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Background: The transmural distribution of apamin-sensitive small conductance Ca(2+)-activated K(+) (SK) current (IKAS) in failing human ventricles remains unclear., Methods and Results: We optically mapped left ventricular wedge preparations from 12 failing native hearts and 2 rejected cardiac allografts explanted during transplant surgery. We determined transmural action potential duration (APD) before and after 100 nmol/L apamin administration in all wedges and after sequential administration of apamin, chromanol, and E4031 in 4 wedges. Apamin prolonged APD from 363 ms (95% confidence interval [CI], 341-385) to 409 (95% CI, 385-434; P<0.001) in all hearts, and reduced the transmural conduction velocity from 36 cm/s (95% CI, 30-42) to 32 cm/s (95% CI, 27-37; P=0.001) in 12 native failing hearts at 1000 ms pacing cycle length (PCL). The percent APD prolongation is negatively correlated with baseline APD and positively correlated with PCL. Only 1 wedge had M-cell islands. The percentages of APD prolongation in the last 4 hearts at 2000 ms PCL after apamin, chromanol, and E4031 were 9.1% (95% CI, 3.9-14.2), 17.3% (95% CI, 3.1-31.5), and 35.9% (95% CI, 15.7-56.1), respectively. Immunohistochemical staining of subtype 2 of SK protein showed increased expression in intercalated discs of myocytes., Conclusions: SK current is important in the transmural repolarization in failing human ventricles. The magnitude of IKAS is positively correlated with the PCL, but negatively correlated with APD when PCL is fixed. There is abundant subtype 2 of SK protein in the intercalated discs of myocytes., (© 2015 American Heart Association, Inc.)

Spinal cord stimulation with implantable devices has been used worldwide for decades to treat regional pain conditions and cardiac angina refractory to conventional therapies. Preclinical studies with spinal cord stimulation in experimental animal models of heart disease have described interesting effects on cardiac and autonomic nervous system physiology. In canine and porcine animals with failing hearts, spinal cord stimulation reverses left ventricular dilation and improves cardiac function, while suppressing the prevalence of cardiac arrhythmias. In this paper, we present further canine studies that determined the optimal site and intensity of spinal cord stimulation that produced the most robust and beneficial clinical response in heart failure animals. We then explore and discuss the clinically relevant aspects and potential impediments that may be encountered in translating spinal cord stimulation to human patients with advanced cardiac disease.

Background: Ischemia suppresses action potentials (APs) by elevating interstitial K(+) and activating KATP channels and alters cytosolic Ca(2+) transients (CaTs) via metabolic inhibition., Objective: To test the hypothesis that AP and CaT respond to ischemia with different spatiotemporal courses and patterns., Methods: Thirty-four transmural wedges were isolated from canine left ventricular free walls, perfused arterially, and stained with voltage- and Ca(2+)-sensitive dyes. Twenty-eight wedges underwent 15 minutes of arterial occlusion during pacing at a cycle length (PCL) of 300 ms (n = 19) or 600 ms (n = 9). Six other wedges had a sequential reduction of perfusion flow from full to 50%, 25%, and 10% at 300 ms PCL. AP and CaT were recorded on the cut-exposed transmural surfaces with an optical mapping system., Results: Although ischemia suppressed APs, it enhanced CaT to 150% ± 10% (more in the endocardium than in the epicardium) and induced CaT alternans during the first 2 minutes of arterial occlusion and then suppressed CaT (PCL = 300 ms). Enhancement of CaT (to 159% ± 23%) also occurred during low flow (25%) perfusion (PCL = 300 ms). Faster suppression of AP occurred with subepicardial preference as compared to that of CaT. After 15 minutes of arterial occlusion, AP and CaT remained in only small regions during 300 ms PCL but were preserved in most regions during 600 ms PCL., Conclusions: Early ischemia induced a surge and alternans in CaT and caused its dissociation from AP both in time course of suppression and in spatial distribution. These results suggested that there were different cellular regulatory mechanisms of AP and of CaT in responding to ischemia from arterial occlusion., (Copyright © 2013 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: We previously reported that IKAS are heterogeneously upregulated in failing rabbit ventricles and play an important role in arrhythmogenesis. This study goal is to test the hypothesis that subtype 2 of the small-conductance Ca(2+) activated K(+) (SK2) channel and apamin-sensitive K(+) currents (IKAS) are upregulated in failing human ventricles., Methods and Results: We studied 12 native hearts from transplant recipients (heart failure [HF] group) and 11 ventricular core biopsies from patients with aortic stenosis and normal systolic function (non-HF group). IKAS and action potential were recorded with patch-clamp techniques, and SK2 protein expression was studied by Western blotting. When measured at 1 μmol/L Ca(2+) concentration, IKAS was 4.22 (median) (25th and 75th percentiles, 2.86 and 6.96) pA/pF for the HF group (n=11) and 0.98 (0.54 and 1.72) pA/pF for the non-HF group (n=8, P=0.008). IKAS was lower in the midmyocardial cells than in the epicardial and the endocardial cells. The Ca(2+) dependency of IKAS in HF myocytes was shifted leftward compared to non-HF myocytes (Kd 314 versus 605 nmol/L). Apamin (100 nmol/L) increased the action potential durations by 1.77% (-0.9% and 7.3%) in non-HF myocytes and by 11.8% (5.7% and 13.9%) in HF myocytes (P=0.02). SK2 protein expression was 3-fold higher in HF than in non-HF., Conclusions: There is heterogeneous upregulation of IKAS densities in failing human ventricles. The midmyocardial layer shows lower IKAS densities than epicardial and endocardial layers of cells. Increase in both Ca(2+) sensitivity and SK2 protein expression contributes to the IKAS upregulation.

