Risk stratification involves identifying patient risk factors in the context of the specific surgical intervention being proposed. Combination of the patient risk factors along with the surgical risks determines the likely risk of cardiac complications in the perioperative period. Initial history and physical exam should focus of identification of conventional cardiac risk factors. These include recent myocardial infarction, unstable angina, decompensated heart failure, and severe symptomatic valvular dysfunction. Additionally, conditions such as diabetes, prior stroke or transient ischemic attack and renal insufficiency should be identified, as they increase the risk of myocardial infarction. The type of surgery determines in part, the surgical risk. In the 2014 European Society of Cardiology/European Society of Anaesthesiology guidelines on non-cardiac surgery, high risk surgeries are those broadly estimated to confer a >5 % risk of 30-day cardiovascular death and MI, including aortic and major vascular surgery, many intra-peritoneal and intra-abdominal surgeries, pneumonectomy, total cystectomy, lung or liver transplant [9]. Intermediate risk procedures are those associated with a 1–5 %, 30-day risk of cardiovascular death and MI and include such operations as endarterectomy or stenting for symptomatic carotid disease, endovascular aneurysm repair, percutaneous peripheral arterial revascularization, head and neck surgery and renal transplant. The 2014 Perioperative Clinical Practice Guidelines put forth by the American College of Cardiology and the American Heart Association use the more parsimonious designations of “low risk” versus “elevated risk” where the combined surgical and patient characteristics predict perioperative MACE rates of <1 % or ≥1 %, respectively [1].

Numerous schema for assessment of patient risk are available, including the Revised Cardiac Risk Index (RCRI), the myocardial infarction/cardiac arrest (MICA) risk calculator by Gupta et al. and the Vascular Study Group of New England Cardiac Risk Index (VSG-CRI) [12, 13], with RCRI remaining the most commonly used. The RCRI, also referred to as the Lee index, was validated in a study of over 2800 patients published in 1999 and has since been shown to be robust in identifying patients with low versus high cardiac risk [13, 14]. The newer MICA score, derived using the National Surgical Quality Improvement Program (NSQIP) database inclusive of 211,410 patients, has been shown to better predict perioperative cardiac risk compared to the RCRI (C statistic 0.874 versus 0.747) however has yet to be confirmed via broad external validation [12]. One of the acknowledged weaknesses of the widely-used RCRI score is its ability to accurately predict the cardiac risk in patients undergoing vascular surgery. The VSG-CRI score was developed specifically for this patient population and has been demonstrated to be superior in predicting risk of adverse cardiac events in patients undergoing vascular surgery compared to RCRI [15].

Once a patient at high perioperative MACE risk has been identified through a combination history, physical examination and aforementioned risk prediction models, the next decisions often relate to proceeding with invasive cardiac diagnostics and coronary revascularization prior to surgery. The role of routine coronary angiography prior to surgery has long been an area of debate with conflicting results in the published literature. Hertzer et al. found that in a prospective cohort of 1000 patients undergoing routine coronary angiography in the context of planned elective vascular surgery, preoperative revascularization with coronary artery bypass grafting (CABG) in patients with severe coronary artery disease (CAD) improved 5-year mortality as compared to those with severe CAD who were not revascularized prior to surgery [16]. A decade later, Eagle et al. published a larger study using medically managed and surgically revascularized patients from the Coronary Artery Surgery Study registry who subsequently underwent noncardiac surgery [17]. In a total of 1961 patients undergoing higher-risk (abdominal, vascular, thoracic, and head and neck) surgery, prior CABG was associated with fewer postoperative deaths (1.7 % versus 3.3 %, P = .03) and MIs (0.8 % versus 2.7 %, P = .002) compared with the cohort of patients with medically managed CAD. In the same analysis it was also noted that patients undergoing low risk surgeries (urologic, orthopedic, breast) had low mortality irrespective of revascularization history [17]. These trials thus indicated that surgical coronary revascularization may be beneficial in patients with severe multivessel coronary artery disease undergoing high risk noncardiac procedures; however, these trials also drew criticism given their retrospective and non-randomized nature and also because of the implicit risk associated with the revascularization itself.

Since then, several randomized controlled trials have been conducted to understand the role of preoperative revascularization (inclusive of percutaneous and surgical revascularization) in patients undergoing high risk surgery. The CARP trial screened 5859 patients from 18 Veterans Affairs medical centers, of which 510 patients (9 %) were randomized to either coronary revascularization or medical management prior to elective vascular procedures (peripheral arterial revascularization or abdominal aortic aneurysm surgery) [18]. Eligibility was determined by a preoperative coronary angiogram that demonstrated ≥70 % stenosis in ≥1 coronary artery, amenable to revascularization. The majority of exclusions were either due to low cardiac risk, need for urgent vascular surgery, or due to history of revascularization with CABG or percutaneous coronary intervention (PCI) without evidence of ischemia. In this pivotal trial, prophylactic revascularization, either with PCI (59 %) or CABG (41 %), did not reduce 30-day MI rates compared to optimal medical management (12 % vs. 14 %). Additionally, there was no difference in mortality at 2.7-year follow-up (22 % vs 23 %) [18]. Limitations of the study included the fact that patients with obstructive left main coronary artery disease and left ventricular ejection fraction <20 % were excluded, and that the majority of the patients either had 1 or 2 vessel disease with preserved left ventricular function, potentially biasing the study towards a lower risk population and therefore fewer potentially preventable events. Indeed, only 32 % of the study population had triple vessel coronary disease and only about 40 % of study patients were reportedly symptomatic. Nevertheless, the topline results of the study left little room to support routine revascularization in stable coronary artery disease patients prior to elective vascular surgery. A separate analysis of patients who were screened and randomized (n = 462) as well as registry patients not randomized (n = 586, some because of high-risk coronary anatomy), lent some insight to the fate of patient cohorts omitted from or under-represented in the original CARP analysis [19]. Garcia et al. found that preoperative revascularization of unprotected left main coronary artery disease (discovered in 4.6 % of patients undergoing coronary angiography before vascular surgery) was associated with improved survival (0.84 vs 0.52, p <0.01). Survival was not improved however, in patients with 2-vessel (0.80 vs 0.79, p = 0.83) or 3-vessel coronary artery disease (0.79 vs 0.71, p = 0.15) undergoing revascularization [19].

