Chest Pain in a Patient with Known CAD and a Nondiagnostic Stress Test
A 64-year-old man with a history of a 3-vessel CABG 6 years ago presents with 2 weeks of exertional chest pressure relieved by rest. He has hypertension, type 2 diabetes, and a BMI of 34. He completed a treadmill ECG stress test that was stopped at 6 minutes for fatigue; the ECG showed 1.5 mm of downsloping ST depression in leads V4-V6 at peak, but he did not develop his typical symptoms. Baseline ECG has a left bundle branch block. Resting LVEF by echocardiogram is 48%. He is on metoprolol, which was held for 24 hours before the test. Renal function is normal (eGFR 88). The referring physician asks whether he needs a stress nuclear study or should go straight to catheterization.
1. Which stress modality (exercise vs. pharmacologic) and which radiotracer/imaging approach would you select, and why? Address the LBBB and beta-blocker issues explicitly.
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The baseline LBBB makes exercise ECG interpretation unreliable and, more importantly, exercise perfusion imaging in LBBB can produce false-positive septal defects from septal dyssynchrony. Vasodilator stress (regadenoson or adenosine) is preferred in LBBB because it avoids the rate-dependent septal artifact and does not depend on achieving target heart rate. Beta-blocker therapy (held only 24 h) further argues against relying on an exercise endpoint. Given a normal eGFR, a technetium-99m perfusion agent (sestamibi or tetrofosmin) is preferred over thallium for better image quality and lower dose, particularly in a large patient (BMI 34). If attenuation is a concern, consider attenuation correction or a PET rubidium-82/ammonia study, which has superior specificity. The appropriate next step is a pharmacologic stress myocardial perfusion study, not automatic catheterization, because the prior ECG stress test was submaximal and confounded by LBBB.
2. The regadenoson study shows a moderate-sized, partially reversible defect in the inferior wall with transient ischemic dilation but no true fixed defect. How do you interpret this in a post-CABG patient, and what does it change?
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A partially reversible inferior defect in a post-CABG patient raises concern for graft disease, particularly to the RCA or a dominant circumflex, or native-vessel progression. Transient ischemic dilation adds prognostic weight and suggests a larger territory of ischemia than the defect alone implies. However, inferior defects are also prone to diaphragmatic attenuation artifact, so the interpreter should confirm reversibility on both rest and stress, review raw projections, and consider attenuation correction before calling it true ischemia. If confirmed, the finding is high-risk enough to warrant invasive angiography with graft evaluation rather than continued medical management, and it also justifies intensifying antiplatelet and statin therapy and re-evaluating diabetic control. The key judgment is not to dismiss a reversible inferior defect as artifact in a patient with known graft disease and a submaximal prior test.