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Nakagawa 2013 - Circ EP - Electrogram amplitude and impedance are poor predictors of CF_OL.unlocked

Atsushi Ikeda, Pasquale Santangeli, Luigi Di Biase and Warren M. Jackman Hiroshi Nakagawa, Josef Kautzner, Andrea Natale, Petr Peichl, Robert Cihak, Dan Wichterle,

Contact Force for Ablation of Atrial Fibrillation

Patients: Electrogram Amplitude and Impedance Are Poor Predictors of Electrode-Tissue

Locations of High Contact Force During Left Atrial Mapping in Atrial Fibrillation Print ISSN: 1941-3149. Online ISSN: 1941-3084

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Circulation: Arrhythmia and Electrophysiology doi: 10.1161/CIRCEP.113.978320

2013;6:746-753; originally published online July 19, 2013;

Circ Arrhythm Electrophysiol.

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uring radiofrequency catheter ablation, low electrode-tissue contact force (CF) is associated with ineffective lesion formation, whereas excessively high CF may result in an increased risk of steam pop and cardiac perforation.1–7 Because ablation systems have not had the ability to measure CF directly, other measures have been used as surrogates for CF, including the pattern of motion of the catheter tip under fluoroscopy, the amplitude of the unipolar and bipolar poten-tials, and impedance.3,6,7 The accuracy of these surrogate mea-sures has not been effectively validated.

Clinical Perspective on p 753

Two designs of ablation catheters using different technolo-gies have recently been developed to measure real-time cath-eter-tissue CF during catheter mapping and radiofrequency

ablation. One type of catheter uses 3 optical fibers to mea-sure microdeformation of a deformable body in the catheter tip (TactiCath; Endosense SA).8–12 The other type of catheter uses a small spring connecting the ablation tip electrode to the catheter shaft with a magnetic transmitter and sensors to measure microdeflection of the spring (THERMOCOOL SMARTTOUCH; Biosense Webster, Inc).13–16 Both systems have CF resolution <1 g in bench testing.8,13–16

The purpose of this study was to test, in patients undergo-ing catheter ablation of paroxysmal atrial fibrillation (AF), the ability of the spring magnetic CF sensing catheter to: (1) identify the range and pattern of CF during mapping of the left atrium (LA) and pulmonary veins (PV); (2) determine the accuracy of electrogram amplitude and impedance in predicting CF; and (3) explore the feasibility of controlling

? 2013 American Heart Association, Inc.Circ Arrhythm Electrophysiol is available at https://www.wendangku.net/doc/0810910356.html,

DOI: 10.1161/CIRCEP.113.978320

Original Article

Background —During radiofrequency ablation, high electrode-tissue contact force (CF) is associated with increased risk of steam pop and perforation. The purpose of this study, in patients undergoing ablation of paroxysmal atrial fibrillation, was to: (1) identify factors producing high CF during left atrial (LA) and pulmonary vein mapping; (2) determine the ability of atrial potential amplitude and impedance to predict CF; and (3) explore the feasibility of controlling radiofrequency power based on CF.

Methods and Res ults —A high-density map of LA/pulmonary veins (median 328 sites) was obtained in 18 patients undergoing atrial fibrillation ablation using a 7.5-Fr irrigated mapping/ablation catheter to measure CF. Average CF was displayed on the 3D map. For 5682 mapped sites, CF ranged 1–144 g (median 8.2 g). High CF (≥35 g) was observed at only 118/5682 (2%) sites, clustering in 6 LA regions. The most common high CF site (48/113 sites in 17/18 patients) was located at the anterior/rightward LA roof, directly beneath the ascending aorta (confirmed by merging the CT image and map). Poor relationship between CF and either unipolar amplitude, bipolar amplitude, or impedance was observed. During ablation, radiofrequency power was modulated based on CF. All pulmonary veins were isolated without steam pop, impedance rise, or pericardial effusion.

Conclusions —High CF often occurs at anterior/rightward roof, where the ascending aorta provides resistance to the LA. Atrial potential amplitude and impedance are poor predictors of CF. Controlling radiofrequency power based on CF seems to prevent steam pop and impedance rise without loss of lesion effectiveness. (Circ Arrhythm Electrophysiol . 2013;6:746-753.)

