Changes In Electrograms Research Articles

Six transition patterns and seven capture types in different left bundle branch bipolar pacing configurations.

This study aims to explore the different transition patterns and capture types during two bipolar pacing tests based on the selective left bundle branch (LBB) capture determined by the continuous pacing and recording technique. In total, 67 patients completed two unipolar and two bipolar pacing tests based on selective LBB capture during screwing-in for left bundle branch pacing (LBBP) using the continuous pacing and recording technique. The electrophysiological characteristics and potential mechanisms of different pacing configurations were further evaluated in this study. We found six transition patterns and derived seven capture types in two bipolar pacing tests according to the analysis of continuous electrocardiogram and electrogram changes. Compared with the conventional configuration of "Tip-Ring+" bipolar pacing, "Ring-Tip+" testing had a lower threshold for simultaneous capture of the LBB and the left and right ventricular septum myocardium (1.57 vs. 2.84 V at 0.5 ms) and was the only configuration to yield the peculiar "LBBP + right ventricular septum pacing (RVSP)" capture type. In this study, we observed for the first time that "Ring-Tip+" bipolar pacing allows for a lower clinically applicable pacing threshold for simultaneous capture of the LBB and left and right ventricular septum myocardium, and the peculiar "LBBP + RVSP" capture type. This may be a more advantageous physiological pacing configuration, warranting further investigation and application in the future. Based on the specific selective LBB capture, we first found six transition patterns and derived seven capture types in two bipolar pacing tests due to the different thresholds of the LBB, left ventricular septal myocardial, and right ventricular septal myocardial. Compared with the conventional configuration of "Tip-Ring+" bipolar pacing, "Ring-Tip+" testing had a lower threshold for simultaneous capture of the LBB and the left and right ventricular septum myocardium (1.57 vs. 2.84 V at 0.5 ms) and was the only configuration to yield the peculiar "LBBP + RVSP" capture type. More pacing strategies should be released and investigated to achieve the best physiological pacing according to the individualized electrophysiological characteristics of patients.

Acute intracardiac electrogram changes and their relation to pulsed field ablation dose in porcine left ventricle

Abstract Background Pulsed field ablation (PFA) is an emerging cardiac ablation modality based on irreversible electroporation with promising preclinical and clinical results. Acute reduction of intracardiac electrograms (bipolar iEGMs) is consistently observed, similar to other ablation modalities, e.g. radiofrequency ablation. We and others have previously reported lesion size dependence on PFA dosing. However, the relevance of iEGM changes and their dependence on the PFA dose is not established. Furthermore, our study shows that unipolar iEGM signals may contain additional information about the effects of PFA in cardiac tissue. Purpose To quantify the effect of different PFA dosing on changes observed in bipolar and unipolar iEGMs within 5 minutes after the ablation. Methods In total, PFA was applied endocardially at 40 sites in the left ventricles of 8 pigs via a 5 mm tip catheter using a modified decapolar catheter in the inferior vena cava for current return (all electrodes). The following PFA doses (voltage and number of pulse trains) were used: 1000 V, 4 trains; 1300 V, 4 trains; 1500 V, 1 train; 1500 V, 4 trains; 1500 V, 8 trains; and 1500 V, 16 trains. For standard bipolar iEGMs (30 Hz – 500 Hz) the reduction in peak-to-peak amplitude after PFA was considered as a measure of the effect. In addition, unipolar iEGMs (0.5 Hz – 500 Hz) were decomposed into non-overlapping frequency sub-bands with Daubechies order 6 discrete wavelet transform (Figure 1A) allowing separate analysis in high-frequency (HF) and low-frequency (LF) ranges (63 Hz – 500 Hz and 0.5 Hz – 8 Hz, respectively). Results In total, 30 standard bipolar and 35 unipolar iEGMs (with at least 3.5 minutes of artefact-free post-ablation duration) were analysed. No dose dependency was observed for standard bipolar iEGMs within 5 minutes post-ablation (data not shown). However, the HF and LF content of unipolar iEGMs revealed opposing effects: a decrease in the HF and an increase in the LF content. Correlation with the dose was clearer in the LF content 3.5 minutes post-ablation, the difference being significant (p<0.05) between the lowest and the highest doses (Figure 1B and C). Discussion The decrease in HF content could reflect electrical silencing, ie. stunning of locally affected cardiomyocytes, most likely caused by irreversibly electroporated (ablated) cells located close to the catheter tip and by reversibly electroporated or otherwise temporarily silenced cells in adjacent tissue. The increase in LF content could reflect the current-of-injury effect, which is a broader area phenomenon derived from electrical potential differences between affected (reversibly and irreversibly electroporated) and non-affected regions. Conclusion Unipolar iEGMs acquired with a broadened frequency range and decomposed into HF and LF content provide new insight into the effects of PFA and correlate with PFA dosing in this pre-clinical porcine model.

