..........................................................................................................................................................................................................................................................................................................................................................................CLINICAL RESEARCH12-lead surface electrocardiogr am r econstructionfr om implanted device electrogr amsG. Stuart Mendenhall*and Samir SabaDepartment of Cardiac Electrophysiology, University of Pittsburgh Cardiovascular Institute, Pittsburgh, PA, USAReceived 28 January 2010; accepted after revision 25 March 2010Aim Reconstruction of the surface electrocardiogram (EKG) from voltage recordings from implanted leads is notperformed by current pacemakers or cardioverter-defibrillators. We investigated the feasibility and accuracy ofreconstruction of a full 12-lead surface EKG from an implanted biventricular device.Methodsand resultsWe applied three techniques for surface EKG reconstruction from multiple intracardiac (IC) vector recordingsfrom implanted cardiac leads: single fixed dipole modelling via exact solution, exhaustive best-fit solution, andtime-independent association using a transfer matrix. Recordings were performed at biventricular generatorchange in 10 patients. Overdetermined projection transformation resulted in high fidelity surface EKG reproductionfor left-sided implanted devices (correlation coefficient 0.84 + 0.13) with computationally lightweight reconstruction.Conclusion After individual post-implantation correlation with the surface EKG, reconstruction using a time-independenttransfer matrix accurately reproduces the surface EKG, is free from gating requirements, and retains validityduring aberrant depolarization. These findings have significant implications for further study relating IC electrogramto surface tracings. The techniques may be used for real-time or remote monitoring and diagnosis of rhythmdisturbances, cardiac ischaemia, and lead integrity and stability.-----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords Electrocardiography † Pacemakers † Arrhythmia † Ischaemia † ComputersIntroductionThe process of reconstruction of the overall depolarization patternof the heart via recording of a subset of electrical potential differ-ence vectors is generally classified as the ‘inverse problem’. The‘forward problem’ is the reverse, that is, the accurate reconstruc-tion of an electrocardiogram (EKG) from knowledge of the spatio-temporal pattern of cardiac depolarization.Single fixed dipole (SFD) representation of cardiac electricalforces models the summed electrical activity of the heart as acharge separation (electrical dipole) at the centre of the chestcavity. This single dipole can be projected onto various recordingvectors and is widely taught to clinicians as a straightforwardreduction of the electrical forces that give rise to the EKG. Themagnitude and direction of the heart dipole changes with time,but the projected lead vectors’ orientation to the centre of thedipole remains fixed. Prior studies have demonstrated variationsof SFD modelling techniques for the correlation of EKG andbody surface potential mapping,1straightforward interpolation ofmissing surface EKG leads,2,3and inverse problem solutions frommeasured body surface mapping potentials.4 – 7Current implanted devices do not attempt reconstruction ofsurface electrocardiography or give depolarization waveform infor-mation to physicians for clinical interpretation. Given the extensivetraining and expertise that physicians invest in learning to recognizeand interpret patterns in the standard 12-lead EKG recording,reconstruction of an accurate surface tracing representation froman implanted device may allow rapid diagnosis without externalrecording. Advantages of this system include low noise artefactfrom the fixed internal recording sources and the ability toobtain diagnostic tracings remotely from the implanted device.This may occur over telephone or internet networks uponsymptom-driven patient activation, continuously, or upon device-detected changes in reconstructed EKG (rEKG) morphology.In this article, we demonstrate the feasibility of reconstruction ofa full surface 12-lead EKG from a series of intracardiac (IC) record-ings from an implanted defibrillator with voltage leads in an arbi-trary location through a transfer matrix relating IC to surface* Corresponding author. Tel: +1 412 647 3429; fax: +1 412 647 0481, Email: [email protected] on behalf of the European Society of Cardiology. All rights reserved.& The Author 2010. For permissions please email: [email protected]:10.1093/europace/euq115 Europace Advance Access published April 21, 2010 at University of Kentucky Libraries on May 28, 2010europace.oxfordjournals.orgDownloaded frompotentials in a time-independent fashion. The resultant reconstruc-tion is highly correlated with the directly recorded surface EKG atthe time of device implantation and retains validity during baselineand aberrant or ectopic cardiac depolarization.MethodsAll enrolled patients were undergoing generator change of animplanted biventricular cardioverter-defibrillator (ICD). Recordingswere performed at the University of Pittsburgh Medical Center fromJune 2007 to June 2009. The UPMC institutional review boardapproved the study protocol and each patient gave written informedconsent.After detachment of the existing device generator, high impedancerecording electrodes were connected directly to the four ventricularlead positions (proximal coil, distal coil, right ventricular electrode,left ventricular electrode) and the atrial lead. The recorded differencepotentials include all or a subset of Can-RV, Can-RA, RA-RV, Can-Distal, Can-LV, Can-Prox, and RA-LV. An electrode connected tothe tissue area at the site of the explanted device was used as a surro-gate for the device ‘can’.All difference potentials were directly measured using the PruckaCardioLab EP system (GE Healthcare, Waukesha, WI, USA). Simul-taneous measurement of all two-lead voltage tracings was obtainedalong with standard surface 12-lead EKG configuration (all algorithms)and modified-Frank vectorcardiogram (VCG)8(Algorithms 1a and 1b).Intracardiac tracings had hardware