Embolic complications associated with radiofrequency catheter ablation. Atakr Investigator Group

Safety of same-day discharge without anticoagulation for left-sided radiofrequency catheter ablations in pediatrics

BACKGROUND

For left-sided radiofrequency catheter ablation (LCA) in pediatrics, significant practice variability exists regarding anticoagulation and discharge practices. Given the lack of data in pediatric patients, the risks and benefits of these practices are not well defined.

OBJECTIVE

The purpose of this study was to evaluate the safety of same-day discharge and use of aspirin (ASA) in pediatric patients following LCA.

METHODS

We performed a retrospective cohort study of pediatric patients who underwent LCA from 2010 to 2020 at our institution. Discharge timing and ASA usage were based on operator preference. The primary outcome was incidence of postablation anticoagulation complications reported within 1 month of the procedure.

RESULTS

Three hundred seventy-six patients underwent LCA and met inclusion criteria. Median [25th, 75th percentiles] age was 13.9 [10.5, 16.2] years; 18 (4.7%) had a history of structural heart disease. The most common substrates for ablation were Wolff-Parkinson-White syndrome (183 patients [48.7%]), concealed accessory pathway (159 patients [42.3%]), and ectopic atrial tachycardia (10 patients [2.7%]). Three hundred thirty-eight patients (89.9%) were discharged on the day of LCA. Seventy-six patients (20.2%) were prescribed ASA at discharge. Of those who underwent follow-up (273 patients [72.6%]), 7 (2.7%) reported an anticoagulation complication (5 with hematoma, 2 with headache). One of these patients was prescribed ASA; none required readmission. There was no correlation between anticoagulation complications and same-day discharge or with ASA usage.

CONCLUSION

Given the rare incidence of anticoagulation complications in pediatric patients undergoing LCAs, same-day discharge from the electrophysiology laboratory without anticoagulation should be considered.

Prevention of venous thromboembolism in right heart-sided electrophysiological procedures: results of an European Heart Rhythm Association survey

Limited data are available regarding venous thromboembolism (VTE), specifically deep vein thrombosis (DVT) and pulmonary embolism (PE), following right-sided ablations and electrophysiological (EP) studies. Compared to left-sided procedures, no guidelines on antithrombotic management strategies for the prevention of DVT and PE are available. The main purpose of the present European Heart Rhythm Association (EHRA) survey is to report the current management of right-sided EP procedures, focusing on anticoagulation and prevention of VTE. An online survey was conducted using the EHRA infrastructure. A total of 244 participants answered a 19-items questionnaire on the periprocedural management of EP studies and right-sided catheter ablations. The right femoral vein is the most common access for EP studies and right-sided procedures. An ultrasound-guided approach is employed by more than 2/3 of respondents. Intravenous heparin is not commonly given by the majority of participants. About 1/3 of participants (34%) routinely prescribe VTE prophylaxis during (mostly aspirin and low molecular weight heparin) and 1/4 of respondents (25%) commonly prescribe VTE prophylaxis after discharge (mostly aspirin). Of note, respectively 13% and 9% of participants observed at least one DVT and one PE related to right-sided ablation or EP study within the last year in their center. The present survey shows that only a minority of operators routinely gives intraprocedural intravenous heparin and prescribes VTE prophylaxis after right-sided EP procedures. Compared to left-sided procedures like atrial fibrillation (AF) ablation, there are no consistent systematic antithrombotic management strategies.

Antiplatelet and Anti-Coagulation Therapy for Left-Sided Catheter Ablations: What Is beyond Atrial Fibrillation?

Aim: International guidelines on the use of anti-thrombotic therapies in left-sided ablations other than atrial fibrillation (AF) are lacking. The data regarding antiplatelet or anticoagulation strategies after catheter ablation (CA) procedures mainly derive from AF, whereas for the other arrhythmic substrates, the anti-thrombotic approach remains unclear. This survey aims to explore the current practices regarding antithrombotic management before, during, and after left-sided endocardial ablation, not including atrial fibrillation (AF), in patients without other indications for anti-thrombotic therapy. Material and Methods: Electrophysiologists were asked to answer a questionnaire containing questions on antiplatelet (APT) and anticoagulation therapy for the following left-sided procedures: accessory pathway (AP), atrial (AT), and ventricular tachycardia (VT) with and without structural heart disease (SHD). Results: We obtained 41 answers from 41 centers in 15 countries. For AP, before ablation, only four respondents (9.7%) used antiplatelets and two (4.9%) used anticoagulants. At discharge, APT therapy was prescribed by 22 respondents (53.7%), and oral anticoagulant therapy (OAC) only by one (2.4%). In patients with atrial tachycardia (AT), before ablation, APT prophylaxis was prescribed by only four respondents (9.7%) and OAC by eleven (26.8%). At discharge, APT was recommended by 12 respondents (29.3%) and OAC by 24 (58.5%). For VT without SHD, before CA, only six respondents (14.6%) suggested APT and three (7.3%) suggested OAC prophylaxis. At discharge, APT was recommended by fifteen respondents (36.6%) and OAC by five (12.2%). Regarding VT in SHD, before the procedure, eight respondents (19.5%) prescribed APT and five (12.2%) prescribed OAC prophylaxis. At discharge, the administration of anti-thrombotic therapy depended on the LV ejection fraction for eleven respondents (26.8%), on the procedure time for ten (24.4%), and on the radiofrequency time for four (9.8%), with a cut-off value from 1 to 30 min. Conclusions: Our survey indicates that the management of anti-thrombotic therapy surrounding left-sided endocardial ablation of patients without other indications for anti-thrombotic therapy is highly variable. Further studies are necessary to evaluate the safest approach to these procedures.

Radiofrequency catheter ablation increases mean platelet volume

OBJECTIVE

Radiofrequency ablation (RFA) may increase the risk of thromboembolic events. The objective of this study was to evaluate the effect of RFA on mean platelet volume (MPV), an indicator of platelet activity.

METHODS

A total of 95 patients undergoing RFA were included in the study. MPV was measured before and one month after the procedure. The control group was formed by 83 individuals of the same sex and age as those in the study group.

