What is the interpretation of a SPECT myocardial perfusion imaging study showing mild tracer attenuation and a left ventricular ejection fraction of 50% in an adult patient with a history of cardiovascular issues or risk factors, presenting with typical atrial flutter?

Interpretation of SPECT Myocardial Perfusion Study in Patient with Typical Atrial Flutter

This study reveals moderate-risk findings requiring coronary angiography evaluation, as the combination of inferior wall perfusion abnormalities (both at rest and stress), regional hypokinesis, borderline LVEF of 50%, and typical atrial flutter presentation strongly suggests underlying coronary artery disease that warrants invasive assessment. 1, 2

Critical High-Risk Features Present

Your study demonstrates several concerning findings that elevate cardiovascular risk:

• Inferior wall perfusion defects present at both rest (basal and mid segments, moderate severity) and stress (mid segment, mild severity), with Summed Rest Score of 8 and Summed Stress Score of 5 3, 2
• Regional wall motion abnormality (inferior hypokinesis) indicating either prior infarction or severe ischemia 1, 2
• Borderline reduced LVEF of 50%, which falls at the lower limit of normal and represents compromised left ventricular systolic function 3
• Suboptimal exercise performance with only 78% of target heart rate achieved and exercise time of 4:34 minutes on Bruce protocol, indicating reduced functional capacity 1

Typical Atrial Flutter as a Coronary Disease Marker

The presence of typical atrial flutter in this clinical context is particularly significant:

• Typical atrial flutter strongly predicts underlying coronary artery disease in previously asymptomatic patients, with studies showing CAD with >50% stenosis in 26.3% of atrial flutter patients versus only 7% in atrial fibrillation patients 4
• Multivessel disease occurs in 10.5% of typical atrial flutter patients, representing a more than five-fold increased likelihood of significant CAD compared to atrial fibrillation 4
• The American College of Cardiology/American Heart Association guidelines recognize that atrial flutter patients have similar thromboembolic risk as atrial fibrillation and often have underlying structural heart disease 3

Perfusion Pattern Analysis

The specific perfusion abnormalities require careful interpretation:

• Rest perfusion defects (SRS = 8, which is ≥4) in the inferior wall suggest either prior myocardial infarction or hibernating myocardium 3, 2
• Persistent abnormalities at stress (SSS = 5) with inferior hypokinesis indicate compromised myocardial viability in this territory 3
• The moderate size and moderate severity of rest defects represent a substantial portion of myocardium at risk 3, 2
• Normal TID ratio of 1.07 (threshold typically >1.2) argues against severe three-vessel or left main disease, though this does not exclude significant single or two-vessel disease 2

Technical Considerations and Potential Artifacts

While the study quality is satisfactory, certain technical factors warrant consideration:

• Inferior wall attenuation is common in SPECT imaging and can produce false-positive defects, but the presence of both rest and stress abnormalities with corresponding wall motion abnormality makes true perfusion defect more likely than artifact 3
• The use of Technetium-99m based tracer (Tetrofosmin) provides superior image quality compared to Thallium-201, particularly for detecting true perfusion abnormalities versus attenuation artifacts 3
• Gated SPECT imaging showing regional hypokinesis in the same territory as perfusion defects strongly supports true ischemia/infarction rather than artifact 3

Recommended Management Pathway

Immediate actions:

• Coronary angiography is indicated based on the combination of perfusion abnormalities, wall motion abnormality, borderline LVEF, and typical atrial flutter presentation suggesting underlying CAD 1, 2, 4
• The American Heart Association recommends invasive evaluation for patients with extensive wall motion abnormalities and reduced ejection fraction 1, 2

Medical optimization pending angiography:

• Intensify guideline-directed medical therapy including antiplatelet therapy, high-intensity statin, beta-blocker, and ACE inhibitor/ARB 2
• Aggressive risk factor modification targeting hypertension, diabetes control, and smoking cessation 2
• Anticoagulation for atrial flutter following ACC/AHA guidelines, as thromboembolic risk equals that of atrial fibrillation 3

Post-angiography strategy:

• If significant CAD is identified, revascularization (PCI or CABG) should be considered based on anatomy and extent of disease 1, 2
• Catheter ablation of the cavotricuspid isthmus should be considered for typical atrial flutter, as it is superior to medical management for rhythm control 3, 5
• Repeat stress imaging at 3-5 years post-revascularization in high-risk asymptomatic patients, or earlier if symptoms recur 1, 2

Critical Pitfalls to Avoid

• Do not dismiss inferior wall abnormalities as solely attenuation artifact when accompanied by wall motion abnormality and clinical context suggesting CAD 2
• Do not delay angiography in patients with combined perfusion defects, wall motion abnormalities, and borderline LVEF, as this represents elevated mortality risk 1, 2
• Do not underestimate the significance of typical atrial flutter as a marker of silent coronary disease, particularly with CHA₂DS₂-VASc score considerations 4
• Globally reduced perfusion should not be ignored, as it may represent balanced multivessel disease, though your TID ratio argues against this 2