Complex temporal patterns of spontaneous initiation and termination of reentry in a loop of cardiac tissue

A two-component model is developed consisting of a discrete loop of cardiac cells that circulates action potentials as well as a pacing mechanism. Physiological properties of cells such as restitutions of refractoriness and of conduction velocity are given via experimentally measured functions. The dynamics of circulating pulses and the pacer's action are regulated by two threshold relations. Patterns of spontaneous initiations and terminations of reentry (SITR) generated by this system are studied through numerical simulations and analytical observations. These patterns can be regular or irregular; causes of irregularities are identified as the threshold bistability (T-bistability) of reentrant circulation and in some cases, also phase-resetting interactions with the pacer.

Supplemental algal meal alters the ruminal trans-18:1 fatty acid and conjugated linoleic acid composition in cattle

The effects of dietary algal supplementation, a source of docosahexaenoic acid, on the fatty acid profile of rumen lipids in cattle were evaluated, with special emphasis on CLA and trans fatty acids produced by rumen microbes. A diet based on corn silage was fed with supplements containing the following: 1) no algal meal and fed at 2.1 kg of DM/d (control), 2) algal meal and fed at 1.1 kg of DM/d (low algal meal), 3) algal meal and fed at 2.1 kg of DM/d (medium algal meal), and 4) algal meal and fed at 4.2 kg of DM/d (high algal meal). A modified lipid extraction procedure was developed to analyze the lipid changes in rumen fluid. The percentage of stearic acid (18:0) in rumen fluid was decreased by algal meal supplementation (P < 0.001) compared with control and was linearly dependent on the level of algal meal supplementation (P = 0.005). Total trans-18:1 in rumen fluid of cattle fed the control diet was 19% of total fatty acids. Addition of algal meal increased (P < 0.001) total trans-18:1 up to 43%, mostly due to 18:1 trans-10 that increased (P = 0.002) to 29.5% of total rumen fatty acids. This increase in 18:1 trans-10 seems to suggest a change in the rumen microbial population. Vaccenic acid (18:1 trans-11) increased quadratically (P = 0.005) with increasing level of algal meal supplementation in the diets. The total CLA content was low in the control (<0.9%) and increased with dietary algal meal addition, although not significantly; the greatest level was 1.5% with the medium algal meal diet. The increase of rumenic acid (cis-9, trans-11 CLA) was quadratic (P = 0.05) with algal meal supplementation, whereas trans-10, cis-12 CLA increased linearly with increased level of algal meal from 0.08 to 0.13% (P = 0.03). The ratio of trans-11 (cis-9, trans-11 CLA + 18:1 trans-11) to trans-10 (trans-10, cis-12 CLA + 18:1 trans-10) decreased from 2.45 to 0.77, 0.87, and 0.21 for the control, low algal meal, medium algal meal, and high algal meal diets, respectively. The content of docosahexaenoic acid in rumen fluid increased (P = 0.002) from 0.3 to 1.4% of total fatty acids with increasing level of algal meal supplementation in the diets. Our results suggest that algal meal inhibits the reduction of trans-18:1 to 18:0, giving rise to the high trans-18:1 content. In conclusion, algal meal could be used to increase the concentration in rumen contents of trans-18:1 isomers that serve as precursors for CLA biosynthesis in the tissues of ruminants.

Colloidal lithography and current fabrication techniques producing in-plane nanotopography for biological applications

Substrate topography plays a vital role in cell and tissue structure and function in situ, where nanometric features, for example, the detail on single collagen fibrils, influence cell behaviour and resultant tissue formation. In vitro investigations demonstrate that nanotopography can be used to control cell reactions to a material surface, indicating its potential application in tissue engineering and implant fabrication. Developments in the catalyst, optical, medical and electronics industries have resulted in the production of nanopatterned surfaces using a variety of methods. The general protocols for nanomanufacturing require high resolution and low cost for fabricating devices. With respect to biological investigations, nanotopographies should occur across a large surface area (ensuring repeatability of experiments and patterning of implant surfaces), be reproducible (allowing for consistency in experiments), and preferably, accessible (limiting the requirement for specialist equipment). Colloidal lithography techniques fit these criteria, where nanoparticles can be utilized in combination with a functionalized substrate to produce in-plane nanotopographies. Subsequent lithographic processing of colloidal substrates utilizing, for example, reactive ion etching allows the production of modified colloidal-derived nanotopographies. In addition to two-dimensional in-plane nanofabrication, functionalized structures can be dip coated in colloidal sols, imparting nanotopographical cues to cells within a three-dimensional environment.

