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Thallium-201 scintigraphy in complete left bundle branch block
Insights
Left bundle branch block (LBBB) can cause false positives for coronary artery disease (CAD) on thallium-201 (TI-201) scans. This study shows LBBB can mimic ischemia due to asynchronous septal contraction, not necessarily CAD.
Area of Science:
- Cardiology
- Nuclear Cardiology
- Diagnostic Imaging
Background:
- Left bundle branch block (LBBB) can complicate the interpretation of myocardial perfusion imaging.
- Anteroseptal perfusion defects are common in patients with LBBB, raising concerns for coronary artery disease (CAD).
Purpose of the Study:
- To investigate whether LBBB itself can cause septal perfusion defects on thallium-201 (TI-201) exercise scintigraphy.
- To differentiate between true CAD-induced ischemia and LBBB-induced artifacts in symptomatic patients.
Main Methods:
- Evaluated 19 symptomatic patients with LBBB using TI-201 exercise scintigraphy and coronary arteriography.
- Induce LBBB in dogs via right ventricular pacing and assessed TI-201 uptake and myocardial blood flow using radioactive microspheres.
Main Results:
- Significant anteroseptal perfusion defects were observed in most LBBB patients, but only 4 had significant CAD.
- In dogs, induced LBBB led to reduced septal TI-201 uptake (69%) and myocardial blood flow (89 ml/min/100 g) compared to the lateral wall.
- These findings suggest LBBB can cause apparent septal ischemia.
Conclusions:
- Symptomatic patients with LBBB may exhibit abnormal TI-201 exercise scintigrams suggestive of anteroseptal ischemia, even with normal coronary arteries.
- Induced LBBB in dogs mimics these findings, indicating that septal perfusion defects in LBBB patients may result from asynchronous septal contraction rather than CAD.
Abstract:
Nineteen symptomatic patients with left bundle branch block (LBBB) were examined by thallium-201 (TI-201) exercise scintigraphy and selective coronary arteriography. All elicited significant anteroseptal perfusion defects in the exercise scintigrams, but in only 4 was coronary artery disease (CAD) involving the left anterior descending coronary artery present. To further elucidate the effect of LBBB on septal TI-201 uptake in the absence of CAD, TI-201 scintigrams combined with regional myocardial blood flow measurements using radioactive microspheres were carried out in 7 dogs during right atrial and right ventricular pacing (LBBB in the ECG) at similar heart rates. During right atrial pacing, TI-201 uptake was homogeneous in the entire left ventricle, as were tissue flows. During right ventricular pacing, TI-201 activity was reduced to 69% of maximal TI-201 activity within the septum, whereas it averaged 90% in the lateral wall (p less than 0.05) in 6 dogs. Correspondingly, regional myocardial blood flow was lower within the septum as compared with that in the lateral wall, averaging 89 and 120 ml/min/100 g, respectively (p less than 0.005). In 1 dog, normal TI-201 distribution and tissue flows were found in both studies. Thus, symptomatic patients with LBBB may elicit abnormal TI-201 exercise scintigrams, suggesting anteroseptal ischemia despite normal coronary arteries. The electrical induction of LBBB in dogs results, in most instances, in a comparable reduction in septal TI-201 uptake associated with diminished septal blood flow. Therefore, exercise-induced septal perfusion defects in the presence of LBBB do not necessarily indicate CAD even in symptomatic patients, but may reflect functional ischemia due to asynchronous septal contraction.