Tedisamil (KC 8857) is a new specific bradycardic drug: does it also influence myocardial contractility? Analysis by the conductance (volume) technique in coronary artery disease

Comparison of the potassium channel blocker tedisamil with the beta-adrenoceptor blocker esmolol and the calcium antagonist gallopamil in patients with coronary artery disease

BACKGROUND

Tedisamil is a new bradycardic agent proven to exert anti-ischemic and antiarrhythmic effects by blockade of the different cardiac and vascular K+ currents.

HYPOTHESIS

It was the aim of the present study to compare the favorable anti-ischemic effects of tedisamil, with two long established representatives in the treatment of coronary artery disease (CAD), namely, the beta1 blocker esmolol and the Ca2 antagonist gallopamil.

METHODS

The hemodynamic and neurohumoral effects of the new potassium channel blocker tedisamil, an agent with negative chronotropic and class III antiarrhythmic properties, were compared with the ultra-short-acting beta1-selective adrenoceptor blocker esmolol and the calcium antagonist gallopamil. A total of 22 patients with angiographically proven CAD and reproducible ST-segment depression in the exercise electrocardiogram was included in two studies with an almost identical design and inclusion criteria. The investigation was carried out using right heart catheterization and bicycle ergometry. A subgroup of 8 patients receiving 0.3 mg/kg body weight tedisamil intravenously (i.v.) in an open dose-finding study was compared with a group of 14 patients who had received esmolol (i.v. bolus of 500 micrograms/kg, maintenance dose 200 micrograms/kg/min) and gallopamil (initial dose 0.025 mg/kg, maintenance dose 0.0005 mg/kg/h) in a second intraindividual comparison.

RESULTS

Tedisamil and esmolol reduced heart rate at rest by 13% (p < 0.001), and 6% (p < 0.05), and at maximum working levels by 8% (p < 0.01) and 9% (p < 0.05), respectively. Gallopamil increased heart rate at rest by 7% (p < 0.05), with only slight changes occurring during exercise. Corresponding findings for each drug were observed for cardiac output both at rest and during exercise [tedisamil: at rest -10% (NS), max. exercise -8%; esmolol: at rest -14% (NS), max. exercise -18% (NS); gallopamil: no significant changes]. Compared with tedisamil, stroke volume was reduced by esmolol [at rest and max. workload: -9% (NS)] and gallopamil [rest: -6% (NS), max. exercise: -2% (NS)]. Of the indirect parameters of ventricular function, that is, mean capillary wedge pressure (PCWPm) and right ventricular ejection fraction, only PCWPm demonstrated significant differences between tedisamil and gallopamil (+18% and -6% at rest, +17% and -21% during exercise, respectively; p < 0.001). Compared with gallopamil, both tedisamil and esmolol were superior in their effects on rate-pressure product, myocardial oxygen consumption, and ST-segment depression, whereas plasma lactate concentration was more reduced by tedisamil and gallopamil. Tedisamil led to a fall in norepinephrine levels in particular.

CONCLUSION

Tedisamil and esmolol showed almost equipotent anti-ischemic effects at the doses administered. Tedisamil acts mainly by reductions in heart rate, and esmolol, though to a lesser degree, also by reductions in systolic blood pressure. The mechanism of gallopamil is to reduce afterload and to improve coronary perfusion. At the doses applied, however, it has lower antianginal potency compared with tedisamil and esmolol.

Tedisamil: a new novel antiarrhythmic

Solvay Pharmaceuticals is currently developing tedisamil (KC-8857), a novel antiarrhythmic with additional anti-ischaemic properties, which acts via potassium channel blockade. This drug can be categorised as a class III antiarrhythmic agent due to its effects of action potential and QT interval prolongation in these patients. This agent was initially developed for its anti-ischaemic properties and Phase I trials have shown tedisamil to be an effective bradycardic agent, as well as causing a reverse rate-dependent QT interval prolongation. Subsequent Phase II results have confirmed that in patients with ischaemic heart disease, tedisamil had beneficial haemodynamic and anti-ischaemic effects. Phase III studies in patients with ischaemic heart disease indicated that tedisamil is an effective agent for the treatment of angina, resulting in a dose-dependent increase in anginal threshold (with a decrease in anginal attacks, increased exercise capacity during treadmill exercise and decreased electrocardiographic signs of exercise induced ischaemia) in comparison to placebo. Although tedisamil has been shown to be an effective anti-ischaemic agent, with Phase III trials for angina pectoris now completed, the company are now pursuing the use of tedisamil for the treatment of atrial fibrillation, for which tedisamil is still in Phase II/III clinical trials. Launch data are not yet known.

