Ann Thorac Surg 2006;82:1489-1493
© 2006 The Society of Thoracic Surgeons
New Technology
Development of a Novel Temporary Epicardial Pacing Wire With Biodegradable Film
Yuji Narita, MD, PhDa,b,*,
Yukako Fukuhira, MSd,
Hideaki Kagami, DDS, PhDa,
Eiichi Kitazono, MSd,
Hiroaki Kaneko, PhDd,
Yoshihiko Sumi, PhDd,
Akihiko Usui, MD, PhDa,
Minoru Ueda, DDS, PhDc,
Yuichi Ueda, MD, PhDa
a Department of Tissue Engineering, Nagoya University School of Medicine, Nagoya, Japan
b Department of Cardiothoracic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
c Department of Oral and Maxillofacial Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
d Department of Tissue Engineering Development, Innovation Research Institute, Teijin Limited, Tokyo, Japan
Accepted for publication April 13, 2006.
* Address correspondence to Dr Narita, Department of Cardiothoracic Surgery, Nagoya University Graduate School of Medicine in 65, Tsurumai-cho, Showa-ku, Nagoya, 466-8550 Japan (Email: ynarita{at}med.nagoya-u.ac.jp).
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Abstract
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PURPOSE: A temporary epicardial pacing wire (TEPW) has been routinely placed in patients undergoing cardiac surgery. However, its fixation or removal occasionally causes troublesome complications. The aim of this study is to develop a novel TEPW using biodegradable film to fix the electrode to the epicardium without needle stabbing.
DESCRIPTION: A biodegradable film was prepared with poly(L-lactide-co-
-caprolactone). The film has a honeycomb-patterned structure that serves as a temporary adhesive for the myocardial surface, and the electrode was incorporated within the film. The novel TEPW was placed on the ventricular epicardium of dogs (group A, n = 5). As a control, conventional TEPW was inserted (group B, n = 6). The pacing threshold, R wave amplitude, impedance, and slew rate were measured at postoperative days 0, 1, 3, 5, 7, and 14, and complications after removal were checked.
EVALUATION: All measurements in both groups were identified and differences were not observed. In addition, the novel TEPWs could be easily removed without related complications.
CONCLUSIONS: This novel TEPW is safe and feasible for postoperative management of cardiac surgeries.
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Introduction
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Temporary epicardial pacing wires (TEPWs) are routinely stabbed in the epicardium after cardiac operation for the treatment and diagnosis of cardiac arrhythmias and cardiac function. They are usually placed by inserting an attached tapered needle and fixing the electrode in the myocardium. Some coil is used to secure the electrode and prevent its accidental slippage out from the heart. Because of the needle stabbing or coil-like structure of the tip of the electrode, bleeding readily occurs, and additional hemostasis sutures are often required. Rarely the TEPWs can even cause complications such as hemorrhage, cardiac tamponade [1–3], ventricular tachycardia [1, 4, 5], infection [6], and migration of the retained wire [7]. These conventional TEPW-related complications occur in approximately 0.4% of patients [1]. After cardiac surgery, some patients should have anticoagulation therapy, especially those who underwent mechanical valve replacement. The anticoagulation therapy may induce fatal bleeding complications at TEPW removal. Cardiac surgery for infants and neonates also poses risks related to TEPWs. Considering these possibly serious complications, there is great need to develop an improved TEPW.
Recently, biodegradable materials have been in clinical use, such as plate and screws to treat bone fractures [8]. These materials are expected to disappear after treatment and require no operation for removal. A honeycomb structure can be generated on the surface of various biodegradable films [9] and can attach the film on various surfaces without sutures or glue. In the present study, we have developed a novel TEPW with a honeycomb-patterned biodegradable film that can attach the electrode without needle stabbing and thus serve to prevent bleeding or other complications.
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Technology
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Design of Novel Temporary Epicardial Pacing Wire
Our novel TEPW consists of four parts: (1) a patch of biodegradable film, (2) a unipolar electrode, (3) a lead covering with polyethylene, and (4) an atraumatic needle (Fig 1A–1C). The biodegradable film on the surface facing the epicardium is covered with a honeycomb-patterned structure (Fig 2). The film adheres to the epicardium, and its bondability keeps it from slipping off. This honeycomb-patterned film was prepared as previously described [9, 10]. Briefly, poly(L-lactide-co--caprolactone) (molecular weight = 163,000) was dissolved in chloroform at the concentration of 5 mg/mL at room temperature. The surfactant, dioleoylphosphatidylethanolamine, was added to poly(L-lactide-co--caprolactone) at 0.5 wt/wt%. This poly(L-lactide-co--caprolactone) consists of approximately 80% poly(lactic acid) and 20% polycaprolactone. The honeycomb-patterned film was fabricated by simple casting under blowing of highly humid air. It was then laminated on the cast film, which was made of poly(L-lactide-co-glycolide). A unipolar temporary pacing wire (Medtronic 6492 [Medtronic, Inc, Minneapolis, MN]) was used as an electrode after the attached needle and coil were chopped off. The electrode was sandwiched between the laminated honeycomb-pattered film and the casting film (Fig 1C). The total thickness of the film was about 120 to 160 µm.
