Hemodynamic effects of a novel sodium channel activator in dogs with chronic heart failure

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

First report on an inotropic peptide activating tetrodotoxin-sensitive, "neuronal" sodium currents in the heart

BACKGROUND

New therapeutic approaches to improve cardiac contractility without severe risk would improve the management of acute heart failure. Increasing systolic sodium influx can increase cardiac contractility, but most sodium channel activators have proarrhythmic effects that limit their clinical use. Here, we report the cardiac effects of a novel positive inotropic peptide isolated from the toxin of the Black Judean scorpion that activates neuronal tetrodotoxin-sensitive sodium channels.

METHODS AND RESULTS

All venoms and peptides were isolated from Black Judean Scorpions (Buthotus Hottentotta) caught in the Judean Desert. The full scorpion venom increased left ventricular function in sedated mice in vivo, prolonged ventricular repolarization, and provoked ventricular arrhythmias. An inotropic peptide (BjIP) isolated from the full venom by chromatography increased cardiac contractility but did neither provoke ventricular arrhythmias nor prolong cardiac repolarization. BjIP increased intracellular calcium in ventricular cardiomyocytes and prolonged inactivation of the cardiac sodium current. Low concentrations of tetrodotoxin (200 nmol/L) abolished the effect of BjIP on calcium transients and sodium current. BjIP did not alter the function of Nav1.5, but selectively activated the brain-type sodium channels Nav1.6 or Nav1.3 in cellular electrophysiological recordings obtained from rodent thalamic slices. Nav1.3 (SCN3A) mRNA was detected in human and mouse heart tissue.

CONCLUSIONS

Our pilot experiments suggest that selective activation of tetrodotoxin-sensitive neuronal sodium channels can safely increase cardiac contractility. As such, the peptide described here may become a lead compound for a new class of positive inotropic agents.

Sodium channel enhancer restores baroreflex sensitivity in conscious dogs with heart failure

We compared the cardiac inotropic, lusitropic, and chronotropic responses to the Na+ channel enhancer LY-368052 in conscious dogs before and after development of congestive heart failure (CHF). We also examined the effect of LY-368052 on baroreflex sensitivity and the efferent neural mechanisms of the bradycardic response in heart failure. Dogs were chronically instrumented, and heart failure was induced by right ventricular pacing at 240 beats/min for 3–4 wk. LY-368052 dose-dependently increased left ventricular contractile performance before and after the development of CHF to a similar extent. The inotropic effect of LY-368052 in heart failure was not altered by either ganglionic or β-adrenergic receptor blockade. LY-368052 improved cardiac relaxation and induced bradycardia in dogs with heart failure but not in normal dogs. The negative chronotropic effect of LY-368052 was eliminated by ganglionic blockade but not β-adrenergic blockade, suggesting that the bradycardia was mediated by the autonomic nervous system via enhanced parasympathetic tone. Baroreflex sensitivity was assessed as the pulse interval-mean arterial pressure slope in response to temporary pharmacological (nitroglycerin or phenylephrine) and mechanical (brief occlusion of inferior vena cava) alterations of arterial pressure in conscious dogs before and after development of heart failure. Baroreflex sensitivity was significantly depressed in heart failure and restored completely by acute treatment with LY-368052. Thus the Na+ channel enhancer LY-368052 maintains its β-receptor-independent inotropic effect in chronic CHF and specifically improves ventricular relaxation and depressed baroreflex function.

Combined inotropic and bradycardic effects of a sodium channel enhancer in conscious dogs with heart failure: a mechanism for improved myocardial efficiency compared with dobutamine

We compared the cardiac inotropic, chronotropic, and myocardial O(2) consumption (MVO(2)) responses to the sodium (Na(+)) channel enhancer, LY341311 [(S)-4-[3-[[1-(diphenyl-methyl)-3-azetidinyl]oxy]-2-hydroxypropoxy]-1H-indole-2-carbonitrile monohydrate], with the beta-receptor agonist dobutamine in conscious dogs with heart failure. Heart failure was induced in chronically instrumented dogs by right ventricular pacing at 240 beats per minute for 3 to 4 weeks. LY341311 (10-100 microg/kg/min i.v.) dose dependently increased cardiac contractile function as reflected, at the highest dose, by increases in left ventricular dP/dt(max) (55 +/- 7%), and fractional shortening (62 +/- 9%), accompanied by increases in cardiac stroke work (111 +/- 18%) and minute work (34 +/- 10%) and decreases in heart rate (33 +/- 4%). Dobutamine (2-15 microg/kg/min i.v.) increased contractile responses to a similar degree but also increased heart rate (15 +/- 5%) at the highest dose. Complete ganglionic blockade with hexamethonium and atropine or with hexamethonium alone abolished the bradycardic effect but not the inotropic response to LY341311. At similar levels of inotropic response, dobutamine (10 microg/kg/min) increased MVO(2) by 23 +/- 7% (P < 0.05), whereas LY341311 (100 microg/kg/min) had no effect. In the presence of left atrial pacing at a constant heart rate and at matched contractile work, MVO(2) was increased by LY341311 to the same extent as dobutamine. These data indicate that autonomically mediated bradycardia produced by LY341311 contributes to a favorable net metabolic effect on myocardial O(2) utilization in the failing heart while providing inotropic support comparable to a beta-receptor-mediated agonist.