Tedisamil attenuates foetal transformation of myosin in the hypertrophied rat myocardium

1 Reduction in repolarizing potassium currents has controversial effects on hypertrophic responses in cardiomyocytes of transgenic models and cultured cardiomyocytes. It remains thus unknown whether a blockade of potassium channels with tedisamil (N,N'dicyclopropylmethylene-9,9-tetramethylene-3,7-diazabicyclo(3.3.1)nonane dihydrochloride) has any effects on cardiac growth during postnatal development or pressure overload. 2 To test the hypothesis that a treatment with tedisamil affects cardiac growth or protein phenotype, sham-operated rats and rats with ascending aorta constriction were treated with tedisamil (36 mg kg day(-1)) for 7 weeks. Left ventricular mass and geometry, relative expression of myosin isoforms, hydroxyproline concentration and isovolumic ventricular function were assessed. 3 Rats with aortic constriction exhibited a marked increase in left ventricular weight and the diastolic pressure-volume relationship was shifted to smaller volumes. The hydroxyproline concentration remained unaltered. The proportion of alpha-myosin heavy chains was, however, reduced (P<0.05). Hypertrophied left ventricles manifested an enhanced overall performance but depressed myocardial contractility. 4 Administration of tedisamil was associated with decreased heart rate (P<0.05). In contrast, cardiac growth in sham-operated rats and concentric left ventricular hypertrophy of pressure-overloaded animals was not significantly altered. Hypertrophied hearts from rats treated with tedisamil expressed more alpha-myosin heavy chains (65+/-4 versus 57+/-4%; P<0.05). Also, maximal rate of wall stress rise and decline was higher (P<0.05) in tedisamil-treated pressure-overloaded rats. 5 In the rat model of pressure-overloaded hypertrophy, tedisamil had no effect on cardiac growth but partially corrected myocardial dysfunction. Postulated mechanism of this effect is the phenotype modification of myosin filaments in hypertrophied myocardium.

Effects of tedisamil on cardiovascular tissues isolated from normo- and hypertensive rats

BACKGROUND

This study was undertaken to characterize the effects of tedisamil on isolated rat cardiovascular tissues, and identify actions that could be beneficial or detrimental in the treatment of cardiac disease.

RESULTS

Tedisamil prolonged the Wistar Kyoto normotensive rat (WKY) left ventricular action potential and augmented the force of contraction of left ventricle strips. On the 12-month-old SHR model of cardiac hypertrophy, the augmenting effects of tedisamil at 10(-6) and 3 x 10(-6) M were reduced. On the 21-month-old SHR model of heart failure, the augmenting effects of tedisamil at 10(-6) and 3 x 10(-6) M were further reduced. The augmenting effect of tedisamil at 10(-5) M was reduced to 47%. The rate of the right atrium of 16- to 17-month-old WKY was reduced by tedisamil at 10(-5) and 10(-4) M, and tedisamil had a similar effect on the SHR right atrium. Tedisamil at 10(-6)--3 x 10(-5) M contracted the portal veins of WKY and aortae of 12-month-old WKY and SHR.

CONCLUSIONS

The positive inotropic and negative chronotropic effects of tedisamil in the rat, which are partially or fully maintained in hypertrophied or failing myocardium would be beneficial in the treatment of heart failure. In contrast, the vasoconstrictor action of tedisamil will be detrimental in heart failure.

Tedisamil: master switch of nature?

Decreasing heart rate is potentially useful in ischaemic heart disease. Tedisamil is a bradycardic agent resulting from its ability to inhibit transient outward current (I(to)) in atria. Tedisamil inhibits I(to), potassium current (IK), K(ATP) and the protein kinase A-activated chloride channel in ventricles as well as vascular IK and Ca(2+)-activated IK (IK((Ca))). Tedisamil prolongs cardiac action potentials and the corrected QT (QTc) of the ECG and also increases cardiac refractoriness. Tedisamil is anti-arrhythmic in animal models of ventricular arrhythmias and atrial flutter. The bradycardic effect of tedisamil is associated with a reduction in myocardial oxygen demand. On isolated rat ventricle, tedisamil is a positive inotrope and on isolated rabbit atria, tedisamil reverses the negative inotropic effect of pinacidil. Tedisamil contracts the isolated rat portal vein and aorta, reduces cromakalim-induced relaxations of contracted rat aorta and increases blood pressure in animals and humans. Tedisamil is 96% bound to plasma proteins, has a plasma half-life of about 10 h and is cleared from the kidney unchanged. Clinical trials have shown that the electrophysiology of tedisamil is that of a class III anti-arrhythmic. In coronary artery disease, tedisamil has no effect on inotropism and increases the threshold for angina. Potassium channel blockade with tedisamil may have advantages over calcium channel blockers or K(ATP) channel openers as an anti-ischaemic mechanism in coronary artery disease. In exercise-induced myocardial ischaemia, beta-blockers are probably favourable to tedisamil, as they will limit the increase in heart rate, contractility and blood pressure caused by sympathetic stimulation, whereas tedisamil will not. In heart failure patients, tedisamil reduces heart rate, but increases blood pressure. The usefulness of tedisamil as a bradycardic agent is limited by the increase in blood pressure. A drug that is bradycardic without increasing blood pressure would be an improvement on tedisamil as the master switch of nature for ischaemic heart disease.

