Endocardial Contact Research Articles

A novel temporary atrioventricular sequential pacing catheter-Characteristics and first-in-human application.

Sequential synchronized atrioventricular (AV) pacing provides enhanced electrophysiologic parameters which contribute to improved hemodynamic parameters and increased cardiac performance to subsequently confer a clinical advantage over traditional ventricular pacing. Current temporary transvenous pacemaker catheters are limited to only one electrode which paces solely the right ventricle, thus lacking the capability to provide the optimal pacing mode. A new multilead pacemaker device was developed in response to the need for improved temporary pacing through the utilization of sequential synchronized atrioventricular pacing (TAVSP). It consists of seven preformed, preshaped nitinol wires electrodes, of which four are for intra-atrial and three for intraventricular positioning and endocardial contact, respectively. Each wire carries a ball tip designed to minimize tissue trauma and provide a high current density for adequate myocardial capture. The device is not yet Food and Drug Administration approved. To present the unique structural components and mechanical properties of a novel sequential synchronized AV pacing device for temporary insertion and to report its first-in-human application with an analysis of the early clinical experience. Following a process of development and proof of concept of the novel pacing modality in an animal model which demonstrated feasibility and safety, a series of patients who were candidates for the device application was identified. During left and right heart catheterization, the novel temporary pacing catheter was inserted transvenously and delivered in most patients under fluoroscopy or echocardiography. The catheter was deployed to its target right heart anatomic sites and then activated in an AV sequential mode. The technical aspects, the corresponding clinical utilization, and device performance were documented and analyzed. The series included 10 enrolled subjects. During planned left and right heart catheterization, the novel TAVSP device was inserted transvenously and then delivered and deployed successfully in a timely fashion in all patients. The pacing catheter achieved proper threshold and impedance in all (100%) patients. The performance of all ventricular leads was adequate; however, in 1 (10%)patient poor performance of the atrial leads was detected. The device was successfully retrieved in all patients. No adverse arrhythmia, impaired hemodynamics, or clinical adverse events occurred. No technical difficulties, component failure, or wires thrombosis were detected. All patients sustained the device application without sequala and were discharged home. Initial clinical experience with the utilization of a novelTAVSPdemonstrates feasibility and safety in humans. The TAVSP modality potentially offers improved pacing capability and subsequent hemodynamic benefits over the current temporary pacing catheters. Further experience with the clinical application of this pacing catheter is warranted.

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.

Non-invasive body surface electrocardiographic imaging for diagnosis of atrial cardiomyopathy.

Atrial cardiomyopathy (ACM) is associated with new-onset atrial fibrillation, arrhythmia recurrence after pulmonary vein isolation (PVI) and increased risk for stroke. At present, diagnosis of ACM is feasible by endocardial contact mapping of left atrial (LA) low-voltage substrate (LVS) or late gadolinium-enhanced magnetic resonance imaging, but their complexity limits a widespread use. The aim of this study was to assess non-invasive body surface electrocardiographic imaging (ECGI) as a novel clinical tool for diagnosis of ACM compared with endocardial mapping. Thirty-nine consecutive patients (66 ± 9 years, 85% male) presenting for their first PVI for persistent atrial fibrillation underwent ECGI in sinus rhythm using a 252-electrode-array mapping system. Subsequently, high-density LA voltage and biatrial activation maps (mean 2090 ± 488 sites) were acquired in sinus rhythm prior to PVI. Freedom from arrhythmia recurrence was assessed within 12 months follow-up. Increased duration of total atrial conduction time (TACT) in ECGI was associated with both increased atrial activation time and extent of LA-LVS in endocardial contact mapping (r = 0.77 and r = 0.66, P < 0.0001 respectively). Atrial cardiomyopathy was found in 23 (59%) patients. A TACT value of 148 ms identified ACM with 91.3% sensitivity and 93.7% specificity. Arrhythmia recurrence occurred in 15 (38%) patients during a follow-up of 389 ± 55 days. Freedom from arrhythmia was significantly higher in patients with a TACT <148 ms compared with patients with a TACT ≥148 ms (82.4% vs. 45.5%, P = 0.019). Analysis of TACT in non-invasive ECGI allows diagnosis of patients with ACM, which is associated with a significantly increased risk for arrhythmia recurrence following PVI.

