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Ann Thorac Surg 1997;63:477-481
© 1997 The Society of Thoracic Surgeons
Department of Cardiothoracic Surgery, Faculty of Medicine, University of Tokyo, Tokyo, Japan
Accepted for publication September 13, 1996.
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentReferences |
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Methods. Cardiomyoplasty by thoracoscopy and by the open method through a thoracotomy was performed in dogs. After 8 to 10 weeks of preconditioning, the hemodynamic effect of burst stimulation was measured.
Results. Cardiomyoplasty by thoracoscopy took 90 ± 21 minutes (mean ± standard deviation), whereas cardiomyoplasty by the open method took 67 ± 10 minutes (p < 0.05). As a result of burst stimulation, aortic pressure, descending aortic flow, and left atrial pressure increased by 15.1% ± 6.5%, 8.6% ± 6.3%, and 3.8% ± 4.6%, respectively, in the dogs that received the cardiomyoplasty by thoracoscopy, whereas those indices increased by 16.5% ± 6.9%, 9.8% ± 5.9%, and 4.8% ± 4.2%, respectively, in dogs that received cardiomyoplasty by the open method. No significant difference between the two groups was shown in any index.
Conclusions. Cardiomyoplasty by thoracoscopy was technically practical, and its hemodynamic effect was similar to that of the open method. The feasibility of cardiomyoplasty by thoracoscopy was thereby suggested.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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Cardiomyoplasty has been performed worldwide following the method described by Carpentier and associates [2]. A patient is placed in the right lateral position while the latissimus dorsi muscle flap (LD) is mobilized through a left flank incision. Then, the patient's position is changed to the supine position and the LD is wrapped around the heart through a median sternotomy. Because a wound retractor is applied to spread the sternal incision, distortion of the pericardium may occur while the LD is being wrapped, which leads to distorted fixation of the LD. By using a thoracoscopic operation, cardiomyoplasty can be completed through a left flank incision without spreading a sternotomy incision. As a result, bleeding, wound pain, and thereby surgical stress will be reduced, and distortion of the pericardium, which may lead to improper fixation of the LD, will be avoided.
On the other hand, thoracoscopic cardiomyoplasty has some drawbacks. The pulmonary vascular resistance may increase due to unilateral ventilation, resulting in deterioration of the right heart failure. Accidental bleeding, which is generally acknowledged as a significant problem of thoracoscopic operations, is unlikely to happen in a cardiomyoplasty procedure.
We conducted this experimental study to investigate the feasibility of cardiomyoplasty by thoracoscopy (thoracoscopic cardiomyoplasty). Our major concerns were (1) whether thoracoscopic cardiomyoplasty was technically practical, (2) whether thoracoscopy compromised postoperative recovery, and (3) whether thoracoscopy attenuated the hemodynamic effect of cardiomyoplasty.
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Material and Methods |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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Technique of Thoracoscopic Cardiomyoplasty
Each dog was anesthetized with intravenous pentobarbital (20 mg/kg), mechanically ventilated through an endotracheal tube, and placed in the right lateral position. The left LD was mobilized, care being taken to preserve the thoracodorsal neurovascular pedicle. Two temporary epicardial pacing leads (6500; Medtronic, Kerkrade, Holland) were sutured to the LD. The left second rib was partly resected and a window was made through which the LD could be introduced into the left thoracic cavity. Three to four thoracostomies were made at the left fifth to seventh intercostal spaces. A rigid 30-degree angulated scope (A5288 OES Telescope 30°; Olympus Optical Co Ltd, Tokyo, Japan) and operating instruments were inserted into the thoracic cavity through 14-mm trocars placed in the thoracostomies or directly through the thoracostomies.
The lung was compressed by placing a lung retractor through the window at the second rib to visualize the pericardium. The pericardium was opened vertically, and seven to eight 2-0 braided polyester sutures were stitched in the pericardium near the atrioventricular groove and the origin of the pulmonary artery under thoracoscopy to fix the LD around the heart, following a modification of the technique described by Carpentier and associates [3] (Figs 1, 2A
). To expose the area for the next pericardial stitches, the sutures already stitched were pulled in desired directions by using a newly developed device that we named the "thread retriever" (Fig 3).
