The purpose of preoperative evaluation for cardiac risk is to answer the question "Can this patient safely undergo major non-cardiac surgery?" Operative risk is a function of the balance between the ability of the patient’s heart to pump blood (cardiopulmonary fitness or functional capacity) during time of need (patient-specific risk) and the amount of cardiac output demanded by the procedure (surgery-specific risk). These components must be addressed independently. The inability to pump adequate blood volume to meet the body's needs during a surgical procedure will result in hemodynamic compromise with subsequent cardiovascular and non-cardiovascular complications.

Cardiac output is a function of stroke volume (SV) and heart rate (HR). Cardiac disorders that compromise SV and HR response will impair the heart's ability to deliver adequate blood supply to the peripheral tissues during times of highest demand. Cardiac output can be impaired by ischemic and non-ischemic etiologies. Multiple etiologies can work synergistically to impair cardiac output response under duress (e.g., diastolic dysfunction + valve disease + microvascular ischemia + impaired pulmonary circulation). All too often, the preoperative cardiac evaluation process attempts to answer, “does the patient have coronary artery disease”. A series of tests designed to assess the state of the coronary arteries may miss underlying impaired cardiac function, if it exists. Assessment of global cardiac function provides the most precise method to assess cardiac risk. There is evidence that patients with coronary artery disease without heart failure are at no higher risk for postoperative cardiac events than the general population. If one does find abnormalities in the state of the coronaries, there is little to no evidence to suggest that procedures on the coronary vasculature improve the outcome of major non-cardiac surgery. Therefore, current ACC-AHA guidelines do not recommend prophylactic revascularization in patients with stable CAD that are undergoing high risk surgery.

According to the executive summary issued by the ACC-AHA task force on preoperative cardiac risk assessment, the purpose of exercise stress testing is two-fold:

Quantify functional capacity

Identify inducible ischemia / cardiac dysfunction

The anaerobic threshold (AT expressed as ml/kg/min) is an effort independent measure of peak cardiac function that can readily be attained even in elderly patients and has been demonstrated to be effective in risk stratification prior to major surgery. This data is in turn used to improve peri-operative management to reduce unnecessary costs in the healthier patients and decrease morbidity and mortality in the sicker patients (flow chart). Estimates of functional capacity have been demonstrated not to be objective or accurate in patients with heart disease. Monitoring of SV, HR and cardiac output response as a function of work rate on a breath-by-breath basis has been demonstrated to be effective in identifying onset of cardiac dysfunction during exertion. Identifying the rate-pressure product at the ischemic threshold (RPP@IT on MET-TEST reports) provides important clinical insight to the anesthesiologist to proactively avoid myocardial dysfunction during surgery with the ability to intervene with intravenous agents. This will avoid myocardial stunning and infarction during the procedure which in turn should avoid cardiovascular compromise and has potential to reduce post-operative complications.

The London Clinic has been utilizing CPET technology for peri-operative management with excellent success. In comparing the first 50 patients screened and managed with this approach vs. 223 patients that were not during the same period, the 50 screened patients had no readmissions and no cardiovascular complications. In the non-screened group, 12% were readmitted to the ICU, almost all with cardiovascular complications and organ failure requiring 87 days of prolonged ICU care with 5% mortality.

In Conclusion

CPET accurately quantifies cardiopulmonary reserve (AT) and the presence or absence of cardiac dysfunction which can be used to optimize outpatient management prior to elective non-cardiac surgery. This approach more precisely reduces complications, morbidity, mortality and costs. 

Case Study Anaesthesia - Journal of the Association of Anaesthetists of Great Britain and Ireland. 2009.