Dynamics of High-Density Unipolar Epicardial Electrograms During PFA.

Pulsed field ablation (PFA) is a novel nonthermal cardiac ablation technology based on irreversible electroporation (IRE). While areas of IRE lead to durable lesions, the surrounding regions, where reversible electroporation occurs, recover. The behavior of local electrograms in areas of different electroporation levels remains unknown. The goal of this study is to characterize electrogram dynamics after PFA in IRE and reversible electroporation areas. A total of 6 domestic swine were used. PFA was applied in the epicardium of the right and left ventricles using a focal monopolar catheter. Additional radiofrequency ablations were performed. Epicardial unipolar electrograms were acquired at baseline and for 60 minutes post PFA/radiofrequency ablation using a high-density electrode matrix attached to the epicardium. Electrogram dynamics were analyzed in areas corresponding to different levels of electroporation. Acute lesion formation was assessed after 3 to 5 hours by triphenyl tetrazolium chloride staining. Electrogram analysis demonstrated a clear association between electrogram changes and the level of electroporation. Immediately after PFA, electrograms displayed the following: a significant decrease in R/S-wave amplitude; a large elevation of the ST-segment; and a large decrease in their |(dV/dt)|max. Marked changes in electrograms were observed beyond the lesion area. Thereafter, a gradual recovery was observed. The evolution of all the electrogram parameters throughout the 60 minutes after PFA was significantly different (P<0.05) between the IRE and reversible electroporation areas. Acute lesion staining showed significantly larger depth for PFA lesions compared with radiofrequency ablation. This study shows that unipolar electrograms can differentiate between reversible electroporation and IRE areas during the first 30 minutes post ablation. Differences after the first 30 minutes are less evident. Our findings could result useful for immediate lesion assessment after PFA and warrant further investigation.

PO-03-037 FEASIBILITY OF UNIPOLAR SIGNAL GUIDED ABLATION IN CREATING CONTIGUOUS LINES OF CONDUCTION BLOCK: A PROOF-OF-CONCEPT STUDY

Contemporary ablation is guided by non-physiological surrogates such as Ablation indexTM (ABi). Dynamic changes in local atrial unipolar electrogram (Uni-EGM) with loss of the negative S component or “R-pattern” change during radiofrequency ablation (RFA) predicts a transmural lesion. To investigate the feasibility of generating contiguous, transmural lesions that result in conduction block, using ablation guided by Uni-EGM modification. This method was compared with ablation guided by standard ABi parameters. In a beating heart Yorkshire swine model, linear transcaval RFA was performed using an irrigated ablation catheter (Thermocool® SmartTouch Surround-Flow, Biosense Webster, Irwindale, CA) with power of 30W. RF delivery was turned off 3 seconds after a stable R-pattern change was seen on the unipolar EGM (Uni t+3). Inter-lesion spacing was directed by a 2nd operator, blinded to the electroanatomical map, and guided solely by Uni EGM morphology characteristic of viable myocardium as well as current of injury marking the contiguous location with ablated tissue (Figure 1A). Uni EGM signals were processed by the PureEP System (BioSig Technologies). Bidirectional block was demonstrated with standard EP maneuvers and histopathology. Uni EGM guided transcaval lines were compared to a historical cohort of ABi=400 guided transcaval lines. In 5 swine, transcaval ablation lines, guided by Uni EGM were performed. Bidirectional block was demonstrated in 4 of 5 lines (80%) and supported by postmortem histopathology (Figure 1B). Compared with transcaval lines with RFA guided by ABi, there was no difference in initial impedance, impendence drop, or mean length of the ablation line (Table). The Uni-t+3 lines were narrower (5.3±1.5mm vs 11.7±4.8mm, <0.001) and comprised of more closely spaced lesions (2.65±1.3mm vs. 3.4±0.5mm, p=0.001). RFA delivery time per lesion, guided by Uni-EGM modification, was substantially shorter (13.7±5.2sec vs. 21.9±5sec, p<0.001). While total RF delivery time did not differ between the groups [695sec (615-697) vs. 639sec (619-693), p=1). Monitoring changes in the local Uni EGM during ablation offers a real-time physiologic endpoint for titration of RF energy delivery. This study demonstrates that it is feasible to create a transmural line with bidirectional block using ablation that is guided by unipolar signals.Tabled 1Unipolar guided ablation lines Vs ABi linesParameterUt+3 LinesN=5Abi lines (control)N=4PImpedance (ohm)139±7.8131±8.50.3Impedance drop (ohm)14±6.816.1±5.10.1Ablation index333 (296-390)400<0.001Ablation time per lesion (sec)13.7±5.221.9±5<0.001Total RF time (sec)695 (615-697)639 (619-693)1Lesions per line49 (40-50)27 (26-31)0.01Inter-lesion distance (mm)2.65±1.33.4±0.50.001Line length (mm)70 (67-70)67 (66-75)0.62Line width (mm)5.3±1.5411.7±4.8<0.001Transmural80%100% Open table in a new tab