Left Atrial Hypertension, Electrical Conduction Slowing, and Mechanical Dysfunction - The Pathophysiological Triad in Atrial Fibrillation-Associated Atrial Cardiomyopathy.

BackgroundAtrial fibrillation (AF) is the most common arrhythmia and a significant burden for healthcare systems worldwide. Presence of relevant atrial cardiomyopathy (ACM) is related to persistent AF and increased arrhythmia recurrence rates after pulmonary vein isolation (PVI).ObjectiveTo investigate the association of left atrial pressure (LAP), left atrial electrical [invasive atrial activation time (IAAT) and amplified p-wave duration (aPWD)] and mechanical [left atrial emptying fraction (LA-EF) and left atrial strain (LAS)] functional parameters with the extent of ACM and their impact on arrhythmia recurrence following PVI.Materials and MethodsFifty patients [age 67 (IQR: 61–75) years, 78% male] undergoing their first PVI for persistent AF were prospectively included. LAP (maximum amplitude of the v-wave), digital 12-lead electrocardiogram, echocardiography and high-density endocardial contact mapping were acquired in sinus rhythm prior to PVI. Arrhythmia recurrence was assessed using 72-hour Holter electrocardiogram at 6 and 12 months post PVI.ResultsRelevant ACM (defined as left atrial low-voltage extent ≥2 cm2 at <0.5 mV threshold) was diagnosed in 25/50 (50%) patients. Compared to patients without ACM, patients with ACM had higher LAP [17.6 (10.6–19.5) mmHg with ACM versus 11.3 (7.9–14.0) mmHg without ACM (p = 0.009)]. The corresponding values for the electrical parameters were 166 (149–181) ms versus 139 (131–143) ms for IAAT (p < 0.0001), 163 (154–176) ms versus 148 (136–152) ms for aPWD on surface-ECG (p < 0.0001) and for the mechanical parameters 27.0 (17.5–37.0) % versus 41.0 (35.0–45.0) % for LA-EF in standard 2D-echocardiography (p < 0.0001) and 15.2 (11.0–21.2) % versus 29.4 (24.9–36.6) % for LAS during reservoir phase (p < 0.0001). Furthermore, all parameters showed a linear correlation with ACM extent (p < 0.05 for all). Receiver-operator-curve-analysis demonstrated a LAP ≥12.4 mmHg [area under the curve (AUC): 0.717, sensitivity: 72%, and specificity: 60%], a prolonged IAAT ≥143 ms (AUC: 0.899, sensitivity: 84%, and specificity: 80%), a prolonged aPWD ≥153 ms (AUC: 0.860, sensitivity: 80%, and specificity: 79%), an impaired LA-EF ≤33% (AUC: 0.869, sensitivity: 84%, and specificity: 72%), and an impaired LAS during reservoir phase ≤23% (AUC: 0.884, sensitivity: 84%, and specificity: 84%) as predictors for relevant ACM. Arrhythmia recurrence within 12 months post PVI was significantly increased in patients with relevant ACM ≥2 cm2, electrical dysfunction with prolonged IAAT ≥143 ms and mechanical dysfunction with impaired LA-EF ≤33% (66 versus 20, 50 versus 23 and 55 versus 25%, all p < 0.05).ConclusionLeft atrial hypertension, electrical conduction slowing and mechanical dysfunction are associated with ACM. These findings improve the understanding of ACM pathophysiology and may be suitable for risk stratification for new-onset AF, arrhythmia recurrence following PVI, and development of novel therapeutic strategies to prevent AF and its associated complications.

