A review of multisite pacing to achieve cardiac resynchronization therapy

Non-response to cardiac resynchronization therapy remains a significant problem in up to 30% of patients. Multisite stimulation has emerged as a way of potentially overcoming non-response. This may be achieved by the use of multiple leads placed within the coronary sinus and its tributaries (dual-vein pacing) or more recently by the use of multipolar (quadripolar) left ventricular pacing leads which can deliver pacing stimuli at multiple sites within the same vein. This review covers the role of multisite pacing including the interaction with the underlying pathophysiology, the current and planned studies, and the potential pitfalls of this technolog

Left ventricular scar and the acute hemodynamic effects of multivein and multipolar pacing in cardiac resynchronization

Background We sought to determine whether presence, amount and distribution of scar impacts the degree of acute hemodynamic response (AHR) with multisite pacing. Multi-vein pacing (MVP) or multipolar pacing (MPP) with a multi-electrode left ventricular (LV) lead may offer benefits over conventional biventricular pacing in patients with myocardial scar. Methods In this multi-center study left bundle branch block patients underwent an hemodynamic pacing study measuring LV dP/dtmax. Patients had cardiac magnetic resonance scar imaging to assess the effect of scar presence, amount and distribution on AHR. Results 24 patients (QRS 171 ± 20 ms) completed the study (83% male). An ischemic etiology was present in 58% and the mean scar volume was 6.0 ± 7.0%. Overall discounting scar, MPP and MVP showed no significant AHR increase compared to an optimized “best BiV” (BestBiV) site. In a minority of patients (6/24) receiver-operator characteristic analysis of scar volume (cut off 8.48%) predicted a small AHR improvement with MPP (sensitivity 83%, specificity 94%) but not MVP. Patients with scar volume > 8.48% had a MPP-BestBiV of 3 ± 6.3% vs. −6.4 ± 7.7% for those below the cutoff. There was a significant correlation between the difference in AHR and scar volume for MPP-BestBiV (R = 0.49, p = 0.02) but not MVP-BestBiV(R = 0.111, p = 0.62). The multielectrode lead positioned in scar predicted MPP AHR improvement (p = 0.04). Conclusions Multisite pacing with MPP and MVP shows no AHR benefit in all-comers compared to optimized BestBiV pacing. There was a minority of patients with significant scar volume in relation to the LV site that exhibited a small AHR improvement with MPP

The interaction of QRS duration with cardiac magnetic resonance derived scar and mechanical dyssynchrony in systolic heart failure:Implications for cardiac resynchronization therapy

Background: Trials using echocardiographic mechanical dyssynchrony (MD) parameters in narrow QRS patients have shown a negative response to CRT. We hypothesized MD in these patients may relate to myocardial scar rather than electrical dyssynchrony. Methods: We determined the prevalence of cardiac magnetic resonance (CMR) derived measures of MD in 130 systolic heart failure patients with both broad (≥130 ms - BQRS) and narrow QRS duration (<130 ms - NQRS). We assessed whether late gadolinium enhancement derived scar might explain the presence of MD amongst narrow QRS patients. Dyssynchrony was calculated on the basis of a systolic dyssynchrony index (SDI). Results: Fifty-nine patients (45%) had a NQRS and the remaining had QRS ≥130 ms (BQRS group). 25% of NQRS patients had MD based on SDI. In all narrow and broad QRS patients with MD there was a significantly lower scar volume than those without MD (7.4 ± 10.5% vs 13.7 ± 13.3% vs. p < 0.01). This was the case in the BQRS group with a significantly lower scar burden in patients with MD (5.0 ± 7.7% vs 15.4 ± 15.6%, p < 0.01). Notably in the NQRS group this difference was absent with an equal scar burden in patients with MD 13.3 ± 13.9% and without MD 12.5 ± 11%, p = 0.92. Conclusions: 25% of patients with systolic heart failure and a NQRS (<130 ms) have CMR derived mechanical dyssynchrony. Our findings suggest MD in this group may be secondary to myocardial scar rather than electrical dyssynchrony and therefore not amenable to correction by CRT. This may give insight into non-response and potential harm from CRT in this group. Keywords: Narrow QRS, Cardiac resynchronization therapy, Dyssynchrony, Cardiac magnetic resonance imagin

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements