Cardiology and Cardiothoracic Surgery/Surgical Myocardial Revascularization

Indications

The American College of Cardiology and American Heart Association have released indications for myocardial revascularization with coronary artery bypass grafting.

Class I Indications for CABG in Patients with Stable Angina
Left main stenosis ≥50%
Left main equivalent (proximal left anterior descending and left circumflex disease)
Three vessel disease
One or two vessel disease in a patient with suitable anatomy and a large area of at-risk, viable myocardium.
Ischemic symptoms refractory to medical management

Class I Indications for CABG in Patients with Prior ST Elevation Myocardial Infarction (STEMI)
Persistent or recurrent ischemic symptoms or cardiogenic shock in a patient with suitable anatomy and in whom fibrinolytics/percutaneous coronary intervention have failed or are contraindicated
Hemodynamic collapse in a patient <75 years of age within 36h of STEMI and in whom CABG can be performed within 18h of shock onset
Life threatening ventricular arrythmias in a patient with left main stenosis ≥50% or triple vessel disease.

Vascular Conduits

The Greater Saphenous Vein

The greater saphenous vein graft (SVG) is a useful conduit for coronary artery bypass surgery due to simple harvesting procedure, resistance to spasm, and well published long-term outcomes.

The Interrupted ("Bridged") Technique for Saphenous Vein Harvest

The bridged technique for SVG harvest minimizes pain, maximizes wound healing, but increases the risk of trauma to the SVG due to the requirement for extensive manipulation.

Incision is made directly over the vein and sharp dissection performed to mobilize the conduit and ligate tributaries. Ligation of tributaries should be made initially long. Further clipping should be performed to render the clips flush with the SVG external wall (be careful not to narrow the vessel in the process).

Following removal of the SVG, it should be flushed with heparinized solution and stored in heparinized solution.

Surgical Pearls: Harvesting the Greater Saphenous Vein
Never grasp the saphenous vein with forceps.
Leave the saphenous vein tributaries long with initial clipping. Clip once again, flush with external wall.

The Left Internal Mammary Artery

The left internal mammary artery (LIMA) anastomosed to the left anterior descending artery (LAD) results in the most patent anastomotic combination for each of these two vessels, respectively. This has shown a clear translation to improved early and late mortality¹. Patency rates have been demonstrated at ~95 and ~90% at 10 and 15 years, respectively. This is in contrast to ~60 and ~32% patency for saphenous vein conduits².

Pedicled Harvesting of the Left Internal Mammary Artery

Following median sternotomy, self-retaining mammary retractors apply oblique traction to the left hemithorax. The operating table may be axially rotated to the patient's left side and tidal volume decreased in order to facilitate visualization of the left internal mammary artery (LIMA). The LIMA is identified in the bare area (see Surgical Anatomy of the Cardiovascular System) by inspection and under the transversus thoracis muscles by palpation.

The first incisions are made in the bare area endothoracic fascia at the level of the third rib 1cm on either side of the LIMA to include the internal mammary veins. The pedicle will be extended both distally (to the bifurcation of the LIMA) and proximally (to the inferior border of the subclavian vein) after this point. Gently move the LIMA to expose branches: these should be ligated after clipping the LIMA and thoracic mural sides.

Following completion of pedicling, heparinization of the patient should be ordered (before transection just proximal to the distal bifurcation). The distal remnant should be ligated with 2-0 silk and clipped. Apply a bulldog clamp to the distal end of the pedicle and wrap the pedicle in a papaverine soaked sponge.

Surgical Pearls: Harvesting the Left Internal Mammary Artery
Excessive retraction with self-retaining mammary retractors can cause costal fracture, excessive pain, and brachial plexus injury.
The first incision should be made under the third rib. Incision in the intercostal space may jeopardize arterial branches unnecessarily.
Never grasp the left internal mammary artery with forceps.
Always cauterize at the furthest distance possible from the LIMA.

References

1. Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal-mammary-artery graft on 10-year survival and other cardiac events. N Engl J Med 1986; 314:1

2. Tatoulis J, Buxton BF, Fuller JA: Patencies of 2127 arterial to coronary conduits over 15 years. Ann Thorac Surg 2004; 77:93