Abstract
Background
Circumstances around ablation catheters placed in the ventricular cavity and pericardial space are not identical, and therefore bipolar (BIP) ablation targeting the interventricular septum (IVS) or left ventricular free wall (LVFW) may induce lesions with different characteristics on either side of the wall.
Methods
Porcine hearts prepared for IVS or LVFW were placed between two inner containers which were set in an outer experimental container. For IVS ablation, each inner container was filled with Tyrode's solution circulated by a pump to mimic the right- and left-ventricular cavities. For LVFW ablation, a plastic board was inserted into one of the inner containers to mimic the pericardial space, thereby minimizing the circulating solution. Thereafter, BIP ablation (30W, 120-s) was attempted 30 applications each in IVS and LVFW.
Results
All 60 applications were successfully accomplished without steam-pop. Total impedance decline (TID) and %-TID were larger in LVFW than IVS ablation (−19.4 ± 5.3 vs. −15.8 ± 4.6 Ω, and −16.2 ± 4.0 vs. −13.2 ± 3.6%), and total lesion depth was deeper in LVFW than in IVS (14.4 ± 2.6 vs. 12.7 ± 3.3 mm) due to deeper lesions in the epicardial wall. Surface lesions were also larger in epicardial than in endocardial wall in LVFW ablation, whereas there were no differences between right- and left-side septal wall. Transmural lesion was created in 13/30 in LVFW and 9/30 in IVS ablation.
Conclusions
As compared to IVS, BIP ablation targeting LVFW demonstrated larger TID and induced deeper lesions in the epicardial wall in this study, probably due to less current leakage into the small space.
Keywords: Bipolar ablation, Lesion characteristics, Pericardial space
1. Introduction
Recent experimental and clinical studies have reported that bipolar (BIP) radiofrequency (RF) ablation can create deeper lesions as compared to those induced by unipolar RF ablation [1,2]. In addition, long application time ablation, which maximally utilizes conductive heating effect, is considered to be useful to treat arrhythmias originating from inside the myocardium [3,4]. However, lesion characteristics created by the combination of these two methods (BIP ablation and long application time ablation) have not been well studied.
In clinical BIP ablation targeting the ventricle, two ablation catheters are individually placed in the cavity of the right or left ventricle (RV or LV) or in the pericardial space. Since circumstances around ablation catheter placement in the ventricular cavity and pericardial space differ, long application time BIP ablation between the interventricular septum (IVS) or left ventricular free wall (LVFW) may induce lesions with different characteristics. We recently reported two dual-bath experimental settings, each mimicking BIP ablation, for either IVS or LVFW [5,6]. In the present study, we attempted long application time (120-s) BIP ablation (30W) using these experimental settings, and systematically assessed the lesion differences between IVS and LVFW.
2. Methods
2.1. Experimental preparation
This study, approved by the animal studies subcommittee of our institutional review board, was in compliance with the guidelines of the United States National Institutes of Health for the Care and Use of Laboratory Animals. The data that support the findings are available from the corresponding author upon reasonable request.
Healthy porcine hearts (43 hearts) were obtained immediately after being killed for food at a meat processing plant and were then transferred to our laboratory within 1 h. Since we obtained the healthy porcine farmed for food from a single facility, the volume and thickness of their hearts are similar in each porcine. The hearts were prepared for the segments of either IVS or LVFW within a container filled with Tyrode's solution (NaCl = 129.0 mmol/L, KCl = 4.0 mmol/L, NaH2PO4 = 0.9 mmol/L, NaHCO3 = 20 mmol/L, CaCl2 = 1.8 mmol/L, MgSO4 = 0.5 mmol/L and glucose = 5.5 mmol/L, buffered with 95% O2 and 5% CO2) warmed to 37 °C. Tyrode's solution is isotonic with interstitial fluid and is used in physiological experiments. Tyrode's solution was gassed with 95% oxygen and 5% carbon dioxide, and achieved an appropriate pH of 7.40 ± 0.08. The proximal portion of the left anterior descending coronary artery in the IVS or left circumflex coronary artery in the LVFW was exposed, and the myocardium was perfused with warmed Tyrode's solution at 60 mL/min. The myocardium was set into the experimental bath as described below.
