Novel contact force sensor incorporated in irrigated radiofrequency ablation catheter predicts lesion size and incidence of steam pop and thrombus

A novel technique for zero-fluoroscopy catheter ablation used to manage Wolff-Parkinson-White syndrome with a left-sided accessory pathway

Conventional catheter ablation of cardiac arrhythmias is associated with the potential adverse effects of low-dose ionizing radiation on both patients and laboratory personnel. Due to the greater radiation sensitivity and the longer life expectancy of children, reduction of radiation exposure for them is of particular importance. A novel technique for zero-fluoroscopy catheter ablation is described using real-time tissue-tip contact force measurements for a 10-year-old boy who had Wolff-Parkinson-White syndrome with a left-sided accessory pathway.

Measuring luminal esophageal temperature during pulmonary vein isolation of atrial fibrillation

AIM

To investigate the luminal esophageal temperature (LET) at the time of delivery of energy for pulmonary vein isolation (PVI).

METHODS

This study included a total of 110 patients with atrial fibrillation who underwent their first PVI procedure in our laboratory between March 2010 and February 2011. The LET was monitored in all patients. We measured the number of times that LET reached the cut-off temperature, the time when LET reached the cut-off temperature, the maximum temperature (T max) of the LET, and the time to return to the original pre-energy delivery temperature once the delivery of energy was stopped.

RESULTS

Seventy-eight patients reached the cut-off temperature. It took 6 s at the shortest time for the LET to reach the cut-off temperature, and 216.5 ± 102.9 s for the temperature to return to the level before the delivery of energy. Some patients experienced a transient drop in the LET (TDLET) just before energy delivery. Ablation at these sites always produced a rise to the LET cut-off temperature. TDLET was not observed at sites where the LET did not rise. Thus, the TDLET before the energy delivery was useful to distinguish a high risk of esophageal injury before delivery of energy.

CONCLUSION

Sites with a TDLET before energy delivery should be ablated with great caution or, perhaps, not at all.

Radiofrequency ablation of cardiac arrhythmias: past, present and future

The treatment of cardiac arrhythmias has been revolutionized by the ability to definitively treat many patients with radiofrequency catheter ablation, rather than requiring lifelong medication. This review covers the history of how this has developed and the methods used currently and explores what the future holds for this rapidly evolving branch of Cardiology.

Use of endogenous NADH fluorescence for real-time in situ visualization of epicardial radiofrequency ablation lesions and gaps

Radiofrequency ablation (RFA) aims to produce lesions that interrupt reentrant circuits or block the spread of electrical activation from sites of abnormal activity. Today, there are limited means for real-time visualization of cardiac muscle tissue injury during RFA procedures. We hypothesized that the fluorescence of endogenous NADH could be used as a marker of cardiac muscle injury during epicardial RFA procedures. Studies were conducted in blood-free and blood-perfused hearts from healthy adult Sprague-Dawley rats and New Zealand rabbits. Radiofrequency was applied to the epicardial surface of the heart using a 4-mm standard blazer ablation catheter. A dual camera optical mapping system was used to monitor NADH fluorescence upon ultraviolet illumination of the epicardial surface and to record optical action potentials using the voltage-sensitive probe RH237. Epicardial lesions were seen as areas of low NADH fluorescence. The lesions appeared immediately after ablation and remained stable for several hours. Real-time monitoring of NADH fluorescence allowed visualization of viable tissue between the RFA lesions. Dual recordings of NADH and epicardial electrical activity linked the gaps between lesions to postablation reentries. We found that the fluorescence of endogenous NADH aids the visualization of injured epicardial tissue caused by RFA. This was true for both blood-free and blood-perfused preparations. Gaps between NADH-negative regions revealed unablated tissue, which may promote postablation reentry or provide pathways for the conduction of abnormal electrical activity.

Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures

BACKGROUND

One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating.

METHODS

A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip.

RESULTS

A maximum temperature rise of 22.4°C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2°C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8°C.

CONCLUSION

Up to a maximum of 22.4°C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner.

