6 Preoperative Coronary Intervention

• Perioperative myocardial infarction (MI) can result from either coronary plaque rupture or a myocardial oxygen supply-demand mismatch related to a preexisting coronary stenosis; it typically occurs in the first 48 hours following surgery. Even if clinically silent, it is a powerful predictor of future adverse cardiac events.

• Beta-blocker therapy is associated with reduced cardiac event rates among properly selected patients at risk for complications during noncardiac surgery, but it can be harmful if used indiscriminately, especially among lower-risk individuals.

• The indications for performing preoperative coronary angiography and revascularization are the same as in the nonoperative setting.

• When it is undertaken in the preoperative period, percutaneous coronary intervention (PCI) is associated with increased procedural risk, especially among patients requiring vascular surgery.

• Because no prospective trial to date has demonstrated short- or long-term benefits from a strategy of routine preoperative PCI among patients with coronary disease, the indications for preoperative PCI are very limited. The use of PCI to “get a patient through” noncardiac surgery is unproven and potentially harmful.

• Noncardiac surgery performed within 6 weeks of bare metal stent (BMS) implantation or 12 months of drug-eluting stent (DES) placement is associated with elevated rates of stent thrombosis, an often catastrophic event associated with substantial mortality.

• Among patients with previously placed drug-eluting stents who require unanticipated noncardiac surgery, the decision to continue or suspend aspirin and thienopyridine therapy for surgery requires individualized assessment of the risks and implications of bleeding complications versus stent thrombosis and should be made with multidisciplinary input from the cardiologist, surgeon, and other involved subspecialists.

• Novel antiplatelet agents and bedside assays of platelet function offer promise in the management of antiplatelet therapy in the perioperative period.

• While prevention of cardiac complications through proper patient selection and management remains the cornerstone of achieving low surgical mortality rates, prompt recognition and treatment of post-operative complications when they do occur represents an equally important factor in optimizing surgical outcomes.

Introduction

Of the over 30 million surgical procedures requiring the use of general anesthesia performed annually in the United States, approximately one-third involve patients who are at risk for or have known coronary artery disease. Given the physiological stresses that accompany surgery, the perioperative period represents a time of substantially heightened risk for adverse cardiac events. Current evidence suggests that the routine use of coronary revascularization in the preoperative setting is unlikely to reduce the incidence of subsequent cardiac events. Nevertheless, selected patients at particularly increased risk for cardiac complications related to noncardiac surgery may benefit from preoperative PCI. Optimal performance of preoperative PCI requires awareness of several procedural issues that are unique to the preoperative setting. This chapter provides a clinically oriented review of preoperative PCI, including the indications for coronary angiography and revascularization prior to upcoming surgery, the utility of various medical and interventional strategies to reduce perioperative risk among patients with known or suspected coronary disease, technical approaches to performing angioplasty and stenting prior to noncardiac surgery, and strategies for managing patients with prior DES placement who subsequently require unanticipated noncardiac surgery.

Overview of Perioperative MI

As with MI outside the context of surgery, perioperative MI can result either from the rupture of an atherosclerotic plaque with thrombotic occlusion of the involved coronary artery or from a transient stress-induced mismatch of myocardial oxygen supply and demand, typically in the setting of a fixed coronary artery stenosis or occlusion.¹ Thrombosis of a previously implanted coronary stent represents another potential mechanism of perioperative MI and has been described among patients undergoing noncardiac surgery early following BMS implantation and up to several years after DES placement. In the vast majority of instances, perioperative MI does not occur during the surgical procedure itself but rather within the first 48 hours following surgery. This period is associated with multiple hemodynamic stresses and hematological alterations that can predispose to plaque rupture, myocardial oxygen supply-demand mismatch, and a hypercoagulable state (Fig. 6-1). The incidence of myocardial ischemia and infarction in the period surrounding noncardiac surgery is a function of both the type of surgery and the risk profile of the population being studied. The ACC/AHA guidelines for perioperative assessment classify specific operations as high risk (>5% reported rate of cardiac death and nonfatal MI), intermediate risk (1%–5%), or low risk (<1%) (Table 6-1).² Perioperative MI, whether clinically apparent or silent, is associated with increased mortality in both the short and long term. In-hospital survival rates for perioperative MI typically exceed 90%, which is similar to that of MI in the nonoperative setting. As with clinically silent MI detected following PCI, even smaller infarcts detected following noncardiac surgery are associated with up to a two- to fourfold increase in medium- to late-term mortality independent of other clinical factors.^3,⁴

Figure 6-1 Pathophysiological events contributing to the genesis of perioperative MI. BP, blood pressure; HR, heart rate; NSTEMI, non-ST-segment elevation myocardial infarction.

