Internal mammary artery bypass graft in reoperative myocardial revascularization

Internal Mammary Artery Bypass Graft in Reoperative

Myocardial

FLOYD D. LOOP, MD NESTOR R. CARABAJAL, MD PAUL C. TAYLOR, MD MANUEL J. IRARRAZAVAL, MD

Thirty-two consecutive patients who earlier received indirect or direct myocardial revascularization underwent reoperation with one or more internal mammary artery grafts either alone or in combination with saphenous vein grafts. The main indication for reoperation was graft closure or progression of coronary atherosclerosis in nongrafted vessels, or both. Graft construction was performed under normothermic perfusion and anoxic arrest with interrupted suture technique. No intraoperative infarctions or hospital deaths occurred. All patients are alive after an average follow-up period of 20 months, and two thirds are asymptomatic. Arteriography after reoperation in nine patients revealed patency of eight of nine internal mammary artery and five of five secondary vein grafts. When angiographic and symptomatic indications for reoperation exist, the internal mammary artery bypass graft has become a valuable alternative, particularly for patients with small coronary vessels or previous vein graft failure.

Cleveland, Ohio

From the Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation and The Cleveland Clinic Educational Foundation, Cleveland, Ohio. Manuscript accepted November 5. 1975. Address for reprints: Floyd D. Loop, MD, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, Ohio 44106.

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Clinical experience since 196@ has thus far confirmed the status of internal mammary artery grafting as a primary operation for ischemit heart disease. Compared with the vein autograft, there is less discrepancy in size between the internal mammary artery and the recipient coronary vessel, and the graft attached to the subclavian source can passively regulate flow according to the peripheral coronary resistance. These features sustain graft patency in the face of a small coronary arterial distribution or compromised coronary arterial runoff. Graft patency at 1 year exceeds 95 percent as reported from several institutions.2-4 Our clinical results, including data from graded exercise tests5 show a favorable symptomatic response similar to that of the vein autograft operation. The technical difficulty related to the internal mammary arterycoronary artery anastomoses can largely be overcome by increased operative experience. Initial graft flow is limited to approximately 150 ml/mins; however, greater flow requirements can usually be anticipated in advance and circumvented by the selection process. Within established clinical and angiographic guidelines, the internal mammary artery is applicable for most elective revascularization cases. Included in the current indications for such grafts are patients who require reoperation for ischemic heart disease. Herein, we describe a subgroup of patients from our reoperative surgical experience in 250 cases through 1974. This series is composed of 32 consecutive patients who underwent direct or indirect revascularization and later received a single or double internal mammary artery graft alone or in combination with other coronary arterial revascularization procedures. Clinical Thirty-two

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INTERNAL MAMMARY ARTERY BYPASS GRAFT-LOOP

tion, these 29 men and 3 women had a previous mid-line sternotomy incision. All primary operations had involved some form of myocardial revascularization. Three patients had received a single Vineburg implant; one patient had a right coronary artery patch graft, and the remainder had single or multiple bypass grafts. The interval between the first and second revascularization procedure was 3 to 86 months (mean 28 months). The primary operation was performed at the Cleveland Clinic in 22 patients and elsewhere in 10 patients. The reasons for operation were (1) graft closure (13 patients: 12 vein autografts and 1 radial artery graft); (2) graft closure and progression of coronary atherosclerosis in one or more nongrafted vessels (8 patients); (3) progression of coronary atherosclerosis only (8 patients), and (4) previous Vineburg implant with unchanged or progressive atherosclerosis (3 patients). Functional classification: Two patients were in New York Heart Association functional class I, 6 in class II, 12 in class III, and 12 in class IV before reoperation. Two patients in functional class IV received an emergency operation for unstable angina pectoris. Coronary arteriography performed shortly before the reoperation disclosed single vessel disease in 3 patients, double vessel disease in 13 and triple vessel disease in 16. Left ventricular contraction was normal or only mildly impaired in 25 patients. One left ventricular segment was hypokinetic or akinetic in six patients, and diffuse impairment of moderate degree was evident in one patient. Left ventricular end-diastolic pressure was increased (15 mm Hg or greater) in four of the patients with impaired left ventricular contraction. Operative procedures: The diverse assortment of primary and secondary procedures makes explicit grouping of the operation lengthy and complex. Figure 1 illustrates in broad categories the relation between the first and second coronary arterial operations. Twenty (63 percent) of the 32 patients had complete revascularization during the second procedure. The remaining 12 had diffuse atherosclerosis that prevented further grafting, an anatomically small coronary arterial distribution or an ungrafted artery or arteries that coursed through a transmural scar. Late follow-up information was obtained in all cases by telephone interview with the patient or his attending physician.

