ACC/AHA and ASNC Release Guidelines for the Clinical Use of Cardiac Radionuclide Imaging

The American College of Cardiology (ACC)/American Heart Association (AHA) Task Force on Practice Guidelines in conjunction with the American Society for Nuclear Cardiology (ASNC) recently published a joint executive summary of recommended indications for the use of specific nuclear cardiologic techniques in three broad areas: acute ischemic syndromes, chronic syndromes, and heart failure. The recommendations appeared in the September 16, 2003, issue of Circulation (http://circ.ahajournals.org/cgi/content/full/108/11/1404) and the full text also can be found online at http://www.acc.org, http://www.americanheart.org, and http://www.asnc.org.

ACC/AHA Classifications

The ACC/AHA classifications are defined as follows:

• Class I: Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective.

• Class II: Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness or efficacy of a procedure or treatment.

• Class IIa: Weight of evidence/opinion is in favor of usefulness or efficacy.

• Class IIb: Usefulness or efficacy is less well established by evidence/opinion.

• Class III: Conditions for which there is evidence and/or general agreement that the procedure or treatment is not useful or effective and in some cases may be harmful.

Acute Syndromes

Patients who present to the emergency department with chest pain should be placed in risk categories based on their probability of acute myocardial infarction, unstable angina, or both. After initial examination of symptoms, electrocardiogram (ECG), and history, rest single-photon emission computed tomography (SPECT) imaging appears to be useful for identifying patients at high risk (those with perfusion defects who should be admitted) and patients at low risk (those with normal scans who, generally, may be discharged). Whether exercise stress imaging for negative resting scans is indicated the same day or at a later date is still under investigation.

When conventional measures do not provide a diagnosis, rest myocardial perfusion imaging with technetium Tc 99m tracers has a high sensitivity for the diagnosis of acute myocardial infarction. However, perfusion defects do not distinguish among acute ischemia, acute infarction, or previous infarction.

Radionuclide techniques also are useful for determining the presence and extent of stress-induced myocardial ischemia. Important prognostic management information can be acquired from the acute or late measurement of ejection fraction, infarct size, and myocardium at risk. For patients with several high-risk factors for unstable angina and ST-elevation myocardial infarction and no serious comorbidities, an early invasive strategy is recommended.

Chronic Syndromes

Myocardial perfusion imaging is most useful in patients with an intermediate likelihood of angiographically significant coronary artery disease (CAD) based on age, sex, risk factors, symptoms, and results of stress testing, if available.

In the management of known or suspected chronic CAD, nuclear tests are most useful for determining risk stratification in patients with a clinically intermediate risk of a subsequent cardiac event. Factors that estimate the extent of left ventricular dysfunction are the best predictors of cardiac mortality, and markers of provocative ischemia are excellent predictors of the subsequent development of acute ischemic syndromes.

The following recommendations apply to patients with chronic syndromes:

• Cardiac stress myocardial perfusion SPECT in patients able to exercise: recommendations for diagnosis of patients with an intermediate likelihood of CAD and/or risk stratification of patients with an intermediate or high likelihood of CAD who are able to exercise to at least 85 percent of maximal predicted heart rate.

CLASS I

1. Exercise myocardial perfusion SPECT to identify the extent, severity, and location of ischemia in patients who do not have left bundle branch block or an electronically paced ventricular rhythm but do have a baseline ECG abnormality that interferes with the interpretation of exercise-induced ST-segment changes (e.g., ventricular pre-excitation, left ventricular hypertrophy, digoxin therapy, more than 1-mm ST depression).

2. Adenosine or dipyridamole myocardial perfusion SPECT in patients with left bundle branch block or electronically paced ventricular rhythm.

3. Exercise myocardial perfusion SPECT to assess the functional significance of intermediate (25 to 75 percent) coronary lesions.

4. Exercise myocardial perfusion SPECT in patients with intermediate Duke treadmill score.

5. Repeat exercise myocardial perfusion imaging after initial perfusion imaging in patients whose symptoms have changed to redefine the risk for cardiac event.

CLASS IIA

1. Exercise myocardial perfusion SPECT at three to five years after revascularization (i.e., percutaneous coronary intervention or coronary artery bypass graft) in selected high-risk asymptomatic patients.

2. Exercise myocardial perfusion SPECT as the initial test in patients who are considered to be at high risk (patients with diabetes or patients otherwise defined as having a more than 20 percent 10-year risk of a coronary heart disease event).

CLASS IIB

1. Repeat exercise myocardial perfusion SPECT one to three years after initial perfusion imaging in patients with known or a high likelihood of CAD and stable symptoms and a predicted annual mortality of more than 1 percent to redefine the risk of a cardiac event.

2. Repeat exercise myocardial perfusion SPECT on cardiac active medications after initial abnormal perfusion imaging to assess the efficacy of medical therapy.

3. Exercise myocardial perfusion SPECT in symptomatic or asymptomatic patients who have severe coronary calcification (computed tomography Coronary Calcium Score more than the 75th percentile for age and sex) in the presence on the resting ECG of pre-excitation (Wolff-Parkinson-White syndrome) or more than 1-mm ST depression.

4. Exercise myocardial perfusion SPECT in asymptomatic patients who have a high-risk occupation.

• Cardiac stress myocardial perfusion SPECT in patients unable to exercise: recommendations for diagnosis of patients with an intermediate likelihood of CAD and/or risk stratification of patients with an intermediate or high likelihood of CAD who are unable to exercise.

