Does the CHA2DS2-VASc scale sufficiently predict the risk of left atrial appendage thrombus in patients with diagnosed atrial fibrillation treated with non-vitamin K oral anticoagulants?

The CHA2DS2-VASc scale does not include potential risk factors for left atrial appendage thrombus (LAAT) formation such as a form of atrial fibrillation (AF) and impaired kidney function. The real risk of thromboembolic complications in AF patients is still unclear as well as an optimal anticoagulant treatment in males with a CHA2DS2-VASc score of 1 and females with a CHA2DS2-VASc score of 2.The aim of this study was to compare the predictive value of the CHA2DS2-VASc scale and other scales to estimate the risk of LAAT formation in AF patients treated with non-vitamin K oral anticoagulants (NOACs) and to assess the prevalence of thrombi in patients at intermediate risk of stroke.The observational study included consecutive patients with a diagnosis of non-valvular AF treated with NOACs, admitted to 3 high-reference institutions between 2013 and 2018. All individuals underwent transoesophageal echocardiography before cardioversion or ablation.Out of 1163 enrolled AF patients (62.1% male, mean age 62 years) the LAAT had been detected in 50 individuals (4.3%). Among patients with LAAT, 1 patient (2.0%) was classified as a low-risk category, 9 (18.0%) were at intermediate-risk, and 40 (80.0%) were at high risk of thromboembolic complications according to CHA2DS2-VASc scale. All patients were treated with NOACs: 51.0% rivaroxaban, 47.1% dabigatran, and 1.9% apixaban.Patients at intermediate stroke-risk with detected LAAT had higher R2CHADS2 score (2.1 ± 1.2 vs 1.2 ± 0.8, P = .007), higher CHA2DS2-VASc-RAF score (6.4 ± 4.4 vs 3.7 ± 2.6, P = .027) and more often had an estimated glomerular filtration rate below 56 mL/min/1.73 m (44.4% vs 13.2%, P = .026) compared to patients without LAAT. The receiver operating characteristics revealed that the CHA2DS2-VASc-RAF scale had better predictive ability to distinguish between patients with and without LAAT in the study group than CHA2DS2-VASc (P = .0006), CHADS2 (P = .0006) and R2CHADS2 scale (P = .0140).The CHA2DS2-VASc scale should be supplemented with an assessment of renal function and form of AF to improve stroke risk estimation. The application of additional scales to estimate the risk of LAAT might be especially useful among males with a CHA2DS2-VASc score of 1 and females with a CHA2DS2-VASc score of 2.

Absence of Functional Nav1.8 Channels in Non-diseased Atrial and Ventricular Cardiomyocytes

PURPOSE

Several studies have indicated a potential role for SCN10A/NaV1.8 in modulating cardiac electrophysiology and arrhythmia susceptibility. However, by which mechanism SCN10A/NaV1.8 impacts on cardiac electrical function is still a matter of debate. To address this, we here investigated the functional relevance of NaV1.8 in atrial and ventricular cardiomyocytes (CMs), focusing on the contribution of NaV1.8 to the peak and late sodium current (INa) under normal conditions in different species.

METHODS

The effects of the NaV1.8 blocker A-803467 were investigated through patch-clamp analysis in freshly isolated rabbit left ventricular CMs, human left atrial CMs and human-induced pluripotent stem cell-derived CMs (hiPSC-CMs).

RESULTS

A-803467 treatment caused a slight shortening of the action potential duration (APD) in rabbit CMs and hiPSC-CMs, while it had no effect on APD in human atrial cells. Resting membrane potential, action potential (AP) amplitude, and AP upstroke velocity were unaffected by A-803467 application. Similarly, INa density was unchanged after exposure to A-803467 and NaV1.8-based late INa was undetectable in all cell types analysed. Finally, low to absent expression levels of SCN10A were observed in human atrial tissue, rabbit ventricular tissue and hiPSC-CMs.

CONCLUSION

We here demonstrate the absence of functional NaV1.8 channels in non-diseased atrial and ventricular CMs. Hence, the association of SCN10A variants with cardiac electrophysiology observed in, e.g. genome wide association studies, is likely the result of indirect effects on SCN5A expression and/or NaV1.8 activity in cell types other than CMs.

The incidence of left atrial appendage thrombi on transesophageal echocardiography after pretreatment with apixaban for cardioversion in the real-world practice

