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Ann Thorac Surg 2000;70:1037-1045
© 2000 The Society of Thoracic Surgeons
a Escorts Heart Institute and Research Centre, New Delhi, India
Address reprint requests to Dr Mishra, Escorts Heart Institute and Research Centre, Okhla Rd, New Delhi 110025, India
e-mail: manishamishra{at}yahoo.com
Presented at the Sixth Annual Cardiothoracic Techniques and Technologies Meeting 2000, Ft Lauderdale, FL, Jan 27–29, 2000.
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Abstract |
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Methods. Between January 1993 and June 1999, 6,138 patients undergoing elective CABG were evaluated by intraoperative transesophageal echocardiography. Patients were screened preoperatively for internal carotid artery disease. Based on the intraoperative transesophageal echocardiography findings the surgical technique was individualized: hypothermic circulatory arrest with aortic atherectomy, CABG combined with transmyocardial laser revascularization on the beating heart, off-pump CABG by midsternotomy, ministernotomy, minimally invasive direct CABG, hybrid procedure, and so on. Patients were divided into four groups: a low-risk group (no significant aortic or carotid disease); an aortic atheromatous disease group (A.ATH); a carotid disease group (CD); and a carotid disease combined with aortic atheromatous disease group (CD + A.ATH).
Results. The incidence of stroke in the low-risk group (n = 5,043) was 0.92% compared with 0.96% in the A.ATH group (n = 918). In the CD group (n = 166) the incidence of stroke was 0.6% whereas it was 0% in the CD + A.ATH group (n = 11).
Conclusions. Preoperative and intraoperative screening can detect extensive atherosclerosis of the proximal aorta and internal carotid artery. Selective use of surgical techniques in this group of high-risk patients can prevent adverse neurologic sequelae while achieving complete myocardial revascularization.
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Introduction |
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TopAbstractIntroductionMaterial and methodsSurgical strategyResultsCommentReferences |
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A number of risk factors for the development of stroke in this setting have been identified [1–3]. Extensive atherosclerosis of the aortic arch and carotid artery disease are associated with high incidence of stroke [4–8]. The experience of Faggioli and associates [5] suggests that prophylactic carotid endarterectomy (CEA) in patients with high grade or bilateral disease may reduce the incidence of perioperative stroke.
Risk of stroke attributable to aortic atheromatous disease is an important consideration in the referral of coronary artery disease patients for surgical revascularization. The significance of the aorta as a source of atheroemboli and hence as a risk factor for perioperative stroke was highlighted by Katz and colleagues [9], who found a stroke incidence of 25% among patients with mobile plaques of the aortic arch. Manipulation of the severely atherosclerotic aorta is believed to be the main factor responsible for atheroembolism during cardiopulmonary bypass (CPB). Several subsequent studies have confirmed the strong correlation between severe aortic atheromatous disease and stroke or death [10, 11]. Although carotid artery stenosis is frequently associated with severe aortic atherosclerosis, it has a positive predictive value of only between 16% and 57% [12].
The availability of intraoperative transesophageal echocardiography (TEE) to image the thoracic aorta and preoperative carotid artery duplex scanning provide the opportunity to determine the prevalence of these two conditions in patients undergoing CABG, and to formulate surgical strategies based on these findings with the goal of reducing the incidence of neurologic injury in this high-risk patient population.
In this report we evaluated the use of an individualized surgical approach for reducing the incidence of neurologic injury in patients undergoing CABG who are at high risk of stroke from extensive aortic atherosclerosis without compromising myocardial revascularization.
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Material and methods |
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On the basis of this evaluation the patients were divided into four groups:
Transesophageal echocardiography
All the patients in the study group were evaluated by TEE according to the protocol followed at our institution since 1993 [14]. After induction of general anesthesia, a multiplane phased-array dual-frequency 3.7/5-MHz transesophageal transducer was placed in position to view the thoracic aorta. Hewlett-Packard SONOS 1500 and 2500 systems were used.
