Coronary Artery Bypass Graft

updated: August 18, 2016

LIMA to LAD (left internal mammary artery to left anterior descending artery)

LIMA to LAD

When looking at the cath lab films, the catheter the interventional cardiologist uses is about 7Fr - 0.3mm/Fr is the size of the vessel. So can guage the approximate size of the target vessel based on this simple math. If the vessel is less than 1.5mm, then it will probably not work because too small. 

Arterial versus venous grafts

  • During CABG arterial grafts are always preferred over venous grafts , for the simple reason the grafted vessel has to carry arterial blood and not the venous blood

  • Saphenous veins are tuned to carry venous blood at low pressure.The mean coronary arterial pressure is around 40mmhg and this will damage the saphenous venous endothelium more quickly

  • The reocculsion rate at 10 years for venous grafts  can reach  60%

  • Left internal mammary artery (LIMA) is the most commonly used arterial graft. This is usually anastamosed with LAD. The lumen of LAD &  LIMA are more or less equal and they match well in character also !

  • The other advantage  of  LIMA graft  is ,   blood    tends to  flow  both during systole and diastole in a smooth fashion.. Since the venous graft which  hangs from the root of aorta , the  ostium  of venous graft lacks the  hemodynamic benefits of   coronary sinus . (We know the coroanry sinus acts like a  reservoir for  the smooth release of  blood flow into coronary arteries.)

  • Finally ,  the most important feature of LIMA is it is a live graft; LIMA’s proximal origin from subclavian is left intact, so LIMA acts as a live vessel with it’s  vasa vasorum intact ,  which means the endothlium derived relaxing factor (EDRF-Nitric oxide) secretion is not interrupted.This makes the LIMA  an excellent graft , self protected against reocclusion. One may call it a drug eluting graft !

  • LIMA patency rates at 10 years is nearly 90 %. But the graft patency depends on many factors , like diabetes, age, gender, surgical technique ,(Now , beating heart CABG is very popular , where the LIMA patency is said to be slightly lower than conventional CABG) Sequential LIMA grafts, free LIMA graft ( Which  loses the advantage of being  a live graft) have relatively lower patency rates.

  • Other arteries that could be used are radial artery, right internal mammary artery, and gastro epiploic artery.The patency rates of all these arteries far less than LIMA .

  • Generally the best patency rates are achieved with the in-situ left internal thoracic artery (the proximal end is left connected to the subclavian artery) with the distal end being anastomosed with the coronary artery (typically the left anterior descending artery or a diagonal branch artery). Lesser patency rates can be expected with radial artery grafts and "free" internal thoracic artery grafts (where the proximal end of the thoracic artery is excised from its origin from the subclavian artery and re-anastomosed with the ascending aorta). Saphenous vein grafts have worse patency rates, but are more available, as the patients can have multiple segments of the saphenous vein used to bypass different arteries.

  • Veins that are used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. LITA grafts are longer-lasting than vein grafts, both because the artery is more robust than a vein and because, being already connected to the arterial tree, the LITA need only be grafted at one end. The LITA is usually grafted to the left anterior descending coronary artery (LAD) because of its superior long-term patency when compared to saphenous vein grafts.

Complications

  • Postperfusion syndrome (pumphead), a transient neurocognitive impairment associated with cardiopulmonary bypass. Some research shows the incidence is initially decreased by off-pump coronary artery bypass, but with no difference beyond three months after surgery.

    • neurocognitive decline over time has been demonstrated in people with coronary artery disease regardless of treatment (OPCAB, conventional CABG or medical management).

    • However, a 2009 research study suggests that longer term (over 5 years) cognitive decline is not caused by CABG but is rather a consequence of vascular disease.

    • Loss of mental function is a complication of bypass surgery in elderly people, and might influence procedure cost benefit considerations. 

    • Several factors may contribute to immediate cognitive decline.

      • The heart-lung blood circulation system and the surgery itself release a variety of debris, including bits of blood cells, tubing, and plaques. For example, when surgeons clamp and connect the aorta to tubing, resulting emboli block blood flow and cause mini strokes.

