Left Bundle Branch Block Negatively Affects Coronary Flow Velocity Reserve and Myocardial Contractile Reserve in Nonischemic Dilated Cardiomyopathy

Background: Coronary flow velocity reserve (CFVR) of the left anterior descending coronary artery (LAD) and myocardial contractile reserve are often impaired in nonischemic dilated cardiomyopathy (DCM). Whether they are affected by the presence of left bundle branch block (LBBB) remains unaddressed. The aim of the study was to investigate how LBBB influences CFVR of the LAD and myocardial contractile reserve in patients with DCM. Methods: One hundred eighty-one patients with DCM (116 men; mean age, 63 +/- 12 years) underwent high-dose dipyridamole (0.84 mg/kg over 6 min) stress echocardiography with CFVR evaluation of the LAD by Doppler. All patients had ejection fractions < 40% (mean, 31 +/- 8%) and angiographically normal or near normal coronary arteries. CFVR was defined as the ratio between hyperemic peak and basal peak diastolic coronary flow velocities. CFVR > 2.0 was considered normal. Inotropic reserve was defined as rest-stress variation in wall motion score index >= 0.20. This was a prospective analysis of an unselected sample consecutively enrolled and retrospectively selected. Results: The study group was separated on the basis of presence (n = 122) or absence (n = 59) of LBBB. Patients with LBBB were older (64 +/- 11 vs 59 +/- 12 years, P = .004) and had reduced resting ejection fractions (30 +/- 9% vs 33 +/- 7%, P = .02), CFVR of the LAD (1.96 +/- 0.41 vs 2.23 +/- 0.73, P = .001), and myocardial contractile reserve (variation in wall motion score index, -0.18 +/- 0.17 vs -0.33 +/- 0.28; P < .001). On multivariate logistic regression analysis, resting ejection fraction (hazard ratio [HR], 1.15; 95% CI, 1.03-1.29; P = .01), smoking habit (HR, 2.63; 95% CI, 1.23-5.62; P = .01), and LBBB (HR, 2.29; 95% CI, 1.05-5.04; P = .04) were independently associated with reduced CFVR, while restrictive transmitral pattern (HR, 2.56; 95% CI, 1.18-5.55; P = .02), end-diastolic volume (HR, 0.98; 95% CI, 0.67-0.99; P = .02), and LBBB (HR, 2.20; 95% CI, 1.11-4.34; P = .02) independently predicted reduced myocardial contractile reserve. Conclusions: CFVR during vasodilator stress echocardiography is a suitable tool for assessing microvascular dysfunction in routine clinical practice. Patients with DCM and LBBB show more severe forms of microvascular dysfunction, which is related to worse left ventricular function and lack of contractile reserve. Therapeutic interventions to restore microvascular function may improve left ventricular function parameters in patients with DCM.