Detailed comparison between the wall thickness and voltages in chronic myocardial infarction

BACKGROUND

The relationship between the local electrograms (EGMs) and wall thickness (WT) heterogeneity within infarct scars has not been thoroughly described. The relationship between WT and voltages and substrates for ventricular tachycardia (VT) was examined.

METHODS

In 12 consecutive patients with myocardial infarction and VT, WT, defined by a multidetector computed tomography, and voltage were compared. In multicomponent EGMs, amplitudes of both far- and near-field components were manually measured, and the performance of the three-dimensional-mapping system automatic voltage measurement was assessed.

RESULTS

Of 15 748 points acquired, 2677 points within 5 mm of the endocardial surface were analyzed. In total, 909 (34.0%) multicomponent EGMs were identified; 785 (86.4%) and 883 (97.1%) were distributed in the WT less than 4 and 5 mm, respectively. Far-field EGM voltages increased linearly from 0.14 mV (0.08-0.28 mV) in the WT: 0 to 1 mm to 0.70 mV (0.43-2.62 mV) in the WT: 4 to 5 mm (ρ = 0.430; P < 0.001), and a significant difference was demonstrated between any two WT-groups (P ≤ 0.001). In contrast, near-field EGM voltages varied from 0.27 mV (0.11-0.44 mV) in the WT: 0 to 1 mm to 0.29 mV (0.17-0.53 mV) in the WT: 4 to 5 mm with a poorer correlation (ρ = 0.062, P = 0.04). The proportion of points where the system automatically measured the voltage on near-field EGMs increased from less than 10% in areas of WT: 4 to 5 mm to 50% in areas less than 2 mm. Of 21 VTs observed, seven hemodynamically stable VTs were mapped and terminated in WT: 1 to 4 mm area.

CONCLUSIONS

Although far-field voltages gradually increase with the WT, near-field does not. The three-dimensional-mapping system preferentially annotates the near-field components in thinner areas (center of the scar) and the far-field component in thicker areas when building a voltage map. Critical sites of VT are distributed in WT: 1 to 4 mm areas.

Compartmentalized Structure of the Moderator Band Provides a Unique Substrate for Macroreentrant Ventricular Tachycardia

Supplemental Digital Content is available in the text.

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation.

Mapping and Ablation of Idiopathic Ventricular Fibrillation

Idiopathic ventricular fibrillation (IVF) is the main cause of unexplained sudden cardiac death, particularly in young patients under the age of 35. IVF is a diagnosis of exclusion in patients who have survived a VF episode without any identifiable structural or metabolic causes despite extensive diagnostic testing. Genetic testing allows identification of a likely causative mutation in up to 27% of unexplained sudden deaths in children and young adults. In the majority of cases, VF is triggered by PVCs that originate from the Purkinje network. Ablation of VF triggers in this setting is associated with high rates of acute success and long-term freedom from VF recurrence. Recent studies demonstrate that a significant subset of IVF defined by negative comprehensive investigations, demonstrate in fact subclinical structural alterations. These localized myocardial alterations are identified by high density electrogram mapping, are of small size and are mainly located in the epicardium. As reentrant VF drivers are often colocated with regions of abnormal electrograms, this localized substrate can be shown to be mechanistically linked with VF. Such areas may represent an important target for ablation.

Effect of bipolar electrode orientation on local electrogram properties

BACKGROUND

The direct effect of bipolar orientation on electrograms (EGMs) remains unknown.

OBJECTIVE

The purpose of this study was to examine the variation of EGMs with diagonally orthogonal bipoles.

METHODS

The HD-32 Grid catheter (Abbott, Minneapolis, MN) can assess the effect of bipolar orientation while keeping the interelectrode distance and center unchanged. Seven sheep with anterior myocardial infarction were analyzed using diagonally orthogonal electrode pairs across splines by comparing local EGMs from each pair of opposing electrodes {eg. A1-B3 (southeast direction [SE]) vs A3-B1 (northeast direction [NE])}.

