Cambios del periodo refractario efectivo auricular y de la IKACh tras estimulación vagal más estimulación eléctrica rápida en venas pulmonares

Regulating the Warburg effect on metabolic stress and myocardial fibrosis remodeling and atrial intracardiac waveform activity induced by atrial fibrillation

Atrial fibrillation (AF) is associated with metabolic stress and induces myocardial fibrosis reconstruction by increasing glycolysis. One goal in the treatment of paroxysmal AF (p-AF) is to improve myocardial fibrosis reconstruction and myocardial metabolic stress caused by the Warburg effect. Adopted male canine that rapid right atrial pacing (RAP) for 6 days to establish a p-AF model. The canines were pre-treated with phenylephrine (PE) or dichloroacetic acid (DCA) before exposure to p-AF or non-p-AF. P-wave duration (P_max), minimum P-wave duration (P_min), P wave dispersion (PWD), atrial effective refractory period (AERP) and AERP dispersion (AERPd) were measured in canine atrial cardiomyocytes. Pyruvate dehydrogenase kinase-1 (PDK-1), PDK-4, lactate dehydrogenase A (LDHA), pyruvate dehydrogenase (PDH), citrate synthase (CS), isocitrate dehydrogenase (IDH), and matrix metalloproteinase 9 (MMP-9) were evaluated by western blotting and reverse transcription polymerase chain reaction (RT-PCR), content of adenosine monophosphate (AMP), adenosine triphosphate (ATP), lactic acid and glycogen, and activity of LDHA, PDK-1 and PDK-4 were evaluated by enzyme-linked immunosorbent assay (ELISA), myocardial tissue glycogen content was evaluated by PAS, myocardial fibrosis remodeling was evaluated by hematoxylin and eosin (H&E) and Masson staining. Our findings demonstrated that p-AF increases the Warburg effect-related metabolic stress and myocardial fibrosis remodeling by increasing the expression and activity of PDK-1, PDK-4, and LDHA, content of AMP and lactic acid, and the ratio of AMP/ATP and decreasing the expression of PDH, CS, and IDH, and glycogen content. In addition, p-AF can induce cardiomyocyte fibrosis remodeling and increase MMP-9 expression, and p-AF also increases atrial intracardiac waveform activity by prolonging P_max, P_min, PWD, and AERPd and shortening AERP. PDK isoforms agonists (PE) produce a similar p-AF pathological effect and can produce synergistic effects with p-AF, further increasing Warburg effect-related metabolic stress, myocardial fibrosis remodeling, and atrial intracardiac waveform activity. In contrast, the use of PDK-specific inhibitors (DCA) completely reverses these pathophysiological changes induced by p-AF. We demonstrate that p-AF can induce the Warburg effect in canine atrial cardiomyocytes and significantly improve p-AF-induced metabolic stress, myocardial fibrosis remodeling, and atrial intracardiac waveform activity by inhibiting the Warburg effect.

In Silico Assessment of Efficacy and Safety of IKur Inhibitors in Chronic Atrial Fibrillation: Role of Kinetics and State-Dependence of Drug Binding

Current pharmacological therapy against atrial fibrillation (AF), the most common cardiac arrhythmia, is limited by moderate efficacy and adverse side effects including ventricular proarrhythmia and organ toxicity. One way to circumvent the former is to target ion channels that are predominantly expressed in atria vs. ventricles, such as K_V1.5, carrying the ultra-rapid delayed-rectifier K⁺ current (I_Kur). Recently, we used an in silico strategy to define optimal K_V1.5-targeting drug characteristics, including kinetics and state-dependent binding, that maximize AF-selectivity in human atrial cardiomyocytes in normal sinus rhythm (nSR). However, because of evidence for I_Kur being strongly diminished in long-standing persistent (chronic) AF (cAF), the therapeutic potential of drugs targeting I_Kur may be limited in cAF patients. Here, we sought to simulate the efficacy (and safety) of I_Kur inhibitors in cAF conditions. To this end, we utilized sensitivity analysis of our human atrial cardiomyocyte model to assess the importance of I_Kur for atrial cardiomyocyte electrophysiological properties, simulated hundreds of theoretical drugs to reveal those exhibiting anti-AF selectivity, and compared the results obtained in cAF with those in nSR. We found that despite being downregulated, I_Kur contributes more prominently to action potential (AP) and effective refractory period (ERP) duration in cAF vs. nSR, with ideal drugs improving atrial electrophysiology (e.g., ERP prolongation) more in cAF than in nSR. Notably, the trajectory of the AP during cAF is such that more I_Kur is available during the more depolarized plateau potential. Furthermore, I_Kur block in cAF has less cardiotoxic effects (e.g., AP duration not exceeding nSR values) and can increase Ca²⁺ transient amplitude thereby enhancing atrial contractility. We propose that in silico strategies such as that presented here should be combined with in vitro and in vivo assays to validate model predictions and facilitate the ongoing search for novel agents against AF.

