Chapter 1 Assessment of Cardiac Risk
The impetus for the development of a risk-adjusted scoring system was the need to compare adult cardiac surgery results in different institutions and to benchmark the observed complication rates.1 The first risk-scoring scheme for cardiac surgery was introduced by Paiement and colleagues at the Montreal Heart Institute in 1983.2 Since then, multiple preoperative cardiac surgery risk indices have been developed. The patient characteristics that affected the probability of specific adverse outcomes were identified and weighted, and the resultant risk indices have been used to adjust for case-mix differences among surgeons and centers where performance profiles have been compiled. In addition to comparisons among centers, the preoperative cardiac risk indices have been used to counsel patients and their families in resource planning, in high-risk group identification for special care or research, to determine cost-effectiveness, to determine effectiveness of interventions to improve provider practice, and to assess costs related to severity of disease.3
CARDIAC RISK ASSESSMENT AND CARDIAC RISK STRATIFICATION MODELS
Consistency among Risk Indices
Many different variables have been found to be associated with the increased risk during cardiac surgery, but only a few variables have consistently been found to be major risk factors across multiple and very diverse study settings. Age, female gender, left ventricular function, body habitus, reoperation, type of surgery, and urgency of surgery were some variables consistently present in most of the models (Box 1-1).
Predictors of Postoperative Morbidity and Mortality
A risk-scoring scheme for cardiac surgery (coronary artery bypass graft [CABG] and valve) was introduced by Paiement and colleagues at the Montreal Heart Institute in 1983.2 Eight risk factors were identified: (1) poor LV function, (2) congestive heart failure, (3) unstable angina or recent (within 6 weeks) myocardial infarction, (4) age older than 65 years, (5) severe obesity (body mass index > 30 kg/m2), (6) reoperation, (7) emergency surgery, and (8) other significant or uncontrolled systemic disturbances. Three classifications were identified: patients with none of these factors (normal), those presenting with one risk factor (increased risk), and those with more than one factor (high risk). In a study of 500 consecutive cardiac surgical patients, it was found that operative mortality increased with increasing risk (confirming their scoring system).
One of the most commonly used scoring systems for CABG was developed by Parsonnet and colleagues4 (Table 1-1). Fourteen risk factors were identified for in-hospital or 30-day mortality after univariate regression analysis of 3500 consecutive operations. An additive model was constructed and prospectively evaluated in 1332 cardiac procedures. Five categories of risk were identified with increasing mortality rates, complication rates, and length of stay. The Parsonnet Index frequently is used as a benchmark for comparison between institutions.
Table 1-1 Components of the Additive Model
Rights were not granted to include this table in electronic media. Please refer to the printed book.
From Parsonnet V, Dean D, Bernstein A: A method of uniform stratification of risk for evaluating the results of surgery in acquired adult heart disease. Circulation 79:I3, 1989.
Higgins and associates5 developed a Clinical Severity Score for CABG at the Cleveland Clinic. Independent predictors of in-hospital and 30-day mortality wereemergency procedure, preoperative serum creatinine level of greater than 168 μmol/L, severe left ventricular dysfunction, preoperative hematocrit of less than 34%, increasing age, chronic pulmonary disease, prior vascular surgery, reoperation, and mitral valve insufficiency. Predictors of morbidity (acute myocardial infarction and use of intra-aortic balloon pump [IABP], mechanical ventilation for 3 or more days, neurologic deficit, oliguric or anuric renal failure, or serious infection) included diabetes mellitus, body weight of 65 kg or less, aortic stenosis, and cerebrovascular disease. Each independent predictor was assigned a weight or score, with increasing mortality and morbidity associated with an increasing total score.
The New York State model of Hannan and coworkers6 collected data from 1989 through 1992, with 57,187 patients in a study with 14 variables. It was validated in 30 institutions. The mortality definition was “in hospital.” Observed mortality was 3.7%, and the expected mortality rate was 2.8%. These researchers included only isolated CABG operations.
The Society of Thoracic Surgeons national database represents the most robust source of data for calculating risk-adjusted scoring systems.7 Established in 1989, the database had grown to include 638 participating hospitals by 2004. This provider-supported database allows participants to benchmark their risk-adjusted results against regional and national standards. New patient data are brought into the Society of Thoracic Surgeons database on an annual and, now, semiannual basis. Since 1990, when more complete data collection was achieved, risk stratification models were developed for both CABG and valve replacement surgery.
European System for Cardiac Operative Risk Evaluation (EuroSCORE) for cardiac operative risk evaluation was constructed from an analysis of 19,030 patients undergoing a diverse group of cardiac surgical procedures from 128 centers across Europe8 (Tables 1-2 and 1-3). The following risk factors were associated with increased mortality: age, female gender, serum creatinine, extracardiac arteriopathy, chronic airway disease, severe neurologic dysfunction, previous cardiac surgery, recent myocardial infarction, left ventricular ejection fraction, chronic congestive heart failure, pulmonary hypertension, active endocarditis, unstable angina, procedure urgency, critical preoperative condition, ventricular septal rupture, noncoronary surgery, and thoracic aortic surgery.
Table 1-2 EuroSCORE: Risk Factors, Definitions, and Weights (Score)
| Patient-Related Factors | Definition | Score |
|---|---|---|
| Age | Per 5 years or part thereof over 60 years | 1 |
| Sex | Female | 1 |
| Chronic pulmonary disease | Long-term use of bronchodilators or corticosteroids for lung disease | 1 |
| Extracardiac arteriopathy | Any one or more of the following: claudication, carotid occlusion or > 50% stenosis, previous or planned intervention on the abdominal aorta, limb arteries, or carotid arteries | 2 |
| Neurologic dysfunction | Disease severely affecting ambulation or day-to-day functioning | 2 |
| Previous cardiac surgery | Requiring opening of the pericardium | 3 |
| Serum creatinine level | >200 μmol/L preoperatively | 2 |
| Active endocarditis | Patient still under antibiotic treatment for endocarditis at the time of surgery | 3 |
| Critical preoperative state | Any one or more of the following: ventricular tachycardia or fibrillation or aborted sudden death, preoperative cardiac massage, preoperative ventilation before arrival in the anesthetic room, preoperative inotropic support, intra-aortic balloon counterpulsation or preoperative acute renal failure (anuria or oliguria < 10 mL/hr) | 3 |
| Cardiac-Related Factors | ||
| Unstable angina | Rest angina requiring intravenous administration of nitrates until arrival in the anesthetic room | 2 |
| Left ventricular dysfunction | Moderate or LVEF 30%–50% | 1 |
| Poor or LVEF > 30% | 3 | |
| Recent myocardial infarct | (<90% days) | 2 |
| Pulmonary hypertension | Systolic pulmonary artery pressure > 60 mmHg |