RESULTS

Beta-blockers, non-dihydropyridine calcium channel blockers, and acetylsalicylic acid use was higher in the ablation group compared with the control group. Other baseline clinical characteristics and baseline hemoglobin, white blood cell count, platelet count, and MPV values were similar between the ablation and control groups. In the ablation group, baseline and post-procedural hemoglobin, white blood cell counts were similar. However, postprocedural MPV values were higher, and platelet counts were lower compared with the preprocedural values.

CONCLUSION

Our results indicate that MPV values are higher after RFA compared with baseline values.

Cryoballoon Ablation for the Treatment of Atrial Fibrillation: A Meta-analysis

BACKGROUND

Ablation therapy is the treatment of choice in antiarrhythmic drugrefractory atrial fibrillation (AF). It is performed by either cryoballoon ablation (CBA) or radiofrequency ablation. CBA is gaining popularity due to simplicity with similar efficacy and complication rate compared with RFA. In this meta-analysis, we compare the recurrence rate of AF and the complications from CBA versus RFA for the treatment of AF.

METHODS

We systematically searched PubMed for the articles that compared the outcome of interest. The primary outcome was to compare the recurrence rate of AF between CBA and RFA. We also included subgroup analysis with complications of pericardial effusion, phrenic nerve palsy and cerebral microemboli following ablation therapy.

RESULTS

A total of 24 studies with 3527 patients met our predefined inclusion criteria. Recurrence of AF after CBA or RFA was similar in both groups (RR: 0.84; 95% CI: 0.65, 1.07; I2=48%, Cochrane p=0.16). In subgroup analysis, heterogeneity was less in paroxysmal AF (I2=0%, Cochrane p=0.46) compared to mixed AF (I2=72%, Cochrane p=0.003). Procedure and fluoroscopy time was less by 26.37 and 5.94 minutes respectively in CBA compared to RFA. Complications, pericardial effusion, and silent cerebral microemboli, were not different between the two groups, however, phrenic nerve palsy was exclusively present only in CBA group.

CONCLUSION

This study confirms that the effectiveness of CBA is similar to RFA in the treatment of AF with the added advantages of shorter procedure and fluoroscopy times.

Analysis of Thrombotic Complications After Catheter Ablation

Introduction: Thromboembolic complications are described in about 1% of the patients undergoing radiofrequency catheter ablation (RFA). The aim of this study was to analyze thrombotic complications after RFA and to determine prothrombotic states in patients with thrombotic complications. Methods: We analyzed data from 400 patients (212 females) who underwent 453 RFA procedures for supraventricular tachycardias. Transthoracic echocardiography was performed one day before and after RFA in all patients. We evaluated the clinical and laboratory (in patients with thrombotic complications after RFA) risk factors of thromboembolism. Results: We observed thrombotic complication in 7 (1.75%) patients (6 females), thrice flail thrombus in the right atrium, flail thrombus in the inferior vena cava, femoral vein thrombosis with massive pulmonary embolism, femoral vein mural thrombus and upper extremity digital arteries embolization; four of them were asymptomatic. As a prothrombotic state we identified factor V Leiden mutation in one case and the use of oral contraceptives in two cases. Two other patients had a positive history of thromboembolic events. In a subgroup of females the use of oral contraceptives (p=0.13) or a positive history of thromboembolism (p=0.21) were not identified as important risk factors. Conclusion: Echocardiographic detection of asymptomatic thrombotic complications contributed to the higher percentage of these complications in our study. Although we can identify the risk factor (laboratory or clinical) in a majority of patients with a thromboembolic complication, occurrence of these complications is unpredictable.

Prevention of Coagulum Formation With Simultaneous Charge Delivery in Radiofrequency Ablation: A Canine Model

OBJECTIVES

This study reports on a novel method to prevent coagulum formation by continuously delivering a negative charge to the catheter tip to repel negatively charged fibrinogen molecules during RF ablation.

BACKGROUND

Radiofrequency (RF) ablation for cardiac arrhythmias is associated with a 70% incidence of coagulum formation on the catheter tip during ablation and a 10% incidence of thromboembolic events. Catheter tip thrombus can impede RF energy to the tissue, reducing efficacy and increasing procedure times.

METHODS

A novel circuit was built to deliver a negative, fixed-offset, direct current-based charge using a 9-V battery, placed in parallel with an RF delivery unit during RF ablation. In in vivo canine experiments, standard ablation catheters were advanced into atria and ventricles under fluoroscopic guidance. The presence of thrombus with and without RF delivery was identified with intracardiac echocardiography.

RESULTS

Scanning electron microscopy of the catheter tips showed clot coverage of the catheter tip to be 90% for noncharged catheters compared to 0% (p < 0.01) in negatively charged catheters. Volume of clot formed on the catheter tip decreased with increased amount of charge (140 ± 5.3 arbitrary units with no charge vs. 0 arbitrary units with a 100-μA current delivering negative charge, p < 0.01). Application of a negative charge did not affect the quality of the intracardiac electrogram or induce malignant ventricular arrhythmias.

CONCLUSIONS

Negative-charge delivery to ablation catheter tips and tissue during RF ablation is feasible and safe and can eliminate coagulum formation, potentially reducing thromboembolic complications.

Neurologic complications of catheter ablation/defibrillators/pacemakers

Approaches to the management of patients with cardiac arrhythmias have significantly evolved over the last decade, with advancement in catheter ablation and device implantation techniques. As the techniques and tools evolve, so does our understanding of the possible complications from these procedures. The focus of this chapter is discussion of the neurologic complications involved with catheter ablation, pacemaker and defibrillation implantation, with the focus on timely diagnosis, and management strategies.

Minimally invasive surgical therapies for atrial fibrillation

Atrial fibrillation is the most common sustained arrhythmia and is associated with significant risks of thromboembolism, stroke, congestive heart failure, and death. There have been major advances in the management of atrial fibrillation including pharmacologic therapies, antithrombotic therapies, and ablation techniques. Surgery for atrial fibrillation, including both concomitant and stand-alone interventions, is an effective therapy to restore sinus rhythm. Minimally invasive surgical ablation is an emerging field that aims for the superior results of the traditional Cox-Maze procedure through a less invasive operation with lower morbidity, quicker recovery, and improved patient satisfaction. These novel techniques utilize endoscopic or minithoracotomy approaches with various energy sources to achieve electrical isolation of the pulmonary veins in addition to other ablation lines. We review advancements in minimally invasive techniques for atrial fibrillation surgery, including management of the left atrial appendage.