Echocardiographic diagnosis of atrial cardiomyopathy allows outcome prediction following pulmonary vein isolation

BackgroundRelevant atrial cardiomyopathy (ACM), defined as a left atrial (LA) low-voltage area ≥ 2 cm2 at 0.5 mV threshold on endocardial contact mapping, is associated with new-onset atrial fibrillation (AF), higher arrhythmia recurrence rates after pulmonary vein isolation (PVI), and an increased risk of stroke. The current study aimed to assess two non-invasive echocardiographic parameters, LA emptying fraction (EF) and LA longitudinal strain (LAS, during reservoir (LASr), conduit (LAScd) and contraction phase (LASct)) for the diagnosis of ACM and prediction of arrhythmia outcome after PVI.MethodsWe prospectively enrolled 60 consecutive, ablation-naive patients (age 66 ± 9 years, 80% males) with persistent AF. In 30 patients (derivation cohort), LA-EF and LAS cut-off values for the presence of relevant ACM (high-density endocardial contact mapping in sinus rhythm prior to PVI at 3000 ± 1249 sites) were established in sinus rhythm and tested in a validation cohort (n = 30). Arrhythmia recurrence within 12 months was documented using 72-h Holter electrocardiograms.ResultsAn LA-EF of < 34% predicted ACM with an area under the curve (AUC) of 0.846 (sensitivity 69.2%, specificity 76.5%) similar to a LASr < 23.5% (AUC 0.878, sensitivity 92.3%, specificity 82.4%). In the validation cohort, these cut-offs established the correct diagnosis of ACM in 76% of patients (positive predictive values 87%/93% and negative predictive values 73%/75%, respectively). Arrhythmia recurrence in the entire cohort was significantly more frequent in patients with LA-EF < 34% and LASr < 23.5% (56% vs. 29% and 55% vs. 26%, both p < 0.05).ConclusionThe echocardiographic parameters LA-EF and LAS allow accurate, non-invasive diagnosis of ACM and prediction of arrhythmia recurrence after PVI.Graphic abstract

2019 APHRS expert consensus statement on three-dimensional mapping systems for tachycardia developed in collaboration with HRS, EHRA, and LAHRS.

2019 APHRS expert consensus statement on three-dimensional mapping systems for tachycardia developed in collaboration with HRS, EHRA, and LAHRS.

Influence of Intramyocardial Adipose Tissue on the Accuracy of Endocardial Contact Mapping of the Chronic Myocardial Infarction Substrate.

Recent studies have demonstrated that intramyocardial adipose tissue (IMAT) may contribute to ventricular electrophysiological remodeling in patients with chronic myocardial infarction. Using an ovine model of myocardial infarction, we aimed to determine the influence of IMAT on scar tissue identification during endocardial contact mapping and optimal voltage-based mapping criteria for defining IMAT dense regions. In 7 sheep, left ventricular endocardial and transmural mapping was performed 84 weeks (15-111 weeks) post-myocardial infarction. Spearman rank correlation coefficient was used to assess the relationship between endocardial contact electrogram amplitude and histological composition of myocardium. Receiver operator characteristic curves were used to derive optimal electrogram thresholds for IMAT delineation during endocardial mapping and to describe the use of endocardial mapping for delineation of IMAT dense regions within scar. Endocardial electrogram amplitude correlated significantly with IMAT (unipolar r=-0.48±0.12, P<0.001; bipolar r=-0.45±0.22, P=0.04) but not collagen (unipolar r=-0.36±0.24, P=0.13; bipolar r=-0.43±0.31, P=0.16). IMAT dense regions of myocardium reliably identified using endocardial mapping with thresholds of <3.7 and <0.6 mV, respectively, for unipolar, bipolar, and combined modalities (single modality area under the curve=0.80, P<0.001; combined modality area under the curve=0.84, P<0.001). Unipolar mapping using optimal thresholding remained significantly reliable (area under the curve=0.76, P<0.001) during mapping of IMAT, confined to putative scar border zones (bipolar amplitude, 0.5-1.5 mV). These novel findings enhance our understanding of the confounding influence of IMAT on endocardial scar mapping. Combined bipolar and unipolar voltage mapping using optimal thresholds may be useful for delineating IMAT dense regions of myocardium, in postinfarct cardiomyopathy.

The Use of Unipolar Endocardial Contact Mapping to Detect the Presence of Intramyocardial Adipose Tissue in the Chronic Myocardial Infarction Substrate

The Use of Unipolar Endocardial Contact Mapping to Detect the Presence of Intramyocardial Adipose Tissue in the Chronic Myocardial Infarction Substrate

Contact forces during hybrid atrial fibrillation ablation: an in vitro evaluation.