Heart failure is the final common pathway in many forms of heart disease, and is associated with excessive morbidity and mortality. Pathophysiologic alterations in the interaction between the heart and the autonomic nervous system in advanced heart failure have been noted for decades. Over the last decade, great advances have been made in the medical and surgical treatment of heart failure - and some of these modalities target the neuro-cardiac axis. Despite these advances, many patients progress to end-stage heart failure and death. Recently, device-based therapy targeting the neuro-cardiac axis with various forms of neuromodulatory stimuli has been shown to improve heart function in experimental heart failure models. These include spinal cord stimulation, vagal nerve stimulation, and baroreflex modulation. Human trials are now underway to evaluate the safety and efficacy of these device-based neuromodulatory modalities in the heart failure population.

Atrial fibrillation (AF) is a common cardiac arrhythmia that is associated with severe consequences, including symptoms, haemodynamic instability, increased cardiovascular mortality and stroke. While other arrhythmias such as torsades de pointes and sinus bradycardia are more typically thought of as drug induced, AF may also be precipitated by drug therapy, although ascribing causality to drug-associated AF is more difficult than with other drug-induced arrhythmias. Drug-induced AF is more likely to occur in patients with risk factors and co-morbidities that commonly co-exist with AF, such as advanced age, alcohol consumption, family history of AF, hypertension, thyroid dysfunction, sleep apnoea and heart disease. New-onset AF has been associated with cardiovascular drugs such as adenosine, dobutamine and milrinone. In addition, medications such as corticosteroids, ondansetron and antineoplastic agents such as paclitaxel, mitoxantrone and doxorubicin have been reported to induce AF. Whether bisphosphonate drugs are associated with new-onset AF remains controversial and requires further study. The potential contribution of specific drug therapy should be considered when patients present with new-onset AF.

