Author + information
- Richard A. Lange, MD⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Richard A. Lange, Department of Medicine, University of Texas Health Science Center, 7703 Floyd Curl Drive, MC 7870, San Antonio, Texas 78229-3901
- computed tomography coronary angiography
- coronary artery calcium score
- intermediate-risk noncardiac surgery
- preoperative cardiovascular risk
- risk factors
Perioperative cardiac events are a leading cause of death (1) in the 234 million major surgical procedures performed worldwide annually (2). Every year approximately 900,000 adults worldwide experience major cardiac complications after surgery (3). Accordingly, risk stratification has become an integral part of the evaluation of patients before major surgery. Providing reliable information about perioperative risk may help identify patients who could benefit from receiving more intensive treatment of their cardiac condition, choosing a less invasive surgical procedure, or opting for nonoperative management of their condition.
The American Heart Association and American College of Cardiology guidelines (4) emphasize the use of clinical risk factors—the so called revised cardiac risk index (RCRI)—for cardiac risk stratification. This simplified scoring system, which is based on the presence of coronary artery disease (CAD), heart failure, cerebrovascular disease, diabetes mellitus requiring insulin, renal insufficiency (serum creatinine concentration > 2 mg/dl), and high-risk noncardiac surgery, has been widely adopted because of its ease of use. It discriminates moderately well among patients at high versus low risk of cardiac events following noncardiac surgery (area under the receiver-operating characteristic curve [AUC], 0.75), except in those undergoing vascular surgery (1).
Pre-operative cardiac testing is often performed in patients at intermediate risk for a cardiac event following their surgical procedure (i.e., RCRI score 1 to 3) and in those undergoing vascular noncardiac surgery to more precisely define their risk. Typically, this is accomplished by assessing the presence and magnitude of myocardial ischemia with single-photon emission computed tomography (SPECT) myocardial perfusion imaging or stress echocardiography. Unfortunately, these tests are not suitable or reliable in some patients (i.e., those with inadequate perfusion or echocardiographic images or left bundle branch block), and the positive predictive value of these tests is relatively low (5% to 20%). In addition, perioperative cardiac events often occur in patients with nonobstructive lesions who experience coronary plaque rupture, fissure, or hemorrhage as a result of the inflammatory and prothrombotic milieu associated with surgery (5–7). In such patients, noninvasive detection of subclinical CAD, rather than ischemia, may better identify those at increased risk of perioperative cardiac events.
In this issue of the Journal, Ahn et al. (8) show that computed tomography coronary angiography (CTCA) provides additive value to the RCRI in assessing the risk of post-operative cardiac events in patients undergoing intermediate-risk noncardiac surgery (i.e., for intrathoracic, intraperitoneal, orthopedic, head and neck, and prostate disease). In their retrospective observational study, 239 patients were identified who underwent CTCA with a 64-slice system before noncardiac surgery. In addition to RCRI score, coronary artery calcium score (CACS) and extent of CAD by CTCA was assessed in each patient. Nineteen (8%) patients experienced a post-operative cardiac event (i.e., cardiac death, acute coronary syndrome, pulmonary edema, ventricular arrhythmia with hemodynamic compromise, or complete heart block) within 30 days of surgery. The RCRI performed moderately well in predicting post-operative cardiac events (AUC 0.652), but significant additive predictive value was obtained by demonstrating high CACS (i.e., score > 113; AUC 0.731) or multivessel (2 or 3 vessel) CAD (AUC 0.719) with CTCA. Furthermore, the combination of both CTCA parameters (AUC 0.77) was more predictive than either single CTCA parameter.
As opposed to SPECT myocardial perfusion and stress echocardiographic imaging that provide information about the hemodynamic significance of coronary artery stenoses, the CTCA parameters examined in the study by Ahn et al. (8) assess anatomic information only. Although the extent of coronary calcification is not synonymous with luminal stenosis or obstruction, it correlates closely with the volume of coronary artery plaque measured and is a surrogate for the overall coronary plaque burden. Hence, it should not be surprising that patients with elevated CACS or multivessel CAD—markers of advanced coronary plaque burden—are at increased risk of perioperative cardiac events, especially those due to coronary plaque rupture, fissure, or hemorrhage.