Rapid detection of isthmus block and rhythm change using local electrogram changes during complex atrial flutter ablation.

Multiple re-entry circuits may operate simultaneously in the atria in the form of dual loop re-entry using a common isthmus, or multiple re-entrant loops without a common isthmus. When two or more re-entrant circuits coexist, ablation of an individual isthmus may lead to a seamless transition (without significant changes in surface electrocardiogram, coronary sinus activation or tachycardia cycle length) to a second rhythm, and the isthmus block can go unnoticed. We hypothesize and subsequently illustrate in three patient cases, methods to rapidly identify a transition in the rhythm and isthmus block using local electrogram changes at the ablation site. Local activation sequence changes, electrogram timing, and the behaviour of pre-existing double potentials can reveal isthmus block promptly when rhythm transitions occur during ablation of multiloop re-entry tachycardias.

Unipolar voltage mapping in right ventricular cardiomyopathy: pitfalls, solutions and advantages

Abstract Funding Acknowledgements Type of funding sources: None. Background Endocardial unipolar and bipolar voltage mapping (UVM/BVM) of the right ventricle (RV) are used for transmural substrate delineation. Epicardial BVM is considered less accurate due to the impact of fat thickness (FT). Data on epicardial UVM are sparse. Far-field electrograms and electrogram changes due to injury current may influence automatically generated UVM, which rely on the largest peak-to-peak amplitude within the window-of-interest (WOI). Purpose To assess the influence of manually corrected WOI and the potential role of epicardial UVM in RV cardiomyopathies. Methods Consecutive patients who underwent endo-epicardial RV mapping with computed-tomography (CT) integration were included. Mapping points were superimposed on short-axis CT-slices and correlated with local FT. All points were manually re-analyzed and the WOI was adjusted to correct for false high UV. Per point-pair endo-epicardial BV and UV were correlated for different FT categories. Results A total of 4225 point-pairs of 33 patients were analyzed. In 71% of endocardial points and 65% of epicardial points the window-of-interest needed to be adjusted, due to inclusion of far-field electrograms, injury current components or RV-pacing artifacts (Figure 1). The median absolute difference between epi- and endocardial UV was -0.21mV (IQR:-1.05-0.36) for FT&amp;lt;1mm, compared to -0.60mV (IQR:-2.00-0.30) for FT≥2.8mm. This difference was larger for BV, with a median of -0.36mV (IQR:-2.03-0.23) and -1.29mV (IQR:-3.36-0.05), respectively (p-value epi-endo difference UV vs. BV in all fat categories: &amp;lt;0.001). The Pearson correlation between corrected endo-epicardial BV and UV was lower for point-pairs with greater FT; however, this correlation was stronger and less influenced by fat for UV (coefficient for UV 0.696 for FT&amp;lt;1mm and 0.544 for FT≥2.8mm; for BV 0.437 and 0.155, respectively; Figure 2). In a subanalysis of point-pairs with distance&amp;lt;5mm and FT&amp;lt;1mm, the Pearson coefficient was 0.789 for UV and 0.525 for BV. Conclusions At the majority of mapping sites the window-of-interest needs to be manually adjusted for correct unipolar voltage mapping. Unadjusted UVM underestimates low UV regions. UV seems to be less influenced by epicardial fat and endo-epicardial wavefront, suggesting a promising role for UVM in epicardial substrate delineation.