SMAC/Diablo mediates the proapoptotic function of PUMA by regulating PUMA-induced mitochondrial events

p53-upregulated modulator of apoptosis (PUMA) is a BH3-only Bcl-2 family protein and an essential mediator of DNA damage-induced apoptosis. PUMA is localized in the mitochondria and induces apoptosis through the mitochondrial pathway. However, the mechanisms of PUMA-induced apoptosis remain unclear. In this study, we found that second mitochondria-derived activator of caspase (SMAC)/Diablo, a mitochondrial apoptogenic protein, mediates the proapoptotic function of PUMA by regulating PUMA-induced mitochondrial events. SMAC is consistently released into the cytosol in colon cancer cells undergoing PUMA-induced apoptosis. In SMAC-deficient cells, execution of PUMA-induced apoptosis is abrogated, in company with decreases in caspase activation, cytosolic release of cytochrome c and collapse of mitochondrial membrane potential. Reconstituting SMAC expression restored these events in the SMAC-deficient cells. Furthermore, SMAC and agents that mimic the inhibitor of apoptosis proteins (IAPs) inhibition function of SMAC significantly sensitize cells to PUMA-induced apoptosis. These results demonstrate an important role of SMAC in executing DNA damage-induced and PUMA-mediated apoptosis and suggest that SMAC participates in a feedback amplification loop to promote cytochrome c release and other mitochondrial events in apoptosis.

Characterizing the efficacy of calcium channel agonist-release strategies for bone tissue engineering applications

We have previously reported on the use of Bay K8644-release strategies in combination with perfusion-compression bioreactor systems for up regulating bone formation in three-dimensional PLLA scaffolds. Here we report on the analysis of Bay activity following its release from our PLLA scaffolds over the culture period imposed in our tissue engineering protocol using UV spectroscopy in combination with whole cell patch clamping techniques. Bay was released continually from scaffolds within the physiological range required for agonist activity (1-10 microM). Patch clamping allowed for the effects of Bay released from scaffolds to be monitored directly with respect to osteoblast electrophysiology. A characteristic shift in the current-voltage (I-V) relationship of L-type VOCC currents was observed in rat osteoblast sarcoma (ROS) cells patched in a solution with Bay released from scaffolds following 14 and 28 days incubation, with statistically significant differences observed in peak currents compared to non-Bay controls. An increase in the magnitude of the peak inward currents was also noted. The electrophysiological response of osteoblasts in the presence of Bay released from scaffolds demonstrates that the released Bay is stable and maintains its bioactivity following culture of up to 28 days.

Testing for loss of protective sensation in patients with foot ulceration: a cross-sectional study

Current recommendations for the prevention of foot ulceration and amputation include screening at-risk individuals by testing for loss of protective sensation at eight sites using 10-g (5.07) nylon monofilaments. Yet measurement of the cutaneous pressure threshold to differentiate one-point from two-point static touch stimuli may allow identification of these at-risk individuals earlier in the clinical course of diabetic neuropathy. The present study tested this hypothesis using a prospective, cross-sectional, multicenter design that included sensibility testing of 496 patients with diabetic neuropathy, 17 of whom had a history of ulceration or amputation. Considering the cutaneous pressure threshold of the 5.07 Semmes-Weinstein nylon monofilament to be equivalent to the 95 g/mm(2) one-point static touch measured using the Pressure-Specified Sensory Device (Sensory Management Services LLC, Baltimore, Maryland), only 3 of these 17 patients with a history of foot ulceration or amputation would have been identified using the Semmes-Weinstein nylon monofilament screening technique. In contrast, using the Pressure-Specified Sensory Device, all 17 patients were identified as having abnormal sensibility, defined as greater than the 99% confidence limit for age, for two-point static touch on the hallux pulp. We conclude that patients at risk for foot ulceration can best be identified by actual measurement of the cutaneous sensibility of the hallux pulp.