Key Words: atrial fibrillation ? catheter ablation ? electrophysiology mapping ? radiofrequency

Received October 18, 2012; accepted June 11, 2013.

From the Heart Rhythm Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK (H.N., A.I., W.M.J.); Department of Cardiology, IKEM, Prague, Czech Republic (J.K., P.P., R.C., D.W.); and Department of Cardiology, Texas Arrhythmia Institute at St David’s Medical Center, Austin, TX (A.N., P.S., L.D.B.).

Correspondence to Hiroshi Nakagawa, MD, PhD, Heart Rhythm Institute, University of Oklahoma Health Sciences Center, 1200 Everett Drive (TUH-6E-103), Oklahoma City, OK 73104. E-mail: hiroshi-nakagawa@https://www.wendangku.net/doc/0810910356.html, Locations of High Contact Force During Left Atrial Mapping in Atrial Fibrillation Patients

Electrogram Amplitude and Impedance Are Poor Predictors of Electrode-Tissue Contact Force for Ablation of Atrial Fibrillation

Hiroshi Nakagawa, MD, PhD; Josef Kautzner, MD, PhD; Andrea Natale, MD; Petr Peichl, MD, PhD; Robert Cihak, MD, PhD; Dan Wichterle, MD, PhD; Atsushi Ikeda, MD, PhD; Pasquale Santangeli, MD; Luigi Di Biase, MD, PhD;

Warren M. Jackman, MD

INTERNAL USE ONLY – NOT FOR DISTRIBUTION OUTSIDE OF BIOSENSE WEBSTER

THE FOLLOWING ARTICLE CONTAINS INFORMATION THAT IS OFF ‐LABEL IN THE UNITED STATES. THIS ARTICLE IS

FOR YOUR INFORMATION ONLY AND MAY NOT BE DISCUSSED WITH U.S. CUSTOMERS.

Nakagawa et al Contact Force During AF Mapping/Ablation 747

radiofrequency power based on CF (ie, lower power with high CF and higher power with low CF) and hence prevent-ing steam pop and impedance rise while producing effective ablation lesions.

Methods

Eighteen (14 male and 4 female, aged 26–71 years, median age 56 years) patients with symptomatic, drug refractory paroxysmal AF were enrolled in this study. All patients provided written informed consent for the study, which was approved by the Institute for Clinical and Experimental Medicine (IKEM) institutional clinical research and ethics committee. A cardiac computed tomographic angiogram was obtained before the procedure to delineate LA and PV anatomy.

CF Sensing Catheter

The 7.5-Fr THERMOCOOL SMARTTOUCH CF sensing catheter has a 3.5-mm tip electrode with 6 small holes (0.4 mm diameter) around the circumference for saline irrigation. A tiny spring is located just proximal to the ablation tip electrode. A magnetic signal emitter is attached to the tip electrode (distal to the spring) and 3 magnetic sensors are located proximal to the spring to measure microdeflec-tion of the spring. The microdeflection is computed to the magnitude and angle of CF every 25.6 ms (Figure 1). CF is displayed both con-tinuously and as the average value (over 1 second) on an electroana-tomical mapping system (CARTO XP; Biosense Webster, Inc). For each mapping point, the system stored the CF for the preceding 10 seconds, the average CF for the preceding 1 second, and the force angle (Figure 2). This catheter also has a magnetic location sensor for conventional electroanatomical mapping.

Electrophysiological Study

The electrophysiological study was performed under intravenous

s edation with midazolam and fentanyl. A multielectrode catheter was inserted transvenously and positioned in the coronary sinus. After in-travenous administration of heparin (maintaining activated clotting

time >300 seconds), double transeptal puncture was performed un-der intracardiac ultrasound guidance (AcuNav, Acuson, Inc), placing 2 8.5-Fr sheaths (SL1; St Jude Medical, Inc) into the LA. A circu-lar electrode catheter for recording PV potentials (Lasso; Biosense Webster, Inc) was inserted into the LA through one of the transeptal sheaths. The quadripolar CF sensing mapping/ablation catheter was inserted through the second transeptal sheath. Under fluoroscopic guidance, the CF catheter was positioned centrally in the LA chamber without endocardial contact, confirmed by intracardiac echocardiog-raphy, to calibrate the CF sensor to 0 g (baseline noncontact value).