CLASS I

1. Adenosine or dipyridamole myocardial perfusion SPECT to identify the extent, severity, and location of ischemia.

2. Adenosine or dipyridamole myocardial perfusion SPECT to assess the functional significance of intermediate (25 to 75 percent) coronary lesions.

3. Adenosine or dipyridamole myocardial perfusion SPECT after initial perfusion imaging in patients whose symptoms have changed to redefine the risk for cardiac event.

CLASS IIA

1. Adenosine or dipyridamole myocardial perfusion SPECT at three to five years after revascularization (i.e., percutaneous coronary intervention or coronary artery bypass graft) in selected high-risk asymptomatic patients.

2. Adenosine or dipyridamole myocardial perfusion SPECT as the initial test in patients who are considered to be at high risk (patients with diabetes or patients otherwise defined as having a more than 20 percent 10-year risk of a coronary heart disease event).

3. Dobutamine myocardial perfusion SPECT in patients who have a contraindication to adenosine or dipyridamole.

CLASS IIB

1. Repeat adenosine or dipyridamole myocardial perfusion imaging one to three years after initial perfusion imaging in patients with known or a high likelihood of CAD and stable symptoms, and a predicted annual mortality of more than 1 percent, to redefine the risk of a cardiac event.

2. Repeat adenosine or dipyridamole myocardial perfusion SPECT on cardiac active medications after initial abnormal perfusion imaging to assess the efficacy of medical therapy.

3. Adenosine or dipyridamole myocardial perfusion SPECT in symptomatic or asymptomatic patients who have severe coronary calcification (computed tomography Coronary Calcium Score more than the 75th percentile for age and sex) in the presence on the resting ECG of left bundle branch block or an electronically paced ventricular rhythm.

4. Adenosine or dipyridamole myocardial perfusion SPECT in asymptomatic patients who have a high-risk occupation.

• Cardiac stress myocardial perfusion positron emission tomography (PET): recommendations for diagnosis of patients with an intermediate likelihood of CAD and/or risk stratification of patients with an intermediate or high likelihood of CAD.

CLASS I

1. Adenosine or dipyridamole myocardial perfusion PET in patients in whom an appropriately indicated myocardial perfusion SPECT study has been found to be equivocal for diagnostic or risk-stratification purposes.

CLASS IIA

1. Adenosine or dipyridamole myocardial perfusion PET to identify the extent, severity, and location of ischemia as the initial diagnostic test in patients who are unable to exercise.

2. Adenosine or dipyridamole myocardial perfusion PET to identify the extent, severity, and location of ischemia as the initial diagnostic test in patients who are able to exercise but have left bundle branch block or an electronically paced rhythm.

• Cardiac stress perfusion imaging before noncardiac surgery: recommendations.

CLASS I

1. Initial diagnosis of CAD in patients with intermediate pretest probability of disease and abnormal baseline ECG or inability to exercise.

2. Prognostic assessment of patients undergoing initial evaluation for suspected or proven CAD with abnormal baseline ECG or inability to exercise.

3. Evaluation of patients following a change in clinical status (e.g., acute coronary syndrome) with abnormal baseline ECG or inability to exercise.

4. Initial diagnosis of CAD in patients with left bundle branch block and intermediate pretest probability of disease, when used in conjunction with vasodilator stress.

5. Prognostic assessment of patients with left bundle branch block undergoing initial evaluation for suspected or proven CAD, when used in conjunction with vasodilator stress.

6. Assessment of patients with intermediate or minor clinical risk predictors and poor functional capacity (less than four metabolic equivalents [METS]) who require high-risk noncardiac surgery, when used in conjunction with pharmacologic stress.

7. Assessment of patients with intermediate clinical risk predictors, abnormal baselines ECGs, and moderate or excellent functional capacity (more than four METS) who require high-risk noncardiac surgery.

CLASS IIB

1. Routine assessment of active, asymptomatic patients who have remained stable for up to five years after coronary artery bypass graft surgery.

2. Routine evaluation of active, asymptomatic patients who have remained stable for up to two years after previous abnormal coronary angiography or noninvasive assessment of myocardial perfusion.

3. Diagnosis of restenosis and regional ischemia in active asymptomatic patients within weeks to months after percutaneous coronary intervention.

4. Initial diagnosis or prognostic assessment of CAD in patients with right bundle branch block or less than 1-mm ST depression on resting ECG.

CLASS III

1. Routine screening of asymptomatic men or women with low pretest likelihood of CAD.

2. Evaluation of patients with severe comorbidities that limit life expectancy or candidacy for myocardial revascularization.

3. Initial diagnosis or prognostic assessment of CAD in patients who require emergency noncardiac surgery.

Heart Failure

Common principles in the assessment of heart failure that affect prognosis and therapy include: left ventricular function and remodeling, the contribution of myocardial ischemia caused by CAD, and myocardial viability.

The initial assessment of left ventricular systolic dysfunction should be done by resting radionuclide angiography. Doppler blood flow velocity should be used for assessing left ventricular diastolic dysfunction.

In patients with heart failure, it should be determined whether the left ventricular dysfunction is caused by the consequences of CAD or one of the other etiologies included in nonischemic cardiomyopathy. Myocardial perfusion imaging has demonstrated excellent sensitivity and negative predictive value for patients with CAD. The specificity of perfusion imaging to eliminate the diagnosis of CAD is modest.