Definition of aortic disease
Three methods were used to evaluate aortic arch disease:
The atheromatous lesions of the aorta were graded by TEE as follows:
Duplex carotid echo Doppler evaluation
Extracranial carotid arteries were evaluated by color flow duplex scanning study; B-mode and color flow images of the common, external, and internal carotid arteries were obtained in longitudinal and transverse planes. Presence of plaques was noted and reduction in the cross-sectional area of the lumen was calculated. Doppler velocity spectra were recorded from each of these vessels, maintaining the angle of insonation as close to 60 degrees as possible. The highest peak systolic velocity and end-diastolic velocity were calculated. According to the flow velocity criteria, severity of internal carotid artery stenosis was calculated.
Severe stenosis was defined as carotid artery narrowing of more than 70% of the vessel diameter. Patients with symptomatic or asymptomatic disease more than 70% confirmed by carotid angiography were treated with simultaneous CEA and CABG.
A cerebrovascular event was classified as a transient ischemic attack (TIA) or a stroke. Transient ischemic attack was defined as focal cerebral dysfunction of presumed vascular origin that resolved completely within 24 hours. A stroke was defined as a focal or global cerebral dysfunction of presumed vascular origin lasting more than 24 hours. For the statistical analysis of neurologic events TIA and stroke were considered as one group.
A cerebrovascular event was considered as embolic only with strong clinical and computed tomographic (CT) evidence. Computed tomography was carried out for every patient who had clinical signs of a neurologic event.
A peripheral vascular event was classified as embolic if there was supporting clinical, angiographic, or surgical findings.
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Surgical strategy |
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After induction of general anesthesia, TEE was performed and the decision made whether to do a conventional CABG, minimally invasive direct CABG (MIDCABG), or off-pump CABG (OPCAB), depending on the location and extent of atheromatous lesion in the thoracic aorta.
Ascending aorta
In the presence of grade II/III atheromatous disease or extensive calcification, if the disease was in the proximal portion, high aortic cannulation was carried out along with relocation of the vein graft and cardioplegia needle to another site. Greater use was made of arterial conduits and a side-biting clamp was avoided. The proximal anastomoses were carried out on cross-clamp (after the distal anastomosis) while rewarming, injecting warm potassium-free perfusate through a retrograde coronary sinus cannula. If fewer proximal anastomoses were possible on the diseased ascending aorta, then the conduits were taken piggy back on internal mammary arteries (IMA) or vein grafts. Patients with disease in the distal portion of the ascending aorta precluding aortic cannulation had CPB established by femoral artery cannulation and fibrillatory arrest without cross-clamping the aorta. Arterial grafts were used. In patients with extensive disease of ascending aorta with suitable coronary anatomy, grafting was carried out on beating hearts without CPB.
Aortic arch
All grade II/III atheromas in the proximal two thirds of the arch had modification in technique, either femoral artery cannulation with fibrillatory arrest or long cannula beyond the atheroma. In 6 patients aortic arch debridement was carried out [14].
Minimally invasive techniques
Changes in technique to less invasive procedures was brought about by our interest in OPCAB, which permitted multivessel coronary grafting because of better anesthetic back up in the form of monitoring and drugs to reduce heart rate, and the availability of a variety of mechanical platforms to stabilize the heart.
Minimally invasive direct coronary artery bypass grafting
This is a technique in which through small incisions and without a full sternotomy conduits are harvested and anastomosed to the target vessel without CPB.
Anterior thoracotomy
This technique is particularly useful for anastomosis to the left anterior descending coronary artery (LAD), diagonal, or ramus on the left and the right coronary artery (RCA) on the right side. In patients who have undergone previous CABG without the use of IMA and on reoperation require only a single graft to the LAD, this is an excellent technique because it obviates the need for sternotomy and extensive dissection along with its attendent risks.
Ministernotomy
A vertical midline skin incision 6 to 8 cm in length is made starting from the fourth intercostal space to the tip of the xiphoid process. If the sternum is very hard or stiff a lateral extension of the sternotomy is done on the left or right side depending on which mammary artery is to be harvested, with the help of the oscillating saw. Complete length of the IMA can be harvested with the help of a long tip electrocautery from interspace until the distal bifurcation of the IMA, under direct vision. Almost the whole length of the LAD can be visualized. Appropriate site of the LAD is selected for the anastomosis.
