Minimally invasive direct coronary artery bypass or MIDCAB is a relatively new procedure for coronary revascularization, which is performed through a limited incision. Under direct vision the technique allows performance of coronary artery bypass grafting on the beating heart without the use of cardiopulmonary bypass. Although the term MIDCAB has been used to describe a variety of operations including gastroepiploic artery to posterior descending coronary artery bypass as well as descending aortic to circumflex marginal coronary artery bypass grafting, the operation which is performed most frequently and has been studied extensively involves left internal mammary artery (LIMA) to left anterior descending coronary artery (LAD) grafting via a small left anterior thoracotomy. While various procedures may fit the definition of "MIDCAB", it is this procedure that has evolved into a reproducible and viable alternative for LAD revascularization. This discussion will be limited to the LIMA to LAD bypass through a small left anterior thoracotomy. The author urges caution when considering other more exotic "MIDCAB" procedures.

The MIDCAB operation has evolved from the initial report by Acuff ¹  into the relatively standardized procedure used by surgeons who perform large numbers of these operations today. Key technical aspects of the operation which must be followed include:

1.  Some means of postoperative pain control [preoperative intrathecal narcotic and postoperative ketorlac have worked well in our center]

2.  Harvest of the entire LIMA to the level of subclavian vein using any of the commercially available retractors designed for this purpose.

3.  Mechanical stabilization of the site of anastomosis which has been clearly shown to improve patency rates.⁵

4.  Provision of a bloodless field using a CO₂ blower and atraumatic target vessel occlusion or shunting.

5.  A means with which the surgeon is extremely comfortable to assess patency at the time of operation. Angiography remains the gold standard and can be performed in the operating room by the surgeon.³

Ultrasonic techniques can also be used by those experienced with these devices. The surgeon must be brutally honest since the success or failure of the entire operation is dependent upon a single anastomosis. A "conversion" should not be considered a complication and a conversion rate of  5 percent to 10 percent is probably the range necessary to assure success in all cases. A number of reports have published excellent graft patency rates when these guidelines are followed and these results are attainable by any skilled coronary surgeon. ^2,3

If one accepts that MIDCAB can be performed with comparable results to CABG, the burden of proving an advantage remains. Several benefits over standard CABG have been described. There is an economic advantage as the cost of the procedure is comparable to percutaneous therapies.² Decreased Intensive Care Unit and total hospital length of stay as well as decreased blood transfusion requirement, have also been shown.² Patient satisfaction is high as they may return to manual labor occupations after two to four weeks rather than the standard six to eight weeks after sternotomy. Furthermore, all of the complications associated with cardiopulmonary bypass (5) are avoided. Interestingly, validating that MIDCAB is superior to CABG for single vessel LAD bypass seems to be much more important to cardiac surgeons than it is to patients or cardiologists. Uniformly, patients are enthusiastic about "mini bypass" and are clearly willing to accept a higher risk of reintervention or a 10 percent risk of conversion in order to avoid a sternotomy. I have not experienced this same enthusiasm when offering off-pump CABG via sternotomy despite my best efforts to describe the advantages of avoiding the pump. Likewise cardiologists are generally supportive of MIDCAB. In each MIDCAB center, the number of single vessel LAD procedures increases dramatically, and not at the expense of decreased CABG procedures. To the referring cardiologist, MIDCAB is an intermediary between PTCA and CABG and herein may be its greatest advantage. There appears to be a significant number of relatively young and otherwise healthy patients with single vessel disease who refuse CABG or are deemed "not ready" for such a big operation. These people are readily referred for MIDCAB and may represent the cardiac surgeon’s last opportunity to intervene in the young and otherwise healthy patient population.

In mature MIDCAB centers, MIDCAB makes up approximately 10 percent of the coronary procedures performed and is clearly not going to eliminate or significantly impact upon multivessel CABG. This 10 percent of procedures does serve to bring the surgeon closer to the coronary stenter however, in terms of both economics and invasiveness. If cardiac surgery is to remain competitive with ever improving percutaneous interventions, we must continue to provide better and more long-lasting alternatives for our patients.

