The effects of slow channel blockers and beta blockers on atrioventricular nodal conduction

Novel Labdane Diterpenes-Based Synthetic Derivatives: Identification of a Bifunctional Vasodilator That Inhibits CaV1.2 and Stimulates KCa1.1 Channels

Sesquiterpenes such as leucodin and the labdane-type diterpene manool are natural compounds endowed with remarkably in vitro vasorelaxant and in vivo hypotensive activities. Given their structural similarity with the sesquiterpene lactone (+)-sclareolide, this molecule was selected as a scaffold to develop novel vasoactive agents. Functional, electrophysiology, and molecular dynamics studies were performed. The opening of the five-member lactone ring in the (+)-sclareolide provided a series of labdane-based small molecules, promoting a significant in vitro vasorelaxant effect. Electrophysiology data identified 7 as a Ca_V1.2 channel blocker and a K_Ca1.1 channel stimulator. These activities were also confirmed in the intact vascular tissue. The significant antagonism caused by the Ca_V1.2 channel agonist Bay K 8644 suggested that 7 might interact with the dihydropyridine binding site. Docking and molecular dynamic simulations provided the molecular basis of the Ca_V1.2 channel blockade and K_Ca1.1 channel stimulation produced by 7. Finally, 7 reduced coronary perfusion pressure and heart rate, while prolonging conduction and refractoriness of the atrioventricular node, likely because of its Ca²⁺ antagonism. Taken together, these data indicate that the labdane scaffold represents a valuable starting point for the development of new vasorelaxant agents endowed with negative chronotropic properties and targeting key pathways involved in the pathophysiology of hypertension and ischemic cardiomyopathy.

Acute echocardiographic and hemodynamic response to his-bundle pacing in patients with first-degree atrioventricular block

BACKGROUND

Atrial pacing and right ventricular (RV) pacing are both associated with adverse outcomes among patients with first-degree atrioventricular block (1°AVB). His-bundle pacing (HBP) provides physiological activation of the ventricle and may be able to improve both atrioventricular (AV) and inter-ventricular synchrony in 1°AVB patients. This study evaluates the acute echocardiographic and hemodynamic effects of atrial, atrial-His-bundle sequential (AH), and atrial-ventricular (AV) sequential pacing in 1°AVB patients.

METHODS

Patients with 1°AVB undergoing atrial fibrillation ablation were included. Following left atrial (LA) catheterization, patients underwent atrial, AH- and AV-sequential pacing. LA/left ventricular (LV) pressure and echocardiographic measurements during the pacing protocols were compared.

RESULTS

Thirteen patients with 1°AVB (mean PR 221 ± 26 ms) were included. The PR interval was prolonged with atrial pacing compared to baseline (275 ± 73 ms, p = .005). LV ejection fraction (LVEF) was highest during atrial pacing (62 ± 11%), intermediate with AH-sequential pacing (59 ± 7%), and lowest with AV-sequential pacing (57 ± 12%) though these differences were not statistically significant. No significant differences were found in LA or LV mean pressures or LV dP/dT. LA and LV volumes, isovolumetric times, electromechanical delays, and global longitudinal strains were similar across pacing protocols.

CONCLUSION

Despite pronounced PR prolongation, the acute effects of atrial pacing were not significantly different than AH- or AV-sequential pacing. Normalizing atrioventricular and/or inter-ventricular dyssynchrony did not result in acute improvements in cardiac output or loading conditions.

Fall-Related Hospitalizations in Nursing Home Residents Co-Prescribed a Cholinesterase Inhibitor and Beta-Blocker

BACKGROUND/OBJECTIVES

To examine the association between hospitalization for a fall-related injury and the co-prescription of a cholinesterase inhibitor (ChEI) among persons with dementia receiving a beta-blocker, and whether this potential drug-drug interaction is modified by frailty.

DESIGN

Nested case-control study using population-based administrative databases.

SETTING

All nursing homes in Ontario, Canada.

PARTICIPANTS

Persons with dementia aged 66 and older who received at least one beta-blocker between April 2013 and March 2018 following nursing home admission (n = 19,060).