ORIGINAL REVASCULARfZAT/ON PROCEDURF

Surgical Technique Before the median sternotomy is opened, a common femoral artery is routinely exposed. This safety measure ensures rapid cannulation of the femoral artery should hemorrhage occur during division of the sternum or as a result of lysis of adhesions. In this series, no accidental bleeding ensued; however, in 2 of the 32 reoperations, the pump arterial line was inserted into the femoral artery rather than into the ascending aorta. In these patients, the ascending aorta was too short to accommodate an aortic cannula and proximal vein graft anastomoses. After removal of the previous sternal wires, the lungs are deflated to retract the mediastinal cardiovascular structures away from the inner chest wall. We avoid subxyphoid probing of the retrosternal space because the adherent right ventricle can easily be penetrated by the surgeon’s index finger. The rim of the sternal notch is exposed to fit the saw flange in place, and the bone is divided in a superior to inferior direction. Rakes are used to retract the sternal edges, which are mobilized sharply before inserting the fixed retractor. Bilaterally, the internal mammary artery must be identified to prevent accidental transection. A Favalor0 sternal elevator (Pilling Corp., Fort Washington, Pa.) lifts the respective hemithorax for dissection of the internal mammary arterial pedicle. Ordinarily, heparin can be withheld until after the pedicle has been mobilized. To promote a dry operative field, hypertension should be avoided during mobilization of the artery. After the pedicle has been separated from the chest wall, heparin is administered and the aorta and right atrium are exposed. The various anatomic structures should be identified by sharp scissor dissection rather than blunt separation, which frequently results in diffuse bleeding. The superior and inferior venae cavae are cannulated and the left atrium is vented through the right superior pulmonary vein. An alternate atrioventricular cannula (U. S. Catheter and Instrument Corp.) can be passed across the mitral valve, thus decompressing both chambers. The latter vent, inserted through the right superior pulmonary vein, obviates a left ventricular apical vent. After the institution of cardiopulmonary bypass, the left ventricle is elevated into the operative field. Whenever possible, the anterior wall should be mobilized from a postero-

RE- O~t%h&AT”” /MA

GRAFT

SINGLE GRAFT

IMA

SINGLE MA+ VENOUS AUTOGRAFT

DOUBLE IMA GRAFT

VENOUS

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AUTOGRAFTI IMA + OTHER PROCEDURES

OTHER CORONARY @/ ARTERY PROCEDURES

May 1976

FIGURE 1. The original revascularization procedure (lefl) is contrasted with the internal mammary artery graft reoperation procedure (right) in 32 consecutive patients. The wide assortment of specific operations is difficult to classify and only the basic procedures are shown here. The four original cases described as other coronary procedures included a vein graft and ventricular aneurysmectomy, a right coronary endarterectomy and patch graft, an internal mammary artery and radial artery graft, and two vein grafts with gas endarterectomy. All reoperations consisted of single or double arterial grafts.

