overestimated. Irrespectively, it is important to point out that there is little information with regards to real-life battery longevity for the studied CRT-D device (Quadra Assura MP, St Jude) given its fairly recent commercialization. Nonetheless, we believe the main value of the present study lies in the reported proportional differences in battery longevity between the different pacing programming protocols. Our results may therefore help clinicians make more informed decisions when considering MPP activation, given the current scarcity of information regarding its impact on battery longevity. ConclusionsIn most cases, MPP activation significantly reduces battery longevity compared with that for conventional CRT configuration. However, when reasonable MPP LV vector PCTs (< _4.0 V) are achieved, the decrease in battery longevity is relatively small and this may prompt the clinician to activate MPP in such scenarios.

ClinicalTrials.gov number NCT00461734.

Background-The relationship between epicardial and body surface potentials defines the forward problem of electrocardiography. A robust formulation of the forward problem is instrumental to solving the inverse problem, in which epicardial potentials are computed from known body surface potentials. Here, the accuracy of different forward models has been evaluated experimentally. Methods and Results-Body surface and epicardial potentials were recorded simultaneously in anesthetized closed-chest pigs (n=5) during sinus rhythm, and epicardial and endocardial ventricular pacing (65 records in total). Body surface potentials were simulated from epicardial recordings using experiment-specific volume conductor models constructed from magnetic resonance imaging. Results for homogeneous (isotropic electric properties) and inhomogeneous (incorporating lungs, anisotropic skeletal muscle, and subcutaneous fat) forward models were compared with measured body surface potentials. Correlation coefficients were 0.85±0.08 across all animals and activation sequences with no significant difference between homogeneous and inhomogeneous solutions (P=0.85). Despite this, there was considerable variance between simulated and measured body surface potential distributions. Differences between the body surface potential extrema predicted with homogeneous forward models were 55% to 78% greater than observed (P<0.05) and attenuation of potentials adjacent to extrema were 10% to 171% greater (P<0.03). The length and orientation of the vector between potential extrema were also significantly different. Inclusion of inhomogeneous electric properties in the forward model reduced, but did not eliminate these differences. Conclusions-These results demonstrate that homogeneous volume conductor models introduce substantial spatial inaccuracies in forward problem solutions. This probably affects the precision of inverse reconstructions of cardiac potentials, in which this assumption is made. (Circ Arrhythm Electrophysiol. 2015;8:677-684.

Inverse potential mapping provides useful information on the origin and spread of epicardial activation. However the spatio-temporal variability of recovered electrograms limit resolution and must constrain the accuracy with which arrhythmia circuits can be identified independently using this approach.