Should the ACC/AHA guidelines be changed in patients undergoing vascular surgery?

In western countries, annually about 4–10% of the population is scheduled for non-cardiac surgery. Patients undergoing vascular surgery are known to be at increased risk of peri-operative mortality and other cardiac complications due to underlying (a)-symptomatic coronary artery disease (CAD). Although the overall peri-operative event rate has declined over the past 30 years, 30-day cardiovascular mortality still remains as high as 3–5%. Myocardial infarction (MI) accounts for 10–40% of post-operative fatalities and can therefore be considered as the major determinant of peri-operative mortality associated with non-cardiac surgery. The pathophysiology of a peri-operative MI (PMI) is not entirely clear. However, similar to MIs occurring in the nonoperative setting, coronary plaque rupture, leading to thrombus formation and subsequent vessel occlusion is suggested as an important causative mechanism. Surgery is an important stress factor leading to an increase in the incidence of plaque rupture. In patients with significant CAD, PMI may also be caused by a sustained myocardial supply/demand imbalance due to prolonged haemodynamic stress inducing sustainedmyocardial ischaemia. Both factors, acute thrombus formation and sustained myocardial ischaemia, probably contribute equally to the pathophysiology of PMI. In order to improve post-operative outcome, the ACC/AHA developed guidelines for pre-operative cardiac risk evaluation. They provide an algorithm for a stepwise approach. Patients are divided into three groups; those who underwent a previous coronary revascularization, previous cardiac testing, and all other remaining patients. If patients underwent a coronary revascularization in the past 5 years and if the clinical status has remained stable without recurrent symptoms or signs of myocardial ischaemia, further cardiac testing is not indicated and the patient can directly send for surgery. Similarly, patients who underwent non-invasive testing or coronary angiography in the past 2 years, in the absence of unfavourable results and without new symptoms, can also send for surgery without further evaluation. All other patients are analysed according to the presence of major, intermediate, and minor clinical risk factors (Table 1) and by addition of procedural risk the individual risk can be assessed. In patients with major risk factors, surgery should be post-poned until these symptoms are adequately treated. Patients with no or only minor risk predictors represent a low-risk population and further evaluation is only necessary for those with a poor functional capacity undergoing vascular surgery. However, in patients with intermediate risk predictors, additional non-invasive evaluation is recommended to assess the presence of myocardial ischaemia and to determine further peri-operative management. The present study of Bursi et al. reported that despite pre-operative risk stratification according to the ACC/AHA guidelines, patients undergoing elective major vascular surgery are still at high risk of MI and death. Event rates were as high as 45, 23 and 9% in patients with previous revascularization without recurrent symptoms or signs of CAD, with intermediate, and those with minor or no clinical predictors, respectively. These findings question the current recommendations and, moreover, indicate that the ACC/ AHA guidelines are of limited use to pre-operative risk stratification in vascular surgery patients. The high event rates (45%) in a small subpopulation of patients who underwent previous revascularization without signs of CAD, might be explained by an incomplete or failed revascularization or silent ischaemia. These pitfalls should be taken into account when stratifying these patients. In addition, it should be noted that atherosclerosis is an ongoing disease and that plaque progression and vulnerability is unpredictable and is responsible for 50% of all PMIs. This also has important implications for the current guideline stating that the subgroup of patients who have undergone (non-)invasive coronary evaluation in the past 2 years, in the absence of unfavourable stress test results or changes of symptoms, can undergo surgery without further evaluation. Because of the unpredictable character of CAD, this 2-year time lap may be much too long.