FBG sensor for contact level monitoring and prediction of perforation in cardiac ablation

Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, the catheter is accidently pushed through the heart wall due to the application of excessive force. Despite the various capabilities of currently available technology, there has yet to be any data establishing how cardiac perforation can be reliably predicted. Thus, two new FBG based sensor prototypes were developed to monitor contact levels and predict perforation. Two live sheep were utilized during the study. It was observed during operation that peaks appeared in rhythm with the heart rate whenever firm contact was made between the sensor and the endocardial wall. The magnitude of these peaks varied with pressure applied by the operator. Lastly, transmural perforation of the left atrial wall was characterized by a visible loading phase and a rapid signal drop-off correlating to perforation. A possible pre-perforation signal was observed for the epoxy-based sensor in the form of a slight signal reversal (12–26% of loading phase magnitude) prior to perforation (occurring over 8 s).

Epicardial ablation with irrigated electrodes: – effect of bipolar vs. unipolar ablation on lesion formation –

BACKGROUND

Ablation of ventricular tachycardia originating from the left ventricular (LV) epicardium is often limited by the radiofrequency power delivery. We compared the effect of bipolar vs. unipolar epicardial ablation on lesion size.

METHODS AND RESULTS

Eleven excised pig hearts were superfused with saline (2 L/min). Unipolar ablation (25 or 30 W for 120 s) was performed between the LV epicardial saline-irrigated electrode and an indifferent electrode (n = 33 lesions). Bipolar ablation (25 or 30 W for 120 s) was performed between a 4-mm saline-irrigated-tip (20 ml/min) electrode on the LV epicardium and an opposing 10-mm non-irrigated-tip electrode on the LV endocardium (n = 38 lesions). Wall thickness did not differ between experiments (15.4 ± 2.4 vs. 15.3 ± 2.1 mm). Impedance was lower at the beginning and end of unipolar ablation than at the beginning and end of bipolar ablation (163.2 ± 20.3Ω and 109.9 ± 16.0Ω vs. 194.6 ± 23.3Ω and 127.1 ± 16.4Ω, respectively) (P<0.001). Epicardial lesion width did not differ between unipolar and bipolar ablation (10.1 ± 2.7 vs. 10.2 ± 2.4 mm), but lesion depth was greater with bipolar ablation (10.6 ± 2.7 vs. 7.5 ± 1.0 mm) (P<0.001). Unipolar ablation produced no transmural lesion, but bipolar ablation produced 15 (46%) (P<0.001). Steam pop occurred in 11 (29%) and 3 (9%) cases, respectively (P = 0.036).

CONCLUSIONS

Bipolar ablation of the LV free wall is highly effective at creating an appropriately deep epicardial lesion.

A piezoresistive tactile sensor for tissue characterization during catheter-based cardiac surgery

BACKGROUND

Currently, most of mitral valve annuloplasty surgeries are performed by using open heart surgery. However, if such operation would be performed by using minimally invasive surgery via catheter-based techniques (CBT), it offers various advantages for both surgeons and patients.

METHODS

Two piezoresistive force sensors are used in the structure of the tactile sensor, which can easily be miniaturized and integrated into surgical catheters. The tactile sensor was fabricated and tested to characterize different elastomers, as the phantom of cardiac tissues. Based on a developed finite element analysis (FEA) of the elastomers, the interaction between the sensor and those materials were modelled to validate the output of the sensor.

RESULTS

The results of the mechanical and psychophysical tests confirm the capability of the proposed sensor to measure the relative hardness/softness of different soft tissues.

CONCLUSIONS

The proposed tactile sensor will help surgeons to characterize different types of cardiac tissues and would facilitate the use of CBT to perform mitral valve annuloplasty.

A novel radiofrequency ablation catheter using contact force sensing: Toccata study

OBJECTIVES

The aim of this multicenter study was to evaluate the device- and procedure-related safety of a novel force-sensing radiofrequency (RF) ablation catheter capable of measuring the real-time contact force (CF) and to present CF data and its possible implications on patient safety.

BACKGROUND

The clinical outcome of RF ablation for the treatment of cardiac arrhythmias may be affected by the CF between the catheter tip and the tissue. Insufficient CF may result in an ineffective lesion, whereas excessive CF may result in complications.

METHODS

Seventy-seven patients (43 with right-sided supraventricular tachycardia [SVT] and 34 with atrial fibrillation [AF]) received percutaneous ablation with the novel studied catheter. The CF applied and safety events related to the procedure were reported.

RESULTS

CF values at mapping ranged from 8 ± 8 to 60 ± 35 g and from 12 ± 10 to 39 ± 29 g in the SVT group and the LA group, respectively, showing a significant interinvestigator variability (P < .0001). High transient CFs (>100 g) were noted in 27 patients (79%) of the LA group. One device-related complication (tamponade, 3%) occurred in the AF group.