Subxiphoid approach
The right coronary system is often the only native coronary artery involved in patients presenting with limited coronary disease. This usually involves the proximal or midportion of the vessel, making these patients poor candidates for this technique of right IMA to mid-RCA grafting. Often the proximal vessel has been heavily instrumented with multiple previous catheter-based interventions, and the patient presents as a therapy failure. The most appropriate site for grafting is usually either the distal RCA or the proximal posterior descending branch in areas that are distal to the acute margin of the heart. Minimally invasive dissection of the right IMA does not yield a long enough conduit to wrap around the acute margin of the heart and anastomose to these targets without undue tension. Therefore, the only other pedicled arterial conduit in that proximity is the right gastroepiploic artery, which has been used clinically for more than 10 years in conventional bypass grafting.
Left lateral thoracotomy
In reoperative CABG, in which only the obtuse marginal branch of the circumflex artery needs to be bypassed, a left lateral thoracotomy approach is ideal. The lung is retracted and the pericardium opened. With minimal dissection the obtuse marginal artery can be exposed. The radial artery can be anastomosed to the obtuse marginal artery and the proximal anastomosis constructed on the descending thoracic aorta, avoiding cannulation of an atheromatous aortic arch.
Off-pump coronary artery bypass grafting
Through a midsternotomy multivessel CABG is performed using stabilization devices like Octopus, Genzyme, and so on. If the ascending aorta is normal then the proximal anastomosis is constructed on the ascending aorta. If it is diffusely diseased then the internal thoracic arteries, gastroepiploic artery, radial artery, or even vein grafts are used in the form of T grafts and sequential anastomosis.
The local area is stabilized for distal anastomosis to LAD with either the Octopus II tissue stabilizer or the Genzyme stabilizer. An oxygen blower is used for providing a bloodless field. The mammary to coronary anastomosis is performed with running 7-0 polypropylene suture.
The obtuse marginal arteries are also bypassed in a similar manner except that deep pericardial sutures are applied to elevate the heart, and wet surgical pads are used to rotate the heart and the right pleura is opened to facilitate tilting of the heart toward the right side. Stabilization is always obtained by the Octopus II tissue stabilizer.
The right coronary anastomosis is also performed in similar fashion except that RCA anastomosis is associated with more frequent and marked hemodynamic and electrocardiographic changes, so an intracoronary shunt is almost always used to maintain the distal perfusion during the anastomosis.
Other strategies
The other procedures performed were MIDCABG or OPCAB. Occasionally the lifting of the heart was not well tolerated hemodynamically by the patient. In such cases after doing the LAD and RCA anastomosis on a beating heart either transmyocardial laser revascularization (TMLR) was performed to the left circumflex territory or the left circumflex underwent percutaneous transluminal coronary angioplasty/stenting (hybrid procedure) to achieve complete myocardial revascularization.
Carotid endarterectomy
The decision to perform CEA was made preoperatively. Symptomatic or asymptomatic patients with more than 70% stenosis of internal carotid artery underwent a simultaneous CEA combined with CABG.
During simultaneous operations the CEA was always carried out before median sternotomy. After adequate carotid mobilization, systemic anticoagulation was established with 5,000 to 7,000 units heparin. Clamps were then placed proximal and distal to the atheromatous lesion. The endarterectomy was then performed from the common carotid past the bifurcation distally past the obvious plaque. A shunt was used selectively. The distal clamp on the internal carotid artery was released to assess the backflow from it, if the backflow was very good then the shunt was not used. The arteriotomy was closed after removing air and flushing out debris, using either a Dacron patch or a vein patch.
The range of blood pressure at which the patient was neurologically asymptomatic, that is, the range of preoperative blood pressure, was identified and maintained within a range of ±10% intraoperatively.
Statistical analysis
The values are expressed as mean ± standard deviation. The categorical data were analyzed using Chi Square test (
2) or Fisher’s Exact test wherever applicable. A value of p less than 0.05 was considered to be significant.