Reproducibility of left atrial ablation with high-intensity focused ultrasound energy in a calf model

OBJECTIVE

Achieving transmural tissue ablation might be necessary for successful treatment of atrial fibrillation. The purpose of this study was to evaluate the reproducibility of transmural left atrial ablation using a high-intensity focused ultrasound energy system in a calf model.

METHODS

Nine heparinized bovines underwent a beating-heart left atrial ablation with a single application of the high-intensity focused ultrasound device. All animals were acutely killed, and the left atrium was fixed in formalin. Protocolized histological sections (5 μm) were obtained throughout each lesion and prepared with Masson trichrome and hematoxylin and eosin staining. Measurements were performed on a total of 359 slides from the 9 lesions. In addition, fresh left atrial tissues from 18 unused human donor hearts that did not meet the criteria for cardiac transplantation were measured at the site where the high-intensity focused ultrasound device is normally applied.

RESULTS

Calf left atrial thickness ranged between 2.5 and 20.1 mm, with a mean of 9.10 mm. High-intensity focused ultrasound ablation consistently produced a 100% transmural lesion in left atrial thickness up to 6 mm. In addition, a transmural lesion was observed in 91% of tissues that were up to 10 mm thick and in 85% that were up to 15 mm thick. Human left atrial thickness ranged between 1.2 to 6 mm, with a mean of 3.7 mm.

CONCLUSIONS

Calf left atrial thickness in this study was greater than human left atrial thickness. Human left atrial thickness is generally less than 6 mm, and in this range high-intensity focused ultrasound ablation achieved 100% transmurality. These histological results might correlate with a high success rate of atrial fibrillation ablation by using the high-intensity focused ultrasound system.

The 'single big cryoballoon' technique for acute pulmonary vein isolation in patients with paroxysmal atrial fibrillation: a prospective observational single centre study

Aims

Cryothermal energy (CTE) ablation via a balloon catheter (Arctic Front, Cryocath™) represents a novel technology for pulmonary vein isolation (PVI). However, balloon-based PVI approaches are associated with phrenic nerve palsy (PNP). We investigated whether ‘single big cryoballoon’-deployed CTE lesions can (i) achieve acute electrical PVI without left atrium (LA) imaging and (ii) avoid PNP in patients with paroxysmal atrial fibrillation (PAF).

Methods and results

After double transseptal punctures, one Lasso catheter and a big 28 mm cryoballoon catheter using a steerable sheath were inserted into the LA. PV angiography and ostial Lasso recordings from all PVs were obtained. Selective PV angiography was used to evaluate balloon to LA–PV junction contact. CTE ablation lasted 300 s, and the PN was paced during freezing at right-sided PVs. Twenty-seven patients (19 males, mean age: 56 ± 9 years, LA size: 42 ± 5 mm) with PAF (mean duration: 6.6 ± 5.7 years) were included. PVI was achieved in 97/99 PVs (98%). Median (Q₁; Q₃) procedural, balloon, and fluoroscopy times were 220 min (190; 245), 130 min (90; 170), and 50 min (42; 69), respectively. Three transient PNP occurred after distal PV ablations. No PV stenosis occurred. Total median (Q₁; Q₃) follow-up time was 271 days (147; 356), and 19 of 27 patients (70%) remained in sinus rhythm (3-month blanking period).

Conclusion

Using the single big cryoballoon technique, almost all PVs (98%) could be electrically isolated without LA imaging and may reduce the incidence of PNP as long as distal ablation inside the septal PVs is avoided.

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

BACKGROUND

An open-irrigated radiofrequency (RF) ablation catheter was developed to measure contact force (CF). Three optical fibers measure microdeformation of the catheter tip. The purpose of this study was to (1) validate the accuracy of CF sensor (CFS) (bench test); and (2) determine the relationship between CF and tissue temperatures, lesion size, steam pop, and thrombus during RF ablation using a canine thigh muscle preparation.

METHODS AND RESULTS

CFS measurements (total 1409) from 2 catheters in 3 angles (perpendicular, parallel, and 45 degrees ) were compared with a certified balance (range, 0 to 50 g). CFS measurements correlated highly (R(2) > or =0.988; mean error, < or =1.0 g). In 10 anesthetized dogs, a skin cradle over the thigh muscle was superfused with heparinized blood at 37 degrees C. A 7F catheter with 3.5-mm saline-irrigated electrode and CFS (Endosense) was held perpendicular to the muscle at CF of 2, 10, 20, 30, and 40 g. RF was delivered (n=100) for 60 seconds at 30 or 50 W (irrigation 17 or 30 mL/min). Tissue temperature (3 and 7 mm depths), lesion size, thrombus, and steam pop increased significantly with increasing CF at each RF power. Lesion size was greater with applications of lower power (30 W) and greater CF (30 to 40 g) than at high power (50 W) with lower CF (2 to 10 g).

CONCLUSIONS

This novel ablation catheter, which accurately measures CF, confirmed CF is a major determinant of RF lesion size. Steam pop and thrombus incidence also increases with CF. CFS in an open-irrigated ablation catheter that may optimize the selection of RF power and application time to maximize lesion formation and reduce the risk of steam pop and thrombus.

Real time assessment of RF cardiac tissue ablation with optical spectroscopy

An optical spectroscopy approach is demonstrated allowing for critical parameters during RF ablation of cardiac tissue to be evaluated in real time. The method is based on incorporating in a typical ablation catheter transmitting and receiving fibers that terminate at the tip of the catheter. By analyzing the spectral characteristics of the NIR diffusely reflected light, information is obtained on such parameters as, contact of catheter with the tissue, lesion formation, depth of penetration of the lesion, formation of char and coagulum during the ablation.