      • Other heart surgery factors related to mental damage may be events of hypoxia, high or low body temperature, abnormal blood pressure, irregular heart rhythms, and fever after surgery

  • Nonunion of the sternum; internal thoracic artery harvesting devascularizes the sternum increasing risk.[17]

  • Myocardial infarction due to embolism, hypoperfusion, or graft failure.

  • Late graft stenosis, particularly of saphenous vein grafts due to atherosclerosis causing recurrent angina or myocardial infarction.[18]

  • Acute renal failure due to embolism or hypoperfusion.[19][20]

  • Stroke, secondary to embolism or hypoperfusion.[21]

  • Vasoplegic syndrome, secondary to cardiopulmonary bypass and hypothermia

  • Graft failure: grafts last 8–15 years, and then need to be replaced.

  • Pneumothorax: An air collection around the lung that compresses the lung[20]

  • Hemothorax: Blood in the space around the lungs

  • Pericardial tamponade: Blood collection around the heart that compresses the heart and causes poor body and brain perfusion. Chest tubes are placed around the heart and lung to prevent this. If the chest tubes become clogged in the early post operative period when bleeding is ongoing this can lead to pericardial tamponade, pneumothorax or hemothorax.

  • Pleural effusion: Fluid in the space around the lungs. This can lead to hypoxia which can slow recovery.

  • Pericarditis

  • Lower extremity edema, extravasation, inflammation, and eccymoses from vein harvest; entrapment of up to 9 pounds (4.1 kg) of fluid in the extremity is common. This is managed with a thigh length compression stocking, elevation of the limb, and early and frequent slow walking; as well as avoidance of standing in place, sitting, and bending the leg at the knee more than a few degrees.

  • Open heart surgery associated[edit]

  • Post-operative atrial fibrillation and atrial flutter.[22]

  • Anemia - secondary to blood loss, plus the anemia of inflammation, inflammation being inevitable with opening the chest plus harvesting of leg vein(s) for grafting. A fall in the hemoglobin from normal preoperative levels (e.g. 15) to postoperative levels of 6 to 10 are inevitable. There is no benefit from transfusions until the hemoglobin falls below 7.5.[23]Institutions should establish protocols to ensure transfusions are not given unless the hemoglobin falls below 7.5 without some additional compelling reason(s).[24]

  • Delayed healing or refracture of sternum - the sternum is bifurcated logitudinally (a median sternotomy) and retracted to access the heart. Failure to follow "sternal precautions" following surgery could result in delayed healing or refracture of the sternum which was sutured at the closure of the chest wound:

  • Hold a pillow against the chest whenever getting out of or into a chair or bed; or coughing, sneezing, blowing nose, or laughing, in order to oppose the intrathoracic outward force created by these activities on the healing sternum.

  • Avoid using the pectoral muscles, such as by pushing on the chair arms to assist one's self out of a chair, or by using the arms to assist in sitting down. Proper standing technique is to rock three times in the chair and then stand to provide momentum for moving the center of gravity from the sitting to the standing position. Proper sitting technique is to slowly lower the bottom toward the chair seat using gluteus and quadriceps muscles ("legs only") without grabbing the chair arms. Second, patients should avoid lifting objects utilizing the pectoral muscles: carrying light objects with arms extended down at sides, and lifting light objects with the elbows pressed to the chest and using the biceps, are acceptable. Also, avoid using the arms overhead.

  • Avoid sitting in the car front seat (no driving) for at least four weeks: the explosion of the deployment of an airbag could refracture the sternal union.

Rewarming is associated with a decrease in ventricular compliance; that it, a decrease in EDV for any given EDP. At the bedside this can be extrapolated to mean that a normal wedge pressure in the early postoperative period represents a low EDV secondary to the amount of myocardial edema from cooling and reperfusion. Therefore, when cardiac output is low and the wedge is not elevated, volume infusion (crystalloid or colloid) is indicated until the wedge is in the range of 20 mmHg. 

 

Medications

 

Aspirin (first dose given within 24 hours post-operatively) 

  • 81 mg PO

  • or PR

... but I would more especially commend the clinician who, in acute diseases, by which the bulk of mankind are cutoff, conducts the treatment better than others.
 
Hippocrates, 400 BC