What is the role of a Positron Emission Tomography (PET) scan in the diagnosis of Coronary Artery Disease (CAD)?

PET Scan for Diagnosis of Coronary Artery Disease

PET myocardial perfusion imaging is recommended for patients with moderate to high pre-test likelihood (>15%-85%) of obstructive CAD who cannot exercise or have abnormal baseline ECGs, and is preferred over SPECT when both modalities are available due to superior diagnostic accuracy. 1

Diagnostic Performance

PET demonstrates exceptional diagnostic capabilities for detecting CAD:

• Sensitivity of 92% and specificity of 85% at the patient level, with positive likelihood ratio of 6.2 and negative likelihood ratio of 0.11 2
• Superior to SPECT imaging, with meta-analyses showing PET outperforms Tl-201 and sestamibi perfusion imaging 2
• Myocardial perfusion PET provides 91% sensitivity and 89% specificity for diagnosing obstructive coronary artery disease 3

Primary Indications (Class I Recommendations)

PET myocardial perfusion imaging is indicated for:

• Patients with moderate or high pre-test likelihood (>15%-85%) of obstructive CAD to diagnose and quantify myocardial ischemia and/or scar, estimate risk of major adverse cardiac events, and quantify myocardial blood flow 1, 4
• Initial diagnostic test in patients unable to exercise with intermediate likelihood of CAD 1
• Patients with left bundle branch block when used in conjunction with vasodilator stress 1
• When SPECT studies are equivocal for diagnostic or risk-stratification purposes 1

Advantages Over SPECT

The 2024 ESC guidelines explicitly state that SPECT or, preferably, PET should be used, reflecting PET's superiority 1:

• Higher diagnostic accuracy with improved sensitivity and specificity compared to conventional nuclear techniques 1, 2
• Quantification of myocardial blood flow and coronary flow reserve, which SPECT cannot provide 1, 3
• Better detection of multivessel CAD through assessment of left ventricular ejection fraction reserve 1
• Improved detection of preclinical and multivessel coronary atherosclerosis through quantitative flow measurements 3

Integration with Coronary CT Angiography

Hybrid PET/CT imaging provides complementary anatomic and functional information:

• Nearly half (47%) of significant angiographic stenoses occur without myocardial ischemia, while 50% of normal PET studies show some CCTA abnormality 1, 5
• Sequential approach is feasible: CCTA can exclude obstructive CAD in 53% of patients, with PET reserved for those with suspected stenosis 6
• Patients with normal PET perfusion have comparable outcomes to those without obstructive CAD on CCTA, regardless of anatomic findings 6
• Fusion imaging allows identification of culprit stenosis and guides revascularization decisions more effectively than either modality alone 3, 7

Prognostic Value

PET provides powerful risk stratification:

• Annual adverse event rate is 5 times higher in patients with abnormal versus normal perfusion (2.5% vs. 0.5%) 6
• Extent and severity of ischemia and scarring provide incremental risk estimates of cardiac death beyond traditional risk factors 1
• Normal PET study predicts excellent prognosis with very low annual event rates 6

Technical Considerations

When performing PET for CAD diagnosis:

• Measure coronary artery calcium score from the unenhanced CT used for attenuation correction to improve detection of both non-obstructive and obstructive CAD 1, 4
• Use adenosine or dipyridamole for pharmacologic stress in patients unable to exercise 1
• Rb-82 PET provides stress LVEF data at rest and peak stress, improving detection of multivessel CAD 1

When NOT to Use PET

PET is not recommended for:

• Routine screening of asymptomatic patients with low pre-test likelihood of CAD 1
• Patients with severe comorbidities limiting life expectancy or candidacy for revascularization 1
• Low to moderate pre-test likelihood (>5%-50%) patients where CCTA is the preferred initial test 1, 4
• Very high pre-test likelihood (>85%) patients with severe refractory symptoms where invasive coronary angiography is recommended as first-line 1, 4

Comparison with Alternative Modalities

For patients with moderate-high pre-test likelihood:

• PET is preferred over SPECT when both are available, with randomized trial evidence showing lower rates of unnecessary invasive angiography with PET (1 in 5 with low-risk SPECT underwent ICA vs. half that rate with PET) 1
• Stress echocardiography and CMR are reasonable alternatives with Class I recommendations for the same patient population 1, 4
• Selection should be based on local expertise and availability, though PET offers unique quantitative flow assessment 1