Coronary Revascularisation

There are three management options for patients with ischaemic heart disease:

• Medical therapy and risk factor modification: main option for stable, low-risk patients, and should be given to all patients with ischaemic heart disease (see articles on secondary prevention and cardiac rehabilitation). In low-risk patients with stable coronary artery disease, aggressive lipid-lowering therapy is at least as effective as angioplasty in reducing the incidence of ischaemic events.¹
• Coronary artery bypass graft surgery (CABG): has been shown to produce better survival rates compared to medical therapy. However the degree of improvement decreases after five years.²
• Percutaneous coronary intervention (PCI): for patients with single-vessel coronary artery disease, PTCA (percutaneous transluminal coronary angioplasty) offers earlier and more complete relief of angina than medical therapy and is associated with better performance on the exercise test. However, PTCA initially costs more than medical treatment and is associated with a higher frequency of complications.³

In general, PTCA is less invasive and requires a shorter hospitalisation and recovery time than does bypass surgery. However, the disadvantages of PTCA include restenosis of treated lesions and a lesser ability to revascularise all lesions in patients with multivessel disease.⁴ Stents are more effective than PTCA in preventing adverse events and revascularisation. Studies comparing drug-eluting stents with CABG have commenced but no reports of results are currently available.⁵

There continues to be controversy and debate regarding the exact indications of CABG and PTCA with arguments in favour of the benefits of CABG⁶ and those who feel modern techniques for PTCA make this the method of choice for the majority of patients.⁷ One recent study found that among patients judged clinically appropriate for coronary revascularisation, coronary artery bypass grafting seemed cost effective but percutaneous coronary intervention did not.⁸

• Risk assessment (and modification) to include smoking, weight, diet, exercise, cardiac function, blood pressure, glucose control, lipids and renal function.
• Methods for recognising severe ongoing ischaemia include:
  • A resting ECG with ST depression in multiple leads in someone who has recently had unstable angina.
  • A strongly positive exercise ECG test e.g. widespread ST depression in the first two stages of the Bruce protocol (less than 6 minutes).
  • Strongly positive myocardial perfusion scan e.g. a large or multiple reversible perfusion defects.
• Angiography for those with:
  • Evidence of continuing extensive ischaemia (e.g. a strongly positive exercise test) and/or,
  • Angina that persists despite optimal medical therapy and lifestyle advice.

Using a published stratification system to help determine the balance of risks and benefits and to help determine each patient's relative priority for treatment.⁹

• The Ontario scoring system: designed to assess the urgency of intervention.
• PARSONNET and EUROSCORE: are both designed to estimate the risk of in-hospital operative mortality.^10,11

• A number of important factors influence the likely balance of risks and benefits. These include:¹¹
• Smoking: associated with poorer long-term survival after CABG. Those who stop smoking are less likely to undergo repeat surgery or to have a heart attack.
• Diabetes mellitus: have poorer long-term survival after revascularisation. Good diabetic and hypertension control reduces the rate of progression of vascular disease.
• Impaired left ventricular function: despite a higher operative mortality, they also obtain greater long-term survival benefit from revascularisation than people without impaired left ventricular function.
• Advanced age: procedure-associated risk rises rapidly with age.
• Gender: women may have a higher procedure-associated mortality than men.¹²
• Recent myocardial infarction or episode of unstable angina: recent coronary events increase procedural risk.
• Unfavourable coronary anatomy: extensive disease in the distal parts of coronary arteries reduces the likely benefits of intervention.

Indications

• Angiogram has shown significant narrowing of:
  • Left main coronary artery, or
  • Three coronary arteries, or
  • Two coronary arteries including the proximal left anterior descending coronary artery or symptom relief (i.e with suitable coronary anatomy where severe angina persists despite optimal medical therapy).
• CABG continues to be the complete revascularisation option for patients with multivessel, multi-lesion CAD, in part because of its application to chronic occlusions.
• The long term outcome for the use of CABG for patients with diabetes have consistently been superior to the use of PCI. The difference is reduced with the use of stents and adjunctive medication but CABG is still the preferred method of revascularisation for patients with diabetes.

Complications

Some of the morbidity following CABG relates to the use of cardiopulmonary bypass and so off-pump coronary artery bypass (OPCAB) surgery has been developed.¹³

• Neurological abnormalities include major focal neurological deficits, stupor, coma, deterioration in intellectual function or memory.
• Mediastinitis.
• Renal dysfunction.
• Approximately 50% of vein grafts are closed by 10 years after operation.¹⁴

Indications

• Operable narrowings of one vessel or two coronary arteries without significant narrowing of the left main stem.
• Although PTCA was initially used only for the treatment of single-vessel CAD, in recent years new medicines (e.g. glycoprotein IIb/IIIa receptor blocking drugs) and new equipment (e.g. intra-coronary stents) have been developed and have resulted in its expanded use for patients with multivessel disease.
• NICE recommends that stents should be used routinely when PCI is used for patients with either stable or unstable angina or with acute myocardial infarction.¹⁵
• The use of stents, aspirin, clopidogrel, and glycoprotein IIb/IIIa inhibitors lowers the rate of restenosis to less than 10% at 6 months in optimal circumstances.¹⁶ Recent studies of stents coated with antiproliferative agents such as sirolimus have shown promise in lowering the restenosis rate after stenting.¹⁷ Folic acid supplementation following stenting has also been shown to lower the restenosis rate.¹⁸
• PCI is the acute stabilisation method of choice for patients with on-going ischaemia and acute myocardial infarction, especially among patients with haemodynamic compromise, and/or major comorbidity.¹⁹
• Emergency PTCA is now used as first line management for all patients following acute myocardial infarctions in some centres and, if not used as a first line intervention, is recommended for those patients who are unsuitable for thrombolysis, or for those for whom thrombolysis has failed.⁷
• If PCI is indicated as part of the early management of unstable angina or non-ST elevation MI, but is delayed, then the use of a glycoprotein IIb/IIIa inhibitor is recommended as an adjunct to PCI.
• It is also recommended that a glycoprotein IIb/IIIa inhibitor is considered as an adjunct to PCI for all patients with diabetes undergoing elective PCI, and for those patients undergoing complex procedures (e.g. multi-vessel PCI, insertion of multiple stents, vein graft PCI or PCI for bifurcation lesions).
• In procedurally uncomplicated elective PCI, where the risk of adverse sequelae is low, use of a glycoprotein IIb/IIIa inhibitor is not recommended unless unexpected immediate complications occur.²⁰

Complications

• The use of coronary stents has reduced the need for repeat revascularisation when compared with previous studies that used balloon angioplasty, though the rate remains significantly higher than in patients managed with CABG.²¹
• As measured one year after the procedure, coronary stenting for multivessel disease is less expensive than bypass surgery and offers the same degree of protection against death, stroke, and myocardial infarction. However, stenting is associated with a greater need for repeated revascularisation.²²