Application of L1-Norm Regularization to Epicardial Potential Solution of the Inverse Electrocardiography Problem
The electrocardiographic inverse problem of computing epicardial potentials from multi-electrode body-surface ECG measurements, is an ill-posed problem. Tikhonov regularization is commonly employed, which imposes penalty on the L2-norm of the potentials (zero-order) or their derivatives. Previous work has indicated superior results using L2-norm of the normal derivative of the solution (a first order regularization). However, L2-norm penalty function can cause considerable smoothing of the solution. Here, we use the L1-norm of the normal derivative of the potential as a penalty function. L1-norm solutions were compared to zero-order and first-order L2-norm Tikhonov solutions and to measured ‘gold standards’ in previous experiments with isolated canine hearts. Solutions with L1-norm penalty function (average relative error [RE] = 0.36) were more accurate than L2-norm (average RE = 0.62). In addition, the L1-norm method localized epicardial pacing sites with better accuracy (3.8 ± 1.5 mm) compared to L2-norm (9.2 ± 2.6 mm) during pacing in five pediatric patients with congenital heart disease. In a pediatric patient with Wolff–Parkinson–White syndrome, the L1-norm method also detected and localized two distinct areas of early activation around the mitral valve annulus, indicating the presence of two left-sided pathways which were not distinguished using L2 regularization.

title: Noninvasive electrocardiographic imaging (ECGI) of a univentricular heart with Wolff-Parkinson-White syndrome.
abstract: Electrocardiographic imaging (ECGI) is a noninvasive functional imaging modality which reconstructs epicardial potentials, electrograms, and activation and recovery maps from body-surface ECG potentials. For this purpose, up to 256 ECGs are recorded by a 256-channel body surface potential mapping (BSPM) system and the heart-torso geometry is obtained using thoracic computed tomography (CT)1,2. This technique was developed and validated extensively in normal and abnormal canine hearts3–11. More recently, ECGI was validated in humans by comparison with direct intra-operative epicardial mapping in patients undergoing open-heart surgery12. To date, ECGI has been applied in adult human subjects for the following purposes: 1. To study cardiac electrophysiology of the normal adult human heart2. 2. To image electrophysiologic responses to pacing in heart failure patients undergoing cardiac resynchronization therapy13 (pacing sites were localized with an accuracy better than 10 mm)14. 3. To guide catheter ablation of focal ventricular and atrial tachycardias15,16. 4. To image typical atrial flutter prior to catheter ablation1 and atypical atrial flutter prior to a surgical Cox-Maze procedure17. 
 
Here we describe for the first time, a case where ECGI was applied to a pediatric patient with a congenital structural heart defect. The patient had a univentricular heart and Wolff-Parkinson-White syndrome, and ECGI was used to localize the accessory pathway and help guide catheter ablation. To date, there have been no reported cases of ECGI in the pediatric population.

title: Cardiac memory in patients with Wolff-Parkinson-White syndrome: noninvasive imaging of activation and repolarization before and after catheter ablation.
abstract: Cardiac memory refers to a change in ventricular repolarization induced by and persisting for minutes to months after cessation of a period of altered ventricular activation (eg, resulting from pacing or preexcitation in patients with Wolff-Parkinson-White syndrome). ECG imaging (ECGI) is a novel imaging modality for noninvasive electroanatomic mapping of epicardial activation and repolarization.



Fourteen pediatric patients with Wolff-Parkinson-White syndrome and no other congenital disease, were imaged with ECGI a day before and 45 minutes, 1 week, and 1 month after successful catheter ablation. ECGI determined that preexcitation sites were consistent with sites of successful ablation in all cases to within a 1-hour arc of each atrioventricular annulus. In the preexcited rhythm, activation-recovery interval (ARI) was the longest (349+/-6 ms) in the area of preexcitation leading to high average base-to-apex ARI dispersion of 95+/-9 ms (normal is approximately 40 ms). The ARI dispersion remained the same 45 minutes after ablation, although the activation sequence was restored to normal. ARI dispersion was still high (79+/-9 ms) 1 week later and returned to normal (45+/-6 ms) 1 month after ablation.



