Ivabradine, coronary artery disease, and heart failure: beyond rhythm control

A Photoactivatable Version of Ivabradine Enables Light-Induced Block of HCN Current In Vivo

Therapeutic drugs, whose bioactivity is hindered by a photoremovable cage, offer the advantage of spatiotemporal confinement of their action to the target diseased tissue with improved bioavailability and efficacy. Here, we have applied such an approach to ivabradine (IVA), a bradycardic agent indicated for angina pectoris and heart failure, acting as a specific HCN channel blocker. To overcome the side effects due to its poor discrimination among HCN channel subtypes (HCN1-4), we prepared a caged version of IVA linked to a photocleavable bromoquinolinylmethyl group (BHQ-IVA). We show that upon illumination with blue light (440 nm), BHQ-IVA releases active IVA that blocks HCN channel currents in vitro and exerts a bradycardic effect in vivo. Both BHQ-IVA and the cage are inactive. Caging is stable in aqueous medium and in the dark, and it does not impair aqueous solubility and cell permeation, indispensable for IVA activity. This approach allows for bypassing the poor subtype-specificity of IVA, expanding its prescription to HCN-related diseases besides cardiac.

The effect of ivabradine therapy on dilated cardiomyopathy patients with congestive heart failure: a systematic review and meta-analysis

Background

Ivabradine improves cardiac function in patients with heart failure, but its effect on dilated cardiomyopathy (DCM) remains unclear. We performed a systematic review and meta-analysis to study the efficacy and potential mechanisms of ivabradine's effect on cardiac function and prognosis in patients with DCM.

Methods

We searched PubMed, Cochrane Library, Embase, Web of Science, and four registers through September 28, 2022. All controlled trials of ivabradine for the treatment of DCM with congestive heart failure were included. Articles were limited to English, with the full text and necessary data available. We performed random- or fixed effects meta-analyses for all included outcome measures and compared the effect sizes for outcomes in patients treated with and without ivabradine. The quality of the studies was assessed using the Cochrane risk-of-bias tool for randomized trials (RoB2.0).

Findings

Five trials with 357 participants were included. The pooled risk ratio was 0.48 [95% confidence interval (CI) (0.18, 1.25)] for all-cause mortality and 0.38 [95% CI (0.12, 1.23)] for cardiac mortality. The pooled mean difference was -15.95 [95% CI (-19.97, -11.92)] for resting heart rate, 3.96 [95% CI (0.99, 6.93)] for systolic blood pressure, 2.93 [95% CI (2.09, 3.77)] for left ventricular ejection fraction, -5.90 [95% CI (-9.36, -2.44)] for left ventricular end-systolic diameter, -3.41 [95% CI (-5.24, -1.58)] for left ventricular end-diastolic diameter, -0.81 [95% CI (-1.00, -0.62)] for left ventricular end-systolic volume, -0.67 [95% CI (-0.86, -0.48)] for left ventricular end-diastolic volume, -11.01 [95% CI (-19.66, -2.35)] for Minnesota Living with Heart Failure score, and -0.52 [95% CI (-0.73, -0.31)] for New York Heart Association class.

Interpretation

Ivabradine reduces heart rate and ventricular volume, and improves cardiac function in patients with DCM, but showed no significant effect on the prognosis of patients.

The Bradycardic Agent Ivabradine Acts as an Atypical Inhibitor of Voltage-Gated Sodium Channels

Background and purpose: Ivabradine is clinically administered to lower the heart rate, proposedly by inhibiting hyperpolarization-activated cyclic nucleotide-gated cation channels in the sinoatrial node. Recent evidence suggests that voltage-gated sodium channels (VGSC) are inhibited within the same concentration range. VGSCs are expressed within the sinoatrial node and throughout the conduction system of the heart. A block of these channels thus likely contributes to the established and newly raised clinical indications of ivabradine. We, therefore, investigated the pharmacological action of ivabradine on VGSCs in sufficient detail in order to gain a better understanding of the pro- and anti-arrhythmic effects associated with the administration of this drug.