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). Every suture was kept loosened so that the LD could be passed through the window. The LD was then introduced into the left thoracic cavity through the window, and the humeral insertion of the LD was anchored to the periosteum of the first rib (Fig 2C). The LD was then wrapped around the heart and every suture was tied under thoracoscopy (Fig 2D). The pacing leads were connected to a cardiac pacemaker (model 8402; Medtronic Inc, Minneapolis, MN), which was placed under the left anterior serratus muscle. The wound was closed, and the animal was allowed to recover.
Technique of Cardiomyoplasty by Left Thoracotomy
General anesthesia was induced, the left LD was mobilized, and pacing wires were sutured as described above. A left thoracotomy was made at the fifth intercostal space. The LD was introduced into the thoracic cavity through a window made at the second rib. The pericardium was opened, and the LD was wrapped around the heart in the clockwise fashion and fixed to the pericardium using seven to eight sutures under direct vision. The rest of the procedure was the same as that in thoracoscopic cardiomyoplasty.
Experimental Design
We defined the duration of LD wrapping as the period from the end of the LD mobilization to skin closure. The duration of LD wrapping, surgical mortality, and surgical morbidity were compared between the thoracoscopy group and the control group.
In the 12 dogs, electrical stimulation of the LD was started immediately after the operation with a single-pulse stimulus (rate, 60 min-1; pulse width, 0.2 ms; pulse amplitude, 5 V) to attain fatigue resistance. After 8 to 10 weeks of electrical stimulation, each dog was anesthetized again, and left thoracotomy was performed. Left atrial and aortic pressures were measured by fluid-filled transducers (Cobe, Lakewood, CO). Blood flow in the descending thoracic aorta was measured by a Doppler flow meter (T201; Transonic Systems, Ithaca, NY).
Propranolol (3 mg/kg) was infused intravenously to induce temporary heart failure. A mannitol solution of 20% concentration was infused to increase left atrial pressure to 18 mm Hg. A temporary transvenous lead (Bi-pacing-cath 1124-13; Vygon, Aacheon, Germany) was inserted in the right ventricle via the pulmonary artery for cardiac sensing. Pacing and sensing leads were connected to an electrical stimulator (Fukuda Denshi, Tokyo, Japan) that was programmed to deliver burst pulses (burst frequency, 50 Hz; burst duration, 150 ms; pulse width, 0.2 ms; voltage, 10 V; synchronization delay, 20 to 100 ms) at a rate of 1:2 in synchrony with the native heart beat. Although burst frequencies of 25 Hz, 30 Hz, and 33 Hz stimulation were used in the majority of experimental studies, we adopted 50 Hz stimulation in this study because we could not demonstrate significant hemodynamic improvement with a burst frequency slower than 50 Hz in the former studies done in our laboratory. Mean left atrial pressure, peak systolic aortic pressure, and flow in the descending thoracic aorta were measured, and the average values of each measurement taken during the five heart beats before heart failure induction, after heart failure induction, and 1 minute after the start of LD stimulation were recorded. The hemodynamic effect of LD stimulation was compared between the two groups.
The dogs were euthanized after the hemodynamic measurements, and had autopsies. The heart-muscle complex, excised en bloc, was macroscopically observed.
Statistical Analysis
Statistical analysis was performed by the paired and unpaired Student's t test where appropriate. Statistical significance was set at a p value of less than 0.05. All data are expressed as the mean ± the standard deviation.
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Results |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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Pharmacologic heart failure induced by propranolol and mannitol resulted in a significant decrease in aortic pressure (p < 0.05), a significant decrease in descending aortic flow (p < 0.01), and a significant increase in left atrial pressure (p < 0.01) in both groups. Electrical burst stimulation of the LD resulted in a significant increase in aortic pressure (p < 0.01), a significant increase in descending aortic flow (p < 0.01), and an increase in left atrial pressure, which was not significant in the thoracoscopy group (thoracoscopy group, p > 0.05; control group, p < 0.05). No significant differences were shown in hemodynamic indices between the two groups before heart failure induction, after heart failure induction, or during LD stimulation (Table 1).
