Nuclear imaging has played a role for two decades in detection of coronary disease and risk stratification of patients after infarction. Its power lies in characterization of prognostic factors such as degree of left ventricular function, presence and extent of residual ischemia within and outside of the infarction, and extent of myocardial viability.

Currently, patients who have preservation of ejection fraction are at sufficiently low risk that further stratification is problematic in value. However, Dr. Dilsizian stressed that further stratification is feasible and clinically relevant for patients who have compromised ejection fractions. Vasodilator Spect perfusion imaging can be done safely before discharge and may identify patients who need additional care.

Imaging may be most valuable for patients who have repeated infarctions and a low ejection fraction because it can determine whether there is enough viable tissue to warrant revascularization.

In this setting, positron emission testing has better resolution than thallium scanning and provides information on tissue metabolism. If a resting patient in a fasting state is tested and shows hypoperfusion with enhanced tracer uptake in the hypoperfused region, metabolism has switched from fatty acids to glucose. Revascularization is likely to succeed.

Future potential for nuclear imaging lies in work done with patients who do not regain ventricular function. The question posed with these patients is "What else is happening in the myocardial interstitium?"

In a study done with 13 patients who received transplants, nuclear findings were compared with pathology results. Regions with poor perfusion with thallium and lack of metabolism with positron emission testing had gross scarring. In addition, non-infarcted regions had layers of collagen that hadn't been detected by imaging.

Some researchers have postulated that such ventricular remodeling is influenced by angiotensin II; if this is true, ACE-inhibitor agents may decrease the response and decrease mortality.

In mice and human studies, there is evidence that angiotensin II does play a role in ventricular remodeling. Positron emission testing ET scans done with a tracer that binds to angiotensin II (type I) demonstrated that angiotensin II was in myocardial cells in the peri-infarct zone. In the future, such scans could detect metabolic signs of remodeling and monitor results of medical therapy.