Eur J Cardiothorac Surg 1999;16:S119-S125
© 1999 Elsevier Science NL
Is there a future for minimally invasive cardiac surgery?
Michael J. Mack*
Cardiopulmonary Research Science And Technology Institute, Suite B 206, 7777 Forest Lane, Dallas, TX 75230, USA
* Tel.: +1-972-566-3929; fax: +1-972-566-3915
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Abstract
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Although cardiac surgery has made significant contributions to the cardiac health of millions of patients over the past 40 years, it has evolved from an ‘emerging growth' to a ‘mature' industry. Along with this maturation has come an ‘inertia of success' and lack of innovation. Minimally invasive cardiac surgery is an attempt to develop more patient friendly cardiac procedures yet maintain the superior long term results of conventional cardiac surgery. A broad spectrum of new surgical techniques and technical innovations has been fostered. The impact has been not only that of ‘discontinuous innovation' of a new type of cardiac surgery but also a significant ‘coat-tail' effect of ‘upgrading' conventional cardiac surgery. It is difficult to adapt to change. But if we maintain an open-mindedness toward evolution with a firm foundation in proven standards, our patients will be the beneficiaries.
Key Words: Coronary artery bypass grafting • Minimally invasive coronary bypass • MIDCAB • Robotics
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1. Why do we change a good operation?
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The question – Is there a future for minimally invasive cardiac surgery? – should more appropriately be asked – Is there a future for cardiac surgery without minimally invasive cardiac surgery? In his article entitled, ‘Cardiac Surgery in the Twenty-First Century' [1] Robert W. Anderson examines the development of cardiac surgery over the past four decades and makes a strong case that cardiac surgery when viewed as an industry has evolved from an early emerging industry phase to a mature industry. In an arena in which there is competition with other methods of coronary revascularization for a fixed amount of available resources, the competition becomes a zero sum game. Therefore, in order to successfully compete, one has to have an open mindedness toward change.
The characteristics of an emerging industry phase include:
- 1. Technological innovation.
- 2. Economic subsidization (fee for service), government reimbursement.
- 3. Protection from free market pricing.
- 4. Increased prices despite increased volume.
- 5. A monopoly.
What caused cardiac surgery to transition from an emerging to a mature industry included:
- 1. Competition – the advent of catheter-based procedures for the treatment of revascularization ended the monopoly.
- 2. Loss of subsidy through managed care delivery.
- 3. There were no technological breakthroughs on the horizon.
Faced with these facts, cardiac surgery became a mature industry. When Anderson's article was published in 1997, he stated, ‘Cardiac surgery appears to be reaching this point, and there appears to be no revolutionary breakthroughs or subsidies on the horizon that will reestablish it as an emerging and rapid growth area in this country.' The transition to maturity signals important changes in the competitive environment, including competition for market share, greater emphasis on cost and service, over capacity in facilities and personnel, changes in methods of providing service and market pricing, falling profits and decreased subsidization.
In an editorial responding to critics of minimally invasive cardiac surgery, entitled ‘Cardiac Surgery of the 1990s: the ‘Inertia of Success' ' [2], we stated that, although conventional coronary bypass surgery has been a good operation for the past 30 years and contributed to the health of millions of patients, innovation, for the most part had stopped. Although there were some advances, including better myocardial protection, more friendly oxygenators and greater use of arterial conduits to prolong longevity, these were merely upgrades of basically a specialty that was not re-inventing itself. As evidence of this, one can look at the frequency of procedures being performed for coronary revascularization. Catheter-based procedures, which were initiated in 1979, took a mere 10 years to surpass cardiac surgical procedures in the number of procedures performed. The latest results in 1998 show that twice the number of catheter-based procedures are performed worldwide (1 500 000) compared with coronary bypass procedures (750 000) (Fig. 1). In the above-mentioned editorial, the authors closed by asking that for our specialties to survive and flourish in these rapidly changing times, we must have the courage to embrace change and continually re-invent ourselves and our practices. We must not become stagnant by the inertia of our past success and fail to grasp the opportunity for change.
