Nuclear Medicine · Supplementary · from Nuclear Medicine
Case 2: Myocardial Perfusion Imaging for CAD
Patient Presentation
Demographics: 59-year-old male construction foreman
Chief Complaint: "I get chest tightness when I walk uphill at work."
History of Present Illness: A 59-year-old male construction foreman presents with a 3-month history of exertional chest tightness. The discomfort occurs when he walks uphill to construction sites or climbs stairs carrying equipment. It is described as a pressure-like sensation across his anterior chest, occasionally radiating to his left shoulder. The symptoms resolve within 3-5 minutes of rest. He has not experienced chest pain at rest, nocturnal symptoms, or dyspnea on exertion beyond what he attributes to the chest tightness. The symptoms have been gradually worsening; 3 months ago they occurred only with heavy lifting, but now occur with moderate uphill walking.
His primary care physician performed an initial assessment. His pre-test probability for coronary artery disease was estimated at 65% using the Duke Clinical Score (age, sex, symptoms). Given his intermediate pre-test probability and ability to exercise, he was referred for exercise myocardial perfusion imaging (MPI) with Tc-99m sestamibi SPECT.
Past Medical History:
- Hypertension (10 years)
- Type 2 diabetes mellitus (5 years)
- Hyperlipidemia
- Obesity (BMI 30.8)
- No prior cardiac history
Medications:
- Metoprolol succinate 50 mg daily (held 48 hours prior to stress test per protocol)
- Lisinopril 20 mg daily
- Metformin 1000 mg BID
- Atorvastatin 40 mg daily
- Aspirin 81 mg daily
Social History:
- Construction foreman, physically demanding work
- Former smoker (quit 2 years ago, 20 pack-year history)
- 1-2 beers on weekends
- Married, three children
- Diet: fast food 3-4 times per week
Family History:
- Father: MI at age 62, survived with stenting
- Brother: MI at age 55
Physical Examination
- Vital Signs: BP 142/88 mmHg, HR 74 bpm (off beta-blocker), RR 14/min, Temp 36.8°C, SpO2 98% on room air, BMI 30.8
- General: Stocky, muscular male in no acute distress
- Cardiovascular: Regular rate and rhythm, no murmurs, S4 gallop at apex, no S3
- Lungs: Clear bilaterally
- Abdomen: Obese, soft, non-tender
- Extremities: No edema, pulses 2+ throughout
Workup and Results
Laboratory Studies:
| Test | Result | Reference Range |
|---|---|---|
| Fasting glucose | 148 mg/dL | 70-100 mg/dL |
| HbA1c | 7.8% | <7.0% |
| Total cholesterol | 228 mg/dL | <200 mg/dL |
| LDL | 132 mg/dL | <100 mg/dL |
| HDL | 36 mg/dL | >40 mg/dL |
| Triglycerides | 298 mg/dL | <150 mg/dL |
| Creatinine | 1.0 mg/dL | 0.7-1.3 mg/dL |
| Resting ECG | Normal sinus rhythm, no ST-T changes | - |
Imaging/Additional Studies:
- Exercise Stress Test (Bruce Protocol):
- Exercise duration: 7 minutes 12 seconds (Stage 3)
- Peak HR: 148 bpm (92% of age-predicted maximum -- adequate stress)
- Peak BP: 198/94 mmHg
- Symptoms: Reproduced typical chest tightness at 6 minutes, resolved in recovery
- ECG: 2 mm horizontal ST-segment depression in leads V4-V6 at peak exercise, resolving in recovery
- Duke Treadmill Score: -8 (moderate risk)
- Tc-99m Sestamibi SPECT Myocardial Perfusion Imaging:
- Stress images: Moderate-sized, moderate-intensity reversible perfusion defect in the anterior wall and anteroseptum (LAD territory), involving approximately 15% of the left ventricular myocardium
- Rest images: Normal perfusion throughout (complete reversibility confirms ischemia, not infarction)
- Gated SPECT: LVEF 58%, normal wall motion at rest, anterior wall hypokinesis on post-stress gated images (ischemic stunning)
- Transient ischemic dilation (TID): Present (stress/rest LV cavity ratio 1.18; abnormal >1.12) -- suggests extensive ischemia or multivessel disease
- Summed Stress Score (SSS): 12 (moderate ischemia)
- Summed Difference Score (SDS): 10 (moderate reversible ischemia)
Clinical Image
Diagram showing a bull's-eye (polar) map display of myocardial perfusion SPECT imaging comparing stress and rest images, with color scale indicating normal perfusion versus reversible ischemic defects in the LAD coronary artery territory. Source: Educational illustration.
Diagnosis
Exercise-Induced Myocardial Ischemia in the LAD Territory (Moderate-Sized Reversible Perfusion Defect), Consistent with Hemodynamically Significant Coronary Artery Disease
Key Diagnostic Criteria:
- Reproducible exertional angina during stress test
- 2 mm horizontal ST depression on stress ECG (V4-V6)
- Moderate-sized reversible perfusion defect in anterior wall and anteroseptum (LAD territory)
- Complete reversibility on rest images (no infarction)
- Transient ischemic dilation (TID) present, suggesting extensive ischemia
- Post-stress wall motion abnormality (ischemic stunning)
- SSS 12 and SDS 10 indicating moderate ischemic burden (>10% ischemic myocardium)
Treatment Plan
- Cardiac catheterization: Recommended given >10% ischemic myocardium on SPECT and high-risk features (TID, ischemic stunning); coronary angiography with FFR-guided PCI if appropriate
- Optimize medical therapy:
- Restart metoprolol succinate 50 mg, titrate to HR 55-60
- Start long-acting nitrate (isosorbide mononitrate 30 mg daily) for angina
- Increase atorvastatin to 80 mg daily (target LDL <70)
- Add ezetimibe if LDL not at goal
- Diabetes optimization: Add SGLT2 inhibitor (empagliflozin 10 mg) for cardiovascular benefit
- Lifestyle modification: Cardiac rehabilitation referral, Mediterranean diet counseling, weight loss goal of 10%
- Activity modification: Avoid heavy exertional activity until revascularization decision
- Follow-up MPI: If treated medically, repeat in 1-2 years to assess ischemic burden
Key Learning Points
- Myocardial perfusion imaging with Tc-99m sestamibi SPECT evaluates the physiological significance of coronary artery stenoses by detecting relative differences in myocardial blood flow between stress and rest
- A reversible perfusion defect indicates ischemia (viable myocardium with flow-limiting stenosis), while a fixed defect indicates scar/infarction
- Transient ischemic dilation (TID) is a high-risk finding on SPECT that suggests extensive ischemia, balanced multivessel ischemia, or subendocardial hypoperfusion
- The summed difference score (SDS) quantifies the extent of reversible ischemia; >10% ischemic myocardium is the threshold at which revascularization may provide survival benefit over medical therapy alone
- Exercise stress is preferred over pharmacologic stress when the patient can exercise adequately (achieving >85% age-predicted maximum heart rate) as it provides additional prognostic information from exercise capacity and hemodynamic response