Electroanatomical Mapping of LA and PVs

An electroanatomical map of the LA and each PV was created during sinus rhythm (10 patients) or AF (8 patients) using the CF catheter guided by fluoroscopy and intracardiac echocardiography. Mapping was performed by 3 operators in different patients (#1, 12 patients; #2, 4 patients; and #3, 2 patients, respectively). During mapping, the transeptal sheath was positioned at the septum or in the right atrium for operator #1 and was located in the LA for opera-tors #2 and #3. The physician maneuvering the catheter was blinded to the CF measurements, to identify the range of CF that occurs during routine mapping.

The electroanatomical maps were displayed in 5 separate formats: (1) map of activation time (sinus rhythm maps); (2) CF map, showing the average CF over 1 second (Figure 2); (3) unipolar voltage map, displaying the peak-to-peak amplitude of the unipolar electrogram filtered at 1 to 400 Hz; (4) bipolar voltage map, displaying the peak-to-peak amplitude of the bipolar electrogram filtered at 30 to 400 Hz; and (5) impedance map, measuring the impedance between the abla-tion tip electrode and the skin patch.

PV Antrum Isolation

PV antrum isolation was performed in all 18 patients using the irrigat-ed CF catheter. The catheter operator was not blinded to CF during ab-lation. During radiofrequency applications, the saline irrigation flow rate was increased from 2 mL/min to 30 mL/min. Radiofrequency power was adjusted based on CF: (1) power 35 to 45 watts at CF <10 g; (2) 25 to 34 watts at CF 11 to 30 g; (3) 15 to 24 watts at CF 31 to 50 g; and (4) 5 to 14 watts at CF >51g. The radiofrequency applica-tion time at each site was variable based on electrogram attenuation, but the usual duration was 20 to 30 seconds. PV antrum isolation was verified (absence of any PV potential and absence of any LA potential in the antral ablation area) using the circular catheter and/or the abla-tion catheter electrograms.

Throughout the procedure, intracardiac echocardiography was used to monitor the mapping catheter tip position and its visual contact with the tissue (whenever possible). At the end of the procedure, intracar-diac echocardiography was used to exclude the presence of PV steno-sis, intracardiac thrombus, and pericardial effusion in all 18 patients. A transthoracic echocardiogram was performed on the day following the procedure to rule out pericardial effusion and other complications.

Follow-Up of Patients

The purpose of follow-up was to identify any procedure-related com-plications. All patients were seen in the IKEM arrhythmia clinic at 1, 3, and 6 months after ablation. A 24-hour Holter recording was ob-tained at the 6-month follow-up in all 18 patients. A repeat computed tomographic angiogram was obtained 3 months after ablation in all 18 patients, to identify the presence or absence of PV stenosis.

Statistical Analysis

The data were analyzed independent of Biosense Webster, Inc. The values are expressed as range and median or mean±SD. Due to the difference in the number of values measured between patients, a log transformation was performed on the variables of interest (ie, uni-polar amplitude, bipolar amplitude, impedance, and average CF) to ensure the variables were normally distributed. A generalized esti-

mating equation was applied on the log-transformed data to assess the

Figure 1. Saline-irrigated contact force (CF) sensing catheter. A small spring coil connects the tip electrode to the catheter shaft. A magnetic signal emitter is located distal to the spring. Three magnetic location sensors, positioned just proximal to the spring, measure the microdeflection of the spring to compute the force (magnitude and angle) on the tip electrode.

748 Circ Arrhythm Electrophy s iol August 2013

significance of the relationships between the CF and unipolar voltage, bipolar voltage, and impedance. The difference of average CF during LA/PV mapping among the 3 operators was assessed using Friedman test. For additional exploration of the differences in the average CF between individual operators, post hoc analysis was performed using Kruskal–Wallis test. During ablation, the equality of the proportions (percentages) of CF across the different categories among 3 opera-tors was assessed using Cochran–Mantel–Haenszel test. A P value of <0.05 was considered to be statistically significant.