Few studies of CTCA for perioperative risk stratification have been published previously, and none have compared it with perfusion or functional imaging. Studies conducted in small numbers of patients who underwent noncardiac or valve surgery (9–12) showed that the absence of coronary artery calcification or stenosis by CTCA identifies subjects who are unlikely to have angiographic evidence of CAD (i.e., 98% negative predictive value) or a post-operative cardiac event. An observational study (13) showed that CACS provided additional predictive value to perfusion imaging for risk stratification before noncardiac surgery; marked coronary calcification (i.e., CACS > 1,314) was independently associated with a higher major adverse cardiac event rate in patients with normal (12% vs. 5%, p < 0.05) or abnormal perfusion (22% vs. 12%, p < 0.05) myocardial perfusion imaging. In the CTCA study by Ahn et al. (8), the positive predictive value of high CACS (9%) or multivessel disease (18%) for predicting cardiac death or myocardial infarction is similar to that reported with myocardial perfusion imaging and dobutamine stress echocardiographic imaging (14). Nevertheless, additional studies are needed to determine whether the extent of plaque burden is more (or less) informative of perioperative cardiac risk than the presence and extent of ischemia.
Ahn et al. (8) acknowledge that their study is retrospective and that routine evaluation for perioperative myocardial infarction was not performed, which may have led to patient selection bias. Furthermore, because few patients in their study experienced an adverse cardiac event after surgery, additional studies with larger numbers of patients need to be performed before CTCA is recommended for pre-operative risk assessment. It is important to note that the optimal CACS (> 113) for predicting post-operative cardiovascular events in their elderly, Korean patients was determined by a receiver-operating characteristic (ROC) curve analysis and no validation cohort was provided; this criteria may not be applicable to younger patients, women, or other ethnic groups undergoing surgery. CACS increases with advancing age, reflecting the natural progression of atherosclerosis, and men generally have higher CAC scores than women of similar age (15). Additionally, both the prevalence and extent of CAC varies among different ethnic groups. Compared with whites, the prevalence is 22% lower in blacks, 15% lower in Hispanics, and 8% lower in Chinese after adjustment for coronary risk factors. The relative amounts of coronary calcification in blacks, Hispanics, and Chinese is also lower than in whites (by 31%, 26%, and 23%, respectively) (16).
When might it be appropriate to recommend CTCA for assessing cardiac risk with noncardiac surgery? The investigators' recommendation (8) that it be considered in patients with poor or unknown functional capacities, high RCRI score (≥ 3), and contraindications to noninvasive stress tests is reasonable and consistent with the guidelines (4). However, their conclusion that CTCA is a “valuable, cost-effective tool” for perioperative risk stratification is unsubstantiated, because data regarding its cost effectiveness for this use have not yet been published. Overutilization of pre-operative cardiac testing is common and profligate, and such use diminishes its cost effectiveness. Hence, it is appropriate to emphasize that pre-operative cardiac testing by any modality is not indicated in asymptomatic persons who are undergoing low-risk surgical procedures (ophthalmologic, breast, endoscopic, and superficial procedures performed on an ambulatory basis) or have undergone coronary revascularization in the past 5 years. Additionally, the investigators' claim that “if patients are deemed to be at low RCRI score, the CTCA might be useful” (8) is speculative and not supported by the guidelines (4).
One of the more difficult problems facing the clinician asked to provide “cardiac clearance” for noncardiac surgery is what to recommend for the patient whose pre-operative cardiac testing shows that he or she is not at low risk for a post-operative cardiac event. Initiation of beta-adrenergic blockade before surgery—once the standard of care—has been associated with an increased risk of side effects and mortality, unless started weeks or months before the procedure (17). Perioperative antiplatelet therapy increases the risk of major bleeding and its effectiveness in preventing post-operative cardiac events has not been established. Although observational studies suggest that patients receiving statin therapy before noncardiac surgery have fewer post-operative cardiac events than patients not receiving them, it is not clear that initiating statin therapy immediately before surgery reduces perioperative mortality (18,19). Finally, the usefulness of pre-operative coronary revascularization is not established in patients with ischemia (4), even in those considered to be at particularly high risk (i.e., abnormal dobutamine stress echocardiogram with at least 5 segments of wall-motion abnormalities) (20). Hence, it is not recommended that routine prophylactic coronary revascularization be performed to prevent myocardial or death in patients with stable CAD before noncardiac surgery (4).
Although CTCA may provide additive value to the RCRI in assessing the risk of post-operative cardiac events, until this information can be translated to an intervention that reduces the perioperative risk or mortality, it is not unlike being “all dressed up, with nowhere to go.”
Dr. Lange has reported that he has no relationships relevant to the contents of this paper to disclose.
↵⁎ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
- American College of Cardiology Foundation
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