Coronary revascularisation techniques

Principle

Early restoration of blood flow through an obstructed coronary vessel will prevent irreversible infarction and/or ongoing ischaemia. Revascularisation leads to benefit after acute coronary syndromes, including myocardial infarction. However, this is more often confined to symptom reduction rather than mortality benefit over medical therapy with efforts to reduce risk factors. High-risk patients, such as those with left main coronary artery disease, are more likely to show better survival rates.

Techniques

Pharmacological

Thrombolytic agents remain in common usage, though contraindicated in 15–20%. Older drugs such as streptokinase are being replaced by recombinant tissue plasminogen activators (rtPA) such as alteplase, reteplase, and tenecteplase these are easier to administer and appear more effective. However, the rate of recanalisation at 90min is only 55–60% and there is a 5–15% risk of early or late reocclusion. There is also a 1–2% risk of intracranial haemorrhage (with 40% mortality) and an increased risk of bleeding elsewhere (e.g. gastrointestinal tract, cannula sites). Other anticoagulant agents are administered alongside rtPA or PCI (see below), including heparin, warfarin, and antiplatelet agents—aspirin, clopidogrel, and the glycoprotein IIb/IIIa inhibitors (e.g. abciximab, eptifibatide, and tirofi ban).

Percutaneous

Percutaneous coronary intervention (PCI) has evolved since the 1980s, when stenotic lesions were simply dilated by transluminal coronary angioplasty (PTCA), to now include stenting of these dilated areas using baremetal and, more recently, drug-eluting stents. Though drug-eluting stents reduce the risk of restenosis and the need for repeat PCI, they carry an increased risk of ‘very late stent thrombosis’ plus undesired effects related to the stent polymer and the stent itself. Next-generation stents using new drugs, polymers, and drug delivery systems are in development to improve on current devices.

Surgical

Coronary artery bypass grafting (CABG), though declining in recent years due to the increasing use of preventive health measures and PCI techniques, still has an important role to play in bypassing stenotic lesions not amenable or suitable for PCI. While PCI is targeted at the ‘culprit’ lesion(s), CABG is directed at the epicardial vessel, including the ‘culprit’ lesion(s) and possible future culprits. Patients with single-vessel disease are more likely to have PCI, while those with triple-vessel disease are more likely to undergo CABG. Despite the increased morbidity and recovery time of CABG, mortality is similar to PCI. The advantages of CABG over PCI are better relief of angina and a lower likelihood of subsequent reocclusion. The magnitude of the latter benefit may decrease with drug-eluting stents. However, the increase in the rate of stroke with CABG offsets these advantages.

Critical care issues

• Increased bleeding risk with the use of anticoagulant agents. The prolonged action of aspirin and clopidogrel on platelet function (lasting 3–7d after discontinuation) will heighten the risk of bleeding, both peri-operatively and during critical illness. Fresh platelet transfusions may be needed to restore platelet functionality. Similarly, warfarin has a prolonged duration of action that can be reversed with fresh frozen plasma, prothrombin complex concentrates (e.g. OctaplexR), or recombinant factor VIIa. A balance has to be sought between bleeding risk (or severity of an existing haemorrhage) and stent thrombosis from discontinuation of the drug(s).

• Arrhythmias—commonly related to reperfusion and may occasionally be life-threatening.

• Mishaps related to PCI, including coronary artery rupture plus restenosis and acute occlusion of the stent.

• Complications related to CABG, including stroke, bleeding, and transient myocardial depression.