Introduction Asymptomatic left bundle branch block (LBBB) is a common indication for referral for cardiovascular magnetic resonance (CMR) imaging. However, it is not known whether referral for LBBB returns a high diagnostic yield. We evaluated the diagnostic value of CMR in these patients.

Methods All clinical CMR referrals for LBBB from January 2005 to November 2010 were reviewed by two independent investigators. Only patients with asymptomatic LBBB and normal echocardiograms (echos) who underwent complete CMR evaluation were included in the study. Patients were excluded if they had cardiac symptoms or known coronary artery disease. Anthropometric data, pre-existing conditions, medications, smoking status, family history and echocardiographic data were recorded.

Results From January 2005 to November 2010, 63 asymptomatic patients with LBBB were referred to our institution for CMR from a total of 3596 CMR referrals. Of these, 34 had normal echos; 20 subjects who had abnormal echos and 9 who had no echos at presentation were excluded from further analysis. Mean age of the 34 patients with normal echos was 54±9 years, and 19 (56%) were men. Demographic data and left ventricular (LV) measurements are presented in the Abstract 119 table 1. The most common associated medical conditions were hypertension (11 patients—33%) and hyperlipidaemia (8 patients—24%). Ten subjects (30%) had a family history of heart disease. Nine (27%) patients underwent coronary angiography which was normal. Of the 34 patients, 14 (41%) were found to have pathological findings on CMR. The commonest abnormalities were dilated cardiomyopathy (DCM) (23%), followed by LV hypertrophy (LVH—defined as LV wall thickness >13 mm) (9%), arrhythmogenic right ventricular cardiomyopathy (ARVC) (6%) and Ebstein anomaly (3%). Two patients (6%) had mid wall late gadolinium enhancement. In the remaining 20 (59%) patients, no abnormalities on CMR were detected.

Conclusions There is a high rate of sub-clinical cardiomyopathy (41%) detected by CMR in asymptomatic patients with LBBB despite normal echocardiograms. These findings support the claim that CMR is a valuable adjunct to conventional investigations in asymptomatic LBBB. Further studies are needed to evaluate the prognostic implications of CMR abnormalities in this cohort of patients.

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Abstract 119 Figure 1

CMR findings in asymptomatic patients with LBBB and normal echocardiogram.