Results

CF Mapping

The number of LA and PV mapping sites for each patient ranged from 142 to 544 (median 328). For the 18 patients, a total of 5682 mapping sites were acquired for analysis (3213 sites during sinus rhythm and 2469 sites during AF). The aver-age and maximum CF for 1-second period at each of the 5682 sites ranged 1 to 144 g (median 8.2 g; Figure 3) and 2 to 170 g (median 12 g), respectively. There was only a small difference in average CF for the 3 operators (median 8.3 g, 7.3 g, and 9.3 g; Figure 3).

High average CF (≥35 g) was observed at only 118 of the 5682 (2%) sites, and at only 1 to 15 (median 5) sites per patient. The sites of high average CF were clustered in 6 regions (Figure 4). The most common site of high CF was located at the rightward superior aspect of the anterior LA wall, accounting for 48 of the 118 (41%) high CF sites and occurring at that location in 17 of the 18 (94%) patients. The high CF occurred transiently during

the inspiratory phase of respiration when the roof of the LA is pressed against the catheter tip (Figure 5). Integrating the CF map with the preablation computed tomographic angiogram showed the highest CF site was located directly beneath the ascending aorta, which provides external support to the atrial wall in this region (Figure 6). Intracardiac echocardiography confirmed the catheter tip was pressed against the aortic wall with increased compression during inspiration. Importantly, a high CF at this site was observed even during pullback of the catheter from the left PVs to this region with the tip of the sheath in the right atrium.

The other sites of high CF were the antrum posterior to the right superior PV (23/118 sites [19%], present in 9/18 patients [50%]), inferior posterior LA wall (23/118 sites [19%], pres-ent in 7/18 patients [39%]), antrum posterior to the left supe-rior PV (11/118 sites [9%], present in 6/18 patients [33%]), LA roof (11/118 sites [9%], present in 4/18 patients [22%]), and the anterior region of the proximal right PVs (3/118 sites [3%], present in 1/18 patients [6%]; Figure 4).

Relationship Between CF and Electrogram Amplitude, Impedance

Unipolar voltage, bipolar voltage, and impedance correlated poorly with average CF at the 2202 LA mapping sites during sinus rhythm in 10 patients and at the 1755 LA sites during AF in 8 patients (Figures 7 and 8). PV mapping sites were excluded from the correlation between electrogram amplitude,

Figure 2. A , Contact force (CF) map of left atrium and pulmonary veins during sinus rhythm, shown in the anterior-posterior (AP) projec-tion. The average CF (over 1 second) ranged 2 to 70 g. Low average CF (≤10 g) is displayed in red. High average CF (≥35 g) is displayed in purple. The CF at site #1 (base of the left atrial [LA] appendage) was low at 5 g. The CF at site #2 (anterior/rightward LA roof, beneath the ascending aorta) was high at 45 g. B , Ten-second continuous tracing of CF with the last 1 second recorded at site #1 (top ; average CF 5 g, force angle 60°) and site #2 (bottom ; average CF 45 g, force angle 45°). C , Atrial potentials recorded at sites #1 and #2. Although CF was low at site #1, the amplitude of the bipolar and unipolar potentials was greater than at site #2, recorded at high CF (2.63 mV vs 1.68 mV and 5.07 mV vs 1.89 mV, respectively). The impedance was also greater at site #1 than site #2 (127 ohms vs 121 ohms). CS indi-cates coronary sinus; LIPV, left inferior pulmonary vein (PV); LSPV, left superior PV; RIPV, right inferior PV; and RSPV, right superior PV.

AP Projection

RSPV

RIPV

LIPV A

Site #1CF 5 g

Site #2

CF 45 g 2g

70g

LSPV

Mitral Annulus

Contact Force (1 sec average)

Time (sec)0246810

1005001

9753

(g)

0246810

100

5001

9753

Contact Force

)

Time (sec)

(g)

Site #1

Site #2

Site #1

Site #2

II V 1CS

Angle (60°Angle (45°

Nakagawa et al Contact Force During AF Mapping/Ablation 749

impedance, and CF, due to the higher impedance and lower amplitude signals deep within the PV .

