Case 15

Published on 02/03/2015 by admin

Filed under Internal Medicine

Last modified 22/04/2025

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Case 15

A 66-year-old man with known severe three-vessel coronary artery disease (CAD) and ischemic cardiomyopathy was referred for myocardial viability assessment.

Heart catheterization demonstrated severe left ventricular systolic dysfunction (left ventricular ejection fraction [LVEF] = 15% to 20%) and severe three-vessel CAD (75% proximal left anterior descending [LAD], 80% proximal circumflex, 80% mid–first obtuse marginal [OM1], 100% proximal right coronary artery [RCA]).

12-Lead ECG

The baseline ECG demonstrates normal sinus rhythm, first-degree AV block, and Q waves suggestive of extensive anterior (and possibly inferior) infarction.

Perfusion and Glucose Metabolism

Rubidium-82 (⁸²Rb) PET MPI demonstrates moderately severe and extensive perfusion defects in the anterior, anteroapical, and anterolateral regions. [¹⁸F]Fluorodeoxyglucose (¹⁸FDG) PET images demonstrate a mild localized area of reduced glucose metabolism in the anteroapical region. The “perfusion-metabolism mismatch” is consistent with preserved myocardial viability and predicts improvement of left ventricular systolic function with revascularization.

Semiquantitative Assessment of Myocardial Perfusion and Glucose Metabolism

The polar plots and 17-segment scoring results confirm that the regional reduction in myocardial perfusion (⁸²Rb) is more severe and extensive than the reduction in glucose metabolism (¹⁸FDG).

Peak stress Perfusion and Glucose Metabolism

The perfusion-metabolism images (shown earlier and shown here again) were actually comparing peak stress myocardial perfusion (using dipyridamole stress) and resting glucose metabolism (¹⁸FDG).

Resting Perfusion and Glucose Metabolism

The images shown here depict resting myocardial perfusion (⁸²Rb) and resting glucose metabolism (¹⁸FDG). This is the more conventional display used for assessment of myocardial viability. Note that the resting perfusion defect is much less severe and extensive than the peak stress perfusion defect (shown previously). The resting perfusion defect is comparable in extent and severity to the resting glucose metabolism defect. This pattern (matched reduction in perfusion and glucose metabolism) implies absence of hibernating myocardium and suggests that the patient is unlikely to benefit from myocardial revascularization. The conclusion derived using the resting ⁸²Rb myocardial perfusion images is completely opposite to the conclusion derived using the peak stress ⁸²Rb perfusion images.

Peak stress and Resting Gated PET Images

Comparison of the peak stress and resting gated PET images also revealed evidence of inducible myocardial ischemia. The computed LVEF declined from 29% at rest to 18% at peak stress. A decline in LVEF at peak stress is an abnormal response to dipyridamole infusion, and it implies the presence of extensive inducible ischemia. The decline in LVEF at peak stress occurred primarily due to an increase in left ventricular end-systolic volume (LVESV). The LVESV increased from 193 mL at rest to 236 mL at peak stress.

Practical Approach to Assessment of Myocardial Viability (See Chapters 37 and 38)

1. Preserved resting perfusion (thallium-201 [²⁰¹Tl], technetium-99m [^99mTc], rubidium-82 [⁸²Rb], nitrogen-13-labeled ammonia [¹³NH₃]) implies myocardial viability.

2. Assessment for inducible ischemia (when clinically feasible) should be included as part of the routine assessment of myocardial viability. The presence of inducible ischemia implies viability and predicts benefit from revascularization. In the present case, the resting and peak stress ⁸²Rb perfusion images and gated PET images demonstrated extensive inducible ischemia (and therefore viability). The ¹⁸FDG metabolism images confirmed the presence of viability but added no additional clinical information.

3. In cases in which there is no detectable ischemia in the myocardial region of interest, ¹⁸FDG PET can be helpful.

An Example in Which ¹⁸FDG Imaging Adds Important Incremental Information to the Assessment of Myocardial Viability

This patient has a severe and extensive nonreversible perfusion defect in the inferior and inferolateral regions (by ⁸²Rb). Based on the perfusion findings alone, this region would appear to be composed of predominantly irreversibly injured (infarcted) myocardium. However, normal myocardial uptake of ¹⁸FDG throughout the defect zone implies preserved glucose metabolism and viable myocardium. In cases such as this (in which there is no detectable ischemia in the myocardial region of interest), ¹⁸FDG PET is especially helpful for clinical decision making.

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