Influence of radiofrequency catheter ablation on platelet aggregation

The objective of this article was to find out how radiofrequency catheter ablation (RFA) influences platelet aggregation (PA), and the dependence on the total energy (TE) of RFA used and the cause of arrhythmia. We investigated 97 patients. PA was analyzed before, after, and in 24 hours after RFA. ADP- and epinephrine-induced PA significantly decreased after RFA by 5% and 8.9% (P < .001), respectively, and increased in 24 hours close to baseline. PA induced by ADP and collagen did not radically depend on the TE. Epinephrine-induced PA decreased after RFA by 0%, 8% (P < .05), and 16.9% (P < .01) in groups of patients where the TEs used were <4000 J, 4000 to 15,000 J, and >15,000 J, respectively. There were no significant differences in PA between groups based on the cause of arrhythmia. ADP- and epinephrine-induced PA significantly decreased after RFA and returned close to baseline in 24 hours. Epinephrine-induced PA was inversely associated with the TE used for RFA.

An overview of energy sources in clinical use for the ablation of atrial fibrillation

Recent years have seen many developments in the field of alternative energy sources for arrhythmia surgery. The impetus behind these advances is to replace the traditional, "cut-and-sew" Cox maze III procedure with lesion sets that are simpler, shorter, and safer but just as effective. There is demand for technology to make continuous, linear, transmural ablations reliably with a versatile energy source via an epicardial approach. This would make minimally invasive endoscopic surgical ablation of atrial fibrillation (AF) without cardiopulmonary bypass and with a closed chest feasible. These advances would shorten cardio-pulmonary bypass and improve outcomes in patients having surgical ablation and concomitant cardiac surgery. This review summarizes the technology behind alternative energy sources used to treat AF. Alternative energy sources include hypothermic sources (cryoablation) and hyperthermic sources (radiofrequency, microwave, laser, ultrasound). For each source, the biophysical background, mode of tissue injury, factors affecting lesion size, and advantages and complications are discussed.

Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop

Background— Electrode cooling by circulating fluid within the electrode (closed loop) or open irrigation facilitates radiofrequency (RF) ablation. This study compared lesion parameters between closed loop and open irrigation with the use of a canine model.

Methods and Results— In 8 anesthetized dogs, the skin over the thigh muscle was incised and raised, forming a cradle superfused with heparinized blood (activated clotting time >350 seconds) at 37°C. A 7F 4-mm closed loop electrode (irrigation 36 mL/min) and 7.5F 3.5-mm open irrigation electrode (irrigation 17 mL/min) were positioned perpendicular to the thigh muscle at 10 g contact weight. RF was applied (n=121) at 20 or 30 W for 60 seconds in low (0.1 m/s) or high (0.5 m/s) pulsatile blood flow. Temperatures were measured in the electrode, electrode-tissue interface, and within the tissue at 3- and 7-mm depths. After each RF, the cradle was emptied to examine the electrode and interface for thrombus. There was no difference between closed loop and open irrigation in impedance, lesion depth, or tissue temperature at 20 or 30 W. Interface temperature and electrode temperature were greater in the closed loop application. Thrombus occurred in 32 of 63 closed loop versus 0 of 58 open irrigation RF applications ( P <0.05) with interface temperature ≥80°C in all 32 (electrode temperature <40°C in 1, 40°C to 50°C in 26, and >50°C in 5). With closed loop, interface temperature and thrombus incidence were greater at 30 W and low blood flow. With open irrigation, interface temperature remained low (≤71°C) with no difference between 20 and 30 W or between low and high blood flow. Steam pop occurred at 20 W in 4 of 35 closed loop and 0 of 30 open irrigation and at 30 W in 15 of 28 closed loop and 4 of 28 open irrigation applications ( P <0.05).

Conclusions— Lower interface temperature, thrombus, and steam pop, especially in low blood flow, indicate greater interface cooling with open irrigation.

Intracardiac Ultrasound Detection of Thrombus on Transseptal Sheath: Incidence, Treatment, and Prevention

BACKGROUND

Transseptal (TS) catheterization is used for left atrial (LA) ablation procedures and a major risk is thromboembolism. The purpose of this study was to assess (1) the value of intracardiac ultrasound (ICUS) monitoring during LA ablation procedures, and (2) a new technique to reduce the risk of thrombus formation.

METHODS AND RESULTS

One hundred and eighty consecutive patients underwent TS catheterization under ICUS guidance with two sheaths for atrial fibrillation ablation and one for other LA procedures. Group I included the initial 90 patients in whom TS sheaths were flushed with a standard 2 U/cc concentration of heparin; group II consisted of the next 90 patients in whom sheaths were flushed with 1,000 U/cc concentration. All patients received bolus and infusion of heparin to maintain ACT between 250-300 seconds. ICUS was monitored throughout. In group I, echodense material at the tip of the sheath consistent with thrombus was observed on ICUS in 8 of 90 patients (9%) within 5-15 minutes of entering the LA. In group II, only 1 of 90 patient (1%) demonstrated thrombus (P < 0.001). There were no significant clinical differences in group I patients with and without thrombus. In all nine patients, the clot was removed with vigorous aspiration. No patients suffered a neurological event.

CONCLUSION

Thrombus formation on TS sheath, detected by ICUS, may be more common than expected despite adequate anticoagulation. Using a higher concentration of heparin for the TS system before deployment reduced the risk. The thrombus was retrieved with aspiration without the need to abort the procedure.

Embolic Events and Char Formation During Pulmonary Vein Isolation in Patients with Atrial Fibrillation: Impact of Different Anticoagulation Regimens and Importance of Intracardiac Echo Imaging

Thromboembolic events are important complications of pulmonary vein isolation (PVI) procedures, occurring in up to 2.8% of patients. In this study, we report the incidence of char formation and embolic events with different anticoagulation protocols prospectively changed to reduce such complication.

METHODS

A total of 785 patients (mean age: 54 years, 83.5% male) underwent catheter-based PVI for treatment of drug refractory, symptomatic atrial fibrillation (AF). PVI was performed utilizing different strategies including radiofrequency (RF) using temperature control energy delivery and RF using intracardiac echocardiography (ICE)-guided power titration. Patients were divided based on the anticoagulation protocol into three groups: in group 1 (194 patients), activation coagulation time (ACT) was maintained between 250 and 300 seconds; in group 2 (180 patients), ACT was maintained between 300 and 350 seconds plus the IV infusion of eptifibatide (135 microg/kg bolus + 0.5 microg/kg/min); and in group 3 (411 patients), ACT was maintained between 350 and 400 seconds.