CF During Radiofrequency Ablation

The operators were not blinded to CF during ablation. The aver-age CF during PV antrum isolation in 18 patients was a median

of only 8 g (range 1–65 g). The range of CF during radiofre-quency application was similar for the 3 operators (Figure 3B). The total radiofrequency time per patient ranged 28.3 to 70.8 (median 45) minutes, without the occurrence in any patient of either an audible steam pop, an impedance rise, or the presence of coagulum or char on the ablation electrode. Acute antrum iso-lation (>30 minutes) was achieved for all PVs in all 18 patients.

Complications

In 1 patient, hospitalization was extended due to the devel-opment of atrial tachycardia on the second day post-ablation. There were no other acute or late complications, including pericardial effusion, pericardial tamponade, stroke, phrenic nerve injury, LA-esophageal fistula, or PV stenosis. At 6 months, 14 (78%) of the 18 patients were free of symptoms, and Holter recording showed no AF or atrial tachycardia with-out antiarrhythmic medication.

10203040506070

90B

Figure 3. Range of contact force (CF) during left atrial (LA)/pul-monary vein (PV) mapping and during ablation. A , Range of CF during LA/PV mapping for all 18 patients (5682 sites, median 8.2 g), and for operator #1 (12 patients, 3846 sites, median 8.3 g), operator #2 (4 patients, 1009 sites, median 7.3 g), operator #3 (2 patients, 827 sites, median 9.3 g). Box plot values are 10th per-centile, 25th percentile, 50th percentile (median), 75th percentile, and 90th percentile of the range of CF. B , CF distribution during ablation for each of the 3 operators. CF was ≤20 g for >80% of

ablation sites for all 3 operators. NS indicates not significant.

Figure 4. Locations of the 6 regions of high average contact force (CF; ≥35 g), shown in the posterior-anterior (PA) pro-jection (left ) and anterior-posterior (AP) projection (right ). LA indicates left atrial; LIPV, left inferior pulmonary vein (PV); LSPV, left superior PV; RIPV, right inferior PV; and RSPV, right superior PV.

Figure 5. Contact force (CF) map in the anterior-posterior (AP) projection and CF recording while catheter was positioned per-pendicular (angle 90°) to the anterior/rightward left atrial (LA) roof (beneath the ascending aorta) shows transient peaks (respiratory cycle) in CF exceeding 100 g. LIPV indicates left inferior pulmo-nary vein (PV); LSPV, left superior PV; RIPV, right inferior PV; and RSPV, right superior PV.

750 Circ Arrhythm Electrophy s iol August 2013

Discussion

This study examined the spatial distribution of electrode-tissue CF during catheter mapping of the LA and PVs (with 3 operators blinded to the CF measurements) in 18 patients undergoing ablation of paroxysmal AF, and tested the abil-ity of electrogram amplitude (unipolar and bipolar voltage) and impedance to predict CF. The results are summarized as follows: (1) there was a wide range of average CF (1–144 g) over 5682 sites during LA/PV mapping, but CF was relatively low over most sites for all 3 operators (median 8.2 g); (2) high average CF (≥35 g) was observed at only 2% of the map-ping sites with the predominant site at the rightward supe-rior aspect of the anterior LA, directly beneath the ascending aorta; (3) unipolar voltage, bipolar voltage, and impedance correlated poorly with average CF both during sinus rhythm and AF; and (4) modulating radiofrequency power based on CF allowed acute PV isolation without audible steam pop, thrombus, or pericardial effusion.

There was a wide range of CF for each operator, but unlike a previous study,12 the range and median values were simi-lar between operators. The present study evaluated the spa-tial distribution of CF within the LA and PVs. High average CF (≥35 g) was observed at only 2% of the mapped sites (118/5682 sites). The sites of high CF were clustered in 6 regions (Figure 4). The most dominant high CF region (pres-ent in 17 of the 18 patients) was the rightward superior aspect of anterior LA, directly beneath the ascending aorta. High CF at this site was usually transient, present mainly during the inspiratory phase of respiration (Figure 5). Intracardiac echocardiography showed the mapping electrode was located directly beneath the ascending aorta. These observations sug-gest the ascending aorta exerts an external force against the LA wall and the catheter (Figure 6). High CF at this site was not dependent on the location of the transeptal sheath, because

the sheath tip was positioned in the right atrium in 12 of the

17 patients.

