Home Feature Assessing cardiac risk before surgery: strategies to make the right call

Assessing cardiac risk before surgery: strategies to make the right call

July 2006

Published in the July 2006 issue of Today’s Hospitalist

When it comes to assessing patients’ risk of cardiac problems during noncardiac surgery, physicians have many tests and therapies to choose from, but little in the way of evidence to guide their decision-making.

When evaluating patients with multiple morbidities, for example, should you consider testing, either invasive or noninvasive, to reduce the risk of cardiac problems? Or should you simply give them prophylactic medical therapy and bypass testing altogether?

The demographics of cardiac problems during the perioperative period are daunting. Each year in the United States, there are more than 50,000 perioperative myocardial infarctions and 1 million cardiac complications.

Perhaps no group of physicians knows this better than hospitalists, who are increasingly being asked to take on the medical management of surgical patients, assessing the risk of “and preventing problems from “cardiac complications. But the bottom line is that identifying which patients should or should not receive a preoperative procedure or therapy is not always easy.

At the American College of Physicians’ annual meeting in Philadelphia in April, Steven L. Cohn, MD, clinical professor of medicine at the State University of New York Downstate in Brooklyn, N.Y., presented information on cardiac risk assessment and management. While the session was designed for internists, it was heavily attended by hospitalists at the meeting.

During the standing-room only session, Dr. Cohn reviewed a number of studies that shed light on the cardiac risks of surgery. He also worked through clinical guidelines from several organizations designed to help physicians assess risk in patients under¬going noncardiac surgery.

A review of the guidelines

While several organizations have published perioperative guidelines to minimize cardiac problems during surgery, Dr. Cohn said that he favors the guidelines created by the American College of Cardiology/American Heart Association (ACC/AHA). The American College of Physicians released guidelines on the topic several years ago, but he said that their strict adherence to evidence often makes them less than useful.

“The ACP guidelines are purely evidence-based,” Dr. Cohn explained, “and when there was no evidence, they made no recommendation.”

Because the ACC/AHA guidelines rely on expert opinion based on consensus, he said, they tend to be more useful in clinical practice. The ACC/AHA guidelines also use factors like functional capacity and surgery-specific risk in assessing patient risk, which makes them more specific than the ACP guidelines.

Dr. Cohn said that he uses the ACC/AHA guidelines to look for three basic types of patients: low-risk patients for whom further evaluation is unnecessary; intermediate-risk patients who may require additional non-invasive testing; and high-risk patients for whom additional non-invasive testing may not be helpful and may be misleading (false negatives).

According to Dr. Cohn, the ACC/AHA guidelines start by taking a look at three factors to determine which patients should have non-invasive testing and which should be sent to the operating room without any further evaluation: clinical predictors, surgery-specific risk and exercise capacity.

“¢ Clinical predictors. The ACC/AHA classifies its clinical predictors as major, intermediate or minor.

Major predictors include an MI within 30 days, class III or IV angina, decompensated congestive heart failure, hemodynamically significant arrhythmias, and severe valvular disease, primarily aortic stenosis.

Intermediate clinical predictors include class I and II angina, a prior MI more than 30 days old, compensated heart failure or past history of heart failure, diabetes and renal insufficiency with a serum creatinine greater than or equal to 2 mg/dl.

“Minor predictors count almost the same as not having any risk factor from a clinical predictor,” Dr. Cohn said. “These include advanced age, abnormal EKG, non-sinus rhythm, low functional capacity, CVA, and uncontrolled hypertension.”

“¢ Surgery-specific risks.Dr. Cohn explained that the ACC/AHA guidelines list three types of surgery-specific risks.

The high-risk category, in which the risk of a cardiac problem is expected to be greater than 5 percent, includes emergency major operations, any procedure involving the aorta, major peripheral vascular surgery like a fem-pop bypass, and some prolonged procedures with large fluid shifts or expected blood loss.

The intermediate group includes carotid endarterectomy, major head and neck surgery, intraperitoneal and intrathoracic procedures, and major orthopedic surgery, mainly joint replacements, hip and knee, and hip fracture.

Procedures that don’t involve a body cavity are considered low risk, which means that there is less than a 1 percent risk of a cardiac problem. These include procedures such as endoscopy, cataract procedures and breast surgery.

“¢ Exercise capacity. When it comes to energy requirements for patient activities, look for patients who require 1 to 4 metabolic equivalents of daily living (METs) including most activities of daily living, walking indoors, walk 1 or 2 blocks outdoors at a normal pace, and the ability to do light housework.

