Diagnosis of exercise-induced left bundle branch block at rest by scintigraphic phase analysis

Accurate diagnosis of diseases of the ventricular conducting system is essential for their appropriate therapy. Some conduction abnormalities, such as exercise-induced left bundle branch block (EX-LBBB), are not apparent on resting electrocardiograms. Phase analysis of rest and exercise radionuclide ventriculograms (RVG's) was used to compare four EX-LBBB patients with six normal controls. All patients had normal resting electrocardiograms, ejection fractions, and visually normal wall motion. First harmonic phase images were generated reflecting the timing of ventricular contraction. Dynamic phase displays were reviewed and graded in a blinded fashion by three independent experienced observers. Phase angle histograms of the right and left ventricle were determined for both resting and exercise images. The mean phase angle and standard deviation were also calculated for each ventricle. Visual grading of the resting phase images failed to show a significant difference between normal patients and patients with EX-LBBB. Quantitative analysis, however, revealed a significant difference in mean phase angle differences (LV-RV) in resting studies: 0.8 degrees (+/- 1.9 degrees SEM) in normals versus 9.3 degrees (+/- 2.3 degrees SEM) in EX-LBBB patients (P less than 0.03). Exercise accentuated the phase angle differences: 1.8 degrees in normals vs. 31.2 degrees in EX-LBBB patients (P less than 0.001). Quantitative phase analysis of resting RVG's permits the diagnosis of cardiac conduction disease that is not apparent on the resting EKG and may result in better monitoring and treatment.