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requiring tracheostomy in three patients. One of the latter had a tracheal stenosis that required operative repair. In the operating room and during hospital convalescence, the 32 patients received 4 to 25 units of blood (average of 9 units). Thirteen vein or arterial graft specimens were removed during the second opand the pathologists reported organized eration, thrombosis in eight vein grafts, intimal hyperplasia in four vein grafts and intimal hyperplasia in one radial artery (Fig. 2). Follow-up results: All patients are still living, and the follow-up period extends from 9 to 46 months (mean 20, median 19 months). Postoperatively, 22 patients are now in functional class I, 8 in class II and 2 in class III. One patient, currently asymptomatic, 13 probably sustained a myocardial infarction

lateral to anterior direction. Dissecting anteriorly, one can unroof the protective epicardium and damage the subepicardial muscle. In cases of occluded saphenous vein grafts, a point beyond the apex of the previous graft is usually selected for reanastomosis. To insure a lumen diameter of at least 2 mm, the appropriate internal mammary artery is usually transected in the area of the fifth or sixth intercostal branch. Spasm in the artery can be released by spraying the vessel with dilute papaverine solution. The artery is divided obliquely and, with an iris scissor, a 3 mm slit is made in the inferior wall. In this series, the interrupted 7-O silk suture technique7 was employed without optical assistance. These grafts have been constructed under normothermic perfusion with the aorta cross-clamped. After the graft is constructed, the pedicle of the internal mammary artery is sutured to the epicardium to prevent the graft from adhering to the overlying chest wall. Pump time is occasionally prolonged during the reoperations, and hemorrhage from adhesions produces substantial cardiotomy return. In view of an increased suction volume and frequently longer perfusion time, we interpose micropore filters below the cardiotomy reservoir and also in the pump arterial line. After the grafting has been completed, hemostasis must be meticulous to prevent recurring postoperative hemorrhage. Whenever operative transfusions exceeded 6 units of blood, fresh blood replacement was instituted.

months postoperatively III, had a documented atively.

and one patient, now in class infarction 8 months postoper-

Postoperative coronary arteriography was performed after the second operation in nine patients (Fig. 3). The interval between the reoperation and the original procedure ranged from 4 to 17 months (mean 10 months). Eight left internal mammary artery grafts constructed to the anterior descending coronary artery and one right internal mammary artery graft performed to the right coronary artery were visualized. Eight grafts are widely patent; however, in the ninth patient, the graft fills only the proximal left anterior descending coronary artery, whereas the distal coronary artery is not identified. Of seven vein autografts studied in the nine patients, five were performed during the reoperation and two during the primary operation. All vein grafts are patent and the grafts performed at reoperation included

Early and Late Results Early results: No intraoperative infarctions and no hospital deaths occurred. Postoperative cardiac complications included atria1 fibrillation that reverted to regular sinus rhythm before discharge in two patients; continued postoperative hemorrhage required reoperation in three patients and, in one of these patients, hepatitis developed. Extracardiac complications included a stroke (temporary left hemiparesis) in one patient and respiratory failure

2. Low power view of a radial artery from the aorta to the left anterior descending coronary artery. The graft closed, and this specimen was removed 4 months after the primary operation. The obstructed radial vessel displays severe intimal hyperplasia; it was replaced with a right internal mammary artery graft. FIGURE

grafted

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FIGURE 3. Coronary arteriograms in a representative case. A, 1967. showing an estimated 60 to 70 percent occlusion of the proximal right coronary artery (arrow). An endarterectomy and patch graft were performed at the occlusive site. B. 1968, postoperative right coronary arteriogram in the left anterior oblique view showing a functioning patch graft. The patient remained asymptomatic for 6 years. C. 1973. second postoperative arteriogram after recurrence of angina. A severe lesion of the right coronary artery is evident beyond the still functioning patch graft. D, 1973, showing a significant proximal obstruction in the relatively small left anterior descending coronary system (arrow). At reoperation, the patient received an aortocoronary saphenous vein graft to the distal right coronary artery and a left internal mammary artery graft to the mid-anterior descending coronary artery. E, 1975, showing a functioning right coronary artery vein graft. F, 1975, the left internal mammary artery-anterior descending coronary artery anastomosis is widely patent. Ventricular contraction has remained normal.