Revealing kinetics and state-dependent binding properties of IKur-targeting drugs that maximize atrial fibrillation selectivity

The K_V1.5 potassium channel, which underlies the ultra-rapid delayed-rectifier current (I_Kur) and is predominantly expressed in atria vs. ventricles, has emerged as a promising target to treat atrial fibrillation (AF). However, while numerous K_V1.5-selective compounds have been screened, characterized, and tested in various animal models of AF, evidence of antiarrhythmic efficacy in humans is still lacking. Moreover, current guidelines for pre-clinical assessment of candidate drugs heavily rely on steady-state concentration-response curves or IC₅₀ values, which can overlook adverse cardiotoxic effects. We sought to investigate the effects of kinetics and state-dependent binding of I_Kur-targeting drugs on atrial electrophysiology in silico and reveal the ideal properties of I_Kur blockers that maximize anti-AF efficacy and minimize pro-arrhythmic risk. To this aim, we developed a new Markov model of I_Kur that describes K_V1.5 gating based on experimental voltage-clamp data in atrial myocytes from patient right-atrial samples in normal sinus rhythm. We extended the I_Kur formulation to account for state-specificity and kinetics of K_V1.5-drug interactions and incorporated it into our human atrial cell model. We simulated 1- and 3-Hz pacing protocols in drug-free conditions and with a [drug] equal to the IC₅₀ value. The effects of binding and unbinding kinetics were determined by examining permutations of the forward (k_on) and reverse (k_off) binding rates to the closed, open, and inactivated states of the K_V1.5 channel. We identified a subset of ideal drugs exhibiting anti-AF electrophysiological parameter changes at fast pacing rates (effective refractory period prolongation), while having little effect on normal sinus rhythm (limited action potential prolongation). Our results highlight that accurately accounting for channel interactions with drugs, including kinetics and state-dependent binding, is critical for developing safer and more effective pharmacological anti-AF options.

Effects of extrinsic cardiac nerve stimulation on atrial fibrillation inducibility: The regulatory role of the spinal cord

OBJECTIVE

To investigate the effect of the mutual regulation of the extrinsic cardiac nerves on atrial electrophysiology and atrial fibrillation (AF) vulnerability.

METHODS AND RESULTS

Fourteen dogs were randomly divided into two groups: spinal cord stimulation (SCS) group (n = 7) and spinal cord block (SCB) group (n = 7). SCS was performed with 90% of the threshold voltage stimulating the T₁ -T₂ spinal level, while SCB was performed by injecting 2% lidocaine into the epidural space at the T_2-3 level. The effective refractory period (ERP), ERP dispersion, and AF inducibility were measured during atrial pacing combined with different extrinsic cardiac nerve stimulation. ERPs were decreased in the atrium and pulmonary veins and ERP dispersion was increased from baseline during left cervical vagus nerve stimulation (VNS) or left stellate ganglion stimulation (SGS) in the two groups. When combined with SCS, VNS resulted in diminished ERPs at all recording sites, longer ERP dispersion and more episodes of AF than were observed during VNS, whereas ERPs were greater and correspondingly fewer episodes of AF occurred during SCS combined with SGS than SGS. In the SCB group, ERPs were shortened, ERP dispersion was lengthened, and episodes of AF were increased during SGS after SCB. SCS enhanced the activity of the left vagus nerve but attenuated the left stellate ganglion and superior left ganglionated plexus.

CONCLUSION

SCS modulates extrinsic and intrinsic cardiac nerve activity among the vagus nerve, stellate ganglion, and ganglionated plexus. SCS facilitates the effect of VNS and attenuates the effect of SGS on atrial electrophysiology.