2.2. Dual-bath experimental settings
Details of our dual-bath experimental settings were reported previously [5,6]. Briefly, two inner plastic containers, each almost half the size (23.5 x 18.0 × 12.0 cm) of the outer experimental container (50.0 x 20.0 × 12.0 cm) and communicating through windows, were set in the outer experimental container (Figure-1). The porcine myocardium was placed between the two inner plastic containers. Each inner container was filled with 3000 mL of Tyrode's solution at 37 °C, circulated by a pump and temperature-controlled by a heater. This dual-bath experimental setting was designed to simulate BIP ablation for IVS (Figure-1A), and to allow most RF current to pass through the myocardium, mimicking clinical treatment [5]. To simulate BIP ablation for LVFW, a plastic board was inserted into one of the inner plastic containers, facing the epicardial myocardium to create a small space (2.5 x 18.0 × 12.0 cm) and minimize the circulation of Tyrode's solution to mimic the pericardial space (Figure-1B) [6]. Tyrode's solution also filled the space around the myocardium to prevent the myocardium from cooling. In these experimental settings, initial impedance was stable without attempting any adjustment (sodium concentration of the solution, using a silicon sheet, etc.), which allowed us to use Tyrode's solution in this study.
Fig. 1.
Schematic representation of experimental preparation
Panel A is an illustration of bipolar ablation for interventricular septum (IVS). The porcine myocardium was placed between the two inner plastic containers. Each inner container was filled with Tyrode's solution, circulated by a pump and temperature-controlled by a heater. Tyrode's solution also filled the space around the myocardium. This dual-bath experimental setting was designed to allow most RF current to pass through the myocardium. Two ablation catheters were placed on opposite surfaces of each porcine myocardium. Panel B is an illustration of bipolar ablation for left ventricular free wall (LVFW), and a plastic board was inserted into one of the inner plastic containers, facing the epicardial myocardium to mimic the pericardial space. See detailed description in the text.
2.3. RF ablation
BIP RF ablation (30 W, 120-s, 20-g contact) was attempted through 8F quadripolar FlexAbility™ open irrigation catheters (Abbott, St. Paul, MN). Two ablation catheters were placed vertically on opposite surfaces of each porcine myocardium, and RF current was delivered between the distal tips of the catheters. In the BIP ablation for IVS, the LV endocardial catheter was connected to the catheter connector and the RV endocardial catheter to the connector for the cutaneous electrode of an Ampere™ RF ablation generator (Abbott, St. Paul, MN). In the BIP ablation for LVFW, the LV endocardial catheter was connected to the catheter connector and the LV epicardial catheter to the connector for the cutaneous electrode of the RF ablation generator. The LV epicardial catheter was placed on those sites not covered by epicardial fat. In all applications, the contact force of each catheter was maintained at 20-g, using pressure control systems based on the strain gauge (YO Technica, Niigata, Japan) and the maximum catheter temperature which connected to the catheter connector was set at 45 °C. From the RF ablation generator, the energy was delivered for 120-s but turned off immediately if audible steam-pop occurred. During the RF application, each ablation catheter was irrigated by 13 mL/min normal saline. RF energy was delivered to 1-3 separate sites in each myocardium depending on the myocardial size. A total of 60 RF applications (30 applications each for IVS and LVFW) were attempted in the present study.
2.4. Impedance measurement
The following impedance indexes were monitored on the RF ablation generator; 1) initial impedance when starting 30 W application, 2) minimum impedance during ablation, 3) total impedance decline (TID), which was calculated as initial minus minimum impedance during ablation, and 4) %-TID, which was calculated as percent TID from the initial impedance.
2.5. Lesion characteristics
The size of the lesions created by RF ablation was measured using a digital caliper (model 19979, Shinwa Sokutei Inc., Sanjyo, Japan) as reported previously [6]. Methodology of the lesion measurement is illustrated in Figure-2. After measuring the longest lesion diameters on the myocardial surface (long-SD), the myocardium was sectioned transmurally in order to assess the maximum transverse lesion width (width-MaxTL) and lesion depth from the surface to width-MaxTL (depth-MaxTL). When two lesions were created separately in each side of the myocardium, and showed non-transmural lesions beneath the myocardium, maximum lesion depth beneath the myocardial surface (max-LD) was measured in each lesion, and total lesion depth (total-LD) was calculated as follows; total-LD in IVS = max-LDs in LV-septum plus in RV-septum, and total-LD in LVFW = max-LDs in endocardial plus epicardial wall. If the lesion extended transmurally, myocardial thickness at the ablation site was used as the parameter for total-LD in both IVS and LVFW.
Fig. 2.
Methodology of the lesion measurement
Panels A and B are illustrations of the non-transmural and transmural lesions created in the IVS and LVFW. Measured parameters (a)-(g) in these lesions are described in the illustrations. See detailed description in the text.
