A 72-year-old man with a history of type 1 diabetes mellitus and coronary artery disease is scheduled to undergo aortobifemoral bypass surgery. As part of preoperative bloodwork, an N-terminal pro-B-type natriuretic peptide (NT-proBNP) measurement is performed and the result is 80 pg/mL. Based on a recent trial evaluating the predictive value of preoperative NT-proBNP, which of the following BEST describes the relationship between the composite of 30-day all-cause mortality or myocardial infarction and preoperative NT-proBNP?

  • □ (A) As NT-proBNP levels increase, the composite outcome also increases.

  • □ (B) As NT-proBNP levels increase, the composite outcome decreases.

  • □ (C) As NT-proBNP levels increase, the composite outcome is unchanged.

Myocardial injury after noncardiac surgery (MINS) is a significant cause of morbidity and mortality. Several indices have been developed to predict the risk of cardiac complications after surgery based on preoperative variables involving the procedure type and patient comorbidities. Among the most popular are the Revised Cardiac Risk Index (RCRI) and the National Surgical Quality Improvement Program Myocardial Infarction and Cardiac Arrest calculator. In general, these indices have been shown to underestimate risk. N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a marker of myocardial wall stress produced by the heart muscle. It is widely used to diagnose and monitor congestive heart failure. The authors of a recent study sought to evaluate whether the addition of preoperative NT-proBNP to the RCRI would confer additional value in predicting MINS within 30 days after surgery. They also sought to determine whether preoperative NT-proBNP measurements had predictive value independently.

This study involved a subset of more than 10,000 patients from the multicenter Vascular Events in Noncardiac Surgery Patients Cohort Evaluation (VISION) trial. Patients were eligible if they were at least 45 years old and undergoing noncardiac surgery with regional or general anesthesia. Postoperative troponin T was measured for three days after surgery and, together with electrocardiogram, was used to diagnose MINS. Patients were also contacted 30 days after surgery to determine whether any outcome occurred.

The mean patient age was 65 years. Comorbidities included diabetes (20.2%), coronary artery disease (14.7%), congestive heart failure (3.3%), peripheral vascular disease (7.7%), and history of cerebrovascular accident (6.9%). One-third of patients were undergoing low-risk surgery, 25.3% were undergoing major orthopedic surgery, 17.9% were undergoing major general surgery, and 13.8% were undergoing major urologic or gynecologic surgery. The outcome of vascular death or MINS occurred in 12.2% of patients. Vascular death was defined as any death with a vascular cause and includes death following a myocardial infarction, cardiac arrest, stroke, cardiac revascularization procedure (i.e., percutaneous coronary intervention or coronary artery bypass graft surgery), pulmonary embolus, hemorrhage, or from an unknown cause.

The following NT-proBNP thresholds were used: <100 pg/mL; 100 to <200 pg/mL; 200 to <1,500 pg/mL; ≥1,500 pg/mL. These thresholds independently predicted outcomes as well as improved the performance of the RCRI at predicting the same events. Adding NT-proBNP thresholds to the RCRI resulted in a reclassification improvement of 258 per 1,000 patients. The analysis showed that a preoperative NT-proBNP value <200 pg/mL was associated with a risk of death or myocardial infarction of 3% or less, while a value between 200 and 1,500 pg/mL was associated with a risk of 7.9%. Preoperative NT-proBNP values were also associated with 30-day all-cause mortality: <100 pg/mL, incidence 0.3%; 100 to <200 pg/mL, incidence 0.7%; 200 to <1,500 pg/mL, incidence 1.4%; ≥1,500 pg/mL, incidence 4.0%.

Several national guidelines have recommended the use of NT-proBNP to enhance preoperative cardiac risk stratification. However, a major limitation to date has been lack of information about suitable NT-proBNP thresholds. The results of this large trial help offer some guidance to advance this goal.

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Answer: A