Modulation of cAMP level by tedisamil in guinea pig heart

Tedisamil is antiarrhythmic class III drug with antifibrillating/defibrillating potency linked to enhancement of intermyocyte gap junctional electrical coupling most likely via its sympathomimetic cAMP-related mechanisms. This study was designed to examine the effect of tedisamil on cAMP level in guinea pig hearts in vivo and in vitro in Langendorff preparation. The drug was administered either as a bolus into vena jugularis in dosage 1.0 and 1.5 mg/kg or into the perfusion solution at a concentration of 1.5 x 10(-6) mol/l. In additional experiments, this period was followed by brief 10 min global ischemia, induced by clamping of the aorta or perfusion. After 10 min from the onset of tedisamil administration as well as after 10 min of ischemia the ventricular tissue was immediately frozen for cAMP immunoassay. Tedisamil caused in normal heart small but significant dose-dependent increase of myocardial cAMP (pmol/mg) level in vivo 1.8 and 2.5 vs. 1.4 as well as in vitro 1.1 vs. 0.8 (p < 0.05) conditions. Ischemia itself induced accumulation of cAMP in both, in vivo and in vitro experiments, 2.6 vs. 1.4 and 1.3 vs. 0.8, respectively. The preischemic elevation of cAMP by tedisamil was not potentiated by following ischemia, on the contrary, decline of the cyclic nucleotide was detected comparing to ischemia itself. In conclusion, tedisamil increased cAMP level in normal heart and prevented additional ischemia-related elevation of this nucleotide. The results indicate modulation of myocardial cAMP level by tedisamil, which may account for its protective effect on gap junctional electrical coupling.

Tedisamil in a chronic canine model of atrial flutter

Tedisamil inhibits several cardiac potassium channels including Ito, Ikr, and the adenosine triphosphate (ATP)-sensitive potassium channel (I(KATP)), which may be important in the initiation and maintenance of atrial arrhythmias. We herein report the efficacy of tedisamil in terminating and protecting against the reinduction of atrial flutter (AFL) in a conscious canine model. Sustained AFL (> 15 min) was induced in eight of 10 mongrel dogs by programmed atrial stimulation (PAS) 2-41 days after producing a surgical barrier to conduction in the right atrium. At the time of surgery, an epicardial electrode was attached to the right atrial appendage for pacing and recording. Normal saline, 1 ml/kg, was infused after 15 min of AFL as placebo. Tedisamil (1.0 mg/kg) was given intravenously after 30 min of sustained AFL while recording surface ECGs and atrial electrograms. Conversion to sinus rhythm was achieved in 10 of 10 trials (eight dogs) in a mean time of 20.5 s (SD, +/- 11.8 s). Tedisamil had a negative chronotropic effect lasting > or =2 h and was protective against the reinduction of AFL. In five dogs, PAS was able to induce AFL in only two of seven trials 2 h after drug infusion. The corrected QT interval (QTc) was lengthened for the first 15 min after tedisamil administration (mean, +/- 39.3 ms; p < 0.05), but thereafter returned to baseline. The QRS interval was not altered by tedisamil. Saline alone, given after 15 min of sustained AFL, converted AFL in one of 11 trials (eight dogs) but did not alter the RR interval, QTc, or QRS interval compared with values measured during AFL. No significant adverse effects of tedisamil were observed. The results indicate that tedisamil is effective in interrupting and/or preventing reinduction of canine AFL, possibly by prolonging atrial refractoriness through inhibition of one or more potassium ion repolarizing currents in atrial muscle. Further studies are required to address the exact mechanism by which tedisamil exerts its antiarrhythmic effect.

What should we expect from the next generation of antiarrhythmic drugs?