2.6. Statistical analysis
The numbers are presented as mean ± standard deviation and a P value < 0.05 was considered statistically significant. When comparing each of the two sets, we applied Student's t-test for continuous variables. Paired t-tests were used to compare the endocardial vs. epicardial lesions and RV-septum vs. LV-septum lesions. Comparison of the results between IVS and LVFW ablation was performed using Fisher's exact test. The SPSS statistical software, version 26 (SPSS Institute Inc., Chicago, IL) was used for these analyses.
3. Results
3.1. RF ablation
All 60 RF applications were successfully accomplished without steam-pop, both in IVS and LVFW (Table-1). Myocardial thickness at the ablation sites and initial impedances were not different between the IVS and LVFW. Minimum impedance during the RF application was higher in IVS than that in LVFW, which resulted in smaller TID and %-TID in IVS (−15.8 ± 4.6 Ω and −13.2 ± 3.6%) as compared to those in LVFW (−19.4 ± 5.3 Ω and −16.2 ± 4.0%). Generator impedance reached a plateau around 80 s after delivering RF current both in IVS (80.4 ± 15.3 s) and in LVFW (80.2 ± 13.6 s) ablations. Delivered energy was 3559 ± 1 J for IVS and 3560 ± 1 J for LVFW ablations.
Table 1.
Comparisons between Bipolar ablation for IVS and LVFW.
| IVS | LVFW | P-value | |
|---|---|---|---|
| Myocardial thickness, mm | 19.1 ± 2.1 | 18.9 ± 2.2 | 0.769 |
| Initial impedance, ohm | 118.6 ± 3.1 | 118.9 ± 3.9 | 0.743 |
| Minimum impedance, ohm | 102.8 ± 3.5 | 99.5 ± 4.2 | 0.001 |
| TID, ohm | −15.8 ± 4.6 | −19.4 ± 5.3 | 0.006 |
| %-TID, % | −13.2 ± 3.6 | −16.2 ± 4.0 | 0.004 |
| Steam pop | 0/30 | 0/30 | - |
| Transmural lesion | 9/30 (30.0%) | 13/30 (43.3%) | 0.422 |
Values are mean ± standard deviation. IVS: interventricular septum, LVFW: left ventricular free wall, TID: total impedance decline.
3.2. RF lesions
-
(1)
Transmural lesions
Transmural lesions were created in 9/30 applications (30.0%) in IVS and in 13/30 applications (43.3%) in LVFW (Table-1). Success rate in creating transmural lesions was not different between IVS and LVFW. Myocardial thickness at the ablation sites was thinner in the myocardium with transmural lesions as compared to those with non-transmural lesions in both IVS and LVFW (17.1 ± 1.7 vs. 19.9 ± 1.7 mm in IVS, and 16.9 ± 1.4 vs. 20.4 ± 1.2 mm in LVFW preparations) (Table-2). BIP ablation creating the transmural lesions showed larger TID and %-TID than those in the non-transmural lesions, both in IVS (−19.0 ± 3.6 Ω and −15.8 ± 2.7% vs. −14.4 ± 4.3 Ω and −12.1 ± 3.4%) and LVFW myocardium (−23.9 ± 4.4 Ω and −19.8 ± 3.0% vs. −15.9 ± 2.6 Ω and −13.5 ± 2.1%).
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(2)
RV-septum vs. LV-septum lesions in IVS
Table 2.
Comparisons between transmural and non-transmural lesions.
| IVS |
LVFW |
|||||
|---|---|---|---|---|---|---|
| Transmural lesion (n = 9) | Non-transmural lesion (n = 21) | P-value | Transmural lesion (n = 13) | Non-transmural lesion (n = 17) | P-value | |
| Myocardial thickness, mm | 17.1 ± 1.7 | 19.9 ± 1.7 | <0.001 | 16.9 ± 1.4 | 20.4 ± 1.2 | <0.001 |
| Initial impedance, ohm | 119.8 ± 3.5 | 118.1 ± 2.8 | 0.173 | 120.1 ± 4.7 | 118.0 ± 3.1 | 0.155 |
| Minimum impedance, ohm | 100.8 ± 2.9 | 103.7 ± 3.3 | 0.031 | 96.2 ± 2.8 | 102.1 ± 3.1 | <0.001 |
| TID, ohm | −19.0 ± 3.6 | −14.4 ± 4.3 | 0.009 | −23.9 ± 4.4 | −15.9 ± 2.6 | <0.001 |
| %-TID, % | −15.8 ± 2.7 | −12.1 ± 3.4 | 0.008 | −19.8 ± 3.0 | −13.5 ± 2.1 | <0.001 |
Values are mean ± standard deviation. Abbreviations are the same as in Table 1.
