The rate of the heart and the force of its contraction are governed by careful balance of the autonomic nervous systems in the human body. The sympathetic nervous system is active in stressful situations or situations where the individual is physically active. Stimulation of this pathway causes an increase in heart rate and an increase in the force of the heart beat. This is balanced in nature by the para-sympathetic nervous system which, via the vagal nerve, slows down the heart rate and modulates the heart beat force. In patients who have angina and heart failure, the over activity of the sympathetic nervous system, is bad news.
What are Beta blockers?
The original prototype beta blocker, such as Propranolol, had excellent effects on the heart rate, but unfortunately, were associated with significant extra cardiac side effects, such as tiredness and in the case of some of the other Beta blockers, significant problems. More modern Beta blockers such as Bisoprolol are very selective for the heart and some are even more clever, having additional nitrate groups added to them, or some alpha blocking properties, such as Nebivolol and Carvidolol respectively & help dilate the blood vessels.
Why might a patient need Beta blockers?
Stable angina: the treatment of angina would involve a combination of revascularisation using coronary angioplasty or bypass surgery, but also the treatment of symptoms with tablets, such as Beta blockers. Beta stimulation primarily causes the heart rate to increase during exercise and stress. Accordingly, Beta blockade decreases or blunts the hearts need for oxygen during these situations.
Hypertension: these drugs are no longer first line agents, but if you are on them and have no problem, there is no need to change therapy
Heart failure: It is established in the treatment of chronic heart failure, that the addition of low dose Beta blockers, carefully titrating up the dose, not only improves patient’s symptomatic status, but moreover has a significant impact in their longevity.
Why is this the case?
In heart failure, it is not simply a case of their being abnormal pump function of the heart. It is a whole body disorder where there is a combination of physical pump dysfunction, abnormalities of the muscle blood flow, abnormalities of the vascular performance and abnormal activation of the neuro-humoral and endocrine systems with high levels of circulating hormones adrenaline, catecholamines and abnormalities of the renin angiotensin and aldosterone systems. Large clinical trials have shown that this therapy saves lives. The effects of Beta blockers in diastolic heart failure are less well defined, but do appear to be beneficial, and larger scale trials are currently underway to underline this.