The risk of thromboembolisms during the post-cardioversion period is high. For patients with persistent atrial fibrillation (AF), anticoagulation with warfarin (INR 2.0~3.0) is recommended for at least three weeks prior and four weeks after cardioversion. We aimed to evaluate the efficacy of apixaban in preventing thromboembolic events during post-cardioversion. We enrolled 127 consecutive persistent AF patients (83 persistent, 44 longstanding persistent AF), scheduled to undergo cardioversion and were pretreated with apixaban. All patients underwent transesophageal echocardiography (TEE) to rule out thrombi in the left atrium (LA) or LA appendage (LAA) after anticoagulation with apixaban. The median duration of anticoagulation before the TEE was 37 (interquartile range [IQR] 34, 50) days. There were 7 patients (5.5%) with visible thrombi in the LAA. A spontaneous echo contrast was noted in 24 (18.9%) patients. Cardioversion was attempted in 117 patients, and they were prescribed amiodarone before the elective DC cardioversion. Sinus rhythm was achieved in 37 patients (31.6%) by amiodarone itself. DC cardioversion was attempted in 80 patients and was successful in 73 (91.3%). None of the cardioverted patients had any thromboembolic events within one month. Transient ischemic attacks were observed in one patient during a median follow up period of 202 days (IQR 143, 294). In conclusion, apixaban could be used as an anticoagulant for patients scheduled for cardioversion. However, the incidence of thrombi was not negligible. TEE or other imaging modalities should be considered before cardioversion or other invasive procedures.

Atrial thrombogenesis in atrial fibrillation : Results from atrial fibrillation models and AF-patients

Atrial fibrillation (AF) is the most common cause of thromboembolic complications. The risk of suffering a thromboembolic complication depends on the accompanying cardiac risk factors and the patient's age. For patients who have an increased risk, which is now classified using the CHA2DS2-VASc score, initiation of long-term oral anticoagulation is the first-line treatment. In AF, thrombi arise in the left atrial appendage. The present review will summarize the basic pathophysiology of thrombogenesis in AF and will provide the molecular basis of a process called prothrombotic endocardial remodeling. Despite oral anticoagulation being a central component of therapy, the present results can be used to support concomitant therapy with statins, angiotensin II blockers, etc. to inhibit atrial thromogenesis.

Resolution of massive left atrial appendage thrombi with rivaroxaban before balloon mitral commissurotomy in severe mitral stenosis: A case report and literature review

RATIONALE

Data on nonvitamin K antagonist oral anticoagulant being used for the treatment of LAA thrombi are limited only in nonvalvular atrial fibrillation. There are no data on the antithrombotic efficacy and safety of nonvitamin K antagonist oral anticoagulant in the resolution of left atrial appendage (LAA) thrombi in patients with rheumatic mitral stenosis.

PATIENT CONCERNS

A 49-year-old woman with known rheumatic mitral stenosis and atrial fibrillation was referred for percutaneous transvenous mitral commissurotomy because of progressive dyspnea on exertion over a period of 3 months.

DIAGNOSES

Transesophageal echocardiography (TEE) demonstrated a large LAA thrombus protruding into left atria cavity before the procedure.

INTERVENTIONS

Direct factor Xa (FXa) inhibitor rivaroxaban (20 mg/d) was started for the patient. After 3 weeks of rivaroxaban treatment TEE showed a relevantly decreased thrombus size, and a complete thrombus resolution was achieved after 5 weeks of anticoagulant therapy with the FXa inhibitor.

OUTCOMES

To the best of our knowledge, this is the first documented case of large LAA thrombus resolution with nonvitamin K antagonist oral anticoagulant in severe mitral stenosis, and in which percutaneous transvenous mitral commissurotomy was performed subsequently.

LESSONS

The report indicated that rivaroxaban could be a therapeutic option for mitral stenosis patients with LAA thrombus. Further study is required before the routine use of rivaroxaban in patients with rheumatic mitral stenosis and atrial fibrillation.

[The cholinergic non-excitability phenomenon in the atrial myocardium of lower vertebrates]

Changes of electric activity induced by acetylcholine were studied in atrial myocardium of fishes (cod and carp) and reptilians (lizard and grass-snake). Standart microelectrode technique and novel method of optical mapping were used in the study. Acetylcholine (1-50 microM) provoked decrease of the action potential amplitude down to full inhibition of electrical activity in wide regions of atrium of cod and carp. We define this phenomenon as cholinergic inexcitability. In other regions excitation persisted even during action of 500 microM acetylcholine. In atria of lizard and grass-snake acetylcholine caused shortening of action potential without changes in it's amplitude. Local cholinergic inexcitability, shown in the atrial myocardium of fishes, is quite similar to the phenomenon, that was described earlier in the atria of frogs. It presents the heart of fish as an interesting model for study of mechanisms of cholinergic atrial arrhythmias initiation.

Carvedilol Therapy Is Associated with an Improvement in Left Atrial Appendage Function in Patients with Congestive Heart Failure

Heart failure is one of the leading death reasons in the world. Left atrial appendage (LAA) is of great importance in maintaining cardiac function. We examined the effect of carvedilol therapy on left atrial appendage functions in patients with symptomatic congestive heart failure. Twenty patients with symptomatic congestive heart failure and resting ejection fraction < or = 40% were included in this study. LAA was visualized by transesophageal echocardiography. LAA area change (LAAAC), LAA empty velocity (LAAEV) and LAA empty velocity time integral (LAAEVTI) were calculated as the average of five cardiac cycles. A minimum dose of carvedilol administered to each patient, was titrated up to maximal dose that the patients could tolerate, during an 8-week period. After the third month of completing treatment, a second transthoracic and transesophageal echocardiographic study was performed. Heart rate (P < 0.001), systolic (P = 0.002) blood pressures were reduced by carvedilol therapy at the end of the third month. LAAEV (P < 0.001), LAAEVTI (P < 0.001), and LAAAC (P < 0.001) were significantly increased at the end of the third month of carvedilol therapy. This study indicates that in patients with symptomatic congestive heart failure, carvedilol therapy is associated with an improvement in left atrial appendage function.

