We report myocardial perfusion SPECT pattern in four subsequent
patients with rate dependent left bundle branch block
(LBBB). Three females and one male (aged 48, 51, 63 and 67
years) were studied. None of the patients had history of typical
chest pain and all suffered from atypical chest pain or dyspnea
on exertion. All patients were tested for baseline and serial heart
rate, blood pressure, and electrocardiogram recordings. The
exercise treadmill tests (ETT) were carried out under the strict
supervision of a cardiologist, a nuclear medicine physician and
close availability of an expert cardio-pulmonary resuscitation team
and cardiac care unit within just few seconds. Maximal stress test
(at least 85% of calculated heart rate, following development of
LBBB) was achieved in all four patients according to standard
Bruce protocol. No adverse cardiac events were noted and all
ETT stress protocols terminated completely and safely. Myocardial
perfusion SPECT imaging showed no evidence of reversible
perfusion defects. The only patient with past history of exercise
induced LBBB showed nonreversible perfusion defects in the
septal and anteroseptal regions and mild LV cavity dilatation. The
limited number of patients enrolled in our study does not allow us to
draw a definite conclusion. Despite the presence of false-positive
defects in myocardial perfusion SPECT in patients with sustained  LBBB, such a finding is not a consistent finding in patients with
rate dependent or exercised-induced LBBB, unlike that which we
expected to see. Maybe it is possible to continue ETT for those
patients undergoing myocardial perfusion scintigraphy and developing
rate dependent LBBB.