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2. How do we change?
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There are a number of lessons to be learned from our cardiology colleagues. First, less invasive is better than more invasive. Although that should be intuitively obvious, cardiac surgeons continually ‘beat the drum' of complete revascularization by standard techniques with no open mindedness toward compromise. The facts are, however, that patients will accept a less optimal result if the procedure is less invasive. Current catheter-based results show better procedure mortality, morbidity and success rates compared with coronary bypass procedures. However, the need for repeat target vessel revascularization at 1 year is consistently 4–5 times higher with angioplasty and stenting than it is with conventional bypass surgery [3,4]. Yet, patients accept this over and over again. They are willing to accept a less optimal result in order to avoid the mortality and morbidity of bypass surgery.
In a recent editorial, [5] Cornelius Borst questioned the assessment that Bonchek and Ullyot expressed in an earlier editorial [6] regarding the ill-guided attempts to deviate from the conventional revascularization procedure that is ‘safe, effective, durable, reproducible, complete, versatile and teachable.' Borst specifically questions whether the ‘excellent results' of conventional bypass surgery really are optimal and, indeed, acceptable and whether, in fact, minimally invasive coronary bypass surgery is an attempt to develop a ‘minimal-adverse-effects' approach. The complications of conventional bypass surgery from Borst's editorial are listed in Table 1
. Borst makes the case that careful exploration in small incremental steps into less invasiveness should be encouraged and a fruitful endeavor to develop a more patient friendly procedure. He states ‘... that one ought not to be deterred from searching for solutions to great technical and surgical challenges if so much is ultimately to be gained for so many patients.'
Robert Kennedy stated ‘Progress is a nice word, but change is its motivator, and change has its enemies.' Not unexpectedly, those who value the status quo have been critical of the attempts to change conventional cardiac surgery. But indeed, change has occurred, and the concerns of the critics are rapidly being answered.
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3. MIDCAB
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Table 2
contains the published results of early angiographic patency of the left internal mammary artery to the left anterior descending performed by conventional cardiac procedures. This is to be compared with Table 3
which documents the published series of early angiographic results performed after minimally invasive direct coronary artery bypass grafting (MIDCAB) procedures [7]. Even at this early stage of evolution, the results of a MIDCAB procedure appear comparable to those of established conventional bypass surgery.
At the current time, the MIDCAB procedure appears to have found its niche in the management of coronary revascularization. In 1998, it is estimated that approximately 7% of all coronary bypass operations performed worldwide were performed by a beating-heart approach. Of these beating-heart procedures, approximately 10% (44 000) appear to be MIDCAB procedures. The narrow niche which the MIDCAB procedure seems to have found is for a number of reasons:- 1. It is applicable, for the most part, to only single vessel disease on the anterior surface of the heart.
- 2. Competition from the wider use of improved catheter-based techniques and stents limits its application.
- 3. The ability to perform a beating-heart anastomosis through a limited access incision has proved a formidable challenge for a many surgeons.
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4. OPCAB
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For these reasons, minimally invasive cardiac surgery appears to have evolved to off-pump beating-heart surgery performed through a median sternotomy approach or OPCAB procedure (off-pump coronary artery bypass grafting). The reason for wider acceptance of OPCAB compared with MIDCAB procedures includes:- 1. the ability to address multi-vessel disease;
- 2. greater surgeon friendliness by utilizing a wide access approach with less concern if conversion is necessary;
- 3. improved technology including second generation stabilizers;
- 4. new techniques that allow access to the posterior circulation of the heart without significant hemodynamic compromise (Fig. 2).
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Fig. 2. Position of the heart for off-pump surgery with the apex out of the chest to access the posterior circulation.
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For all these reasons, OPCAB procedures for coronary bypass grafting are rapidly evolving. In many centers in Europe and in the United States, greater than 90% of all coronary bypass grafting is now performed by OPCAB techniques. The current published results of OPCAB procedures are listed in Table 4
. Although no series documents on a randomized basis the benefits of OPCAB versus conventional coronary bypass procedures, with the rapid evolution of these techniques, those results should be forthcoming quickly.
