Zatebradine, a specific bradycardic agent, enhances the positive inotropic actions of dobutamine in ischemic myocardium

Ivabradine prevents deleterious effects of dopamine therapy in heart failure: No role for HCN4 overexpression

BACKGROUND

Exacerbations of chronic heart failure (CHF) are often treated with catecholamines to provide short term inotropic support, but this strategy is associated with long-term detrimental hemodynamic effects and increased ventricular arrhythmias (VA), possibly related to increased heart rate (HR). We hypothesized that ivabradine may prevent adverse effects of short-term dopamine treatment in CHF.

METHODS

Rats with post-myocardial infarction CHF received 2-week infusion of saline, dopamine(D), ivabradine(I) or D&I; cardiac function was assessed using echocardiography and pressure-volume loops while VA were assessed using telemetric ECG recording. Expression of HCN4, a potentially proarrhythmic channel blocked by ivabradine, was assessed in left ventricular (LV) myocardium. HCN4 expression was also assessed in human explanted normal and failing hearts and correlated with VA.

FINDINGS

Dopamine infusion had detrimental effects on hemodynamic parameters and LV remodeling and induced VA in CHF rats, while ivabradine completely prevented these effects. CHF rats demonstrated HCN4 overexpression in LV myocardium, and ivabradine and, unexpectedly, dopamine prevented this. Failing human hearts also exhibited HCN4 overexpression in LV myocardium that was unrelated to patient's sex, CHF etiology, VA severity or plasma NT-proBNP.

INTERPRETATION

HR reduction offered by ivabradine may be a feasible strategy to extract benefits of inotropic support in CHF exacerbations, avoiding detrimental effects on CHF biology or VA. Ivabradine may offer additional beneficial effects in this setting, going beyond pure HR reduction, however prevention of ventricular HCN4 overexpression is unlikely to play a major role.

Ivabradine improves left ventricular twist and untwist during chronic hypertension

BACKGROUND

Left ventricular (LV) dysfunction develops during LV hypertrophy and particularly during tachycardia. Thus we investigated the effects of heart rate (HR) reduction with ivabradine, an I_f-channel blocker, on LV twist and untwist which represents myocardial deformation occurring during the overall systole and diastole and therefore provide valuable evaluation of global LV systolic and diastolic function.

METHODS

Eight chronically instrumented pigs receiving continuous angiotensin II infusion during 28days to induce chronic hypertension and LV hypertrophy. Measurements were performed at Days 0 and 28 after stopping angiotensin II infusion in the presence and absence of ivabradine.

RESULTS

At Day 0, reducing HR from 75±3 to 55±2beats/min with ivabradine did not affect LV twist but slowed LV untwist along with an increase in LV end-diastolic pressure. At Day 28, LV posterior and septal wall thickness as well as the estimated LV mass increased, indicating LV hypertrophy. LV twist and untwist were significantly reduced by 33±4% from 16±1° and 32±6% from -154±9°/s, respectively, showing global LV systolic and diastolic dysfunction. In this context, ivabradine decreased HR by 25% from 86±5beats/min and significantly improved LV twist from 11±1 to 14±1° and LV untwist from -104±8 to -146±5°/s.

CONCLUSIONS

Administration of ivabradine during chronic hypertension and LV hypertrophy improved LV twist and untwist. This further supports the beneficial effect of this drug on both LV systolic and diastolic function during the development of LV hypertrophy.

Hemodynamic effects of Ivabradine in addition to dobutamine in patients with severe systolic dysfunction

BACKGROUND

Dobutamine induced tachycardia increases myocardial oxygen consumption and impairs ventricular filling. We hypothesized that Ivabradine may be efficient to control dobutamine induced tachycardia.

METHODS

We assessed the effects of Ivabradine in addition to dobutamine in stable heart failure (HF) patients (LVEF < 35%, n = 22, test population) and validated its effects in refractory cardiogenic shock patients (n = 9, validation population) with contraindication to cardiac assistance or transplant. In the test population (62 ± 17 years, LVEF = 24 ± 8%), systolic and diastolic function were assessed at rest and under dobutamine [10 γ/min], before and after Ivabradine [5mg per os]. In the validation population (54 ± 11 years, LVEF = 22 ± 7%), Ivabradine [5mg twice a day] was added to the dobutamine infusion.

