Effects of Interpolation on the Inverse Problem of Electrocardiography.

Electrocardiographic Imaging (ECGI) aims to reconstruct electrograms from the body surface potential measurements. Bad leads are usually excluded from the inverse problem solution. Alternatively, interpolation can be applied. This study explores how sensitive ECGI is to different bad-lead configurations and interpolation methods. Experimental data from a Langendorff-perfused pig heart suspended in a human-shaped torso-tank was used. Epicardial electrograms were acquired during 30 s (31 beats) of RV pacing using a 108-electrode array, simultaneously with torso potentials from 128 electrodes embedded in the tank surface. Six different bad lead cases were designed based on clinical experience. Inverse problem was solved by applying Tikhonov regularization i) using the complete data, ii) bad-leads-removed data, and iii) interpolated data, with 5 different methods. Our results showed that ECGI accuracy of an interpolation method highly depends on the location of the bad leads. If they are in the high-potential-gradient regions of the torso, a highly accurate interpolation method is needed to achieve an ECGI accuracy close to using complete data. If the BSP reconstruction of the interpolation method is poor in these regions, the reconstructed electrograms also have lower accuracy, suggesting that bad leads should be removed instead of interpolated. The inverse-forward method was found to be the best among all interpolation methods applied in this study in terms of both missing BSP lead reconstruction and ECGI accuracy, even for the bad leads located over the chest.

Reduction of Effects of Noise on the Inverse Problem of Electrocardiography with Bayesian Estimation.

To overcome the ill-posed nature of the inverse problem of electrocardiography (ECG) and stabilize the solutions, regularization is used. Despite several studies on noise, effect of prefiltering of ECG signals on the regularized inverse solutions has not been explored. We used Bayesian estimation for solving the inverse ECG problem with and without applying various prefiltering methods, and evaluated our results using experimental data that came from a Langendorff-perfused pig heart suspended in a human-shaped torso-tank. Epicardial electrograms were recorded during RV pacing using a 108-electrode array, simultaneously with ECGs from 128 electrodes embedded in the tank surface. Leave-one-beat-out protocol was used to obtain the prior probability density function (pdf) of electro-grams and noise statistics. Noise pdf was assumed to be zero mean-Gaussian, with covariance assumptions: a) independent and identically distributed (noi-iid), b) correlated (noi-corr). Reconstructed electrograms and activation times were compared to those directly recorded by the sock for 3 beats selected from the recording. Noi-corr is superior to noi-iid when the training set is a good match to data, but for applications requiring activation time derivation, careful selection of preprocessing methods, in particular to adequately remove high-frequency noise, and an appropriate noise model is needed.

Polycaprolactone/glass bioabsorbable implant in a rabbit humerus fracture model.

Research in improved materials and methods for internal fixation has centered on internal fixators made of bioabsorbable materials such as polylactic acid, polyglycolic acid, and polyparadioxanone. These materials have two problems: the first is a postoperative complication related to a delayed inflammatory response; and the second is low strength characteristics. An alternative material developed to alleviate these problems is a composite of phosphate glass fibers embedded in the polymer polycaprolactone, referred to as PCL. In this study, intramedullary pins made of PCL were compared to stainless steel pins in a rabbit humerus osteotomy model. Specimens were harvested at 0, 6, and 12 weeks postoperatively, radiographs and mechanical testing to failure were performed at each time interval, and tissue was examined microscopically at 6 and 12 weeks. Histologic results showed PCL pins to be well tolerated with minimal inflammation around the pin. Mechanical testing revealed the PCL fixation to be weaker initially than the stainless steel fixation. There was significant stress shielding of stainless-steel-healed rabbit humeri when compared to the PCL/bone humeri. All osteotomies immobilized with PCL healed with abundant periosteal callus production.

Biomechanics of rigid tibial nail insertion sites.

The use of a very proximal insertion site for rigid intramedullary nailing was evaluated in a biomechanical study. The purpose of this study was to compare the bursting strains generated in a proximal tibia fracture fragment during rigid nailing, using the recommended insertion sites versus a more proximal site just anterior to the tibial plateau in the midline. Proximal one-third tibia fractures were created in 12 pairs of fresh cadaver specimens. Strain gauges were applied to the medial and lateral cortices of the proximal fragments. Lottes nails, Grosse-Kempf nails, and unreamed Russell-Taylor nails were inserted in four successive pairs of specimens. In each pair, one side used the recommended starting point, and the other side used the proximal insertion site. The strain was recorded at successive 2- to 4-cm depth intervals during nail insertion. In the Lottes group, much larger bursting strains were generated in the lateral cortex when using a distal starting point (P < 0.05). In the unreamed Russell-Taylor group, the anteromedial surface strains were significantly increased using a distal starting point (P < 0.05). The Grosse-Kempf group showed no significant difference in strains associated with any insertion point during tibial intramedullary nailing.

Mechanical behavior of mandibular continuity defects reconstructed using combinations of hydroxylapatite and autogenous bone.