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5. Port access coronary artery bypass surgery
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There has been extensive debate in the early stages of minimally invasive coronary surgery over which is more advantageous: to eliminate cardiopulmonary bypass or to eliminate the median sternotomy incision and perform coronary bypass grafting through a limited access incision on an arrested heart (Port Access surgery). Although numerous published series exist attesting to the ability to perform multi-vessel coronary bypass grafting through limited access, the field of minimally invasive surgery has more widely adopted the beating heart approach performed through limited or wide access incisions [8]. Numerous refinements to the Heartport platform, including direct thoracic cannulation, thereby eliminating concerns about retrograde dissection and embolization from femoral artery cannulation, as well as further upgrades, including changing the shape of the balloon, promise to make Port Access surgery more user friendly and potentially adaptable to a wider number of patients.
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6. The tools of change – new enabling technology
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Technology continues to evolve and continues to expand the applicability of minimally invasive cardiac surgery, but also improves conventional surgical techniques. Indeed, one of the more significant contributions of minimally invasive surgery may be the ‘coat-tail effect' that is conveyed to conventional bypass surgery. After many years of minimal technological innovation to make conventional bypass surgery on an arrested heart more patient friendly, there is a plethora of new technology that attempts to eliminate the undesirable adverse effects of conventional bypass surgery. Some of these include new materials and oxygenators that cause less systemic inflammatory response. Other ingenious technology includes arterial aortic filters to trap and, hopefully, eliminate the potential for atherosclerotic cerebral emboli from the ascending aorta, (Fig. 3) a known cause of major morbidity with conventional surgical techniques [9]. If the adverse neurological sequelae can be minimized by such innovation, conventional bypass surgery becomes more patient friendly.
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Fig. 3. Aortic filtration device for ‘trapping' atherosclerotic debris with potential for cerebral embolization.
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Another significant area of interest is circulatory assistance for off-pump beating-heart surgery. A number of axial flow micropumps have been developed that allow univentricular or biventricular assist support without the need for artificial oxygenation. The principle behind these circulatory support systems is that by eliminating the oxygenator from cardiopulmonary bypass, the major component inducing the systemic inflammatory response is eliminated. Although significant interest exists in support of the left side of the heart, more intriguing is interest in support of the right side. The impairment of systemic circulatory hemodynamics during cardiac positioning to access the posterior circulation during OPCAB procedures appears to be due in large part to right-sided compromise rather than solely left-sided compromise. With the institution of circulatory support on the right side, some degree of circulatory support appears to be offered, yet minimizing the adverse systemic inflammatory response associated with conventional bypass surgery and avoiding cannulation of the arterial circulation which further minimizes the potential for adverse effects, including dissection (Fig. 4).
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7. Endoscopic coronary artery bypass surgery
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The ability to perform coronary bypass surgery by a totally endoscopic approach is a formidable challenge which is being addressed in numerous centers with varying technology and techniques. There has been an intense interest in the field of robotics to facilitate endoscopic coronary bypass surgery. The principle underlying role of robotics for coronary bypass surgery is that the introduction of ‘computer assistance' with robotics allows the enhanced precision necessary for an endoscopic vascular anastomosis to be performed. The challenges of limited access procedures performed totally with video assistance with long instrumentation through a chest wall has proved to be a daunting challenge. Robotics offers the benefits of scaled motion, tremor filtration and remote telemanipulation which, hopefully, by allowing more precise movements, will make a totally endoscopic anastomosis more practical [10]. Two currently available robotics systems are the Intuitive system, (Intuitive Surgical, Mountain Viewm CA), (Fig. 5) and the Zeus system (Computer Motion, Goleta, CA) (Fig. 6). There have been at least 250 robotically assisted operations performed worldwide among of which 80 have been cardiac procedures (Intuitive Surgical Systems, pers. commun.). The cardiac procedures performed using robotic or computer assistance include internal mammary artery harvest, atrial septal defect repair, mitral valve repair, and coronary artery bypass grafting. Although the safety and feasibility have been demonstrated in early clinical studies [11], the ultimate ability to develop a procedure that is adaptable enough for broad usage remains to be defined. Over the next 5 years, continuing evolution in this technology will, hopefully, allow true minimally invasive coronary bypass grafting to be performed by a totally endoscopic approach. In the quest for endoscopic coronary bypass surgery, visualization is paramount. The ability to perform a microvascular anastomosis using two-dimensional visualization has been problematic. Recently, state-of-the-art three-dimensional visualization with resolution comparable to threechip 2D systems have been introduced. It is hoped that these three-dimensional systems will prove to be further enabling technology that will lead contribute significantly toward the path to totally endoscopic surgery.