Torsade de pointes in a patient with complex medical and psychiatric conditions receiving low-dose quetiapine

OBJECTIVE

Describe potential cardiac complications of low-dose quetiapine and other atypical antipsychotic drugs.

METHOD

We present a case report of a 45-year-old Black woman with multiple medical and psychiatric problems taking low-dose quetiapine.

RESULTS

Coincident with a generalized seizure, the patient developed 'ventricular fibrillation'. She was countershocked with restoration of normal sinus rhythm. The initial electrocardiogram showed QT interval prolongation. Shortly thereafter, classical torsade de pointes appeared, lasted 10 min, and resolved spontaneously. Hypomagnesemia was present. A cardiac electrophysiologist was concerned that the very slow shortening of the prolonged QTc interval after magnesium replacement implicated quetiapine as a risk factor for QTc interval prolongation and torsade de pointes. A psychosomatic medicine consultant asserted that the fragmented medical and psychiatric care almost certainly contributed to the patient's medical problems. We discuss other cases of QT interval prolongation by newer antipsychotic drugs and previous reports by our group concerning the association of psychotropic drugs, QT interval prolongation, and torsade de pointes.

CONCLUSION

Atypical antipsychotic drug administration, when accompanied by risk factors, may contribute to cardiac arrhythmias including torsade de pointes.

Decompression of peripheral nerves for diabetic neuropathy in the lower extremity

Consideration of the presence of a compressive neuropathy overlying an existing diabetic neuropathy in symptomatic patients and surgical decompression of these compressed nerves in selected patients is presented. The short-term results of 33 lower extremities treated with external neurolysis of the common peroneal, deep peroneal, and tarsal tunnel nerves are presented with a mean follow-up time of 3 months (range, 1 to 6 months). The surgery was performed in an attempt to relieve pain and to restore normal sensation in the foot. All procedures were performed under spinal or general anesthesia. Candidates for the procedure were type 1 or type 2 diabetics with symptomatic somatosensory neuropathy (pain, burning, tingling, and/or numbness) and preoperative computer-assisted neurosensory testing that confirmed the presence of elevated nerve threshold levels and axonal degeneration in the foot and leg. External neurolysis of the involved nerves provided good to excellent results in 90.0% of those patients with preoperative neuropathic pain, and restored sensation at good to excellent levels in 66.7% of those patients with preoperative neuropathic numbness. The mean visual analog score for pain assessment was 9.0 preoperatively and 3.2 postoperatively for those patients with pain as a symptomatic complaint (n = 30). There were 4 complications (12%) and all were early cases consisting of a noninfected wound dehiscence of the tarsal tunnel incision, which went on to heal without consequence. These initial short-term results suggest that external neurolysis of the common peroneal, deep peroneal, and tarsal tunnel nerves in selected patients with symptomatic diabetic neuropathy and an overlying compression neuropathy as determined by using computer-assisted neurosensory testing appears to be an effective treatment for providing pain relief and restoration of sensation in the foot.

Substratum nanotopography and the adhesion of biological cells. Are symmetry or regularity of nanotopography important?

Animal cells live in environments where many of the features that surround them are on the nanoscale, for example detail on collagen molecules. Do cells react to objects of this size and if so, what features of the molecules are they responding to? Here we show, by fabricating nanometric features in silica and by casting reverse features in polycaprolactone and culturing vertebrate cells in culture upon them, that cells react in their adhesion to the features. With cliffs, adhesion is enhanced at the cliff edge, while pits or pillars in ordered arrays diminish adhesion. The results implicate ordered topography and possibly symmetry effects in the adhesion of cells. Parallel results were obtained in the adhesion of carboxylate-surfaced 2-microm-diameter particles to these surfaces. These results are in agreement with recent predictions from non-biological nanometric systems.