References

1.  Acuff TE, Landreneau RJ, Griffith BP, Mack, MJ. Minimally Invasive Coronary Artery Bypass Grafting. Annals of Thoracic Surgery. 1996;61:135-7.

2.  Doty JR, Fonger JD, Nicholson CF, Sussman MS, Salomon NW. Cost Analysis of Current Therapies for Limited Coronary Artery Revascularization. Circulation. 1997;96(Suppl):II-18 – II-20

3.  Elbeery JR, Chitwood WR. Intraoperative Catheterization of the Left Internal Mammary Artery via the Left Radial Artery. Annals of Thoracic Surgery. 1997;64:1840-2

4.  Roach GW, Kanchuger M, Mangano CM, et al. Adverse Cerebral Outcomes after Coronary Bypass Surgery. N Engl J Med. 1996;335:1857-63

5.  Subramanian VA, Sani G, Bennetti FJ, Calafiore AM. Minimally Invasive Coronary Bypass Surgery: A Multi-Center Report of Preliminary Clinical Experience. Circulation. 1995;92(Suppl):1645

6.  Subramanian VA. Less Invasive Arterial CABG on a Beating Heart. Annals of Thoracic Surgerty. 1997;63:S68-71

7.  Zenati M, Domit TM, Saul M, Gorcsan III J, Katz WE, Hudson M, Courcoulas AP, Griffith BP. Resource Utilization for Minimally Invasive Direct and Standard Coronary Artery Bypass Grafting. Annals of Thoracic Surgery. 1997;63:S84-7.

Minimally invasive coronary artery surgery is being applied to treat a wider range of coronary lesions in a more diverse patient population. Newer techniques and instrumentation now allow grafting of all coronary distributions, and multiple variations are being implemented in the search for the least traumatic and most reproducible approach, including minimally invasive direct coronary artery bypass (MIDCAB), port-access with cardiopulmonary bypass, and full or partial sternotomy without cardiopulmonary bypass. Early encouraging results have been reported by several authors using all of these techniques. ^{1,3,4,5,9,19,20}

MIDCAB techniques were originally developed to treat single vessel coronary disease in patients who were considered to be at high risk for conventional coronary artery bypass (CAB) surgery. The smaller incisions, elimination of cardiopulmonary bypass, avoidance of great vessel or existing graft manipulation, and use of arterial conduits are all thought to be advantageous for patients in which conventional cardiac surgery might represent an inordinate risk. Minimally invasive coronary surgery allows a more rapid postoperative recovery and reduces some of the complications associated with traditional CAB.

Experience with MIDCAB grafting with several different arterial conduits continues to accumulate. This three-year analysis demonstrates that minimally invasive techniques can result in more rapid recovery and lower costs when compared to conventional CAB surgery. When used in carefully selected patients, MIDCAB grafting can reduce some of the morbidity associated with conventional CAB surgery. Certain risk factors, however, remain formidable, and high-risk patients must be carefully evaluated in order to provide the optimum therapy. Long-term outcomes to assess graft patency and need for reintervention are essential to completely evaluate the value of the MIDCAB approach.

Patient Selection

Patients were selected who had significant coronary artery stenosis (>50 percent angiographic narrowing) limited to a single coronary distribution. All patients had symptoms refractory to medical therapy, including catheter-based interventions. Patients were not excluded on the basis of age, functional status, presence of functional grafts to other areas of the heart, or other preoperative risk factors such as previous stroke or myocardial infarction.

Patients undergoing MIDCAB surgery had the anastomosis created under direct vision using local coronary occlusion and partial heparinization on the non-arrested heart. The anastomotic site was stabilized using a hand-held right angle clamp without mechanical stabilizing devices.

