Half a million Canadian adults undergo major non-cardiac surgery each year. Physicians are often asked to “please clear this patient for surgery.” But recent data shows that our interventions, such as beta-blockers and revascularization, don’t prevent perioperative heart attacks or deaths. That’s a surprise to many of us, including myself.

Latterly, a few small randomized controlled trials have suggested that preoperative statins help reduce surgical complications over 30 days. But the data is inconclusive. What we’ve really learned is that physicians can predict risk, but reducing it is another matter entirely.

Predicting peri-operative risk

A study by Lee et al aimed to devise an index to help physicians predict risk in patients undergoing non-cardiac surgery. Looking at 4,315 patients undergoing non-cardiac surgery, they discovered six independent predictors that replace the nine predictors of Goldman’s original Cardiac Risk Index for non-cardiac surgery:

Lee index of cardiac risk in non-cardiac surgery

• History of ischemic heart disease — defined as a history of myocardial infarction, positive exercise test, current complaint of ischemic chest pain or nitrate use or ECG with pathological Q waves (patients with prior coronary bypass surgery or angioplasty are only counted if they still meet other criteria for ischemic heart disease)
• History of congestive heart failure — defined as a history of heart failure, pulmonary edema or paroxysmal nocturnal dyspnea; S3 gallop or bilateral rales on physical examination; or a chest radiograph showing pulmonary vascular resistance
• History of cerebrovascular disease (i.e. stroke or transient ischemic attack)
• High-risk type of surgery — intraperitoneal, intrathoracic or suprainguinal vascular surgery
• Diabetes mellitus requiring treatment with insulin
• Preoperative serum creatinine > 175 µmol/L

Analysis of this Lee Index (or Revised Goldman Risk Index) proved its superiority over other risk prediction indexes in identifying patients that are at a higher risk for cardiac complications when undergoing major noncardiac surgery.

Table 1 shows the risk of patients suffering a major perioperative cardiac event based on their number of risk factors.

Beware the beta-blocker

Beta-blockers can reduce the frequency of cardiac perioperative complications. But they don’t reduce the overall risk of death — far from it. A recent landmark randomized controlled study, PeriOperative Ischemic Evaluation (POISE), followed 8,351 patients with, or at risk of, atherosclerotic disease, who were studied with respect to the effects of a beta-blocker (metoprolol) vs a placebo 2-4 hours before undergoing noncardiac surgery. Of all the major perioperative vascular complications (vascular death, nonfatal myocardial infarction, nonfatal cardiac arrest and nonfatal stroke) the most common occurrence within the first 30 days was myocardial infarction (MI). This trial suggested a major vascular complication rate at 30-day follow up of 1 in 15 patients.

The POISE results suggest that within 1,000 patients undergoing noncardiac surgery, the use of a beta-blocker such as metoprolol would protect 15 patients from MI, 3 from cardiac revascularization and 7 from new clinically significant atrial fibrillation. That said, POISE also found that metoprolol would result in an excess of 8 patient deaths, 5 strokes, 53 cases of clinically significant hypotension and 42 of clinically significant bradycardia. Earlier trials highlighted the benefits of pre-operative beta-blockers in preventing MI, but didn’t cast a wide enough net. POISE spotlights the risk of using perioperative beta-blockers without knowledge of the harm they may cause.

One explanation for the higher overall mortality is that beta-blockers block the catecholamine system, a natural defence mechanism for patients who run into hypotensive or septic events during their operative recovery. It should be noted that POISE excluded patients who were already on long-term beta-blockers and continued them, so there’s no evidence that these patients’ medication should be stopped.

So what can we do?

Personally, I’m now using the revised (Lee) risk index to determine risk, and then using clinical judgement to fine-tune my assessment. I make sure that patients are clinically stable and don’t have an existing indication for revascularization such as severe angina, widespread ischemia on cardiac testing, significant congestive heart failure or other major comorbidities.

Patients having two or more vascular risk factors often face a significant possibility of suffering a major cardiovascular complication and should be kept in a monitored unit for at least 48 hours, taking serial cardiac markers such as troponin. MI is the most common major cardiovascular complication, with most of these patients showing little or no sign of classic angina. Research by Dr. P.J. Devereaux of McMaster University, the lead POISE investigator, suggests that 12% of patients suffering a perioperative MI will die within 30 days.

As he puts it: “It is a tragedy that some patients undergoing non-cardiac surgery (e.g. to obtain a cure from cancer) will not enjoy the benefits of their surgery because they suffer a major perioperative vascular complication that takes their life.”

References

1. Devereaux PJ, et al. CMAJ 2005;173:627-34
2. Auerbach A, Goldman L. Circulation 2006;113:1361-76