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8. Alternative methods of coronary revascularizaton
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There are numerous various alternative methods of myocardial revascularization have been developed and implemented by a minimally invasive approach. Transmyocardial laser revascularization (TMR) has recently been shown to relieve angina in patients with Class IV angina who are not candidates for more conventional techniques [12]. The technique involves drilling multiple holes in an area of ischemic myocardium that does not have an adequate target vessel for revascularization. This technique has been performed by a totally endoscopic approach, as well as a catheter-based approach [13], and it is anticipated that a minimally invasive approach will become the access of choice for TMR when performed as stand-alone therapy.
Recent interest in coronary revascularization by the administration of genes or gene products that induce angiogenesis in ischemic myocardium has received an intense area of interest. Numerous delivery systems which are adaptable to minimally invasive techniques in a totally endoscopic approach are being developed. If gene therapy ultimately proves to be effective management for coronary artery disease, the optimal mechanism of delivery, whether by epicardial or endocardial injection or transcoronary delivery, remains to be defined. Minimally invasive surgical approaches appear to be inviting for the administration of gene therapy.
There is intense interest in direct myocardial revascularization in which new channels are open directly between the left ventricle and the coronary arterial system, the coronary sinus or coronary veins. These procedures are all in an early ‘proof of concept' stages with hopes of opening up a whole new area of myocardial revascularization to minimally invasive approaches.
The concept of combining minimally invasive cardiac surgical procedures with catheter-based approaches thereby achieving a synergistic therapeutic effect has been an intriguing one. The logic of this approach is that by combining the superior long term results of a left internal mammary artery placed to the left anterior descending by a minimally invasive procedure and combining that with a catheter-based procedure for other vessels of circulation, that an optimal procedure would be developed. Although numerous published series exist, the experience is overwhelmingly small [14] and early experience indicates that this may not have widespread application.
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9. Where is this change leading us?
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As cardiac surgeons are in a competitive field with other practitioners of coronary revascularization, it behooves surgeons to know the results of competitive strategies. For example, although the mortality and morbidity of catheter-based intervention is equal to or less than cardiac surgery, the need for repeat target vessel revascularization, even in optimal patients, remains 4–5 times higher with catheter-based therapy than surgery, even in the best of series [3,4]. In addition, as catheter-based therapy becomes more complex with the use of multiple stents per procedure and with the use of expensive 2b/3a agents and the need for repeat target vessel revascularization, cardiac surgery, especially when performed by a minimally invasive approach may become the most cost effective treatment for coronary vascular disease. The cost of surgical conduits (arteries and veins) compares favorably with those stents (0 vs. $1500). A careful cost analysis along the trend toward less invasive surgery, not only can we survive by better long-term results, but also less expensive therapy.
However, one must be open and ready to adapt what is best from other fields. The specialty of cardiac surgery will, in all likelihood, ‘morph' into a unified field of cardiac intervention. As cardiac surgery becomes less invasive and cardiology becomes more invasive, in all likelihood, both specialties will evolve into one in which a ‘cardiac interventional physician' will have the ability to perform catheter-based techniques along with surgical intervention. This ability to deliver multi-modality cardiac interventional therapy will, in all likelihood, define the cardiac revascularization specialist of the next decade.