PO-711-02 POST- ABLATION UNIPOLAR ELECTROGRAM CHANGES: A PRECLINICAL EVALUATION COMPARING RADIOFREQUENCY VS PULSED FIELD ABLATION USING A “MAP AND ABLATE” MULTIELECTRODE ARRAY CATHETER

A multielectrode spherical array catheter (Globe, Kardium Inc, Canada) capable of mapping and ablation with either radiofrequency (RF) and pulsed field (PF) energy has been developed. To compare acute unipolar electrogram changes in atrial tissue after RF vs PF ablation. Healthy canines underwent transseptal access under general anesthesia, followed by circumferential pulmonary vein isolation, as well as linear and focal ablation as part of an efficacy and safety evaluation. Temperature controlled RF ablation (63ºC for 3 min) or PF using 1.6-2 kV/application (either gated or ungated modes) were used in separate animal cohorts. Only animals where focal/linear ablations were placed on the left atrial roof were selected so as to compare electrogram features at identical anatomic sites in both cohorts. We compared pre-ablation with post-ablation unipolar electrograms (1-225 Hz) recorded at i) the electrodes selected for ablation (Row 1), ii) from immediately adjacent electrode rows (Row 2, 3.5-6mm away), and iii) from electrodes 2 rows away (Row 3, 7-12 mm away; Figure). A total of 21 ablated sites (Row 1) and 27 adjacent Rows (2 & 3) were analyzed in the RFA group; similarly 77 and 81 sites were analyzed in the PFA group. Lesion transmurality was seen across the focal lesions on the left atrial roof for both the RF and PF applications. With both RF and PF ablation, there was complete loss of the negative deflection of the unipolar electrogram, as well as diminution of the R wave accompanied by a current of injury in Row 1. In the RF cohort, Row 2 demonstrated minimal loss of the negative deflection with mild injury current. However, PF ablation resulted in significantly greater loss of the negative deflection and current of injury was observed in Row 2, compared to RF ablation. Furthermore, in the PF group, even Row 3 demonstrated some degree of loss of negative deflection and injury current, whereas in the RF group this row was completely preserved. Loss of negative deflection of the unipolar electrogram, a feature that suggests transmural ablation in the setting of RF ablation is also seen with PF . However, the extent of unipolar changes extend further (7-12 mm) from the site of ablation with PF compared to RF, where these changes were milder and restricted to 3.5-6 mm.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Multisite conduction block in the epicardial substrate of Brugada syndrome.

The Brugada pattern manifests as a spontaneous variability of the electrocardiographic marker, suggesting a variability of the underlying electrical substrate. The purpose of this study was to investigate the response of the epicardial substrate of Brugada syndrome (BrS) to programmed ventricular stimulation and to Na blocker infusion. We investigated 6 patients (all male; mean age 54 ± 14 years) with BrS and recurrent ventricular fibrillation. Five had no type 1 BrS electrocardiogram pattern at admission. They underwent combined epicardial-endocardial mapping using multielectrode catheters. Changes in epicardial electrograms were evaluated during single endocardial extrastimulation and after low-dose ajmaline infusion (0.5 mg/kg in 5 minutes). All patients had a region in the anterior epicardial right ventricle with prolonged multicomponent electrograms. Single extrastimulation prolonged late epicardial components by 59 ± 31 ms and in 4 patients abolished epicardial components at some sites, without reactivation by surrounding activated sites. These localized blocks occurred at an initial coupling interval of 335 ± 58 ms and then expanded to other sites, being observed in up to 40% of epicardial sites. Ajmaline infusion prolonged electrogram duration in all and produced localized blocks in 62% of sites in the same patients as during extrastimulation. Epicardial conduction recovery after ajmaline occurred intermittently and at discontinuous sites and produced beat-to-beat changes in local repolarization, resulting in an area of marked electrical disparity. These changes were consistent with models based on microstructural alterations under critical propagation conditions. In BrS, localized functional conduction blocks occur at multiple epicardial sites and with variable patterns, without being reactivated from the surrounding sites.