MEASUREMENTS

Cases were persons with dementia with a hospitalization (emergency department visit or acute care admission) for a fall-related injury with concurrent beta-blocker use. Each case (n = 3,038) was matched 1:1 to a control by age (±1 year), sex, cohort entry year, frailty, and history of fall-related injuries. The association between fall-related injury and exposure to a ChEI in the 90 days prior was examined using multivariable conditional logistic regression. Secondary exposures included ChEI type, daily dose, incident versus prevalent use, and use in the prior 30 days. Subgroup analyses considered frailty, age group, sex, and history of hospitalization for fall-related injuries.

RESULTS

Exposure to a ChEI in the prior 90 days occurred among 947 (31.2%) cases and 940 (30.9%) controls. In multivariable models, no association was found between hospitalization for a fall-related injury and prior exposure to a ChEI in persons with dementia dispensed beta-blockers (adjusted odds ratio = .96, 95% confidence interval = .85-1.08). Findings were consistent across secondary exposures and subgroup analyses.

CONCLUSION

Among nursing home residents with dementia receiving beta-blockers, co-prescription of a ChEI was not associated with an increased risk of hospitalization for a fall-related injury. However, we did not assess for its association with falls not leading to hospitalization. This finding could inform clinical guidelines and shared decision making between persons with dementia, caregivers, and clinicians concerning ChEI initiation and/or discontinuation.

Pharmacological management of atrial fibrillation in patients with heart failure with reduced ejection fraction: review of current knowledge and future directions

Introduction: Both heart failure with reduced ejection fraction (HFrEF) and atrial fibrillation (AF) independently cause significant morbidity and mortality. The two conditions commonly coexist and AF in the setting of HFrEF is associated with worse mortality, hospitalizations, and quality of life compared to HFrEF without AF. Despite the large burden of these conditions, there is no clear optimal management strategy for when they occur together.Areas covered: This review focuses on the pharmacological management of AF in HFrEF. Studies were identified through PubMed search of relevant keywords. The authors review key clinical trials that have influenced management strategies and guidelines. The authors focus on the classes of drugs used to treat AF for both rate and rhythm control strategies including beta-blockers, digoxin, amiodarone, and dofetilide. Additionally, the authors discuss select non-antiarrhythmic medications that affect AF in HFrEF. The authors highlight the strengths and weakness of the data supporting the use of these medications and suggest future directions.Expert opinion: The pharmacological treatment of AF in HFrEF will need further refinement alongside the emerging role of catheter ablation. Novel HF medications and antiarrhythmics offer new tools to prevent the development of AF, as well as for rate and rhythm control strategies.

CRT Pacing: Midterm Follow-Up in LV Only Pacing without RV Lead in Patients with Normal AV Conduction

Background: The aim of our study was to assess the real life cardiac resynchronization therapy (CRT) fusion left ventricular (LV) only pacing in patients with normal AV conduction (NAVc) without right ventricular (RV) lead. Methods: Consecutive NAVc patients with CRT indication were implanted with a right atrium RA/LV DDD pacing system. Complete follow-up at 1, 3 and every 6 months thereafter included echocardiography and stress testing. Results: We analysed 55 patients (62 ± 11 years). All patients were responders with significant LV reverse remodelling (LV end-diastolic volume 193.7 ± 81 vs. 243.2 ± 82 mL at baseline, p < 0.002) and increased LV ejection fraction (38 ± 7.9% vs. 27 ± 5.2% at baseline, p < 0.001). Mitral regurgitation decreased in 38 patients (69%). During follow-up (35 ± 18 months), 20 patients (36%) needed reprogramming sensed/paced AV delay or maximum tracking rate (MTR) because of inadequate or lost LV capture at exercise test; personalized programming to achieve up to 100% fusion pacing was used in all patients. One patient developed Mobitz II second degree AV block and triple chamber CRT-P upgrade was performed; defibrillator upgrade was not necessary. Conclusions: LV only pacing CRT-P without RV lead showed a positive outcome in carefully selected patients.

