Acute Myocardial Infarction

Cardiac cell death that occurs due to ischaemia resulting from blockage of the coronary arteries

The most common cause is atherosclerotic narrowing with plaque rupture and formation of thrombus occluding the vessel as precipitating events. Depending on the rate and degree of vessel occlusion, a number of clinical conditions can result from plaque rupture and these are known as the acute coronary syndromes (ACS), AMI is the most severe of these and can be divided into 2 categories based on the ECG at time of diagnosis – ST elevation (STEMI) or non-ST elevation (NSTEMI).

In the early 1980s the importance of prompt opening of the occluded artery was recognised with the first study identifying the high prevalence of total coronary artery occlusion in the early hours following an AMI (68). This was the dawn of the era of interventional cardiology and there had already been pilot studies of mechanically opening the infarct related artery as well as selective use of lytic agents such as streptokinase (69;70). In 1983, the first case series on the feasibility of percutaneous transluminal coronary angioplasty (PTCA) during AMI in patients treated with and without prior thrombolysis was published (71). The use of balloon angioplasty as a means of opening an occluded vessel (instead of thrombolysis) was originally known as ‘primary angioplasty’. However, in the current era of intracoronary stents and other devices it is known as primary percutaneous coronary intervention (PPCI).

One of the main limitations of angioplasty in the setting of STEMI is the risk of vessel re-occlusion as well as restenosis. Stenting was first compared to balloon angioplasty in the Stent-PAMI Trial (72). This showed an overall benefit for stenting as compared to angioplasty that was driven by a reduction in target vessel revascularisation (TVR). The CADILLAC Trial showed a clear benefit of stenting over angioplasty (MACE 10.5% vs. 18.0% for angioplasty, p.

Drug eluting stents (DES) are more effective at reducing the need for repeat revascularisation than bare metal stents (BMS) in elective patients (77-78). Specific studies were designed to address whether they would have the same impact in PPCI (74-76). Furthermore with the questions regarding risk of late stent thrombosis with DES, there has been particular concerns regarding their use in the acute setting of MI, with high thrombus burden. Currently there remains a lack of consensus as to whether DES are superior to BMS in the PPCI setting. The need for TVR post PPCI has not been as great as that seen in other trials in other settings, and therefore uncertainty remains as to the cost-effectiveness of routine DES use in patients with AMI. Longer term follow up from the randomised trials (74-76), will allow evaluation of the risk of very late stent thrombosis. Currently most operators restrict use of DES in this setting to those patients deemed to be at especially high risk of restenosis.