Chemical mapping as a predictor of vein of Marshall ethanol ablative effects.

The aim of this study was to test regional pharmacological effects of an antiarrhythmic agents to predict ablative effects. The vein of Marshall (VOM) providing vascular access to myocardial tissue has been used for ablative purposes using ethanol. A total of 35 patients (male 21, 63.2±7.8 years old) were included. A balloon-tipped infusion catheter was inserted into the VOM. Endocardial ultrahigh-resolution mapping was performed along the VOM region to record the change in atrial electrograms (AEs) after VOM injection of cibenzoline of 3.5mg during sustained atrial fibrillation (AF). Subsequently, ethanol was infused into the VOM and ablative region was mapped. In 17 patients (49 %), cibenzoline reduced AEs amplitude by>50%, all of which had also complete elimination of AEs following ethanol (Group A). In 18 patients (Group B), cibenzoline failed to eliminate AEs; yet, in 13 of 18 AEs were eliminated by ethanol. In the remaining five patients, ethanol did not eliminate AE. Cibenzoline into the VOM could reliably predicts the results of subsequent ethanol infusion into the VOM using ultrahigh-resolution mapping system, which leads to avoid unnecessary permanent lesion creation by ethanol infusion.

CHANGES IN ELECTROGRAM AMPLITUDE AND INAPPROPRIATE SHOCKS IN PATIENTS WITH SUBCUTANEOUS IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS

Subcutaneous implantable cardioverter-defibrillators (S-ICDs) may change orientation or migrate over time, leading to changes in sensing vectors and inappropriate shocks (IAS). Current literature has reported S-ICD vector changes in more than one-third of S-ICD patients during follow-up. Conversely, serial electrogram (EGM) changes in implantable cardiac monitors have demonstrated maturation of the electrical signal over time. OBJECTIVE: Interrogation reports for S-ICD patients were evaluated for EGM changes over time.

'CLOSE'-Guided Pulmonary Vein Isolation and Changes in Local Bipolar and Unipolar Atrial Electrograms: Observations from the EP Lab.

'CLOSE'-guided pulmonary vein isolation (PVI) is a point-by-point, contact force (CF)-guided radiofrequency (RF) approach aiming to enclose the PVs with contiguous RF lesions by targeting strict criteria for interlesion distance and ablation index (AI). We characterized real-time changes in bipolar (B-EGMs) and unipolar electrograms (U-EGMs) during AI-targeted RF delivery. EGM changes during 56 RF applications in 7 patients with paroxysmal atrial fibrillation (AF) undergoing 'CLOSE'-guided PVI were studied. CF-guided RF was delivered with 35W targeting an AI of 400 at posterior and 550 at anterior wall. 336 B-EGMs and 336 U-EGMs before, during and after RF delivery were analyzed with their RF characteristics. Amplitude of the B-and U-EGM and morphology of the U-EGM were measured at each 5-second step using custom-made software. We observed a significant reduction in B-EGM amplitude (0.43 [IQR=0.25, 0.55] to 0.11 [0.07, 0.22] mV, p<0.001) and U-EGM amplitude (0.57 [0.40, 0.87] to 0.22 [0.10, 0.34] mV, p<0.001) within 5 seconds, after which no more changes were observed. Impedance drop was 18.3±1.1Ω. Loss of the unipolar terminal S-wave occurred in 59% of applications. There was no correlation between U-EGM morphology changes and RF characteristics. In AI-guided RF delivery there is a significant reduction in EGM amplitude within 5 seconds. Loss of the unipolar terminal S wave occurred in 59% of applications and was not related to RF characteristics suggestive of adequate lesion formation. These findings suggest that there is a limited value in monitoring electrograms to further optimize 'CLOSE'-guided PVI.

Tolerance of isolated rabbit hearts to short ischemic periods is affected by increased LV mass fraction.

