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Ann Thorac Surg 2000;69:1297-1298
© 2000 The Society of Thoracic Surgeons
a Dameron Hospital Heart Institute, 420 W Acacia St, Stockton, CA 95203, USA
e-mail: ctsurg2{at}inreach.com
To the Editor
The recent case report by Miyaji and colleagues [1] brings to the forefront some controversial issues in minimally invasive direct coronary artery bypass (MIDCAB) surgical procedures. In their article [1], a saphenous vein graft was placed between the left internal mammary artery (LIMA) and the left anterior descending coronary artery (LAD) to avoid the stress of mobilizing the LIMA as the patient was elderly and had significant comorbidities. We are entirely in agreement with this approach [2], and in our original article we also described additional ways of reducing surgical stress. The platform stabilizer should be attached to the operating room table rather than to the patient’s rib cage to reduce chest wall trauma. Removal of appropriate intercostal nerves and implantation of a pain catheter for postoperative bupivacaine injections also contribute to a striking reduction in postoperative pain and morbidity.
From this point on, however, we find ourselves in disagreement with Miyaji and colleagues’ technique. The "H" graft is essentially an extended side-to-side LIMA-to-LAD anastomosis that leaves the distal internal mammary artery (IMA) patent and in continuity with the LAD. As the authors state, this may "detract from the blood flow going to the coronary artery." It would thus probably be better in these cases to use the truly minimally invasive coronary artery bypass (TRUCAB) technique [3], in which the IMA distal to the anastomosis, the draining limb of the "H" arrangement, is clipped to prevent steal.
We have found that using a clip to occlude the distal IMA results in increased flow in the conduit. In addition, once the distal IMA is removed from the equation, it is easy to measure simultaneous pressures in the proximal IMA and in the conduit going to the LAD. In this way, it can be established that there is a satisfactory diastolic pressure gradient during the operation, and if necessary, appropriate corrections can be made [4]. Unfortunately, with the "H" arrangement, this critical measurement cannot be made.
Another point of contention relates to the lie of the graft. In the "H" graft technique, as the name implies, the conduit necessarily enters the coronary artery at a right angle. This may cause turbulence in the lumen of the LAD and may contribute to the premature formation of neointimal hyperplasia. In the TRUCAB technique, the graft is positioned so that it enters the coronary artery at an acute angle, in the manner of a freeway on-ramp. Blood from the graft merges with the extant coronary blood flow in a hemodynamically superior manner.
The direct LIMA-to-LAD anastomosis is the gold standard in MIDCAB surgical procedures. Because it is technically so easy to perform, it is tempting to use the TRUCAB instead of the MIDCAB. However, until it is proved that long-term patency of the TRUCAB is equivalent to that of conventional MIDCAB, the TRUCAB technique is best reserved for use as a palliative procedure in the high-risk patient population in whom there is no intention of ever reoperating. In this context, there may be a small subset of younger patients in whom the "H" arrangement could be used as a temporizing procedure when it is anticipated that the whole length of the IMA will be needed for more extensive revascularization procedures in the years ahead.
References
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