Rationale: Fibrillation/defibrillation episodes in failing ventricles may be followed by action potential duration (APD) shortening and recurrent spontaneous ventricular fibrillation (SVF)., Objective: We hypothesized that activation of apamin-sensitive small-conductance Ca(2+)-activated K(+) (SK) channels is responsible for the postshock APD shortening in failing ventricles., Methods and Results: A rabbit model of tachycardia-induced heart failure was used. Simultaneous optical mapping of intracellular Ca(2+) and membrane potential (V(m)) was performed in failing and nonfailing ventricles. Three failing ventricles developed SVF (SVF group); 9 did not (no-SVF group). None of the 10 nonfailing ventricles developed SVF. Increased pacing rate and duration augmented the magnitude of APD shortening. Apamin (1 μmol/L) eliminated recurrent SVF and increased postshock APD(80) in the SVF group from 126±5 to 153±4 ms (P<0.05) and from 147±2 to 162±3 ms (P<0.05) in the no-SVF group but did not change APD(80) in nonfailing group. Whole cell patch-clamp studies at 36°C showed that the apamin-sensitive K(+) current (I(KAS)) density was significantly larger in the failing than in the normal ventricular epicardial myocytes, and epicardial I(KAS) density was significantly higher than midmyocardial and endocardial myocytes. Steady-state Ca(2+) response of I(KAS) was leftward-shifted in the failing cells compared with the normal control cells, indicating increased Ca(2+) sensitivity of I(KAS) in failing ventricles. The K(d) was 232±5 nmol/L for failing myocytes and 553±78 nmol/L for normal myocytes (P=0.002)., Conclusions: Heart failure heterogeneously increases the sensitivity of I(KAS) to intracellular Ca(2+), leading to upregulation of I(KAS), postshock APD shortening, and recurrent SVF.

Background: Although radiofrequency catheter ablation (RFCA) has been used to treat patients with Brugada syndrome (BS), it is difficult to eliminate polymorphic ventricular tachycardias (VTs) completely., Objective: The purpose of this study was to determine the efficacy of RFCA in eliminating recurrent VTs in an experimental model of BS., Methods: We optically mapped electrical activity on the epicardial (n = 9) or transmural (n = 8) surface in 17 arterially perfused canine right ventricle preparations. Using pinacidil (5 microM) and pilsicainide (5 microM), we induced a model of BS that showed spontaneous VT. We then applied RFCA to the earliest activation site of premature ventricular complexes (PVCs) in the epicardium (EPI) or endocardium (ENDO) of the RV., Results: After induction of BS, the transmural electrocardiogram (ECG) showed BS-type ECG in association with prominent heterogeneity of action potential duration (APDs) within the EPI (APD: maximum 272 +/- 39 ms, minimum 200 +/- 39 ms, P < .01), but not within the ENDO. PVCs originated in the EPI region having short APDs and triggered functional reentry causing VT. Multiple epicardial foci of PVCs existed in each tissue (3.7 +/- 1.9 foci/tissue). RFCA at the earliest activation site of PVCs in the EPI disconnected the short and long APD regions and eliminated all PVCs and VTs, although APD heterogeneity still existed. All successful RFCA lesions were confined to the EPI. RFCA in the ENDO failed to eliminate VT or PVCs., Conclusion: These experimental observations suggest that RFCA applied to the EPI may be more effective than applied to the ENDO in eliminating VT in patients with BS.

The high-affinity choline transporter (CHT1) system is an attractive target for the development of positron emission tomography (PET) biomarkers to probe brain, cardiac, and cancer diseases. An efficient and convenient synthesis of new radiolabeled CHT1 inhibitors [(11)C]hemicholinium-3 and [(18)F]hemicholinium-3 by solid-phase extraction (SPE) technique using a cation-exchange CM Sep-Pak cartridge has been well developed. The preliminary evaluation of both tracers through biodistribution studies in 9L-glioma rats has been performed, and the uptakes in the heart and tumor were observed, while very low brain uptake was seen.