RESULTS

A total of 4084 EGMs (1 in each direction) were analyzed for 2042 sites (544 in the infarcted area, 488 in the border area, and 1010 in the normal area). The higher and lower voltages measured using each pair of opposing electrodes significantly differed (1.10 mV [0.43-2.56 mV] vs 0.69 mV [0.28-1.58 mV]; P < .0001), and the median variation was 0.28 mV (0.11-0.80 mV) (31.7% [16.0%-48.9%]). The voltage variation was maximized to 48.7% (37.7%-61.6%) (P < .0001) on sites where the activation wavefront was perpendicular to the one bipolar direction and parallel to the other. A total of 594 of 719 (82.6%) sites with the voltage <0.5 mV and 539 of 699 (77.1%) sites with the voltage >1.5 mV in NE stayed in the same voltage range as those in SE. However, only 348 of 624 (55.8%) sites with the voltage 0.5-1.5 mV in NE stayed in the same range as those in SE. Local ventricular abnormal activities (LAVAs) were detected in 592 of 2042 (29.0%) sites in total, frequently distributed in the border area. A total of 177 (29.9%) LAVAs were missed in one direction and 180 (30.4%) in the other. When 415 (70.1%) LAVAs detected in NE are defined as the reference, 235 of 415 (56.6%) matched with those detected in SE.

CONCLUSION

The bipolar voltage and distribution of LAVAs may differ significantly between diagonally orthogonal bipolar pairs at any given site.

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.

Revisiting anatomic macroreentrant tachycardia after atrial fibrillation ablation using ultrahigh-resolution mapping: Implications for ablation

BACKGROUND

Anatomic macroreentrant atrial tachycardias (MATs) are conventionally reported to depend on the cavotricuspid isthmus, the mitral isthmus, or the left atrial roof, and are commonly seen following catheter ablation for atrial fibrillation.

OBJECTIVES

To define the precise circuits of anatomic MAT with ultrahigh-resolution mapping.

METHODS

In 57 patients (mean age, 62 years; 10 female) who developed ≥1 anatomic MAT, we analyzed 88 MAT circuits including 16 peritricuspid, 42 perimitral, and 30 roof-dependent circuits, using high-density mapping and entrainment.

RESULTS

Of 16 peritricuspid atrial tachycardias (ATs), 8 (50.0%) showed a circuit not limited to the tricuspid annulus. However, cavotricuspid isthmus ablation terminated the tachycardia in all patients. Similarly, 26 of 42 perimitral ATs (61.9%) showed a circuit not limited to the mitral annulus, and a low-voltage zone <0.1 mV around the mitral annulus was associated with nontypical perimitral ATs (P < .0001). The practical isthmus was not in the mitral isthmus in 13 of these 26 perimitral ATs (50%). Finally, 22 of 30 roof-dependent ATs (73.3%) had a circuit not rotating around both pairs of pulmonary veins. Brief assessment of the activation direction on the posterior wall in relation to that on the septal, anterior, and lateral wall helped deduce the circuit of roof-dependent AT in 27 of 30 (90.0%). Practical isthmus was not in the roof in 8 of 22 (36.4%). Practical isthmuses mapped with the system were significantly shorter than the usual anatomic isthmuses (16.1 ± 8.2 mm vs 33.7 ± 10.4 mm) (P < .0001).

CONCLUSIONS

High-density mapping successfully identified the precise circuits and the practical isthmus of anatomic MATs in patients with prior atrial fibrillation ablation.

Electrogram signature of specific activation patterns: Analysis of atrial tachycardias at high-density endocardial mapping

BACKGROUND

The significance of fractionated electrograms (EGMs) is object of debate, with multiple mechanisms described.

OBJECTIVE

Using Rhythmia, a high-density mapping system, we sought to investigate the relationship between specific electrophysiological phenomena and EGM characteristics at those sites.

