Sudden death is a public health issue and is related to malignant ventricular arrhythmias in 80%. Structural heart diseases may be involved, sometimes detected by ECG abnormalities. Increase in QRS duration is an accepted marker for arrhythmic events. However, consequences of decreased QRS durations are unknown. Some genetic cardiomyopathies may be associated with very narrow QRS.

To determine the association between an increased left ventricular mass (LVM) in a population of sarcomeric hypertrophic cardiomyopathy (HCM) and left ventricular non compaction (LVNC) population and a shortened duration of ventricular depolarization.

4 groups were retrospectively formed: HCM, LVNC, post hypertensive Hypertrophy Left Ventricular (LVH) and controls. Indexed automatic LVM on MRI was correlated to automatic measurement of QRS duration on ECG. Potential confounding factors that can modify intraventricular conduction were collected.

Our population includes 221 patients with HCM, 28 with LVNC, 16 patients with LVH and 40 controls. Median QRS duration was 92ms (95% CI 81–96) for HCM, 104ms (95% CI 82–124) for LVNC, 110ms (95% CI 92–128) for LVH and 92ms (95% CI 85–96) for controls (P<0.01). LVM was 100g/m² (95% CI 80–115), 90g/m² (95% CI 75–100), 108g/m² (95% CI 78–123) and 68g/m2 (95% CI 59–76) respectively (P<0,01). A negative correlation was found between LVM and QRS duration in the HCM group (rho=−0.22, P=0.03). The relationship is the opposite in LVNC (rho=0.46, P=0.01), LVH (rho=0.13, P=0.62) and controls (rho=0.35, P=0.29). Multivariate analysis confirms this trend with significant results.

QRS duration increases with LVM in the case of NCVG, HVG or without heart disease, while it decreases with increasing LVM in the case of HCM. This could reflect a more developed Purkinje network, with better electrical synchronization and faster ventricular activation. These results could be used as diagnostic criteria in the future.