The second most common region of high CF (present in 9 of the 18 patients) was located at the antrum, posterior to the right superior PV . Typically, this occurred as the catheter was moved across the superior posterior LA toward the right PVs with clockwise catheter torque. The catheter seemed to fall into this site, resulting in a transient high CF.

Respiratory movement (inspiration) contributed to transient high CF in the LA roof region. On the other hand, having only a short segment of the catheter exposed from the sheath was a factor for high CF in the infero-posterior LA region.

Although electrogram amplitude and impedance have been used to estimate CF, we found a poor relationship between CF and the unipolar or bipolar atrial potential amplitude or the impedance (Figures 7 and 8). In a previous study using a canine model with the catheter positioned at a single ven-tricular endocardial site, applying a progressive increase in CF was surprisingly not associated with a significant increase in either ventricular potential amplitude or ST elevation (injury current).9 Baseline impedance is also heavily influenced by the location of the electrode within the heart relative to high impedance extracardiac structures, such as lung. These obser-vations support the importance of directly measuring elec-trode-tissue CF.

The relationship between CF and radiofrequency lesion depth has been examined in the canine thigh muscle prepara-tion and canine right and left ventricles.8,13,15 Increasing CF (2, 10, 20, 30, and 40 g) in the canine thigh muscle produced a progressive increase in lesion depth for constant radiofre-quency power (30 watts, median lesion depth 6.2–9.9 mm ) and for high radiofrequency power (50 watts, median lesion depth 7.1–11.2 mm ). Lesion depth was greater at 30 watts radiofrequency power at 40 g CF than at 50 watts and 10 g CF (median depth 9.9 mm versus 8.5 mm , P <0.01).8 The inci-dence of steam pop and thrombus formation also increased with increasing CF at both 30 and 50 watts.

In canine beating heart studies, increasing CF similarly increased radiofrequency lesion depth in the canine right ventricle (25 watts; median depth 4.6–7.4 mm) and left ven-tricle (40 watts; median depth 5.3–9.5 mm). Lesion depth was greater for radiofrequency applications at 25 watts at high CF (≥40 g) than at 40 watts at low CF (<10 g; median depth 7.4 mm versus 5.3 mm).13 Based on these observations, the fea-sibility of modulating radiofrequency power based on CF to achieve desired lesion depth was explored in the canine right and left ventricles. Deceasing radiofrequency power from 40 Watts to 10 Watts with increasing CF from 10 g to 40 g in the right ventricle and 50 to 25 watts (when increasing CF from 10 to 40 g) in the left ventricle resulted in a similar range of lesion depth (median: 5.2–5.0 mm in the right ventricle; 8.6–8.0 mm in the left ventricle) with a decrease in steam pop at high CF and no thrombus on the electrode.15 In the present study, radiofrequency power was modulated for 4 ranges of CF. In addition, radiofrequency power was not delivered at average CF >65 g. Although the number of patients is small, there was no audible steam pop, thrombus, or pericardial effu-sion in any of the 18 patients. Acute PV antrum isolation was

achieved in all patients with total radiofrequency application

Figure 6. Computed tomograph (CT) image of the aorta merged with the contact force (CF) map in the right anterior oblique (RAO) projection shows the region of very high CF (144 g) at the ante-rior/rightward left atrial (LA) roof in this patient is located directly beneath the ascending aorta. RIPV inidcates right inferior pulmo-nary vein (PV); and RSPV, right superior PV.

Nakagawa et al Contact Force During AF Mapping/Ablation 751

Figure 7. Comparison of maps of contact

force (CF; A), unipolar atrial potential

amplitude (Unipolar Voltage Map; B),

bipolar atrial potential amplitude (Bipolar

Voltage Map; C), and impedance (D) in

the same patient. Note that a site of high

CF (black arrow in the left) demonstrates

a low unipolar amplitude, a moderate

bipolar amplitude, and a low impedance.