[(11)C]Hemicholinium-15 ([(11)C]HC-15) and [(18)F]hemicholinium-15 ([(18)F]HC-15) have been synthesized as new potential PET tracers for the heart high-affinity choline uptake (HACU) system. [(11)C]HC-15 was prepared by N-[(11)C]methylation of the appropriate precursor, 4-methyl-2-phenyl-morpholin-2-ol, using [(11)C]CH(3)OTf in 55-70% radiochemical yield decay corrected to end of bombardment (EOB) and 2-3Ci/mumol specific activity at end of synthesis (EOS). [(18)F]HC-15 was prepared by N-[(18)F]fluoromethylation of the precursor using [(18)F]FCH(2)OTf in 20-30% radiochemical yield decay corrected to EOB and >1.0Ci/mumol specific activity at EOS. The biodistribution of both compounds was determined in rats at 20min post-intravenous injection, and the results show the heart region uptakes 1.32+/-0.75%ID/g in R-ventricle for [(11)C]HC-15 and 1.28+/-0.81%ID/g in L-ventricle for [(18)F]HC-15, respectively. The dynamic PET imaging studies of [(11)C]HC-15 in rats were acquired 60min post-intravenous injection of the tracer using the IndyPET-II scanner. For the blocking experiments, the rats were intravenously pretreated with 3.0mg/kg of unlabeled HC-15 prior to [(11)C]HC-15 injection. [(11)C]HC-15 rat heart PET studies show rapid heart uptake to give clear heart images. The rat heart PET blocking studies found no significant blocking effect. The dynamic PET studies in normal and ablated dogs were performed using Siemens PET scanner with [(13)N]NH(3), [(11)C]HC-15, and [(18)F]HC-15. PET studies in dogs of both [(11)C]HC-15 and [(18)F]HC-15 also show significant heart uptake and give images of the heart. However, there is no significant change in [(11)C]HC-15 L-ventricle uptake following radiofrequency ablation in the dog. These results suggest that the localization of HC-15 tracers in the heart is mediated by non-specific processes, and the visualization of HC-15 tracers on the heart is related to non-specific binding of HACU.

A new AChE tracer N-[(11)C]methyl-3-[[(dimethylamino)carbonyl]oxy]-2-(2',2'-diphenylpropionoxymethyl)pyridinium ([(11)C]MDDP, [(11)C]1) has been synthesized in 40-65% radiochemical yield. Initial PET dynamic studies of [(11)C]MDDP in rat heart showed rapid heart uptake and blood pool clearance to give high-quality heart images. Blocking studies of [(11)C]MDDP with pretreatment drug neostigmine in rats found only minor reductions in rat heart [(11)C]MDDP retention. The results suggest that [(11)C]MDDP delineates the heart very clearly, and the uptakes of [(11)C]MDDP in rat heart might be related to non-specific binding.

Objectives: We used optical mapping to characterize the reentrant circuit of ventricular tachycardia (VT) during acute myocardial infarction (MI) in isolated canine left ventricular preparations., Background: The nature of the reentrant circuit that underlies VT during acute MI is not well understood., Methods: Using optical mapping in isolated canine left ventricular preparations, we characterized the reentrant circuit of monomorphic VT (mean cycle length 245.3 +/- 15.6 ms, n = 7) induced by programmed stimulation during acute MI., Results: Optical mapping during VT revealed a functional reentrant circuit consisting of four components: (1) a protected isthmus located between the infarction area and the functional line of block; (2) an entrance site located at one end of the isthmus; (3) an exit site located at the other end of the isthmus; and (4) an outer loop consisting of nonischemic normal tissue, connecting the exit and entrance sites. Rate-dependent slow conduction within the border zone was associated with significant changes (n = 6) in action potential amplitude (99.1 +/- 0.4 vs 71.4 +/- 0.6 mV, P < .01), maximal diastolic potential (-80.6 +/- 0.2 vs -65.4 +/- 0.6 mV, P < .05), action potential duration at 90% repolarization (APD(90); 188.4 +/- 1.0 vs 164.3 +/- 3.1 ms, P < .05), and dV/dt (302.4 +/- 7.9 vs 168.5 +/- 3.6 V/s, P < .05). Compared to preparations with no inducible VT (n = 7), formation of a functional line of block was the key mechanism for initiation of functional reentry in preparations with VT. When comparing preparations with sustained and nonsustained VT, preservation of slow conduction over the isthmus was the key component for maintenance of sustained VT., Conclusions: The reentrant circuit of monomorphic VT in the setting of acute MI involved both the infarction border zone and nonischemic normal tissue. The underlying mechanism is related to the presence of rate-dependent slow conduction and the development of a functional line of block in the border zone.