Effect of diltiazem and metoprolol on left atrial appendix functions in patients with nonvalvular chronic atrial fibrillation

OBJECTIVES

Thrombo-embolic events are the important cause of mortality and morbidity in patients with chronic atrial fibrillation (CAF). The origin of thromboembolism is often the left atrial appendix (LAA). Flow rate velocity (FRV) inside the LAA is the major determinant of thrombus formation. The aim of our study was to investigate the effects of diltiazem and metoprolol used for ventricular rate control on FRV of the LAA in CAF patients and thus to evaluate the positive or negative effects of these two drugs on thromboembolic events.

METHODS

Sixty-four patients were included in the study. All patients were suffering from CAF for more than a year. The patients were allocated to two groups according with agent used for rate control- metoprolol (Group 1; n=31) and diltiazem (Group 2; n=33). Transesophageal echocardiography was applied to all patients and LAA FRV was measured by a pulse wave Doppler in the 1/3 proximal portion of the LAA. The measurements were repeated after applying 5 mg metoprolol to Group 1 and 25 mg diltiazem to Group 2 via venous cannula.

RESULTS

In Group 1 after metoprolol LAA flow velocity changed from 0.25 +/- 0.90 m/s to 0.25 +/- 0.10 m/s (p>0.05). In group 2 after diltiazem left atrial appendix FRV decreased from 0.21 +/- 0.9 m/s to 0.19 +/- 0.6 m/s (p>0.05).

CONCLUSIONS

In patients with CAF metoprolol used for ventricular rate control had no effect on LAA flow velocity and the observed decrease in LAA flow rate velocity with intravenous diltiazem was insignificant.

(-)-Adrenaline elicits positive inotropic, lusitropic, and biochemical effects through beta2 -adrenoceptors in human atrial myocardium from nonfailing and failing hearts, consistent with Gs coupling but not with Gi coupling

Activation of either coexisting beta1- or beta2 -adrenoceptors with noradrenaline or adrenaline, respectively, causes maximum increases of contractility of human atrial myocardium. Previous biochemical work with the beta2 -selective agonist zinterol is consistent with activation of the cascade beta2 -adrenoceptors-->Gsalpha-protein-->adenylyl cyclase-->cAMP-->protein kinase (PKA)-->phosphorylation of phospholamban, troponin I, and C-protein-->hastened relaxation of human atria from nonfailing hearts. However, in feline and rodent myocardium, catecholamines and zinterol usually do not hasten relaxation through activation of beta2 -adrenoceptors, presumably because of coupling of the receptors to Gi protein. It is unknown whether the endogenously occurring beta2 -adrenoceptor agonist adrenaline acts through the above cascade in human atrium and whether its mode of action could be changed in heart failure. We assessed the effects of (-)-adrenaline, mediated through beta2 -adrenoceptors (in the presence of CGP 20712A 300 nM to block beta1 -adrenoceptors), on contractility and relaxation of right atrial trabecula obtained from nonfailing and failing human hearts. Cyclic AMP levels were measured as well as phosphorylation of phospholamban, troponin I, and protein C with Western blots and the back-phosphorylation procedure. For comparison, beta1 -adrenoceptor-mediated effects of (-)-noradrenaline were investigated in the presence of ICI 118,551 (50 nM to block beta2 -adrenoceptors). The positive inotropic effects of both (-)-noradrenaline and (-)-adrenaline were accompanied by reductions in time to peak force and time to reach 50% relaxation. (-)-Adrenaline caused similar positive inotropic and lusitropic effects in atrial trabeculae from failing hearts. However, the inotropic potency, but not the lusitropic potency, of (-)-noradrenaline was reduced fourfold in atrial trabeculae from heart failure patients. Both (-)-adrenaline and (-)-noradrenaline enhanced cyclic AMP levels and produced phosphorylation of phospholamban, troponin I, and C-protein to a similar extent in atrial trabeculae from nonfailing hearts. The hastening of relaxation caused by (-)-adrenaline together with the PKA-catalyzed phosphorylation of the three proteins involved in relaxation, indicate coupling of beta2 -adrenoceptors to Gs protein. The phosphorylation of phospholamban at serine16 and threonine17 evoked by (-)-adrenaline through beta2 -adrenoceptors and by (-)-noradrenaline through beta1 -adrenoceptors was not different in atria from nonfailing and failing hearts. Activation of beta2 -adrenoceptors caused an increase in phosphorylase a activity in atrium from failing hearts further emphasizing the presence of the beta2 -adrenoceptor-Gsalpha-protein pathway in human heart. The positive inotropic and lusitropic potencies of (-)-adrenaline were conserved across Arg16Gly- and Gln27Glu-beta2 -adrenoceptor polymorphisms in the right atrium from patients undergoing coronary artery bypass surgery, chronically treated with beta1 -selective blockers. The persistent relaxant and biochemical effects of (-)-adrenaline through beta2 -adrenoceptors and of (-)-noradrenaline through beta1 -adrenoceptors in heart failure are inconsistent with an important role of coupling of beta2 -adrenoceptors with Gialpha-protein in human atrial myocardium.