PurposeData on epicardial contact force efficacy in dual epicardial–endocardial atrial fibrillation ablation procedures are lacking. We present an in vitro study on the importance of epicardial and endocardial contact forces during this procedure.MethodsThe in vitro setup consists of two separate chambers, mimicking the endocardial and epicardial sides of the heart. A circuit, including a pump and a heat exchanger, circulates porcine blood through the endocardial chamber. A septum, with a cut out, allows the placement of a magnetically fixed tissue holder, securing porcine atrial tissue, in the middle of both chambers. Two trocars provide access to the epicardium and endocardium. Force transducers mounted on both catheter holders allow real-time contact force monitoring, while a railing system allows controlled contact force adjustment. We histologically assessed different combinations of epi-endocardial radiofrequency ablation contact forces using porcine atria, evaluating the ablation’s diameters, area, and volume.ResultsAn epicardial ablation with forces of 100 or 300 g, followed by an endocardial ablation with a force of 20 g did not achieve transmurality. Increasing endocardial forces to 30 and 40 g combined with an epicardial force ranging from 100 to 300 and 500 g led to transmurality with significant increases in lesion’s diameters, area, and volumes.ConclusionsIncreased endocardial contact forces led to larger ablation lesions regardless of standard epicardial pressure forces. In order to gain transmurality in a model of a combined epicardial–endocardial procedure, a minimal endocardial force of 30 g combined with an epicardial force of 100 g is necessary.

Open-irrigated laser catheter ablation: influence of catheter–tissue contact force on lesion formation

Catheter-tissue contact force (CF) is a major determinant for radiofrequency (RF) ablation lesion size and quality. We sought to test the influence of catheter CF on lesion formation by using an open-irrigated electrode-laser mapping and ablation (ELMA) catheter. With the ELMA catheter in a stable vertical position, continuous wave 1064 nm laser impacts at 15 W (9.5 W/mm(2)), 30 s (285 J/mm(2)), irrigation flow 30 mL/min, were aimed at the endocardial surface of bovine myocardium in heparinized stagnant blood (ACT >350 s) at room temperature (18 °C). Lesions were produced with CFs of 100 g, 10 g, in contact but without pressure, with the catheter tip 2.0 mm, and 5.0 mm away (n = 10, each). Lesions were evaluated morphometrically and were compared by the unpaired t tests. There were no significant differences between volumes of lesions achieved with catheter-tissue CF of 100 g, 10 g, and in contact without pressure: 297 ± 56.0 vs. 300 ± 39 vs. 320 ± 24, respectively (p > 0.05). However, volumes of lesions produced at a distance of 2 mm (95 ± 14 mm(3)) were significantly smaller (p < 0.0001), whereas at a distance of 5.0 mm, no lesions were produced. No steam-pop with crater or thrombus formation occurred. By using an open-irrigated ELMA catheter, catheter-tissue CF is not a determinant for laser ablation lesion size and quality. Maximum sizes of lesions can be achieved with the catheter in intimate endocardial contact without pressure. However, lesions can be produced also at a catheter-tissue distance of 2.0 mm. Noticeably, there is no thrombus formation during laser application with the free floating ELMA catheter in the stagnant blood.

Contact force mapping and voltage thresholds during high-frequency stimulation of human cardiac ganglionated plexuses†.