CONCLUSIONS

Catheter ablation using real-time CF technology is safe for the treatment of SVT and AF. High CFs may occur during catheter manipulation and not just during ablation, suggesting that measuring CF may provide additional useful information to the operator for safe catheter manipulation. In the future, CF-sensing catheters may also increase the effectiveness of RF ablations by allowing better control of the RF lesion size.

Complications of atrial fibrillation ablation: when prevention is better than cure

As atrial fibrillation ablation is becoming increasingly popular in many cardiac electrophysiological laboratories around the world, preventing, avoiding, or treating procedure-related complications is of utmost importance. In our review of the literature regarding this issue, we addressed in detail all the potential collateral and undesired effects associated to this intervention.

Temperature-controlled cooled-tip radiofrequency linear ablation of the atria guided by a realtime position management system

Due to the difficulty in producing a transmural linear lesion and the possibility of complications such as thrombus formation leading to thromboembolism, the catheter-based maze procedure remains problematic. We tested, in pigs, the possibility of using a temperature-controlled cooled-tip radiofrequency (RF) ablation system together with a realtime position management (RPM) system to create a transmural linear lesion uncomplicated by thrombus formation.Nine pigs underwent insertion of two electrode catheters (each with two ultrasound electrodes), one into the coronary sinus (CS) and one into the right ventricular apex (references for ultrasound-based non-fluoroscopic three-dimensional mapping). A cooled-tip catheter (with two ultrasound electrodes) was introduced into the right atrium. Linear right atrial ablation was performed with a custom radiofrequency (RF) generator. The catheter was perfused with 0.66 mL/second of saline. RF was delivered for 60 seconds at a target temperature of 40°C. A linear ablation line was created between the superior vena cava and inferior vena cava. Three-dimensional isochronal maps were created during CS pacing before and after ablation. In 4 of the 9 pigs, a transmural linear ablation line was confirmed by three-dimensional mapping and postmortem macroscopic examination. No endocardial thrombus formation was noted. Temperature-controlled cooled-tip RF linear ablation guided by an RPM system appears to have potential for creating linear lesions in the atria. Further studies are needed to determine whether such an ablation technique and the parameters used will facilitate successful completion of the catheter-based maze procedure.

Advances in imaging for atrial fibrillation ablation

Over the last fifteen years, our understanding of the pathophysiology of atrial fibrillation (AF) has paved the way for ablation to be utilized as an effective treatment option. With the aim of gaining more detailed anatomical representation, advances have been made using various imaging modalities, both before and during the ablation procedure, in planning and execution. Options have flourished from procedural fluoroscopy, electroanatomic mapping systems, preprocedural computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and combinations of these technologies. Exciting work is underway in an effort to allow the electrophysiologist to assess scar formation in real time. One advantage would be to lessen the learning curve for what are very complex procedures. The hope of these developments is to improve the likelihood of a successful ablation procedure and to allow more patients access to this treatment.

Steerable versus nonsteerable sheath technology in atrial fibrillation ablation: a prospective, randomized study

BACKGROUND

Steerable sheath technology is designed to facilitate catheter access, stability, and tissue contact in target sites of atrial fibrillation (AF) catheter ablation. We hypothesized that rhythm control after interventional AF treatment is more successful using a steerable as compared with a nonsteerable sheath access.

METHODS AND RESULTS

One hundred thirty patients with paroxysmal or persistent drug-refractory AF undergoing their first ablation procedure were prospectively included in a randomized fashion in 2 centers. Ablation was performed by 10 operators with different levels of clinical experience. Treatment outcome was measured with serial 7-day Holter ECGs and additional symptom-based arrhythmia documentation. Single procedure success (freedom from AF and/or atrial macroreentrant tachycardia) was significantly higher in patients ablated with a steerable sheath (78% versus 55% after 3 months, P=0.005; 76% versus 53% after 6 months, P=0.008). Rate of pulmonary vein isolation, procedure duration, and radiofrequency application time did not differ significantly, whereas fluoroscopy time was lower in the steerable sheath group (33±14 minutes versus 45±17 minutes, P<0.001). Complication rates showed no significant difference (3.2% versus 5%, P=0.608). On multivariable analysis, steerable sheath usage remained the only powerful predictor for rhythm outcome after 6 months of follow-up (hazard ratio, 2.837 [1.197 to 6.723]).

CONCLUSIONS

AF catheter ablation using a manually controlled, steerable sheath for catheter navigation resulted in a significantly higher clinical success rate, with comparable complication rates and with a reduction in periprocedural fluoroscopy time.