MC225, a Novel Probe for P-glycoprotein PET Imaging at the Blood-brain Barrier: In Vitro Cardiovascular Safety Evaluation

The P-glycoprotein (P-gp) substrate MC225, at concentrations ≤10 nM, is a valuable radiotracer for positron emission tomography imaging of P-gp function in rats and mice. The aim of this study was to evaluate its potential toxic hazard toward the cardiovascular system through an in-depth analysis of its effects on rat aorta rings, on CaV1.2 channel current (ICa1.2) of A7r5 cells and on Langendorff-perfused rat heart. In aortic rings, MC225 relaxed phenylephrine-induced contraction in a concentration-dependent and endothelium-independent manner, with an IC50 value of about 1 μM. At concentrations ≥3 μM, it antagonized the response to cumulative concentrations of K. MC225, 1 and 10 μM, inhibited ICa1.2 by 15% and 31%, respectively, without affecting either current activation or inactivation kinetics. In Langendorff-perfused rat hearts, only 10 μM MC225 significantly decreased left ventricular pressure and increased coronary perfusion pressure while reducing heart rate and prolonging the cardiac cycle length as well as the atrioventricular conduction time (PQ interval) on the electrocardiogram. Lower concentrations of the drug were ineffective. These findings demonstrate that MC225-induced cardiovascular effects took place at concentrations that are at least 2 orders of magnitude higher than those allowing in vivo measurement of P-gp function. Therefore, MC225 represents a promising positron emission tomography tool for in vivo straightforward P-gp quantification.

Antimalarial agents against both sexual and asexual parasites stages: structure-activity relationships and biological studies of the Malaria Box compound 1-[5-(4-bromo-2-chlorophenyl)furan-2-yl]-N-[(piperidin-4-yl)methyl]methanamine (MMV019918) and analogues

Therapies addressing multiple stages of Plasmodium falciparum life cycle are highly desirable for implementing malaria elimination strategies. MMV019918 (1, 1-[5-(4-bromo-2-chlorophenyl)furan-2-yl]-N-[(piperidin-4-yl)methyl]methanamine) was selected from the MMV Malaria Box for its dual activity against both asexual stages and gametocytes. In-depth structure-activity relationship studies and cytotoxicity evaluation led to the selection of 25 for further biological investigation. The potential transmission blocking activity of 25 versus P. falciparum was confirmed through the standard membrane-feeding assay. Both 1 and 25 significantly prolonged atrioventricular conduction time in Langendorff-isolated rat hearts, and showed inhibitory activity of Ba²⁺ current through Ca_v1.2 channels. An in silico target-fishing study suggested the enzyme phosphoethanolamine methyltransferase (PfPMT) as a potential target. However, compound activity against PfPMT did not track with the antiplasmodial activity, suggesting the latter activity relies on a different molecular target. Nevertheless, 25 showed interesting activity against PfPMT, which could be an important starting point for the identification of more potent inhibitors active against both sexual and asexual stages of the parasite.

Long term impact of cardiac contractility modulation on QRS duration

BACKGROUND AND PURPOSE

Cardiac contractility modulation (CCM) is an implantable device treatment for heart failure with reduced ejection fraction. CCM therapy improves patient functional status but its effect on intra-ventricular conduction remains unknown.

METHODS

70 patients treated with CCM between 12/2002 and 5/2013 had 12-vector-ECG recordings made at baseline and final follow-up visits. QRS complex duration was measured at each time point.

RESULTS

Mean follow-up was 2.8 years. Mean QRS duration was unchanged from baseline (112.0 ms) to last follow up (112.9 ms, p=n.s.). These results are strikingly different from comparative published data of several studies with heart failure patients without CCM, consistently indicating an increase in QRS duration (6.0-23.4 ms) over a similar time period.

CONCLUSIONS

CCM prevents chronic ventricular depolarization delay that occurs in heart failure and that is associated with poorer outcomes. This supports the safety of long-term CCM therapy and suggests a possible long-term benefit in maintaining QRS duration.