Methods

From May 1994, to October 1997, 278 patients underwent single vessel bypass grafting by one of five operative approaches. Two hundred thirty-nine patients underwent MIDCAB grafting, including 146 patients with left or right internal mammary artery (MIDCAB-IMA), 70 patients with right gastroepiploic artery (MIDCAB-GEA), and 23 patients with saphenous vein or radial artery via left thoracotomy (MIDCAB-THOR). These groups were compared to 12 patients with single vessel grafting via sternotomy without cardiopulmonary bypass (STERN-OFF CPB) and 27 patients with single vessel grafting via sternotomy on cardiopulmonary bypass (STERN-CONV). All patients were analyzed for outcomes after surgery, including conversion to conventional CAB, mortality, length of stay, and subsequent recatheterization and reintervention. Hospital charges, including room and board and operating room charges, were collected for each patient.

Results

Thirty-day mortality for MIDCAB-IMA was 3.4 percent, MIDCAB-GEA 8.6 percent, MIDCAB-THOR 8.7 percent, STERN-OFF CPB 0.0 percent, and STERN-CONV 3.7 percent (p - NS) (Table I). Mean overall postoperative length of stay was 2.5 days for all MIDCAB patients and 4.0 days for STERN-CONV patients (p = 0.006). Three (2.1 percent) MIDCAB-IMA patients, four (5.7 percent) MIDCAB-GEA patients, one (4.3 percent) MIDCAB-THOR, one (8.3 percent) STERN-OFF CPB, and one (3.7 percent) STERN-CONV patients required reintervention to the graft within 30 days of operation (p = NS) (Table II). Overall hospital charges were less for the MIDCAB-IMA and MIDCAB-GEA groups but more for the MIDCAB-THOR group compared to the STERN-CONV group, generally reflecting the length of stay (p < 0.05 for all groups). Operating room charges were less for the MIDCAB-IMA and MIDCAB-GEA groups compared to the STERN-CONV group, mainly due to the absence of disposable perfusion supplies (p < 0.05 for both groups) (Table III).

Conclusion

The higher incidence of mortality, morbidity, and reintervention in the MIDCAB groups reflects the impact of patient co-morbidities in high-risk patients (Table IV) as well as early experience with rudimentary instrumentation and techniques. MIDCAB grafting has and will continue to have significant applicability in the future, but appropriate patient selection guidelines need to be established. Technologic advances are ongoing and have already improved results. Long-term outcomes for graft patency and reintervention are necessary to completely

evaluate the value of the MIDCAB approach. Rigorous patient follow-up is essential for accurate comparison with existing techniques.
 

References

1.  Acuff TE, Landreneau RJ, Griffith BP, Mack MJ. Minimally invasive coronary artery bypass grafting. Annals of Thoracic Surgery. 1996;61:135-7.

2.  Allen KB, Matheny RG, Robison RJ, Heimansohn DA, Shaar CJ. Minimally invasive versus conventional reoperative coronary artery bypass. Annals of Thoracic Surgery. 1997;64:616-22.

3.  Benetti FJ, Naselli G, Wood M, Geffner L. Direct myocardial revascularization without extracorporeal circulation. Experience in 700 patients. Chest. 1991;100:312-6.

4.  Buffalo E, de Andrade JCS, Branco JNR, Teles CA, Aguiar LF, Gomes WJ. Coronary artery bypass grafting without cardiopulmonary bypass. Annals of Thoracic Surgery. 1996;61:63-6.

5.  Calafiore AM, Di Giammarco G, Teodori G, Bosco G, D’Annunzio E, Barsotti A, Maddestra N, Paloscia L, Vitolla G, Sciarra A, Fino C, Contini M. Left anterior descending coronary artery grafting via left anterior small thoracotomy without cardiopulmonary bypass. Annals of Thoracic Surgery. 1996;61:1658-65.

6.  Doty JR, Fonger JD, Nicholson CF, Sussman MS, Salomon NW. Cost analysis of current therapies for limited coronary artery revascularization. Circulation 1997;96(Suppl II):II-16-II-20.

7.  Dudley RA, Harrell FE Jr, Smith LR, Mark DB, Califf RM, Pryor DB, Glower D, Lipscomb J, Hlatky M. Comparison of analytic models for estimating the effect of clinical factors on the cost of coronary artery bypass graft surgery. J Clin Epidemiol. 1993;46:261-71.

