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In this era of increasingly procedural cardiology, many physicians regard the cognitive exercise of preoperative evaluation for non-cardiac surgery as an onerous task. In reality, the preoperative period affords a window of opportunity for the consulting cardiologist to minimise surgical risk by maximising medical treatment, directing appropriate testing, and communicating effectively with the surgical team. Many physicians are unaware that nearly half of all perioperative deaths are related to cardiac events, and they may greatly underestimate the degree to which heart failure contributes to this cardiac mortality. It is imperative as a consulting cardiologist to develop a consistent approach to heart failure patients in order to avoid unnecessary, and potentially dangerous, preoperative diagnostic and therapeutic interventions.
In this article we will briefly review recent data relating to predictors of surgical risks, and propose an approach for integrating the clinical evaluation of cardiac status and surgical risk in order to provide a frame of reference for preoperative consultation. We have no hard evidence, either observational or in the form of prospective, randomised trials, to support many of our current recommendations. The landmark studies of preoperative risk assessment focused primarily on identifying ischemic risk with a lesser emphasis on heart failure.1 ,2 Our suggestions are based on heart failure data extrapolated from these studies, as well as from broad experience at a high volume cardiac centre.
Determinants of risk
There are four major determinants of risk for any cardiac patient undergoing non-cardiac surgery: urgency of the surgery; complexity of the procedure; extent of medical comorbidities; and the extent and severity of the underlying heart disease. Shah and associates underscored the importance of these variables in their evaluation of 688 patients with cardiovascular disease undergoing non-cardiac surgery.3 Patients requiring emergency surgery had an 18% incidence of perioperative myocardial infarction or death, as opposed to a 3.7% incidence in those patients undergoing elective surgery. Similarly, high risk surgical procedures involving intrathoracic, intra-abdominal, or major vascular reconstruction carried an 8.2% incidence of perioperative myocardial infarction or death as opposed to a 3.5% incidence of these complications in less physiologically stressful surgery.
In an attempt to dissect medical versus surgical risk factors, Ali and associates assigned patients both a surgical and a medical risk score based on the complexity of the proposed surgery and the patient's cardiac status, respectively.4 The medical score provided significantly better risk prediction for adverse perioperative cardiac events than the surgical score. A high medical score identified 87% of those who suffered a cardiac event, while a high surgical risk score identified only 33%. The authors emphasised that the extent of cardiac disease is an even greater determinant of outcome than the nature of the proposed surgery.
These findings related primarily to ischaemic complications, and did not specifically address complications caused by heart failure. In a later modification of the original Goldman risk assessment, Detsky and colleagues differentiated risk based on recent clinical status.2 In this analysis, pulmonary oedema within a week before surgery conferred a substantially higher risk than remote episodes of decompensation.
Once the surgical and medical risk has been assessed, the consultant's task is twofold: to outline the most appropriate preoperative and intraoperative medical treatment, and to direct the judicious use of additional diagnostic testing. We recommend beginning with the patient's current clinical status. Patients with decompensated heart failure should have surgery postponed in all but the most emergent circumstances. In cases of newly diagnosed heart failure, a cause should be determined through a diagnostic evaluation that is beyond the scope of this article. In those patients with chronic heart failure and an acute decompensation, one needs to ascertain the cause of the decompensation (that is, medical non-compliance, worsening ischaemia, atrial fibrillation, etc). Once the patient has stabilised, surgery should be postponed at least two weeks to ensure that the new medical regimen is appropriate and that the underlying process has been adequately addressed.
Compensated heart failure
Patients with compensated heart failure generally pose less of a challenge. If they have been clinically stable over the past several weeks, there is no indication for further testing. Many physicians advocate routine preoperative assessments of left ventricular ejection fraction (LVEF); however, there are little data to support this practice. Several studies have demonstrated a correlation between ejection fraction, particularly those less than 35%, and adverse perioperative events; however, there are no data to suggest that patients with established heart failure benefit from routine repeat preoperative assessment of LVEF.5-7 In fact, patients with heart failure and preserved LVEF (so called “diastolic dysfunction”) do not tolerate tachycardia and intravascular volume shifts well, and may pose more perioperative management problems than stable, well compensated patients with a low LVEF.
In terms of optimising medical treatment, overwhelming evidence now points to the benefits of β blockers and angiotensin converting enzyme (ACE) inhibitors in heart failure patients.8-12Additionally, there have been reports of improved surgical outcomes with the use of perioperative β blockers; however, the actual number of patients studied was quite small.13 ,14 It should be emphasised that despite recent data suggesting a benefit of β blocker treatment in New York Heart Association (NYHA) functional class III and IV heart failure,15 we do not recommend instituting these drugs in an acutely decompensated patient, particularly when emergency surgery is planned. Our goal is to deliver the surgeons a well compensated patient on an ACE inhibitor and β blocker, with the addition of a diuretic and/or digoxin when indicated.
Accurate assessment of the patient's clinical status and the risk of the proposed surgery are fundamental components of the preoperative evaluation and are essential in making recommendations for intraoperative monitoring. We have developed a simple grid (fig 1) that assists in this assessment by combining the risk of the proposed surgery with the patient's current functional status based on the NYHA classification (see box). Despite numerous techniques for evaluating cardiac status, the NYHA functional class has stood the test of time as an inexpensive, reproducible, and reliable indicator of long term prognosis. Low risk surgeries are defined as superficial procedures such as breast biopsies, endoscopic surgeries, or arthroscopic procedures. Intermediate risk procedures include orthopaedic, head and neck, genitourinary, and intra-abdominal procedures. High risk surgery includes major emergency procedures, aortic or vascular reconstructive surgery, and any prolonged procedure with predictable substantial changes in intravascular volume.
New York Heart Association functional class
- Class I: Patient has no limitation of regular physical activities
- Class II: Mild limitation of physical activities; comfortable at rest; normal physical activity results in dyspnoea, fatigue or angina
- Class III: Major limitation of physical activities; comfortable at rest; minimal physical activity results in dyspnoea, fatigue, or angina
- Class IV: Inability to perform any physical activity without symptoms; symptoms are present at rest, and are worsened with any activity
As shown in fig 1, we recommend delaying high risk surgery, when possible, in those patients who are in NYHA functional class III and IV. Additionally, we advocate intraoperative invasive haemodynamic monitoring with a pulmonary artery catheter in those patients who fall into the “caution” category. Admittedly, there are no conclusive data from randomised prospective trials to support this recommendation; however, it is in keeping with the American Society of Anesthesiologists class I and class II indications for the use of intraoperative pulmonary artery catheters.16 Furthermore, in those patients with decompensated heart failure requiring high risk, emergent surgery, we advise case-by-case consideration for circulatory support with an intra-aortic balloon pump.
In summary, accurate assessment of a patient's clinical status and the risk of the proposed surgery are critical elements in the preoperative evaluation of heart failure patients. Once the initial evaluation is complete, surgical risk can be minimised through a combination of optimal perioperative medical therapy with appropriate monitoring and support for higher risk cases.