Myocardial contractility after in Vitro treatment with class III antiarrhythmic drug Nibentan

Myocardial contractility was studied in vitro in response to treatment with class III antiarrhythmic drug Nibentan. The contractile response to Nibentan in increasing concentrations of 1.66, 2.5, and 3.5 mM was estimated on strips of animal myocardium and human right atrial auricle.

Interaction between simvastatin and metoprolol with respect to cardiac beta-adrenoceptor density, catecholamine levels and perioperative catecholamine requirements in cardiac surgery patients

Beta-blockade is a standard cardiovascular therapy known to induce the up-regulation of beta-adrenoceptor density. Upon ligand-binding, beta-adrenoceptors are normally internalised via the arrestin pathway, and after dissociation they are re-inserted into the membrane. This means that at high catecholamine levels the adrenoceptor density is low and under beta-blockade it is high. The insertion of receptors into the membrane is often dependent on farnesylation processes that can be inhibited by statins. We carried out a prospective, controlled, observational study to determine whether beta-blockade-induced up-regulation of beta-adrenoceptor density is attenuated by statin therapy and whether this would subsequently affect catecholamine consumption during surgery. We obtained pre-operative blood samples and intra-operative biopsies of the right atrial appendage from 39 patients (age: 65+/-5 years; BMI: 28+/-1) undergoing coronary bypass surgery with or without simvastatin (20 mg/day) therapy and with or without concomitant metoprolol therapy (50 mg/day). The atrial tissue was used for radioligand-binding studies with (-)-[125I]-iodocyanopindolol (ICYP) and for assessment of the beta-adrenoceptor subtype distribution following standard protocols. In the blood samples, plasma adrenaline and noradrenaline concentrations were determined using HPLC. In all tissue samples, we found a total beta-adrenoceptor density of 38+/-4 fmol/mg protein in untreated controls; this which was up-regulated to 55+/-5 fmol/mg protein in patients receiving metoprolol. This increase in receptor number was nearly prevented completely by simvastatin therapy (42+/-5 fmol/mg protein). The up-regulation could be attributed to increases in the beta1-adrenoceptor subtype. In contrast, simvastatin alone had no effect on beta-adrenoceptor density. Pre-operative adrenaline levels were slightly reduced in all drug therapy groups (nonsignificant differences), while the levels noradrenaline were not significantly different among the groups. With respect to the perioperative catecholamine requirements, patients on metoprolol needed significantly less dopamine than control patients, while patients undergoing simvastatin/metoprolol therapy needed as much as the controls. The post-operative total catecholamine requirements were not different among the four groups of patients. There were no differences in plasma metoprolol concentration between patients receiving metoprolol alone and those receiving a combination of metoprolol and simvastatin.

IN CONCLUSION

Simvastatin therapy seems to counter-regulate the up-regulation of beta-adrenoceptor density. In the up-regulated state induced by metoprolol therapy, the patients seemed to need less catecholamines during cardiac surgery, which may be due to the higher number of beta-adrenoceptors. Additional simvastatin therapy did not reduce post-operative catecholamine consumption.

Is cyclic AMP formation desensitized in patients with end-stage renal failure?

1 Cyclic AMP formation has consistently been reported to be desensitized in various tissues including heart of animal models of end-stage renal failure (ESRF). In contrast, reports on desensitization of cAMP formation in ESRF patients remain contradictory. Whether this discrepancy results from a difference between human ESRF and its animal models or from the use of circulating blood cells in the human and various solid tissues in the animal studies, remains unclear. Therefore, we performed three studies with heart and platelets of ESRF patients undergoing haemodialysis or continuous ambulatory peritoneal dialysis and age- and gender-matched controls with normal renal function (n = 11-13 each). 2 In platelets from haemodialysis patients adenylyl cyclase activity in response to receptor-dependent and -independent agonists was reduced by approximately 30%, and this could be explained by an alteration at the level of adenylyl cyclase itself. However, no such desensitization was seen in platelets from peritoneal dialysis patients. 3 In hearts from ESRF patients undergoing haemodialysis, beta-adrenoceptor density and subtype distribution, cAMP formation in response to the beta-adrenoceptor agonist isoprenaline or various receptor-independent stimuli, were very similar to those in control patients but activity of G-protein-coupled receptor kinase was increased by approximately 20%. 4 We conclude that conflicting reports on the desensitization of cAMP formation between ESRF patients and ESRF animal models are not explained by the use of solid tissues in animal studies vs. circulating blood cells in patient studies. Rather desensitization of cAMP formation seems to be a less consistent feature of human ESRF than of its animal models.