RESULTS

In the test population, Ivabradine decreased heart rate [HR] at rest and during dobutamine echocardiography (-9 ± 8 bpm, P = 0.0004). The decrease in HR was associated with a decrease in cardiac power output and an increase in diastolic duration at rest (+ 74 ± 67 ms, P = 0.0002), and during dobutamine infusion (+ 75 ± 67 ms, P < 0.0001). Change in LVEF during dobutamine was greater after Ivabradine treatment than before (+ 7.2 ± 4.7% vs. + 3.6 ± 4.2%, P = 0.002). In the validation population, Ivabradine decreased HR (-18 ± 11 bpm, P = 0.008) and improved diastolic filling time (+ 67 ± 42 ms, P = 0.012) without decreasing cardiac output. At 24h, Ivabradine improved systolic blood pressure (+ 9 ± 5 mmHg, P = 0.007), daily urine output (+ 0.7 ± 0.5L, P = 0.008), oxygen balance (ΔScv02 = + 13 ± 15%, P = 0.010), and NT-pro BNP (-2270 ± 1912 pg/mL, P = 0.017). Finally, only 2/9 (22%) patients died whereas expected mortality determined from a historical cohort was 78% (P = 0.017).

CONCLUSION

This pilot study demonstrates the safety and potential benefit of a HR lowering agent in cardiogenic shock.

Acute effects of zatebradine on cardiac conduction and repolarization

Zatebradine, a potent bradycardic agent, is believed to act selectively at the sinoatrial node. The selectivity of such a property relative to various electrophysiologic classes of action is not well defined. To characterize the electrophysiologic properties of zatebradine, the corrected sinus node recovery time, sinoatrial conduction time, conduction intervals, atrial effective refractory period and monophasic action potential duration in the ventricle were measured before and after incremental doses of zatebradine (0.1-1.5 mg/kg) in 15 anesthetized dogs. The electrophysiologic effects of zatebradine developed immediately after a single i.v. bolus dose, reaching steady-steady-state at 15 minutes with the maximum effect evident at 0.75 mg/kg. The IC(50) was 0.23 mg/kg. There was no significant effect on the sinus node recovery time. The PR interval on the electrocardiogram was significantly increased when the dose was higher than 0.25 mg/kg. The duration of the P wave and the PA interval were not changed. Zatebridine greatly increased the AH (from 135 to 178 milliseconds) without changing the HH and HV intervals in His bundle recordings. The EC(50) of this effect was 0.58 mg/kg. The QRS interval was not changed. The QTc was significantly increased from 0.43 to 0.56 s(1/2) (P < 0.05). The action potential duration was significantly increased by high dose zatebradine (> 0.5 mg/kg), the EC(50) for this effect was 0.76 mg/kg. The atrium effective refractory period was significantly increased (31%) with an EC(50) 0.69 mg/kg. These results indicate that zatebradine selectively inhibits sinus node automaticity at low doses. The inhibition of the AV nodal conduction and the lengthening of the refractory period and repolarization in the atria and the ventricles occur at higher dose.

Effects of the specific bradycardic agent zatebradine on hemodynamic variables and myocardial blood flow during the early postresuscitation phase in pigs

Cardiopulmonary resuscitation (CPR) leads to an excessive stimulation of the sympathetic nervous system that may result in tachycardia and malignant arrhythmias in the postresuscitation phase. The attenuation of this reaction by a specific bradycardic agent has not been compared to beta-blockade and placebo. After 4 min of ventricular fibrillation, and 3 min of CPR, 21 pigs were randomized to receive 45 microg/kg epinephrine in combination with either a specific bradycardic agent (0.5 mg/kg zatebradine; n = 7), or a beta-blocker (1 mg/kg esmolol; n = 7), or placebo (normal saline; n = 7). Two minutes after drug administration, defibrillation was performed to restore spontaneous circulation (ROSC). Hemodynamic variables, left ventricular contractility, right ventricular function, and myocardial blood flow were studied at prearrest, and for 3 h after ROSC. In comparison with esmolol and placebo, zatebradine resulted in a significant reduction in heart rate during the postresuscitation period, and reduced the number of premature ventricular contractions in the first 5 min after ROSC. This reduction in heart rate was associated with a significantly higher right ventricular ejection fraction, stroke volume, and endocardial/epicardial perfusion ratio at 5 min after ROSC. In comparison with placebo, esmolol administration decreased heart rate only moderately, but significantly reduced right ventricular stroke volume and cardiac output at 5 min after ROSC. Although only one dose and only one administration pattern of zatebradine has been investigated, we conclude that zatebradine administration during CPR effectively reduced heart rate without compromising myocardial contractility during the postresuscitation phase in pigs.