TABLE 6-1 Cardiac Risk * for Noncardiac Surgical Procedures

Vascular (reported cardiac risk often greater than 5%)

Aortic and other major vascular surgery

Peripheral vascular surgery

Intermediate (reported cardiac risk generally less than 5%)

Intraperitoneal and intrathoracic surgery

Carotid endarterectomy

Head and neck surgery

Orthopedic surgery

Prostate surgery

Low (reported cardiac risk generally less than 1%)

Endoscopic procedures

Superficial procedure

From The ACC/AHA Guidelines on Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery.²

Determining Operative Risk

Concepts

For the process of preoperative evaluation to be a clinically useful exercise, two goals must be met: (1) the evaluation must result in the identification of a subgroup of patients at heightened risk of short- or long-term cardiac complications during or after surgery, and, equally important; (2) once this higher-risk group is identified, there must exist some intervention that can modify that risk, whether the intervention involves canceling surgery, or serves to make surgery safer (for example by prescribing a medication, changing operative approach or route of anesthesia, or intervening to correct an underlying problem, as through coronary revascularization). Several models have been devised that allow prediction of operative risk based on a patient’s clinical history and the results of noninvasive testing. In culling findings from a wealth of studies, the ACC/AHA consensus guidelines for preoperative evaluation prior to noncardiac surgery have become a widely used clinical tool not only to identify operative risk but also to serve as a guideline for the appropriateness of further testing and intervention.

The guidelines recommend a stepwise approach in determining the need for invasive testing prior to noncardiac surgery. First, patient-specific risk is determined through the assessment of clinical risk factors and symptoms, overall functional capacity, and the timing and results of prior coronary evaluation and treatment if applicable. Second, surgery-specific cardiac risk is determined based on the expected incidence of cardiac events associated with the particular surgery the patient is scheduled to undergo, as previously discussed. The decision of whether to perform noninvasive stress testing is then based on assessment of the patient and surgery-specific risks. Despite the comprehensive nature of the ACC/AHA preoperative guidelines, adherence to the guidelines in “real-world” clinical practice is highly variable.⁵

Indications for Coronary Angiography

The indications for performing coronary angiography as part of a preoperative assessment are identical to those in the nonoperative setting, and include the following ^2,⁶:

• Noninvasive test results suggesting a high risk of adverse outcomes, such as extensive (multivessel distribution) myocardial ischemia, prior to high-risk surgery.

• An equivocal noninvasive test result in a patient with multiple clinical risk factors facing high-risk surgery

• The presence of exertional angina not responsive to appropriate medical therapy, especially when the patient is facing a moderate- or high-risk surgical procedure.

• The presence of unstable angina or recent MI.

It must be emphasized that, given the absence of prospective data indicating that surgical risk can be favorably influenced by preoperative coronary revascularization, the concept that PCI or coronary artery bypass grafting (CABG) should be undertaken to “get the patient through” a subsequent noncardiac surgery is not supported by evidence-based standards; these interventions should be used sparingly if at all for this indication. The ACC/AHA consensus guidelines assert that preoperative coronary revascularization is likely “appropriate for only a small subset of patients at very high risk.”

Pharmacological Therapy

Because all individuals with known or suspected coronary disease have the potential to benefit from appropriate pharmacological therapy at the time of surgery regardless of whether preoperative coronary revascularization is undertaken, current principles regarding the use of perioperative beta-blocker and statin therapy are briefly reviewed.

Beta Blockers

Beta blockers are thought to ameliorate cardiac stress in the perioperative setting by a number of mechanisms, including reduction of adrenergic stimulation, improvements in the balance of myocardial oxygen demand and supply, diminution of arrhythmic potential, and potential anti-imflammatory and plaque-stabilizing effects. Based on the results of two relatively small trials published in the 1990s demonstrating significant reductions in mortality associated with perioperative beta-blocker therapy among patients at risk for coronary events, guidelines advocating routine beta-blocker administration for patients at risk for cardiac complications or undergoing higher-risk surgical procedures became widely adopted. Several ensuing trials failed to demonstrate benefit from routine perioperative beta-blocker therapy among higher-risk patients, raising questions regarding therapeutic efficacy (Table 6-2). Publication of the more recent DECREASE-IV (Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echo) and POISE (Patients Undergoing Non-Cardiac Surgery) trials has provided new insights while simultaneously raising new questions regarding the role of perioperative beta-blocker therapy.^7,⁸ The DECREASE-IV trial, which demonstrated a significant reduction in the incidence of cardiac death or nonfatal MI associated with perioperative bisoprolol therapy among patients at intermediate cardiac risk undergoing noncardiac surgery, appeared to settle the controversy in favor of beta-blocker therapy. In DECREASE-IV, bisoprolol was initiated at a low dose 30 days prior to surgery and carefully titrated to a goal heart rate of 50 to 70 beats per minute in 1,066 patients. Conflicting findings from the much larger POISE trial, however, again raised doubts regarding the safety and effectiveness of routine perioperative beta-blocker use. In POISE, 8,351 patients at risk for or with known coronary artery disease were assigned to receive either extended-release metoprolol or placebo beginning 2 to 4 hours before noncardiac surgery and continued for 30 days. At 30-day follow-up, the incidence of the composite primary endpoint of cardiovascular death, nonfatal MI, or nonfatal cardiac arrest was significantly lower among those assigned to metoprolol (5.8% vs. 6.9%), yet this advantage was offset by significantly increased frequencies of both all-cause mortality and stroke among individuals treated with beta blockers rather than placebo.

