In this issue of Anesthesia & Analgesia, Biccard1 presents a state-of-the-art review of the widely used Revised Cardiac Risk Index (RCRI),2 incorporating a systematic review of other risk prediction studies that have used this index as a comparator. Using standards for the development of clinical risk prediction models proposed by Steyerberg and Vergouwe,3 he presents a thorough analysis of the strengths and weaknesses of the RCRI, along with an elegant and understandable road map of where future research efforts need to be focused, including a concise explanation of the most commonly used statistical techniques relevant to this arena. I invited this review because we need a discussion on the limits of existing risk indices and a thoughtful approach to address these.
Biccard hails from South Africa, a country with its feet planted in both the developed and the developing world. In South Africa, and in the United Kingdom where he studied, Biccard and his colleagues have a stellar track record of evaluating scoring systems that predict perioperative cardiac risk for patients undergoing noncardiac surgery.4–8 In South Africa, Biccard daily assesses the risks of major noncardiac surgery in patients with human immunodeficiency virus (HIV) disease. This adds a unique global public health perspective to the discussion.9–11 In this setting, he has faced challenges predicting cardiovascular risk using a system developed in a single tertiary care metropolitan medical center in the northeastern United States, a population with few similarities to the population he cares for in South Africa. In a country (and continent) with severely constrained resources, the appeal of the RCRI is the simplicity of using just 6 additive predictors. Certainly, this simplicity is just as appealing to United States physicians confronted daily by information overload in their clinical practice. As Biccard explains, in the years since the initial publication of the RCRI, researchers have “tweaked” it adding factors while attempting to maintain its simplicity. These include age, ASA physical class, peripheral vascular disease, functional status, expanded surgical procedure type, the presence of HIV, and concurrent medications.
The definitions of what constitutes perioperative cardiac morbidity have evolved over the past decade. Biccard, through his involvement in the multinational Vascular events In noncardiac Surgery patIents cOhort evaluatioN (VISION) study and his own literature review,12–14 understands the need to systematically reevaluate the predictive abilities of the RCRI. The original RCRI considered several cardiac outcomes in aggregate: myocardial infarction, pulmonary edema, ventricular fibrillation or primary cardiac arrest, and complete heart block.2 At that time, the available cardiac biomarker was creatine kinase (CK) and its MB isoenzyme fraction. CK has been replaced by the troponins, assays for which are also evolving rapidly in their sensitivity (although CK-MB fraction can still be of clinical value in evaluating reinfarction given it shorter half-life in plasma). Readers of this journal are aware of the burgeoning literature on perioperative troponin leaks, including the newly proposed classification of myocardial injury after noncardiac surgery promulgated by the VISION investigators.12–17 The controversy surrounding the significance of troponin as a marker of primary myocardial injury versus troponin release secondary to noncardiac etiologies (most of which are more common than myocardial injury) has been expertly reviewed in recent editorials.18,19
There are controversial methodologic questions related to outcomes assessment in the original RCRI publication.2 The use of a single individual to classify all complications was controversial at the time of the study. Today, it would not be acceptable, “data monitoring boards” are the accepted standard to ensure uniform and unbiased adjudication. Inclusion of pulmonary edema as an outcome is likewise controversial, given the dynamic changes in blood pressure, intravascular volume, or lung function that may occur perioperatively. However, the original authors did present a carefully thought-out schema consistent with their desires to segregate “cardiac” from “noncardiac” etiologies (including their explicit definition of a “primary” cardiac arrest). Whether or not this was truly realized remains controversial. This issue continues to engender controversy as illustrated by a contentious letter to the editor by Lee and Goldman20 and reply by the authors of the new Gupta American College of Surgeons National Surgical Quality Improvement Program risk calculator, debating which outcomes really are cardiac (or not).
Risk calculators based on the American College of Surgeons National Surgical Quality Improvement Program system21–24 use considerably more risk factors and are tailored to specific surgical procedures. Biccard opines that given newer systems that “the preeminence of the RCRI is now in question.” He also reviews the newly released American College of Cardiology/American Heart Association Guidelines on Perioperative Cardiovascular Evaluation and Management of Patents undergoing Noncardiac Surgery,25 in which the new American College of Surgeons National Surgical Quality Improvement Program systems are given considerable attention (and directly compared with the RCRI in a comprehensive table). Biccard suggests that the RCRI may have an “uncertain future in the American College of Cardiology/American Heart Association Guidelines.” His predictions may or may not come to pass. However, the trends toward analysis of perioperative “big data,” as evidenced by efforts of the Anesthesia Quality Institute, the Multicenter Perioperative Outcomes Group, and others, seem to favor multivariate risk calculators that likely will improve predictive accuracy for risk prediction substituting computer horsepower for the 6-factor additive simplicity of the RCRI.
Perioperative medicine is rapidly evolving. To practitioners who worked in the early 1990s, current surgical technologies border on the realm of science fiction. Anesthesia practice is safer and more sophisticated. Transesophageal or transthoracic perioperative echocardiography is now routine, allowing us a much clearer window on our patients’ cardiac condition. Cardiac pathologies are generally better managed, often using evidenced-based guidelines. Newer clinical entities including stress-related cardiomyopathies,26 damage related to chemotherapy (engendering a new specialty of cardio-oncology),27 and HIV-induced atherosclerosis28,29 are increasingly appreciated as potential risk factors. Complex multivariate relations among cardiovascular risk factors, race, gender, and long-term outcome have evolved.30 However, as evidenced by the recent firestorm over the new American Heart Association cholesterol management guidelines (and their very liberal statin recommendations),31 precise delineation of cardiovascular risk factors continues to challenge our diagnostic and therapeutic acumen. Most recently, evidence points to substantially elevated long-term risk of the nonobstructive coronary artery disease, raising new management concerns for cardiologists,32 complicating our perioperative risk assessment.
Medicine constantly advances, based on new science, new findings, and new therapies. The RCRI has had a very good run. It may well be of value into the future, one of the successful examples of perioperative risk assessment. Biccard presents a clear path to follow in developing the next successful risk assessment tool. His approach should be embraced by researchers. I welcome the spirited discussion that I hope his thoughtful and provocative proposal will engender, a discussion that will further our quest to improve global cardiovascular perioperative outcomes.
Name: Martin J. London, MD.
Contribution: This author conceived and wrote the manuscript.
Attestation: Martin J. London approved the final manuscript.
Dr. Martin London is the Section Editor for Perioperative Echocardiography and Cardiovascular Education for Anesthesia & Analgesia. This manuscript was handled by Dr. Steven L. Shafer, Editor-in-Chief, and Dr. London was not involved in any way with the editorial process or decision.
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