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Fig 1. Schema and photograph of novel temporary epicardial pacing wire (TEPW). (A) It consists of four parts including: (1) a patch of biodegradable film (30 mm in diameter), (2) a unipolar electrode (3) lead covered with polyethylene, and (4) an atraumatic needle. (B) The electrode is from the Medtronic 6492 (Medtronic, Inc, Minneapolis, MN) unipolar temporary pacing lead. (C) The cross-sectional diagram of a novel TEPW is shown. The (a) surface film and (b) the cast film sandwiches (c) the wire in between them.
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Fig 2. Scanning electron microscopic image of surface structure of biodegradable film. The caliber of honeycomb-like pattern structure is approximately 5 µm in diameter. This characteristic structure enables it to be attached to the tissue without glue. The original magnification of (A) is x5,000 and (B) is x10,000.
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Technique
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All animal experimentation was performed in accordance with the "Guideline for Animal Experiments of Nagoya University," and approved by the "Animal Experiment Advisory Committee at Nagoya University School of Medicine."
TEPW Implantation Procedure
Male and female beagle dogs (weighing 8.2 to 12.0 kg, aged 2 to 2.7 years old [Kitayama Labs, Japan]) were used. General anesthesia was induced by intramuscular injection of ketamine (10 mg/kg), xylazine (1 mg/kg), and atropine sulfate (0.01 mg/kg). After intravenous injection of thiamyral (5 mg/kg), intratracheal intubation was performed. Anesthesia was maintained by inhalation of N2/O2/halothan. A preoperative and postoperative dose of cefazolin sodium (100 mg/kg) was given intravenously. Right lateral thoracotomy was made through the fourth intercostal space to enter the pleural cavity, and a right-side pericardiotomy was done ahead of the phrenic nerve to expose the right ventricle. The novel TEPWs with the film were placed onto the right ventricular epicardium (group A: experimental group, n = 5) of the dogs and conventional TEPWs (Medtronic 6492 heart wire [Medtronic Inc]) were sutured in the right ventricular myocardium of the control animals (group B, n = 6). One indifferent (reference) electrode was placed in the subcutaneous tissue near the thoracic incision in all cases. In addition, one case in group A had undergone a previous cardiac operation.
Measurement of Electrical Performance
The pacing threshold at a 0.5 ms pulse width of stimulation (V), sensed R wave amplitude (mV), impedance at 5.0 V pacing (ohms), and slew rate (V/s) were measured on the day of the operation, and postoperative days (POD) 1, 3, 5, 7, and 14. These measurements were measured by unipolar technique using the Analyzer 2290 (Medtronic Inc).
Complications After Removal
The TEPWs were removed at POD 14. Approximately half an hour after removal, echocardiography was performed to detect possible complications such as hemopericardium and cardiac tamponade. Mitral flow of peak atrial systolic velocity/peak early diastolic velocity ratio and pericardial thickness were measured to validate pericardial inflammation, such as constrictive pericarditis, approximately 1 month after implantation. The electrocardiogram was also monitored to detect arrhythmia. Re-exploration was done to evaluate the degree of adhesion inside the pericardium 1 month after the first dog operation.
Statistical Analysis
The data of evaluation measurements were expressed as mean ± standard deviation. Statistical analysis was performed by one-way analysis of variance, and multiple comparisons were made by the Scheffe procedure, both with Stat View J-5.0 (SAS Institute, Cary, NC), considering a p value of < 0.05 as statistically significant.
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Results
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The values and the postoperative time course of the pacing threshold, sensed R wave amplitude, impedance, and slew rate are shown in Figure 3. The mean pacing threshold increased gradually in both pacing wires from POD 0 to POD 14 (0.80 ± 0.25 to 3.08 ± 0.69 V and 1.03 ± 0.34 to 3.12 ± 1.61 V, in groups A and B, respectively). The mean sensing R wave amplitude decreased in group A (25.1 ± 6.2 to 12.2 ± 7.7 mV) from POD 0 to POD 14. In contrast, the amplitude was almost fixed in group B (11.3 ± 5.0 to 11.4 ± 5.8 mV). The impedance in group A (1,821 ± 787 to 1,145 ± 337 µ) was relatively higher than that in group B (1,359 ± 540 to 853 ± 142 µ), but never significant at any time point. The slew rate was also stable in both groups from POD 0 to POD 14 (3.8 ± 0.4 to 3.4 ± 1.0 mV/S and 3.0 ± 0.7 to 2.8 ± 1.6 mV/S in groups A and B, respectively). The slew rate was relatively higher in group A than in group B. However, the difference was only significant on day 1. All of these novel TEPW values were within an acceptable range, assuring safe pacing function. There were no significant differences between groups A and B, except for the R wave amplitude on the day of operation and POD 1, and in the slew rate on POD 1.
