Introduction
The most widely performed surgical coronary revascularization technique remains the left internal mammary artery (LIMA) to the left anterior descending (LAD) artery and reversed long saphenous vein aortocoronary bypass grafts to other arteries, performed using cardiopulmonary bypass on an arrested heart. However, there are two potential drawbacks to this technique. First, the known failure rate of long saphenous vein grafts and the accumulating evidence that the use of multiple arterial grafts significantly improve long-term outcomes .
The second drawback is the high rate of neurologic injury. The incidence of cerebrovascular events (stroke, transient ischemic attack, or neurocognitive decline) after isolated coronary artery bypass grafting (CABG) varies from 1% to 5% depending on the patient population and the criteria for diagnosis . In addition, in the SYNTAX trial the major disadvantage of CABG was the increased risk of periprocedural stroke, as compared to percutaneous coronary intervention (PCI) (2.2% CABG vs 0.6% PCI; P =.003) . These neurologic events are not benign: they have an important effect on patient quality of life and significantly reduce both early and late survival. In a recent metaanalysis a postoperative stroke resulted in early mortality of 21.3% (vs 2.4% without stroke) and in those who survived to discharge the mortality at 8 years postoperatively was 10.9% (vs 3.4% without stroke) .
Most neurologic events after CABG are ischemic in nature, with atheroembolic events playing a major part. The role of atheromatous disease of the ascending aorta ( Fig. 18.1 ) in these events has been postulated for almost four decades . The pathogenesis includes detachment of atheroma from the aortic intima as a result of external manipulation such as aortic cross-clamping, partial-occlusion clamping, cannulation, and internal disruption caused by the “sandblasting” effect of the high-velocity jet of blood exiting the aortic cannula and impacting the intima or pedunculated atheroma ( Fig. 18.2 ) . These mechanisms have been confirmed by multiple cadaveric and in vitro studies ; studies demonstrating the preponderance for right hemispheric involvement ; real-time transcranial Doppler studies during the various maneuvers ; as well as numerous case-series and cohort studies demonstrating the association of imaging evidence of atheromatous disease and peri-operative stroke .
Surgical techniques have long focused on minimizing neurologic injury following CABG. Off-pump coronary artery bypass (OPCAB) surgery, which avoids the use of cardiopulmonary bypass, was initially postulated . This may reduce the risk by avoiding cross-clamping, cannulation, emboli generated by the bypass circuit, and the sandblasting effect, but ultimately, off-pump surgery alone failed to improve outcomes in the large randomized trials . These trials however did not focus on aortic manipulation as their primary stratification method, and many patients still received partial-occlusion clamping for construction of proximal anastomosis. Techniques have now evolved to focus on eliminating all aortic manipulation (“aortic no-touch” or “anaortic”), and there is accumulating evidence to support this ( Table 18.1 ) . Anaortic OPCAB grafting (anOPCAB) in network metaanalysis against on-pump CABG with single cross-clamp, on-pump CABG with cross-clamp and partial-clamp, OPCAB with partial-clamp, and OPCAB with “clampless” devices (e.g. Heartstring) has been demonstrated as the superior technique . As a result, the 2018 European Guidelines on Myocardial Revascularization recommends “off-pump CABG and preferably no-touch techniques on the ascending aorta, by experienced operators, in patients with significant atherosclerotic aortic disease (Class IB)” . Indeed, anOPCAB may result in a risk of peri-operative stroke equivalent to that of PCI .
