Prevalence of ventricular discordance and its relation to functional capacity in idiopathic dilated cardiomyopathy.

Introduction: Although left ventricular (LV) dilatation is the most distinguishing morphologic feature of idiopathic dilated cardiomyopathy (IDC), right ventricular (RV) dilatation may variably contribute to total cardiac enlargement. The prevalence and functional importance of the relative degree of left and right ventricular dilatation has not been comprehensively studied using cardiac magnetic resonance imaging (MRI).

Methods: Our prospective study included 58 consecutive IDC patients with a LV ejection fraction <40% and NYHA functional class > or =2. MRI was performed with a 1.5 Tesla scanner for RV and LV dimensional and functional analysis. Cardiopulmonary exercise testing was used for evaluation of exercise capacity. Patients were grouped into tertiles based on the distribution of LV end-diastolic volume.

Results: Compared to control subjects a considerable heterogeneity in the relative degree of left and right ventricular dilatation was noted in IDC patients. Within the entire patient group, a strong correlation between the degree of ventricular volume discordance and the extent of LV enlargement was observed (r = 0.8; P < 0.001). Tertile analysis revealed that the LV/RV volume ratio significantly differed in the three subgroups of patients (1.0 +/- 0.3 vs. 1.5 +/- 0.4 vs. 2.1 +/- 0.9; P < 0.001). Only weak correlations between MRI data and patients' functional capacity were found. LV ejection fraction was identified as the only independent predictor of maximum oxygen consumption in our setting.

Conclusion: In IDC patients the degree of ventricular volume discordance is strongly related to the extent of left ventricular enlargement. However, comprehensive biventricular assessment of cardiac function by MRI adds little to our understanding of the cardiac mechanisms limiting exercise tolerance when compared to exclusive left ventricular measurements.