RESULTS

Char formation was detected in 69 patients of group 1, 5 of group 2, and 8 of group 3. An embolic event was observed in 7 patients of group 1, 3 of group 2, and 2 of group 3 (P = 0.01; group 1 vs group 3). Higher degree of anticoagulation with heparin was associated with a reduced incidence of embolic events even after removing the patients undergoing ICE-guided ablation (P = 0.04).

CONCLUSION

More aggressive anticoagulation with heparin reduced periprocedural embolic events. The use of platelet inhibition does not have incremental beneficial effect. None of the anticoagulation protocol abolished char formation.

High‐Flow Perfusion of Sheaths for Prevention of Thromboembolic Complications During Complex Catheter Ablation in the Left Atrium

INTRODUCTION

Mechanisms for thromboembolic complications during complex ablation procedures in left atrium (LA) have not been defined. The aim of this study was to determine the effect of the perfusion rate of the transseptal sheath on the incidence of thromboembolic complications during catheter ablation for atrial fibrillation (AF) or LA macroreentrant tachycardia.

METHODS AND RESULTS

We analyzed clinical and procedural data from 86 consecutive patients (153 procedures) referred for catheter ablation of AF (74 patients) or LA macroreentrant tachycardia (12 patients). The transseptal sheath was continuously perfused at a low flow rate (3 mL/hour) for the first 32 patients and at a high flow rate (180 mL/hour) for the subsequent 54 patients. Ablation was mainly performed using map-guided isolation of pulmonary veins for AF and three-dimensional electroanatomic mapping for LA macroreentrant tachycardia. Five patients (6% of patients and 3.5% of procedures) developed a cerebral thromboembolic complication, all during procedures using low-flow perfusion. Sheath perfusion rate and total procedure duration were the two variables significantly associated with the occurrence of stroke (P = 0.013 and 0.001, respectively). After adjustment in a multivariable analysis, sheath perfusion rate remained the only risk factor for stroke. The risk was 17 times higher using low-flow than high-flow perfusion (odds ratio 17.26, 95% confidence interval 1.14-260.81, P = 0.04). No other clinical or procedural parameters had any significant effect.

CONCLUSION

Sheath perfusion rate is an important determinant of the risk factor for stroke during complex LA ablation procedures. Continuous high-flow perfusion appears to be effective in preventing this complication.

Physiological consequences of bipolar radiofrequency energy on the atria and pulmonary veins: a chronic animal study

BACKGROUND

Alternative energy sources have been proposed for the transvenous and surgical treatment of atrial fibrillation. This study examined the physiologic consequences of a novel energy source, bipolar radiofrequency energy, in a chronic animal model in order to determine its ability to produce transmural lesions on the beating heart.

METHODS

Five dogs underwent baseline pacing from the following target areas: right and left atrial appendage, superior and inferior vena cavae, and right and left pulmonary veins. A cuff of atrial myocardium, proximal to the target tissue was clamped and ablated between the arms of the bipolar radiofrequency energy device. Tissue conductance was used as a transmural indicator. After ablation, the pacing protocol was repeated. Baseline and postablation pulmonary vein flows were measured. Animals were survived for 30 days, and permanent electrical isolation was evaluated by pacing, epicardial mapping, and histology.

RESULTS

Mean ablation time was 5.0 +/- 1.8 seconds and mean peak tissue temperature was 46.7 degrees C +/- 2.8 degrees C. All lesions (30/30) acutely and permanently isolated atrial tissue. There was no change in pulmonary vein flow. Mapping studies with pacing of atrial tissue on both sides of the lesion confirmed isolation. Histology demonstrated that all lesions were linear, continuous, and transmural with no thrombus formation or stenosis.

CONCLUSIONS

Bipolar radiofrequency energy rapidly produced permanent transmural linear lesions on the beating heart. Measurement of tissue conductance reliably predicted transmural lesions. This new technology may enable the development of a less invasive, surgical approach to atrial fibrillation.

High incidence of thrombus formation without impedance rise during radiofrequency ablation using electrode temperature control

The authors hypothesized that during RF ablation, the electrode to tissue interface temperature may significantly exceed electrode temperature in the presence of cooling blood flow and produce thrombus. In 12 anesthetized dogs, the skin over the thigh muscle was incised and raised to form a cradle that was superfused with heparinized canine blood (ACT > 350 s) at 37 degrees C. A 7 Fr, 4-mm or 8-mm ablation electrode containing a thermocouple was held perpendicular to the thigh muscle at 10-g contact weight. Interface temperature was measured at opposite sides of the electrode using tiny optical probes. RF applications (n = 157) were delivered at an electrode temperature of 45 degrees C, 55 degrees C, 65 degrees C, and 75 degrees C for 60 seconds, with or without pulsatile blood flow (150 mL/min). Without blood flow, the interface temperature was similar to the electrode temperature. With blood flow, the interface temperature (side opposite blood flow) was up to 36 degrees C and 57 degrees C higher than the electrode temperature using the 4- and 8-mm electrodes, respectively. After each RF, the cradle was emptied and the electrode and interface were examined. Thrombus developed without impedance rise at an interface temperature as low as 73 degrees C without blood flow and 80 degrees C with blood flow (11/16 RFs at 65 degrees C electrode temperature using 4 mm and 13/13 RFs at an electrode temperature of 55 degrees C using an 8-mm electrode with blood flow). With blood flow, interface temperature markedly exceeded the electrode temperature and the difference was greater with an 8-mm electrode (due to greater electrode cooling). In the presence of blood flow, thrombus occurred without an impedance rise at an electrode temperature as low as 65 degrees C with a 4-mm electrode and 55 degrees C with an 8-mm electrode.

Lower incidence of thrombus formation with cryoenergy versus radiofrequency catheter ablation

BACKGROUND

Radiofrequency (RF) catheter ablation is limited by thromboembolic complications. The objective of this study was to compare the incidence and characteristics of thrombi complicating RF and cryoenergy ablation, a novel technology for the catheter-based treatment of arrhythmias.