Long-SD, width-MaxTL and depth-MaxTL were not different between RV-septum vs. LV-septum lesions in all 30 applications (Table-3) (Figure-3). In the 21 non-transmural lesions, max-LD was not different between RV-septum vs. LV-septum lesions.
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(3)
Endocardial vs. epicardial lesions in LVFW.
Table 3.
Lesion created in the IVS and LVFW.
| IVS (LV septum/RV septum) | LVFW (Endocardial lesion/Epicardial lesion) | P-value (IVS vs. LVFW) | |
|---|---|---|---|
| long-SD, mm | 5.1 ± 0.5/5.2 ± 0.5 | 5.3 ± 0.6/5.7 ± 0.5 | 0.083/0.001 |
| width-MaxTL mm | 8.2 ± 1.3/8.4 ± 1.2 | 8.6 ± 1.5/12.0 ± 1.6 | 0.292/<0.001 |
| depth-MaxTL, mm | 1.4 ± 0.1/1.4 ± 0.3 | 1.4 ± 0.2/1.7 ± 0.3 | 0.560/<0.001 |
| max-LD (non-transmural), mm | 5.3 ± 0.7/5.4 ± 0.8 (n = 21) | 5.5 ± 0.9/6.9 ± 0.8 (n = 17) | 0.513/<0.001 |
| total-LD (non-transmural), mm | 10.7 ± 1.5 (n = 21) | 12.4 ± 1.1 (n = 17) | 0.001 |
| total-LD (all applications), mm | 12.7 ± 3.3 | 14.4 ± 2.6 | 0.030 |
| Comparisons | (LV vs. RV septum) | (Endocardial vs. Epicardial lesion) | |
| long-SD | 0.254 | 0.010 | |
| width-MaxTL | 0.449 | <0.001 | |
| depth-MaxTL | 0.075 | <0.001 | |
| max-LD (non-transmural) | 0.533 | 0.001 | |
Values are mean ± standard deviation. long-SD: longest lesion diameters on the myocardial surface, width MaxTL: maximum transverse lesion width, depth-MaxTL: lesion depth from the surface to width-MaxTL, max-LD: maximum lesion depth beneath the myocardial surface, total-LD: total lesion depth. Other Abbreviations are the same as in Table 1.
Fig. 3.
Gross macroscopic examination of the lesions
Fig. 3A has examples of non-transmural lesions created in the interventricular septum (IVS) (left column) and left ventricular free wall (LVFW) (right column). Upper panels are a left ventricular (LV) septal lesion in the IVS and an LV endocardial lesion in the LVFW. Lower panels are a right ventricular (RV) septal lesion in the IVS and an LV epicardial lesion in the LVFW. Middle panels are the IVS and LVFW lesions sectioned transmurally. Panel 3B is examples of transmural lesions created in the IVS and LVFW. The arrangement of the figures is the same as in Panel 3A. Measurement method in each parameter (a)-(g) are shown in Fig. 2 and the measured values are shown in each lesion in this Fig. 3AB. Each lesion is surrounded by small dots. Epicardial lesions in the LVFW are larger than those in others. See detailed description in the text.
Long-SD, width-MaxTL and depth-MaxTL were larger in epicardial as compared to those in endocardial lesions in all 30 applications (Table-3) (Figure-3). In the 17 non-transmural lesions, max-LD was deeper in the epicardial than in the endocardial lesions.
-
(4)
Comparisons in the lesions between IVS and LVFW.
When comparing the LV endocardial lesions in IVS and LVFW, long-SD, width-MaxTL and depth-MaxTL were not different in all 60 RF applications (Table-3) (Figure-3). For the non-transmural lesions (21 lesions in IVS and 17 lesions in LVFW), max-LD was not different in the LV endocardial lesions between IVS and LVFW.
In the analysis of all 60 applications, total-LD in the IVS (LV-septum plus in RV-septum) was less than that in the LVFW (endocardial plus epicardial wall) (12.7 ± 3.3 vs. 14.4 ± 2.6 mm). Similarly, in the analysis within non-transmural lesions (21 lesions in IVS and 17 lesions in LVFW), total-LD in the IVS was less than that in the LVFW (10.7 ± 1.5 vs. 12.4 ± 1.1 mm, p = 0.001).