Atrioventricular block following lacosamide intoxication

Lacosamide (LCM) is a novel anticonvulsant that modulates voltage-dependent sodium channels. Although it is known to cause a slight, dose-dependent prolongation of the PR interval on the ECG, third-degree atrioventricular (AV) block has been described as an adverse event in only a few patients participating in diabetic neuropathic pain studies and in no patient with epilepsy. We describe an 89-year old patient with decreased renal function and taking two other negative dromotropic agents who accidentally received two intravenous boli of 400 mg LCM within 6 hours. She had a normal PQ interval before and after the first dose of LCM and developed a reversible complete AV block approximately 30 minutes after the second bolus. We conclude that particular caution must be exercised when using very high doses of LCM in patients with significant cardial and renal risk factors.

Cardiac adrenergic control and atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and it causes substantial mortality. The autonomic nervous system, and particularly the adrenergic/cholinergic balance, has a profound influence on the occurrence of AF. Adrenergic stimulation from catecholamines can cause AF in patients. In human atrium, catecholamines can affect each of the electrophysiological mechanisms of AF initiation and/or maintenance. Catecholamines may produce membrane potential oscillations characteristic of afterdepolarisations, by increasing Ca(2+) current, [Ca(2+)](i) and consequent Na(+)-Ca(2+) exchange, and may also enhance automaticity. Catecholamines might affect reentry, by altering excitability or conduction, rather than action potential terminal repolarisation or refractory period. However, which arrhythmia mechanisms predominate is unclear, and likely depends on cardiac pathology and adrenergic tone. Heart failure (HF), a major cause of AF, causes adrenergic activation and adaptational changes, remodelling, of atrial electrophysiology, Ca(2+) homeostasis, and adrenergic responses. Chronic AF also remodels these, but differently to HF. Myocardial infarction and AF cause neural remodelling that also may promote AF. beta-Adrenoceptor antagonists (beta-blockers) are used in the treatment of AF, mainly to control the ventricular rate, by slowing atrioventricular conduction. beta-Blockers also reduce the incidence of AF, particularly in HF or after cardiac surgery, when adrenergic tone is high. Furthermore, the chronic treatment of patients with beta-blockers remodels the atria, with a potentially antiarrhythmic increase in the refractory period. Therefore, the suppression of AF by beta-blocker treatment may involve an attenuation of arrhythmic activity that is caused by increased [Ca(2+)](i), coupled with effects of adaptation to the treatment. An improved understanding of the involvement of the adrenergic system and its control in basic mechanisms of AF under differing cardiac pathologies might lead to better treatments.

Electrophysiological effects of the aqueous extract of Averrhoa carambola L. leaves on the guinea pig heart

This work aims to describe some electrophysiological changes promoted by the aqueous extract (AEx) from Averrhoa carambola leaves in guinea pig heart. The experiments were carried out on isolated heart or on right atrium-ventricle preparations. In 6 hearts, the extract induced many kinds of atrioventricular blocks (1st, 2nd, and 3rd degrees); increased the QT interval from 229+/-23 to 264+/-19 ms; increased the QRS complex duration from 27+/-3.1 to 59+/-11 ms, and depressed the cardiac rate from 136+/-17 to 89+/-14b pm. Furthermore, it decreased the conduction velocity of atrial impulse (17+/-3%); reduced the intraventricular pressure (86+/-6%), and increased the conduction time between the right atrium and the His bundle (27+/-6.5%). The conduction time from the His bundle to the right ventricle was not altered. Atropine sulfate did not change either the electrocardiographic parameters or the intraventricular pressure effects promoted by the A. carambola AEx. Based on these results, the popular use of such extracts should be avoided because it can promote electrical and mechanical changes in the normal heart.

