Left ventricular remodelling and haemodynamic effects of multisite biventricular pacing in patients with left ventricular systolic dysfunction and activation disturbances in sinus rhythm: sub-study of the MUSTIC (Multisite Stimulationin Cardiomyopathies) trial,

Aims To use echocardiography to determine early and late haemodynamic effects of atrio-biventricular (A-BiV) pacing on left ventricular (LV) function and their interrelations with exercise tolerance. Methods Thirty-four patients with ejection fraction <35% (18 idiopathic dilated cardiomyopathy (DCM) and 16 ischaemic cardiomyopathy, in sinus rhythm and with intra-ventricular conduction delay (IVCD)) were implanted with transvenous A-BiV pacemakers. Echocardiographic measurements were compared before implantation, after 3 months A-BiV pacing, and 3 months inactive pacing (ventricular inhibited pacing at 40beatsmin⁻¹as part of a crossover design, and at 9- and 12-month longitudinal follow-up. Results Total isovolumic time (IVT) halved after 3 months A-BiV pacing (from 20.1±4.4 to 10.7±4.9smin⁻¹, \(P{<}0.001\) ⁠) and did not change thereafter. LV cavity size fell after 3 months (end-diastolic dimension (EDD) 7.3±0.8 to 6.8±0.8cm, \(P{<}0.001\) ⁠, and end-systolic dimension (ESD) 6.2±0.8 to 5.9±0.8cm, \(P{<}0.05\) ⁠), with a further fall in EDD and ESD (by 8.4±7.8 and 8.8±7.8mm, respectively, both \(P{<}0.001\) ⁠) after 12 months. Although not a primary end-point of the study, the 12-month reduction in LVEDD and LVESD was greater in idiopathic DCM (by 8.9 and 9.8mm, \(P{<}0.01\) ⁠, respectively) compared with ischaemic cardiomyopathy. The 6-min walk rose by 15% (⁠ \(P{<}0.01\) ⁠) and peak VO₂by 10% \((P{<}0.05)\) after 3 months, with no further increase by 12 months, and no difference between idiopathic DCM and ischaemic cardiomyopathy. The increase in peak VO₂at 12 months correlated with the fall in ESD (⁠ \(r=0.47\) ⁠, \(P=0.03\) ⁠). Conclusions A-BiV pacing shortens total IVT, reduces LV cavity size, and increases exercise tolerance in patients with DCM and IVCD. Ischaemic cardiomyopathy does not affect the exercise response, although it does reduce the extent of reverse remodelling.