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Results |
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TopAbstractIntroductionMaterial and methodsSurgical strategyResultsCommentReferences |
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In the A.ATH group there were 918 patients with grade II/III atheromatous lesions in the ascending aorta or aortic arch, adding 11 patients from CD + A.ATH group, a total of 929 patients underwent modification in surgical technique (Table 4). Of these 929 patients, 404 underwent CPB. Six patients had grade III atheroma and 14 had grade II atheroma in the ascending aorta. In 9 of these patients OPCAB was performed using total arterial grafts. Four patients had femoral cannulation and arterial grafts on hypothermic fibrillation, without aortic cross-clamping.
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Now we prefer to tackle this group of patients with OPCAB using multiple grafts to achieve complete myocardial revascularization. This group of 525 patients underwent OPCAB (Table 5). The mean number of distal anastomoses was 3.2. Internal mammary artery grafts were used in 99.04% of patients. In 14 patients grafts were combined with TMLR. Transmyocardial laser revascularization was performed in the arterial territory with diffuse disease or in the left circumflex territory when lifting of the heart could not be tolerated. In 129 patients MIDCABG was performed. It was done by anterior thoracotomy in 42 and by ministernotomy in 44 patients, whereas MIDCABG was combined with percutaneous transluminal coronary angioplasty in 14 and with TMLR in 29 patients. Sole TMLR was performed in 12 patients due to diffuse disease of the coronary arteries.
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In the 11 patients belonging to the CD + A.ATH group concomitant CEA was carried out along with modification in surgical technique of CABG depending on the location and grade of aortic atheromatous lesion, which has already been discussed earlier.
Neurologic complications
A total of 53 patients (0.65%) sustained a transient or permanent neurologic deficit in the immediate postoperative period. Of these, 9 patients had a stroke and 44 had a TIA (Table 7). In the 9 patients with stroke, 1 had a grade II atheroma in the proximal two thirds of the aortic arch and modification in surgical technique was done in the form of long aortic cannulation beyond the left subclavian artery. Another of these patients had a concomitant CEA performed. The stroke was attributable to acute thrombosis of the internal carotid artery in this patient and the infarct was ipsilateral to the carotid lesion. Postoperative CT scan revealed fresh cerebral infarct in all the patients with stroke. None of these patients had any other risk factors for stroke. There were 5 deaths due to neurologic injury, 4 of these patients belonged to the low-risk group and 1 to the CD group. Other vascular events were observed in 6 patients: 4 patients had peripheral embolism that resolved on its own and the 2 other patients in this group developed acute abdominal symptoms. Laparotomy revealed massive gangrene of the gut suggestive of superior mesenteric artery embolism. Both these patients died after 48 to 76 hours. No surgical modifications had been carried out in these 2 patients, the atheroma was grade III present in the descending aorta, and CABG was performed in the routine fashion, on CPB.
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Comment |
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TopAbstractIntroductionMaterial and methodsSurgical strategyResultsCommentReferences |
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In a recent collective review of more than 35,000 patients the stroke rate ranged from 0.9% to 3.9% following isolated CABG with a mean stroke rate of 2%. The mortality from stroke in this review was 13% to 26% [15]. The overall stroke rate in our series was 0.9%.
It has been well established that the incidence of aortic atherosclerosis increases with age [12, 16]. In the present series, 28.13% of patients younger than 70 years and 33.55% of patients above 70 had aortic atheromatous disease. The distribution of aortic atherosclerosis has an important bearing on the safety of cardiac operation, particularly CABG. Using TEE routinely during CABG, we have found the highest incidence of atheroma in the distal aortic arch, followed by the proximal aortic arch, and the lowest incidence in the ascending aorta. This finding is in agreement with the autopsy study of 1,486 patients by Sternby [17], who found severe atherosclerotic disease more commonly located in the aortic arch and descending thoracic aorta. Ulcerations are seen four to five times more frequently in the descending aorta and aortic arch [17].
The embolic potential of severe atherosclerotic disease has been documented in clinical and autopsy studies. Karalis and coworkers [16] found atherosclerotic debris in 38 of 556 patients who underwent TEE. A history of embolic events was present in 8 of 11 (73%) patients with mobile plaque versus 3 of 25 (12%) patients with no mobile plaque [16].