Hypertrophied hearts are known for increased risk of arrhythmias and are linked with reduced ischemic tolerance. However, still little is known about state characterized only by increased left ventricle (LV) mass fraction. Seventeen isolated rabbit hearts with various LV mass were divided into two groups according to LV weight/heart weight ratio (LVW/HW ratio), namely group H and L (with higher and lower LVW/HW ratio, respectively) and underwent three short cycles of global ischemia and reperfusion. The differences in electrogram (heart rate, QRS(max), mean number, onset and dominant form of ventricular premature beats) and in biochemical markers of myocardial injury (creatine kinase, lactate dehydrogenase - LDH) and lipid peroxidation (4-hydroxy-2-nonenal - 4-HNE) were studied. As compared to group L, hearts in group H exhibited lower tolerance to ischemia expressed as higher incidence and severity of arrhythmias in the first ischemic period as well as increase of LDH and 4-HNE after the first reperfusion. In the third cycle of ischemia-reperfusion, the preconditioning effect was observed in both electrophysiological parameters and LDH release in group H. Our results showed consistent trends when comparing changes in electrograms and biochemical markers. Moreover, 4-HNE seems to be good potential parameter of moderate membrane alteration following ischemia-reperfusion injury.

Validation of device algorithm to differentiate pacemaker-mediated tachycardia from tachycardia due to atrial tracking

Current cardiac devices cannot always differentiate between pacemaker-mediated tachycardia (PMT) and tracking of sinus or atrial tachycardia. We previously derived a novel algorithm for distinguishing the 2 mechanisms based on the specific termination response to postventricular atrial refractory period extension, atrial rates, and changes in atrial electrogram morphology. The purpose of this study was to evaluate how this algorithm would have performed in a clinical setting based on previously recorded PMT events. We applied our algorithm to a database of 122 de-identified stored electrograms that were classified as PMT by 43 remotely monitored devices. Of the 122 events stored as "PMT," 3 episodes were excluded because the device recording was consistent with atrial fibrillation. Of the remaining 119 episodes, our algorithm was able to correctly reclassify 92 events (77%) as tracking of sinus or atrial tachycardia rather than true PMT. The VAV response following postventricular atrial refractory period extension, which is specific to tracking of atrial or sinus tachycardia, was seen in 72% of these cases. Changes in atrial rate and atrial electrogram morphology were able to reclassify the remainder of episodes. Finally, we observed that 12 of 83 episodes (14%) misclassified as PMT in cardiac resynchronization devices resulted in loss of cardiac biventricular pacing. Applying a novel diagnostic algorithm to current cardiac devices improves the proper diagnosis of true PMT rather than tracking of atrial or sinus tachycardia. Enhanced accuracy of diagnosis reduces the likelihood of inappropriate clinical decisions.

Real-time atrial wall imaging during radiofrequency ablation in a porcine model.

Real-time monitoring of radiofrequency (RF) ablation remains challenging. We used intravascular ultrasound (IVUS) to describe atrial wall changes during RF ablation and to assess the extent of RF-induced lesions. In 9 piglets, RF and IVUS catheters were coupled and introduced into the right atrium. RF applications were performed along the intercaval line. Corresponding IVUS images were analyzed. Wall thickness was correlated with electrogram (EGM) changes (n = 9) and histology (n = 5). There were 66 RF applications performed in 57 sites. IVUS provided real-time imaging of the atrial wall during RF application in all but 2 sites. IVUS demonstrated significant (>20%) and immediate increase in atrial wall thickness in 71.4% of RF applications. It showed epicardial or intramyocardial effusion in 30% of cases, 2 steam pops, 1 intramural hematoma, and 1 thrombus. EGM amplitude decreased and thickness increased after RF application than at baseline (2.20 ± 1.11 to 0.99 ± 0.62 mV and 1.34 ± 0.53 to 1.93 ± 0.80 mm, respectively; P < .001 for each). However, EGM and thickness changes were poorly correlated (r = 0.43; P < .05). Histologically and echographically measured thicknesses were correlated (r = 0.71; P = .004), but echographic thickness change was not related to histological lesion transmurality. An IVUS probe coupled to an RF catheter can provide relevant real-time imaging of the atrial wall during ablation. Although thickness change does not appear as a good predictor of the transmural extent, direct visualization and monitoring of RF application may provide new information to guide and secure RF ablation.