The intrinsic cardiac nervous system consists of ganglionated plexuses (GPs) localized epicardially to specific regions of the left atrium (LA). The relation between voltage thresholds and endocardial contact force associated with autonomic effects during stimulation of GPs has not previously been evaluated. Sixteen patients with symptomatic atrial fibrillation (AF) underwent mapping of GPs prior to radiofrequency ablation of AF. Pre-acquired computed tomographic images were merged with 3D non-fluoroscopic electroanatomic mapping of the LA. Using high-frequency stimulation (HFS), the voltage thresholds of GPs was obtained while patients received conscious sedation. At each location, the contact force measurement from the catheter was correlated with the voltage applied during HFS at 5, 10, or 15 V to obtain an autonomic effect, usually associated with asystole, or marked bradycardia. There were 192 applications of HFS, resulting in GP identification in all patients (mean 3.4 per patient, range 1-5). During HFS, an autonomic response was significantly more likely to occur at 10 V as compared with 5 V (P < 0.008). There was no significant relation between the measured contact force and the likelihood of obtaining an autonomic response. When performing HFS at 15 V, a sudden overshoot with maximal values of contact force of up to 100 g was also observed. High-frequency stimulation was well tolerated, without associated adverse events. An autonomic response during HFS was significantly more likely to occur at 10 V as compared with 5 V. Although the GPs are epicardial structures, significant contact force was not required for their localization.

PT005 Presence of thrombus in left atrium in patients with atrium fibrillation anticoagulated with coumarin anticoagulants versus dabigatran

O ST E R A B ST R A C T S theoretical and experimental studies, our group has shown that high bipolar electrogram Shannon entropy (ShEn) distinguishes the pivot and periphery of rotors. We hypothesised that ablation directed towards regions of high ShEn could slow or terminate AF. Objectives: The aim was to determine if directed ablation of regions of high ShEn would slow or terminate human persistent AF. Methods: The study enrolled 9 patients undergoing persistent AF ablation. (Left atrial diameter 45 6mm, LV ejection fraction 52 5%). Patients in spontaneous or induced AF were mapped with a 20-pole PentaRay catheter and NavX system. 8-second recordings of each mapped point were acquired, with endocardial contact verified by fluosocopy at each site. After mapping, mapped point electrophysiologic data and location data were exported to a PC where Shannon entropy (ShEn) was calculated for each mapped point. Points were ranked by entropy value, and colour-coded ShEn maps constructed. The top 10% of ShEn points were annotated on to the NavX map, and used to guide selection of regions for ablation. Ablation of pre-identified ShEn regions was performed after pulmonary vein antral isolation without CFAE or linear ablation. The study endpoints were: (i) AF cycle length change; and (ii) AF termination. Results: Mapping was able to be performed in all cases, with 621 26 points/pt acquired. AF termination occurred in 6/9 cases, with 3/9 cases requiring cardioversion. 5/9 cases showed AF termination co-localised with pre-specified regions of ShEn. In 3 of these cases, termination occurred at pre-specified regions of ShEn encountered during pulmonary vein antral isolation. In 2 cases,termination occurred at ShEn sites outside the pulmonary vein antra. Mean AFCL change post PV isolation was 11.8 13ms (p1⁄40.07), and AFCL change post-ShEn ablation was 29.1 26ms (p1⁄40.02). 6/9 cases remained in sinus rhythm at median follow-up 274 148 days . Sites of ShEn region termination included the base of LA appendage, right anterior wall, roof, posterior wall, and left superior PV ridge. Conclusion: The study demonstrates the feasibility of ablation of high ShEn regions, associated with termination of AF and/or AF cycle length slowing in selected AF patients, and requires further investigation in AF ablation. Disclosure of Interest: None Declared

Open-irrigated laser catheter ablation: influence of catheter irrigation and of contact and noncontact mode of laser application on lesion formation in bovine myocardium

Lesions achieved by radiofrequency application increase with catheter irrigation and with catheter pressure on the endocardial surface. Purpose of this study was to test the influence of catheter irrigation and of contact vs. noncontact mode of laser application on lesion formation in bovine myocardium. By applying continuous wave 1,064 nm laser light via an open-irrigated catheter lesions were produced at 15 W (9.5 W/mm(2))/30 s (285 J/mm(2)), in stagnant blood (activated clotting time > 350 s) at 18 °C, on bovine myocardium. During flow rates of 15, 30, and 50 ml/min radiation was applied with the catheter end hole in contact (n = 10, each) or 2 mm away from the endocardial surface (n = 5, each). Lesions were evaluated morphometrically, and groups of lesions were compared by using the unpaired t test. By augmentation of irrigation flow from 15 to 30 ml/min, contact lesions increased significantly (p = 0.0001). A further increase of flow from 30 to 50 ml/min increased lesions significantly in depth (p = 0.0011) but not in width (p = 0.639) and volume (p = 0.218). Noncontact lesions were significantly smaller than contact lesions (p > 0.05). Lesions of homogenous coagulation necrosis were clear-cut and sharply demarcated from the surrounding normal myocardium. There was no occurrence of steam-pop with intramural cavitation or with tissue vaporization with crater or thrombus formation. It is suggested that by using an open-irrigated laser catheter as described in this study, catheter irrigation at flow rates of 30 to 40 ml/min are optimal for myocardial coagulation, and catheter pressure on the endocardial surface is not needed for lesion formation. Laser lesions can be achieved also without intimate endocardial catheter contact.

