How should a positron emission tomography (PET) myocardial perfusion stress test performed with regadenoson be interpreted?

How to Interpret a PET Myocardial Perfusion Stress Test with Regadenoson

Interpret PET stress perfusion imaging by comparing rest and stress perfusion patterns using a 17-segment model, quantifying myocardial blood flow (MBF) when available, and assessing for reversible perfusion defects that indicate ischemia, with normal perfusion (>70% of remote myocardium) indicating viability and reduced perfusion with preserved FDG uptake (mismatch pattern) indicating hibernating but viable myocardium. 1, 2

Core Interpretation Framework

Perfusion Pattern Analysis

The fundamental interpretation relies on identifying four distinct patterns when comparing rest and stress images:

1. Normal Pattern

• Preserved perfusion at both rest and stress (>70% of remote myocardium uptake)
• Indicates healthy myocardium or potentially stunned myocardium following transient ischemia
• Associated with excellent prognosis (annual cardiac death/MI rate <1%) 1, 3

2. Reversible Defect (Ischemia)

• Normal or near-normal perfusion at rest but reduced perfusion during stress
• This is the hallmark of inducible ischemia indicating flow-limiting coronary stenosis
• Dysfunctional myocardium with stress-induced ischemia is considered viable 1
• Use the 17-segment model to quantify extent: 0-1 segments = minimal, 2-4 segments = moderate, ≥5 segments = extensive ischemia 4

3. Fixed Defect (Scar)

• Reduced perfusion at both rest and stress (match pattern)
• When combined with reduced FDG uptake, indicates non-viable myocardium (scar)
• Unlikely to recover function after revascularization 1

4. Mismatch Pattern (Hibernating Myocardium)

• Reduced perfusion but preserved or increased FDG uptake
• Cardinal feature of hibernating myocardium—ischemic but metabolically active
• Viable tissue with potential to regain function following revascularization 1

Quantitative Assessment

PET's unique advantage is absolute quantification of myocardial blood flow 2:

• Stress MBF: Measure hyperemic flow during regadenoson stress
• Rest MBF: Baseline myocardial perfusion
• MBF Reserve: Ratio of stress to rest MBF (normal typically >2.0)
• Relative MBF Reserve: Regional comparison to remote myocardium

Low MBF reserve independently predicts mortality and helps identify patients who benefit from revascularization beyond the extent of ischemia alone 2. This is particularly valuable for detecting balanced multivessel disease or microvascular dysfunction that may appear normal on relative perfusion imaging.

Regadenoson-Specific Considerations

Timing and Image Acquisition

• Regadenoson is administered as a fixed 0.4 mg bolus over 10 seconds, followed immediately by saline flush and radiopharmaceutical 4
• Optimal imaging window: 2-4 minutes post-injection for perfusion assessment 5
• Peak vasodilatory effect occurs rapidly and is sustained, unlike adenosine which requires continuous infusion 5

Performance Characteristics

Regadenoson demonstrates high diagnostic accuracy 4, 6, 7:

• Sensitivity: 92-95% for detecting obstructive CAD
• Specificity: 77%
• Normalcy rate: 97%
• Particularly effective for single-vessel disease detection (89% sensitivity)

The agreement rate between regadenoson and adenosine for detecting reversible perfusion abnormalities is 62-63%, demonstrating comparable performance 4.

Risk Stratification Algorithm

Low Risk (Annual Event Rate <1%)

• Normal perfusion study (0-1 reversible segments)
• Normal stress MBF and MBF reserve
• Preserved LVEF reserve (increase >5% from rest to stress) 6

Intermediate Risk (Annual Event Rate 2-5%)

• Mild perfusion abnormality (2-4 reversible segments)
• Mildly reduced MBF reserve (1.5-2.0)
• Minimal LVEF reserve (0-5% increase)

High Risk (Annual Event Rate >5%)

• Extensive ischemia (≥5 reversible segments or summed stress score >13)
• Severely reduced MBF reserve (<1.5)
• Negative LVEF reserve (stress LVEF < rest LVEF) 3, 6
• Significant jeopardized myocardium (Duke score ≥6)

Viability Assessment Protocol

When assessing viability in dysfunctional myocardium, combine perfusion with FDG metabolic imaging 1:

1. First: Perform rest perfusion study to assess baseline perfusion
2. Second: Perform stress perfusion study to detect inducible ischemia
3. Third: Acquire FDG scan 60-90 minutes after tracer injection under glucose loading conditions

Interpretation criteria for viability 1:

• Viable: Rest perfusion >70% of remote myocardium AND FDG uptake >70% of remote myocardium
• Viable: Reduced perfusion with preserved/increased FDG (mismatch)
• Viable: Stress-induced ischemia in dysfunctional segments
• Non-viable: Reduced perfusion AND reduced FDG uptake (match pattern)

Critical Pitfalls to Avoid

1. Balanced Ischemia

• Severe multivessel disease may appear normal on relative perfusion imaging
• Solution: Always assess absolute MBF and MBF reserve quantitatively 2

2. Attenuation Artifacts

• Breast tissue, diaphragm, or body habitus can create false defects
• Solution: Use CT-based attenuation correction (mandatory for PET) and correlate with wall motion 2

3. Caffeine Interference

• Methylxanthines block adenosine receptors, reducing regadenoson effectiveness
• Solution: Ensure 12-hour caffeine abstinence before study 4

4. Timing After Inadequate Exercise

• If regadenoson follows inadequate exercise stress, wait at least 1 hour to avoid serious cardiac adverse reactions 4

5. Reverse Mismatch Pattern

• Reduced FDG uptake despite normal perfusion
• Can occur in non-ischemic cardiomyopathy, LBBB, or diabetes
• May reflect non-ischemic scarring rather than ischemic disease 1

Reporting Structure

Your interpretation should systematically address:

1. Technical quality: Adequate stress response, image quality, attenuation correction
2. Perfusion pattern: Normal, reversible defect, fixed defect, or mismatch
3. Quantitative data: Stress MBF, rest MBF, MBF reserve (if available)
4. Extent and severity: Number of segments involved, summed stress score
5. Functional data: LVEF at rest and stress, LVEF reserve
6. Viability assessment: If applicable, FDG uptake pattern
7. Risk stratification: Low, intermediate, or high risk based on above findings
8. Clinical correlation: Integrate with symptoms, ECG changes, and hemodynamic response

The 2024 ESC guidelines strongly recommend PET myocardial perfusion imaging for patients with moderate to high pre-test probability of obstructive CAD (15-85%), particularly when quantitative flow assessment is needed 2. PET is considered the gold standard for viability assessment due to its superior ability to combine perfusion and metabolic information 1.