Percutaneous Coronary Intervention for ST-elevation Myocardial Infarction
Achieving reperfusion in a timely fashion in patients with ST-elevation myocardial infarction (STEMI) has been established as an effective and life-saving treatment.1–4 This has usually been measured as door-to-balloon time with an established goal of 90 minutes as the time within which reperfusion should be achieved. Moreover, this measure is being incorporated as a core measure of quality care by a number of regulatory bodies in the US and Europe.5,6 However, when it became apparent that most centres in the US were not achieving this door-to-balloon time, a nationwide initiative to improve door-to-balloon times was launched.7–9 Subsequent assessments of door-to-balloon times have indicated a marked improvement in door-to-balloon times, primarily as a result of eliminating delays in the initial diagnosis of STEMI and earlier activation of the cardiac catheterisation laboratory.8,10,11
The mortality benefit of thrombolytic therapy is time-dependent, with the greatest benefit observed in those receiving therapy the earliest.12 The mortality advantage of primary percutaneous coronary intervention (PCI) is also critically dependent on the time required to achieve reperfusion. Although the data examining the relationship of time to primary PCI in STEMI patients have yielded somewhat inconsistent findings, most of the information available provides strong evidence that a shorter time to reperfusion with PCI is more efficacious.1,8,13 Moreover, there appears to be an almost linear relationship between door-to-balloon time and mortality, at least with times longer than 90 minutes;14 the door-to-balloon time and mortality relationship is less well characterised for times less than 90 minutes. By extrapolation from the thrombolytic era, where a mortality benefit was observed in reducing time to lytics from 60 to 30 minutes,12 it could be postulated that a similar mortality benefit should be observed by shortening door-to-balloon times as much as possible.
The Role of Culprit Percutaneous Coronary Intervention
In spite of the recent emphasis on reducing door-to balloon times, there has been little change in the management of patients once in the catheterisation laboratory to further reduce door-to-balloon times.6,15,16 As a result, relatively few data exist to guide strategies to decrease the ‘artery-to- balloon’ time, i.e. the time elapsed between the establishment of arterial access in the catheterisation laboratory and coronary angioplasty.
PCI for STEMI usually follows the traditional method observed in elective cases: initial diagnostic coronary angiography of all coronary territories to define the extent and severity of coronary artery disease (CAD), coronary dominance and the potential presence of collateral circulation. Frequently, left ventriculography is also performed prior to PCI to evaluate left ventricular function, measure end-diastolic pressure and check for the presence of mechanical complications, including ventricular septal defect or mitral regurgitation. Coronary angiography and left ventriculography can usually be rapidly performed. However, they may require significant time and substantially delay the PCI portion of the procedure. This delay may be of particular importance in older patients, in patients with prior bypass grafting and in patients with concomitant aortic valvular disease and/or significant disease of the aorta. Whether door-to-balloon time could be reduced by first performing culprit-vessel PCI and then completing coronary angiography and left ventriculography after reperfusion had been achieved, without undermining subsequent care, has not been studied.
In a small non-randomised pilot study, we evaluated the impact of culprit-vessel PCI without traditional diagnostic coronary angiography on doorto- balloon times.17 In this study, 50 patients underwent PCI of the coronary artery thought to be the culprit vessel for STEMI based on an electrocardiogram (ECG) prior to complete coronary angiography or left ventriculography. Door-to-balloon times and clinical outcomes were compared with those of a group of 85 patients with STEMI who underwent initial diagnostic coronary angiography followed by PCI of the culprit vessel. In the group undergoing traditional initial diagnostic coronary angiography, left ventriculography was performed at the discretion of the interventionalist, although it was usually performed after the PCI in most cases. Door-to-balloon times were reduced with culprit-vessel PCI to 66+20 minutes for STEMI compared with 79+28 minutes for traditional complete coronary angiography followed by PCI. The vascular-access- to-balloon time decreased by seven minutes. Importantly, these benefits were achieved when efforts to reduce door-to-balloon times to under 90 minutes had already been implemented, with over 90% of patients achieving door-to-balloon times under 90 minutes in the traditional PCI group. Significant left main or three-vessel CAD, cardiogenic shock or mechanical complications of MI were infrequently observed and similar in each group.
In-hospital and 30-day outcomes were similar in these small groups of patients. Although there is evidence supporting better outcomes with decreased time to treatment in STEMI, the potential benefit resulting from a seven-minute decrease in arterialaccess- to-balloon time is unclear. Thus, while the strategy of performing culprit-vessel PCI alone for STEMI showed promise based on the results of these trials, further studies will be needed to determine whether this strategy translates into better patient outcomes.