CLINICAL TRIAL REGISTRATION

URL: http://clinicaltrials.gov. Unique identifier: NCT00469638.

MRI-compatible intensity-modulated force sensor for cardiac catheterization procedures

This paper presents a novel, magnetic resonance imaging (MRI)-compatible, force sensor suitable for cardiac catheterization procedures. The miniature, fiber-optic sensor is integrated with the tip of a catheter to allow the detection of interaction forces with the cardiac walls. The optical fiber light intensity is modulated when a force acting at the catheter tip deforms an elastic element, which, in turn, varies the distance between a reflector and the optical fiber. The tip sensor has an external diameter of 9 Fr (3 mm) and can be used during cardiac catheterization procedures. The sensor is able to measure forces in the range of 0-0.85 N, with relatively small hysteresis.  A nonlinear method for calibration is used and real-time MRI in vivo experiments are carried out, to prove the feasibility of this low-cost sensor, enabling the detection of catheter-tip contact forces under dynamic conditions.

Remote-Controlled Magnetic Pulmonary Vein Isolation Using a New Irrigated-Tip Catheter in Patients With Atrial Fibrillation

Background—

Lack of an irrigated-tip magnetic catheter has limited the role of remote-controlled magnetic navigation (Niobe II, Stereotaxis) for catheter ablation of atrial fibrillation (AF).

Methods and Results—

A novel 3.5-mm-tip irrigated magnetic catheter (group 1, Thermocool Navistar RMT, Biosense Webster) was used for 3D left atrial reconstruction (CARTO RMT) and remote-controlled magnetic pulmonary vein isolation. A redesigned catheter was used in group 2. The primary end point was wide area circumferential pulmonary vein isolation confirmed by spiral catheter recording during ablation; secondary end points included procedural data, complications, and AF recurrence. Fifty-six consecutive patients [group 1: 28 patients, 22 males, age 64 (38 to 78) years, left atrium: 47 (34 to 52) mm; paroxysmal AF: n=21, persistent AF: n=7; group 2: 28 patients, 20 males, age 60 (24 to 78) years, left atrium: 40 (35 to 53) mm; paroxysmal AF: n=18, persistent AF: n=10] were included. The primary end point was achieved in a total of 52 of 56 (93%) patients. Median procedure duration was 315 (125 to 550) minutes (group 1: 370 [230 to 550] minutes; group 2: 243 [125 to 450] minutes). Median fluoroscopy exposure to the investigator was reduced by 31%. Tip charring in 17 of 28 (61%) and complications in 3 of 28 (11%) patients in group 1 resulted in a catheter redesign. Sinus rhythm was maintained by 35 of 50 (70%) patients during a median follow-up period of 545 (100 to 683) days.

Conclusions—

Remote-controlled magnetic AF ablation with real-time verification of pulmonary vein isolation is feasible with a comparable success rate to manual ablation. Safety improved after a redesign of the catheter.

Temperature-controlled cooled-tip radiofrequency ablation in left ventricular myocardium

Steam pop and intramural charring have been reported during cooled-tip radiofrequency catheter ablation (RFCA). We studied the feasibility of temperature-controlled cooled-tip RFCA in the canine heart.An internally cooled ablation catheter was inserted into the left ventricle. A custom-made radiofrequency (RF) generator capable of controlling the tip-temperature at the preset level by slow increases in the power was used. Temperature-controlled cooled-tip RF applications were performed at a target temperature of 40 degrees C for 90 seconds. Acute study: Intramyocardial temperature was measured at the ablation site in 10 dogs by inserting a fluoroptic probe. Chronic study: Lesion depth and volume were measured in 5 dogs after 3 weeks of survival. In the acute study, no pop or abrupt impedance rise was observed. Maximum intramyocardial temperature was 72.4 + or - 14.4 degrees C at 2-4 mm above the endocardium. No coagulum formation, craters, or intramural charring were observed. Maximum lesion depth was 6.7 + or - 1.5 mm, and lesion volume was 404 + or - 219 mm3. In the chronic study, maximum lesion depth was 5.9 + or - 1.1 mm, and lesion volume was 281 + or - 210 mm(3).Temperature controlled RFCA is feasible with a cooled-tip catheter and an RF generator that slowly increases the RF power until the preset catheter-tip temperature is reached.

