When a patient’s pretest probability of CAD is intermediate to high, myocardial perfusion imaging (MPI) may be an appropriate modality for risk stratification and patient management.1
Either SPECT or positron emission tomography (PET) MPI can be used to identify ischemia and prior infarction, risk stratify patients with known or suspected CAD, and guide clinical management decisions regarding medical therapy or revascularization.2 There are some differences between these modalities that should be considered when selecting the right modality for the right patient.
SPECT MPI continues to be the most commonly used imaging modality in nuclear cardiology today. It plays an important role in the risk assessment and evaluation of CAD and is widely available and accessible for patients who are known or suspected to have CAD.2
SPECT can be performed with exercise or pharmacologic stress. Exercise stress is the preferred imaging procedure because the ability or inability to adequately exercise has independent prognostic and diagnostic value.2 Exercise capacity is a strong indicator of long-term risk, including death, for men and women with known or suspected CAD.1
For patients unable to exercise adequately, pharmacologic stress testing may be appropriate. With SPECT MPI, appropriate patients can be converted from exercise to pharmacologic stress.5
Advances in stress imaging protocols, camera technology, and processing software can enhance diagnostic accuracy and reduce radiation exposure.2 More advanced techniques help reduce motion artifacts and potentially improve the patient experience due to reduced imaging times.2 In addition, because contemporary SPECT cameras have made the acquistion of dynamic SPECT easier, quantification of myocardial blood and flow reserve is now possible to detect multivessel CAD.7
Myocardial perfusion defects are typically graded by their extent and severity. In addition to qualitative evaluation of perfusion defects, semiquantitative interpretation of MPI helps standardize visual interpretation of scans, reduce the likelihood of overlooking significant defects, and provide an important semiquantitative index that is applicable to diagnostic and prognostic assessments.7
Current ASNC SPECT Imaging Guidelines recommend semiquantitative analysis using a segmental 5-point scale system on a 17-segment model of the left ventricle7:
aAdapted from the American Society of Nuclear Cardiology; originally presented in Cerqueira MD, et al. Circulation 2002;105(4):539-42.
In addition to individual segmental scores, ASNC SPECT imaging guidelines recommend that summed scores be calculated. These scores represent the summed stress scores (SSS) of all segments and the summed rest scores (SRS) of all segments. The summed difference score (SDS) is the difference between the SSS and SRS7:
The SSS represents the extent and severity of stress perfusion abnormality, the SRS represents the extent of infarction, and the SDS represents the extent and severity of reversible ischemia.2
These semiquantitative metrics help guide decisions about the appropriate use of coronary revascularization.7
Functional assessment of wall motion and thickening as well as left ventricular ejection fraction (LVEF) also help stratify risk. According to ASNC guidelines, regional wall motion should be analyzed and classified using a semiquantitative scoring system7:
Software algorithms can help with semiquantitative scoring of wall motion and thickening.
LVEF can be categorized as follows7:
Astellas offers information and educational resources to help support shared clinical decision-making, collaborative care, and appropriate testing referrals.
For more information on noninvasive cardiac testing modalities, download this booklet or explore a more complete library of resources on CardiacTesting.com.
1. Fihn SD, Gardin JM, Abrams J, et al. 2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease. J Am Coll Cardiol 2012;60(24):e44-164. Erratum in: J Am Coll Cardiol 2014;63(15):1588-90. 2. Udelson JE, Dilsizian V, Bonow RO. Nuclear cardiology. In: Zipes DP, Libby P, Bonow RO, Mann DL, Tomaselli GF, Braunwald E, eds. Braunwald’s Heart Disease. 11th ed. Philadelphia, PA: Elsevier Saunders, 2019:261-300. 3. Driessen RS, Raijmakers PG, Stuijfzand WJ, Knaapen P. Myocardial perfusion imaging with PET. Int J Cardiovasc Imaging 2017;33(7):1021-31. 4. Bateman TM, Heller GV, McGhie AI, et al. Diagnostic accuracy of rest/stress ECG-gated Rb-82 myocardial perfusion PET: comparison with ECG-gated Tc-99m sestamibi SPECT. J Nucl Cardiol 2006;13(1):24-33. 5. Henzlova MJ, Duvall WL, Einstein AJ, Travin MI, Verberne HJ. ASNC imaging guidelines for SPECT nuclear cardiology procedures: stress, protocols, and tracers. J Nucl Cardiol 2016;23(3):606-39. Erratum in: J Nucl Cardiol 2016;23(3):640-2. 6. DePuey EG, Mahmarian JJ, Miller TD, et al. Patient-centered imaging. J Nucl Cardiol 2012;19(2):185-215. Erratum in: J Nucl Cardiol 2012;19(3):633. 7. Dorbala S, Ananthasubramaniam K, Armstrong IS, et al. Single Photon Emission Computed Tomography (SPECT) myocardial perfusion imaging guidelines: instrumentation, acquisition, processing, and interpretation. J Nucl Cardiol 2018;25(5):1784-846.