UL-FS 49 (zatebradine) does not affect arterial baroreflex in conscious normal or aortic-constricted rats

Heart-rate reduction is an important element of patient management during cardiac bypass surgery and in therapeutic measures for combating ischemia and relieving pain in patients with angina. UL-FS 49 is a novel bradycardic agent that purportedly acts solely on the sinoatrial node without potentially deleterious effects on arterial pressure and cardiac inotropism. However, little is known about influences of this agent on neuronal tissue and cardiovascular reflexes. Moreover, left ventricular hypertrophy, which often accompanies cardiovascular disease, is known to attenuate the arterial baroreflex and could have effects interactive with those of UL-FS 49. In this study, the effects of UL-FS 49 on the arterial baroreflex were tested in normal rats (N), rats with left ventricular hypertrophy 14 days after abdominal aortic constriction (AC), and sham-operated controls (SH). Arterial baroreflex sensitivity (BRS) was estimated as the slope of the relation between mean arterial pressure (independent variable) and the RR interval (dependent variable). At the time of study, the AC group had significantly greater mean arterial pressure than either SH or N (159 +/- 2, 122 +/- 3, and 124 +/- 3 mm Hg, respectively; mean +/- SEM, p < 0.01) and significantly greater left ventricular mass to body mass ratio than did SH (3.73 +/- 0.11, 2.33 +/- 0.11 mg/g; p < 0.01). As expected, BRS was significantly depressed in AC, compared with either SH or N (0.52 +/- 0.16, 1.48 +/- 0.12, 1.69 +/- 0.25 ms/mm Hg, respectively; p < 0.01). Despite its potent dose-dependent bradycardic effects in all three groups, UL-FS 49 did not affect BRS significantly in any group. These results show that the arterial baroreflex is largely unaffected by UL-FS 49 in both normal rats and rats with systemic hypertension and left ventricular hypertrophy.

Role of zatebradine and propranolol in attenuation of tachycardia produced by dobutamine in pigs

BACKGROUND

Zatebradine is a new specific bradycardiac agent that selectively slows the depolarization in the pacemaker cells of the sinoatrial node. The purpose of our investigation was to determine whether the tachycardia induced by dobutamine can be attenuated by the administration of zatebradine. The results were compared with those produced by propranolol, which is used in the treatment of sinus tachycardia.

METHODS

Twelve pigs were anesthetized with sodium pentobarbital, intubated, and ventilated. After baseline hemodynamic measurements were obtained, dobutamine was administered until the heart rate reached 25% above baseline. Animals were randomized to one of two groups. Group I received zatebradine, 0.5 mg/kg i.v., and Group II received propranolol, 0.5 mg/kg i.v.

RESULTS

Dobutamine 10 micrograms.kg-1.min-1 increased the heart rate (FIR) by 25%, and increased mean arterial blood pressure (MAP) left ventricular (LV) dp/dt, and cardiac output (CO) (P < 0.05). Zatebradine decreased the HR to baseline (P < 0.05) without affecting left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), LV dP/dt, or CO. Stroke volume (SV) increased significantly (P < 0.05). Propranolol also reduced HR to baseline, but decreased LV dP/dt, LVSP, CO, and SV (P < 0.05).

CONCLUSION

Zatebradine effectively attenuates the tachycardia caused by dobutamine in anesthetized pigs, without reducing cardiac performance.

Zatebradine inhibits tachycardia induced by bronchodilators without affecting respiratory resistance in dogs

Bronchodilators used for bronchial asthma reduce respiratory resistance but also increase heart rate to some extent. It is often difficult to use such bronchodilators with elderly patients and patients with heart disease. The object of our study was to investigate whether a specific bradycardic agent, zatebradine, inhibited the heart rate increased by bronchodilators without affecting respiratory resistance. We evaluated the effects of zatebradine on the increases in heart rate and inhibition of the respiratory resistance in response to the bronchodilators, isoproterenol, procaterol (a beta 2-adrenoceptor agonist), 6-(3-dimethylaminopropionyl)-forskolin, NKH 477 (an adenylyl cyclase activator) and aminophylline in the anesthetized and artificially ventilated dog. When zatebradine in doses of 0.05-1.5 mg/kg i.v. decreased heart rate without affecting arterial blood pressure, it dose dependently attenuated the increase in heart rate in response to isoproterenol, procaterol, NKH 477 and aminophylline but did not affect the inhibition by these substances of the increase in respiratory resistance induced by histamine. Propranolol (0.01-0.3 mg/kg i.v.) dose dependently inhibited not only the increase in heart rate but also the inhibition of the respiratory resistance induced by isoproterenol and procaterol. The present results indicate that zatebradine selectively inhibits the increase in heart rate in response to cyclic AMP-dependent bronchodilators without affecting their bronchodilator effects in anesthetized dogs and suggest that zatebradine may be a useful drug for prevention of the tachycardia induced by bronchodilators used for patients with bronchial asthma.