Comparison of the electropharmacological effects of verapamil and propranolol in the halothane-anesthetized in vivo canine model under monophasic action potential monitoring

The cardiovascular profile of verapamil was assessed in the halothane-anesthetized canine model and compared with that of propranolol. Verapamil was infused at the rates of 1, 3 and 10 microg x kg(-1) x min(-1) (n=6), whereas propranolol was administered at a fixed rate of 10 microg x kg(-1) x min(-1) (n=6). Each infusion was performed over 30 min, and the parameters were assessed for 20-30 min after the start of each infusion. Verapamil in a dose of 10 microg x kg(-1) x min(-1) significantly suppressed atrio-ventricular (AV) node conduction and slightly decreased the mean blood pressure, but no significant change was detected in the left ventricular end-diastolic pressure, maximum upstroke velocity of the left ventricular pressure, sinus automaticity, double product, cardiac output, intraventricular conduction, and ventricular repolarization phase and refractoriness. Propranolol suppressed AV node conduction to an extent similar to that of verapamil, but it also inhibited intraventricular conduction, sinus automaticity and ventricular contraction, increased the ventricular refractoriness, and decreased the double product and cardiac output, without any significant change in the other variables measured. These results suggest that verapamil can selectively affect the AV node, and that the greater part of the suppressive action of propranolol on the multiple cardiovascular performance is through a beta-blocking action and direct membrane effect, although the halothane inhalation itself might have modified each of the drug's effects. The abbreviation of the relative refractory period of the ventricle by propranolol may show its potential utility for re-entry type ventricular tachycardia.

Contemporary approaches in medical management of patients with stable coronary artery disease

CAD continues to be the principal cause of mortality in the United States, and the largest group of patients with CAD are those with stable angina. Among this group of patients, the most common manifestation of CAD is presence of transient episodes of myocardial ischemia. The presence of transient ischemia and not the severity of angina has been found to be associated with poor clinical outcome in patients with stable CAD. As part of a global treatment strategy for patients with stable CAD, changes in lifestyle and modification of coronary risk factors should be emphasized as an integral part of treatment. Conventional antianginal therapy is quite effective in controlling anginal attacks. Currently, several drugs and therapeutic strategies are available for the treatment of patients with angina (see Table 5). Nitrates are highly effective antianginal drugs with complex beneficial actions in patients with CAD, but their usefulness is limited by development of tolerance during long-term use. When clinically indicated, the use of nitrates should be supplemented with another longer-acting antianginal drug, such as a beta-blocker or a calcium channel blocker. Based on the available data, beta-blockers, when tolerated, seem to be the most effective antianginal drugs for most patients with stable CAD. Beta-blockers are also the most effective anti-ischemic drugs that reduce the magnitude of myocardial ischemia detected during routine daily activities. Calcium channel blockers are also effective vasodilators and good antianginal drugs. The clinician should become familiar with the different actions that this heterogeneous group of drugs has on the heart and vessels. This knowledge allows the clinician to choose the appropriate combination of different antianginal drugs for patients on an individualized basis. It is also critical to develop the treatment strategy by carefully taking into account other associated medical conditions that are frequently encountered in patients with CAD.

Calcium antagonists in cardiology: update on sustained-release drug delivery systems

One limitation of standard oral formulations of calcium antagonists has been the need for multiple daily dosing. Sustained-release dosage forms permit simpler regimens and a smoother therapeutic effect. Differences in drug pharmacokinetic and pharmacodynamic properties have led to development of several sustained-release delivery systems. Three major types are available: the osmotic pump, coated pellet, and slow-dissolving material released from a matrix. Each is currently utilized with specific calcium antagonists. The osmotic pump system with nifedipine (Procardia XL, Pfizer) allows once-daily dosing as well as improvements in certain side effects. Verapamil is available in formulations employing dissimilar release systems. The original sustained-action products (Calan SR, Searle; Isoptin SR, Knoll) utilize a matrix system; a subsequent product (Verelan; Lederle, Wyeth-Ayerst, A. H. Robins) utilizes timed-release pellets. Importantly, clinical efficacy appears to be maintained with these several drugs and formulations for their approved indications. Although a specific formulation may alter the absorption, metabolism, excretion, and blood levels of a drug, it does not alter basic drug properties. Thus, the major impact of sustained-release drug delivery system lies in potential compliance improvement and possible reduction of side effects related to serum drug profiles.