A sodium channel enhancer, LY341311, increases myocardial contractile performance without increasing heart rate in conscious normal dogs: a comparison with dobutamine

BACKGROUND

Catecholamines and many inotropic agents increase cardiac contractility but also cause excessive myocardial O2 consumption (MVO2). We determined if the novel Na+ channel enhancer LY341311, which increases myocardial contractility independent of beta receptors, can produce significant cardiac inotropic effects compared with dobutamine but at lower oxygen cost in conscious dogs.

METHODS AND RESULTS

Mongrel dogs were chronically instrumented for measurement of arterial pressure, left ventricular (LV) pressure and internal diameter, coronary blood flow, and arterial and coronary sinus O2 content. Both LY341311 and dobutamine produced dose-dependent increases in LV dP/dt, dP/dt/40, fractional shortening, and cardiac stroke work and minute work estimated from the LV pressure-diameter loop. The major difference between LY341311 and dobutamine was an opposing effect on heart rate with LY341311 slightly reducing it but dobutamine markedly increasing it. LY341311 caused a significantly smaller increase in MVO2 than dobutamine (P <.05) and produced similar cardiac inotropic effects, yielding a higher cardiac mechanical efficiency than dobutamine. However, after pacing to match heart rate with dobutamine LY341311 increased MVO2 markedly, approaching the same level as with dobutamine.

CONCLUSIONS

The novel Na+ channel enhancer LY341311 caused significant increases in myocardial contractility and contractile performance without increasing heart rate. It had a beneficial energetic effect on the heart with significantly less O2 cost and improved cardiac mechanical efficiency.

Cardiac contractility modulation with the impulse dynamics signal: studies in dogs with chronic heart failure

The intravenous use of positive inotropic agents, such as sympathomimetics and phosphodiesterase inhibitors, in heart failure is limited by pro-arrhythmic and positive chronotropic effects. Chronic use of these agents, while eliciting an improvement in the quality of life of patients with advanced heart failure, has been abandoned because of marked increase in mortality when compared to placebo. Nevertheless, patients with advanced heart failure can benefit from long-term positive inotropic support if the therapy can be delivered 'on demand' and in a manner that is both safe and effective. In this review, we will examine the use of a novel, non-stimulatory electrical signal that can acutely modulate left ventricular (LV) contractility in dogs with chronic heart failure in such a way as to elicit a positive inotropic support. Cardiac contractility modulation (CCM) with the Impulse Dynamic(trade mark) signal was examined in dogs with chronic heart failure produced by intracoronary microembolizations. Delivery of the CCM signal from a lead placed in the great coronary vein for periods up to 10 minutes resulted in significant improvements in cardiac output, LV peak+dP/dt, LV fractional area of shortening and LV ejection fraction measured angiographically. Discontinuation of the signal resulted in a return of all functional parameters to baseline values. In cardiomyocytes isolated from dogs with chronic heart failure, application of the CCM signal resulted in improved shortening, rate of change of shortening and rate of change of relengthening suggesting that CCM application is associated with intrinsic improvement of cardiomyocyte function. The improvement in isolated cardiomyocyte function after application of the CCM signal was accompanied by an increase in the peak and integral of the Ca(2+) transient suggesting modulation of calcium cycling by CCM application. In a limited number of normal dogs, intermittent chronic delivery of the CCM signal for up to 7 days showed chronic maintenance of LV functional improvement. In conclusion, pre-clinical results to date with the Impulse Dynamics CCM signal indicate that this non-pharmacologic therapeutic modality can provide short-term positive inotropic support to the failing heart and as such, may be a useful adjunct in the treatment of advanced heart failure. Additional, long-term studies in dogs with heart failure are needed to establish the safety and efficacy of this therapeutic modality for the chronic treatment of this disease syndrome.