No other imaging discipline has demonstrated the same rigorous and comprehensive approach to the assessment of noninvasive risk stratification that has been displayed by nuclear cardiology.  In addition, as the discipline nuclear cardiology matured, the American Society of Nuclear Cardiology (ASNC) was created and provided the field with a stature of a significant professional society.  The Journal of Nuclear Cardiology (JNC) provided a vehicle and stimulus for development of the field.

The Certification Board of Nuclear Cardiology was created and is a well-established benchmark for the clinical practice of nuclear cardiology. Nuclear laboratory accreditation followed and establishes a serious emphasis on quality within the field (7).

Nuclear stress tests are routinely performed either with exercise protocols or pharmacological drug effects, i.e., adenosine, dipyridamole, regadenosine and dobutamine.  Exercise testing is the preferred modality, although pharmacological testing has been increasing yearly and is now over 40% of patients studied (8). Pharmacological stress test is reserved for patients with exercise limitations. Vasodilator stress testing is preferred in patients with left bundle branch block or electronically paced rhythms as well as recent myocardial infarction of less than 72 hours and abdominal aortic aneurysm.  Dobutamine is used in patients with COPD and bronchospasm.  Vasodilator agents like dipyridamole and adenosine cause a three to five fold increase in myocardial blood inflow and both cause more increase in myocardial blood flow than exercise and dobutamine (9).  Contraindication to pharmacological myocardial perfusion imaging is listed on Table 1.  Myocardial perfusion protocols used with technetium-labeled agents can be same day stress-rest or rest-stress or two-day stress-rest.  The thallium protocol is stress and four-hour redistribution/reinjection.  Dual isotope protocols, i.e. rest thallium stress technetium, carry a high radiation exposure to patients and thus more laboratories are eliminating this approach.

The major goal of noninvasive risk stratification in patients presenting with chest pain or known coronary artery disease (CAD) is the identification of high risk sub-groups for subsequent cardiac death or nonfatal myocardial infarction that may benefit from early revascularization.  In addition, low risk patients can be spared unnecessary invasive evaluation.  Prognosis for patients with suspected or known CAD depend on several variables including the degree of left ventricular dysfunction, extent of CAD, total myocardial ischemic burden and comorbidities.

 A number of studies have been performed supporting myocardial perfusion images (MPI) primarily with

SPECT technology in sub-groups of patients with specific issues:

1. Imaging in women- for instance where now data exist in over 8,000 women suggesting cardiac event rates in patients with normal stress myocardial perfusion study is less than 1% (10).

2. Risk stratification of preoperative patient –MPI in stratifying patients at high risk i.e. peripheral vascular disease, vascular surgery and intermediate risk, i.e. carotid endarterectomy, orthopedic or prostate surgeries. Testing allows determination of which patient need to continue on to invasive procedure and those that can be optimized medically.

3.  Known coronary artery disease patients – including those with percutaneous coronary intervention, coronary artery bypass surgery, and those requiring viability determinations.

4.  Patients with diabetes mellitus – identifying patients with silent ischemia and those at risk for myocardial infarction and sudden cardiac death.

Other sub-groups of patients benefiting from MPI include congestive heart failure, cardiomyopathy, cardiotoxic chemotherapy, renal failure etc. (11).

Even though SPECT MPI has been the main stay of noninvasive cardiovascular testing for the last few decades, recent data suggest that positron emission tomography (PET) offers additional superior technology in subgroups of patients.

Bateman et al described in the Journal of Nuclear Cardiology (April 2006; 13;24-33) in a large population of matched pharmacological stress patients that myocardial perfusion (PET) was superior to SPECT in image quality (79 versus 62%), interpretive certainty (96 versus 81%) and diagnostic accuracy (89% versus 79%), as well as increased identification of multivessel coronary artery disease (12).  There are several potential advantages of PET MPI leading to these results, including higher spatial resolution, greater counting efficiencies and robust attenuation correction.  Similar results were obtained in a meta-analysis reported in 2,442 patient studies from 1977 to 2007 (13). At present, PET imaging’s primary limitation is requirement for pharmacological testing. Appropriate patient population for PET testing is listed on Table 2. An example is shown in Figure1 of a SPECT study with resolution of attenuation artifact following PET MPI. In addition, it is a faster study, completed in 45 minutes and with less radiation exposure than some SPECT protocols.

With today’s health care environment of cost containment, a recent study compared PET MPI to SPECT MPI and looked at downstream cost, including invasive procedures, utilization, cost and clinical outcomes.  In-patients matched for pretest likelihood of CAD, the study concluded  PET MPI in patients with intermediate risk for CAD resulted in a greater than 50% reduction in invasive arteriography and CABG and a 30% cost saving with excellent clinical outcomes at one year compared to conventional SPECT (14).

 The field of clinical nuclear cardiology continues to grow and expand its role in the practice of cardiovascular diseases.  SPECT and PET MPI will likely continue contributing to clinical outcomes and with respect to cost containment.

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