Effect of continuous enhanced vagal tone on atrioventricular nodal and sinoatrial nodal function in humans

A constant intravenous infusion of phenylephrine (0.74 +/- 0.41 micrograms/kg/min) was given to 10 patients to cause a continuous augmentation in reflex vagal tone. After the infusion, the diastolic blood pressure increased from 76 +/- 7 to 89 +/- 11 mm Hg (p less than 0.01). The sinus cycle length and atrial-His (AH) interval were measured, and incremental atrial pacing was performed before and during phenylephrine infusion until atrioventricular (AV) nodal block was achieved. For each patient, the AV nodal function curve (i.e., the AH interval plotted as a function of the atrial pacing cycle length) was compared during both the control state and phenylephrine infusion; the AH intervals during each condition at chosen short (AHS) and long (AHL) cycle lengths were compared. The sinus cycle length increased during phenylephrine infusion from 941 +/- 294 to 1,115 +/- 347 msec (p = 0.013). The AH interval during sinus rhythm was not significantly prolonged (77 versus 82 msec, p = NS). The shortest atrial pacing cycle length yielding 1:1 AV nodal conduction increased during phenylephrine infusion from 412 +/- 120 to 575 +/- 211 msec (p less than 0.01). Of note, the degree of sinus cycle length prolongation did not correlate with the degree of prolongation in the shortest atrial pacing cycle length yielding 1:1 AV nodal conduction. The AV nodal function curve was shifted markedly to the right and only slightly upward.(ABSTRACT TRUNCATED AT 250 WORDS)

Stable angina pectoris: 3. Medical treatment

The therapeutic goals for the patient with angina pectoris are to minimize the frequency and severity of angina and to improve functional capacity at a reasonable cost and with as few side effects as possible. An integrated approach necessitates attention to conditions that might be aggravating angina, such as anemia or hypertension. Alterations in life-style and personal habits, such as cessation of cigarette smoking, are often necessary and should be continually reinforced by the physician. Certain concomitant diseases, such as chronic obstructive pulmonary disease, may influence the selection of drug therapy. Nitrates, beta-adrenergic blockers, and calcium entry blockers are the major classes of drugs that can be used alone or in combination in a program that is designed for the individual patient.

Verapamil. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in hypertension

Although verapamil is a well-established treatment for angina, cardiac arrhythmias and cardiomyopathies, this review reflects current interest in calcium antagonists as anti-hypertensive agents by focusing on the role of verapamil in hypertension. Verapamil is a phenylalkylamine derivative which antagonises calcium influx through the slow channels of vascular smooth muscle and cardiac cell membranes. By reducing intracellular free calcium concentrations, verapamil causes coronary and peripheral vasodilation and depresses myocardial contractility and electrical activity in the atrioventricular and sinoatrial nodes. Verapamil is well suited for the management of essential hypertension since it produces generalised systemic vasodilation resulting in a marked reduction in systemic vascular resistance and, consequently, blood pressure. Evidence from clinical studies supports the role of oral verapamil as an effective and well-tolerated first-line treatment for the management of patients with mild to moderate essential hypertension. Clinical studies have shown that verapamil is more effective the higher the pretreatment blood pressure and some authors have found a more pronounced antihypertensive effect in older patients or in patients with low plasma renin activity. Sustained release verapamil formulations are available for oral administration which, as a single daily dose, are as effective in lowering blood pressure over 24 hours as equivalent doses of conventional verapamil formulations given 3 times daily. As a first-line antihypertensive agent, oral verapamil is equivalent to several other calcium antagonists, beta-blockers, diuretics, angiotensin-converting enzyme (ACE) inhibitors and other vasodilators, and is not associated with many of the common adverse effects of these treatments. Verapamil may be preferred as an alternative first-line antihypertensive treatment to diuretics in elderly patients because it has similar efficacy in these patients without causing the adverse effects commonly linked with diuretic treatment. Furthermore, because verapamil does not cause bronchoconstriction, it may be used in preference to beta-blockers in patients with asthma or chronic obstructive airway disease. Reflex tachycardia, orthostatic hypotension or development of tolerance is not evident following verapamil administration. As a second- or third-line treatment for patients refractory to established antihypertensive regimens, verapamil produces marked blood pressure reductions when combined with diuretics and/or ACE inhibitors, beta-blockers and vasodilators such as prazosin.(ABSTRACT TRUNCATED AT 400 WORDS)