Characterization of radiofrequency ablation lesion development based on simulated and measured intracardiac electrograms.

Radiofrequency ablation (RFA) therapy is the gold standard in interventional treatment of many cardiac arrhythmias. A major obstacle is nontransmural lesions, leading to recurrence of arrhythmias. Recent clinical studies have suggested intracardiac electrogram (EGM) criteria as a promising marker to evaluate lesion development. Seeking for a deeper understanding of underlying mechanisms, we established a simulation approach for acute RFA lesions. Ablation lesions were modeled by a passive necrotic core surrounded by a borderzone with properties of heated myocardium. Herein, conduction velocity and electrophysiological properties were altered. We simulated EGMs during RFA to study the relation between lesion formation and EGM changes using the bidomain model. Simulations were performed on a three-dimensional setup including a geometrically detailed representation of the catheter with highly conductive electrodes. For validation, EGMs recorded during RFA procedures in five patients were analyzed and compared to simulation results. Clinical data showed major changes in the distal unipolar EGM. During RFA, the negative peak amplitude decreased up to 104% and maximum negative deflection was up to 88% smaller at the end of the ablation sequence. These changes mainly occurred in the first 10 s after ablation onset. Simulated unipolar EGMs reproduced the clinical changes, reaching up to 83% negative peak amplitude reduction and 80% decrease in maximum negative deflection for transmural lesions. In future studies, the established model may enable the development of further EGM criteria for transmural lesions even for complex geometries in order to support clinical therapy.

Serial Atrial Tachycardias

Complex serial type of atrial tachycardias could be encountered in the context of atrial fibrillation ablation. Careful conventional mapping and precise interpretation of electrograms are required for the diagnosis and treatment. Subtle changes in electrogram could be a sign of transition of atrial tachycardia. A conduction delay in left atrial appendage should be checked after extensive ablation and/or multiple procedures to avoid its electrical isolation.

The Implantable Cardioverter-Defibrillator Minimalist

The implantable cardioverter-defibrillator (ICD) was devised to satisfy the unmet need for an effective, instantaneous therapy to prevent sudden cardiac death (SCD) due to ventricular fibrillation (VF) in at-risk, ambulatory patients. That therapy was a high-voltage electric shock delivered directly into the heart muscle. More than 3 decades later, shocks are still the defining operating characteristic of ICDs, and no other instantaneously effective therapy for VF exists. This elite status was clinched by large randomized clinical trials1,2 which demonstrated that ICDs improved mortality in patients with reduced left ventricular ejection fraction, regardless of pathogenesis or accompanying symptoms of heart failure (HF), by primary prevention of SCD due to ventricular tachyarrhythmia (VTA). Like bradycardia pacemakers for asystole, the ICD resides as a therapy genre of one, with no peer, and no competitor on the horizon. These sibling therapies for lethal heart rhythm disturbances will stand prominently among the greatest medical achievements of the 20th century. The ICD is a mature technology, and neither the technique nor the tools have changed much for several decades. Despite a certain evolutionary elegance of the operating system, the ICD is still a blunt instrument. Although it is true that some innovation has occurred, it is still a matter of a shock delivered by insulated metal conductors residing somewhere in direct proximity to the heart. No innovation beyond the fundamental of a timed shock for VF has proven to enhance mortality benefit. The basic design persists simply because no one can think of a suitable alternative and the self-satisfying aphorism that “shocks save lives.” Yet there is a growing intellectual dissatisfaction with the unintended consequences of this powerful, irreplaceable therapy. The stimulus for this self-inspection is an awareness of the very high morbidity risk overhead borne by the primary prevention patient, in particular, …

Two-year clinical follow-up after pulmonary vein isolation using high-intensity focused ultrasound (HIFU) and an esophageal temperature-guided safety algorithm