A series of 11C-labeled analogs of the acetylcholinesterase (AChE) inhibitor pyridostigmine have been synthesized for evaluation as new potential positron emission tomography (PET) imaging agents for heart AChE. The appropriate precursors for radiolabeling were slightly modified from commercial reagents. The new tracers [11C]pyridostigmine (1), [11C]para-pyridostigmine (2) and [11C]ortho-pyridostigmine (3) were prepared by N-[11C]methylation of the precursors using [11C]methyl triflate. Pure target compounds were isolated by a solid-phase extraction (SPE) purification procedure with 60-85% radiochemical yields (decay corrected to end of bombardment), and a synthesis time of 10-15 min. The initial PET dynamic studies of compounds (1-3) in rat heart showed rapid heart uptake and blood pool clearance to give high quality heart images. These results suggest the new tracers delineate the heart very clearly and could be potential heart AChE imaging agents.

Management of anti-coagulation in the early period after orthotopic heart transplantation, when the frequency of invasive procedures to assess for graft rejection is high, presents a difficult clinical problem in which the need for effective therapy must be weighed against the desire for outpatient treatment. In this report, we summarize the clinical course and long-term outcome of 6 patients from our center in whom vascular thrombosis was treated on an outpatient basis with enoxaparin. We conclude that the use of enoxaparin may provide a safe and reasonable alternative to conventional anti-coagulation therapy during this period.

Introduction: We previously demonstrated in dogs that a transient rate increase superimposed on bradycardia causes prolongation of ventricular refractoriness that persists for hours after resumption of bradycardia. In this study, we examined changes in membrane currents that are associated with this phenomenon., Methods and Results: The whole cell, patch clamp technique was used to record transmembrane voltages and currents, respectively, in single mid-myocardial left ventricular myocytes from dogs with 1 week of complete AV block; dogs either underwent 1 hour of left ventricular pacing at 120 beats/min or did not undergo pacing. Pacing significantly heightened mean phase 1 and peak plateau amplitudes by approximately 6 and approximately 3 mV, respectively (P < 0.02), and prolonged action potential duration at 90% repolarization from 235+/-8 msec to 278+/-8 msec (1 Hz; P = 0.02). Rapid pacing-induced changes in transmembrane ionic currents included (1) a more pronounced cumulative inactivation of the 4-aminopyridine-sensitive transient outward K+ current, Ito, over the range of physiologic frequencies, resulting from a approximately 30% decrease in the population of quickly reactivating channels; (2) increases in peak density of L-type Ca2+ currents, I(Ca.L), by 15% to 35 % between +10 and +60 mV; and (3) increases in peak density of the Ca2+-activated chloride current, I(Cl.Ca), by 30% to 120% between +30 and +50 mV., Conclusion: Frequency-dependent reduction in Ito combined with enhanced I(Ca.L) causes an increase in net inward current that may be responsible for the observed changes in ventricular repolarization. This augmentation of net cation influx is partially antagonized by an increase in outward I(Ca.Cl).

Treatment with proinflammatory prostaglandin E2 (PGE2) produced a transient sensitization of whole-cell currents elicited by the vanilloid capsaicin. The intracellular signaling pathways that mediate the initiation of this PGE2-induced sensitization of the capsaicin-elicited current in rat sensory neurons are not well established. Treatment with either forskolin (100 nM to 10 microM) or membrane-permeant analogs of cAMP, 8-bromo-cAMP (8-Br-cAMP) and chlorphenylthio-cAMP (10 microM to 1 mM), transiently sensitized neuronal responses elicited by capsaicin in a manner analogous to that produced by PGE2. The duration of sensitization was lengthened with increasing concentrations of forskolin; however, higher concentrations of 8-Br-cAMP or chlorphenylthio-cAMP led to a shortening of sensitization. The inactive analog of forskolin, dideoxy-forskolin, had no effect on capsaicin responses. Inclusion of the inhibitor of protein kinase A in the recording pipette completely suppressed the sensitization produced by PGE2 or forskolin. In recordings from membrane patches in the cell-attached configuration, the bath application of capsaicin evoked single-channel currents in which the level of channel activity was concentration-dependent and had an EC50 of 1.4 microM. These single-channel currents evoked by capsaicin exhibited an apparent reversal potential of +4 mV and were blocked by the capsaicin antagonist capsazepine. Exposure of the sensory neuron to either PGE2 or forskolin produced a large and transient increase in the mean channel activity (NPo) elicited by capsaicin, although the unitary conductance remained unaltered. Taken together, these observations suggest that modulation of the capsaicin-gated channel by the cAMP-protein kinase A signaling pathway enhanced the gating of these channels and consequently resulted in the sensitization of the whole-cell currents.