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Fig 3. Graphs showing time course of four measurements: (A) pacing threshold at 0.5 ms pulse width stimulation (V), (B) sensed R wave amplitude (mV), (C) impedance at 5.0V pacing (µ), and (D) slew rate (V/s) in group A (novel temporary epicardial pacing wire [TEPW], white circle) and group B (conventional TEPW, black box). Data were presented as mean ± standard deviation. (OP = operation; POD = postoperative day.)
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The TEPWs were easily removed by gentle traction, and all electrodes were collected on POD 14 in group A. There were no bleeding complications in either group for more than 14 days after wire removal. However, ventricular arrhythmia was often observed in group B. One dog case in group B experienced nonsustained ventricular tachycardia during wire removal. However, there were no other complications (including arrhythmia) in group A. Diastolic dysfunction and pericardial thickness were not observed at 1 month after implantation in either group (Table 1).
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Comment
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A novel TEPW, which does not require suturing, was evaluated in this study. Given the measurements, the novel TEPW proved acceptable for ventricular temporary pacing wire after cardiac surgery, and comparable with the conventional TEPWs. However, there were several differences between the novel and the conventional TEPWs.
Among the measurements, R wave amplitudes in group A were higher than those in group B on the day of operation and POD 1. The R wave amplitude is generated as the total amount of action potential emanating from the myocardial cells attached to the electrode. The major reason for this difference is presumably that the electrode area attached to the myocardium by the novel TEPW was smaller than that by the conventional TEPWs. The electrode of the conventional TEPW was inserted into the myocardium, whereas the electrodes of the novel TEPW were only placed on the surface of the epicardium. Actually, the detected R wave amplitude is the average potential of the attached cells. It is assumed that the larger electrode may detect potentials from cells with different levels of depolarization, which results in a smaller R wave amplitude. However, it is not clear why the R wave amplitude became identical after POD 2. The sensitivity of the electrode might be decreased after exposure to fluid and reactive tissue.
In the novel TEPW, the lead was bonded to the film and sandwiched between the laminated honeycomb-patterned and the cast films. Removal of the wires is affected by the degradation of those films as well as the loosening of the bonding between films. In the samples used in this study, all lead wires were stable during the experiment. However, our preliminary study showed that we could remove this TEPW without traction even on the day after the operation. Therefore the strength of the bonding method and the rate of degradation should be further optimized to secure the lead wire at the myocardium.
The biodegradable film fabricated by poly(L-lactide-co--caprolactone) and Poly(L-lactide-co-glycolide) is absorbed by a hydrolysis reaction, which produces a hydroxylic acid monomer. Therefore, it is important to check for possible effects of the degraded material, such as an inflammatory reaction on the surrounding tissue. In this study we performed echocardiography to evaluate pericardial thickness and peak atrial systolic velocity/peak early diastolic velocity ratio of mitral flow for estimation of diastolic function, both preoperatively and postoperatively. We did not detect any sign of inflammation or cardiac dysfunction for at least 1 month after surgery. In fact, the films did not induce any severe inflammatory reaction histologically for 1 month after implantation in the back of rats (data not shown). In addition, the films were absorbed completely 6 months after implantation. In some animals used in this study, the film was left on the myocardium for more than 1 year without any significant complication. However, further investigation is required to confirm the safety of this material for a longer period.
If we encountered an adhered pericardium (ie, a redo case), there was not enough space to secure the TEPW electrode. Moreover, the threshold of sensing or pacing may be increased by scar tissue that covered the surface of the heart. However in this study there was no difference between a redo and the normal heart in terms of electrical performance.
We also checked for the atrial setting and found that the TEPW can also work when used for atrial pacing in a few cases. The films did not injure the atrial wall. Therefore this TEPW may be acceptable as an atrial temporary pacing wire. However, further study may be necessary for commercialization of the product.
In conclusion, the novel TEPW is promising because it is safe, feasible, and effective, providing satisfactory pacing and sensing performance at low thresholds with no complications.
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Disclosures and Freedom of Investigation
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Conventional temporary epicardial pacing wires (Medtronic 6492 heart wire [Medtronic Inc]) were purchased commercially at the regular market price in Japan. The biodegradable film with honeycomb structure and the electrode with this film were developed by our group. The patents for the film and electrode are pending (patent no. WO2004-089434 and no. 2005-124840). The authors had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report.
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Disclaimer
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The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
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Acknowledgments
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We thank Masatsugu Shimomura, PhD, Hisao Moriya, Yosuke Murase, MD, Aika Yamawaki, Taeko Komada, and A.C.T. Ltd for their scientific and technical support.
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References
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Abstract
Introduction