Experimental Approach: Ivabradine was tested on VGSCs in native cardiomyocytes isolated from mouse ventricles and the His-Purkinje system and on human Na_v1.5 in a heterologous expression system. We investigated the mechanism of channel inhibition by determining its voltage-, frequency-, state-, and temperature-dependence, complemented by a molecular drug docking to the recent Na_v1.5 cryoEM structure. Automated patch-clamp experiments were used to investigate ivabradine-mediated changes in Na_v1.5 inactivation parameters and inhibition of different VGSC isoforms.

Key results: Ivabradine inhibited VGSCs in a voltage- and frequency-dependent manner, but did not alter voltage-dependence of activation and fast inactivation, nor recovery from fast inactivation. Cardiac (Na_v1.5), neuronal (Na_v1.2), and skeletal muscle (Na_v1.4) VGSC isoforms were inhibited by ivabradine within the same concentration range, as were sodium currents in native cardiomyocytes isolated from the ventricles and the His-Purkinje system. Molecular drug docking suggested an interaction of ivabradine with the classical local anesthetic binding site.

Conclusion and Implications: Ivabradine acts as an atypical inhibitor of VGSCs. Inhibition of VGSCs likely contributes to the heart rate lowering effect of ivabradine, in particular at higher stimulation frequencies and depolarized membrane potentials, and to the observed slowing of intra-cardiac conduction. Inhibition of VGSCs in native cardiomyocytes and across channel isoforms may provide a potential basis for the anti-arrhythmic potential as observed upon administration of ivabradine.

Frequency-Dependent Properties of the Hyperpolarization-Activated Cation Current, If, in Adult Mouse Heart Primary Pacemaker Myocytes

A number of distinct electrophysiological mechanisms that modulate the myogenic spontaneous pacemaker activity in the sinoatrial node (SAN) of the mammalian heart have been investigated extensively. There is agreement that several (3 or 4) different transmembrane ionic current changes (referred to as the voltage clock) are involved; and that the resulting net current interacts with direct and indirect effects of changes in intracellular Ca²⁺ (the calcium clock). However, significant uncertainties, and important knowledge gaps, remain concerning the functional roles in SAN spontaneous pacing of many of the individual ion channel- or exchanger-mediated transmembrane current changes. We report results from patch clamp studies and mathematical modeling of the hyperpolarization-activated current, I_f, in the generation/modulation of the diastolic depolarization, or pacemaker potential, produced by individual myocytes that were enzymatically isolated from the adult mouse sinoatrial node (SAN). Amphotericin-mediated patch microelectrode recordings at 35 °C were made under control conditions and in the presence of 5 or 10 nM isoproterenol (ISO). These sets of results were complemented and integrated with mathematical modeling of the current changes that take place in the range of membrane potentials (−70 to −50 mV), which corresponds to the ‘pacemaker depolarization’ in the adult mouse SAN. Our results reveal a very small, but functionally important, approximately steady-state or time-independent current generated by residual activation of I_f channels that are expressed in these pacemaker myocytes. Recordings of the pacemaker depolarization and action potential, combined with measurements of changes in I_f, and the well-known increases in the L-type Ca²⁺ current, I_CaL, demonstrated that I_CaL activation, is essential for myogenic pacing. Moreover, after being enhanced (approximately 3-fold) by 5 or 10 nM ISO, I_CaL contributes significantly to the positive chronotropic effect. Our mathematical model has been developed in an attempt to better understand the underlying mechanisms for the pacemaker depolarization and action potential in adult mouse SAN myocytes. After being updated with our new experimental data describing I_f, our simulations reveal a novel functional component of I_f in adult mouse SAN. Computational work carried out with this model also confirms that in the presence of ISO the residual activation of I_f and opening of I_CaL channels combine to generate a net current change during the slow diastolic depolarization phase that is essential for the observed accelerated pacemaking rate of these SAN myocytes.