4. Discussion
The main findings of this study were 1) long application time BIP RF ablation (30W and 120-s duration) was successfully accomplished in thick porcine myocardium (IVS and LVFW) placed in the dual-bath experimental settings, with, respectively, 30.0% or 43.3% successful creation of transmural lesions, 2) BIP ablation for IVS showed smaller TID (%-TID) as compared to BIP ablation for LVFW, and 3) BIP ablation for IVS created similar lesions both in the RV-septum and LV-septum, whereas BIP ablation for LVFW induced larger lesions in the epicardial than in endocardial wall.
4.1. Long application time BIP ablation
BIP ablation is reported to create deep lesions inside the thick myocardium [1,5]. This is caused by the high energy loading on the target myocardium due to current distribution between the two electrode tips of the ablation catheters [7]. In addition, long application time ablation, which is presumed to fully utilize conductive as well as resistive heating effects [1,3,4], would be useful to increase the interior myocardial temperature to a coagulation necrosis-inducing level. In unipolar RF ablation in clinical treatment, a longer application time (≧ 90 s, etc.) is sometimes required to terminate ventricular arrhythmias from thick myocardium [8,9]. In the present study, we combined these two factors (BIP and long application time ablation) to ensure the ability in creating deep lesions in thick myocardium.
In the protocol we used (30W, 120-s, 20-g contact, 13-mL/min irrigation), steam-pop did not occur in any of the RF applications. This was probably because we used thick myocardium, and maximum TID and %-TID were limited to −15.8 ± 4.6 Ω and −13.2 ± 3.6% in IVS and to −19.4 ± 5.3 Ω and −16.2 ± 4.0% in LVFW, respectively (Table-1). It has been reported that steam-pop occurrence was associated with large TID and %-TID (usually more than 20-25 Ω and/or 20-25% decline), and thin myocardium at the target ablation site presented further risk of steam-pop [10,11]. Therefore, we need to emphasize that our results do not imply the safe performability of long application time BIP in various ablation modes but are limited to the experimental conditions used in this study.
4.2. Lesions created in IVS and LVFW
As accurate measurement of lesions created by RF ablation is difficult in clinical treatment, the lesion characteristics created by each ablation method are estimated from the results of basic experiments. In this study, BIP ablation for LVFW induced larger lesions in the epicardial than in endocardial myocardium. On the other hand, BIP ablation targeting the IVS created similar lesions in both the RV- and LV-side of the septum. This was probably due to the small volume of non-circulating Tyrode's solution in the narrow space in the container, facing the epicardium and mimicking the pericardial space, in LVFW ablation. This hypothesis appears to be supported by our previous results that, when using the dual-bath experimental setting for IVS, BIP ablation in the LVFW created the same size of lesions between the endocardial and epicardial walls [5,11].
In the ex-vivo (bovine myocardium) and in-vivo (swine hearts) experimental studies, Aryana et al. examined RF lesions in the epicardial wall with the modification of solution volume within the pericardial space [12]. As the results showed, RF ablation attempted after saline infusion into the pericardial space created smaller lesions as compared to ablation performed in the absence of saline infusion. In another study using computer simulation, Cuenca-Dacal et al. demonstrated that myocardial lesion volume and depth decreased with increasing intrapericardial fluid volume, probably due to reducing the amount of energy that reaches the myocardium [13]. Distribution of the epicardial fat (usually distributed into the basal LV portions around coronary vessels) can be a cause of smaller epicardial lesions by RF ablation [14,15]. However, in the present study, we placed the epicardial ablation catheter on sites not covered by epicardial fat.
Since TID or %-TID is reported to be associated with myocardial heating and tissue injury during RF ablation [7,15,16], larger TID and %-TID in LVFW than in IVS ablation would suggest higher temperature elevation within the LVFW in the present study. Individual catheter temperature monitoring may clarify the different heating between both sides of the myocardium, but in ablation using irrigation catheter, temperature measured by the ablation catheter does not precisely represent the temperature under the catheter contacting myocardium.