The effect of gliclazide and glibenclamide on preconditioning of the human myocardium

The cardioprotection of ischaemic preconditioning may be abolished in diabetic patients especially when some oral hypoglycaemics are used. The dose-response effect of gliclazide and glibenclamide on ischaemic preconditioning and the action of glibenclamide on signal transduction in human myocardium were investigated using right atrial appendages from cardiac surgery patients. Glibenclamide (0.1, 1, 3 and 10 microM) and gliclazide (1, 10, 30 and 100 microM) were added for 10 min prior to ischaemic preconditioning. The cardioprotection was abolished by glibenclamide at all concentrations and by gliclazide at supratherapeutic concentrations of 30 and 100 microM. Glibenclamide abolished the protective effect of mitoK(ATP) channel opening but not that of protein kinase C (PKC) or p38 mitogen activated protein kinase (p38MAPK) activation. In conclusion, glibenclamide and gliclazide differential effects may be a result of differential sensitivities. Glibenclamide does not block protection conferred by either PKC or p38MAPK activation. These findings may have clinical implications in ischaemic heart disease.

Electrophysiological effects of flecainide and sotalol in the human atrium during persistent atrial fibrillation

AIMS

Atrial fibrillation (AF) shortens the atrial action potential and the atrial refractory period. These changes promote persistence of AF. Pharmacological prolongation of atrial action potential duration (APD) may therefore help to prevent recurrent AF. In addition to prolonging APD, sodium channel blockers may prevent AF by inducing post-repolarization refractoriness (PRR). We studied whether two antiarrhythmic drugs (sotalol, flecainide) prolong APD or induce PRR in the fibrillating human atrium.

METHODS

In 12 patients with persistent AF (11 male, 58 +/- 5 yrs, 27 +/- 7 months duration of AF), we recorded monophasic action potentials from the right atrial appendage and inferior right atrium at baseline and 15 minutes after intravenous administration of sotalol (1.5 mg/kg) or flecainide (2 mg/kg). APD and effective refractory periods (ERP) were determined.

RESULTS

Both drugs prolonged APD90 during AF (flecainide from 109 +/- 7 ms to 137 +/- 10 ms, sotalol from 108 +/- 6 ms to 131 +/- 8 ms, both p < 0.05 vs. baseline). Sotalol prolonged ERP in parallel to APD (from 119 +/- 8 ms to 139 +/- 8 ms, p < 0.05). Flecainide induced PRR by prolonging ERP more than APD90 (from 134 +/- 9 ms to 197 +/- 28 ms, p < 0.05 vs. baseline and vs. sotalol).

CONCLUSIONS

Flecainide and sotalol prolong the atrial action potential during atrial fibrillation in humans. In addition, flecainide induces atrial PRR. These electrophysiological effects may reduce AF recurrences and prevent their persistence.

Hypotensive activity of the ethanol extract of Pavetta crassipes leaves

Pavetta crassipes leaf is routinely used locally in Nigeria for the management of respiratory disorders and hypertension. The hypotensive and other cardiovascular effects of Pavetta crassipes were investigated in cats and rats. The effects of the extract on rat and cat blood pressures, isolated rat atria, rat portal vein, isolated rat aorta and rat vas deferens were studied. Specific receptor antagonists (atropine, mepyramine, phentolamine, propranolol) were used to elucidate the underlying mechanism(s) involved in the cardiovascular changes induced by P. crassipes. The results revealed that the ethanolic extract of Pavetta crassipes lowered the blood pressures of cats and rats in a dose dependent manner. The extract also caused a concentration-dependent decrease in the force of contraction of the isolated rat atria and rat portal vein. The decreases in blood pressure values were attenuated in the presence of a beta-adrenoceptor antagonist, propranolol. The extract also attenuated isoprenaline-induced contraction of the rat atria. However, the extract did not affect contractions evoked by KCl, norepinephrine and 5-HT on the rat aorta. Pavetta crassipes contains biologically active substances that may be useful in the management of hypertension.

Role of I Kur in Controlling Action Potential Shape and Contractility in the Human Atrium

Background— The ultrarapid outward current I Kur is a major repolarizing current in human atrium and a potential target for treating atrial arrhythmias. The effects of selective block of I Kur by low concentrations of 4-aminopyridine or the biphenyl derivative AVE 0118 were investigated on right atrial action potentials (APs) in trabeculae from patients in sinus rhythm (SR) or chronic atrial fibrillation (AF).