METHODS

Twenty-five consecutive patients underwent high-density atrial mapping during atrial tachycardias. Bipolar EGMs were recorded with a 64-electrode basket catheter. The following atrial phenomena were identified: slow conduction (SC) areas, lines of block (LB), wavefront collisions (WFC), pivot sites (PS), and gaps. EGMs collected at these predefined areas were analyzed in terms of amplitude, duration, and morphology.

RESULTS

Twenty-five atrial maps with 195 sites of interest (1755 EGMs) were object of our analysis. Thirty-five percent were sites of SC: fractionation had low amplitude (0.16 ± 0.07 mV) and long duration (87.8 ± 10.7 ms); wavefront collisions were seen in 38% of sites with EGMs shorter in duration (46.5 ± 4.5 ms) and higher in voltage (0.58 ± 0.13 mV); 17% were lines of block, never responsible for fractionation (0.13 ± 0.05 mV; 122.4 ms ± 24.8 ms); 9% were PS with a high degree of fractionation (0.55 ± 0.15 mV; 85.8 ± 7.9 ms). Two gaps were identified (1%) with a low degree of fractionation.

CONCLUSION

Specific EGM characteristics in atrial tachycardia can be reproducibly linked to electrophysiological mechanisms. High-voltage and short-duration EGMs are associated with collision sites and PS that are unlikely to form critical sites for ablation; long-duration, low-voltage EGMs are associated with SC. However, not all SC regions will lie within the critical circuit and identification by only EGM characteristics cannot guide ablation.

Frontiers in non-invasive cardiac mapping: future implications for arrhythmia treatment

Electrocardiographic mapping (ECM) is a noninvasive technique using body surface potentials and CT geometry to reconstruct epicardial maps. ECM is emerging as an important tool not only for diagnostic mapping, but also as a guide for trans-catheter ablation of complex arrhythmias such as atrial fibrillation. It provides the clinician with an immediate global view of the substrate, allowing easier pre-procedural planning, potentially improving clinical outcomes. Panoramic mapping of ventricular fibrillation (VF) is helping to develop a better understanding of its physiology, with future implications for the identification of therapeutic targets in patients with structural heart disease, as well as in idiopathic VF.

Distinctive Left Ventricular Activations Associated With ECG Pattern in Heart Failure Patients

Background—

In contrast to patients with left bundle branch block (LBBB), heart failure patients with narrow QRS and nonspecific intraventricular conduction delay (NICD) display a relatively limited response to cardiac resynchronization therapy. We sought to compare left ventricular (LV) activation patterns in heart failure patients with narrow QRS and NICD to patients with LBBB using high-density electroanatomic activation maps.

Methods and Results—

Fifty-two heart failure patients (narrow QRS [n=18], LBBB [n=11], NICD [n=23]) underwent 3-dimensional electroanatomic mapping with a high density of mapping points (387±349 LV). Adjunctive scar imaging was available in 37 (71%) patients and was analyzed in relation to activation maps. LBBB patients typically demonstrated (1) a single LV breakthrough at the septum (38±15 ms post-QRS onset); (2) prolonged right-to-left transseptal activation with absence of direct LV Purkinje activity; (3) homogeneous propagation within the LV cavity; and (4) latest activation at the basal lateral LV. In comparison, both NICD and narrow QRS patients demonstrated (1) multiple LV breakthroughs along the posterior or anterior fascicles: narrow QRS versus LBBB, 5±2 versus 1±1; P =0.0004; NICD versus LBBB, 4±2 versus 1±1; P =0.001); (2) evidence of early/pre-QRS LV electrograms with Purkinje potentials; (3) rapid propagation in narrow QRS patients and more heterogeneous propagation in NICD patients; and (4) presence of limited areas of late activation associated with LV scar with high interindividual heterogeneity.

Conclusions—

In contrast to LBBB patients, narrow QRS and NICD patients are characterized by distinct mechanisms of LV activation, which may predict poor response to cardiac resynchronization therapy.

A Multicentre Trial of Patient specific Rehearsal Prior to EVAR: Impact on Procedural Planning and Team Performance

OBJECTIVE

Patient specific rehearsal (PsR) prior to endovascular aneurysm repair (EVAR) enables the endovascular team to practice and evaluate the procedure prior to treating the real patient. This multicentre trial aimed to evaluate the utility of PsR prior to EVAR as a pre-operative planning and briefing tool.