The promise and problems of metabolic-based therapies for heart failure

Despite standard therapies, heart failure patients have high rates of morbidity highlighting the need to develop alternative therapeutic approaches. Heart failure has been described as an energy-starved condition that is hypothesized to drive the pathological remodeling of the heart. Numerous studies have described the metabolic defects that occur when the heart fails and adaptive changes that take place to maintain the energy needed for the heart to function properly. In this review we will summarize the metabolic requirements of a normal heart and what happens during failure. We will also summarize the various metabolic therapeutic strategies that have been developed over the years to treat heart failure and their results from clinical trials.

Ivabradine Monotherapy for the Treatment of Congenital Junctional Ectopic Tachycardia in a Premature Neonate

Congenital junctional ectopic tachycardia is a rare and special type of supraventricular arrhythmia. Junctional ectopic tachycardia is characterized by persistently elevated heart rates that may cause an impairment in cardiac function. Junctional ectopic tachycardia is considered one of the most difficult-to-treat conditions even with a combination of antiarrhythmic medications. Ivabradine is a novel antiarrhythmic medication used to decrease the heart rate in adults with angina pectoris. We report a first case of a premature neonate with a normal heart structure who developed junctional ectopic tachycardia and was subsequently treated successfully with ivabradine.

Association of pulse rate with outcomes in heart failure with reduced ejection fraction: a retrospective cohort study

BACKGROUND

In a real-world setting, the effect of pulse rate measured at the time of diagnosis and serially during follow-up and management, on outcomes in heart failure with reduced ejection fraction (HFrEF), has not been well-studied. Furthermore, how beta-blockade use in a real-world situation modifies this relation between pulse rate and outcomes in HFrEF is not well-known. Hence, we identified a large, national, real-world cohort of HFrEF to examine the association of pulse rate and outcomes.

METHODS

Using Veterans Affairs (VA) national electronic health records we identified incident HFrEF cases between 2006 and 2012. We examined the associations of both baseline and serially measured pulse rates, with mortality and days hospitalized per year for heart failure and for any cause, using crude and multivariable Cox proportional hazards and Poisson or negative binomial models, respectively. The exposure was examined as continuous, dichotomous, and categorical. Post-hoc analyses addressed the interaction of pulse rate and beta-blocker target dose.

RESULTS

We identified 51,194 incident HFrEF cases (67 ± 12 years, 98% male, 77% white. A significant positive, near linear relationship was observed for both baseline and serially measured pulse rates with all-cause mortality, all-cause hospitalization and heart failure hospitalization after adjusting for covariates including beta-blocker use. Patients who had a pulse rate ≥ 70 bpm in the past 6 months had 36% (95% CI: 31-42%), 25% (95% CI: 19-32%), and 51% (95% CI: 33-72%) increased rates of mortality, all-cause hospitalization, and heart failure hospitalization, respectively, compared to patients with pulse rates < 70 bpm. A minority of subjects (15%) were treated with guideline directed beta blockade ≥50% of recommended target dose, among whom better outcomes were seen compared to those who did not achieve target dose in patients with pulse rates both above and below 70 beats per minute.

CONCLUSIONS

High pulse rate, both at the time of diagnosis and during follow-up, is strongly associated with increased risk of adverse outcomes in HFrEF patients, independent of the use of beta-blockers. In a real-world setting, the majority of HFrEF patients do not achieve target dose of beta-blockade; greater use of strategies to reduce heart rate may improve outcomes in HFrEF.

Sequence analysis and variant identification at the APOC3 gene locus indicates association of rs5218 with BMI in a sample of Kuwaiti's

Background

APOC3 is important in lipid transport and metabolism with limited studies reporting genetic sequence variations in specific ethnic groups. The present study aimed to analyze the full APOC3 sequence among Kuwaiti Arabs and test the association of selected variants with lipid levels and BMI.

Methods

Variants were identified by Sanger sequencing the entire APOC3 gene in 100 Kuwaiti Arabs. Variants and their genotypes were fully characterized and used to construct haplotype blocks. Four variants (rs5128, rs2854117, rs2070668, KUAPOC3N3 g.5196 A > G) were selected for testing association with serum lipid levels and BMI in a cohort (n = 733).