“If a patient can walk at least two to four blocks at a good pace or climb at least one flight of stairs without having any symptoms or without having to stop,” Dr. Cohn said, “you can assume that they have adequate exercise capacity.”

The Lee Revised Index

Dr. Cohn pointed to another tool that can be helpful in assessing cardiac risk in the perioperative setting. The Lee Revised Cardiac Risk Index is based on a study of more 4,000 patients that identified six independent clinical predictors for major cardiac complications. Those predictors are high-risk surgery, history of ischemic heart disease, heart failure, stroke, diabetes requiring insulin, and a creatinine level greater than 2.

Patients who have none or only one of the above risk fac¬tors are considered to be a low risk, which means they’re likely to have a 1 percent rate of complications. Patients with two risk factors fall into the intermediate category, with about a 5 percent complication rate. Three or more risk factors put pa¬tients into a relatively high-risk group, with about a 10 percent chance of complications.

“Either using the ACC guidelines or using the Lee Revised Index,” Dr. Cohn said, “combined with your clinical judgment, you can assess patients and put them into a low, moderate or high type of risk group.”

Urgent vs. emergent surgery

Once you’ve assessed your patient’s risk of cardiac complications, Dr. Cohn said, you need to next consider whether the surgery is urgent or emergent. If the surgery is urgent, he explained, “The patient has to go to the operating room and you don’t have time to do any tests or really optimize the patient with any interven¬tion other than medical therapy.”

If the surgery is elective, your decision-making becomes more complicated. Dr. Cohn said that the ACC/AHA guidelines say that if patients have been revascularized in the last five years and are asymptomatic, they can go to the operating room with no testing. If a patient has new symptoms, has not been revascular¬ized and has not passed a stress test in the last two years, you need to examine the clinical predictors.

According to Dr. Cohn, most of these patients will fall into the intermediate-risk group. If they’re undergoing a low-risk procedure, he explained, they will typically not need any ad¬ditional tests.

“These patients are going for a procedure that has such a low risk that anything we’re going to do for them can’t make them any better,” he said, “and we can actually make them worse. If you have somebody with an old MI or diabetes who is going for cataract surgery, let them go.”

Exercise capacity and risk

If patients are about to undergo an intermediate-risk procedure, pay particular attention to their exercise capacity. If it’s adequate, Dr. Cohn explained, you can send them for surgery.

When patients are facing a high-risk procedure and have poor exercise capacity, Dr. Cohn said, it’s time to consider non-invasive testing. “I say consider,” he added, “because we’re questioning whether all of these patients need to be tested. And I don’t think they do.”

While minor or no clinical predictors are generally a good sign, there are times when either should raise a red flag. Dr. Cohn said that when these patients also have poor exercise capacity and are facing high-risk surgery, non-invasive testing might be indicated. He was quick to add, however, that this approach is being ques¬tioned for certain patients.

When it comes to patients with major clinical predictors, you need to proceed with caution. “Anybody with a major clinical predictor should not go for elective surgery.” Dr. Cohn explained. “They should all be delayed for further evaluation and treatment. If the stress test results are OK, they go to the operating room without any further testing.”

Invasive strategies

For years, the conventional wisdom has said that invasive procedures like coronary artery bypass surgery can help some patients avoid cardiac complications during noncardiac surgery. But as Dr. Cohn pointed out, the evidence to support that thinking has been sketchy at best.

“¢ Bypass. For patients facing a lower risk procedure, Dr. Cohn said that there appears to be no benefit to performing coronary artery bypass surgery before other noncardiac procedures.

He pointed to the CASS study, which was done more than 20 years ago. Researchers found that patients who were randomized to bypass surgery (as opposed to medical therapy) and went on to have a noncardiac surgical procedure had less perioperative mortality and a lower rate of non-fatal perioperative MI. Most of the benefit came in patients undergoing higher risk procedures.

Dr. Cohn noted that the study failed to consider the risk of a preoperative MI. In the hands of a competent surgeon, he said, the average patient faces a 1 percent to 2 percent mortality rate, a 1 percent to 3 percent chance of perioperative MI, and a 2 percent to 3 percent chance of stroke.

“Once you take that into account,” he said, “there’s probably no overall benefit. Therefore, the ACC recommended that bypass not be done prophylactically just to get a patient through surgery.”

“¢ PCI. While observational data have suggested that percutane¬ous coronary intervention (PCI) may reduce the death rate and perioperative MI rate, Dr. Cohn said, that thinking has been turned upside down by the CARP trial.