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Comment |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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In clinical open chest cardiomyoplasty, an epicardial electrode is implanted for the R-wave synchronization. Clinical cases of endoscopic implantation of epicardial electrodes have already been reported [4]. Although we did not implant epicardial electrodes in the initial operations, we assume that implantation of epicardial electrodes can be done by thoracoscopy. Meanwhile, the use of transvenous endocardial leads would be convenient and perhaps preferable in thoracoscopic cardiomyoplasty because it precludes tangling of epicardial sensing leads with all the sutures being placed and pulled.
Latissimus dorsi muscle wrapping in the thoracoscopy group took 23 minutes longer than in the control group. However, clinical thoracoscopic cardiomyoplasty will not necessarily take longer than does the conventional cardiomyoplasty method because it takes more than 23 minutes to open and close a median sternotomy in adult patients.
The mortality and morbidity rates of the thoracoscopy group were not greater than those of the control group. The animals seemed to recover similarly in both groups. These findings show that thoracoscopy did not complicate postoperative recovery.
Many experimental heart failure models exist such as propranolol infusion, doxorubicin infusion, coronary ligation, microsphere infusion into the coronary arteries, and rapid cardiac pacing [5]. However, a representative dilated cardiomyoplasty model in a large animal suitable for experimental cardiomyoplasty has not yet been established. Because one of our concerns was postoperative recovery, we preferred not to induce chronic heart failure, which may alter the postoperative course. Although propranolol infusion is an easy and reliable method of acute heart failure induction, 3 mg/kg body weight of propranolol reportedly decreased cardiac output to 30% of the control value [6]. Such a hemodynamic state should be regarded as cardiogenic shock rather than congestive heart failure. Congestive heart failure is characterized by fluid retention; we therefore decided to infuse mannitol to achieve a more clinically realistic heart failure model.
No significant differences in changes of hemodynamic indices by LD stimulation were shown between the thoracoscopy group and the control group. The conformational muscle adaptability may be a primary reason why such similar hemodynamic effects were obtained by such different procedures [7]. Latissimus dorsi muscle stimulation increased the left atrial pressure in the present study, possibly because LD contraction compressed the left atrium. If measurements had been carried out after chronic burst stimulation, the left atrial pressure may have been decreased because of renal feedback. However, it is too early to speculate on the clinical effectiveness of thoracoscopic cardiomyoplasty, because not only the beat-to-beat hemodynamic effect, the so-called squeezing effect that we assessed in this study, but also several other mechanisms such as the sparing effect and the girdling effect influence clinical improvement of cardiomyoplasty [8].
The limitations of the present study are threefold. First, the technical difficulty of cardiomyoplasty in clinical patients could not be assessed completely. The wide human thoracic cavity offers sufficient space of maneuvering, and this is advantageous in performing thoracoscopic cardiomyoplasty. However, the wide mediastinal tissue of humans and cardiomegaly in patients with heart failure may hinder visibility and maneuverability. Second, the importance of the problem of right heart failure deterioration as a result of unilateral ventilation was not tested. Finally, the hypothesis concerning distorted and improper wrapping of the LD by pericardial distortion was not tested.
In conclusion, cardiomyoplasty by thoracoscopy was found to be technically practical, seemed not to complicate postoperative recovery, and had similar hemodynamic effects as compared with the conventional open method in this experimental animal study. The feasibility of thoracoscopic cardiomyoplasty was supported by our results.
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Footnotes |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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References |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentReferences |
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This article has been cited by other articles:
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  H. Inaba, Y. Kaneko, T. Ohtsuka, M. Ezure, K. Tanaka, K. Ueno, and S. Takamoto Minimal damage during endoscopic latissimus dorsi muscle mobilization with the harmonic scalpel Ann. Thorac. Surg., May 1, 2000; 69(5): 1399 - 1401. [Abstract] [Full Text] [PDF]
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