| Author | Type of study | Total patients | Comparison | Main findings |
|---|---|---|---|---|
| Calafiore | Single center | 4823 |
| The presence of any aortic manipulation rather than the use of CPB itself was identified as an independent predictor of cerebrovascular accidents, especially in patients with extracoronary vasculopathy |
| Kapetanakis | Single center | 7272 |
| Patients operated on-pump with double clamp were 1.8 times more likely to have a stroke versus those without any aortic manipulation (95% confidence interval: 1.15–2.74, P <.01) |
| Kim | Single center | 345 |
| Anaortic OPCAB grafting is associated with significant reduction in stroke risk compared to OPCAB with side-clamping and On-pump CABG (0% vs 0.8% vs 3.9%; P =.017) |
| Patel | Single center | 484 |
| There was a significantly lower incidence of permanent focal neurological events in OPCAB patients compared to the ONCAB group (0.4% vs 3.9%; P =.012) |
| Vallely | Single center | 1758 |
| Anaortic technique showed a significant neurological protection compared to the use of a side-biter clamp or PAD (stroke rate 0.25% vs 1.1% respectively; P =.037) |
| Lev-Ran | Single center | 700 |
| The use of partial aortic clamping was the only independent predictor of postoperative stroke (increasing the risk 28-fold; 0.2% vs 2.2%, P =.01) |
| Moss | Single center | 12,079 |
| Aortic clamping was independently associated with an increase in postoperative stroke compared with no-touch technique (adjusted OR 2.50; P <.01) |
| Albert | Single center | 13,279 |
| The anOPCAB technique reduced the overall and early postoperative stroke rate compared to on-pump CABG (overall: 0.49% vs 1.31%, P <.0001; early: 0.09% vs 0.83%; P <.0001) |
| Arrigoni | Single center | 400 |
|
|
| Zhao | Network metaanalysis | 68,837 |
| There was no difference in 30-day stroke risk when comparing anOPCAB with PCI (OR 0.92, 95% CI 0.47–1.78). Compared with CABG, anOPCAB (OR 0.28, 95% CI 0.20–0.38) and PCI (OR 0.31, 95% CI 0.17–0.55) were associated with 72% and 69% reductions in 30-day stroke risk, respectively |
| Misfeld | Metaanalysis |
|
| The rate of postoperative CVA was significantly lower in anaortic OPCAB (0.5% vs 1.4%; odds ratio, 0.46; 95% confidence interval, 0.29–0.72; I 2 =0.8%; P =.0008 |
| Pawliszak | Metaanalysis |
|
| Aortic “no-touch” was associated with a statistically lower risk of CVA as compared to side-clamp OPCAB (0.36% vs 1.28%; risk ratio 95% CI: 0.41 (0.27–0.61); P <.01; I 2 =0%) |
| Zhao | Network metaanalysis |
|
| An OPCAB was the most effective treatment for decreasing the risk of postoperative stroke (−78% vs CABG, 95% CI: 0.14–0.33; −66% vs side-clamp OPCAB, 95% CI: 0.22–0.52; −52% vs OPCAB-PAD, 95% CI: 0.27–0.86) |
Critics of OPCAB argue that increased technical difficulty may result in reduced graft patency and reduced graft numbers that lead to incomplete surgical revascularization and worse long-term outcomes . The ROOBY trial, in which OPCAB was performed by relatively inexperienced OPCAB grafting surgeons (20 cases to be eligible, 55% performed by residents), demonstrated this . However, this is not the experience in centers with high-volume and expertise in these techniques. Techniques are described herein to allow surgeons to achieve complete revascularization without manipulating the ascending aorta or its branches and utilizing a total-arterial grafting strategy.
Operative technique
Preoperative assessment and investigations
All patients referred for CABG undergo routine blood tests, ECG, chest X-ray, spirometry, and a transthoracic echocardiogram to assess for valvular disease and ventricular function and dilatation. All patients undergo bilateral carotid, vertebral, and subclavian artery duplex scans to assess concomitant peripheral vascular disease and the suitability of the internal mammary arteries for inflow. If significant carotid or subclavian disease is detected, then the patients undergo a CT aortogram with 4-vessel runoff to assess the arch vessel branches and the Circle of Willis. If a critical stenosis of either subclavian arteries is confirmed proximal to the take-off of the IMAs, we advocate for subclavian angioplasty and stenting before coronary revascularization in order to avoid coronary-subclavian steal syndrome . The radial artery is assessed with an Allen’s test (<5 seconds deemed suitable) . In borderline cases a pulse oximeter is used to perform Allen’s test, and if a pulsatile waveform is obtained with no reduction in oxygen saturation, then the artery is harvested, and if not then an alternative conduit is used. In selected patients (patients with diabetes, severe peripheral vascular disease, end-stage renal failure), we perform an ultrasound of the radial artery to look for extensive calcifications that would limit its use. Aspirin is continued up to the time of surgery.
Anesthetic considerations
Maintenance of normothermia throughout the operation is important and active warming with a forced-air warming blanket is commenced on arrival to the anesthetic room. All patients have a Swan–Ganz pulmonary artery catheter inserted and transesophageal echocardiogram (TEE). Elevation of the pulmonary artery diastolic (PAD) pressure in the presence of hypotension and regional wall motion abnormalities, respectively, is sensitive indicators of ischemia.
Low dose intravenous milrinone (0.1–0.2 μg/kg/min) is started after induction of anesthesia. This has a twofold benefit in increasing cardiac output for end-organ perfusion and as a systemic vasodilator when using all-arterial grafts . Avoiding a loading dose of milrinone reduces hemodynamic instability caused by vasodilation . Patients usually require a background noradrenaline infusion (0.01–0.2 μg/kg/min). The use of intravenous beta-blockers (metoprolol 2.5–5 mg boluses) is often required to achieve an optimal heart rate of 60–70 bpm.