The study demonstrates that ECGI can noninvasively localize ventricular insertion sites of accessory pathways to guide ablation and evaluate its outcome in pediatric patients with Wolff-Parkinson-White syndrome. Wolff-Parkinson-White is associated with high ARI dispersion in the preexcited rhythm that persists after ablation and gradually returns to normal over a period of 1 month, demonstrating the presence of cardiac memory. The 1-month time course is consistent with transcriptional reprogramming and remodeling of ion channels.

title: Accuracy of Quadratic Versus Linear Interpolation in Noninvasive Electrocardiographic Imaging (ECGI)
abstract: Electrocardiographic Imaging (ECGI) is a cardiac functional imaging modality, noninvasively reconstructing epicardial potentials, electrograms and isochrones (activation maps) from multi-channel body surface potential recordings. The procedure involves solving Laplace’s equation in the source-free volume conductor between torso and epicardial surfaces, using Boundary Element Method (BEM). Previously, linear interpolation (LI) on three-noded triangular surface elements was used in the BEM formulation. Here, we use quadratic interpolation (QI) for potentials over six-noded linear triangles. The performance of LI and QI in ECGI is evaluated through direct comparison with measured data from an isolated canine heart suspended in a human-torso-shaped electrolyte tank. QI enhances the accuracy and resolution of ECGI reconstructions for two different inverse methods, Tikhonov regularization and Generalized Minimal Residual (GMRes) method, with the QI-GMRes combination providing the highest accuracy and resolution. QI reduces the average relative error (RE) between reconstructed and measured epicardial potentials by 25%. It preserves the amplitude (average RE reduced by 48%) and morphology of electrograms better (average correlation coefficient for QI ∼ 0.97, LI ∼ 0.92). We also applied QI to ECGI reconstructions in human subjects during cardiac pacing, where QI locates ventricular pacing sites with higher accuracy (≤ 10 mm) than LI (≤ 18 mm).

title: Hypertrophic cardiomyopathy with preexcitation: insights from noninvasive electrocardiographic imaging (ECGI) and catheter mapping.
abstract: Hypertrophic Cardiomyopathy and Preexcitation.



Fasciculoventricular pathway has been described as an unusual variant of preexcitation. Electrocardiographic imaging (ECGI) is a novel imaging modality for noninvasive electroanatomic mapping of epicardial activation and repolarization.



We present a case of an 18-year-old male with hypertrophic cardiomyopathy (HCM) and an electrocardiogram (ECG)-based diagnosis of Wolff-Parkinson-White (WPW) syndrome, who underwent a noninvasive ECGI study to image ventricular activation, followed by an electrophysiology study (EPS). The ECGI electroanatomic isochrone map showed early activation of the epicardial aspect of the atrioventricular (A-V) groove and an aberrant posterior-base-to-apex progression of activation in the left ventricular (LV) epicardium. The EPS showed a likely fasciculoventricular pathway (FVP) without any inducible tachycardia.



While FVP has been described before, this is the first report of detailed quantitative three-dimensional characterization of electrical activation sequence of a heart with this type of preexcitation, using a novel noninvasive imaging modality (ECGI). In spite of abnormal ventricular activation, the EPS demonstrated that the FVP is not capable of supporting reentrant supraventricular tachycardia or rapidly conducted atrial fibrillation.

title: Fatal Morganella morganii bacteraemia in a diabetic patient with gas gangrene.
abstract: We report a case of a 60-year-old lady with a history of a heel ulcer that had not responded to antibiotic therapy. This progressed to involve the right leg, which was swollen and erythematous. Radiological imaging revealed the presence of gas within the fascial planes. Blood cultures on admission yielded Morganella morganii. Due to the extent of the gas gangrene and her co-morbidities the patient was not suitable for surgical intervention and was treated conservatively with antibiotics. She deteriorated and died within 72 h of presentation. Non-clostridial gas gangrene is relatively rare, and diagnosis is frequently delayed and often missed. Early aggressive surgical intervention combined with appropriate antibiotic therapy is essential. Bacterial species other than Clostridium should be considered in all cases of gas gangrene.

