The latest generation of beta-blockers: New pharmacologic properties

Control of hypertension in the critically ill: a pathophysiological approach

Severe acute arterial hypertension can be associated with significant morbidity and mortality. After excluding a reversible etiology, choice of therapeutic intervention should be based on evaluation of a number of factors, such as age, comorbidities, and other ongoing therapies. A rational pathophysiological approach should then be applied that integrates the effects of the drug on blood volume, vascular tone, and other determinants of cardiac output. Vasodilators, calcium channel blockers, and beta-blocking agents can all decrease arterial pressure but by totally different modes of action, which may be appropriate or contraindicated in individual patients. There is no preferred agent for all situations, although some drugs may have a more attractive profile than others, with rapid onset action, short half-life, and fewer adverse reactions. In this review, we focus on the main mechanisms underlying severe hypertension in the critically ill and how using a pathophysiological approach can help the intensivist decide on treatment options.

Both morning and evening dosing of nebivolol reduces trough mean blood pressure surge in hypertensive patients

The morning blood pressure surge (MBPS) has been shown to be an independent predictor of cardiovascular events. There is insufficient evidence on the effect of nebivolol, a vasodilating β1-receptor blocker, on the MBPS when given in the morning or the evening. This is a prospective, randomized, double-blind, crossover study designed to test morning vs. evening dosing of nebivolol in nondiabetic, hypertensive patients. Patients received nebivolol 5 mg/day (force-titrated to 10 mg/day after 1 week) in the morning or evening and corresponding placebos. Patients underwent ambulatory BP monitoring at baseline and after each treatment phase. Forty-two patients were randomized, of whom 38 completed both study periods. Both morning and evening dosed nebivolol significantly lowered daytime, nighttime, and 24-hour BP after 3 weeks of treatment. Evening (but not morning) dosing significantly reduced prewaking systolic BP from baseline (8.64 ± 26.46 mm Hg, P = .048). Nebivolol given in the morning or the evening significantly reduces 24-hour BP parameters. Evening dosed nebivolol may confer some advantage over morning dosing in reducing prewaking systolic BP.

Modulation of beta-adrenergic receptor signaling in heart failure and longevity: targeting adenylyl cyclase type 5

Despite remarkable advances in therapy, heart failure remains a leading cause of morbidity and mortality. Although enhanced beta-adrenergic receptor stimulation is part of normal physiologic adaptation to either the increase in physiologic demand or decrease in cardiac function, chronic beta-adrenergic stimulation has been associated with increased mortality and morbidity in both animal models and humans. For example, overexpression of cardiac Gsalpha or beta-adrenergic receptors in transgenic mice results in enhanced cardiac function in young animals, but with prolonged overstimulation of this pathway, cardiomyopathy develops in these mice as they age. Similarly, chronic sympathomimetic amine therapy increases morbidity and mortality in patients with heart failure. Conversely, the use of beta-blockade has proven to be of benefit and is currently part of the standard of care for heart failure. It is conceivable that interrupting distal mechanisms in the beta-adrenergic receptor-G protein-adenylyl cyclase pathway may also provide targets for future therapeutic modalities for heart failure. Interestingly, there are two major isoforms of adenylyl cyclase (AC) in the heart (type 5 and type 6), which may exert opposite effects on the heart, i.e., cardiac overexpression of AC6 appears to be protective, whereas disruption of type 5 AC prolongs longevity and protects against cardiac stress. The goal of this review is to summarize the paradigm shift in the treatment of heart failure over the past 50 years from administering sympathomimetic amine agonists to administering beta-adrenergic receptor antagonists, and to explore the basis for a novel therapy of inhibiting type 5 AC.

Role of beta-adrenergic receptor blocking agents in hypertensive diseases: personal thoughts as the controversy persists

The long history of the beta-adrenergic receptor blockers for the treatment of hypertension is fraught with many controversies. The first compound had severe untoward effects preventing their use until propranolol was introduced. It was found effective for treatment of angina pectoris since not all patients with hypertension responded to monotherapy with a meaningful reduction of pressure. Nevertheless, the beta-blockers were most effective in: younger patients, especially with hyperkinetic circulation; with co-morbid diseases (e.g. coronary arterial disease with or without prior myocardial infarction); or when used with a diuretic. Subsequently with the advent of meta-analysis to evaluate more generalized experience, controversy resumed with statements made to exclude beta-blockers for initial hypertensive therapy. Support for this argument was gained with reports of patients developing 'dysglycemia' with treatment. However, exclusion of any one therapeutic class for a multifactorial disease such as hypertension seems unrealistic. Meta-analysis confounded this conclusion since inadequate numbers of patients having specific clinical and biological characteristics were included (especially young patients). This is particularly important at this time when third-party reimbursement procedures are particularly relevant and when the primary care physician must deal with the individual patient. The NICE report has introduced specific thinking along these lines. In-and-of itself, its recommendations are reasonable, but current articles continue to suggest that the 'older' beta-blockers should be excluded from national guidelines for initial antihypertensive therapy. Personally, I disagree; and, no doubt, controversy will continue.