Maintaining normovolemia is important, as hypovolemia is poorly tolerated particularly during repositioning of the heart. TEE and observation of cardiac filling by the surgeon are useful to guide volume status, together with arterial systolic pressure variation and dynamic responses to fluid boluses in the central venous pressure and PAD. Intravascular volume is maintained with synthetic colloids and intracellular volume is maintained with a background maintenance of balanced salt solution crystalloid. Systemic heparinization is used to maintain an activated clotting time greater than 450 seconds. Cell salvage is used in all cases. Point-of-care coagulation testing is performed routinely using rotational thromboelastometry and multiplate platelet function analysis .
The patient is positioned supine with the left arm gently abducted on an arm-board ( Fig. 18.3 ), prepped and draped and with a forced-air warming blanket covering the lower limbs.
Conduit and graft configurations
Our standard operation is to revascularize the LAD with an in situ skeletonized LIMA. The lateral and inferior walls are revascularized with an in situ skeletonized right internal mammary artery (RIMA)/radial tandem graft brought via the transverse sinus ( Fig. 18.4 ). This separates the anterior wall blood supply from the rest of the heart, thus protecting the integrity of the LIMA to LAD graft. There are also no grafts crossing the midline anteriorly making the management of mediastinitis and redo surgery safer. Performing multiple sequential grafts using the radial artery is technically easier than using a RIMA, a view shared by others . Another strategy is the use of LIMA/radial composite T or Y graft: LIMA to LAD and radial to the other targets . We consider this to be a good option in patients who have a contraindication to having both internal thoracic arteries harvested.
Finally, in the case of isolated left main disease or disease confined to the left system, then bilateral IMAs can be deployed with one of the following configurations: (1) RIMA to LAD and LIMA to the marginal branches of the circumflex ( Fig. 18.5 ); (2) LIMA to the LAD and RIMA off the LIMA as a T graft to the intermediate or marginal branches of the circumflex ( Fig. 18.6 ). A possible caveat of the first configuration is the RIMA crossing the midline anteriorly, which might pose a challenge in the case of redo sternotomy. It is important that the RIMA is adequately covered by anterior mediastinal fat and pericardium. If the LAD needs to be grafted more distally or there is cardiomegaly requiring more RIMA length, then the RIMA can be extended using the distal LIMA or a short length of radial artery. This can also assist in giving the RIMA a lie more superiorly in the mediastinum, which gives the graft more soft-tissue cover.
Our aim is to utilize all-arterial grafts. However, this is not always possible: (1) radial arteries may not be suitable (e.g., negative Allen’s test or dystrophic calcification), (2) the patient’s occupation (e.g., guitar virtuoso) or a patient’s personal wishes, (3) degree of right coronary artery stenosis <70% may dictate the saphenous vein as the graft of choice to extend the RIMA. Mid- to long-term data with IMA/vein composite grafts are satisfactory . Rarely, the right gastroepiploic artery is used.
Conduit harvesting and management
The internal mammary arteries are harvested using a fully skeletonized technique ( Fig. 18.7 ). This minimizes chest wall trauma, achieves maximum length, and reduces the risk of deep sternal wound infection during bilateral internal mammary artery harvest . The LIMA is harvested first. The left sternal edge is retracted using a Rultract Skyhook (Rultract, Cleveland, United States) as this provides optimal exposure. The LIMA is exposed by pushing the pleura laterally, using a combination of blunt dissection using a small surgical swab and sharp dissection using diathermy. The endothoracic fascia is carefully incised directly below and along the length of the LIMA using long Dietrich’s forceps and low power diathermy (20 W). The medial internal mammary vein is identified at the subclavian vein and divided after double-clipping both sides, as this improves the final length and lie of the LIMA and makes proximal harvest safer. The LIMA is harvested from above the left subclavian vein to its bifurcation, using a combination of blunt and sharp diathermy dissection and dividing the branches with diathermy after clipping the graft side. Alternatively, the Harmonic scalpel (Ethicon, Somerville, United States) can be used with a hook tip to harvest the LIMA. The curved edge is used to incise the fascia and divided coagulated branches, whilst the forward edge is used to liquify the fat surrounding the artery and coagulate side branches. The RIMA is harvested using a similar technique to the LIMA: it is mobilized up to the subclavian vein, with the medial soft-tissue swept back to the strap muscles to allow an unimpeded lie for the graft as it is brought medially. After systemic heparinization both IMAs are sprayed liberally with papaverine solution before being divided distally and then wrapped in a warm, papaverine soaked gauze. Length is not usually an issue with this operation and the RIMA can be divided proximal to the bifurcation to preserve lower sternal blood supply.