The Case for Traditional Catherisation and Percutaneous Coronary Intervention for ST-elevation Myocardial Infarction
Concerns about adopting direct culprit-vessel PCI in STEMI include the possibility of precluding optimal therapy in patients whose anatomy is better suited for surgical rather than percutaneous revascularisation, or in patients with mechanical complications of MI necessitating surgery; only limited data are available to guide decision-making in this area. In our small study, only 6% of patients from both groups were found to have three-vessel or severe left main CAD on coronary angiography. No patients were reported to have mechanical complications of MI necessitating surgery. Disease that could potentially alter the decision to proceed with PCI is infrequently found in STEMI patients, which is manifested by an extremely low rate of immediate coronary artery bypass graft (CABG) (0.1%), as shown in a recent study of fibrinolytic and PCI treatment of STEMI patients.18 Although patients with complex or mechanical complications may ideally be better treated in the operating room, it is usually impractical to take these patients to the operating room in a timely fashion. In our experience, after consultation with the surgical team in these types of cases, we were invariably asked to perform PCI of the occluded culprit vessel with re-evaluation of the patient for surgery after some degree of recovery had occurred. Based on these experiences, where potential surgical disease is present we now proceed with PCI for STEMI without waiting for surgical consultation, but alert the surgical team that the patient should be followed after the PCI and evaluated for surgery as necessary.
The Case for Culprit Percutaneous Coronary Intervention for ST-elevation Myocardial Infarction
The principal argument for performing culprit PCI for STEMI is that it provides the fastest means possible of obtaining effective reperfusion. Moreover, several other factors influence the argument for performing culprit PCI for STEMI versus the traditional approach. While CABG is appropriate for many patients with advanced CAD and/or mechanical complications of MI, its role in the initial treatment of STEMI has evolved.
First, the actual number of cases undergoing emergency revascularisation procedures requiring CABG has dramatically fallen in the past decade.19,20 This is likely due to both better and safer PCI procedures and earlier treatment of patients with STEMI. Second, mobilisation of the operating room, even under the best of circumstances, generally exceeds a satisfactory time to achieve reperfusion in STEMI patients. Finally, there has been a growing acceptance of staged PCI procedures, as well as hybrid revascularisation procedures utilising both PCI and CABG, either at the same time or as part of a planned revascularisation strategy.21 Thus, the identification of left main or three-vessel coronary disease itself is not a contraindication to performing PCI of a culprit vessel in a STEMI patient with a staged PCI or CABG as deemed necessary later.
Towards an Optimal Strategy for Percutaneous Coronary Intervention for ST-elevation Myocardial Infarction
Understanding the extent and severity of CAD present at the time of STEMI not only is relevant to decision-making about the type of revascularisation (percutaneous versus surgical), but also provides information that can guide the type of PCI (balloon only versus stent) and type of stent (bare-metal stent [BMS] versus drug-eluting stent [DES]) that should be used during PCI. The decision, at least in the US, about how to proceed with percutaneous therapy for STEMI hinges on two factors: will the patient need to have early post-PCI cardiac surgery, and can the patient take clopidogrel for a prolonged period of time? If information is available that suggests that surgery should be performed for additional disease or mechanical complication, strategies that limit post-PCI clopidogrel use can be chosen (i.e. percutaneous transluminal coronary angioplasty [PTCA] versus stent or BMS versus DES). The surgeon can then proceed with confidence that the optimal strategy has been chosen.
While culprit PCI for STEMI is the quickest way to achieve reperfusion in general, there are specific circumstances in which a tailored approach may provide a more optimal strategy. In almost all cases of STEMI, we use guide catheters as the initial diagnostic catheter to allow rapid transition to PCI once the culprit vessel has been identified.
For anterior or lateral STEMI, the initial guide shot provides sufficient information about possible left main or severe three-vessel involvement that proceeding with PCI without visualising the right coronary artery should not hamper decision-making about possible surgical revascularisation. For inferior or posterior STEMI, initial limited angiography of the left main, anterior descending and circumflex prior to PCI of the right coronary artery (the presumed culprit vessel) can provide important information about the extent of disease. In patients with prior CABG and STEMI the optimal approach is problematic. We favour a culprit strategy because some information about the patient’s anatomy is usually available, and the STEMI often reflects occlusion of a vein graft supplying the culprit territory. In patients with cardiogenic shock, an initial assessment of the possibility of a mechanical complication should be performed by physical examination and/or a bedside echo prior to catheterisation, or during insertion of an intra-aortic balloon pump. Ultimately, a balance must be struck between the benefits of immediate reperfusion and a comprehensive, if rapid, assessment of the overall needs of the patient at the time of the STEMI.