Cardiovascular nuclear imaging employs non-invasive techniques to assess alterations in coronary artery flow, and ventricular function.
The specific imaging technique (perfusion versus ventricular function) and the reason for the imaging determine which radionuclide agent is employed. A myocardial perfusion study utilizes an imaging isotope agent that reflects segmental and global myocardial blood flow and uptake, the interpretation of which is used to make inference about the presence of scar and ischemia.
Ventricular function studies utilize specific imaging isotopes to outline the borders of the ventricular endocardium, or to identify the ventricular blood pool independent of the surrounding myocardium. The motion of the left ventricle, synchronized with the electrocardiogram, is used to generate wall motion and ejection fraction information.
These tests may be performed at rest and during exercise, or with pharmacologic intervention when exercise cannot be performed. The acquisition of the images may be planar (single plane) or by multiple planes with computer integration, SPECT (single-photon emission computer tomography).
Cardiovascular nuclear imaging is indicated for the following:
Assessment of the functional and prognostic importance of angina;
Diagnostic evaluation of patients with chest pain and uninterpretable or equivocal ECG changes caused by drugs, bundle branch block, or left ventricular hypertrophy;
Assessment of congenital anomalies of coronary arteries;
Risk assessment or re-evaluation of disease in patients who are asymptomatic or have stable symptoms, with known atherosclerotic heart disease on catheterization or SPECT perfusion imaging, who have not had a revascularization procedure within the past two years;
Detection of coronary artery disease in patients, without chest pain syndrome, with new-onset of diagnosed heart failure or left ventricular systolic dysfunction;
Evaluation of ischemic versus non-ischemic cardiomyopathy when cardiac catheterization / coronary angiography are not planned;
Evaluation of myocardial perfusion and/or function before and after coronary artery bypass surgery or other re-perfusion procedures;
Quantification and surveillance of myocardial infarction and prognostication in patients with infarction;
Preoperative assessment for non-cardiac surgery, when used to determine risk for surgery and/or perioperative management in:
- patients with minor or intermediate clinical risk predictors and poor functional capacity;
- patients with intermediate or high likelihood of coronary heart disease, or
- patients with poor functional capacity undergoing high risk non-cardiac surgery;
The "ACA/AHA 2007 Guidelines on Perioperative Cardiovascular Evaluation and Care for Non-Cardiac Surgery" (JACC 2007; 50:e159-e242) provides this information:
High risk surgery: aortic and peripheral vascular surgery
Intermediate risk surgery: intraperitoneal and intrathoracic surgery, carotid endarterectomy, head & neck surgery, orthopedic surgery, prostate surgery.
Low risk surgery: endoscopic procedures, superficial surgery, cataract surgery, breast surgery, ambulatory surgery
Poor functional capacity = less than 4 METS
Clinical risk factors:
1) history of ischemic heart disease
2) history of compensated or prior heart failure
3) history of cerebrovascular disease
Decision-making for testing is based upon the presence of multiple clinical risk factors, the level of functional capacity, the risk of the surgery and the likelihood that the results of the cardiac testing would change the management.
Evaluation of ventricular function in patients with non-ischemic myocardial disease;
Evaluation of patients in whom an accurate measure of the ejection fraction is needed to make a determination of whether to implant a defibrillator or biventricular pacemaker;
Evaluation of a patient receiving chemotherapeutic drugs which are potentially cardiotoxic (e.g., adriamycin).
First pass studies will be considered medically necessary only when information sought is immediately relevant to the management of the patient’s clinical condition, and has not been previously obtained or likely to be obtained from other planned tests such as echocardiography or equilibrium gated blood pool studies. First pass studies may be indicated for the assessment and identification of shunts.
Infarct avid scintigraphy is indicated in patients in whom it is not possible to make a definitive diagnosis of myocardial infarction by EKG or enzyme testing.
Patient selection should be based on clinical grounds:
Patients with a high pretest probability of disease are not usually candidates for a study for diagnostic purposes, though the size and reversibility of a defect and its functional consequences may be required for clinical decision-making.
Patients with a moderate probability of disease benefit the most from the study when the diagnosis is in question.
Selection of tests should be made within the context of other tests, scheduled and previously performed, so that the anticipated information obtained is unique and not redundant.
Special Equipment Requirements:
Given the limitations of uptake, low photon energy and redistribution, the cardiac blood pool codes and perfusion imaging codes are not generally covered on the same date of service. However, in light of the predictive value of exercise-induced changes in ejection fraction, an exception will be made to allow first pass, single study with exercise along with the appropriate perfusion studies. Providers who bill this service must certify within their records that their laboratories are specially equipped to process such studies.
All cardiovascular nuclear tests and stress tests must be referred by a physician or a qualified non-physician provider.
All stress tests must be performed under the direct supervision of a physician. The nuclear test components must be performed under the general supervision of a physician.
Myocardial perfusion studies performed based on the presence of risk factors in the absence of cardiac symptoms, cardiac abnormalities on physical examination, or abnormalities on cardiac testing (e.g., electrocardiographic tests, echocardiography, etc) will be considered screening and denied as not covered by Medicare.
Tests that are anticipated to provide information duplicative of another test already performed will be denied as not medically necessary.
Tests performed when the results would not be anticipated to influence medical management decisions will be denied as not medically necessary.
Myocardial perfusion studies performed subsequent to a diagnostic myocardial PET scan will denied as not medically necessary.
Infarct avid scintigraphy will be denied if the diagnosis of myocardial infarction has already been confirmed by enzymes and/or EKG.
Tests performed unrelated to changes in a patient's signs or symptoms, or for immediate pre-operative evaluation will be denied as medically unnecessary.
Tests performed for risk assessment prior to high risk non-cardiac surgery in asymptomatic patients within one year following normal catheterization or non-invasive test will be considered medically unnecessary and denied.
Tests performed for preoperative evaluation in patients undergoing low-risk surgery will be denied.