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three to the circumflex and two to the right coronary artery. Left ventricular function was unchanged from the preoperative status in eight patients and improved in one patient.

two iatrogenic catheter dissections of the artery that resulted in graft closure. Operative mortality: Although no deaths or intraoperative myocardial infarction occurred, substantial morbidity was experienced by approximately 10 percent of patients. Many complications stemmed from vascular adhesions that produce extensive blood loss and consequently prolong cardiopulmonary bypass time. Each of three patients who experienced respiratory distress postoperatively received more than 12 blood transfusions. Comprehensive reviews of these and other technical problems have been publishedg-l2 and the reported approaches to management have generally been similar to ours. Johnson et a1.i3 have indicated the merit of the internal mammary artery graft in reoperative cases. Technically, grafts to the anterior descending and right coronary arteries can be constructed with relative ease through the adhesive process, but vessels on the posterolateral wall are difficult to identify, especially if they are small or assume an intramyocardial location. Contraindications: Our guidelines for internal mammary artery grafting encompass certain relative contraindications. At present, we advocate use of this graft only for patients younger than 65 years. We have found that elderly patients frequently have more sclerotic mammary arteries than younger patients, and the incidence of subclavian artery obstruction increases with age. We are cautious about use of the internal mammary artery in those with extensive brachiocephalic disease or subclavian bruits. The time required to mobilize the arterial pedicle causes some delay in emergency revascularization and ordinarily the arterial graft is not used in cases of unstable angina or evolving infarction. Patients with a large left ventricular mass and large coronary arteries should receive aortocoronary vein autografts because of their greater flow requirements. Graft patency: If the vein graft patency in this series equals the results of internal mammary artery grafting, one may question the need for arterial grafting. The answer lies in the established patency of the internal mammary artery for small vessel grafts. Six of the 9 arterial grafts restudied and 21 of 32 overall were performed for vein graft closure. In the majority of cases, the diameter of the coronary artery was small, and the internal mammary artery was judged a more suitable alternative than another vein graft. In contrast with the experience of the Stanford group,14 we found no wide discrepancy in clinical or angiographic results between patients operated on solely for graft closure and those who underwent revascularization for progressive atherosclerosis. The explanation of the Stanford investigators for their finding is logical in that factors such as small vessel caliber and poor distal runoff that influence the initial graft occlusion may adversely affect another vein autograft. Perhaps greater use of the internal mammary artery graft in our series accounted for our more favorable results in those with previously occluded vein grafts.

Discussion Indications for reoperation: Postoperative coronary arteriography is recommended for patients who experience a return of angina after primary revascularization. Currently, our indications for a second surgical procedure are based on three documented angiographic findings in symptomatic patients: (1) primary graft failure, (2) progressive narrowing of at least 60 to 70 percent in one or more ungrafted major coronary arteries, and (3) coronary artery obstructions suitable for bypass in patients who received Vineburg implants before the advent of direct revascularization. Although the indications for both primary and reoperative revascularization are based predominantly on the angiographic findings, occlusion of a vein autograft constructed to an anatomically small or diffusively atherosclerotic coronary vessel is not necessarily grounds for reoperation. The final decision is based on the patient’s level of physical discomfort, the pathologic anatomy of the involved vessels, and the presence or absence of sustained additional and irreversible ventricular damage. We emphasize that selection for reoperation is ultimately determined by high quality coronary arteriography. Arterial versus vein grafts: In this series, the major indication for reoperation was graft failure or progression of coronary atherosclerosis, or both. The internal mammary artery graft is preferred since it does not seem logical to replace an occluded saphenous vein graft with a second vein autograft. An internal mammary artery graft is most easily applied to the vessels on the anterolateral wall and, in cases of occluded vein grafts to the anterior descending coronary artery, the internal mammary artery serves as a reliable conduit for perfusion of the distal segment. Although vein grafts were frequently utilized in this series, they were reserved mainly for patients who had obstruction in a right or circumflex coronary artery not grafted previously. Occluded vein grafts were replaced with another vein graft only rarely and, in those few cases, the primary graft failure was attributed to a technical problem. Internal mammary arteriography: No attempt was made to study the internal mammary artery preoperatively, since injury during the first operation is uncommon and the incidence of atherosclerosis in this vessel appears to be small. However, routine internal mammary arteriograms have been advised.8 This recommendation becomes important if no alternate graft is available as, for example, in patients with previous vein stripping or with extensive brachiocephalic disease or a subclavian bruit. Unfortunately, internal mammary arteriography is not without danger. In our experience with 400 postoperative graft arteriograms through 1974, we have witnessed