In a similar timeframe, the DECREASE-V study also examined this issue by screening 1880 preoperative vascular surgery patients and further stratifying those with ≥3 risk factors (n = 430) using either dobutamine stress echocardiography or stress nuclear imaging [20]. Patients found to have extensive stress-induced ischemia on the non-invasive test (n = 101) were then randomized to revascularization (n = 49) or no revascularization (n = 52). In this relatively small but admittedly high-risk cohort of patients with inducible ischemia, there was no difference in non-fatal MI or overall survival rate at 30 days, 1 year and 2.8 years of follow-up, once again questioning the value of prophylactic revascularization prior to surgery [20, 21].

Another prospective, randomized study published in 2009 by Monaco et al., assigned 208 patients with an RCRI score ≥2 undergoing high risk vascular surgery, to either a “selective” angiography strategy where coronary angiography was performed only on the basis of a positive noninvasive stress test or to a “systematic” angiography strategy where coronary angiography was performed in all patients [22]. Not surprisingly, the rate of revascularization was higher in the “systematic angiography group” (58.1 % vs. 40.1 %; p = 0.01) and while there was a numerical reduction in MACE at 30 days in the systematic strategy, this did not reach statistical significance (4.8 % vs. 11.7 %, p = 0.1). At long term follow-up the “systematic angiography” strategy was associated with statistically significant reduction in cardiac events, including mortality at 4 years (69.6 % vs. 86.6 %, p = 0.003). The results were both provocative and impressive given that both groups were medically optimized with aggressive beta-blockade to HR <60 beats per minute. Important differences exist between the previously detailed CARP and DECREASE trials and the study by Monaco et al. Less severe coronary artery disease was encountered in CARP versus in this study (44 % of patients with 3-vessel CAD) potentially reducing the benefits of revascularization in the former. It should also be noted that both DECREASE-V and CARP required a demonstration of ischemia on noninvasive stress testing prior to revascularization. A number of limitations to this study have also been pointed out including its small size, and unblinded design [23–25]. In a similar study, Illuminati et al. randomized 426 patients pending carotid endarterectomy, with no evidence of CAD on history, ECG or echocardiogram to coronary angiography with selective revascularization versus carotid endarterectomy without prior coronary angiography. The authors concluded that routine (“systematic”) use of angiography significantly reduced the incidence of late MI and improved long-term survival, even after adjustment for covariates although lack of blinding was cited as an important limitation of this study as well [26]. Still other investigators have evaluated the utility of coronary angiography in other high risk cohorts such as patients undergoing surgery for type A aortic dissection, and have found no difference in mortality or MACE between those who underwent coronary angiography and those that did not [27].

In deference to the totality of observational and trial literature, the current ACC/AHA and ESC/ESA clinical practice guidelines are in general agreement as to the matter of prophylactic revascularization in stable or low-intermediate risk patients with CAD, for the purpose of reducing perioperative cardiac events: In both guideline statements, prophylactic revascularization garners a Class III designation (not recommended), Level of Evidence B and the stipulation in the ACC/AHA guidelines that there is “no benefit” [1, 9]. Both documents do however, endorse the performance of coronary revascularization before noncardiac surgery for accepted clinical indications (ACC/AHA guidelines: “when indicated by existing clinical practice guidelines”, ESC/ESA guidelines: “according to the applicable guidelines for management in stable coronary artery disease”, Class of recommendation: 1 (both), Level of evidence: C (ACC/AHA), B (ESC/ESA) [1, 9]. The European recommendations are further nuanced, stating that “late revascularization after successful non-cardiac surgery should be considered, in accordance with ESC Guidelines on stable coronary artery disease” (Class 1, Level of evidence C) and that “prophylactic myocardial revascularization before high-risk surgery may be considered, depending on the extent of a stress-induced perfusion defect” (Class IIb, Level of evidence B) [1, 9].

There is also general agreement with respect to revascularization in patients presenting with non-ST- elevation acute coronary syndromes (NSTE-ACS) and ST-elevation myocardial infarction (STEMI) in the setting of a pending elective noncardiac surgery even in the absence of any prospective trial to date addressing this clinical scenario. Both U.S and European recommendations support revascularization in accordance with the relevant clinical practice guidelines. Similarly, in patients requiring urgent or emergency surgery (without unstable cardiac disease) clinical risk stratification, guideline-directed medical therapy (if time and clinical condition permit) and proceeding with surgery without angiography/revascularization, is recommended [1, 6, 9].

When percutaneous revascularization is being considered for any of the aforementioned indications, the complex interplay between the completeness and durability of the revascularization, the anticipated duration of dual antiplatelet therapy, the type of stent(s) used and the urgency of the noncardiac surgery, must be taken into careful consideration.