Results

APOC3 sequence (4.3 kb) of a Kuwaiti Arab was deposited in Genbank (accession number KJ437193). Forty-two variants including 3 novels were identified including an “A” insertion at genomic positions 116,700,599–116,700,600 (promoter region) and two substitutions in intron 1 at genomic positions 116,700,819 and 116,701,159. Only three variants, (rs5128, rs2854117, and rs2070668) were analyzed for association of which rs5128 showed a trend for association with increased BMI, TG and VLDL levels that was further investigated using multivariate analysis. A significant association of rs5128 with BMI (p <  0.05) was observed following a dominant genetic model with increased risk by an OR of 4.022 (CI: 1.13–14.30).

Conclusion

The present study is the first to report sequence analysis of APOC3 in an Arab ethnic group. This study supports the inclusion of rs5128 as a marker for assessing genetic risk to dyslipidemia and obesity and the inclusion of the novel variant g.5196 A > G for population stratification of Arabs.

New Novel Treatment Approaches for Heart Failure With Reduced Ejection Fraction

Despite availability of standardized drug therapies with proven beneficial outcomes, heart failure is associated with poor quality of life, increased hospital readmission, and high mortality rate. In the recent years, comprehensive understanding of the pathophysiological mechanisms of heart failure has led to the development and approval of 2 new pharmacological agents, sacubitril–valsartan and ivabradine. These agents are currently approved for use in heart failure with reduced ejection fraction (HFrEF) and present as novel approaches to further improve prognosis and outcomes in patients with HF. They offer alternative treatment options for patients who are intolerant or continue to be symptomatic despite utilization of standard HF drug therapies at optimally tolerated dosages. A review of these 2 novel agents in HFrEF, including information on pivotal trials that led to its approval and its place in therapy for HFrEF, is presented.

A New Mechanism of Action in Heart Failure: Angiotensin-Receptor Neprilysin Inhibition

Objective: To evaluate the efficacy, safety, and clinical significance of sacubitril/valsartan (Entresto) in patients with heart failure with a reduced ejection fraction (HFrEF). Data Sources: An extensive search was conducted on Ovid MEDLINE using keywords and medical subject headings LCZ696, sacubitril/valsartan, angiotensin-receptor neprilysin inhibitor, and Entresto. Study Selection and Data Extraction: The search was conducted to retrieve clinical trials comparing sacubitril/valsartan to current guideline-directed therapy for HF. Articles using the limits of clinical trials "all" (phase I to IV), in English, and published within the past 5 years were reviewed. Supplemental sources included the Entresto package insert via the manufacturer's website. Primary end points included all-cause mortality and time to first hospitalization. Safety end points included incidence and severity of angioedema, cough, hyperkalemia, increased serum creatinine, and hypotension. Data Synthesis: This review critiques both clinical and statistical significance of the "Prospective Comparison of ARNi with ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure" or PARADIGM-HF and other phase II to III clinical trials. Sacubitril/valsartan showed a 20% reduction in cardiovascular death and first hospitalization from HF compared with enalapril. Despite an overall reduction in adverse events, sacubitril/valsartan had increased occurrences of hypotension and nonserious angioedema. Conclusion: Sacubitril/valsartan is a viable option for newly diagnosed New York Heart Association (NYHA) class II to III and is an alternative to patients who are currently being treated with the maximum doses of current gold standard treatment. Clinicians initiating sacubitril/valsartan must monitor patients closely for signs, symptoms, and history of hypotension and angioedema.

Age-associated expression of HCN channel isoforms in rat sinoatrial node

The expression of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel isoforms varies among species, cardiac tissues, developmental stages, and disease generation. However, alterations in the HCN channels during aging remain unclear. We investigated the protein expressions of HCN channel isoforms, HCN1-HCN4, in the sinoatrial nodes (SANs) from young (1-month-old), adult (4-month-old), and aged (30-month-old) rats. We found that HCN2 and HCN4 proteins were present in rat SAN using immunohistochemistry; therefore, we quantitatively analyzed their expression by Western blot. Aim to correlate protein expression and pacemaking function, specific blockade of HCN channels with 3 µmol/L ivabradine prolonged the cycle length in the intact rat heart. During the senescent process, the HCN2 and HCN4 protein levels declined, which was accompanied with a decreased effect of ivabradine on rat SAN automaticity. These results indicated the age-associated expression and relative function of HCN channel isoforms.

