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(Circulation. 2008;117:1832-1841.)
© 2008 American Heart Association, Inc.

Imaging

Effects of Left Bundle-Branch Block on Cardiac Structure, Function, Perfusion, and Perfusion Reserve

Implications for Myocardial Contrast Echocardiography Versus Radionuclide Perfusion Imaging for the Detection of Coronary Artery Disease

S.A. Hayat, MBChB, MRCP; G. Dwivedi, MD, DM, MRCP; A. Jacobsen, MD; T.K. Lim, MD; C. Kinsey, HND; R. Senior, MD, DM, FRCP, FESC

From the Department of Cardiology and Institute of Postgraduate Medical Education and Research, Northwick Park Hospital, Harrow, UK.

Correspondence to Professor Roxy Senior, MBBS, MD, DM, FRCP, FESC, FACC, Consultant Cardiologist and Director of Cardiac Research, Honorary Professor, Middlesex University London, Honorary Senior Lecturer, Imperial College, London, Department of Cardiology, Northwick Park Hospital, Harrow HA1 3UJ, UK. E-mail roxysenior{at}cardiac-research.org

Received February 22, 2007; accepted January 22, 2008.

Background— We aimed to investigate the cardiac effects of left bundle-branch block (LBBB) using myocardial contrast echocardiography (MCE) to ascertain the value of MCE for detecting coronary artery disease (CAD) and to uncover the mechanism that affects the accuracy of single-photon emission computed tomography (SPECT) in these patients.

Methods and Results— Sixty-three symptomatic LBBB patients (group A), 10 left ventricular ejection fraction–matched control subjects without LBBB and no CAD (group B), and 10 normal control subjects (group C) underwent resting echocardiography. Rest and vasodilator MCE and SPECT were undertaken in LBBB patients. Septal (SW) and posterior wall (PW) thickness, thickening, quantitative myocardial blood flow (MBF), and MBF reserve were measured. SW/PW thickness and percentage thickening ratios were lower (P<0.01 and P<0.05, respectively) in group A compared with both groups B and C, but resting SW/PW MBF and MBF reserve ratios were similar in all 3 groups. MBF reserve but not MBF was reduced in groups A and B (2.2±0.7 versus 2.2±0.2; P=0.98) compared with group C (3.1±0.5; P<0.01). SW thickness was an independent predictor (P=0.006) of SPECT perfusion defects in LBBB patients without CAD. MCE (92%) had a sensitivity similar to SPECT (92%); however, the specificity of MCE (95%) was superior (P<0.0001) to SPECT (47%) for the detection of CAD.

Conclusions— Despite asymmetrical reduction in SW thickness and function, MBF is preserved and MBF reserve is homogeneously reduced in LBBB patients with left ventricular systolic dysfunction. Because of partial volume effects, the accuracy of SPECT for detecting CAD was significantly compromised compared with MCE in this patient cohort.

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CLINICAL PERSPECTIVE

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Clinical Summaries
Circulation 2008 117: 1769. [Full Text]

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