Transseptal Conduction as an Important Determinant for Cardiac Resynchronization Therapy, as Revealed by Extensive Electrical Mapping in the Dyssynchronous Canine Heart

Simple conceptual ideas about cardiac resynchronization therapy assume that biventricular (BiV) pacing results in collision of right and left ventricular (LV) pacing-derived wavefronts. However, this concept is contradicted by the minor reduction in QRS duration usually observed. We investigated the electric mechanisms of cardiac resynchronization therapy by performing detailed electric mapping during extensive pacing protocols in dyssynchronous canine hearts. Studies were performed in anesthetized dogs with acute left bundle-branch block (LBBB, n=10) and chronic LBBB with tachypacing-induced heart failure (LBBB+HF, n=6). Activation times (AT) were measured using LV endocardial contact and noncontact mapping and epicardial contact mapping. BiV pacing reduced QRS duration by 21±10% in LBBB but only by 5±12% in LBBB+HF hearts. Transseptal impulse conduction was significantly slower in LBBB+HF than in LBBB hearts (67±9 versus 44±16 ms, respectively), and in both groups significantly slower than transmural LV conduction (≈30 ms). In both groups QRS duration and vector and the epicardial AT vector amplitude and angle were significantly different between LV and BiV pacing, whereas the endocardial AT vector was similar. During variation of atrioventricular delay while LV pacing, and ventriculo-ventricular delay while BiV pacing, the optimal hemodynamic effect was achieved when epicardial AT and QRS vectors were minimal and endocardial AT vector indicated LV preexcitation. Due to slow transseptal conduction, the LV electric activation sequence is similar in LV and BiV pacing, especially in failing hearts. Optimal hemodynamic cardiac resynchronization therapy response coincides with minimal epicardial asynchrony and QRS vector and LV preexcitation.

Contact Force Monitoring for Cardiac Mapping in Patients with Ventricular Tachycardia

Although the importance of contact force monitoring during mapping and ablation procedures is widely recognized, only indirect measurements have been validated. Real-time force values were measured using the force-sensing catheter and electroanatomical mapping system from 27 chambers (13 LVs, 6 RVs, and 8 epicardial space) in 17 patients affected by ventricular tachycardia. Left ventricular mapping was performed by the transaortic approach in all patients and in 5 patients also by a transseptal approach with the aid of a deflectable sheath. All points were divided into 2 groups according to the presence of positive contact force during diastole: good and poor contact. The frequency of good contact and its impact on electrophysiological parameters such as signal amplitude, local impedance, and frequency of late potentials was evaluated. The best cut-off value to discriminate the 2 groups was calculated by a generalized linear mixed-effects model. Among all 5,926 points, 1,566 (26%) points were taken with poor contact. In healthy tissue, categorical increase of contact force caused the increase of unipolar and bipolar signal potential amplitude followed by plateau. The frequency of late potentials in the poor contact group was significantly lower when compared to the good contact group (11.9 vs 23.2%; P < 0.0001). The best cut-off force value to predict good contact during left ventricular endocardial and epicardial mappings was 9 g. A combined transaortic and transseptal approach allows better endocardial contact during left ventricular mapping. Ventricular mapping with sufficient contact force produces better substrate characterization within pathological areas.