4.3. Creation of transmural lesions
Recent mapping technologies can determine the arrhythmogenic substrate more accurately, but it is still uncertain how deep the arrhythmogenic substrate is located under the surface. Therefore, if transmural lesions could be created more consistently and safely, because the transmural lesion includes arrhythmogenic substrates at whatever depth they are distributed, outcomes of RF ablation for deep myocardial origin would be improved. Although the success rate for creation of transmural lesions was less than 50%, this was probably associated with the thick tissue of the porcine hearts we used in this study. Since the average total lesion depth was 12.7 ± 3.3 mm in IVS and 14.4 ± 2.6 mm in LVFW, long application time BIP RF ablation (30W and 120-s duration) may have the potential to create transmural lesions in most clinical treatment. In addition, further experimental studies with larger numbers of RF application may demonstrate a higher inducibility of transmural lesions in LVFW than in IVS, because of the deeper total lesion depth and larger TID (%-TID) in LVFW ablation. However, this is a single small ex-vivo experiment, and the results of the present study are not meant to simply be applied clinically. To date, a safe and effective long application time BIP RF ablation method has not yet been well established. In addition, there are no reliable ablation parameters to confirm the accomplishment of the transmural lesions during RF application in clinical RF ablation. Further studies are required to identify reasonable parameters in predicting lesion volumes during RF ablation.
4.3.1. Clinical implications
In VT presumed to originate intramyocardially within the LV myocardium, the earliest activation site is usually mapped from both sides of the ventricular wall (the RV and LV endocardial septal walls of the IVS, as well as the endocardial and epicardial surfaces of the LVFW). If unipolar RF energy application from each side of the myocardium is ineffective or shows insufficient therapeutic effect (only transient VT suppression or slowing of the VT rate, etc.), BIP ablation may be considered as the next option to achieve successful outcomes.
The results of this study suggest that BIP ablation for the IVS appears to provide similar therapeutic effects regardless of whether the VT origin is located closer to the RV or LV septal wall. In contrast, BIP ablation for the LVFW may be more advantageous for VT origins located closer to the epicardial rather than the endocardial myocardial wall. In addition, caution is required when prolonged BIP ablation is performed for VT origins close to the endocardial LV free wall, because steam pop due to excess temperature rise may occur in the epicardial myocardium. Since catheter temperature is usually monitored from the LV endocardial side, temperature monitoring from the LV epicardial side may be safer during BIP ablation of the LVFW.
4.4. Study limitations
First, ablation was attempted by a single energy delivering protocol (30 W, 120-s duration and 20-g catheter contact) using a single manufacturer's equipment, and the ablation catheter was in vertical contact with the myocardial surface. Therefore, further experiments (various application modes using other manufacturer's equipment, parallel catheter contact, etc.) need to be performed to identify and detail differences in BIP ablation targeting between the IVS and LVFW. In addition, different from in this experimental study, contact pressure and angles of the ablation catheters toward the myocardial surface are unable to be stabilized in clinical treatment and such dynamics can affect the results of RF ablation. Second, solution volume in the pericardial space and its fluid characteristics are variable in each patient. Therefore, we need to emphasize that the experimental environment in this study is different from clinical treatment, and the results of the present study are not meant to simply be applied clinically. Results observed in this ex-vivo experimental study need to be reconfirmed using in-vivo experimental studies, but such studies are currently unperformable in our laboratory. Nevertheless, as a first step assessment in this issue, it is important to understand the possibility that, depending on the anatomical location of target myocardium, BIP ablation may create different lesions between both sides of the myocardium. Fourth, lesion volume created by BIP ablation varies depending on target myocardial characteristics, but the present study reported the results from healthy porcine myocardium. Different from healthy porcine hearts, arrhythmogenic myocardium in the human heart includes heterogeneous tissues (fibrosis, scar, fat, etc.) and efficacy of RF ablation would be attenuated in such pathological tissues. Further studies are required to identify the ideal ablation protocol in the pathological myocardium and to clarify how the long application time BIP ablation can best be utilized either for IVS or LVFW in clinical arrhythmia treatments. Fifth, the lesion characteristics should be assessed by both gross macroscopic and histological examinations. Microscopic histological assessment of the RF lesion would have provided more detailed information, but that was not performed in the present study. Finally, steam-pop is not the only complication of RF ablation; other complications, such as coagulum or char formation, were not studied in this experiment.
5. Conclusions
In the present experimental study, long application time BIP ablation (30W, 120-s) is feasible for thick porcine myocardium with successful creation of transmural lesions without steam-pop in 30.0% of IVS and in 43.3% in LVFW. BIP ablation in LVFW may induce larger lesions in the epicardium than in endocardium, probably due to less energy leakage into the pericardial space, although further studies and technological adjustments are definitely required before standardized clinical use.
Data availability statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Approval statement
This study was approved by the animal studies subcommittee of our institutional review board.
Source of funding
None.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.