Elevated Total Homocysteine Levels in Acute Ischemic Stroke Are Associated With Long-Term Mortality

Background and Purpose—

Total homocysteine (tHcy) levels are associated with secondary vascular events and mortality after stroke. The aim of this study was to investigate whether tHcy levels in the acute phase of a stroke contribute to the recurrence of cerebro-cardiovascular events and mortality.

Methods—

A total of 3799 patients were recruited after hospital admission for acute ischemic stroke. Levels of tHcy were measured within 24 hours after primary admission. Patients were followed for a median of 48 months.

Results—

During the follow-up period, 233 (6.1%) patients died. After adjustment for age, smoking status, diabetes mellitus, and other cardiovascular risk factors, patients in the highest tHcy quartile (>18.6 μmol/L) had a 1.61-fold increased risk of death (adjusted hazard ratio [HR], 1.61; 95% confidence interval [CI], 1.03–2.53) compared with patients in the lowest quartile (≤10 μmol/L). Further subgroup analysis showed that this correlation was only significant in the large-artery atherosclerosis stroke subtype (adjusted HR, 1.80; 95% CI, 1.05–3.07); this correlation was not significant in the small-vessel occlusion subtype (adjusted HR, 0.80; 95% CI, 0.30–2.12). The risk of stroke-related mortality was 2.27-fold higher for patients in the third tHcy quartile (adjusted HR, 2.27; 95% CI, 1.06–4.86) and 2.15-fold more likely for patients in the fourth quartile (adjusted HR, 2.15; 95% CI, 1.01–4.63) than for patients in the lowest tHcy quartile. The risk of cardiovascular-related mortality and the risk of recurrent ischemic stroke were not associated with tHcy levels.

Conclusions—

Our findings suggest that elevated tHcy levels in the acute phase of an ischemic stroke can predict mortality, especially in stroke patients with the large-vessel atherosclerosis subtype.

hERG potassium channel blockade by the HCN channel inhibitor bradycardic agent ivabradine

Background

Ivabradine is a specific bradycardic agent used in coronary artery disease and heart failure, lowering heart rate through inhibition of sinoatrial nodal HCN‐channels. This study investigated the propensity of ivabradine to interact with KCNH2‐encoded human Ether‐à‐go‐go–Related Gene (hERG) potassium channels, which strongly influence ventricular repolarization and susceptibility to torsades de pointes arrhythmia.

Methods and Results

Patch clamp recordings of hERG current (I_hERG) were made from hERG expressing cells at 37°C. I_hERG was inhibited with an IC₅₀ of 2.07 μmol/L for the hERG 1a isoform and 3.31 μmol/L for coexpressed hERG 1a/1b. The voltage and time‐dependent characteristics of I_hERG block were consistent with preferential gated‐state‐dependent channel block. Inhibition was partially attenuated by the N588K inactivation‐mutant and the S624A pore‐helix mutant and was strongly reduced by the Y652A and F656A S6 helix mutants. In docking simulations to a MthK‐based homology model of hERG, the 2 aromatic rings of the drug could form multiple π‐π interactions with the aromatic side chains of both Y652 and F656. In monophasic action potential (MAP) recordings from guinea‐pig Langendorff‐perfused hearts, ivabradine delayed ventricular repolarization and produced a steepening of the MAPD₉₀ restitution curve.

Conclusions

Ivabradine prolongs ventricular repolarization and alters electrical restitution properties at concentrations relevant to the upper therapeutic range. In absolute terms ivabradine does not discriminate between hERG and HCN channels: it inhibits I_hERG with similar potency to that reported for native I_f and HCN channels, with S6 binding determinants resembling those observed for HCN4. These findings may have important implications both clinically and for future bradycardic drug design.