Diaphragmatic implantation of the HeartWare ventricular assist device

The HeartWare (HeartWare Inc., Framingham, MA) ventricular assist device (HVAD) is designed to be implanted with the pump in the pericardial space and its integrally attached inflow cannula in the left ventricle. The uniquely incorporated inflow cannula was originally designed to be inserted into the diaphragmatic surface of the heart, allowing the pump to sit on the flattened diaphragmatic surface. Commonly, however, the inflow cannula is placed through the usual left ventricular assist device insertion site, anterolateral to the left ventricular apex. We describe the original, intended technique for inflow cannula insertion and HVAD placement on the diaphragmatic surface of the left ventricle. Our experience has confirmed that this placement results in the optimal left ventricular position, with orientation of the inlet cannula parallel to the short axis of the left ventricle and anterior to the papillary muscle insertion. This approach should protect against inflow obstruction and endocardial contact, with resulting arrhythmias. In addition, this position results in lateral placement of the outflow graft, avoiding the anterior and retrosternal surface of the right ventricle.

Ultrasonic measurements of local activation times: Toward the realization of a clinical intramural cardiac electrical mapping?

i t t t s u g s a c f B Starting from the early 1930s with pioneering studies such as those by Barker et al, the mapping of the surface ocal activation times of the human cardiac tissue, i.e., the ocal timings of the excitatory process, has been a key lement in electrophysiological studies aimed at identifying rrhythmogenic sources. In common clinical procedures, this is usually achieved invasively by measuring the local electrograms using epicardial or endocardial contact leads. Aside from the clinical and financial drawbacks of n invasive catheterization surgery, the important informaion regarding the intramural electrical activity can only be oosely inferred from the surface measurements and thus emains largely unknown. Three dimensional (3D) mapping f the cardiac electrical activity has so far been preliminary nd experimental, and mostly inapplicable to intact hearts. lthough arrays of plunge electrodes can be used to map the nstantaneous distribution of the excitatory process in the D cardiac tissue, this technique suffers from substantial echnical limitations, is restricted to isolated hearts, and herefore cannot be applied in surgery. Recent attempts to perform 3D cardiac mapping include trans-illumination, whereby the subendocardial and subepicardial electrical activity can be accessed via optical mapping in combination with photon diffusion theory, yet this technique is relevant only to thin tissues, requires toxic dyes, and can only be applied in laboratory setups. A major step toward a clinially feasible noninvasive mapping of the cardiac electrical ctivity is the electrocardiographic imaging method, which nvolves the solution of a highly ill-conditioned inverse roblem, thus providing relatively low spatial resolution of he activation waves, and which is highly sensitive to noise. dditionally, it requires an auxiliary imaging modality that ither utilizes ionizing radiation (e.g., X-ray computed toography) or is costly (e.g., magnetic resonance imaging). evertheless, electrocardiographic imaging has been shown n preliminary research to be clinically informative to some xtent and is still under validation studies. Despite the ongoing efforts to map the cardiac 3D electrical excitatory process, no satisfactory technologies have

Percutaneous Microwave Ablation with a Long Side‐Firing Antenna Array Can Successfully Treat a Nonsurgical Chronic Ovine Atrial Flutter Model

Long side-firing microwave (MW) arrays can deliver energy uniformly over its length without the need for intimate endocardial contact. We hypothesize that a novel 6 Fr 20 mm long percutaneous high-efficiency MW antenna array ablation catheter can rapidly create long, continuous, and transmural linear ablation lesions. Cavotricuspid isthmus (CTI)-dependent atrial flutter (AFL) was created in 11 sheep by a line of radiofrequency ablation lesions in the posterior right atrium (RA) linking the venae cavae. After 4-6 weeks recovery, CTI-dependent AFL was still inducible in all 11 sheep (cycle length 178 +/- 13 ms). MW ablation of the CTI at 100 W for 30 seconds was then performed with an endpoint of AFL noninducibility. AFL was not inducible in all 11 sheep after 4.3 +/- 3.3 MW applications (129 +/- 99 seconds). The last 6 animals needed fewer ablations (2.2 +/- 1.5) and 3 of these sheep required only a single ablation. Although conduction times from proximal coronary sinus to lateral RA and vice versa increased postablation (51 +/- 14 ms to 118 +/- 31 ms [P = 0.0002] and 60 +/- 13 ms to 119 +/- 28 ms [P = 0.0001], respectively), AFL was still inducible in 2 sheep and further ablation was needed to reach the endpoint. High-efficiency side-firing MW array ablation can rapidly create long linear and electrically intact lesions in an ovine AFL model. AFL noninducibility may be a more reliable indicator than CTI conduction times of an intact line of ablation in this animal model.