Implantable cardioverter defibrillator T wave oversensing caused by hyperglycemia

This case report highlights a previously unreported cause of T wave oversensing in a patient with an ICD and recent onset diabetes. Consistent T wave oversensing was observed at elevated serum glucose levels and this finding was reproduced with a glucose challenge. No T wave oversensing was seen during treatment of hyperglycemia. Alterations in serum chemistry may account for intermittent T wave oversensing in patients with ICDs.

Effects of sodium channel blockade on ibutilide induced prolongation of repolarization in the isolated rabbit ventricle

INTRODUCTION

Ibutilide fumarate is indicated for the termination of atrial fibrillation and atrial flutter. It's mechanism of action is unclear but may involve activation of a late inward Na(+) current.

METHODS AND RESULTS

Twenty seven experiments were performed using an isolated perfused rabbit right ventricle preparation. In each experiment effective refractory periods (ERP) and transmembrane 90% action potential durations (APD) were measured. In 8 experiments ERP and APD were measured at baseline, in the presence of ibutilide (0. 1[emsp4 ]uM), and in the presence of both ibutilide and tetrodotoxin (TTX, 2[emsp4 ]uM). In 8 experiments lidocaine (10[emsp4 ]uM) was used in place of TTX. Measures were made at 200, 400, and 800[emsp4 ]msec paced cycle lengths under each condition. The baseline values for APD at 200, 400 and 800[emsp4 ]msec cycle lengths for the experiments treated with ibutilide and TTX were 111+/-8, 140+/-14 and 159+/-22[emsp4 ]msec, respectively. In the presence of ibutilide, APD increased to 130+/-19, 192+/-26 and 217+/-35[emsp4 ]msec at 200, 400 and 800[emsp4 ]msec cycle lengths, respectively (all p< or =0.03). After the addition of TTX there was no shortening of APD or ERP compared to treatment with ibutilide alone at any cycle length (all p> or =0.062). Similarly, in the presence of ibutilide and lidocaine there were no changes in APD or ERP compared to treatment with ibutilide alone (all p > or =0.41). In 11 control experiments, there were no changes in APD or ERP on serial measures after placebo and TTX or lidocaine.

CONCLUSION

Ibutilide induced prolongation of ventricular repolarization is not affected by Na(+) channel blockade with lidocaine or TTX in the isolated rabbit heart. These findings suggest that the effects of ibutilide are not mediated by a Na(+) channel dependent late current or that this mechanism contributes minimally to its action in this model.

Influence of autothreshold sensing and sinus rate on mode switching algorithm behavior

Mode switching is beneficial to pacemaker patients with paroxysmal atrial tachyarrhythmias. However, the optimal mode switching algorithm is still in evolution. Mode switching algorithms and atrial sensing circuitry can influence mode switching behavior. This study compared the mode switching behavior of four Medtronic, Inc. implantable devices: Thera DR model 7960 pacemaker, Kappa 700 model KDR701 pacemaker, Gem DR model 7271 dual chamber pacing defibrillator, and Jewel AF model 7250 dual chamber pacemaker atrial and ventricular defibrillator. The Thera and Gem DR use the same mean atrial rate mode switch algorithm. The Kappa and Jewel AF use four of seven short atrial intervals and an atrial fibrillation evidence counter algorithm, respectively. The Thera and Kappa devices use fixed gain sensing and the Gem DR and Jewel AF use autothreshold atrial sensing. Digitally recorded atrial electrograms from 52 episodes of human atrial fibrillation were fed into each device with differing simulated sinus rates before and after the atrial fibrillation. The percent of appropriate mode switching was highest for the Kappa 700 (94%) and lowest for the Thera (85%) (P = 0.046). The time to mode switching was significantly longer for the Thera and Gem DR compared to the Kappa 700 or Jewel AF (all P < 0.05). The time to mode switching was shorter for the Gem DR (9.0 +/- 1.6 s) using autothreshold atrial sensing than for the fixed gain Thera (11.1 +/- 2.1 s, P < 0.05). The mean atrial electrogram amplitude and cycle length were not correlated with the time to mode switching for any device. Faster sinus rates shortened the time to mode switching and prolonged the time to resynchronization in the two devices using the mean atrial interval algorithm. In conclusion, (1) mode switching function among these devices is influenced by algorithms and sensing circuitry, (2) the time to mode switching among these devices is influenced by the algorithm and use of autothreshold atrial sensing, and (3) the sinus rate before and after episodes of atrial fibrillation greatly influences the times to mode switching and resynchronization in devices using the mean atrial interval algorithm.