Five drugs currently constitute approximately 70% of the world market for antiarrhythmic medications. Since the publication of studies documenting that certain Class I drugs may increase mortality in high-risk postinfarction patients, basic science and clinical studies have focused on Class III antiarrhythmic drugs. However, drugs that prolong repolarization and cardiac refractoriness are sometimes associated with potentially lethal torsades de pointes. Amiodarone, a multichannel blocker, may be the exception to this observation, but it nevertheless fails to reduce total mortality compared with placebo in high-risk patients following myocardial infarction. However, Class III agents remain the focus of drug development efforts because they lack the negative hemodynamic effects, affect both atrial and ventricular tissue, and can be administered as either parenteral or oral preparations. Developers of newer antiarrhythmic agents have focused on identifying antiarrhythmic medications with the following characteristics: appropriate modification of the arrhythmia substrate, suppression of arrhythmia triggers, efficacy in pathologic tissues and states, positive rate dependency, appropriate pharmacokinetics, equally effective oral and parenteral formulations, similar efficacy in arrhythmias and their surrogates, few side effects, positive frequency blocking actions, and cardiac-selective ion channel blockade. New and investigational agents that more closely approach these goals include azimilide, dofetilide, dronedarone, ersentilide, ibutilide, tedisamil, and trecetilide. In the near future, medications will increasingly constitute only part of an antiarrhythmic strategy. Instead of monotherapy, they will often be used in conjunction with an implanted device. Combination therapy offers many potential advantages. Long-term goals of antiarrhythmic therapy include upstream approaches, such as identification of the biochemical intermediaries of the process and, eventually, of molecular and genetic lesions involved in arrhythmogenesis.

Cardiac and hemodynamic effects of the sinus node inhibitor tedisamil dihydrochloride in patients with congestive heart failure due to dilated cardiomyopathy

Clinical and experimental investigations have demonstrated an inverse relation between heart rate and myocardial performance in patients with congestive heart failure. Accordingly, this study was designed to investigate the hemodynamic effect of the novel bradycardic compound tedisamil in patients with heart failure. We hypothesized that tedisamil would reduce heart rate and thereby improve hemodynamic parameters of failing hearts with an inverse force-frequency relation. Tedisamil was administered intravenously in nine patients with dilated cardiomyopathy (NYHA II-III). Hemodynamic measurements by right heart catheterization were carried out at time points -30, 10, 20 min, 1, 2, 4, and 6 h. Tedisamil decreased heart rate significantly from 84 +/- 6 beats/min to 73 +/- 4 beats/min (at 10 min; p < 0.05). Stroke volume index remained unchanged, and cardiac index tended to decrease transiently. Mean blood pressure increased from 98 +/- 5 to 104 +/- 6 mm Hg (p < 0.05) because of an increase in systemic vascular resistance from 1,619 +/- 145 to 2,079 +/- 198 dyn x s x cm(-5) (at 20 min; p < 0.05). Diastolic pulmonary pressure and pulmonary vascular resistance showed similar changes. Pulmonary capillary wedge pressure increased from 12 +/- 3 to 16 +/- 4 mm Hg (at 20 min; p < 0.05). Although tedisamil resulted in a significant heart-rate reduction, this was not associated with an improvement of hemodynamics. This may be due to increased afterload of the left and right ventricle. In these patients, tedisamil increased vascular resistance, which is unwanted in the treatment of congestive heart failure.

Mechanism of block by tedisamil of transient outward current in human ventricular subepicardial myocytes

1. Tedisamil is a new antiarrhythmic drug with predominant class III action. The aim of the present study was to investigate the blocking pattern of the compound on the transient outward current (I(to)) in human subepicardial myocytes isolated from explanted left ventricles. Using the single electrode whole cell voltage clamp technique, I(to) was analysed after appropriate voltage inactivation of sodium current and block of calcium current. 2. Tedisamil reduced the amplitude of peak I(to), but did not affect the amplitude of non-inactivating outward current. The drug accelerated the apparent rate of I(to) inactivation. The reduction in time constant of I(to) inactivation depended on drug concentration, the apparent IC50 value was 4.4 microM. 3. Tedisamil affected I(to) amplitude in a use-dependent manner. After 2 min at -80 mV, maximum block of I(to) was reached after 4-5 clamp steps either at the frequency of 0.2 or 2 Hz, indicating that the block was not frequency-dependent in an experimentally relevant range. Recovery from block was very slow and proceeded with a time constant of 12.1+/-1.8 s. Also in the presence of drug, a fraction of channels recovered from inactivation with a similar time constant as in control myocytes (i.e. 81+/-40 ms and 51+/-8 ms, respectively, n.s.). 4. From the onset of fractional block of I(to) by tedisamil during the initial 60 ms of a clamp step, we calculated k1 = 9 x 10(6) mol(-1) s(-1) for the association rate constant, and k2 = 23 s(-1) for the dissociation rate constant. The resulting apparent KD was 2.6 microM and is similar to the IC50 value. 5. The effects of tedisamil on I(to) could be simulated by assuming a four state channel model where the drug binds to the channel in an open (activated) conformation. It is concluded that in human subepicardial myocytes tedisamil is an open channel blocker of I(to) and that this effect probably contributes to the antiarrhythmic potential of this drug.