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Eight of nine internal mammary artery grafts and seven saphenous vein grafts studied in nine patients after the second operative procedure are widely patent. Five of the eight patent arterial grafts had been constructed to coronary arteries initially bypassed by vein grafts that subsequently became occluded. Clinically, 22 of the 32 patients have returned to functional class I status. Two patients had a late myocardial

ET AL.

infarction during an average follow-up period of 20 months. Although vein graft and internal mammary artery graft patency is approximately equal in this small group, our past experience with the arterial graft indicates that it is an attractive substitute for the vein graft in patients who require reoperation after graft closure or for progressive coronary atherosclerosis.

References 1. Green GE, Stertrer 2. 3.

4.

5.

6. 7.

SH, Reppert EH: Coronary arterial bypass grafts. Ann Thorac Surg 5443-450. 1968 Green GE: Internal mammary artery-to-coronary artery anastomosis. Ann Thorac Surg 14:260-27 1, 1972 Loop FD, Spampinato N. Siegel W, et al: Internal mammary artery grafts without optical assistance. Clinical and angiographic analysis of 175 consecutive cases. Circulation 47, 48: Suppl III: 111-162-111-167,1973 Kay EB, Naraghipour H, Beg RA, et al: Internal mammary artery bypass graft: Long-term patency rate and follow-up. Ann Thorac Surg 18:269-279, 1974 Siegel W, Loop Fb, Proudfit WL, et al: Comparison of internal mammary artery and saphenous vein grafts for myocardial revascularization by exercise testing (abstr). Circulation 52: Suppl ll:ll-142, 1975 Green GE: Rate of blood flow in the internal mammary artery. Surgery 70809-813, 1971 Loop FD, Effler DB, Spampinato N, et al: Myocardial revascularization by internal mammary artery grafts: a technique without optical assistance. J Thorac Cardiovasc Surg 63:674-680, 1972

8. Rainer WG, Sadler TR Jr, Llgget MS: Internal mammary arteriography prior to coronary artery bypass surgery. Chest 64: 523-524, 1973 9. Benedict JS, Buhl TL, Henney RP: Revascularization of the ischemic myocardium. Study of 38 reoperations for coronary insufficiency. Arch Surg 108:40-42, 1974 10. Skow JR, Carey JS, Plested WG Ill, et al: Saphenous vein bypass as a secondary cardiac procedure. Arch Surg 107:34-36. 1973 11. Adam M, Geisler GF, Lambert CJ, et al: Reoperation following clinical failure of aorta-to-coronary artery bypass vein grafts. Ann Thorac Surg 14:272-281, 1972 12. Londe S, Sugg WL: The challenge of reoperation in cardiac surgery. Ann Thorac Surg 17:157-162, 1974 13. Johnson WD, Hoffman JF Jr, Flemma RJ, et al: Secondary surgical procedure for myocardial revascularization. J Thorac Cardiovasc Surg 64:523-529, 1972 14. Winkle RA, Alderman EL, Shumway NE, et al: Results of reoperation for unsuccessful coronary artery bypass surgery. Circulation 52: Suppl 1:1-61-l-65. 1975

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