A prospective randomized-controlled trial of ventricular fibrillation detection time in a DDDR ventricular defibrillator. Ventak AV II DR Study Investigators

Implantable cardioverter defibrillators (ICDs) with dual chamber and dual chamber rate responsive pacing may offer hemodynamic advantages for some ICD patients. Separate ICDs and DDDR pacemakers can result in device to device interactions, inappropriate shocks, and underdetection of ventricular fibrillation (VF). The objectives of this study were to compare the VF detection times between the Ventak AV II DR and the Ventak AV during high rate DDDR and DDD pacing and to test the safety of dynamic ventricular refractory period shortening. Patients receiving an ICD were randomized in a paired comparison to pacing at 150 beats/min (DDD pacing) or 175 beats/min (DDDR pacing) during ICD threshold testing to create a "worst case scenario" for VF detection. The VF detection rate was set to 180 beats/min, and VF was induced during high rate pacing with alternating current. The device was then allowed to detect and treat VF. The induction was repeated for each patient at each programmed setting so that all patients were tested at both programmed settings. Paired analysis was performed. Patient characteristics were a mean age of 69 +/- 11 years, 78% were men, coronary artery disease was present in 85%, and a mean left ventricular ejection fraction of 0.34 +/- 0.11. Fifty-two episodes of VF were induced in 26 patients. Despite the high pacing rate, all VF episodes were appropriately detected. The mean VF detection time was 2.4 +/- 1.0 seconds during DDD pacing and 2.9 +/- 1.9 seconds during DDDR pacing (P = NS). DDD and DDDR programming resulted in appropriate detection of all episodes of VF with similar detection times despite the "worst case scenario" tested. Delays in detection may be seen with long programmed ventricular refractory periods which shorten the VF sensing window and may be avoided with dynamic ventricular refractory period shortening.

Clinical characteristics of patients intolerant to VVIR pacing

The incidence and clinical predictors of the development of intolerance to VVIR pacing have not been extensively studied in prospective long-term randomized trials comparing different pacing modes. The frequency and clinical factors predicting intolerance to ventricular pacing are controversial. The Pacemaker Selection in the Elderly (PASE) Trial enrolled 407 patients aged >/=65 years in a 30-month, single-blind, randomized, controlled comparison of quality of life and clinical outcomes with ventricular pacing and dual-chamber pacing in patients undergoing dual-chamber pacemaker implantation for standard clinically accepted indications. We reviewed the clinical, hemodynamic, and electrophysiologic variables at the time of pacemaker implantation in 204 patients enrolled in the PASE trial and randomized to the VVIR mode, some of whom subsequently required crossover (reprogramming) to DDDR pacing. During a median follow-up of 555 days, 53 patients (26%) crossed over from VVIR to DDDR pacing. A decrease in systolic blood pressure during ventricular pacing at the time of pacemaker implantation (p = 0.001), use of beta blockers at the time of randomization (p = 0.01), and nonischemic cardiomyopathy (p = 0.04) were the only variables that predicted crossover in the Cox multivariate regression model. After reprogramming to the dual-chamber mode, patients showed improvement in all aspects of quality of life, with significant improvements in physical and emotional role. The high incidence of crossover from VVIR to DDDR pacing along with significant improvements in quality of life after crossover to DDDR pacing strongly favors dual-chamber pacing compared with single-chamber ventricular pacing in elderly patients requiring permanent pacing.

