythmia after repeated pulmonary vein isolation (PVI) performed in the era of contact force without additional substrate ablation. One of the predictors studied, ablation index (AI), incorporates power, contact force, and time in a weighted formula and is reported to predict lesion size in animals. Design. Consecutive patients (n = 108) undergoing repeat PVI without additional substrate modification using a contact force sensing catheter were included retrospectively at a tertiary center. All ablation points were analyzed offline. A new variable, normalized AI (AI corrected for the location of the lesion-anterior vs. posterior) was calculated. The patients were systematically followed with clinical visit and 12-lead ECG as well as review of the regional electronic patient files at 3 and 12 months after the procedure with 5-day Holter at 12 months. Results. Electrical reconnection to at least one pulmonary vein (PV) was seen in 97% of the patients. The recurrence rate was 35%. There was no recurrence in patients with nAI above 1.15 (n = 26). Patients with electrical reconnection of up to two PVs had a higher risk of recurrence compared with patients having electrical reconnection of three or four PVs (p = .003), and this risk was especially high in patients with persistent atrial fibrillation (69 [39-91]%). Conclusions. The risk of recurrence is higher in patients with ablations performed with low levels of AI and in patients with reconnection to up to two PVs. Our data may indicate the need for higher target levels of AI during repeat PVI than normally used during de-novo PVI.

Multisize Electrodes for Substrate Identification in Ischemic Cardiomyopathy: Validation by Integration of Whole Heart Histology.

OBJECTIVES: This study sought to evaluate the value of combined electrogram (EGM) information provided by simultaneous mapping using micro- and conventional electrodes in the identification of post-myocardial infarction ventricular tachycardia substrate. BACKGROUND: Ventricular tachycardias after myocardial infarction are related to scars with complex geometry. Scar delineation and ventricular tachycardia substrate identification relies on bipolar voltages (BV) and EGM characteristics. Early reperfusion therapy results in small, nontransmural scars, the details of which may not be delineated using 3.5 mm tip catheters. METHODS: Nine swine with early reperfusion myocardial infarction were mapped using Biosense Webster's QDOT Micro catheter, incorporating 3 microelectrodes at the tip of the standard 3.5 mm electrode. Analysis of EGM during sinus rhythm, right ventricular pacing, and short-coupled right ventricular extrastimuli was performed. The swine were sacrificed and mapping data were projected onto the heart. Transmural biopsies (n = 196) corresponding to mapping points were obtained, allowing a head-to-head comparison of EGM recorded by micro- and conventional electrodes with histology. RESULTS: To identify scar areas using standard electrodes, unique cutoff values of unipolar voltage <5.44 mV, BV <1.27 mV (conventional), and BV <2.84 mV (microelectrode) were identified. Combining the information provided by unipolar voltage and BV mapping, the sensitivity of scar identification was increased to 93%. Micro-EGM were better able to distinguish small near-fields corresponding to a layer of viable subendocardium than conventional EGM were. CONCLUSIONS: The combined information provided by multisize electrode mapping increases the sensitivity with which areas of scar are identified. EGM from microelectrodes, with narrower spacing, allow identification of near-fields arising from thin subendocardial layer and layers activated with short delay obscured in EGM from conventional mapping catheter.

Radiofrequency ablation lesions in low-, intermediate-, and normal-voltage myocardium: an in vivo study in a porcine heart model.

AIMS: Contact force (CF) between radiofrequency (RF) ablation catheter and myocardium and ablation index (AI) correlates with RF lesion depth and width in normal-voltage (>1.5 mV) myocardium (NVM). We investigate the impact of CF on RF lesion depth and width in low (<0.5 mV) (LVM) and intermediate-voltage (0.5-1.5 mV) myocardium (IVM) following myocardial infarction. Correlation between RF lesion depth and width evaluated by native contrast magnetic resonance imaging (ncMRI) and gross anatomical evaluation was investigated. METHODS AND RESULTS: Twelve weeks after myocardial infarction, 10 pigs underwent electroanatomical mapping and endocardial RF ablations were deployed in NVM, IVM, and LVM myocardium. In vivo ncMRI was performed before the heart was excised and subjected to gross anatomical evaluation. Ninety (82%) RF lesions were evaluated. Radiofrequency lesion depth and width were smaller in IVM and LVM compared with NVM (P < 0.001). Radiofrequency lesion depth and width correlated with CF, AI, and impedance drop in NVM (CF and AI P < 0.001) and IVM (CF and AI depths P < 0.001; CF and AI widths P < 0.05). Native contrast magnetic resonance imaging evaluated RF lesion depth and width correlated with gross anatomical depth and width (NVM and IVM P < 0.001; LVM P < 0.05). CONCLUSIONS: Radiofrequency lesions deployed by similar duration, power and CF are smaller in IVM and LVM than in NVM. Radiofrequency lesion depth and width correlated with CF, AI, and impedance drop in NVM and IVM but not in LVM. Native contrast magnetic resonance imaging may be useful to assess RF lesion depth and width in NVM, IVM, and LVM.