Background: Reduced septal uptake of 201-Thallium in patients with left bundle branch block is reported in literature as having a variable frequency (between 14% and 100%) and in such patients the value of exercise Thallium-scintigraphy for the diagnosis of the left anterior descending coronary artery disease is limited by the great number of false-positive tests. The aim of this study was to assess the prevalence and the diagnostic sensitivity of this septal defect in a group of patients with left bundle branch block.
Methods: We evaluated the exercise 201-Thallium myocardial scintigraphy of 54 patients with a stable left bundle branch block. The clinical and/or echocardiographic evaluation excluded the presence of primitive, valvular and hypertensive cardiomyopathies and of previous myocardial infarction. The planar myocardial scintigraphic imaging was acquired according to the "stress-redistribution" protocol. Only 37 patients underwent an echocardiographic examination and following clinical and/or scintigraphic indications; 27 patients underwent a coronary angiography for the evaluation of coronary stenosis.
Results: The 201-Thallium imaging showed septal defects in 36 patients (67%) and the presence of defects in other segments in 14 patients. The echocardiographic evaluation showed an interventricular septal defect contraction abnormality in 19 cases in the 27 patients with septal defect and in 4 cases in the 10 patients with negative scintigraphy (Fisher NS). Twenty-seven patients (23 with- and 4 without septal defect) underwent a coronary angiography, which showed in 6 cases critical stenosis of the left descending anterior artery, in 5 of the right coronary, in 3 of the Circumflex artery and in 16 normal coronary angiograms. The presence of the septal uptake defect showed a diagnostic sensitivity and specificity for the detection of the left anterior descending coronary artery disease of respectively 67% and 52% (whereas using a semi-quantitative analysis of 100% and 19%). The scintigraphy showed a sensitivity and specificity for the detection of the right coronary artery disease of respectively 80% and 100% and for the circumflex coronary artery stenosis of 0% and 100%.
Conclusions: We found a high prevalence of septal perfusion defects (67%) and this results shows a high sensitivity but a low specificity for the diagnosis of the left anterior descending coronary disease; the semi-quantitative analysis improves the sensitivity, but leads to a further reduction of the specificity. The female patients had a prevalence (70%) similar to the general population but demonstrated a higher percentage of false-positive. The 201-Thallium scintigraphy has a high diagnostic accuracy for the detection of the right coronary artery stenosis, while it is less accurate regarding the circumflex artery disease.