High-intensity frequency ultrasound (HIFU) can achieve pulmonary vein isolation (PVI), but severe complications have happened. An esophageal temperature (ET)-guided safety algorithm was implemented. We investigated medium-term outcome. After left atrial access, HIFU was applied until complete PVI. The safety algorithm was as follows: ≤3 complete ablations per pulmonary vein, early abortion when ET ≥40.0°C, use of Power Modulation at ET >39.0°C or when after 20 to 30 seconds no change in PV electrograms: to reduce the ablation temperature in the surrounding tissue, acoustic power is switched on and off with a frequency of 1 Hz; in all first ablations, use of Power Modulation after 50% of programmed time. Touch-up radiofrequency ablation when PVI failed. Follow-up included interviews and Holter electrocardiograms. Recurrence was defined as atrial fibrillation (AF) >30 seconds without a blanking period. A total of 28 symptomatic patients (18 males, age 63 years), with paroxysmal AF (n = 19) and persistent AF (n = 9) were included. After a median follow-up of 738 days, 22 of the 28 patients (79%) were free of AF without antiarrhythmic drugs. After 1 repeat procedure with radiofrequency ablation, 5 patients remained free of AF. The complications were as follows: 1 lethal atrial-to-esophageal fistula at day 31, 1 pericardial effusion at day 48, 1 unexplained death at day 49, and 2 persistent phrenic nerve palsies with full recovery within 12 months. Two-year follow-up after PVI using HIFU and an ET-guided safety algorithm shows success rates similar to those of radiofrequency-based procedures but with higher complication rates. Importantly, the ET-guided safety algorithm failed to prevent severe complications. HIFU does not meet safety standards required for the treatment of AF, and this led to a halt of its clinical use.

Instantaneous Electrophysiological Changes Characterizing Achievement of Mitral Isthmus Linear Block

Achievement of complete conduction block across left mitral isthmus (MI) is a challenging endpoint of linear lesion, and recognizing the precise moment of block is important during ongoing ablation. The objective of this study is to evaluate the changes in P wave morphology and local MI potential at the moment of block during ongoing radiofrequency (RF) application. We evaluated 69 patients (procedures) in whom successful MI linear conduction block was achieved during coronary sinus (CS) pacing. P wave morphology and/or local MI potential could be evaluated in 64 (93%) and 69 (100%) procedures, respectively. The achievement of MI block was associated with substantial instantaneous changes in 57/69 (82.6%) procedures. P wave morphology changed in 44 (64%) procedures with the change restricted to lateral leads in 39 (57%). Abrupt prolongation of local conduction delay from 106 ± 24 ms to 167 ± 39 ms (P < 0.0001) was observed on proximal bipole of ablation catheter in 34/69 (49.3%) procedures during ongoing RF application. In addition, prolongation of conduction delay was associated with significant change in the electrogram amplitude and polarity in 11 and 19 procedures, respectively. The substantial change in P wave morphology was not observed in any patients without achievement of complete block. The achievement of conduction block across MI line is associated with recognizable changes in the local MI electrograms and the P wave morphology especially in the lateral leads. These instantaneous critical changes may assist catheter ablation and indicate the requirement for prolonged RF application, if necessary.

Serial changes in epicardial electrograms during and after a coronary artery occlusion

Suddenly occurring ventricular tachyarrhythmias are a complication during off-pump coronary artery bypass (OPCAB) surgery, potentially leading to the need for conversion to on-pump surgery. We examined serial changes in the spatial dispersion of the electrical activity and refractoriness at the myocardial ischemia border zones during and after coronary occlusion. Unipolar epicardial electrograms were continuously recorded from the anterior left ventricle at the border zones during and after a 10-min occlusion of the left anterior descending (LAD) coronary artery in 22 patients undergoing OPCAB. The local electrogram amplitude and local refractoriness were evaluated by the unipolar peak-to-peak amplitude (UPPA) and activation recovery interval (ARI), respectively. The spatial dispersion of the electrical activity and refractoriness were examined using the coefficient of variation of these parameters. No sustained ventricular tachyarrhythmias occurred in any patients. The UPPA dispersion significantly increased up to 5 min after the LAD occlusion and then returned to a nonsignificant level and again increased after reperfusion. The ARI dispersion gradually increased after the LAD occlusion, reached a significantly increased level 3 min after the occlusion, and stayed at a significantly increased level for at least 5 min after the reperfusion. There were unique serial changes in the spatial dispersion of the electrical activity and refractoriness at the myocardial ischemia border zones during and after coronary occlusions. Continuous monitoring of these parameters may be useful for predicting the critical electrophysiological conditions prone to the occurrence of ventricular tachyarrhythmias in patients undergoing OPCAB.