Title: A Sensitive Cardiac Troponin T Assay in Stable Coronary Artery Disease
Topic: General Cardiology
Date Posted: 1/19/2010
Author(s): Omland T, de Lemos JA, Sabatine MS, et al., on behalf of the Prevention of Events With Angiotensin Converting Enzyme Inhibition (PEACE) Trial Investigators.
Citation: N Engl J Med 2009;361:2538-2547.
Clinical Trial: No
Study Question: What are the prognostic implications of elevated troponin T levels in stable coronary artery disease (CAD) patients?
Methods: A new highly sensitive troponin T assay was used in 3,679 patients with stable CAD and preserved left ventricular function. Patients were followed for an average of 5.2 years for cardiovascular (CV) events.
Results: Concentrations of cardiac troponin T were at or above detection limit (0.001 μg/L) in 97.7% of patients (n = 3,593) and at or above the 99th percentile for apparently healthy subjects (0.0133 μg/L) in 11.1% of patients (n = 407). After adjustment for other prognostic indicators, there was a strong and graded increase in the cumulative incidence of CV death (hazard ratio [HR] per unit increase in natural log of troponin T level, 2.09; 95% confidence interval [CI], 1.60-2.74; p < 0.001) and of heart failure (HR, 2.20; 95% CI, 1.66-2.90; p < 0.001). Increased risk with higher troponin T levels was evident well below the limit of detection of conventional cardiac troponin T assays and below the 99th percentile of values in a healthy population. There was no association between troponin T levels, as measured with this assay, and incidence of myocardial infarction (MI) (HR, 1.16; 95% CI, 0.97-1.40; p = 0.11).
Conclusions: The authors concluded that after adjustment for other prognostic indicators, cardiac troponin T levels, as measured with a highly sensitive assay, were significantly associated with incidence of CV death and congestive heart failure, but not with MI in patients with stable CAD.
Perspective: Troponins T and I have become the ‘gold standard’ for the diagnosis of myocardial necrosis. However, low level elevations of cardiac troponins have been shown to be elevated in a small percentage of stable patients without evidence of acute coronary syndromes. These minor elevations are associated with adverse cardiac outcomes indicating that circulating levels of these contractile proteins may provide useful information beyond that gleaned in the setting of acute MI. With development of a highly sensitive troponin T assay, the authors of the current study have demonstrated that low troponin T levels may be useful in predicting some adverse CV outcomes, independent of conventional risk factors. Several questions are raised including the cellular source and mechanism of low level troponin generation, which may provide guidance to the appropriate management of these patients. The clinical utility of this sensitive screening assay will require additional studies. Daniel T. Eitzman, M.D., F.A.C.C.
Title: Perioperative Practice: Time to Throttle Back
Topic: General Cardiology
Date Posted: 1/25/2010
Author(s): Chopra V, Flanders SA, Froehlich JB, Lau WC, Eagle KA.
Citation: Ann Intern Med 2010;152:47-51.
Clinical Trial: No
Perspective: This perspective discusses how the current practice of perioperative risk assessment often conflicts with trial-based evidence; and advocates that, by heeding existing evidence and by implementing the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines, perioperaive costs can be reduced while outcomes are improved. The following are points to remember.
1. Screening stable patients for coronary artery disease (CAD) before noncardiac surgery does not improve perioperative outcomes.
Data suggesting benefit came from retrospective studies conducted almost exclusively in patients undergoing vascular surgery (and therefore predominantly at high risk).
In those retrospective trials, patients who underwent revascularization may have done so for indications other than upcoming surgery, again implying an independent assessment of high risk.
2. The preoperative identification of significant CAD does not necessarily lead to the identification of patients at increased perioperative cardiac risk.
Preoperative testing, whether noninvasive or invasive, screens for obstructive coronary lesions.
Data from autopsy studies reveal that fatal perioperative myocardial infarction frequently originated with a nonstenotic coronary lesion.
Increased perioperative risk often is associated with an angiographically low-grade lesion vulnerable to plaque rupture.
3. Preoperative coronary revascularization does not lower perioperative cardiac risk.
Among patients with stable CAD, coronary revascularization has no advantage over medical therapy in the prevention of myocardial infarction or death.
Among patients undergoing vascular surgery, randomized, prospective data demonstrate no advantage associated with revascularization compared to good medical therapy.
One relatively small study even demonstrated no clinical benefit associated with preoperative coronary revascularization among patients with high-risk coronary anatomy undergoing high-risk surgery.
4. Failure of a strategy to reduce risk using preoperative coronary revascularization might fail for several reasons.
The existing ‘gold standard’ for detecting CAD using coronary angiography is flawed.
Coronary artery biology appears to matter more than anatomy in defining risk.
Preoperative coronary revascularization is, as with any interventional procedure, associated with inherent risk.
5. The routine use in all patients of perioperative beta-adrenergic antagonists does not reduce perioperative adverse events.
Bradycardia and hypotension associated with indiscriminate beta-blocker use presumably add to adverse perioperative outcomes.
One large study found that perioperative beta-blocker therapy was beneficial only in patients at intermediate or higher risk.
6. Data support a strategy of beta-blocker therapy, titrated to hemodynamic variables, in high-risk patients with ischemic heart disease who are undergoing high-risk surgery.
These recommendations are reflected in the 2009 ACC/AHA Focused Update on Perioperative Beta-Blockers.
7. The implementation of an evidence-based doctrine of selective beta-blocker therapy among high-risk patients with ischemic heart disease undergoing high-risk surgery, selective preoperative functional testing only to identify those high-risk patients, and preoperative coronary revascularization only in very selected cases, is not necessarily the current standard of practice.
Factors affecting this might include legal concerns, pressure from surgeons, and provider bias caused by testing- and procedure-related income.
8. At the authors’ institution, two educational initiatives supporting the ACC/AHA perioperative guideline recommendations resulted in lower costs associated with preoperative risk assessment, but preserved or improved perioperative patient outcomes. David S. Bach, M.D., F.A.C.C.