8.  Engelman RM. Mechanisms to reduce hospital stays. Annals of Thoracic Surgery. 1996;61:S26-9.

9.  Fanning WJ, Kakos GS, Williams TE Jr. Reoperative coronary artery bypass grafting without cardiopulmonary bypass. Annals of Thoracic Surgery. 1993;55:486-9.

10.  Gill IS, FitzGibbon GM, Higginson LA, Valji A, Keon WJ. Minimally invasive coronary artery bypass: a series with early qualitative angiographic follow-up. Annals of Thoracic Surgery. 1997;64:710-4.

11.  Grover FL, Johnson RR, Marshall G, Hammermeister KE. Factors predictive of operative mortality among coronary artery bypass subsets. Annals of Thoracic Surgery. 1993;56:1296-307.

12.  Gu YJ, Mariani MA, van Oeveren W, Grandjean JG, Boonstra PW. Reduction of the inflammatory response in patients undergoing minimally invasive coronary artery bypass grafting. Annals of Thoracic Surgery. 1998;65:420-4.

13.  Hlatky MA. Analysis of costs associated with CABG and PTCA. Annals of Thoracic Surgery. 1996;61:S30-2.

14.  King RC, Reece TB, Hurst JL, Shockey KS, Trible CG, Spotnitz WD, Kron IL. Minimally invasive coronary artery bypass grafting decreases hospital stay and cost. Annals of Thoracic Surgery. 1997;225:805-11.

15.  Lazar HL, Fitzgerald C, Gross S, Heeren T, Aldea GS, Shemin RJ. Determinants of length of stay after coronary artery bypass graft surgery. Circulation. 1995;92(Suppl II):II-20-II-24.

16.  Mark DB. Implications of cost in treatment selection for patients with coronary heart disease. Annals of Thoracic Surgery. 1996;61:S12-5.

17.  Ovrum E, Tangen G, Holen EA. Facing the ear of minimally invasive coronary grafting: current results of conventional bypass grafting for single vessel disease. Annals of Thoracic Surgery. 1997;64:159-62.

18.  Perrault LP, Menasche P, Peynet J, Faris B, Bel A, de Chaumaray T, Gatecel C, Touchot B, Bloch G, Moalic JM. On-pump, beating-heart coronary artery operations in high-risk patients: an acceptable trade-off? Annals of Thoracic Surgery. 1997;64:1368-73.

19.  Reichenspurner H, Gulielmos V, Wunderlich J, Dangel M, Wagner FM, Pompili MF, Stevens JH, Ludwig J, Daniel WG, Schuler S. Port-access coronary artery bypass grafting with the use of cardiopulmonary bypass and cardioplegic arrest. Annals of Thoracic Surgery. 1998;65:413-9.

20.  Robinson M, Gross D, Zeman W, Stedje-Larsen E. Minimally invasive coronary artery bypass grafting: a new method using an anterior mediastinotomy. J Card Surg. 1995;10:529-36.

21.Salomon NW, Page US, Bigelow JC, Krause AH, Okies JE, Metzdorff MT. Coronary artery bypass grafting in elderly patients. Comparative results in a consecutive series of 469 patients older than 75 years. J. Thorac Cardiovasc Surg 1991;101:209-18.

22.  Zenati M, Domit TM, Saul M, Gorcsan J III, Katz WE, Hudson M, Courcoulas AP, Griffith BP. Resource utilization for minimally invasive direct and standard coronary artery bypass grafting. Annals of Thoracic Surgery. 1997;63:S84-7

Questions

1.  The patient group with the lowest graft reintervention rate was the:

a) MIDCAB-LIMA
b) MIDCAB-GEA
c) STERN-OFF CPB
d) STERN-CON
 
2.  The highest mean hospital charges for any group were seen in the:

a) MIDCAB-LIMA
b) MEDCAB-THORACOTOMY
c) STERN-OFF CPB
d) STERN-CONV
 
3.  Graft reintervention within 30 days for all MIDCAB groups was:

a) Less than 6%
b) Between 6-10%
c) Greater