Increases in inotropic state without change in heart rate: combined use of dobutamine and zatebradine in conscious dogs

The cardiovascular and left ventricular functional effects of dobutamine (5, 10 and 20 micrograms kg-1 min-1) were examined in conscious, chronically instrumented dogs in the presence and absence of control of heart rate with the specific bradycardic agent, zatebradine. Dobutamine increased heart rate, cardiac output, stroke volume, diastolic coronary blood flow velocity and pressure-work index (calculated myocardial oxygen consumption) and decreased systemic vascular resistance and diastolic coronary vascular resistance. Mean arterial pressure and left ventricular systolic and end-diastolic pressures were unchanged. Dobutamine-induced increases in heart rate and pressure-work index were attenuated by zatebradine. Dobutamine alone increased preload recruitable stroke work slope (63 +/- 6 to 116 +/- 11 mmHg) and +dP/dt. These positive inotropic effects were unaffected by zatebradine. Dobutamine decreased the time constant of isovolumic relaxation (30 +/- 3 to 25 +/- 2 ms). Dobutamine-induced decreases in the time constant of isovolumic relaxation were not altered by zatebradine, indicating that changes in the time constant occurred independent of heart rate. Dobutamine also increased the maximal segment lengthening velocity to a similar degree in zatebradine-treated versus untreated dogs. Control of dobutamine-induced tachycardia by zatebradine decreases myocardial oxygen consumption but does not alter the positive inotropic and lusitropic effects of dobutamine.

Acute and chronic cardiac and regional haemodynamic effects of the novel bradycardic agent, S16257, in conscious rats

1. We carried out experiments to assess the cardiac and regional haemodynamic effects of single or repeated injections of the novel bradycardic agent. S16257, (7,8-dimethoxy 3-[3-([(IS)-(4,5-dimethoxybenzocyclobutan-1- yl)methyl]methylamino)propyl] 1,3,4,5-tetrahydro-2H-benzapin 2-one), in conscious rats. 2. In the first experiment, male Long Evans rats were chronically instrumented for the measurement of cardiac or regional haemodynamics (n = 9 in each group), and, on separate experimental days, were randomized to receive i.v. bolus injections of vehicle (5% dextrose) or S16257 at a dose of 1 mg kg-1. 3. In animals instrumented for the measurement of cardiac haemodynamics (n = 9), following injection of vehicle, there were no immediate changes, and 7-8 h later there were slight reductions in heart rate and mean arterial blood pressure only. Injection of S16257 caused an immediate, transient, pressor effect but thereafter there were reductions in heart rate, mean arterial blood pressure, cardiac index and total peripheral conductance, together with increases in stroke index and peak aortic flow. The integrated decreases in heart rate, mean arterial blood pressure, cardiac index and total peripheral conductance and increases in stroke index, peak aortic flow, dF/dtmax and central venous pressure following S16257 were all significantly greater than the changes after vehicle injection. After injection of S16257, the fall in heart rate and fall in cardiac index were not linearly related. 4. In animals instrumented for the measurement of regional haemodynamics (n = 9). the bradycardic effect of i.v. S16257 was accompanied by reductions in renal, mesenteric and hindquarters blood flows and vascular conductances that were greater than the changes seen following injection of vehicle, but only for the first 1 h. Considering animals instrumented for the measurement of cardiac and regional haemodynamics together, the bradycardic effect of S16257 was greater the higher the resting heart rate.5. In the second experiment, animals chronically instrumented for the measurement of cardiac or regional haemodynamics (n = 9 in each group) were given s.c. injections of S16257 (1 mg kg-1) on four consecutive days. The general patterns of change in cardiac and regional haemodynamics following s.c.injection of S16257 were as described above for i.v. injection, although the rates of onset of effects were slower. The bradycardic effect of S16257 was less on the first, than on the subsequent, three days.6 Overall, these results indicate that the bradycardic action of S16257 is not associated with any signsof negative inotropic action. Only the initial depressor effect of i.v. S16257 is associated with reductions in renal, mesenteric and hindquarters flow and vascular conductance significantly greater than those seen after vehicle injection. With repeated s.c. injection of S16257, there are no signs of desensitization to its bradycardic actions, nor impairment of regional perfusion. If these results extrapolate to the clinical setting, it seems likely that S16257 will have beneficial bradycardic effects, with no concurrent undesirable actions on other aspects of cardiovascular function.