The acute effects of biatrial pacing on atrial depolarization and repolarization

Permanent biatrial and/or multisite atrial pacing may prevent atrial fibrillation (AF), but the effects on atrial electrophysiology remain incompletely understood. Acute biatrial pacing was studied in 20 patients with and 28 without (controls) a history of atrial fibrillation and/or flutter. Twelve-lead electrocardiograms were recorded during pacing from the high right atrium (RA), from the distal coronary sinus (LA), and biatrial pacing. P wave duration was measured in each lead and the difference between maximum and minimum P duration was termed P wave dispersion. Effective refractory periods (ERPs) were measured during each pacing mode. The dispersion of P wave duration was 35 +/- 14 ms in controls and 40 +/- 29 ms in AF patients (P = 0.17). Compared to RA pacing, LA pacing shortened P duration in controls (127 +/- 18 to 107 +/- 16 ms, P < 0.05) and biatrial pacing markedly shortened P duration in controls (127 +/- 18 to 93 +/- 14 ms, P < 0.05) and AF patients (114 +/- 43 to 97 +/- 21 ms, P < 0.05). P wave dispersion was unaffected. In controls, the LA ERP was longer than the RA ERP. This phenomenon was not present in AF patients, whose LA ERP was shorter than that of controls. Biatrial pacing had no effect on atrial ERPs or the dispersion of atrial refractoriness. In conclusion, acute biatrial pacing does not affect atrial repolarization but it does cause a marked shortening of global biatrial depolarization. Distal coronary sinus pacing produces a shorter P wave than RA pacing. There is substantial dispersion in the surface P wave of the electrocardiogram, the significance of which awaits further study.

Left ventricular tachycardia originating near the left main coronary artery

Eight patients with idiopathic ventricular tachycardia (VT) underwent mapping and radiofrequency ablation. Mapping showed VT originating in the high posterolateral left ventricular outflow tract in proximity to the left main and proximal circumflex coronary arteries. Ablation was not attempted due to this proximity to the left main and proximal circumflex coronary arteries. Ablation was not attempted due to this proximity in 2 patients and limited in 1 patient. It was successful in VT suppression in 5 of 6 patients.

Smoothed Particle Hydrodynamics Simulations of Apsidal and Nodal Superhumps

In recent years, a handful of systems have been observed to show "negative" (nodal) superhumps, with periods slightly shorter than the orbital period. It has been suggested that these modes are a consequence of the slow retrograde precession of the line of nodes in a disk tilted with respect to the orbital plane. Our simulations confirm and refine this model: they suggest a roughly axisymmetric, retrogradely precessing, tilted disk that is driven at a period slightly less than half the orbital period as the tidal field of the orbiting secondary encounters, in turn, the two halves of the disk above and below the midplane. Each of these passings leads to viscous dissipation on one face of an optically thick disk-observers on opposite sides of the disk would each observe one brightening per orbit, but 180 degrees out of phase with each other.

Clinical outcomes after ablation and pacing therapy for atrial fibrillation : a meta-analysis

BACKGROUND

Radiofrequency ablation of the atrioventricular node and permanent pacing are used for symptomatic relief in patients with medically refractory atrial fibrillation. In this study, meta-analysis was used to clarify clinical outcomes and survival after ablation and pacing therapy using data from the published literature.

METHODS AND RESULTS

We used 21 studies with a total of 1181 patients in the meta-analysis. All patients had medically refractory atrial tachyarrhythmias, primarily atrial fibrillation (97%). Nineteen measures of clinical outcome, encompassing quality of life, ventricular function, exercise duration, and healthcare use, were derived from the studies. The meta-analysis demonstrated significant improvement after ablation and pacing therapy in all outcome measures except fractional shortening, which demonstrated a trend toward improvement (P=0.08). Ejection fraction did show significant improvement (P<0.001). The calculated 1-year total and sudden death mortality rates after ablation and pacing therapy were 6.3% and 2.0%, respectively.