MATERIAL AND METHODS

Patients with an aneurysm suitable for EVAR were randomised to pre-operative or post-operative PsR. Before and after the PsR, the lead implanter completed a questionnaire to identify any deviation from the initial treatment plan. All team members completed a questionnaire evaluating realism, technical issues, and human factor aspects pertinent to PsR. Technical and human factor skills, and technical and clinical success rates were compared between the randomised groups.

RESULTS

100 patients were enrolled between September 2012 and June 2014. The plan to visualise proximal and distal landing zones was adapted in 27/50 (54%) and 38/50 (76%) cases, respectively. The choice of the main body, contralateral limb, or iliac extensions was adjusted in 8/50 (16%), 17/50 (34%), and 14/50 (28%) cases, respectively. At least one of the abovementioned parameters was changed in 44/50 (88%) cases. For 100 EVAR cases, 199 subjective questionnaires post-PsR were completed. PsR was considered to be useful for selecting the optimal C-arm angulation (median 4, IQR 4-5) and was recognised as a helpful tool for team preparation (median 4, IQR 4-4), to improve communication (median 4, IQR 3-4), and encourage confidence (median 4, IQR 3-4). Technical and human factor skills and technical and initial clinical success rates were similar between the randomisation groups.

CONCLUSION

PsR prior to EVAR has a significant impact on the treatment plan and may be useful as a pre-operative planning and briefing tool. Subjective ratings indicate that this technology may facilitate planning of optimal C-arm angulation and improve non-technical skills.

TRIAL REGISTRATION

URL://www.clinicaltrials.gov. Unique identifier: NCT01632631.

Spatially Coherent Activation Maps for Electrocardiographic Imaging

OBJECTIVE

Cardiac mapping is an important diagnostic step in cardiac electrophysiology. One of its purposes is to generate a map of the depolarization sequence. This map is constructed in clinical routine either by directly analyzing cardiac electrograms (EGMs) recorded invasively or an estimate of these EGMs obtained by a noninvasive technique. Activation maps based on noninvasively estimated EGMs often show artefactual jumps in activation times. To overcome this problem, we present a new method to construct the activation maps from reconstructed unipolar EGMs.

METHODS

On top of the standard estimation of local activation time from unipolar intrinsic deflections, we propose to mutually compare the EGMs in order to estimate the delays in activation for neighboring recording locations. We then describe a workflow to construct a spatially coherent activation map from local activation times and delay estimates in order to create more accurate maps. The method is optimized using simulated data and evaluated on clinical data from 12 different activation sequences.

RESULTS

We found that the standard methodology created lines of artificially strong activation time gradient. The proposed workflow enhanced these maps significantly.

CONCLUSION

Estimating delays between neighbors is an interesting option for activation map computation in electrocardiographic imaging.

The clinical benefits of long-term supplementation with omega-3 fatty acids in cystic fibrosis patients - A pilot study

Effectiveness of omega-3 supplementation in cystic fibrosis (CF) remains controversial. This study sought to evaluate clinical status, exercise tolerance, inflammatory parameters, and erythrocyte fatty acid profile after 1 year of oral omega-3 supplementation in CF patients. Fifteen ΔF508-homozygous patients undergoing chronic azithromycin were randomized to receive omega-3 fish oil supplementation at a dose of 60mg/Kg/day or placebo. In comparison with the previous year, in the supplemented group, the number of pulmonary exacerbations decreased at 12 months (1.7 vs. 3.0, p<0.01), as did the duration of antibiotic therapy (26.5 days vs. 60.0 days, p<0.025). Supplementation significantly increased the levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) as early as <3 months of administration, with concomitant decreases in arachidonic acid (AA) levels. This pilot study suggests that long-term omega-3 supplementation offers several clinical benefits as to the number of exacerbations and duration of antibiotic therapy in CF patients.