METHODS AND RESULTS

Ablation lesions (n=197) were performed in 22 mongrel dogs at right atrial, right ventricular, and left ventricular sites preselected by a randomized factorial design devised to compare RF ablation with cryocatheter configurations of varying sizes (7F and 9F), cooling rates (-1 degrees C/s, -5 degrees C/s, and -20 degrees C/s) and target temperatures (-55 degrees C and -75 degrees C). Animals were pretreated with acetylsalicylic acid and received intraprocedural intravenous unfractionated heparin. Seven days after ablation, the incidence of thrombus formation was significantly higher with RF than with cryoablation (75.8% versus 30.1%, P=0.0005). In a multiple regression model, RF energy remained an independent predictor of thrombus formation compared with cryoenergy (OR, 5.6; 95% CI, 1.7, 18.1; P=0.0042). Thrombus volume was also significantly greater with RF than with cryoablation (median, 2.8 versus 0.0 mm3; P<0.0001). More voluminous thrombi were associated with larger RF lesions, but cryolesion dimensions were not predictive of thrombus size.

CONCLUSIONS

RF energy is significantly more thrombogenic than cryoenergy, with a higher incidence of thrombus formation and larger thrombus volumes. The extent of hyperthermic tissue injury is positively correlated with thrombus bulk, whereas cryoenergy lesion size does not predict thrombus volume, most likely reflecting intact tissue ultrastructure with endothelial cell preservation.

New cryotechnology for electrical isolation of the pulmonary veins

INTRODUCTION

Creation of radiofrequency lesions to isolate the pulmonary veins (PV) and ablate atrial fibrillation (AF) has been complicated by stenosis of the PVs. We tested a cryoballoon technology that can create electrical isolation of the PVs, with the hypothesis that cryoenergy will not result in PV stenosis.

METHODS AND RESULTS

Lesions were created in 9 dogs (weight 31-37 kg). Cryoenergy was applied to the PV-left atrial (LA) interface. Data collected before and after ablation included PV orifice size, arrhythmia inducibility, electrogram activity, and pacing threshold in the PVs. Tissue examination was performed immediately after ablation in 3 dogs and after 3 months (4.8 +/- 1.0) in 6 dogs. After ablation there was no localized P wave activity in the ablation zone and no LA-PV conduction. Before ablation, the pacing threshold was 1.9 +/- 1.1 mA in each PV. After ablation, the pacing threshold increased significantly to 7.2 +/- 1.8 mA, or capture was not possible. Burst pacing did not induce any sustained arrhythmias. Most dogs had hemoptysis during the first 24 to 48 hours. Acute tissue examination revealed hemorrhagic injury of the atrial-PV junction that extended into the lung parenchyma. After recovery, the lesions were circumferential and soft with no PV stenosis. Histologic examination revealed fibrous tissue with no PV-LA interface thickening.

CONCLUSION

This new cryoballoon technology effectively isolates the PVs from LA tissue. No PV stenosis was noted. Acute tissue hemorrhage and hemoptysis are short-term complications of this procedure. After 3 months of recovery, cryoablated tissue exhibits no collagen or cartilage formation.

Delayed thrombogenesis following radiofrequency catheter ablation

The cause and duration of the thrombogenesis provoked by radiofrequency catheter ablation (RF-CA) was investigated by measuring the thrombin-antithrombin III complex (TAT) in 43 patients who underwent RF-CA and in 20 control subjects who underwent an electrophysiologic study. Blood samples were collected at 7 different times: before introducing the sheaths, during the ablation procedure and at 30 min, 6 and 24h, and 3 and 6 days after the procedure. Hepatocyte growth factor (HGF) was simultaneously measured in the ablation group. Plasma TAT concentration exhibited a double peaked pattern in the ablation group: the first peak occurred during the ablation procedure (42.8+/-15.5 ng/ml), and the second peak 3 days later. Plasma TAT at 3 days after the procedure was significantly higher than that of the control group (21.3+/-19.0 vs 2.5+/-1.4, p=0.0003). The first peak significantly correlated with the procedure time prior to the administration of heparin (r=0.669), but the second peak did not (r=0.132). A subgroup with a serum HGF >0.40 ng/ml at 6 h after the procedure exhibited a significantly high second peak. The thrombogenesis caused by RF-CA has 2 phases; in the acute phase, there is hemostasis during placement of the catheters, and in the delayed phase thrombogenesis is the result of endothelial damage from the RF current.

Radiofrequency catheter ablation of left-sided accessory pathways in pediatric patients

In many cases, radiofrequency catheter ablation has replaced the long-term use of antiarrhythmic medication for symptomatic tachycardia, and has all but eliminated arrhythmia surgery. The most common substrate for radiofrequency catheter ablation in pediatric patients is atrioventricular (AV) reentry tachycardia due to a concealed or manifest accessory pathway. Accessory pathways are distributed unevenly along the right and left atrioventricular valve annuli, and left-sided accessory pathways are most common. Although some centers advocate an abbreviated diagnostic and mapping approach to both concealed and manifest left-sided accessory pathways, most still use a complete electrophysiological evaluation and complex catheter manipulation for mapping, followed by the application of radiofrequency energy. Left-sided accessory pathways may be approached from the transatrial approach, the retrograde aortic approach, or less commonly from within the coronary sinus. Each approach has proven to be associated with success, but also with a distinct set of risks. Possibly because left-sided accessory pathways are most common, catheter ablation of this substrate has proven highly successful and has the lowest risk of recurrence. However, recent data also suggest that this substrate is associated with greater risk of complications than of right-sided accessory pathways or pathways located in the posteroseptal region. The following report reviews some of the recently described diagnostic and mapping techniques, success rates, risks and follow-up data in pediatric patients undergoing radiofrequency catheter ablation of left-sided accessory pathways.

Complications associated with radiofrequency catheter ablation of cardiac arrhythmias

Catheter ablation using radiofrequency energy has evolved as a safe and effective means for the treatment of various supraventricular and ventricular arrhythmias. Despite the overall efficacy of radiofrequency catheter ablation, cardiovascular complications can occur in a small number of patients. The purpose of this article is to review the current understanding of the risks and complications that can occur during catheter ablation procedures.

