What does an abnormal Myocardial Perfusion Imaging (MPI) stress study indicate?

Abnormal MPI Stress Study Meaning

An abnormal Myocardial Perfusion Imaging (MPI) stress study indicates the presence of myocardial ischemia and/or infarction, identifying significant coronary artery disease (CAD) that may require intervention to reduce the risk of cardiac death or myocardial infarction. 1

What MPI Shows and Its Diagnostic Value

Stress SPECT MPI reveals:

• Perfusion defects: Areas of reduced blood flow to the heart muscle
• Reversibility: Distinguishes between:
  • Reversible defects (ischemia) - improve at rest
  • Irreversible defects (infarction) - persist at rest 1
• Territory involvement: Identifies which coronary artery is likely involved 1
• Disease extent: Distinguishes between single-vessel and multivessel coronary disease 1

The diagnostic accuracy of stress SPECT MPI for detecting angiographically significant CAD is high with:

• Sensitivity: 87-89%
• Specificity: 73-75% 1

Clinical Significance of Abnormal Results

An abnormal MPI stress test has significant prognostic implications:

1. Mortality risk: The extent and severity of ischemia and scarring provide powerful predictors of cardiac death risk 1

2. Vessel-specific information:

   • Multivessel fixed defects are associated with the highest cardiac death rates (13.6% in diabetics) 2
   • Three-vessel ischemia correlates with the highest myocardial infarction rates 2

3. Risk stratification: Identifies patients who would benefit from revascularization versus those who can be managed medically 1

4. Prognostic value: Provides long-term risk assessment - abnormal results predict major adverse cardiac events over periods as long as 11 years 3

Interpreting Different Types of Abnormalities

Type of Defect	Clinical Meaning	Management Implications
Reversible defect	Active ischemia - inadequate blood flow during stress	May benefit from revascularization [1]
Fixed defect	Prior infarction/scarring	Higher cardiac death risk, especially if multivessel [2]
Size/extent of defect	Correlates with disease severity	Larger defects indicate worse prognosis [1]

Important Considerations

1. Normal vs. Abnormal: A normal stress SPECT MPI in patients with intermediate to high likelihood of CAD predicts a very low rate (1% per year) of cardiac death or nonfatal MI 1

2. Special populations: Diabetic patients with abnormal MPI have worse outcomes, with diabetic women showing the poorest prognosis for any given extent of ischemia 2

3. False positives: The yield of stress MPI can be low in certain populations, such as those presenting with syncope without known CAD 4

4. Hybrid imaging: Combining SPECT with coronary CT angiography (CCTA) enhances diagnostic accuracy (sensitivity 96%, specificity 95%) compared to either modality alone 1

5. Limitations: Despite high sensitivity, specificity can be lower (52-75%), meaning some abnormal results may not correlate with significant stenosis on angiography 1

Clinical Applications

The American College of Cardiology recommends stress MPI for:

• Assessment of known or suspected CAD
• Risk stratification
• Evaluation after myocardial infarction 5

MPI is particularly valuable in patients with:

• Baseline ECG abnormalities
• Left bundle branch block
• Paced rhythm 5

By identifying both the presence and extent of myocardial ischemia or infarction, an abnormal MPI stress study provides crucial information for determining appropriate management strategies and assessing long-term cardiovascular risk.