Unexpected high incidence of esophageal injury following pulmonary vein isolation using robotic navigation

INTRODUCTION

Robotic navigation (RN) is a novel technology for pulmonary vein isolation (PVI). We investigated the incidence of thermal esophageal injury using RN with commonly used power settings in comparison to manual PVI procedures. methods: Thirty-nine patients underwent circumferential PVI using a 3.5-mm irrigated-tip-catheter. In the manual (n = 25) and the RN(1) group (n = 4) power was limited to 30 W (17 mL/min flow, maximal temperature 43 degrees C, max. 30 sec/spot) at the posterior left atrial (LA) wall. In RN-based procedures, ablation was performed with a contact force of 10-40 g. The operator was blinded to the esophageal temperature (T(eso)). In the RN(2) group ablation power along the posterior LA wall was reduced to 20 W and ablation terminated at T(eso) of 41 degrees C. Endoscopy was carried out 2 days post-ablation.

RESULTS

PVI was achieved in all patients. In the manual group no esophageal lesions, minimal lesions, or ulcerations were found in 15 of 25 (60%), 7 of 25 (28%), and 3 of 25 (12%) patients, respectively. All patients in the RN(1) group had an ulceration and one developed esophageal perforation. A covered stent was placed 14 days post-PVI and removed at day 81. In the RN(2) group, only a single minimal lesion was found.

CONCLUSIONS

A high incidence of thermal esophageal injury including a perforation was noted following robotic PVI using 30 W along the posterior LA wall. During RN-based PVI procedures esophageal temperature monitoring is advocated. Reduction of ablation power to 20 W and termination of energy delivery at T(eso) of 41 degrees C significantly reduced the risk of esophageal injury.

Importance of catheter contact force during irrigated radiofrequency ablation: evaluation in a porcine ex vivo model using a force-sensing catheter

INTRODUCTION

Ablation electrode-tissue contact has been shown to be an important determinant of lesion size and safety during nonirrigated ablation but little data are available during irrigated ablation. We aimed to determine the importance of contact force during irrigated-tip ablation.

METHODS AND RESULTS

Freshly excised hearts from 11 male pigs were perfused and superfused using fresh, heparinized, oxygenated swine blood in an ex vivo model. One-minute ablations were placed using one of 3 different power control strategies (impedance control-15 Omega target impedance drop, and 20 W or 30 W fixed power) and 3 different contact forces (2 g, 20 g, and 60 g) to give a grid of 9 ablation groups. The force sensing catheter (Tacticath, Endosense SA) was irrigated at 17 mL/min for all of the ablations. Of a total 101 ablations, no thrombus formation was noted but popping was seen in 17 lesions. The lesion depth and incidence of pops was 5.0 +/- 1.3 mm /0%, 5.0 +/- 1.6 mm /10% and 6.7 +/- 2.5 mm /45% for the 15 Omega, 20 W, and 30 W groups (P < 0.01), respectively, and 4.4 +/- 1.8 mm /3%, 5.8 +/- 1.6 mm /17% and 6.6 +/- 2.0 mm /37% for the 2 g, 20 g, and 60 g groups, respectively (P < 0.01). The impedance drop in the first 5 seconds was significantly correlated to catheter contact force: 9.7 +/- 9.9 Omega, 22.3 +/- 11.0 Omega, and 41.7 +/- 22.1 Omega, respectively, for the 2 g, 20 g, and 60 g groups (Pearson's r = 0.65, P < 0.01).

CONCLUSION

Catheter contact force has an important impact on both ablation lesion size and the incidence of pops.

A fibre-optic catheter-tip force sensor with MRI compatibility: a feasibility study

This paper presents the development of a low-cost, Magnetic Resonance Imaging (MRI) compatible fibre-optic sensor for integration with catheters allowing the detection of contact forces between blood vessel walls and the catheter tip. Three plastic optical-fibres are aligned inside a plastic catheter in a circular pattern. A reflector is attached to a separate small part of the catheter tip, which is connected with a small deformable material to the aligned optical-fibres. In this manner a force at the catheter tip leads to a deformation of the elastic material and thus a modulation of the light yields, this is sent and received through the optical-fibres. An electronic circuit amplifies the retrieved light signal and the output voltage is used to classify the forces on the tip. The materials used are of the shelf and have a low magnetic susceptibility making this sensor fully MRI-compatible and inexpensive. Preliminary, experimental results demonstrated good force linearity in static loading and unloading conditions. The sensor was also tested in an artificial blood artery showing good dynamic response.