The effect of ablation sequence and duration on lesion shape using rapidly pulsed radiofrequency energy through multiple electrodes

Sequences of energy application to multiple electrodes and a study of ablation duration with distal tip and multi-electrode ablations were explored with a radiofrequency controller that distributes energy from a generator to up to 4 electrodes with various duty cycles. In vitro ablations were performed on bovine left ventricle in circulating blood and lesions in goats were performed to verify the in vitro results. All of the ablation sequences with simultaneous electrode activation of contiguous electrodes resulted in deeper lesions than those created in sequence. There was also no scalloping of the lesion if contiguous electrodes were activated simultaneously. During all distal tip ablations, lesion volume and depth was greater after 3 minutes of energy delivery than after 1 minute, but did not increase from 3 minutes to 5 minutes. There was a significant increase in multi-electrode ablation lesion depth with each additional minute in the ablation cycle. The in vivo ablations verified these results at 120 and 300 second ablations. Pulsed energy distal tip ablations resulted in deeper lesions than continuous only if power amplitudes over 50 W were employed. In conclusion, contiguous electrodes in simultaneous use create lesions that resemble one large lesion rather than two lesions positioned next to each other. Multi-electrode ablation lesions continue to grow at ablation durations of up to 5 minutes compared to distal tip lesions which reach steady-state between 1 and 3 minutes. Pulsed energy delivery to distal tips may result in deeper lesions than conventional if high powers are employed.

Thrombus formation at the site of radiofrequency catheter ablation

A 55-year-old woman with a history of resected atrial myxoma with residual patched atrial septal defect (ASD) underwent a successful radiofrequency (RF) ablation of reentry atrial tachycardia. She presented with progressive dyspnea 5 days later. Transesophageal echocardiography revealed a 1-cm right atrial mass attached to the intraatrial septum at the ablation site. Repeat study after anticoagulation for 5 weeks showed complete resolution of the thrombus. Thrombus formation at the site of RF ablation is a potential complication that may require aggressive anticoagulation. Patients with patched ASD might be at higher risk.

Electrophysiologic procedures and activation of the hemostatic system

BACKGROUND

Thromboembolism occurs in 0.4% to 2% of the subjects undergoing radiofrequency ablation (RFA), but its mechanisms remain unclear. Our aim was to evaluate several parameters of the hemostatic system in relation to the electrophysiologic procedure.

METHODS

Thirty consecutive patients were enrolled in the study. Fifteen underwent electrophysiologic study and 15 underwent radiofrequency ablation. Before the ablation procedure, all subjects were given an intravenous heparin bolus (2500 IU). Blood samples were drawn immediately before, at the end of, and 24 hours after the procedures. Spontaneous platelet aggregation in whole blood and in platelet-rich plasma, markers of clotting activation (prothrombin fragment 1+2 and the thrombin-antithrombin complex) and the fibrinolytic system (plasminogen activator inhibitor and D-dimer) levels were evaluated.

RESULTS

At the end of the procedure, spontaneous platelet aggregation in whole blood, prothrombin fragment 1+2, thrombin-antithrombin complex, and D-dimer levels increased significantly in all patients. The hemostatic changes were more marked after RFA than after electrophysiology. Spontaneous aggregation in whole blood, prothrombin fragment 1+2, and thrombin-antithrombin complex levels at 24 hours after the procedure were similar to those observed before the procedure in both groups; D -dimer levels were still elevated with respect to preprocedure levels, with a trend toward higher levels in patients undergoing RFA rather than electrophysiology. A significantly more marked activation of coagulation (prothrombin fragment 1+2, P <.005) was found in patients in whom the mean duration of energy application was higher than 23.5 seconds.

CONCLUSIONS

Our data suggest that antithrombotic prevention with a prolonged administration of heparin and/or the association of antiplatelet agents should be considered in patients undergoing RFA.

The activation of platelet function, coagulation, and fibrinolysis during radiofrequency catheter ablation in heparinized patients

INTRODUCTION

Catheter ablation may be complicated by clinical thromboembolism in about 1% of patients.

METHODS AND RESULTS

We studied the activation of coagulation (prothrombin fragment 1+2 [PF1+2]), platelets (beta-thromboglobulin [beta-TG])) and fibrinolysis (plasmin-antiplasmin complexes [PAP] and D-dimer) during radiofrequency (RF) ablation in 13 patients. They received heparin 100 U/kg intravenously after the initial electrophysiologic study, prior to the delivery of RF current; thereafter 1,000 U/hour throughout the procedure. PF1+2 increased fourfold (P < 0.001) during the diagnostic study, but gradually declined to upper reference value during heparin administration. There was a strong correlation between procedure duration prior to heparin bolus (range 39 to 173 min); and (a) the maximal rise of PF1+2 (r = 0.83, P < 0.001) and (b) the increase of PF1+2 from baseline to end of the procedure (r = 0.74, P = 0.004). There was no correlation between postheparin changes of PF1+2 and (a) postheparin procedure duration (range 40 to 317 min), (b) number of RF pulses (range 1 to 16), or (c) RF current duration (range 46 to 687 sec). Plasma beta-TG concentration showed similar trends. Fibrinolytic activity increased moderately from baseline until heparin administration; then remained around the upper reference values. PAP at the end of procedure and D-dimer at the time of heparin administration both correlated with preheparin procedure duration (r = 0.70, P = 0.007 and r = 0.69, P = 0.01, respectively). All parameters were normal the next morning.

CONCLUSION

Procedure duration prior to heparin administration, and not the delivery of RF current per se, determines activation of hemostasis and fibrinolysis during RF ablation.

Thromboembolic complications of cardiac radiofrequency catheter ablation: a review of the reported incidence, pathogenesis and current research directions

INTRODUCTION

Radiofrequency catheter ablation (RFCA) has become established as an effective therapy for the treatment of many cardiac tachyarrhythmias. The principle limitation of conventional RFCA continues to be the risk of thromboembolism. This risk is of particular concern for the ongoing development of the catheter maze procedure for the treatment of atrial fibrillation, which currently involves the creation of extensive linear lesions in the left atrium.