Characterisation of Direction-dependent Conduction Abnormalities Predisposing to Atrial Arrhythmias

Methods:Mappingwasperformed in eight sheeps, 60± 54 weeks post-MI. Twenty multielectrode needles were deployed at thoracotomy in the left ventricle within and surrounding scar. Needles were located using EnsiteTM. Endocardial contact (needle) and noncontact unipolar electrograms were recorded simultaneously during SR and multisite pacing. DSM maps were calculated as a ratiometric consensus of peak negative voltage (PNV). ADSM maps were calculated using a root mean square consensus of peak–peak voltage (P2PV). Scar was quantified histologically and correlated with mapping criteria using receiver operator curves with 50% scar density cutoff. Results: All modalities could identify scar (symbols †p 2mA=29± 8%, AUC=0.93†) and conduction delay (ADSM%, ≤30ms= 63± 19%, >30ms= 45± 23%, AUC=0.72‡) were associated with decreased ADSM%. ADSM sensitivity was improved with limited distance from the array (r< 40mm, AUC=0.74†). Conclusions: ADSM is more reliable in detecting scar p< 0.001); delayed activation in the high-posterior (78± 14ms vs. 46± 15ms, p< 0.05), high-septal (81± 27ms vs. 46± 7ms, p< 0.05) and low-septal RA (87± 41ms vs. 42± 13ms, p< 0.05); greater proportion of DP/FS (48% vs. 7%, p< 0.001) and lower regional voltage (1.4± 0.3mV vs. 2.1± 0.5mV, p< 0.005) compared to SR. Anatomical regions of FS correlated with regions of low voltage (r=−0.63, p= 0.01). Septal-paced and SR-maps showed lines of block at: the crista terminalis (10 vs. 11), septum (8 vs. 2, p= 0.02), lateral RA (4 vs. 1), eustachian ridge (2 vs. 0) and appendage (1 vs. 0). Septal-paced maps identified significantly more lines (25 vs. 14, p= 0.03) of greater length (60± 27mm vs. 43± 12mm, p< 0.05). Additionally, the crista terminalis identified in septal-paced maps was significantly longer (80± 24mm vs. 42± 10mm, p< 0.001). Conclusions: Direction-dependent analysis revealed significant changes in regional conduction velocities, voltage and fractionation. These heterogeneous changes suggest ectopy from septal sites may be more likely to initiate arrhythmiabyconductingaroundareasof functionalblock to promote re-entry. doi:10.1016/j.hlc.2008.05.283

Transcatheter Cryoablation Part I: Preclinical Experience

The concept of cooling to treat medical disorders dates back to the ancient Egyptian Edwin Smith Papyrus on surgical trauma, written between 3000 and 2500 B.C. Hypothermic therapy was recommended for abscesses that were “oily, like fluid under thy hand, [which] produce some clamminess of the surface.”1 Modern forms of cryothermal tissue ablation have been used surgically for decades in numerous organ systems and for various pathologies. Unlike heat that destroys cells by coagulation and tissue necrosis with potential for thrombus formation and aneurysmal dilatation, cryoablation involves a distinct pathophysiological process. As such, it carries a unique safety and efficacy profile. While not novel as an energy modality, harnessing cryoenergy into a steerable transcatheter format represents a more recent landmark in the history of arrhythmia therapy. In Part I of this two-part series, we will focus on the body of knowledge underlying the development of a transcatheter cryoablation system. Pertinent features related to biophysics and mechanisms of cryothermal tissue injury will be highlighted, key historical developments considered, and experience gained from cryosurgery with hand-held probes summarized. Preclinical studies with transcatheter cryoablation will be detailed, setting the framework for human applications. Part II of this series will review the current state of knowledge regarding clinical experience with transcatheter cryoablation.