Effects of tedisamil (KC-8857) on cardiac electrophysiology and ventricular fibrillation in the rabbit isolated heart

1. The direct cardiac electrophysiological and antifibrillatory actions of tedisamil (KC-8857) were studied in rabbit isolated hearts. 2. Tedisamil (1, 3, and 10 microM), prolonged the ventricular effective refractory period (VRP) from 120 +/- 18 ms (baseline) to 155 +/- 19, 171 +/- 20, and 205 +/- 14 ms, respectively. Three groups of isolated hearts (n = 6 each) were used to test the antifibrillatory action of tedisamil. Hearts were perfused with 1.25 microM pinacidil, a KATP channel activator. Hearts were subjected to hypoxia for 12 min followed by 40 min of reoxygenation. Ventricular fibrillation (VF) developed during hypoxia and reoxygenation in both the control and 1 microM tedisamil-treated groups (5/6 and 4/6, respectively). Tedisamil (3 microM) reduced the incidence of VF (0/6, P = 0.007 vs. control). 3. In a separate group of hearts, VF was initiated by electrical stimulation. The administration of 0.3 ml of 10 mM tedisamil, via the aortic cannula, terminated VF in all hearts, converting them to normal sinus rhythm. 4. Tedisamil (3 microM) reversed pinacidil-induced negative inotropic effects in rabbit isolated atrial muscle which were equilibrated under normoxia, as well as in atrial muscle subjected to hypoxia and reoxygenation. 5. The results demonstrate a direct antifibrillatory action of tedisamil in vitro. The mechanism responsible for the observed effects may involve modulation by tedisamil of the cardiac ATP-regulated potassium channel, in addition to its antagonism of IK and Ito.

Left ventricular end-systolic elastance is incorrectly estimated by the use of stepwise afterload variations in conscious, unsedated, autonomically intact dogs

BACKGROUND

End-systolic elastance (Ees), the slope parameter of the end-systolic pressure (ESP)-volume (ESV) relation (ESPVR), is usually estimated in patients by producing stepwise, steady-state pharmacological afterload variations and collecting one ESP-ESV point from each step. The ESPVR is then constructed by fitting a linear equation to these points. In sedated, autonomically blocked dogs, it has been shown that when one point from control, one point from a state of increased afterload, and one point from a state of decreased afterload are used, the resulting Ees incorrectly estimates true Ees, defined as the slope of the ESPVR obtained by transient vena caval occlusion. We investigated if this was also the case in unsedated, autonomically intact dogs when the points used belonged to steady states of progressively decreasing or progressively increasing afterload pressure.

METHODS AND RESULTS

In 10 conscious dogs instrumented with left ventricular (LV) endocardial sonomicrometers to measure LV volume, a LV pressure transducer, and an inferior vena caval (IVC) occluder, two protocols were carried out on separate days. In each protocol, an ESPVR was generated by IVC occlusion in the control state and in two steady-state levels of afterload change produced by stepwise infusion of nitroprusside (protocol 1, afterload decrease) and angiotensin II (protocol 2, afterload increase). In each protocol, steady-state ESP-ESV data points were averaged from the control state and from each level of afterload variation. Linear equations were fitted to the three steady-state points from each protocol, and the estimated Ees values obtained (EesEST) were compared with the Ees values of the control ESPVRs obtained by IVC occlusion (EesTRUE). In protocol 1, EesEST underestimated EesTRUE by about 16% (EesEST, 6.49 +/- 1.55 mm Hg/mL; EesTRUE, 7.48 +/- 1.29 mm Hg/mL; P < .02). In protocol 2, EesEST overestimated EesTRUE by about 37% (EesEST, 9.99 +/- 3.97 mm Hg/mL; EesTRUE, 6.43 +/- 3.88 mm Hg/mL; P < .007).

CONCLUSIONS

In conscious, autonomically intact dogs, the use of stepwise, steady-state afterload variations to obtain ESP-ESV data points to construct the ESPVR incorrectly estimates Ees. In the case of afterload reduction, EesTRUE is underestimated an average of 16.3%, and in the case of afterload increase, EesTRUE is overestimated an average of 37.1%. These errors should be taken into account when interpreting clinical studies using this methodology.