METHODS AND RESULTS

A Medline search of the literature over the last ten years was performed. Focused review of the reported thromboembolic complications of RFCA indicates an overall incidence of 0.6%. However, the risk is increased when ablation is performed in the left heart (1.8% to 2%) and for ventricular tachycardia (2.8%). It is of concern that intravenous heparin and the use of temperature feedback to control radiofrequency current do not eliminate the risk of thromboembolic events.

CONCLUSION

The thromboembolic complications of RFCA are not eliminated by the treatment of intravenous herapin and mode of temperature control during ablation. Potential approaches to further reduce the risk of thromboembolism include the adjunctive administration of specific inhibitors of platelet activation and aggregation, intraprocedural intracardiac echocardiography, irrigated radiofrequency ablation, and cryoablation catheter systems.

Does radiofrequency ablation induce a prethrombotic state? Analysis of coagulation system activation and comparison to electrophysiologic study

INTRODUCTION

Although thromboembolism is an uncommon complication of radiofrequency (RF) ablation, some preliminary reports have suggested that RF ablation results in activation of the coagulation system, possibly increasing this risk. We hypothesized that the insertion of intravenous catheters and their prolonged intravenous placement rather than RF ablation activates the coagulation cascade.

METHODS AND RESULTS

Thirty-seven patients, group 1 (n = 21) during RF ablation, and group 2 (n = 16) during routine electrophysiologic studies (EPS), were studied prospectively. Blood was drawn for coagulation and fibrinolytic studies following insertion of venous sheaths (T0), following catheter placement (T1), and 1 hour after completion of RF ablation or EPS (T2). Conversion of prothrombin to thrombin was measured using thrombin-antithrombin complex (TAT) and prothrombin activation peptide (F1+2), and fibrinolytic activity was assessed using D-dimer concentration. Levels of D-dimer increased in group 1 from 823.52+/-323.52 ng/mL at T0 to 1,314.28+/-297.63 ng/mL at T2 (P = 0.005), and in group 2 from 658.15+/-161.70 ng/mL at T0 to 1625+/-641.45 ng/mL at T2 (P = 0.064). TAT levels increased from to 27.74+/-5.6 microg/L at T0 to 52.99+/-5.93 microg/L at T2 in group 1 (P = 0.09), and from 19.79+/-5.14 microg/L at T0 to 73.5+/-24.15 microg/L at T2 in group 2 (P = 0.05). F1+2 concentration increased from 1.52+/-0.30 nmol/L at T0 to 3.06+/-0.41 nmol/L at T2 in group 1 (P = 0.004), and from 1.32+/-0.30 nmol/L at T0 to 3.11+/-0.46 nmol/L at T2 in group 2 (P = 0.087). There was no significant difference in the concentration of the three coagulation variables between group 1 and group 2 at any given time point. No correlation was demonstrable between concentration of D-dimers, TAT, or F1+2 and variables of RF delivery such as cumulative energy, number of RF energy applications, or number of impedance rises. However, a significant positive correlation (r = 0.65, P<0.01) was noted between the duration of the RF ablation procedure and the concentration of D-dimers.

CONCLUSION

We conclude that activation of the coagulation cascade in RF ablation procedures is not related to the delivery of RF energy, but is related to the placement of intravascular catheters and to the duration of the ablation procedure.

Nonuniform heating during radiofrequency catheter ablation with long electrodes: monitoring the edge effect

BACKGROUND

Long, narrow electrodes are being considered for radiofrequency ablation of atrial fibrillation; however, preliminary work revealed coagulum formation on the electrodes and lack of lesion continuity. This may be due to the "edge effect," which concentrates radiated energy at sharp geometric gradients. It is proposed that temperature sensors at electrode edges are preferable to a single centered sensor for temperature feedback and monitoring of long electrode geometries.

METHODS AND RESULTS

A finite element model was used to predict the heating properties of new long electrode geometries. Sixteen dogs with atrial fibrillation underwent left and right atrial ablation using catheters with multiple 12.5-mm coil electrodes. Electrodes with a single thermistor were compared with electrodes with dual thermocouples placed at opposite ends and on opposing sides of the electrode. Power, temperature, and impedance were recorded for all lesions, and coagulum adhesion and magnitude were noted in a subset of lesions. Finite element analysis shows uneven heating, with the main heating concentrated at the electrode edges and a propensity toward temperatures >100 degrees C with single-thermistor feedback control. Ablations with dual thermocouple electrodes achieved higher measured temperatures at lower power levels than those that used single-thermistor electrodes. Impedance rises and coagulum adherence occurred less frequently with dual thermocouple electrodes than with single, centered thermistor electrodes (176 of 395 versus 9 of 425 lesions; P<.0001; 46 of 98 versus 7 of 150 lesions; P<.0001, respectively).

CONCLUSIONS

Maximum heating from radiofrequency energy occurs at the electrode edges, particularly with long electrodes. The safety of temperature-feedback atrial ablation with these electrodes is significantly improved by monitoring temperatures at the edges.

Five-year experience with radiofrequency catheter ablation: implications for management of arrhythmias in pediatric and young adult patients

OBJECTIVE

A review of the results of the first 5 years of radiofrequency catheter ablation procedures performed at Children's Hospital, Boston, a large tertiary referral center for patients with congenital heart disease and arrhythmias common to the infant, child, and young adult.

STUDY DESIGN

A retrospective review of 410 consecutive procedures in 346 patients who underwent at least one application of radiofrequency energy for the treatment of recurrent supraventricular or ventricular tachycardia.

RESULTS

The overall final success rate for all diagnoses was 90%, with a higher success rate in patients with an accessory pathway (96%). During the 5-year study period, the success rate improved while the rates of failures and late recurrences declined. The incidence of serious complications was 1.2% (1 late death, 1 ventricular dysfunction, 1 complete heart block, 1 cardiac perforation, and 1 cerebrovascular accident).

CONCLUSIONS

This report of a large series of radiofrequency catheter ablation procedures performed at an institution committed to treating congenital heart disease and pediatric arrhythmias confirms the safety and efficacy of this procedure. The pediatric cardiologist/electrophysiologist treating such patients must be aware of specific technical, anatomic, and electrophysiologic variations in the pediatric patient that are critical to the success of this therapy.