Methods and Results— AP duration at 90% repolarization (APD 90 ) was shorter in AF than in SR (300±16 ms, n=6, versus 414±10 ms, n=15), whereas APD 20 was longer (35±9 ms in AF versus 5±2 ms in SR, P <0.05). 4-Aminopyridine (5 μmol/L) elevated the plateau to more positive potentials from −21±3 to −6±3 mV in SR and 0±3 to +12±3 mV in AF. 4-Aminopyridine reversibly shortened APD 90 from 414±10 to 350±10 ms in SR but prolonged APD 90 from 300±16 to 320±13 ms in AF. Similar results were obtained with AVE 0118 (6 μmol/L). Computer simulations of I Kur block in human atrial APs predicted secondary increases in I Ca,L and in the outward rectifiers I Kr and I Ks , with smaller changes in AF than SR. The indirect increase in I Ca,L was supported by a positive inotropic effect of 4-aminopyridine without direct effects on I Ca,L in atrial but not ventricular preparations. In accordance with the model predictions, block of I Kr with E-4031 converted APD shortening effects of I Kur block in SR into AP prolongation.

Conclusions— Whether inhibition of I Kur prolongs or shortens APD depends on the disease status of the atria and is determined by the level of electrical remodeling.

Effects of intravenous nifekalant, a class III antiarrhythmic drug, on atrial vulnerability parameters in patients with paroxysmal atrial fibrillation

Nifekalant, a class III antiarrhythmic drug, has been shown to suppress ventricular tachyarrhythmias, but its effects on AF are unclear. The aim of this study was to clarify the effects of nifekalant on the atrial vulnerability parameters in patients with paroxysmal AF. The study included 18 patients with paroxysmal AF who underwent electrophysiological study before and after intravenous infusion of nifekalant. The atrial electrophysiological parameters including the atrial effective refractory period (AERP), maximum intraatrial conduction delay, and wavelength index, calculated as the ratio of AERP to the maximum conduction delay, were quantitatively measured at baseline and during nifekalant infusion. The mean AERP was significantly prolonged from 214 +/- 27 ms at baseline to 242 +/- 39 ms after nifekalant (P < 0.001). Although earlier studies have shown that nifekalant does not affect the atrial conduction time, the mean maximum conduction delay of the study patients was significantly prolonged from 59 +/- 19 ms at baseline to 72 +/- 28 ms after nifekalant (P = 0.015). There was no significant difference in the wavelength index at baseline (4.1 +/- 1.7) and after nifekalant (4.1 +/- 2.5). However, when the differences of AERP and wavelength index were defined as each parameter during nifekalant infusion minus that at baseline, the difference of AERP showed a direct positive correlation with that of the wavelength index (P = 0.013). In conclusion, nifekalant may be effective in the prevention of AF due to prolongation of the AERP. However, in those patients who have a lesser degree of prolongation of the AERP by nifekalant, the wavelength index tended to be decreased, suggesting that the drug might augment the propensity for AF.

Neuropeptide Y inhibits acetylcholine release in human heart atrium by activation of Y2-receptors

Congestive heart failure and other cardiac diseases are characterized by increased activity of the sympathetic nervous system, whereas at the same time parasympathetic activity is often suppressed. Such imbalance may be a result of or at least enhanced by presynaptic inhibitory effects of sympathetic neurotransmitters on acetylcholine release. We investigated whether the sympathetic cotransmitters neuropeptide Y (NPY), norepinephrine (NE), and ATP are capable of modulating acetylcholine release in human heart atrium. Human atrial appendages were incubated with [(3)H]-choline to label cholinergic transmitter stores and placed in superfusion chambers. Electrical field stimulations (S1, S2) induced a tetrodotoxin-dependent [(3)H]-release, which was taken as an index of endogenous acetylcholine release. NE, NPY, ATP, and a P2-receptor analogue were added before S2. NPY (0.05-1.0 micromol/l) concentration dependently inhibited acetylcholine release. This effect was prevented by the NPY-Y(2)-receptor antagonist BIIE 0246 (0.1 micromol/l) but not by the NPY-Y(1)-receptor antagonist BIBP 3226 (10 micromol/l). ATP (10 micromol/l), a stable analogue ADP-beta S (3 micromol/l), and NE (1 micromol/l) had no effect on acetylcholine release. m-RNA for the NPY-receptor subtypes Y(1), Y(2), Y(4), Y(5), and y(6) was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR). The results suggest that the sympathetic neurotransmitter NPY inhibits parasympathetic neurotransmission in the human heart through activation of presynaptic Y(2)-receptors. NE and ATP seem not to play a role. Since NPY plasma levels are high in chronic heart failure patients, NPY may be one component leading to impaired parasympathetic neurotransmission in those patients.