title: Evidence for interstate transmission and increase in prevalence of bovine group B rotavirus strains with a novel VP7 genotype among diarrhoeic calves in Eastern and Northern states of India.
abstract: During a surveillance study (2003-2005) in a cattle market in Kolkata city, state of West Bengal, Eastern India, 34 (13.0%) of 260 calves with diarrhoea were positive for group B rotaviruses (GBR) by RNA electrophoresis in polyacrylamide gels. Analysis of the partial VP7 gene sequence of 28 of the 34 GBR strains revealed maximum identities (97.7-99.5% at nucleotide level and 97.8-100% at amino-acid level) with the novel bovine GBR 'Kolkata strains' reported in an earlier surveillance study (1.5%, n=192, 2001-2002) from the same cattle market, and shared low identities of 73.7-78.9% and 80.8-89.6%; 62.6-66.2% and 59.8-65.4%; 58.9-62.2% and 48.6-54.9% at nucleotide and amino-acid level with other bovine, human, and murine GBR. The GBR-infected calves were traced to districts in neighbouring states of West Bengal. Therefore, the present study reports a rapid increase in prevalence (13.0% in 2003-2005 against 1.5% in 2001-2002) of novel GBR strains among calves with diarrhoea, and provides evidence for interstate transmission of GBR.

title: Interference in free thyroxine immunoassay.
abstract: We report two patients who presented with non-specific symptoms of tiredness that prompted their clinician to order a thyroid function test. In both cases, free thyroxine (T4) was reported to be high, with a normal thyroid-stimulating hormone (TSH). Repeated blood tests from the same laboratory using the same assay method yielded similar results. Due to discrepancies between the clinical and laboratory findings, we decided to repeat the blood tests at another laboratory using a different assay method. This revealed normal free T4 and TSH levels, suggesting that heterophile antibodies were interfering with the free T4 assay, leading to clinical confusion.

title: Interfacial and self-aggregation of binary mixtures of anionic and nonionic amphiphiles in aqueous medium.
abstract: Interfacial and bulk properties of sodium dodecyl sulfate (SDS), polyoxyethylene (20) sorbitan monooleate (Tween-80), and their binary mixtures in aqueous medium have been investigated using surface tension, conductance, and fluorescence measurements at different temperatures. The critical micelle concentration (CMC), counterion binding, polarity index, aggregation number, thermodynamics of interfacial adsorption, and micellization are evaluated. The entropic contribution is found to be the predominant factor in micelle formation. The aggregation number and the polarity index of the micelle interior estimated by the pyrene fluorescence technique show interesting temperature dependence. The size and composition of the mixed micelles vary with the total concentration. The micellar compositions, activities of the individual components in the mixed species, and intersurfactant interactions are also estimated following regular solution theory, excess thermodynamic functions, and a molecular thermodynamic model. The surfactant mixtures are found to be nonideal with a lower degree of counterion binding compared to the individual members. Mixed micelles are nonspherical in nature at all temperatures when the mole fraction (α) of the ionic part in mixtures is high but transform to spherical when α(SDS) is ≤0.50.

title: Beating-heart mitral valve surgery in patients with poor left ventricular function.
abstract: Mitral valve surgery in the presence of poor left ventricular (LV) function is associated with higher mortality. One surgeon's (S. K. N.) evolving practice of mitral valve surgery on the beating heart using normothermic cardiopulmonary bypass (CPB) in a cohort of patients is described.



Between July 2000 and December 2002, 23 patients (13 men, 10 women; mean age 68.6 +/- 4.8 years; range: 54-81 years) with mitral regurgitation and LV ejection fraction <30% undergoing isolated mitral valve repair (n = 4) or replacement (n = 19) were investigated. All patients received maximal drug therapy. Among patients, 17 were in NYHA class III, and six in class IV.



The mean duration of follow up was 17 +/- 14 months, and was complete for all survivors. The visual field of the on-pump beating heart was equal to that of conventional valvular surgery, and technical accuracy was not compromised. The mean ICU and hospital stays were 2.4 +/- 1.3 days and 8.9 +/- 2.6 days, respectively. Mean CPB time was 74.3 +/- 14.8 min. Thirty-day mortality was significantly lower (8.7%) when compared to mean Euroscore-predicted mortality for this high-risk group (16.9%; p <0.001). The medium-term one- and two-year survivals were 87% and 78%, respectively. Mean NYHA class was improved, from 3.6 +/- 0.5 preoperatively to 1.9 +/- 0.7 at follow up (p = 0.037).



On-pump, beating-heart mitral valve surgery is a good option in patients with poor LV function, and is advantageous as conditions for the heart are more physiological with a beating tonus than with cardioplegia.