TABLE 6-2 Results of Randomized Trials of Beta-Blocker Therapy during Noncardiac Surgery

Many observers believe that the discordant results of trials examining perioperative beta blockade are multifactorial and likely attributable to differences with respect to the baseline cardiac risk of the populations under study, the particular beta blocker used, and whether therapy was begun well in advance of surgery and titrated to effect or simply started at a fixed uniform dose a few hours before the operation.^9,¹⁰ Based on the latest study data, the ACC/AHA established updated guidelines in 2009 for the use of beta blockers for noncardiac surgery. The guideline statement concludes that while the most recent studies suggest that “beta blockers reduce perioperative ischemia and may reduce the risk of MI and cardiovascular death in high-risk patients, routine administration of higher-dose long-acting metoprolol in beta-blocker naive patients on the day of surgery and in the absence of dose titration is associated with an overall increase in mortality.” The lone class-I recommendation for beta blockade in the current guidelines states that “beta blockers should be continued in patients undergoing surgery who are [already] receiving beta blockers” for appropriate indications. Class IIa recommendations support the use of beta blockers titrated to heart rate and blood pressure for patients undergoing vascular or intermediate-risk surgery who are at high cardiac risk as a result of either (1) known coronary artery disease, (2) the finding of cardiac ischemia on preoperative testing, or (3) the presence of more than one clinical risk factor for coronary disease. The routine administration of high-dose beta blockers in the absence of dose titration is now contraindicated (class III) for patients undergoing noncardiac surgery who are not currently taking beta blockers.

Statin Therapy

Proposed mechanisms by which statins may reduce perioperative cardiac complications relate to the plaque-stabilizing effects of these agents, including their anti-inflammatory and anti-thrombotic properties, and the favorable influences these drugs exert on plaque-related endothelial dysfunction.¹¹ The withdrawal of statin therapy in the perioperative period has been associated with increased cardiac events.¹² Recent randomized trials have supported earlier observational studies suggesting that statin therapy administered prior to noncardiac surgery may be associated with a reduction in major adverse events. The DECREASE-III trial randomized 497 statin-naive patients scheduled to undergo vascular surgery to receive fluvastatin 80 mg daily or placebo started a median of 37 days preoperatively.¹³ All patients also received titrated beta-blocker therapy. Fluvastatin therapy was associated with significant reductions in the incidence of perioperative myocardial ischemia on continuous ECG monitoring (10.8% vs. 19%, hazard ratio [HR] 0.55; 95% confidence interval [CI], 0.34–0.88) and in 30-day cardiovascular death or MI (HR, 0.47; 95% CI, 0.24–0.94) (Fig. 6-2). In the DECREASE-IV trial, which utilized a 2 × 2 factorial design to study the effects of perioperative fluvastatin and bisoprolol therapy, randomization to fluvastatin 80 mg daily was associated with a nonsignificant trend toward reduced 30-day cardiac events (HR, 0.65; 95% CI, 0.35–1.10).⁸

Figure 6-2 Kaplan-Meier estimate of the cumulative probability of cardiovascular death or MI during the 30-day follow-up period after surgery among subjects randomized to fluvastatin (red line) or placebo (blue line) in the DECREASE-III trial (4.8% vs. 10.1%, HR for fluvastatin 0.47; 95% CI, 0.24-0.94).

(From Schouten O, Boersma E, Hoeks SE, et al. Fluvastatin and perioperative events in patients undergoing vascular surgery. N Engl J Med 2009;361:980–989.)

Current ACC/AHA guidelines recommend (with a class I indication) that patients currently taking statins who are scheduled for noncardiac surgery should continue therapy. In addition, the guidelines provide class II support for statin use among patients undergoing vascular surgery with or without clinical risk factors and for patients undergoing intermediate-risk procedures who have at least one clinical risk factor for coronary disease.