At a site of low CF (black arrow in the

right), unipolar and bipolar amplitudes

are high and an impedance is moderate

(not low). AP indicates anterior-posterior;

LIPV, left inferior pulmonary vein (PV);

LSPV, left superior PV; PA, posterior-

anterior; RIPV, right inferior PV; and

RSPV, right superior PV.

752 Circ Arrhythm Electrophy s iol August 2013

times (median 45 minutes) similar to those expected by each of the 3 operators using conventional, non-CF sensing irri-gated catheters, suggesting little or no loss of lesion effective-ness despite decrease in radiofrequency power at higher CF.

Limitations of the Study

There are 3 principal limitations for this study. First, the number of patients is too small to confirm a reduction in the incidence of steam pop and other complications by modulating radiofre-quency power based on CF (ie, reducing radiofrequency power with increasing CF). The second limitation relates to the inabil-ity to use acute PV isolation to measure lesion effectiveness during the titration of radiofrequency power. Acute PV isolation does not confirm transmural necrosis. In addition, adenosine

testing was not performed to identify dormant PV conduction. Studies with larger numbers of patients and long-term follow-up will be required. The third limitation relates to the observa-tion that more than 80% of radiofrequency applications were delivered at CF ≤20 g. This limits the assessment of safety and efficacy of the power modulation algorithm at high CF.

Conclusions

There was a wide range of CF during catheter mapping and ablation of the LA and PVs. High average CF (≥35 g) occurred at 6 regions in the LA, most at anterior/rightward roof, where the ascending aorta provides resistance to the LA. Unipolar and bipolar atrial potential amplitude and impedance

were found to be poor predictors of CF, suggesting there is no

Figure 8. Poor relationship between contact force (CF) and unipolar left atrial potential amplitude during sinus rhythm (A ) and atrial fibril-lation (AF; B ), bipolar left atrial potential amplitude during sinus rhythm (C ) and AF (D ), and impedance during sinus rhythm (E ) and AF (F ). CI indicates confidence interval.

Nakagawa et al Contact Force During AF Mapping/Ablation 753

present substitute for measuring catheter-tissue CF. Although the number of patients was small, controlling radiofrequency power based on CF seems to reduce or prevent steam pop, impedance rise, and pericardial effusion/tamponade without loss of lesion effectiveness.

Sources of Funding

This study was supported in part by a grant from Biosense Webster, Inc.

Disclosures

Drs Nakagawa, Kautzner, Natale, Di Biase, and Jackman are consul-tants for Biosense Webster, Inc. The other authors report no conflicts.

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CLINICAL PERSPECTIVE

This study tested, in patients undergoing catheter ablation of paroxysmal atrial fibrillation, the ability of a contact force (CF) sensing catheter to: (1) identify the range and spatial distribution of CF during catheter mapping of the left atrium and pulmonary veins with 3 operators blinded to the CF measurements; (2) determine the accuracy of atrial potential amplitude and impedance in predicting CF; and (3) explore the feasibility of controlling radiofrequency power based on CF (ie, lower power with high CF and higher power with low CF) to achieve effective radiofrequency lesions while preventing steam pop and impedance rise. There was a wide range of CF during mapping and ablation within and between the 3 operators. High average CF (≥35 g) was observed at only 2% of mapped sites (118/5682 sites). The sites of high CF were clustered in 6 left atrium regions. The dominant high CF region (present in 17 of the 18 patients) was the rightward superior aspect of anterior left atrium, directly beneath the ascending aorta. High CF at this site was usually transient, present mainly during inspiration, suggesting the ascending aorta exerts an external force against the left atrium wall and the catheter. Unipolar and bipolar atrial potential amplitude and impedance were found to be poor predictors of CF, suggesting there is no present substitute for measuring catheter-tissue CF. Controlling radiofrequency power based on CF seems to reduce or prevent steam pop, imped-ance rise, and pericardial effusion/tamponade without loss of lesion effectiveness, measured as pulmonary vein isolation.

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