The study, published in December of 2004, looked at prophylactic coronary artery revascularization and is really the only randomized, controlled trial to look at this issue. It looked at the effects of prophylactic revascularization on long-term mortality in vascular surgery patients who had stable cardiac symptoms, compared to no revascularization.

“The researchers concluded that coronary artery revascularization before elective vascular surgery in patients with stable cardiac symptoms did not significantly alter outcomes and could not be recommended on that basis,” Dr. Cohn said. “Basically, they found that the ACC guidelines were right.”

He added that there are some caveats to the study. Many of the study subjects were treated with beta-blockers, and half were tak¬ing statins and ACE inhibitors.

“It may be more difficult to show that this intervention on top of already good medical therapy offered any benefit,” he said. In addition, the study targeted a narrow group of subjects “VA patients “and wasn’t powered to detect short-term outcomes. Certain high-risk patients were also excluded from randomization.

Timing after a stent has been placed

Even if you choose to not use bypass or PCI as a perioperative strategy, you may encounter patients who have recently undergone the procedure and now need another type of surgery. How long should the patient wait before undergoing additional surgery?

While Dr. Cohn said that it’s probably safe to perform non-cardiac surgery a week or two after percutaneous transluminal coronary angioplasty (PTCA), he added that relatively few patients undergo that procedure these days. And if your patient has recently received a stent, he explained, you’ll want to wait longer than two weeks.

He pointed to studies showing that the risks of MI and death are significantly higher for surgeries performed within two weeks of a bare metal stent procedure. As a result, Dr. Cohn said, the recommendation is to wait at least four weeks, but preferably six weeks, after a bare-metal stent has been inserted.

Drug-eluting stents present additional considerations. Paclitaxel delays endothelialization for a long period of time, possibly indefinitely, because the drug remains in the stent.

“Many patients are getting the Cypher stent with sirolimus, which essentially becomes a bare-metal stent in about four to six weeks,” Dr. Cohn explained. “If you need to do non-cardiac surgery within two months of one of these interventions and the surgeon won’t allow dual antiplatelet therapy, consider either a non-drug-eluting stent or balloon angioplasty.”

Medical strategies

Because the evidence doesn’t favor invasive strategies like PCI or CABG, some physicians have turned their attention to medical therapies to help reduce the risk of cardiac complications during surgery. While the evidence is a little more encouraging on using agents like beta-blockers, Dr. Cohn said, it’s far from unequivocal.

“¢ Beta-blockers. While a number of studies have looked at using beta-blockers before or after surgery, Dr. Cohn reported that the evidence as a whole provides an unclear picture.

“Some show benefits in terms of reduced mortality rates and incidence of ischemia,” Dr. Cohn said. “Other studies concluded that there was little or no benefit.”

The recently updated ACC/AHA guidelines reflect that uncertainty by strongly recommending beta-blockers be administered only to patients who show signs of ischemia on a stress test and are about to undergo vascular surgery. Dr. Cohn said the guidelines also suggest that beta-blockers may help patients with known coronary disease who are going for vascular surgery or other intermediate to high-risk surgery.

“The ACC may revisit this again at the end of the year when it updates the guidelines,” he explained, “but right now there is no new information to make any stronger recommendations.”

He noted that despite the uncertain body of evidence, physicians may feel pressure to put more of their patients on beta-blockers.

“This is one of the safety issues that hospitals are looking at: What we can do to put everybody on perioperative beta-blockers,” Dr. Cohn said. “I don’t think we have strong enough evidence, certainly in the lower risk patients, to do that. In high-risk patients, it’s probably reasonable.”

The ACC/AHA guidelines also say that beta-blockers may be considered in vascular surgery patients who are not in the highest risk group. Dr. Cohn indicated that there was insufficient information to make any recommendation for patients who fall in other risk groups or are having lower risk surgeries.

“¢ Statins. Will statins prevent perioperative MIs? “We know that a lot of MIs are caused by plaque rupture, thrombus formation, and vascular occlusion,” said Dr. Cohn, “and we know that statins do more than lower cholesterol, such as lowering CRP and stabi¬lizing existing plaque.”

While the manufacturers of statins say that the drugs should be stopped before surgery, he pointed to data from a number of ob¬servational studies that showed that patients undergoing surgery while taking some form of statin therapy had lower mortality rates than patients who were not taking statins.

“My recommendation is to not discontinue the statins, but to continue them for anybody who is already taking statins,” Dr. Cohn said. “And in certain cases, maybe we should start them prophylactically.”

Michael Krivda is a freelance writer specializing in health care. He is located in Perkasie, Pa.