Clarithromycin reducesIsusandItocurrents in human atrial myocytes with minor repercussions on action potential duration

The macrolide antibacterial agent clarithromycin has been shown to cause QT interval prolongation on the electrocardiogram. In rabbit heart preparations clarithromycin (concentration dependently) lengthened the action potential duration and blocked the delayed rectifier current. The aim of the present study was to investigate the clarithromycin effects: (i) on the Ca2+ L-type and the main K+ repolarizing currents on human atrial myocytes, using whole-cell patch clamp recordings and (ii) on action potentials recorded from human atrial and ventricular myocardium using conventional microelectrodes. It has been found that (i) 10-30 microM clarithromycin reduced the sustained current Isus significantly and that a 100 microM concentration was needed to cause a significant reduction in the transient outward current Ito, whereas clarithomycin did not affect the calcium current and (ii) clarithromycin (10-100 microM) prolonged the action potential duration in atrial preparations but did not alter the different parameters of the ventricular action potential. It is concluded that clarithromycin exerts direct cardiac electrophysiological effects that may contribute to pro-arrythmic potential.

Electromechanical impairment of human auricle and rat myocardial strip subjected to exogenous oxidative stress

OBJECTIVE

Animal myocardial dysfunction induced by remote ischemia-reperfusion (IR) was shown to be partly accomplished via a direct effect of the pro-oxidant xanthine oxidase (XO). This direct remote effect was not tested in humans. We now assessed the performance of human auricles in the presence of solutions containing XO and/or allopurinol and compared them to those of rat myocardial strips.

METHODS

Human and rat specimens (n=64) were separately exposed for 2h to Krebs-Henseleit solution that either (1) exited from rat livers that were earlier perfused for 2h (control-human or control-rat), (2) exited from livers that were earlier made ischemic for 2h (IR-human, IR-rat), (3) contained xanthine (X) 3.8 microM + XO 3 mU ml(-1) (X+XO-human, X+XO-rat), or (4) exited from post 2h-ischemic livers and contained 100 microM allopurinol (human or rat IR + allopurinol groups).

RESULTS

Unlike the unchanged electromechanical performance in the control and IR+allopurinol auricles and strips, the rates of contraction, maximal force of contraction and working index of either preparation were reduced by 75-98% (P<0.01) when exposed to the IR reperfusate or to the X+XO-enriched Krebs. The basal amplitudes of contraction in these four latter groups increased twofold (P<0.01). XO activity was similarly low in the control and in the IR+allopurinol groups, but four- to 45-fold (P<0.001) higher in the IR and the X+XO groups, both in the rat and human organs. The reduced glutathione was reduced by approximately 50% (P<0.01) in either preparation in the IR and the X+XO groups compared to the control and IR+allopurinol groups.

CONCLUSIONS

Remotely and exogenously originated oxidative burst directly induces electromechanical dysfunction and disrupts oxidant/antioxidant balance in human auricles as it does in the rat myocardial strip.

Use of transesophageal contrast echocardiography for excluding left atrial appendage thrombi in patients with atrial fibrillation before cardioversion

Transesophageal echocardiographic (TEE) guidance of cardioversion in patients with atrial fibrillation is an alternative method to conventional anticoagulation. Although TEE is considered the gold standard for excluding left atrial (LA) thrombi, in some patients dense spontaneous echo contrast (SEC) and artifacts may hamper the identification or exclusion of LA thrombi. Often those patients are refused cardioversion. The purpose of this study was to determine whether the application of echo contrast (Optison, Mallinckrodt, San Diego, Calif) facilitates the exclusion of LA appendage thrombi in this patient group and allows for safer cardioversion. Forty-one patients with atrial fibrillation and dense SEC or inconclusive TEE findings were given echo contrast. Fourteen patients with sinus rhythm served as control participants. Echo contrast completely reduced artifacts in 13 of 22 patients. In 12 of 19 patients with SEC, the LA appendage was completely filled after the application of echo contrast and, thus, SEC was completely suppressed. In 13 of 41 patients, it was filled incompletely and in 9 of 41 patients, a new mass resembling a thrombus was detected. In total, of 25 of 41 patients with inconclusive TEE findings an atrial thrombus was definitively excluded. Those patients underwent cardioversion. None of those patients had a cerebral embolic complication as assessed by cranial magnetic resonance imaging. Thus, the application of echo contrast may facilitate the TEE exclusion of LA appendage thrombi and, hence, improve the safety of TEE-guided cardioversion.

Effect of low-dose isoproterenol infusion on left atrial appendage function soon after cardioversion of chronic atrial tachyarrhythmias

BACKGROUND

Cardioversion of chronic atrial fibrillation or atrial flutter to sinus rhythm is often associated with transient atrial mechanical dysfunction, i.e. 'atrial stunning', which may increase the risk of subsequent thromboembolic events. We hypothesized that, because of its positive inotropic action, a low-dose isoproterenol infusion might improve postcardioversion atrial mechanical function.

METHOD

Eighteen patients (15 male, three female; 12 atrial fibrillation, six atrial flutter; mean age 65+/-10 years) exhibiting atrial postcardioversion stunning were included in the study. Isoproterenol was infused for 10 min at a dose sufficient to increase the heart rate by about 10%. Using transesophageal echocardiography, both the left atrial appendage emptying/filling flow velocity and function (fractional area change) were examined at baseline, before isoproterenol (immediately after cardioversion) and after isoproterenol.