Is there a future for minimally invasive cardiac surgery? Indeed, there is not only a future, but a bright and promising one as the specialty of cardiac surgery has been rejuvenated and redefined by minimally invasive techniques. It will not only survive, but will thrive. By learning from our past and accepting the proven standard of the past 40 years but with open-mindedness to change and evolution, the end product of our endeavors will be better patient care.
‘To exist is to change, to change is to mature, to mature is to go on creating one's self endlessly.' Henri Bergson
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Footnotes
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Presented at the International Symposium ‘Present State of Minimally Invasive Cardiac Surgery – Meet The Experts', Dresden, Germany, December 3–5, 1998.
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References
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- Anderson RW. Cardiac surgery in the 21st century. Ann Thorac Surg 1997;64:1575-1578.
- Mack M, Damiano R, Matheny R, Reichenspurner H, Carpentier A. ‘The Inertia of Success' a response to minimally invasive coronary bypass, a dissenting opinion. Circulation 1999;99:1404-1406.[Free Full Text]
- Pocock SJ, Henderson RA, Rickards AF, et al. Meta-analysis of randomized trials comparing coronary angioplasty with bypass surgery. Lancet 1995;346:1184-1189.[Medline]
- Hannon EL, Racz MJ, McCallister BD, Ryan TJ, et al. A comparison of three-year survival after coronary artery bypass graft surgery and percutaneous transluminal coronary angioplasty. J Am Coll Cardiol 1999;33(1):63-72.[Abstract/Free Full Text]
- Borst C, Grundeman PF. Minimally invasive coronary artery bypass grafting: an experimental perspective. Circulation 1999;99(11):1400-1403.[Free Full Text]
- Bonchek LI, Ullyot DJ. Minimally invasive coronary bypass: a dissenting opinion. Circulation 1998;98:495-497.[Free Full Text]
- Mack MJ, Osborne JA, Shennib H. Arterial graft patency in coronary artery bypass grafting: what do we really know?. Ann Thorac Surg 1998;66(3):1055-1059.[Abstract/Free Full Text]
- Reichenspurner H, Boehm DH, Welz A, et al. Minimally invasive coronary artery bypass grafting: Port-access approach versus off-pump techniques. Ann Thorac Surg 1998;66:1036-1040.[Abstract/Free Full Text]
- Reichenspurner HH, Navia J, Berry GJ, Robbins RC, Gold JP, Reichart B. Emboli management with a novel aortic filtration system: histopathological confirmation of atheromatous plaque capture in cardiac surgery. J Thorac Cardiovasc Surg 1999;in press.
- Stephenson Jr ER, Sankholkar S, Ducko CT, Damiano Jr RJ. Successful endoscopic coronary artery bypass grafting: an acute large animal trial. J Thorac Cardiovasc Surg 1998;116:131-138.[Abstract/Free Full Text]
- Reichenspurner H, Damiano R, Mack M, Bohm D, et al. Experimental and first clinical use of the voice-controlled and computer-assisted surgical system ZeusTM for endoscopic coronary artery bypass grafting. J Thorac Cardiovasc Surg 1999;118(1):11-16.[Abstract/Free Full Text]
- Allen KB, Delrossi AJ, Realyvasquez R, Lefrak EA, Dowling RD, et al. Transmyocardial revascularization combined with coronary artery bypass grafting versus bypass grafting alone: a prospective, randomized multi-center trial. J Thorac Cardiovasc Surg 1999;in press.
- Oesterle SN. Beyond stents: third generation coronary devices. Ann Thorac Surg 1998;66(3):1045-1049.[Abstract/Free Full Text]
- Riess FC, Schofer J, Kremer P, et al. Beating heart operations including hybrid revascularization: initial experiences. Ann Thorac Surg 1998;66:1076-1081.[Abstract/Free Full Text]
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Abstract
1. Why do we...