Pro-inflammatory prostaglandins are known to enhance the sensitivity of sensory neurons to various modalities of stimulation, including the excitatory chemical agent, capsaicin. In this report, we examined the capacity of prostaglandin E2 (PGE2) to enhance the capsaicin response recorded from sensory neurons isolated from embryonic rats and grown in culture. Previous work demonstrated that the cyclic adenosine 3',5'-monophosphate pathway mediates initiation of the PGE2-induced sensitization, however, little is known about the pathways regulating the recovery from sensitization. Therefore, we examined the neuronal transduction cascades that control the duration of sensitization. Treatment with PGE2 enhanced the capsaicin-evoked current by two- to threefold, however, this sensitization was transient even in the continued presence of prostaglandin. The duration of sensitization produced by PGE2 was related inversely to the extracellular Ca2+ concentration with the shortest recovery times observed in cells exposed to 2 mM Ca2+-Ringer. Inclusion of the Ca2+ chelator, bis-(o-aminophenoxy)-N, N,N',N'-tetraacetic acid, in the recording pipette greatly lengthened the period of sensitization. Pretreatment with either the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (L-NAME), or the inhibitor of the cyclic guanosine 3', 5'-monophosphate (GMP)-dependent protein kinase, KT-5823, before the application of PGE2 increased the duration of sensitization even in the presence of 2 mM Ca2+. In contrast, after attaining maximal sensitization in 2 mM Ca2+-Ringer containing L-NAME, the addition of either nitric oxide donors (3-morpholinosydnonimine or s-nitroso-n-acetylpenicillamine) or 8-Br-cyclic GMP led to a rapid decrease in the level of sensitization. In the absence of sensitization, nitric oxide-cyclic GMP modulating agents had no effect on the capsaicin-evoked current. Therefore, these results suggest that capsaicin-induced elevations in intracellular Ca2+ levels lead to an enhanced production of cyclic GMP, via the nitric oxide pathway, that ultimately activates cyclic GMP-dependent protein kinase. This protein kinase inactivates or terminates the sensitization produced by PGE2 by an as yet unidentified mechanism.

The capacity of the proinflammatory cytokines, tumor necrosis factor alpha (TNF alpha) and interleukin 1 beta (IL-1 beta), to modulate the sensitivity of isolated sensory neurons grown in culture to the excitatory chemical agent capsaicin was examined. Alterations in capsaicin sensitivity were assessed by quantifying the number of neurons labeled with cobalt after exposure to capsaicin and by recording the whole-cell response from a single neuron to the focal application of capsaicin. A 24 hr pretreatment of the neuronal cultures with TNF alpha (10 or 50 ng/ml), but not IL-1 beta (10 or 50 ng/ml), produced a concentration-dependent increase in the number of cobalt-labeled neurons after exposure to 100 nM capsaicin. The peak increase in the number of labeled neurons was attained after a 4 hr treatment with 10 ng/ml TNF alpha. Similarly, pretreatment with TNF alpha (10 ng/ml for 4, 12, and 24 hr) produced a greater than twofold increase in the average peak amplitude of the inward current evoked by 100 nM capsaicin. Both the TNF alpha-induced increase in labeling and current amplitude were blocked by treating the neuronal cultures with indomethacin before the addition of TNF alpha. Enhancement of the capsaicin-evoked current also was blocked by the specific cyclo-oxygenase-2 inhibitor SC-236. These results indicate that TNF alpha can enhance the sensitivity of sensory neurons to the excitation produced by capsaicin and that this enhancement likely is mediated by the neuronal production of prostaglandins. Isolated sensory neurons grown in culture may prove to be a useful model system in which to explore how prolonged exposure to mediators associated with chronic inflammation alter the regulatory pathways that modulate the excitability of the nervous system.