RESULTS

With infusion of 0.005-0.008 microg/kg/min isoproterenol, heart rate increased by 11.1+/-2.9%, and left atrial appendage emptying velocity, which was diminished following cardioversion, increased significantly (P<0.001) (baseline, before and after isoproterenol: 41.1+/-18.0, 20.3+/-8.5 and 27.3+/-9.6 cm/s, respectively). No major complications were associated with isoproterenol infusion.

CONCLUSIONS

Short-term infusion of low-dose isoproterenol improved atrial function after cardioversion of chronic atrial fibrillation and atrial flutter.

Cardiovascular effects of isorhamnetin and quercetin in isolated rat and porcine vascular smooth muscle and isolated rat atria

Isorhamnetin and quercetin produced endothelium-independent vasodilator effects in rat aorta, rat mesenteric arteries, rat portal vein and porcine coronary arteries. The effects of the two flavonoids were similar in arteries stimulated by noradrenaline, KCl, U46619 or phorbol esters but the two flavonoids were more potent in the coronary arteries than in the aorta. At high concentrations, they also induced a positive inotropic effect in isolated rat atria. Therefore, at least part of the in vivo effects of quercetin may result from its conversion to isorhamnetin which is the main metabolite of quercetin found in plasma. The arterial, venous and coronary vasodilator effects may contribute to the protective effects of flavonoids in ischaemic heart disease observed in epidemiological studies.

Does acute-phase beta blockade reduce left atrial appendage function in patients with chronic nonvalvular atrial fibrillation?

To investigate whether acute-phase beta-blocker therapy has a harmful effect on left atrial appendage (LAA) function in patients with chronic nonvalvular atrial fibrillation by transesophageal echocardiography (TEE), we evaluated 21 patients with normal left ventricular systolic function and a poorly controlled ventricular rate, despite the use of digoxin. Baseline parameters that were obtained included heart rate, blood pressure, LAA emptying velocities, and left atrial spontaneous echo contrast intensity. Then, each patient was given a bolus dose of 5 mg metoprolol. Ten minutes later, a second set of assessments was performed. After the first TEE studies, each patient began treatment with metoprolol (50 mg orally twice daily for 1 week). A second TEE study was performed after 1 week of continuous oral metoprolol therapy at maintenance dose, and values were again determined. The average resting apical heart rate was 91 +/- 7 bpm. As expected, beta-blocker therapy showed a marked decrease in heart rate at 10 minutes (79 +/- 6 bpm, P <.001) and at 1 week (71 +/- 4 bpm, P <.001). Beta-blocker therapy caused a significant reduction in systolic and diastolic blood pressures (144 +/- 16 / 93 +/- 6 mm Hg at baseline, 137 +/- 16 / 87 +/- 9 mm Hg at 10 minutes, and 135 +/- 12 / 86 +/- 8 mm Hg at 1 week, P <.001). With the beta-blocker therapy, the baseline transesophageal Doppler parameter of LAA emptying velocities (at baseline 24 +/- 7 cm/s) fell significantly at 10 minutes (19 +/- 7 cm/s, P <.001) and at 1 week (17 +/- 6 cm/s, P <.001) after initiation of beta-blocker therapy. After a bolus of metoprolol, spontaneous echo contrast intensity did not change in any patients, but 1 week later, it increased in 1 patient. In 2 patients who had not been found to have an LAA thrombus at baseline TEE study, the second TEE examination demonstrated new thrombi in the LAA. In conclusion, our findings suggest that in patients with chronic nonvalvular atrial fibrillation who have normal left ventricular systolic function and a poorly controlled ventricular rate despite the use of digoxin, acute-phase beta blockade may have a harmful effect on LAA function.

Effect of inotropic stimulation on left atrial appendage function in atrial myopathy of chronic atrial fibrillation

Atrial fibrillation (AF) leads to remodeling of the left atrium (LA) and left atrial appendage (LAA), resulting in atrial myopathy. Reduced LA and LAA function in chronic AF leads to thrombus formation and spontaneous echo contrast (SEC). The effect of inotropic stimulation on LAA function in patients with chronic AF is unknown. LAA emptying velocity (LAAEV) and maximal LAA area at baseline and after dobutamine were measured by transesophageal echocardiography in 14 subjects in normal sinus rhythm (NSR) and 6 subjects in AF. SEC in the LA was assessed before and after dobutamine. LAAEV increased significantly in both groups. However, the LAAEV at peak dobutamine in patients with AF remained significantly lower than the baseline LAAEV in patients who were in NSR (P = 0.009). Maximal LAA area decreased significantly with dobutamine in both groups, but LAA area at peak dose of dobutamine in patients with AF remained greater than baseline area in those in NSR (P = 0.01). Despite the increase in LAAEV, SEC improved in only two of five patients. We conclude that during AF, the LAA responds to inotropic stimulation with only a modest improvement in function.