By-pass surgery - CABG
Along with angioplasty this is the other coronary revascularisation technique used for the treatment of IHD (ischaemic heart disease).
Indications
- Various studies have shown that high and medium risk patients can benefit from CABG, but there is no benefit to low risk patients.
o The greatest degree of benefit is for those with LAD disease and 1/3 artery disease. Those with only one artery involved (and it is not the LAD) have less benefit
o The benefits are reduced the longer you leave it between identifying those who would benefit, and carrying out the surgery.
PCI or CABG?
Not that – (according to the oxford handbook) – PCI has no effect on mortality, but CABG does!
- Single lesions in nice straight vessels – PCI
- Calcified lesion is tortuous vessels – CABG
- LAD – CABG
- Other single or double vessel involvement – PCI
- Strongly positive ETT – CABG
Single, double triple?
This refers to the number of coronary arteries bypassed by the procedure. This however, does not necessarily reflect the severity of the disease. For example somebody may have very severe disease in one artery, whilst somebody else may have less severe disease, but spread over 3 arteries.
Procedure
- Normally performed through a mid sternal inscision (medial sternotomy)
- Veins are usually harvested from the saphenous vein of the legs – however, arteries may also be used, and arteries tend to give better results. This often occurs after the thorax has been opened and the surgeon has examined the arteries.
o Arteries that can be used include; internal thoracic arteries (internal mammary), gastro-epiploic, inferior epigastric, radial artery.
o Over 75% of patients have 3 grafts or more – at least one of these grafts is usually an artery
o After 10 years, 83% of internal thoracic grafts are still patent, but only 41% of saphenous grafts.
- The arteries to be by-passed are reviewed an angiography by the surgeon before the procedure.
- Most surgeons prefer to perform the operation with cardioplegia. This is where the heart is manually stopped during an operation. It usually involves cooling the heart to around 34’C (mild hypothermia), before injecting cold crystalloid cardioplegic solution into the coronary circulation. This induces asystole but it also protects the myocardium from damage.
o Antegrade cardioplegia – this is where the solution is introduced via the aortic root
o Retrograde cardioplegia – this is where the solution is introduced via the coronary sinus
o During cardioplegia, blood is diverted from the SVC and IVC via venous cannulae to a heart lung machine. This device both oxygenates and pumps the blood, as well as removing CO2.
o Many surgeons also use an aortic cross clamp. This is a device that goes across the aorta and limits the systemic circulation.
o During the operation the heart may be cooled to 15-20’. This slows down the metabolism of the heart and thus reduces the risk of damage to the myocardium.
o Blood may be injected into the coronary arteries in a bid to reduce myocardium damage if the surgery last longer than ½ hour.
Operating without a pump – off pump coronary artery bypass grafting (OFCAB)
Developed in the 1990’s, this is being increasingly used. it has shorter procedure times and fewer complications.
Prognosis
- A successful graft lasts about 10-15 years.
- The surgery decreases the risk of death from CVD. However, 5 years after the surgery, the risk is about the same as somebody who has always been managed on drug treatments
- The age of the patients affects the prognosis – generally, the younger the patient the better the prognosis, and longer the graft will be viable for.
- The surgery significantly increases the quality of life, reduces symptoms, and increases exercise tolerance, as well as reducing the need for anti-anginal medications.
- 75% of patients are free of ischaemic events at 5 years. This is around 50% at 10 years
- At 10 years:
o Those who had a saphenous graft have no benefit over those on medical therapy
o Those who had an arterial graft do still have benefit
- The greatest benefit is to those with left main stem disease.
- Women, on average, have worse outcomes than men. This is thought to be the result of a combination of factors, including; smaller coronary arteries, higher age at operation.
Complications
- Death – (1-3%) – the risk of this is increased in those that are:
o Smokers
o Overweight
o Obese
o Diabetic
o Female
o Older
o Short (height)
o Having an emergence operation for an acute coronary syndrome
- MI – 2%
- Ventricular arrhythmias – such as broad complex tachycardia
- Stroke – 2%. Reducing the amount of handling of the aorta can reduce the risk of embolism. The risk of stroke is also higher in those that have carotid artery stenosis.
- Bleeding – clopidogrel and aspirin should be stopped 7 days before surgery. Note that in PCI, they are often actually used during and after surgery!
o CABG seems to increase the resistance of patients to aspirin. Thus the drug is not as effective in these patients due to increased cell turnover.
- Cognitive decline – has been reported in many patients but is difficult to measure. It is often mild and will reverse several months after treatment.
Long-term management
- Cessation of smoking
- Aspirin
- ACE inhibitor
- Beta-blocker
- Statin
- Control of BP
- Control of diabetes
- Weight and exercise management
Notes by Tom Leach
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