The purpose of this investigation was to determine the mechanical behavior of primate (Macaca mulatta) mandibles with continuity defects reconstructed using varying ratios of an alloplastic hydroxylapatite (HA) implant material mixed with autogenous bone (AB). The defects were allowed to heal for 6 and 18 months before killing the animals and mechanical testing. Each animal had one side of the mandible restored with 100% AB as control. The fracture strength and section modulus of the opposite side of the mandible, containing the test ratio of HA-AB, were directly compared with the mechanical behavior of the control side. The fracture strength and section modulus were evaluated by a cantilever type of mechanical test that took into account the anisotropic, viscoelastic, and geometric nature of the mandible. The type of bone and tissue at the fracture site was examined by scanning electron microscopy and a direct correlation between the amount of bone and/or fibrous tissue growth around the HA implant material and the fracture strength and section modulus values was established. The average fracture strength of the AB graft sites at 18 months was 9,975 +/- 4,300 psi, with ratios of 25:75 and 50:50 HA-AB giving test results approaching those of the AB graft sites.

Experimental intra-articular calcaneal fractures: anatomic basis for a new classification.

Experimental calcaneus fractures were produce by axially loading 18 specimens. Anatomic dissections were performed and documented. Two constant primary fracture lines were identified, dividing the calcaneus in the coronal and sagittal planes. A constant anterolateral fragment was identified, as were three patterns of calcaneocuboid joint fracture involvement. Based on the pathoanatomy and surgical anatomy of the calcaneus, a medial and lateral column classification is proposed. The medial column includes the superomedial fragment. The lateral column includes the calcaneocuboid joint, lateral wall and posterior facet. This concept can help identify fracture displacements and correlate them with a treatment plan.

A randomized study of cyclosporine with and without prednisone in renal allograft recipients. Canadian Transplant Group.

Sixty-nine patients receiving Cs after cadaveric or LRD renal transplants were randomly allocated to receive prednisone or no prednisone beginning on the day of transplant. There were 36 in the prednisone group and 33 in the group assigned to no prednisone. Of these latter, only seven (21%) never received prednisone and an additional four had one short course for rejection episodes (11%). Of the remaining 22 who were placed on continuous steroids, only 12 met rejection criteria and either some or all of the remainder probably had Cs nephrotoxicity. The patient and graft survival were better but not statistically so in the no-prednisone group (97% v 89%) and (88% v 78%), and the number of infections was only half that of the prednisone-treated group (22% v 42%). A policy of withholding steroids except for rejection episodes does not prejudice graft or patient survival in Cs-treated patients.

Vascular retinopathy in migraine.

After years of episodic monocular visual loss, two migraineurs suffered sudden, persisting loss of vision from retinal vascular occlusion. One was a 34-year-old woman with systemic lupus erythematosus who showed abnormalities of the cilioretinal arterial and retinal venous circulations. The other was a 62-year-old man with hypertension and arteriosclerosis who had a central retinal vein occlusion. Persisting monocular visual loss is a rare consequence of migraine. Our cases suggest a role for venous lesions. Occlusion of retinal vessels in some migraineurs may result from the synergistic effect of another vascular disorder with the migraine.

Neovascular glaucoma and carotid artery obstructive disease.

Carotid artery obstructive disease, although infrequently diagnosed as a primary or contributing cause of neovascular glaucoma, can produce distinctive characteristics. Decreased perfusion of the ciliary body may decrease aqueous humor production. As a result, such eyes with neovascular glaucoma may occasionally be normotensive or even hypotensive. Fluorescein angiography may show an increased arm-to-retina time and leakage from the major retinal arterioles. Panretinal photocoagulation may not eliminate the anterior segment neovascularization because of anterior segment ischemia. Endarterectomy can significantly increase intraocular pressure as perfusion to the ciliary body returns to normal. These characteristics were found in two patients, a 67-year-old woman and a 49-year-old man, with diabetes and hypertension. In both cases cyclocryotherapy significantly reduced the intraocular pressure and the rubeosis iridis regressed.

Downbeat nystagmus. Long-term therapy with moderate-dose lithium carbonate.

Downbeat nystagmus developed in a 67-year-old hypomagnesemic woman while she was receiving lithium carbonate for depression. This nystagmus abated each time lithium carbonate therapy was withdrawn, and no alternative causes of nystagmus were demonstrated. However, this nystagmus occurred despite serum lithium carbonate levels in the nontoxic range. Total-body magnesium deficiency may have enhanced the toxic effect of lithium carbonate on cerebellomedullary connections.

Foster-Kennedy syndrome caused by solitary intracranial plasmacytoma.

The first case of typical Foster-Kennedy syndrome, including decreased olfaction of the side of the optic atrophy due to a primary solitary intracranial extraskeletal plasmacytoma, is reported. Its appearance on a computed tomography scan was compatible with a meningioma or subdural hematoma. The patient demonstrated a chronic, corticosteroid-sensitive, relapsing optic neuropathy associated with an elevated sedimentation rate and a monoclonal gammopathy. The diagnosis, treatment, and prognosis of such tumors are reviewed.

Optimized graphical analysis of Gaussian and lognormal assumptions for intraocular and vascular pressure distributions.

The design of optimized histogram and probability graphs needed to detect a lognormal distribution in surveys of intraocular pressure (IOP), mean ophthalmic arterial pressure (OAP) and mean ocular perfusion pressure (OPP) is described. Applications are demonstrated in a sample of 58 normal adult eyes. A lognormal distribution was found for IOP and for OAP and OPP estimates obtained with a noncontact noncompressive method. Conversely, the absence of an identifiable linear distribution for OAP and OPP estimates obtained with compression ophthalmodynamometry was noteworthy. The implications of lognormality for definitions of a normal range and for correlations involving IOP, OAP and OPP data are briefly discussed.