Acute Chest Pain TC-99m Sestamibi Scan

Abstracts & Commentary

Synopsis: Acute chest pain myocardial perfusion scintigraphy reduced hospital admissions and resource use by inpatients.

Sources: Heller GV. J Nucl Cardiol. 2002;9:350-352; Knott JC, et al. J Nucl Cardiol. 2002;9:257-262.

Due to lack of redistribution, tc-99m sestamibi can be used to image the myocardium for up to 6 hours after administration; permitting acute administration during spontaneous chest pain and imaging at leisure. However, the use of this approach to acute chest pain management is unclear. Thus, Knott and colleagues from Melbourne, Australia, evaluated this technique in 120 consecutive patients with acute chest pain presenting to the emergency department (ED) (68%) or on the ward (32%) who, on clinical grounds, were thought to be at intermediate risk for myocardial ischemia. Patients whose chest pain resolved while waiting for the scan or patients with definite ischemia were excluded. Single photon emission computed tomography was performed 1-6 hours after the isotope injection. The effect of scanning on subsequent decision making was assessed.

There was a significant change in management plans for the ED patients; a 34% reduction in admissions and a 59% reduction in planned coronary care unit (CCU) admissions (P < 001). Also, 7 patients had ED discharge canceled and 17 admitted patients were upgraded to CCU. The presence of known coronary artery disease did not reduce the effect of the scans, nor did ECG results. In the ward patients there was a 40% reduction in planned cardiac catheterization because of scan results, but 4 new patients were sent to catheterization. The authors concluded that acute chest pain myocardial perfusion scintigraphy reduced hospital admissions and resource use by inpatients.

Comment by Michael H. Crawford, MD

The diagnostic accuracy of acute chest pain myocardial perfusion imaging for myocardial infarction (MI) has been shown to be quite high (up to 99% sensitivity and negative predictive value), but acute MI can easily be diagnosed by serum biological markers today. Also, studies of MI showed considerable false positives; positive scans who turned out not to have MI. Presumably these patients had myocardial ischemia. This study is one of the first to evaluate the value of an ischemia scan in chest pain patients who did not have acute MI by other criteria. The methods were somewhat unique in that the caring physicians had to commit in writing to a management plan before and after the scan results. The difference was impressive; a 34% reduction in admissions, a 59% reduction in planned CCU admissions, and a 40% reduction in planned cardiac catheterization. The total CCU admissions were not changed significantly because some patients destined for the ward were sent there after the scan results. These observations could result in a decrease in hospital costs, but this was not tested.

There are limitations to this study. The most important is that there are no outcome data for the outpatients sent home. Also, the total number of patients is small, so certain subgroup analyses are not robust such as like the reduction in cardiac catheterization, which was not statistically significant. There were false-positive results that occasioned admission, but these patients usually went home the next day and may have been offset by the 7 patients whose ED discharge was canceled by a positive scan. Regardless, total admissions were decreased significantly. The accompanying editorial by Gary Heller asks why this technique isn’t used more often? Historically, interest was low when 201 Th was our only choice since imaging had to be done within 10 minutes of injection. TC-99m sestamibi has solved that problem, but still many nuclear labs do not function 24/7/365. The one in this study didn’t. It is difficult to expect physicians to use one image technique during weekday hours and another the rest of the time, especially when one is expensive (nuclear imaging). Consequently, unless nuclear imaging is more available than it was at the institution in this study, I don’t see increased use of this approach, despite its attractiveness.

Dr. Crawford is Professor of Medicine, Mayo Medical School; Consultant in Cardiovascular Diseases, and Director of Research, Mayo Clinic, Scottsdale, AZ.