Phasic coronary flow pattern and flow reserve in patients with left bundlebranch block and normal coronary arteries

OBJECTIVES The purpose of this study was to determine whether scintigraphic myocardial perfusion defects in patients with left bundle branch block (LB BB) and normal coronary arteries are related to abnormalities in coronary f low velocity pattern and/or coronary flow reserve. BACKGROUND Septal or anteroseptal defects on exercise myocardial perfusion scintigraphy are common in patients with LBBB and normal coronary arteries. METHODS Thirteen patients (7 men, age 61 +/-: 8 years) with LBBB and normal coronary arteries underwent stress thallium-201 scintigraphy and cardiac c atheterization. In all patients and in 11 control subjects coronary blood f low parameters were calculated from Doppler measurements of flow velocity i n the left anterior descending coronary artery (LAD) before and after adeno sine administration. RESULTS The time to maximum peak diastolic flow velocity was significantly longer both for the seven patients with (134 +/-: 19 ms) and for the six wi thout (136 +/- 7 ms) exercise perfusion defects than for controls (105 +/- 12 ms, p < 0.05), whereas the acceleration was slower (170 +/- 54, 186 +/- 42 and 279 +/- 96 cm/s(2), respectively p < 0.05). Coronary flow reserve in the patients with exercise perfusion defects (2.7 +/- 0.3) was significant ly lower than in those without (3.7 +/- 0.5, p < 0.05) or in the control gr oup (3.4 +/- 0.5, p < 0.05). CONCLUSIONS Patients with LBBB have an impairment of early diastolic blood flow in the LAD due to an increase in early diastolic compressive resistanc e resulting from delayed ventricular relaxation. Furthermore, exercise scin tigraphic perfusion defects in these patients are associated with a reduced coronary flow reserve, indicating abnormalities of microvascular function in the same vascular territory (C) 1999 by the,American College of Cardiolo gy.