Coronary artery bypass grafting in patients with severe aortic atherosclerosis poses a challenge to the surgeon. The strategies that have been used range from the minimally invasive to the maximally invasive procedures. The decision making requires individualization for each patient, depending on the coronary anatomy, the location and extent of aortic atherosclerosis, and associated systemic problems.
With our increasing interest in OPCABs, we have been able to perform multivessel CABG without the need for CPB in this group of patients. In patients with small, localized atheroma of the ascending aorta the site for the aortic cannula and the partial occlusion clamp are selected carefully to avoid plaque disruption and embolization. Where it is not safe to apply a clamp on the aorta, T or Y grafts are established from in-situ arterial grafts. Extra anatomical bypass conduits placed proximally on arterial inflow sources other than the ascending aorta have been described.
Severe atherosclerosis of the aortic arch may cause embolization by the sand blast effect. During the early part of the series patients with proximal arch atheroma precluding aortic cannulation had femoral cannulation for CPB, followed by conventional techniques of cross-clamping and proximal anastomosis.
At present all patients with proximal arch atheromas and grade III distal arch atheroma undergo OPCAB. With the advances in beating heart techniques, off-pump revascularization is a very reasonable approach to the problem [18, 19]. It offers the major advantage that, in addition to not applying the aortic cross-clamp, the damaging effects of CPB to the brain are avoided [18].
Patients with grade II distal arch atheroma are done either as OPCAB or on CPB using a short aortic cannula or a Soft Flow cannula, depending on coronary anatomy. Seven patients in the OPCAB series could not tolerate lifting of the heart for distal anastomosis to the lateral wall and had to be put on CPB, using a Soft Flow cannula. None of these patients has adverse neurologic outcome. Nine patients who could not tolerate OPCAB had CABG + TMLR as they had a very ominous looking mobile atheroma in the arch of the aorta.
Unrecognized carotid disease is generally present in elderly patients who are asymptomatic. Ricotta and colleagues [20] demonstrated that significant (more than 75%) carotid artery stenosis was present in 11.3% of asymptomatic patients older than 60 years of age who were screened with duplex ultrasonography before elective CABG. D’Agostino and coworkers [21] found in their patients undergoing CABG an incidence of carotid stenosis greater than 50% in 20% of patients, and greater than 80% in 8%. Demopoulos and coworkers [22] reported an association of carotid stenosis greater than 80% with large mobile aortic atheromas in 15% of their patients. In our series, however, we could not demonstrate any correlation between the two.
Patients with coexistent carotid and coronary atherosclerosis present a major management problem because they represent a high-risk group for either surgery. Dashe and colleagues [23], in their report of 1,022 patients undergoing isolated CABG, found that stroke rate increased in a graded fashion in relation to the degree of carotid stenosis: 1.4% for the 0% to 24% stenosis subgroup, 4.1% for the 25% to 49% stenosis subgroup, 10.4% for the 50% to 69% stenosis subgroup, and 50% for the 70% to 99% stenosis group. In patients with symptomatic or asymptomatic carotid disease who undergo only CABG the incidence of stroke has been found to be as high as 17% in various reports [24–26]. Hertzer and coworkers [24] randomized patients prospectively to CABG followed by CEA or combined CABG and CEA. Their results favored combined CABG and CEA.
Our policy is in accordance with the recommendations of the North American Symptomatic Carotid Endarterectomy Trial [27] and the Asymptomatic Carotid Atherosclerosis Study trial [28] where benefit has been demonstrated for CEA in centers having perioperative complication rates of less than 6% and 3% for symptomatic and asymptomatic carotid stenosis, respectively.
The stroke rate in the low-risk group was 0.91% whereas in the various high-risk groups it was 0% to 0.65% (A.ATH = 0.65%; CD = 0.60%; CD + A.ATH = 0%). There was clearly a drastic reduction in the expected stroke rate (in agreement with available literature) in the high-risk group of patients by individualizing the surgical technique. There was no increase in perioperative myocardial injury and complete revascularization could be achieved in all patients.
In summary, preoperative and intraoperative screening was able to detect extensive atherosclerosis of the proximal aorta and internal carotid arteries. By a selective use of a variety of surgical techniques in this group of high-risk patients we could prevent adverse neurologic sequelae while achieving complete myocardial revascularization.
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