Realities of newer beta-blockers for the management of hypertension

Beta-blockers are prescribed for a variety of cardiovascular conditions including hypertension, heart failure, primary treatment of myocardial infarction (MI), and secondary prevention of ischemic cardiac events. Yet they remain underprescribed in populations at increased risk for cardiovascular disease because of tolerability and safety concerns. Beta-blockers are heterogeneous with respect to pharmacokinetic and pharmacodynamic effects. "Original" agents were nonselective, blocking both beta1-adrenoceptors and beta2-adrenoceptors. Later, new agents were developed with selectivity for beta1-adrenoceptors, and were subsequently followed by beta-blockers, which exhibit additional effects, such as vasodilation. Among newer agents, labetalol, carvedilol, and nebivolol have been approved for use in the United States. Nebivolol possesses both beta1-selectivity and nitric oxide-mediated vasodilatory effects, while carvedilol has attractive effects on insulin resistance and exhibits antioxidant effects. Newer beta-blockers may overcome concerns about efficacy, adverse effects, and tolerability, while delivering cardiovascular protection.

Beta-blocker use for the stages of heart failure

The 2005 American Heart Association/American College of Cardiology heart failure (HF) guidelines contributed to a renewed focus on "at-risk" patients and emphasized HF as a progressive disease. Patient categorization by stages focused attention on customization of therapy to achieve optimal, evidence-based treatments across the HF continuum. Therapy for risk factors that predispose patients to left ventricular dysfunction or other symptoms may help reduce HF development. beta-Blockers are valuable for treatment of HF; however, the class is heterogeneous, and proper beta-blocker selection for each HF stage is important. beta-Blockers have been used routinely to treat patients with stage A HF with hypertension. Recent controversy regarding the detrimental effects that some beta-blockers have on metabolic parameters has raised inappropriate concerns about the use of any beta-blocker for diabetes. beta-Blockade is standard therapy for the patient with stage B HF who has had a myocardial infarction, but few data are available concerning use in asymptomatic patients with left ventricular dysfunction. Additionally, beta-blockers are part of the core therapy for stage C HF and selected patients with stage D HF. This review examines the role and use of beta-blockers in each HF stage through an evidence-based approach to provide better understanding of their importance in this progressive disease. PubMed searches (1980-2008) identified large clinical trials that evaluated cardiovascular events and outcomes in any HF stage or hypertension. Search terms were heart failure, hypertension, beta-blocker, ACEI, ARB, and calcium channel blocker AND blood pressure coronary artery disease, diabetes, efficacy, left ventricular dysfunction, metabolism, mortality, myocardial infarction, or stroke.

Arterial stiffness, hypertension, and rational use of nebivolol

Arterial stiffness plays a key role in the pathophysiology of the cardiovascular system. Some indices of arterial stiffness (pulse wave velocity, augmentation index, characteristics of central blood pressure waveform) may be presently calculated and evaluated in the clinical setting. Age and blood pressure are the two major clinical determinants of increased arterial stiffness, while molecular determinants of arterial stiffness are related to fibrotic components of the extracellular matrix, mainly elastin, collagen and fibronectin. Increased arterial stiffness has been consistently observed in conditions such as hypertension, dyslipidemia and diabetes. Arterial stiffness evaluated by means of carotid-femoral pulse wave velocity yielded prognostic significance beyond and above traditional risk factors. A more favorable effect of calcium channel blockers, diuretics and ACE inhibitors compared with β-blockers on indices of arterial stiffness was observed in several studies. It is conceivable that newer β-blockers with additional vasodilating properties, such as nebivolol, which has favorable effects on carbohydrate and lipid metabolism, as well as on endothelial function and on oxidative stress, may have favorable effects on arterial stiffness, compared with atenolol. In fact, in recent studies, nebivolol was demonstrated to improve artery stiffness to a greater extent than older β-blockers. Because endothelial dysfunction and increased arterial stiffness play an important role in the early atherosclerotic processes and are associated with poor outcomes and increased mortality, independently of blood pressure, the ability of nebivolol to enhance release of endothelium-derived nitric oxide, and consequently improve endothelial function and arterial stiffness, may have significant clinical implications for the use of this agent in the treatment of hypertension and cardiovascular diseases.

The vasodilatory beta-blockers

Although well established in treating hypertension and cardiovascular (CV) disease, clinical trial data suggest that beta-blockers (eg, atenolol) may be less effective than other antihypertensive classes in reducing stroke and CV mortality despite similar blood pressure (BP) reductions. One possible explanation is that atenolol is less effective in reducing central aortic pressure. Newer vasodilating beta-blockers may prove more effective in reducing central pressure and cardiovascular events. Carvedilol and labetalol appear to cause vasodilation through alpha(1)-receptor blockade; nebivolol induces endothelium-dependent vasodilation by stimulating nitric oxide bioactivity. Their favorable hemodynamic profile includes reduction of peripheral vascular resistance (PVR) while maintaining or improving cardiac output (CO), stroke volume, and left ventricular function, whereas nonvasodilating beta-blockers tend to raise PVR and reduce CO and left ventricular function. Compared with conventional beta-blockers, vasodilating beta-blockers have beneficial hemodynamic effects including decreased pressure wave reflection from the periphery, leading to decreases in central aortic blood pressure. Larger trials are needed to determine whether reduced central pressure will translate into improved CV outcomes compared with nonvasodilating beta-blockers.