CONCLUSIONS

Ablation and pacing therapy improves a broad range of clinical outcomes for patients with medically refractory atrial fibrillation. The calculated 1-year mortality rates after this therapy are low and comparable with medical therapy.

An ATPase/helicase complex is an essential cofactor for oncogenic transformation by c-Myc

The c-Myc transactivation domain was used to affinity purify tightly associated nuclear proteins. Two of these proteins were identified as TIP49 and a novel related protein called TIP48, both of which are highly conserved in evolution and contain ATPase/helicase motifs. TIP49 and TIP48 are complexed with c-Myc in vivo, and binding is dependent on a c-Myc domain essential for oncogenic activity. A missense mutation in the TIP49 ATPase motif acts as a dominant inhibitor of c-Myc oncogenic activity but does not inhibit normal cell growth, indicating that functional TIP49 protein is an essential mediator of c-Myc oncogenic transformation. The TIP49 and TIP48 ATPase/helicase proteins represent a novel class of cofactors recruited by transcriptional activation domains that function in diverse pathways.

Automated pacemaker function

Pacemakers have used automated functions since the introduction of the inhibited mode more than 30 years ago. Currently, virtually all aspects of pacemaker function are subject to automated control, including automated threshold tracking and sensitivity adjustment. These features are designed to enhance patient safety and quality of life, extend battery life, and simplify pacemaker programming and follow-up for health care providers. Many of these automated algorithms are still in evolution and the clinical benefits are not clearly demonstrated for all functions. Although pacemaker function will become increasingly automated, these features should not be accepted uncritically and without demonstrating benefit to the pacemaker patient.

The essential cofactor TRRAP recruits the histone acetyltransferase hGCN5 to c-Myc

The c-Myc protein functions as a transcription factor to facilitate oncogenic transformation; however, the biochemical and genetic pathways leading to transformation remain undefined. We demonstrate here that the recently described c-Myc cofactor TRRAP recruits histone acetylase activity, which is catalyzed by the human GCN5 protein. Since c-Myc function is inhibited by recruitment of histone deacetylase activity through Mad family proteins, these opposing biochemical activities are likely to be responsible for the antagonistic biological effects of c-Myc and Mad on target genes and ultimately on cellular transformation.

Induction of ventricular fibrillation by T wave shocks: observations from monophasic action potential recordings

INTRODUCTION

Shocks given during the vulnerable period of cardiac repolarization may induce ventricular fibrillation (VF). However, the relationship of the vulnerable period and the monophasic action potential (MAP) has not yet been reported in humans. The purpose of this study was, therefore, to determine how the monophasic action potential recorded from the right ventricle correlates with inducibility of VF using T wave shocks during ventricular pacing.

METHODS

Eleven patients undergoing implantable cardioverter defibrillator (ICD) implantation had a MAP catheter positioned in the right ventricle (RV). The local monophasic action potential duration at 90% repolarization (MAP90) duration was measured during pacing at 400 ms. VF induction was attempted by pacing at 400 ms for 10 cycles and then giving a 1.0 joule monophasic T wave shock at varying coupling intervals (CI) to the last paced stimulus. The maximum and minimum CI that induced VF were determined and mapped in relation to the MAP90 recording.

RESULTS

The average paced MAP duration was 275 +/- 20 ms. The minimum and maximum CI to induce VF were 255 +/- 24 ms and 325 +/- 36 ms respectively. This ranged from 93% to 118% of the MAP90 duration but because of delay in conduction time to the MAP catheter, shocks that induced ventricular fibrillation occurred between 74% and 99% of local repolarization time.

CONCLUSION

VF is inducible with low energy T wave shocks falling during the last 25% of the right ventricular MAP90 recording. This corresponds with VF initiation during phase III repolarization.